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1. Friedberg BL: Propofol-ketamine technique. Aesth Plast Surg
sia. One of the most cogent points contained in the ASA
17:297,1993.
position on MAC was the statement that it is not always
2. Friedberg BL: Minimally invasive anesthesia for minimally
possible to predict how an individual patient will respond! invasive surgery. Outpatient Surgery Magazine. Paoli, PA,
Herrin Publishing Partners LP 2:57,2004.
3. Friedberg BL: Does LMA equal GA? (letter). Outpatient
CORRELATING DEFINITIONS WITH Surgery Magazine. Paoli, PA, Herrin Publishing Partners LP
6:15,2003.
CLINICAL PRACTICE
4. Friedberg BL: Brain is target organ for anesthesia. Anes-
thesia Patient Safety Foundation Newsletter (www.apsf.org)
Benzodiazepines may be used to provide minimal, moder-
20(3),Fall 2005.
ate, and deep states of sedation. Propofol can produce all
5. Kearse LA, Rosow C, Zaslavsky A, et al.: Bispectral analysis of
four levels of hypnosis for sedation/anesthesia. However, the electroencephalogram predicts conscious processing of
benzodiazepines are not well measured by the BIS or other information during propofol hypnosis and sedation. Anes-
thesiol 88:25,1998.
currently commercially available level-of-consciousness
6. Twersky RS: Of¬ce-based anesthesia: Considerations for
monitors. Propofol is well measured by BIS17,18 (see anesthesiologists in setting up and maintaining a safe of¬ce
Table 1-4). Propofol alone can provide minimal seda- anesthesia environment. Park Ridge, IL, American Society
of Anesthesiologists. 2000.
tion “anxiolysis” (BIS 78“85). Propofol in conjunction
2 Preoperative Instructions and Intraoperative Environment
Barry L. Friedberg, M.D.



PREOPERATIVE INSTRUCTIONS
Adjusting Surgeon Expectations
Adjusting Patient Expectations
CONCLUSION




PREOPERATIVE INSTRUCTIONS
observed in about 1“2% of patients. Laryngospasm is the
antithesis of depressed laryngeal re¬‚exes. Laryngospasm has
Nothing per os (NPO), or nothing by mouth, after mid-
been observed as long as several hours after a single 50-mg
night is the most commonly given preoperative instruction
dose of ketamine! Laryngospasm is the ultimate in height-
to all surgical patients. This is not unreasonable given the
ened laryngeal re¬‚ex activity. Because it does not depress
fact that the majority of surgical patients are exposed to
the “life-preserving” re¬‚exes, PK MAC/MIA„ technique
emetogenic inhalational vapors and/or emetogenic intra-
is exempted from AB595 mandating of¬ce accreditation.
venous opioids. Both inhalational vapors and intravenous
Notwithstanding the AB595 exemption, the medical lia-
opioids depress the laryngeal or “life-protecting” re¬‚exes.
bility carriers will still require that the ASA monitoring
California Assembly Bill (AB)595 speci¬cally mandated
standards (i.e., NIABP, SpO2 , EKG) be followed in any
of¬ce accreditation when sedatives and analgesics are used
anesthetizing situation.
in a manner that has the probability to depress the “life-
Temperature measurement is not especially relevant with
preserving” re¬‚exes. The “Catch-22” is that neither the leg-
a nontriggering anesthetic technique. EtCO2 tends 38“42
islature nor the anesthesia community ever de¬ned what the
with PK MAC or the MIA„ technique, when measured.
“life-preserving” re¬‚exes are. In both the peer-reviewed lit-
Being able to observe the waveform of the exhaled CO2 may
erature1 and in unrebutted public testimony before the CA
give additional reassurance to the anesthesiologist that the
Medical Board when Dr. Thomas Joas, a prominent anesthe-
patient is, in fact, breathing. This is potentially signi¬cant if
siologist, was its presiding chairman, Friedberg has unequiv-
the patient is draped in a manner that precludes observation
ocally de¬ned the laryngeal re¬‚exes as the “life-preserving”
of the rise and fall of the chest wall (Barinholtz D, personal
re¬‚exes.
communication. 2005). EtCO2 monitoring, per se, does little
Emetogenic inhalational vapors and/or emetogenic
to enhance patient safety with an opioid avoidance technique
intravenous opioids expose the surgical patient to an
like the PK MAC/MIA„ technique.
increased likelihood of aspiration and death. If surgical
Additionally, there must be a source of oxygen (i.e.,
patients cannot re¬‚exly protect their trachea, they cannot
an E tank), a means of positive pressure ventilation (i.e.,
preserve their lives. The lack of pharyngeal re¬‚exes or swal-
an Ambu r bag), and suction readily available in any
lowing seen with propofol sedation/anesthesia does not
anesthetizing situation. Lastly, insurers will defer to the
necessarily mean that the laryngeal re¬‚exes are similarly
state authorities for any requirement for a crash cart and a
depressed. In fact, when ketamine is added to the regimen
de¬brillator (see Chapter 18). Friedberg has never discour-
of propofol sedation and opioids are scrupulously avoided
aged of¬ces from seeking accreditation despite the fact
(i.e., PK MAC/MIA„ technique), laryngospasm has been



14
Preoperative Instructions and Intraoperative Environment 15


that PK MAC/MIA„ technique is exempted from AB595. on their preoperative regimen of medications should
However, he has safely administered PK MAC/MIA„ continue taking those medications with the following
technique for of¬ces either in the process of accreditation exceptions. Hypertensive patients on diuretics like
or unaccredited ones that have met the prerequisites for the furosemide or hydrochlorothiazide are instructed not to
safe administration of PK MAC/MIA„ technique. take their a.m. dose as this will tend to cause their bladder
In every state except Florida, PK MAC/MIA„ technique to become full under anesthesia. A full bladder can cause
is recognized as IV sedation. Florida Medical Board patients to squirm about the OR table, elevate their blood
regulations follow those of the American Association for pressures, or void spontaneously (enuresis). Owing to the
the Accreditation of Surgical Facilities (AAAASF). The higher probability of blood loss and ¬‚uid replacement,
Medical Board of Florida has arbitrarily classi¬ed PK a three-to-four“hour hospital-type noncosmetic surgery
MAC/MIA„ technique as GA. The net effect of this ruling is case is often begun with a Foley bladder catheter. PK
to require every of¬ce-based surgery suite in Florida desiring MAC/MIA„ technique does not routinely require blad-
to have the safer, superior outcomes of PK MAC/MIA„ der catheterization. The exception to this caveat is for a case
technique to be required to increase their classi¬cation from scheduled for at least ¬ve to six hours. For many patients,
a “B” to a “C” facility. All “C” facilities must have (1) an eliminating the catheterization eliminates the risk of an
anesthesia machine, (2) scavenging, (3) dantrolene. PK iatrogenic bladder infection, a decidedly undesirable out-
MAC/MIA„ technique is a nontriggering IV technique. come in an of¬ce-based, elective cosmetic surgical patient.
Florida™s requirements add substantial costs without adding Elective cosmetic surgical patients fasted overnight are
a scintilla of patient safety. Both the AAAASF and the not generally 500“1,000 ccs “behind” on ¬‚uid volume,
Florida Medical Board have rebuffed numerous phone calls as is traditionally taught. Blood loss and replacement
and e-mail entreaties to calendar this item on their meeting are not contemplated. Fluid shifts do not occur. The
agenda to even permit a discussion of the factual de¬nition physiologic insult of liposuction is not analogous to burn
of sedation versus general anesthesia (see Chapter 1, cases! Even with a tumescent or “super wet” liposuction
Appendix 1-1). procedure, the “third space” created by the aspiration of
Friedberg™s preoperative instructions have evolved fat is functionally obliterated by the use of compression
after lengthy experience with a nonemetogenic anesthetic garments! A recent article in the plastic surgery literature
regimen (see Table 2-1). In general, patients who are stable was disingenuous when the authors suggested that
liposuction was not for the treatment of obesity.2 The
article subsequently described the means to safely extract
Table 2-1. Preoperative instructions more than 5,000 ccs per operative visit! Rebuttal to the
liposuction advisory panel was subsequently published.3
1. Patients taking antihypertensives, antidepressants,
Liposuction is clearly safer when 5,000 ccs or less are
beta-blockers, asthma medications, or oral
hypoglycemic agents should maintain their usual aspirated. Friedberg supports both the Florida and
morning dosage with enough water to comfortably
California medical boards™ limitations (4,000 and 5,000
get their medications down. Asthmatics should bring
ccs of fat, respectively) on the amount of liposuction that
their inhalers with them to surgery.
may be safely performed in a single of¬ce-based surgery.
2. Patients who regularly consume caffeinated
beverages and who experience headache without Florida™s board mandates the reporting of hospital
the usual morning caffeine dose are encouraged to
admissions and deaths from of¬ce-based cosmetic surgery.
have their usual morning dose of caffeine WITHOUT
Public safety also demands the same mandatory reporting
any dairy product. Nondairy creamers are
acceptable, if needed. requirements for elective cosmetic surgery deaths in hos-
3. Patients who are very hungry upon awakening may pital and ASC settings! An eight-hour limitation in Florida
have toast and jam and/or apple juice if so desired.
on of¬ce-based surgical procedures is reasonable and
4. Patients who are scheduled for afternoon surgery
likely to improve patient safety. Both mandatory reporting
may have a light breakfast not closer than four hours
prior to their surgery. Again, “light” means NO and surgery time limitations are supported by Friedberg.
DAIRY PRODUCTS (i.e., milk, cream, butter, yogurt,
Patients who are very hungry upon awakening may
or cheese).
have toast and jam and/or apple juice if so desired. Simple
16 Barry L. Friedberg


sugars and carbohydrates are readily absorbed from the their morning drink. For those who answered af¬rma-
stomach. The stomach will be empty without having the tively (not all caffeine drinkers will answer so), allowing
patient present hypoglycemic (or, at the least, unhappily them to have some caffeine preoperatively will avoid the
hungry) before surgery. Management of the patients™ postoperative complaint of headache.
blood sugar has been greatly facilitated by the advent of Taken without dairy products, a cup of caffeinated coffee
the battery-operated glucose meter, that is, Accu-Check r or tea will have no greater effect on gastric content than
or One Touch. r Nonetheless, it is still incumbent on water in this author™s clinical experience.
the anesthesiologist to assure that hypoglycemia under For patients who desire some whitening of their coffee,
anesthesia does not occur. Juvenile, Type I, or insulin- a nondairy “creamer” is acceptable. For anesthesiologists
dependent diabetic patients should avoid their full a.m. who have dif¬culty allowing patients to have their coffee,
dose of insulin. However, they should have some insulin! one tablet of No Doze, r an over-the-counter caffeine
One half to one third of their usual morning insulin dose tablet, with sips of water may be a suitable alterna-
should be satisfactory for control without substantially tive. Caffeine maintenance has the same logic as does
risking hypoglycemia for two-to-four“hour morning maintenance of preexisting prescription drug therapy.
cases. For these patients, an hourly check of their blood Patients who are stable on their preoperative prescription
sugars during anesthesia is strongly recommended. medications are best left stable.
Insulin-dependent diabetics should not be scheduled as Do not abruptly withdraw these agents (caffeine or
afternoon elective cosmetic surgery cases! prescription drugs) unless there is a pressing reason to
Diabetics brittle enough to require an insulin infusion do so. If any doubt exists, consult with the prescribing
are not suitable candidates for of¬ce-based cosmetic physician. Lastly, patients who are scheduled for afternoon
surgery. Postoperative nausea may sometimes be an surgery may have a light breakfast not closer than four
expression of hypoglycemia. Nausea of this etiology is hours prior to their surgery. “Light” means NO DAIRY
more appropriately treated with oral or IV glucose, not PRODUCTS, that is, milk, cream, butter, yogurt, or
antiemetic medication. Whether or not the patient is cheese. Water or apple juice may be consumed up to one
diabetic, it is useful for patient comfort to offer apple hour preoperatively if so desired.
juice or a glucose-containing sports drink like Gatorade r Table 2-2 summarizes the elements of the preoperative
at the conclusion of any case, especially those that run information routinely elicited from patients (see Chapter
longer than two hours. By eliminating the root causes 14 for an in-depth discussion of preoperative assessment).
of PONV (i.e., inhalational anesthetics and opioids), Middle-aged (i.e., 35“60), sedentary adults, both men
patients rapidly emerge PONV free and able to resume PO and women, may have signi¬cant coronary artery disease
¬‚uid intake after the propofol is discontinued. Therefore, (CAD) without symptoms or taking medications like
resumption of PO ¬‚uids is an irrelevant discharge criterion
for patients anesthetized with PK MAC/ MIA„ technique.
Given the enormous commercial success of the Table 2-2. Preoperative patient information
Starbucks r coffee company, no account of preoperative
1. Age and weight
instructions would be complete without some discussion
2. Current medications, including herbal supplements
of the issue of PO intake of caffeinated beverages in like Ginko Biloba, garlic, or St. John™s Wort
the morning of surgery. From 1992 to 1994, Friedberg 3. Smoking status, pack-year history, time from last
cigarette
noted a number of patients complaining of postoperative
4. Pregnancy status, “Do you believe that you may be
headache after PK MAC. He asked the patients with
pregnant at this time?”
headache complaints if they were regular consumers of 5. Allergies to medication and the speci¬c reaction, i.e.,
caffeinated beverages, coffee, tea, or so-called “energy” urticaria (hives), problem breathing
6. History of asthma or hepatitis
drinks like Red Bull. r Most patients experiencing
7. Previous anesthetic experience, i.e., prolonged
headaches answered in the af¬rmative. Patients who
emergence or PONV
regularly consume caffeinated beverages should be asked 8. History of motion sickness
preoperatively if they experience headache if they miss
Preoperative Instructions and Intraoperative Environment 17


nitroglycerin to alert the anesthesiologist. These patients Those anesthesiologists unwilling to prevent tachy-
are particularly at risk for destabilization of their asymp- cardia may ¬nd the ACLS algorithm for ventricular
tomatic, underlying CAD. The stress of the injection of tachycardia/¬brillation useful.
epinephrine-containing local anesthetic at the beginning Cardiac destabilization does not require a full thick-
of all cosmetic surgical procedures can potentially produce ness myocardial infarction. Destabilization with a low
a “chemical” stress treadmill. probability of resuscitation may occur just as easily with
Much confusion continues over whether ketamine a subendocardial infarction.
produces tachycardia and hypertension. The answer is To anticipate destabilization, it may be useful to
both “yes” and “no” depending on the context in which routinely monitor a modi¬ed V5 (MV5) EKG. This may
ketamine is administered! be accomplished by ¬rst selecting lead I on the monitor.
Ketamine is often given in close temporal sequence Then, place the left arm (black) lead over the point of
to the injection of local anesthesia by the surgeon. maximum impulse or apex of the left ventricle, and
When a tachycardia occurs in this context, it is clearly use the third lead (green or red) on the left shoulder
impossible to differentiate a ketamine effect from an to observe the ST-T waves as an indicator of coronary
epinephrine effect. When given as a single anesthetic ischemia. Obviously, monitoring an MV5 during a breast
agent (i.e., 1“2 mg · kg’1 ), ketamine will produce hyper- augmentation or mastoplexy case will not be practical.
tension and tachycardia, just as the original investigators Even more useful than monitoring MV5 is preventing
described. (Using doses of 2.0“4.0 mg · kg’1 in 1968, tachycardia in all patients over the age of 35 with the
Corssen reported an 8.1% incidence of hypertension judicious use of beta-blockers. Friedberg advocates 10 mg
[25% above resting baseline] and a 4.1% incidence of labetolol (Trandate r or Normodyne r ) IV push but rec-
tachycardia.)4 ognizes propranolol (Inderal r ) or esmolol (Brevibloc r )
However, the context in which ketamine is given in PK may be acceptable alternatives. In the context of opioid
MAC/MIA„ technique is entirely different. The incre- administration, it may be unwise to administer more than
mental induction technique with propofol is designed to 5 mg labetolol at a time. However, dividing the labetolol
create a stable level of propofol in the brain. By titrating the doses may be ineffective in preventing the “chemical”
propofol to a quantitative level with the BIS (i.e., 70“75), stress treadmill in a timely fashion.
the context in which the ketamine interacts with the brain Another advantage of opioid avoidance PK MAC/MIA„
is precisely and reproducibly de¬ned. Friedberg has admin- technique is that one may administer labetolol as a 10 mg
istered the ketamine on many occasions in the course of bolus without creating a severe bradycardia.
administering PK MAC/MIA„ technique with ten to Elicitation of the patient™s body weight will facilitate
twenty minutes elapsing before the surgeon was ready using any syringe-pump-type device for the administra-
to inject the local. In none of those “ketamine-without- tion of propofol. The utility of body weight based dosing of
local-anesthetic-injection” contexts did tachycardia or propofol is limited by the fact that there may be as great as
a nineteenfold variability in propofol hydroxylation.5 This
hypertension occur.
Fifty mg ketamine, in the context of a stable brain level of variability was most closely correlated with cytochrome
P450 P2B6.5 This interindividual variability confounds
propofol, produces neither tachycardia nor hypertension.
The epinephrine in the surgeon™s local anesthetic the best pharmacokinetic or pharmacodynamic mod-
may cause the heart rate to increase. Diastolic ¬lling eling. Interindividual variability is another foundation
time shortens as heart rate increases. Normal coronary for using a level-of-consciousness monitor, like BIS, to
arteries dilate to compensate for the shortened ¬lling titrate propofol to produce PK MAC/ MIA„ technique
time. Plaque-¬lled or atherosclerotic coronaries are (see Chapter 3).
unable to dilate in response to the demand for increased See Chapter 14 and Appendix A for a discussion of
oxygen with tachycardia. When oxygen demand exceeds the potential impact current medications and herbal
the diseased coronaries™ ability to supply it to the supplements may have on anesthetic management.
myocardium, the patient™s heart will most likely become Patient™s smoking status is a concern because smokers
destabilized. often do not tolerate oral airways as well as nasal airways.
18 Barry L. Friedberg


by considerations raised by the new federal privacy statute
Table 2-3. Airway management algorithm for the
(HIPAA). HIPAA is principally applicable for medically
MIA R technique (assumes incremental propofol
indicated, third-party, or insurance cases. Elective cos-
induction)
metic patients are not covered by this statute. A binding
1. Head extended, rotated laterally (facelift position) arbitration agreement is currently being utilized, placing
2. 1,000 cc IV bag (or shoulder roll) under shoulders
one more step in the patient™s process of ¬ling a lawsuit.
3. Nasal airway (#28, most commonly), lubricated
Most allergy histories, if carefully taken, involve known
4. LMA (#4, most commonly), lubricated. Patients will
breath spontaneously throughout the case. side effects from drugs rather than true allergic reactions.
Supplemental oxygen will be applied to maintain
Examples are, “my heart races every time my dentist
SpO2 > 90% and the following sequence of airway
injects my teeth,” or “I vomit every time I take codeine.”
interventions will be started until saturation is
One must take cognizance of true allergic phenomenon
satisfactory.
like urticaria, rash, and anaphylaxis. By avoiding neuro-
muscular blocking agents, especially succinylcholine, PK
MAC/MIA„ technique eliminates many of the offending
agents. Avoiding morphine will eliminate histamine-type
Coughing is more likely to result if the anesthesiologist
reactions. Avoiding meperidine adds more safety to
tries to maintain a patent airway with an oral device instead
PK MAC/MIA„ technique, especially if patients are
of the recommended PK MAC/MIA„ airway management
taking the monamine oxidase inhibitors (MAOI) like
algorithm.
phenelzine (Nardil r ) or tranylcypromine (Parnate r ).
All MIA„ patients are managed with the same airway
The hypertensive crisis precipitated by the administration
algorithm, namely, whatever level of intervention is
of meperidine to patients on MAOI, although not an
required to maintain a patent airway (see Table 2-3).
allergic reaction, will nevertheless cause considerable but
In Friedberg™s experience, smokers tend to have heightened
avoidable stress in the of¬ce-based surgical suite along
sensitivity of their glottic chink. They are more susceptible
with the signi¬cant potential of the loss of patient life.
to laryngospasm, especially if there is a history of a recent
When one elicits a history of asthma, inquire about the
upper respiratory infection (URI).
most recent attack and what measures were taken to break
Wide variability among cosmetic surgery practices
it. A common response to the question about asthma has
exists on how to deal with the sensitive issue of the patient™s
been, “I had it as a child but haven™t had any problems
pregnancy status. At one end of the spectrum of contem-
in years.” For the patient who has an active asthmatic
porary practice is a patient disclosure: “I do not believe
history, it is imperative that they bring whatever inhalers
that I am pregnant at this time.” An intermediate position
they typically use to the of¬ce prior to having anesthesia
would be to use an over-the-counter pregnancy urine spot
for cosmetic surgery. It is also important to inquire about
test to rule out pregnancy. At the other extreme of practice
how well the patient feels they are breathing on admission
is demanding a human chorionic gonadrotropin (HCG)
to the of¬ce surgery suite. It is not unreasonable to ask the
assay on every female patient prior to giving potentially
patient to take a few puffs of their inhaler of choice before
teratogenic anesthetic agents. In many private practice set-
inducing anesthesia. Avoiding both inhalational agents
tings, an HCG test imposes an additional ¬nancial burden
as well as endotracheal intubation with PK MAC/MIA„
on the cash-paying cosmetic surgery patient. An HCG test
technique are signi¬cant advantages for the asthmatic
is not as relevant in the menopausal rhytidectomy patient,
patient. Ketamine has some bronchodilating properties
despite reproductive technology having pushed the typical
that may also be advantageous for the asthmatic patient.
age boundaries for pregnancy. The HCG test is more
An asthmatic attack may be triggered by administering
relevant to the younger and more fertile breast augmen-
beta-blocking drugs to treat tachycardia. Fortunately,
tation or liposuction patient who tends to be more cost-
actively asthmatic patients tend to be more tolerant
conscious. Increasing the ¬nancial burden exacted on
of tachycardia than nonasthmatics. Be judicious when
these patients preoperatively may increase their motiva-
deciding to treat tachycardia with beta-blocking agents in
tion to ¬nd a different cosmetic surgeon who may be will-
this group of patients.
ing to forego this testing. The issue is further compounded
Preoperative Instructions and Intraoperative Environment 19


Eliciting a history of hepatitis will not change the dosing before avoiding pain. Essentially, all patients who sign up
of propofol or ketamine but should alert the anesthesiolo- for elective surgery know, at some level (consciously or
gist to take greater care with blood and bodily ¬‚uid expo- subconsciously), that they are going to experience some
sure. In the era of HIV/AIDS, anesthesiologists are obliged to level of discomfort or pain on emergence. What they are
use “universal precautions” for all patients. Nonetheless, one trying to ask of their anesthesiologist is not to “rub salt
tends to exercise even more caution when dealing with a in their wounds” by making them throw up in addition
patient whose lifestyle suggests a greater likelihood of being to their pain! For many reasons, not the least of which
positive (i.e., intravenous drug using, homosexual males). is production pressure, anesthesiologists tend not to take
Acutely jaundiced patients are not suitable candidates for cognizance of their patients™ concerns on this issue. It is
of¬ce-based elective cosmetic surgery. easier to give ondansetron, et cetera, than to modify one™s
Patients with previous hepatic injury would probably anesthetic “game plan” of nearly always administering
be better served by avoidance of halogenated inhalational opioids.
anesthetic agents for elective cosmetic surgery, especially Once the hospital or ASC patient is deposited in
since a suitable alternative in PK MAC/MIA„ technique the PAR, PONV is often no longer the problem of the
exists. anesthesiologist. Small wonder why some surgeons regard
During the ten years Friedberg logged his PK their anesthesia colleagues as indifferent to the surgeon™s
MAC/MIA„ technique cases, approximately 35% of problems. Many surgeons (and patients) rightly perceive
all patients admitted to having PONV with previous the anesthesia as the cause. The hostility generated by
anesthetic experiences. Few patients answered positively the anesthesiologists™ apparent indifference to PONV is
to the open-ended question “Have you had any problems a signi¬cant impediment to securing the cooperation of
with previous anesthesia?” Only by asking the close- the surgeon to implement the paradigm shift involved in
ended question “Did you throw up after your previous performing PK MAC/MIA„ technique.
anesthesia?” will one discover the surprisingly high The of¬ce-based anesthesiologist, in comparison to his
levels of previous PONV in the cosmetic surgical patient institutionally based colleague, does not require a Level
population. So many patients have experienced PONV I study to learn if his patient is experiencing PONV on
that they believe it is a normal part of the anesthetic emergence. The of¬ce-based anesthesiologist is typically
experience! Both Gan6 and Apfel7 agree that a positive physically present with the patient during emergence
history of previous PONV is only one marker to determine and can readily observe with his own eyes the results
high risk of repeat PONV. Other risk markers include of his anesthetic regimen. There is no hiding from the
female gender, nonsmoking status, history of motion outcomes. They may be quite literally in his face!
sickness and plastic surgery. By all standards, Friedberg™s
Adjusting Surgeon Expectations
practice would qualify as high risk for PONV. Despite the
risk of PONV, antiemetics are not used preemptively for There is little likelihood of successfully implementing PK
patients receiving the MIA„ technique, even those with MAC/MIA„ technique without eliciting the active coop-
a positive history of PONV. Only 13 patients experienced eration of the surgeon. It is incumbent on the anesthesiol-
PONV out of a total 2,680 patients, an astounding and ogist attempting to introduce the MIA„ technique to seek
unprecedented 0.5% PONV rate, anesthetized with PK to educate his surgeons about the need for adequate local
MAC/MIA„ technique from March 26, 1992 through analgesia. A blanched ¬eld does not always mean adequate
March 26, 2002.8 All thirteen patients who experienced analgesia. Patient movement in the presence of BIS 60“75
PONV stated they would still prefer PK MAC/MIA„ is an indication for the reinjection of the ¬eld on which
technique to their previous anesthetic. The patients stated the surgeon is working.
that their emesis was a “once-and-done” experience Speci¬cally, the advantages of the MIA„ technique are
compared to the hours and, sometimes, even days of nonopioid, preemptive analgesia (NOPA), the subsequent
PONV. elimination of PONV and the overwhelming majority of
Patients repeatedly con¬rmed Macario™s scienti¬cally postoperative pain. One cannot hope to effect this educa-
validated survey9 that it was preferable to avoid vomiting tion in the heat of an incipient surgery. Speci¬cally, do not
20 Barry L. Friedberg


attempt to introduce the MIA„ technique while looking
Table 2-4. The surgeon™s “golden” rules for the
over the ether screen or in the surgical lounge immediately
MIA„ technique
preceding the case. The surgeon is typically distracted by
1. BIS 60“75 means the patient is adequately asleep.
the anticipation of the operation and is rarely receptive to
2. A blanched surgical ¬eld does not guarantee
instituting profound changes on the spot. Much preferable
complete analgesia.
to the lounge or the OR is to schedule an outside meeting 3. Reinject the ¬eld if the patient moves at BS 60“75.
(i.e., the hospital cafeteria or medical library) to begin a
dialogue with the surgeon. Even better, a meeting outside
the hospital, ASC, or surgical of¬ce is much more likely to
the surgeon from his work. In the context of the MIA„
produce a more receptive audience and the desired effect
technique, it is almost always dif¬cult to discern from the
of cooperation.
conduct of a smooth general anesthetic. It is so if the sur-
The greater the distance is from the stressor environment
geon can learn to follow the “golden” rules of the MIA„
(i.e., the OR), the greater the likelihood is of gaining the
technique (see Table 2-4).
surgeon™s undivided attention.
In this unfettered setting, try to explain to the sur-
Adjusting Patient Expectations
geon that the BIS monitor helps to tell the difference
between patient movement that originates from the spinal Elective cosmetic surgery patients complain after anesthe-
cord (meaning no issue of awareness or recall) from that sia for cosmetic surgery for a variety of reasons. Sometimes
originating from the brain. If he appears not to under- the anesthesiologist wasn™t nice to them, didn™t appear to
stand, consider using the example of the chicken mov- take their concerns to heart, or was too busy to listen. This
ing after its head has been severed. Still, no guarantee of type of complaint illustrates why many otherwise com-
success can be offered, even under these circumstances. petent anesthesiologists may be unsuited for of¬ce-based
All people resist change: lay people, surgeons, and even cosmetic surgery anesthesia. Some anesthesiologists may
anesthesiologists. feel that “frivolous” cosmetic surgery patients are wasting
Having the anesthesiologist express his genuine desire the anesthesiologist™s time when there are medically indi-
to eliminate PONV for his patients and their surgeons is cated surgeries that need his expertise. Worse still, some
an enormous act of kindness. “A single act of kindness anesthesiologists may offer their unsolicited and unwel-
throws out roots in all directions, and the roots spring up come opinion that they do not see anything wrong with
and make new trees. The greatest work that kindness does the cosmetic surgery patients™ appearance. Sometimes the
to others is that it makes them kind themselves” (Amelia complaint is only that the anesthesiologist was rough or
Earhart, missing pioneering female aviatrix). hurt them starting the IV.
The MIA„ technique is not universally acceptable be- Other complaints that can be avoided are those neces-
cause not all surgeons take their own postoperative patient sary to disclose because they are known outcomes or side
calls. Therefore, the advantage of decreasing the number effects. If patients know what to expect, then it is less likely
of those calls for PONV and pain management is not offset that they will complain.
by the minor inconvenience of having to stop operating Glycopyrrolate causes dry mouth. Complaints about
for ten to ¬fteen seconds to reinject a ¬eld. Most surgeons™ dry mouth can usually be circumvented by explaining that
eyebrows arch upward when approached with the ques- dryness is expected for six to eight hours after surgery. It is
tion, “Are you interested in working with me to eliminate also useful to apologize, in advance, for the inconvenience
PONV and postoperative pain in our patients?” of the dry mouth in front of a witness (when available)
Many surgeons have unpleasant memories of perform- who will be with the patient after surgery. That the patient
ing surgery on patients under IV sedation. (The modern may drink and eat freely but their mouth will remain dry
practice of TIVA has helped to erase many of those mem- until the medicine wears off satis¬es most patients. For
ories. See Chapter 11.) Those memories usually consist those still unsatis¬ed, it may be helpful to explain that the
of intolerable patient movement, patients being too asleep alternative to the dry mouth could be a sore throat from
and then too awake, generally distracting and annoying suctioning the excess secretions caused by the ketamine.
Preoperative Instructions and Intraoperative Environment 21


the skin, even though it is slightly uncomfortable when
Table 2-5. Preoperative admonitions
applied. Many patients have stated that the sensor feels
like Velcro r being stuck to their head. Explaining that BIS
1. Dry mouth for six to eight hours postoperatively
2. Blurry vision empowers patients to be in “control” while they are asleep
3. Slight discomfort on application of BIS sensor is very comforting for some anxious patients. During the
4. One out of twenty, or 5%, experience pleasant,
preoperative patient interview, Friedberg writes a series of
colorful dreams
four numbers with accompanying phrases on the BIS sen-
sor package: 0“100 (range), 98“100 (awake), 60“75 (MIA),
To date, given a choice, no cosmetic surgery patient has and 45“60 (GA). The explanation goes as follows: “For the
preferred the pain of a sore throat to the annoyance of a ¬rst twenty years of my practice, I, like most anesthesiolo-
dry mouth. All inconveniences are relative. gists, would guess how asleep you were based on your heart
Some patients will complain about blurry vision upon rate and blood pressure. We anesthesiologists formerly
emergence unless they are told that ointment intended to believed that any changes in your level of anesthesia in your
protect their corneas (or eyes) will be put in after they are brain would be re¬‚ected by changes in your heart rate and
asleep. To date, no cosmetic surgery patient has chosen blood pressure. For fear of giving you too little medicine,
dry, burning eyes to transient blurry vision. see Table 2-5 I would routinely overmedicate by a factor of 20“30% for
If a level-of-consciousness monitor like the BIS is used, fear of administering too little. By giving me a number
it may be helpful to permit patients to touch the back of the by which I may help judge how asleep you are, BIS has
sensor where it will meet their skin. The anesthesiologist revolutionized the delivery of anesthesia care for you, the
can reassure the patient that the sensor will not puncture patient.
BIS is an index with no units like pounds or inches.
The range is from 0“100. Right now, all of us in the
preoperative room are between 98“100. The deeper
your anesthetic becomes, the lower your BIS value will
become. By gradually getting you off to sleep with a
series of minidoses of propofol, I am able to carefully
custom ¬t your anesthetic to you, the individual, at this
moment in time, rather than relying on an off-the-rack,
one-size-¬ts-most approach. By medicating you only to
the level of 60“75, we are able to give you the illusion of
general anesthesia in that you neither hear, nor feel, nor
remember the surgery. I refer to this state as the minimally
invasive anesthesia (MIA)„ technique. Giving still more
medication will take you down to the level recognized
as ˜general anesthesia™ at 45“60. Using this numerical
scale helps to avoid the unnecessary medication we were
formerly obliged to administer for fear of giving you too
little medication. Why would I not want to know how
asleep you are? Isn™t measuring better than guessing? The
medication I am giving you is not designed to medicate
your heart rate or blood pressure. I am trying to medicate
your brain! Hopefully, my presentation was simple and
easy to understand. Do you have any questions for me?”
If one was initially seated for the interview, try to remain
Figure 2-1. Dr. Friedberg holding the left hand of a consenting
seated when asking if the patients have any questions.
patient prior to induction. Witnesses are in the OR but out of the
Remaining seated conveys a more sincere interest on the
picture ¬eld.
22 Barry L. Friedberg


part of the anesthesiologist than standing up and REFERENCES
beginning to exit the room. 1. Friedberg BL: Propofol-ketamine technique, dissociative
As long as the patient is asked for permission in advance, anesthesia for of¬ce surgery: A ¬ve-year review of 1,264 cases.
Aesth Plast Surg 23:70,1999.
it is a very supportive gesture to hold the patient™s hand
2. Iverson, R. E., Lynch, D. J., and the ASPS Committee on
during induction see Fig 2-1. Never induce the patient Patient Safety: Practice advisory on liposuction. Plast Recon-
without another person present in the room. “No adminis- str Surg 100:1478,2004.
3. Friedberg BL: Inaccuracies and omissions with the report of
trator of an anesthetic is safe from having such a charge
the ASPS Committee on Patient Safety Practice Advisory on
preferred against him, and if he and his supposed victim
Liposuction. Plast Reconstr Surg 117:2142,2005.
are alone, it is simply a case of word against word.”10 Lia- 4. Corssen G, Miyasaka M, Domino EF: Changing concepts
bility suits have been ¬led when the patient has fantasized in pain control during surgery: Dissociative anesthesia with
CI-581. Anesth Analg Curr Res 47:746,1968.
and subsequently alleged inappropriate, unprofessional
5. Court MH, Duan SX, Hesse LM, et al.: Cytochrome P-450
behavior on the part of the anesthesiologist.11 The
2B6 is responsible for interindividual variability of propo-
anesthesiologist is defenseless without a witness. fol hydroxylation by human liver microsomes. Anesthesiol
94:110,2001.
CONCLUSION 6. Gan TJ, Meyer T, Apfel CC, et. al.: Consensus guidelines for
managing postoperative nausea and vomiting. Anesth Analg
The of¬ce-based nurses who are full-time employees (as 97:62,2003.
7. Apfel CC, Korttila K, Abdalla M, et al.: A factorial trial of
opposed to leased solely for the surgical schedule) are more
six interventions for the prevention of PONV. N Engl J Med
likely to have personal contact with the patients on preop-
350:2441,2004.
erative as well as postoperative visits in addition to the sur- 8. Friedberg BL: Propofol ketamine anesthesia for cosmetic
gical experience. In contradistinction to the nursing staff surgery in the of¬ce suite, in Osborne I (ed.), Anesthe-
sia for Outside the Operating Room. International Anesthe-
in the hospital or ASC (who are more like the leased of¬ce
siology Clinics. Baltimore, Lippincott, Williams & Wilkins,
employee), the of¬ce-based nurses tend to take their work
41:39,2003.
more personally and “bond” with the patients because of 9. Macario A, Weinger M, Carney K, et al.: Which clinical anes-
the extended contact. This continuity of care promotes the thesia outcomes are important to avoid ? The perspective of
patients. Anesth Analg 89:652,1999.
personalization of medical care that is a reason, beyond
10. Buxton D: Anaesthetics. London, H.K. Lewis, 1888;
the welcome ¬nancial advantage, that growing numbers p 145.
of patients prefer to have cosmetic surgery in the of¬ce 11. Balasubramaniam B, Park GR: Sexual hallucinations dur-
ing and after sedation and anaesthesia. Anaesthesia 58:1149,
setting. There is a greater perception of “caring” in their
2003.
care!
3 Level-of-Consciousness Monitoring
Scott D. Kelley, M.D.



INTRODUCTION
EVOLUTION OF PATIENT MONITORING
LEVEL-OF-CONSCIOUSNESS MONITORING
BISPECTRAL INDEX: THE PROTOTYPE LEVEL-OF-CONSCIOUSNESS
MONITOR
Bispectral Analysis
BIS Algorithm
BIS Index
VALIDATION OF THE BIS INDEX
ASSESSING THE BIS INDEX IN RECOVERY OF CONSCIOUSNESS
ASSESSING CONSISTENCY OF BIS INDEX PERFORMANCE
FACTORS AFFECTING THE CONSCIOUSNESS-MONITOR VALUES
USING CONSCIOUSNESS MONITORS IN ANESTHESIA PRACTICE
CONSCIOUSNESS MONITORING DURING TYPICAL GENERAL ANESTHESIA
Consciousness Monitoring During the Induction of Anesthesia
Consciousness Monitoring During Endotracheal Intubation
Consciousness Monitoring During the Maintenance of Anesthesia
Maintenance strategies using BIS monitoring
Consciousness Monitoring During Emergence from Anesthesia
Responding to Consciousness-Monitoring Changes During Anesthesia
CONSCIOUSNESS MONITORING AND GLOBAL CNS FUNCTION
EEG Variants and EEG Signal Analysis
Paradoxical delta phenomenon
Small-amplitude EEG
Epileptiform activity
High-frequency artifacts
Pacemakers
Medical/surgical devices
Electrocautery devices
CONSCIOUSNESS MONITORING AND THE “ABNORMAL” BRAIN
BIS AND PHARMACOLOGIC RESPONSES
Nitrous oxide N 2 O
Ketamine
Etomidate
CLINICAL MANAGEMENT
SUMMARY: CLINICAL BENEFITS OF CONSCIOUSNESS MONITORING




23
24 Scott D. Kelley


combination with assessment of clinical signs and tradi-
INTRODUCTION
tional monitoring, permit a more complete approach to
Level-of-consciousness monitoring allows anesthesia clin-
adjusting the dosing and mixture of anesthetic, sedative,
icians to measure the effects of anesthesia and sedation
and analgesic agents.
on the brain, allowing them to deliver anesthesia with
more precision. With the variety of anesthetic techniques,
agents, and approaches utilized during anesthesia for cos- LEVEL-OF-CONSCIOUSNESS MONITORING
metic surgery, a consciousness monitor is one of the
Consciousness-monitoring technologies provide mea-
important tools that aid in the goal of improving patient
surement of the hypnotic effect of anesthesia. They have
care and achieving excellent outcomes.
proven to be accurate and reliable in nearly all patients
and clinical settings and are robust in the presence of the
most commonly used anesthetic and sedative agents. At
EVOLUTION OF PATIENT MONITORING
the core of most consciousness-monitoring technologies
Patient assessment and intraoperative monitoring during is the surface electroencephalogram (EEG). This complex
anesthesia has undergone gradual change and re¬nement. physiologic signal is a waveform that represents the sum
Observations of clinical signs such as pupil response, pat- of all brain activity produced by the cerebral cortex. The
terns of respiration, quality of the pulse, and movement EEG changes in response to the effects of anesthetic and
sedative/hypnotic agents.2 Although individual drugs can
were ¬rst augmented by direct measurement of physiologic
endpoints including blood pressure, heart rate, and respi- induce some unique effects on the EEG, the overall pattern
ratory rate and volume. With the development of pulse of changes is quite similar for many of these agents. During
oximetry and capnography, precise assessments of venti- general anesthesia, typical EEG-changes responses include
latory management could be made. The use of end-tidal an increase in average amplitude (power) and a decrease
agent analysis and peripheral nerve stimulation provided in average frequency. These changes become more evident
anesthesia clinicians the ability to measure pharmacologic as the EEG waveform frequency patterns move from beta
agent concentration and effect, respectively. Although not to delta”the pattern consistent with deep anesthesia.
used during cosmetic surgery, cardiac function can be The complex EEG waveform can be broken down into
evaluated using technologies that range from pulmonary its individual components, analyzed using a mathematical
artery catheters and transesophageal echocardiography to technique called power spectral analysis and displayed as
new methods of continuous blood pressure and cardiac power per frequency component in a “power spectrum.”
output monitoring. Power spectral analysis results in one or more numeric
descriptors known as processed EEG parameters.3
Despite the remarkable improvements in assessment of
the cardiovascular and pulmonary function during anes- Many attempts have been made to utilize power spec-
thesia, direct determination of the effect of the anesthetic tral analysis and processed EEG parameters to gauge the
and sedative agents on the central nervous system has effect of anesthesia on the brain. Processed EEG parame-
remained limited. Careful clinical investigations demon- ters that have been investigated as indicators of anesthetic
strated that hemodynamic responses do not necessarily effects include the 95% spectral edge frequency as well as
provide an accurate representation of the central ner- the median frequency. These parameters are various char-
vous system responsiveness to anesthetic agents. Therefore, acteristics that describe the EEG power spectrum. Median
hemodynamic responses were unreliable indicators of brain frequency and 95% spectral edge frequency indicate the
status.1 spectral frequency below that contains either 50% or 95%
In contrast, technologies that permit independent of the power in the EEG.
neurophysiological monitoring of the central nervous Unfortunately, for most anesthetic drugs, the relation-
system provide a direct measure of brain response ship between dosage and changes in EEG power and fre-
during anesthesia and sedation, allowing clinicians to quency is not straightforward, so it has been dif¬cult to use
¬ne-tune the perioperative management of each patient. traditional processed EEG parameters in a clinically reli-
Accurate monitoring and targeting of brain effect, in able way. A clear challenge for further adoption of the EEG
Level-of-Consciousness Monitoring 25


as a reliable indicator of anesthetic effect was to overcome method to examine this class of anesthesia-effect monitors.
the lack of adequate correlation between anesthetic dose BIS monitoring provides a direct and accurate method for
and processed EEG parameters derived from power spec- continuous level-of-consciousness monitoring through-
tral analysis. New waveform analysis techniques have been out the course of anesthetic or sedative administration in
developed. Algorithms have been introduced to translate the setting of cosmetic surgery.
EEG waveform analysis into clinical monitoring platforms. The BIS Index is a numerically processed, clinically val-
The challenge of using processed EEG parameters to suc- idated EEG parameter. Unlike traditional processed EEG
cessfully monitor hypnotic level during anesthesia and parameters derived from power spectral analysis, the BIS
sedation has been met. Index is derived utilizing a composite of multiple advanced
EEG signal-processing techniques”including bispectral
analysis, power spectral analysis, and time domain analy-
BISPECTRAL INDEX: THE PROTOTYPE
sis.4 As seen in Figure 3-1, these components are combined
LEVEL-OF-CONSCIOUSNESS MONITOR
to optimize the correlation between the EEG and the clin-
ical effects of anesthesia.
The Bispectral Index (BIS Index) is the most widely utilized
The U.S. Food and Drug Administration cleared the BIS
level-of-consciousness monitor. Because of its wide avail-
Index (Aspect Medical Systems) as an aid in monitoring
ability and extensive investigation, BIS provides the best



EEG




Bispectrum
Power Spectrum
Pu [IV2 nd3]




log-v2




r2 (Hz)
r1 (Hz)
Frequency (Hz)




Near Suppression
and Suppression
Measurement




BIS=40
Figure 3-1. Components of Bispectral (BIS) Index.
26 Scott D. Kelley


the hypnotic effect of anesthetics and sedatives in 1996, a clinically tuned, validly processed EEG parameter was
allowing its introduction into routine clinical practice. developed.
Subsequent to BIS, other level-of-consciousness moni-
tors now cleared to measure anesthetic effect in surgi-
BIS Index
cal patients include Patient State Index (Physiometrix);
The BIS Index is a number between 0 and 100 scaled to
Entropy (GE Healthcare), SNAP II (Everest Biomedi-
correlate with important clinical endpoints during admin-
cal), Cerebral State Monitor (Danmeter), and Narcotrend
istration of anesthetic agent (see Fig. 3-2). BIS values near
(Schiller Medical).
100 represent an “awake” clinical state while 0 denotes the
Focusing on the BIS technology as the prototype con-
maximal EEG effect possible (i.e., an isoelectric EEG).
sciousness monitor, there are three key elements integral
As the BIS Index value decreases <70, the probability
to the system as it functions as a consciousness monitor
of explicit recall decreases dramatically. At a BIS Index
during anesthesia:
value of <60, a patient has an extremely low probability of
consciousness.
1. EEG Signal Analysis: Bispectral Analysis
BIS Index values <40 signify a greater effect of the
2. BIS Algorithm
anesthetic on the EEG. At low BIS values, the degree of
3. BIS Index
EEG suppression is the primary determinant of the BIS
value.6 Prospective clinical trials have demonstrated that
Bispectral Analysis
maintaining BIS Index values in the range of 40“60
A portion of the cortical EEG re¬‚ects changes attributable
improves the perioperative period following general anes-
to harmonic and phase relationships between cortical
thesia and reduces the risk of intraoperative awareness.7
and subcortical neural generators. These relationships are
During sedation care, BIS Index values >70 may be
altered during hypnosis, producing characteristic patterns
observed during adequate levels of sedation, but patients
in the EEG. Bispectral analysis”and its mathematical
may have a greater probability of consciousness and poten-
results, for example, bicoherence, bispectrum, real triple
tial for recall.
product”is a sophisticated signal-processing methodol-
ogy that assesses relationships among signal components
and captures synchronization within signals like the EEG.
VALIDATION OF THE BIS INDEX
By quantifying the correlation between all the frequencies
within the signal, bispectral analysis (together with power A number of studies have validated the accuracy of the BIS
spectral and cortical EEG analysis) yields an additional Index in assessing hypnotic drug effect on level of con-
EEG descriptor of brain activity during hypnosis.4 sciousness. In one investigation utilizing common anes-
thetic agents and combinations (propofol, midazolam,
BIS Algorithm iso¬‚urane, midazolam-alfentanil, propofol-alfentanil, and
A key milestone in the development of a consciousness propofol-nitrous oxide), simultaneous measurements of
the BIS Index and sedation state were obtained.8 In
monitor was to identify EEG features or “descriptors””
bispectral or otherwise”that were highly correlated with Figure 3-3, logistic regression curves display the proba-
sedation/hypnosis induced by the most commonly used bility of response to voice and the probability of free recall
anesthetic agents. During development of the BIS Index, as a function of BIS Index for all agents tested. The overall
several EEG features were identi¬ed by analyzing a sigmoid shape of the curve indicates that the BIS Index
database of EEGs from more than 5,000 subjects who had proved to be a good indicator of hypnotic state. The BIS
received one or more of the most commonly used hyp- Index performed as well as (or better than) measured or
notic agents and who had been evaluated with simultane- targeted drug concentration as an indicator of the hyp-
ous sedation assessment.5 Multivariate statistical models notic state. Free recall of word or picture cues is lost when
were used to derive the optimum combination of EEG fea- the BIS Index decreases to the 70“75 range, indicating that
tures to correlate with clinical endpoints of sedation. From memory impairment occurs at higher BIS Index values than
this iterative process, the BIS algorithm that would yield loss of consciousness.
Level-of-Consciousness Monitoring 27




100
BIS=90



Awake
80

BIS=70

Moderate




BIS INDEX RANGE
sedation
60

BIS=50

General
anesthesia

40

BIS=30



Deep
20
anesthesia

BIS=10




0


Figure 3-2. BIS index range.


Further investigation has suggested that some memory of the accuracy of the BIS Index in the assessment of
function”that is, “learning” memory formation without unconsciousness.
conscious recall”may occur at lower BIS Index values.9
This early data has been supported by subsequent inves-
tigations that tested the ability of the BIS Index to accu- ASSESSING THE BIS INDEX IN RECOVERY
rately predict the state of consciousness. In one study, the OF CONSCIOUSNESS
BIS Index had signi¬cantly higher prediction probability
for level of consciousness when compared to the tradi- Taken together, these studies support the accuracy of the
tional hemodynamic variables (blood pressure and heart BIS Index as a measure of hypnotic state. In particular, they
rate).10 More importantly, in this study of volunteers dur- validate the ability of the BIS Index to determine the tran-
ing propofol anesthesia, a BIS Index threshold value of sition into unconsciousness. During general anesthesia
60 achieved a sensitivity of 99% and a speci¬city of 81% care, a key imperative is the maintenance of unconscious-
to predict responsiveness to verbal command, indicative ness. Using the isolated forearm technique, accuracy of BIS
28 Scott D. Kelley


of anesthesia or sedation, the BIS Index is a stable mea-
1.00
surement of hypnotic effect and does not vary signi¬cantly
0.80 over time.
Probability of Response




Responsiveness Patient age is a strong determinant of the anesthetic
0.60 dose required to produce a clinical effect. For example,
Explicit Recall
the MAC values for inhalation agents decrease as patient
0.40
age increases. In a study of the in¬‚uence of age on hyp-
notic dose requirements, the dose of sevo¬‚urane required
0.20
to achieve hypnotic effect differed markedly among dif-
ferent age groups and showed the expected decrease in
0.00
0 20 40 60 80 100 dose required with increasing age. The BIS Index value
BIS
displayed a consistent relationship to the sedative effects
Figure 3-3. Probability of response at differing BIS levels. of sevo¬‚urane across this wide range of age groups “ unre-
lated to dosage.11 Thus, the BIS Index offers a distinct
advantage over anesthetic-dose monitoring as a tool to
Index monitoring to predict the return to consciousness measure and manage depth of sedation.
following induction of anesthesia was investigated.1 After
a single bolus dose of propofol or thiopental, patients were
FACTORS AFFECTING THE
assessed for consciousness at intervals by asking them to
CONSCIOUSNESS-MONITOR VALUES
squeeze the investigator™s ¬ngers while the BIS Index was
monitored continuously. Although the intensity and dura- Displayed values on consciousness monitors, such at the
tion of hypnotic effect varied considerably among patients, BIS monitor, are derived from the preceding ten to thirty
the recovery of consciousness occurred consistently at a seconds of EEG data. As such, the displayed value of a brain
BIS Index value above 60. A BIS Index value <65 indicated monitor is a measure of the state immediately prior to the
a probability of <5% that consciousness would return calculation. A similar analogy would be the data provided
within ¬fty seconds. Changes in blood pressure and heart by pulse oximetry during management of a dif¬cult air-
rate, in contrast, were poor predictors for the recovery of way. There is an expected delay in oxygen saturation that
consciousness. results from physiologic processes, and airway dif¬culty
may be clearly evident prior to any changes in saturation.
Similarly, increases in saturation will lag behind the
ASSESSING CONSISTENCY OF BIS
restitution of adequate ventilation and oxygenation of the
INDEX PERFORMANCE
lungs.
Crucial to the value of level-of-consciousness monitor- Under steady-state conditions (e.g., in a controlled
ing is consistency of performance with different anesthetic research trial), most consciousness monitors predict sub-
agents and different patient populations. This consistency sequent responses to voice command or memory for
is extremely important to anesthesia providers because of words. However, the clinical situation during surgery is
the broad range of agents utilized and intrinsic patient notably different because of the lack of steady-state condi-
variability. tions. Intraoperative consciousness-monitor values will be
The consistency of the relationship between the BIS in¬‚uenced by a number of variables including brain con-
Index value and brain status has been tested across dif- centration of anesthetic, level of analgesia (via in¬ltrated
ferent hypnotic agents (intravenous and inhalation anes- local anesthetic or systemic analgesic administration), and
thetics) as well as different patient types. In the validation degree of surgical stimulation.
studies mentioned earlier, the relationship between the BIS It must be recognized that the net brain state, as mea-
Index and level of clinical response was nearly identical for sured by the BIS Index or another consciousness-monitor
all hypnotic agents tested or when two anesthetic drugs are parameter, changes as a result of these dynamic variables.
combined.8 Furthermore, during steady-state conditions Nevertheless, consciousness monitors provide an accurate
Level-of-Consciousness Monitoring 29


measure of the net effect and responses of the brain to new
Table 3-1. Considerations in hemodynamic
conditions. They are unable, however, to predict future
monitoring
changes.
Average hours at work monitoring traditional vital signs
provide a measure of cardiovascular responses to
anesthesia administration and surgical stimulation.
Although changes in blood pressure and heart rate may
USING CONSCIOUSNESS MONITORS IN
correlate with the anesthetic effect in some instances,
ANESTHESIA PRACTICE many factors can interfere with this relationship,
including the following:
The addition of BIS or other forms of level-of-conscious- 1. Vasoconstrictor additives to local anesthetic
ness monitoring adds a new dimension to patient man- solutions
2. Interaction of multiple anesthetic agents
agement during anesthesia and sedation. These monitors
3. Unexpected synergistic drug effects
complement other forms of monitoring and potentially
4. Patient cardiovascular status
impact all phases of anesthesia care. 5. Medications that attenuate cardiovascular
Despite signi¬cant advances in patient monitoring tech- responses (e.g., clonidine premedication or
other antihypertensives)
niques, most clinicians would agree that patient responses
to anesthesia are frequently unpredictable and precise dos-
ing of anesthetics and sedatives remains a challenge. Much
of the uncertainty in anesthesia centers on the fundamen-
tal concern of “adequacy of anesthesia.” Traditionally, this Anesthetic dosing that ensures adequacy of anesthesia
concern is justi¬ed since the hemodynamic parameters may produce hemodynamic changes close to acceptable
used to infer adequacy of anesthetic effect have been limits of cardiovascular response. This approach is fur-
shown to be unreliable indicators of brain status. Clin- ther complicated by the dif¬culty of measuring the thera-
ical judgment and experience remain the cornerstones peutic window in some patients. In these cases, the anes-
for managing uncertainty, and consciousness monitor- thesia provider may be unable to discriminate between
ing provides valuable additional data that enhances such the dose required to achieve the therapeutic effect (i.e.,
judgment. Direct measurement of the hypnotic effect of unconsciousness) and the dose producing undesired car-
the agent, through continuous consciousness monitor- diovascular effects.
ing, substantially facilitates intraoperative patient assess- Anesthetic agent monitoring (e.g., end-tidal agent anal-
ment, titrated dosing and balance of anesthetic agents, and ysis), although common in hospital and surgery center
patient recovery process. locations, is not routinely available in many of the loca-
Some of the challenges and clinical considerations asso- tions where cosmetic anesthesia is provided. Some of the
ciated with hemodynamic monitoring are outlined in clinical considerations important in utilizing anesthetic
Table 3-1. Because heart rate and blood pressure are not agent analysis are highlighted in Table 3-2. End-tidal agent
exquisitely sensitive to changing levels of consciousness, the analysis, although very accurate, measures only anesthetic
patient™s hypnotic state cannot be accurately inferred from dose, not the anesthetic effect on the target organ, the brain.
changes in these vital signs.12 For example, administration Thus, agent-analysis measurements cannot identify alter-
of cardiovascular agents will change blood pressure and/or ations in expected levels of hypnosis due to pharmaco-
heart rate, typically without affecting anesthetic depth. dynamic variability among patients. Rather, the existence
A variety of anesthetic adjuvants, such as neuromuscular of this variability means that identical drug concentra-
blocking agents, reversal agents, and local anesthetic solu- tions commonly produce considerably different hypnotic
tions with vasoconstrictors, may have an effect on both responses among individuals or within the same person at
cardiovascular reactivity and the anesthetic state but with- different times.
out a direct correlation between the two. Finally, changing Consciousness monitoring continually measures the
levels of surgical stimulation may impact hemodynamics hypnotic effects of administered anesthetic doses, regard-
or level of consciousness independently. less of pharmacokinetic or pharmacodynamic variability.
30 Scott D. Kelley


Monitoring level of consciousness during all phases of
Table 3-2. Considerations in anesthetic agent
anesthesia can assist in evaluating a patient™s current status
measurement
and will provide a continuous indicator of the hypnotic
Measurement of end-tidal inhalation agent state.
concentration is an effective method of con¬rming Most consciousness-monitoring systems display a
agent delivery and assessing anesthetic uptake and
graphical trend that represents the ongoing calculations of
distribution. Empiric-dosing regimens to maintain
consciousness index during the case. A typical BIS trend
end-tidal agent concentration at certain values (e.g.,
greater than MACawake ) provide useful guidelines obtained during general endotracheal anesthesia is dis-
during anesthesia care. However, anesthetic dosing
played in Figure 3-4. The BIS value itself is displayed as a
using only this measurement does not necessarily
single value that is calculated from data gathered over the
consider the following:
last ¬fteen to thirty seconds of EEG recording and updated
1. Changing requirement due to varying levels of
surgical stimulation or adequacy of local every second. Deriving the BIS Index value from several
anesthetic effect
seconds of EEG data effectively “smooths” the data to pre-
2. Individual responses and sensitivity to an agent
vent excessive ¬‚uctuations in BIS values and allows a value
3. Impact of age, gender, or metabolic rate on
anesthetic requirement to be determined even if the EEG signal is brie¬‚y inter-
4. Synergistic interactions among multiple anesthetic rupted. When abrupt changes occur in hypnotic state”
agents
for example, during induction or rapid emergence”the
5. Impact of coexisting disease, or preexisting
BIS value may lag behind the observed clinical change by
alcohol/drug dependence
approximately ¬ve to ten seconds. A BIS value, although
extremely responsive, is not instantaneously altered by
For example, use of BIS values and responses as a guide changes in clinical status.
allows the anesthesia provider to administer a particular Monitoring the BIS trend is particularly useful during
anesthetic agent at the dose required to achieve the desired surgery. Changing anesthetic dosing to lighten or deepen
hypnotic effect in the individual patient. anesthesia will usually manifest as a slow upward or down-
ward trend, respectively. As seen in Figure 3-4, for exam-
ple, a small bolus of propofol will be displayed as a short-
CONSCIOUSNESS MONITORING DURING
lived downward dip in the BIS trend. In contrast, a cortical
TYPICAL GENERAL ANESTHESIA
response caused by intense surgical stimulation is often sig-
A “typical” general anesthetic case involves three phases: naled by large, abrupt increases in the BIS trend. This latter
trend change is most likely to occur when the anesthetic
1. induction of anesthesia (and frequently airway
technique relies heavily on hypnotic agents but includes
management)
little or no analgesic component (local analgesia, opioids,
2. maintenance of anesthesia
or other analgesic agent).
3. emergence from anesthesia


100

80 Induction Maintenance Emergency

60
BIS




Figure 3-4. BIS trend during a typical gen-
eral anesthesia procedure.
40

20

0
08.45 08.55 09.05 09.15 09.25 09.35
Time
Level-of-Consciousness Monitoring 31


Clinicians should be cautious about using a particular lation, thus preventing resultant hypertension and tachy-
consciousness-monitor value in isolation as a predictor of cardia. Several strategies are commonly used to blunt the
patient responsiveness, because arousal responses to pain blood pressure and heart rate response, including the
are not well correlated with absolute hypnotic effect. How- following:
ever, BIS monitoring will document the cortical EEG reac-
tivity responses associated with stimulation.
1. Suf¬cient dosing of intravenous induction agent
Further, even allowing for the delay associated with sig-
(e.g., propofol, thiopental)
nal processing, surgical stimulation can sometimes pro-
2. Opioid supplementation (e.g., fentanyl)
duce a rapid increase in BIS values prior to the appearance
3. Administration of intravenous or endotracheal
of other clinical signs such as hypertension or movement,
lidocaine
facilitating timelier anesthesia management.
4. Administration of antihypertensives (e.g., esmolol)
Cyclic oscillation in BIS under steady-state conditions
5. Alternative intubation methods (e.g., ¬beroptic
may provide an indication of the shifting balance between
intubation)
sensory suppression and sensory stimulation. In volunteer
studies, greater BIS variability was observed when seda-
tives were used alone compared to when an analgesic agent With the use of these concomitant medications, how-
(i.e., alfentanil) was used concurrently.13 ever, the potential for hypotension during the induction
period may also increase (vide supra).
Consciousness Monitoring During BIS responses to stimulation associated with laryn-
the Induction of Anesthesia goscopy and intubation can be markedly attenuated in
Induction of anesthesia may have individualized goals that a dose-dependent fashion with opioid administration, for
are case-speci¬c or patient-speci¬c. The overall goal of example, fentanyl or remifentanil. It should be noted that
induction is to produce unconsciousness rapidly. a single BIS value during the induction period is unable to
Another induction goal may be to potentially manage predict subsequent BIS responses to signi¬cant stimula-
the airway in the unconscious patient and establish ade- tion. For example, in one study examining hemodynamic,
quate anesthesia conditions for surgery. The most com- BIS, and awareness responses, BIS values less than 60 prior
mon forms of controlling the airway during general anes- to intubation did not guarantee a lack of arousal responses
thesia are either via endotracheal intubation or insertion following laryngoscopy and intubation. The utility of the
of a laryngeal mask airway (LMA). In each of these situa- BIS monitor is greatly enhanced by trending the EMG as
tions, production of certain anesthetic conditions related a secondary trace. BIS values lag 30 seconds behind real
to the airway need to be ideal. Consciousness monitor- time. Typically, arousal responses are preceded by a spike
ing can assist the anesthesia professional to achieve those in (real time) EMG. This study did note that BIS Index
conditions. was an accurate indicator of current clinical state: arousal
As seen in Figure 3-4, the BIS Index trend clearly responses were observed only in patients with high BIS
values.14
displays the effects of anesthesia induction in a patient
undergoing hernia repair. Close inspection of the left In other settings, particularly in elderly patients or
portion of the trend demonstrates rapid decrease of the patients with signi¬cant coexisting illness, a gentle induc-
BIS Index during induction using bolus administration tion technique is sometimes used to minimize perturba-
of intravenous hypnotic in preparation for endotracheal tion of blood pressure and heart rate.
intubation. This can be achieved with smaller and/or divided
dose administration of induction agent or with low-dose
administration of an inhalation agent. During this method
Consciousness Monitoring During
of induction, BIS monitoring can measure achievement
Endotracheal Intubation
of the desired hypnotic effect from the various induction
During endotracheal intubation, one general goal of the
protocols.
anesthesia provider is to minimize cardiovascular stimu-
32 Scott D. Kelley


Consciousness Monitoring During patient management. Table 3-1 outlines conceptual man-
the Maintenance of Anesthesia agement strategies based on integration of clinical pro¬le
with BIS data for “balanced” anesthesia techniques uti-
In most surgical cases, the “maintenance” phase of anes-
lizing hypnotic and analgesic components. Using the BIS
thesia care is the longest. During this intraoperative period,
value in combination with hemodynamic data improves
anesthesia care focuses on the following:
the rational selection of sedatives, analgesics, and auto-
1. Maintenance of an adequate anesthetic state
nomic blockers in what can otherwise be very confusing
2. Maintenance of physiologic homeostasis during
clinical situations.
surgical events
Although a BIS value of 45“60 is a typical target dur-
3. Avoidance of potential adverse events
ing the maintenance phase, the BIS value target range
4. Preparation for smooth, rapid emergence
needs to be tailored to the anesthetic technique. For
Consciousness monitoring during anesthesia mainte- example, in cases of balanced anesthesia involving suf-
nance can help meet these goals of intraoperative care by ¬cient analgesia administration or other agents to assure
providing continuous con¬rmation of hypnotic effect” adequate analgesia, the typical target range of 45“60 is
for all classes of anesthetics, under most operative condi- most appropriate for general anesthesia. However, for
tions, and for nearly all types of patients. anesthesia techniques that utilize little or no opioid or
Level-of-consciousness monitoring can improve intra- analgesic supplementation, increased dosing of the hyp-
operative decision making. For example, observation of notic agent”typically, an inhalation anesthetic”to pro-
the BIS trend can facilitate diagnostic evaluation of unex- duce acceptable suppression of noxious stimulation will
pected changes in cardiovascular system reactivity, per- result in lower BIS values, frequently in the 25“35 range.
mitting rapid restoration of homeostasis. Consciousness BIS values in the range of 60“75 may produce excel-
monitoring can also guide adjustments in anesthesia lent results in cosmetic procedures performed with local
care”for example, an increase in administered anesthetic anesthetic in¬ltration and intravenous sedation/analgesia
administration.17
dose, analgesic supplementation, or the addition of an
antihypertensive. With the addition of consciousness- It is again important to note that reliance on
monitoring information, the anesthesia provider can consciousness-monitoring information alone for intra-
monitor not only cardiovascular responses but central ner- operative anesthetic management is not appropriate.
vous system”speci¬cally, cortical”responses as well. Clinical judgment is crucial when interpreting this data.
Patient assessment should include evaluation and corre-
Maintenance strategies using BIS monitoring lation of level-of-consciousness data with hemodynamic
and other monitoring data as well as observation of clinical
Two important clinical trials have demonstrated that the
signs. Consciousness-monitoring data should be thought
adjustment of anesthetic delivery to maintain the BIS
of as an additional piece of information that must be inter-
Index within a bracketed target range during mainte-
preted in the context of all other information available for
nance of general anesthesia results in improved periop-
patient assessment.
erative recovery patterns as compared to standard anes-
thesia care.15,16 These studies and several others have
Consciousness Monitoring During
highlighted the positive patient outcomes realized when
Emergence from Anesthesia
consciousness monitoring is combined with assess-
ment of intraoperative hemodynamic data and clinical Level-of-consciousness monitors document the decreas-
observations of movement and autonomic response to ing effect of anesthesia when agent delivery is reduced
generate patient-management strategies. Consciousness- or stopped and the patient enters the emergence phase.
monitoring data can ensure that the key anesthetic goals Because these monitors provide a real-time measure of
of hypnosis and analgesia are met throughout the main- level of consciousness, it allows the anesthesia provider
tenance phase. to ¬ne-tune titration downward according to individ-
The integration of consciousness monitoring with ual patient response. Consciousness monitoring permits
other traditional monitoring creates new insight regarding reduction in anesthesia dosing in tandem with the decrease
Level-of-Consciousness Monitoring 33


in surgical stimulation, promoting a rapid emergence that CONSCIOUSNESS MONITORING AND GLOBAL
avoids premature recovery of consciousness as well as CNS FUNCTION
delayed emergence from anesthesia.
As seen in Figure 3-4, in the patient undergoing hernia Consciousness-monitoring technologies aim to provide a
repair, emergence was heralded by the rapid increase in consistent and reliable measure of level of consciousness
the BIS Index. BIS monitoring of brain status documented across a wide spectrum of patients and anesthetic agents.
the decreasing anesthetic effect and the increased level of Nevertheless, in certain circumstances, displayed values on
consciousness that correlated with patient eye opening in consciousness monitors may not be an accurate re¬‚ection
response to voice command. of the hypnotic state of the patient. As noted earlier, con-
sciousness monitoring is an adjunct to clinical judgment,
Responding to Consciousness-Monitoring not a substitute for it. This section presents certain unusual
Changes During Anesthesia circumstances that may produce inaccurate readings and
the management of those situations.
When consciousness monitoring is used during anesthe-
Most signal artifact in waveforms such as the ECG,
sia care, it is necessary to note ¬‚uctuations in calculated
SpO2 , or arterial blood pressure is easier to detect than
level-of-consciousness values. However, many such ¬‚uc-
artifact within the EEG waveform. Indeed, with the vari-
tuations, like a single ¬‚uctuation in blood pressure, are
able frequency and amplitude of the EEG waveform, the
not necessarily clinically signi¬cant. However, in some sit-
presence of certain types of artifact may be extremely dif¬-
uations, additional assessment is required in response to
cult to recognize visually. Most consciousness-monitoring
changes in these values.
systems utilize a variety of signal analysis methods to detect
Changes in the hypnotic state due to changes in dose
and reduce extraneous artifacts that contaminate the EEG.
and/or patterns of agent delivery will produce changes
For example, many of the improvements in the BIS sys-
in the consciousness-monitoring value. Normally, if the
tem over the past decade have been in the area of artifact
change in anesthetic dosing was incremental”for exam-
processing. Despite these improvements, however, artifact
ple, slight adjustment in the vaporizer setting or modest
produced by some non-EEG signals can potentially inter-
changes in intravenous anesthetic infusion dosing”these
fere with the ability of these systems to render an accurate
changes in BIS values are gradual. In contrast, sudden
value. Given this potential for artifact contamination, the
changes would not be expected and would require con-
clinician must identify situations where the underlying
¬rmation and assessment.
EEG signals”and hence the calculated value”may not
accurately re¬‚ect the clinical endpoints of sedation and
CONSCIOUSNESS MONITORING
hypnosis.
AND GLOBAL CNS FUNCTION
Inaccurate calculation of level-of-consciousness values
due to artifact contamination of the EEG signal may result
Since the introduction of more routine cortical EEG mon-
from electromyogram (muscle) activity, high-frequency
itoring using BIS and other consciousness-monitoring
artifacts (e.g., from medical devices), EEG variants and
technologies, a variety of clinical reports have noted anec-
dotal bene¬ts offered by this form of brain monitoring.18 signal analysis, and unique pharmacologic responses (elec-
tromyogram [EMG]).
Although consciousness monitoring is not intended to
The most frequent source of EEG contamination in
be used for regional ischemia monitoring”for exam-
sedated and lightly anesthetized patients is the EMG.
ple, during carotid endarterectomy procedures”the rela-
This contamination results from increased tone of
tionship of the EEG and to global CNS function does
the frontalis muscle of the forehead that lies beneath
provide an indication of patient response and tolerance
the BIS sensor. Typically, signi¬cant EMG activity is
to intraoperative conditions. As such, acute variations
present during awake states and during emergence from
may alert the anesthesia and surgical teams to changes
anesthesia.
in the patient condition that indicate the need for addi-
The frequency spectrum of endogenous EMG activ-
tional evaluation of brain status, including adequacy of
perfusion.19 ity partially overlaps with the frequency spectrum of the
34 Scott D. Kelley


awake EEG. In order to maximize the sensitivity of BIS to 3. Epileptiform activity
detect wakefulness, high frequency signals are analyzed by 4. Missed near-suppression
the BIS processing system. As a result, in the presence of
Paradoxical delta phenomenon
signi¬cant EMG activity, calculated BIS values may tend
to be higher”in a range that normally may indicate the In a small percentage of patients, a paradoxical response
potential for inadequate anesthesia”than would actually develops in the EEG during a lightening of anesthesia
re¬‚ect the true hypnotic state of the patient.20 As in all clin- effect or in response to surgical stimulation. This phe-
ical situations, patient-care decisions should not be based nomenon, known as “paradoxical arousal” or “paradox-
solely upon the displayed BIS value but rather upon com- ical delta,” is characterized by a slowing of the EEG,
with large delta waves.21 In response to this unusual EEG
plete clinical assessment of the patient. During intraoper-
ative anesthesia situations where EMG is biasing BIS to a slowing, the level-of-consciousness value may decrease
higher value, administration of either increased anesthetic suddenly.
or a muscle relaxant can produce a signi¬cant decrease in
Small-amplitude EEG
EMG.
As noted, appearance of high-frequency facial EMG In one case report, an awake individual had a very low BIS
activity commonly occurs during awakening and, in fact, value. This was presumed to be the result of EEG vari-
has been incorporated into other consciousness moni- ant activity”speci¬cally, a congenital, extremely small-
amplitude EEG.22
tors. During emergence from anesthesia, BIS frequently
increases in conjunction with this increased EMG activity,
Epileptiform activity
although the presence of EMG is not required for BIS to
track the return of consciousness. The occurrence of epileptiform activity, for example, dur-
Although EMG activity can sometimes be seen in the ing the administration of high concentrations of sevo¬‚u-
raw EEG trace, typically it is more dif¬cult to discern. rane anesthesia, can also lead to temporal increases in BIS
Therefore, in situations with the potential for EMG con- values. In one report, BIS values were appropriately low
tamination, it is important to note the amount of activ- during administration of high concentrations of sevo¬‚u-
ity generated by EMG. BIS systems display an EMG rane. However, with the development of epileptiform
parameter that shows total power of electrical activity activity, BIS values increased abruptly during the epilep-
seen in the frequency bandwidth of 70“110 Hz. When tic discharge, corresponding to increases in cerebral blood
the EMG power exceeds 50 dB, there is greater poten- ¬‚ow (and presumably glucose metabolism) measured with
PET scanning.23 Also of note is the transient dip in BIS
tial for EMG contamination of the underlying EEG
signal. following discontinuation of sevo¬‚urane and cessation of
To further address the problem of EMG contamination, seizure activity. In situations of concern regarding sevo¬‚u-
Aspect Medical Systems developed the BIS-XP platform. rane administration or potentially local anesthetic toxic-
This system uses dual-channel EEG processing, making it ity, unexpected increases in BIS, particularly following an
more resistant to the effects of EMG. The potential for spu- increase in the administered dose, should prompt a rapid
rious BIS values is reduced when using the XP platform; inspection of the raw EEG to assess for the presence of
however, it is not eliminated entirely. epileptiform activity.

High-frequency artifacts
EEG Variants and EEG Signal Analysis
A variety of medical devices generate high-frequency sig-
Two challenges to any EEG-based assessment of the level
nals that can contaminate the EEG signal. If this extraneous
of consciousness are the presence of EEG variant activity
artifact is not detected, the inclusion of the high-frequency
and the recognition of anesthesia-induced EEG effects.
signal could lead to errors in the calculation of BIS. Some
Speci¬cally, these challenges are presented by:
of the devices that have been reported, in rare settings, to
1. Paradoxical delta phenomenon produce artifact and resultant inaccuracy of the BIS are
2. Small-amplitude EEG listed in Table 3-3.
Level-of-Consciousness Monitoring 35


In many situations, the elec-
ELECTROCAUTERY DEVICES.
Table 3-3. External sources of electrical/
trical signature of an electrocautery device is recognized
mechanical artifact
as nonphysiological and is not processed with the EEG
1. Warming systems (¬‚uid and forced-air warming data. However, these devices can generate a variety of
systems) electrical artifacts that may affect level-of-consciousness
2. Circulatory-assist systems (CPB, VAD, ECMO)
monitors as well as other patient-monitoring systems used
3. High-frequency ventilators
in the operating room. In situations of prolonged elec-
4. Suctioning systems
5. Surgical instruments (shavers, drills, radiofrequency trocautery, there may be a reduction in the amount of
devices)
artifact-free EEG available for analysis and calculation of
6. Cardiac-pacing devices (pacemakers, de¬brillators)
level-of-consciousness value. Most level-of-consciousness
monitors include signi¬cant mechanisms designed to ¬lter
out electrical artifact produced by electrocautery use.25
For an external device with the potential to generate
artifact, proximity to the EEG sensor increases the risk CONSCIOUSNESS MONITORING
of EEG signal contamination and effects on calculated AND THE “ABNORMAL” BRAIN
values. Therefore, it is critical to consider the physical loca-
Some anesthesia providers have appropriately expressed
tion of such devices in relation to level-of-consciousness“
concern about the accuracy and reliability of the con-
monitoring system components. To con¬rm artifact in sit-
sciousness monitors in patients who have abnormal brain
uations where an external device may be interfering with
structure or function as the result of injury or disease.
the level-of-consciousness monitor, temporary cessation
This would include patients with clear evidence of CNS
of the device usage (if appropriate) may reveal a charac-
disease such as prior cerebral vascular accident with resid-
teristic pattern of interference.
ual neurologic impairment. It would also include patients
A few important external sources of artifact noted in
with systemic illness who may have neurologic implica-
Table 3-1 include the following:
tions, for example, those with encephalopathy compli-
cating hepatic or renal disease. Because of limited clini-
1. Pacemakers
cal experience with such patients, level-of-consciousness
2. Medical/surgical devices
values should be interpreted cautiously in patients with
3. Electrocautery device
known neurological disorders. For example, one case
series reported response to command at lower BIS values
Typically, signals emitted from pacemakers
PACEMAKERS.
(50“70) in patients while undergoing tumor resection dur-
have a high amplitude and regular pattern. As a result, they
ing awake craniotomy.26 All of these patients were taking
are readily identi¬ed as artifact by most consciousness-
anticonvulsant medication. One approach advocated by

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