MAO inhibitors (MAOI) and anesthesia

There is a section in this paper that deals with MAO inhibitors (MAOI) and anesthesia:

Monoamine oxidase inhibitors (MAOI) Scenario A 45-yr-old woman with recurrent
depression is scheduled for nasoseptorhinoplasty in a freestanding ambulator y
surger y centre. Past medical histor y includes severe depression,
treated with tranyl- cypromine. Recent psychiatric evaluation reveals that
the patient is stable, but at a high risk for relapse if her MAOI is withdrawn.
Discontinuation of her MAOI two weeks prior to surgery was discussed with
the patient but she refused. Her surgery requires either topical cocaine
or an epinephrine containing local anesthetic for hemostasis.

Discussion MAOI increase brain monoamines and cytoplasmic concentration of
MAO substrates by inhibiting metabolism of cytoplasmic
neurotransmitters.80

Classic MAOI, phenelzine and tranylcypromine, irre- versibly inhibit MAO
for two to three weeks until a new enzyme is synthesized.80 Moclobemide, a
reversible inhibitor of MAO-A (RIMA) causes enzyme inhibition for less than
24 hr.81,82 Selegiline, an anti- Parkinsonian agent, is a short-acting,
reversible MAO- B inhibitor at its usual dose.83

What is the evidence linking MAOI to serotonergic crises? Serotonergic
reactions to meperidine have been described for all MAOI,80,84,85 including
moclobemide81,82 and selegiline.83 Meperidine blocks neuronal serotonin reup-
take, resulting in serotonergic overactivity, agitation, hyper/hypotension,
convulsions, hyperthermia, and coma.82 However, serotonin concentration must
reach a critical level, as evidenced by one patient who reacted to meperidine
only after increasing her phenelzine dose80 and by a randomized,
controlled trial, in which 15 patients on MAOI given meperidine and
morphine all responded normally.85 Cocaine also reduces serotonin
inactivation and blocks monoamine reuptake.80,86 A delayed excitatory reaction
occurred in a patient on phenelzine 70 min after topical laryngeal
cocaine.86 Serotonergic crises may follow the administration of meperidine
or cocaine (grade C).

Are MAOI associated with atypical responses to all cat- echolamines? Elevated
preganglionic MAO substrates can cause an exaggerated response to indirect-
acting sympath- omimetics as long as three weeks after classic MAOI are
discontinued.80 A patient on selegiline developed hypertension and
supraventricular tachycardia after receiving ephedrine87 whereas a patient who
omitted one dose of moclobemide responded normally to both phenylephrine and
ephedrine.81 Indirect-acting cate- cholamines should be avoided (grade C).
Although it has been recommended to avoid epi- nephrine-containing
solutions,80 there is no evidence to support this. In fact, direct-acting
sympathomimet- ics such as epinephrine are the recommended pressor agents for
patients on MAOI.80,84 Patients on MAOI/RIMA do not have clinically significant
potentiation of cardiovascular effects of iv infusions of norepinephrine or
epinephrine.82,88 Vasopressors at concentrations contained in local anesthetics
are not likely to be significantly potentiated in otherwise healthy patients
on MAOI.88 Direct-acting sympath- omimetics may be used safely (grade C).

Do MAOI interact with anesthetic drugs? MAOI inhibit microsomal enzymes,
theoretically potentiating barbituates and opioids.80 Three cases of excessive
barbiturate/opioid effects were reported from 1960 to 1970.80,84 Since then,
numerous reports have described uneventful anesthetics using barbitu- rates
and various opioids: remifentanil,89 alfen- tanil,89,90 sufentanil,91
fentanyl,80,81 hydromorphone91 and morphine80,81,81,85,89 for patients
continuing to take MAOI. Other agents including propofol,90,92 ket- amine,93
midazolam,92 ketorolac,92 vecuronium,92 and atracurium92 have also been used
safely. Severe hyper- tension on induction with etomidate and atracurium has
occurred, although the patients blood pressure was 200/90 immediately
prior to induction.94 Regional anesthesia has been performed without inci-
dent when hypotension was treated appropriately with volume and direct-acting
sympathomimetics.80,81,95,96 Normal responses to most anesthetic agents can be
expected (grade C).

Is the continuation of MAOI associated with adverse outcomes? Much of our
understanding of the interactions between MAOI and anesthetic drugs
comes from reports of isolated events in individual patients. A con- trolled
prospective evaluation of 27 patients chronical- ly treated with MAOI
undergoing 36 anesthetics reported no adverse cardiovascular
responses.95 Changes in blood pressure and heart rate were not sig- nificantly
different from control patients without prior MAOI exposure. Anesthetic agents
included sodium thiopental, etomidate, diazepam, succinylcholine, nitrous
oxide, volatiles, pancuronium, morphine, spinal tetracaine, epidural
bupivacaine, and phenyle- phrine.95 Similarly a review of a series of 32
orthope- dic patients on MAOI who underwent 46 general anesthetics and five
regional anesthetics for elective surgery found no adverse hemodynamic
events.96 Agents used in this series included sodium thiopental, ketamine,
volatiles, morphine and meperidine. Aside from sporadic case reports, the
continued use of MAOI/RIMA has not been associated with adverse
perioperative events when meperidine and indirect acting catecholamines
are avoided (grade B).

Conclusion MAOI Case reports of sporadic MAOI-related drug interac- tions
prompted many to advise discontinuation of classic MAOI two to three weeks
before surgery.80,84,95 Withdrawal of MAOI is not without risks. Many
patients have severe depression refractory to other treatment and are at risk
for life-threatening psychi- atric illness. Acute exacerbation of depression
with sui- cidal ideation has been reported after discontinuation of MAOI prior
to elective cardiac surgery.97 There is no literature specifically concerning
MAOI and ambu- latory anesthesia. MAOI-related drug interactions are possible
and have been reported; however, patients continuing to take either
classic or selective MAOI remain suitable candidates for ambulatory anesthesia
if meperidine, cocaine and indirect-acting cate- cholamines are avoided.

Some see things as they are and ask why.
I dream of things that never were and ask why not.

- George Bernard Shaw

MAO inhibitors (MAOI) and anesthesia

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