Understanding Anesthesiology - The Global Regional Anesthesia ...

Successful treatment of an MH crisis requires prompt
recognition, discontinuation of triggering agents and
administration of dantrolene. Dantrolene is a direct
skeletal muscle relaxant which acts at the muscle cellular
level. It is administered intravenously in 2.5 mg/kg
doses until clinical signs show reversal of the hypermetabolic
state. In most cases the symptoms will abate
with a total dose of less than 20 mg/kg but the anesthesiologist
must not hesitate to administer more dantrolene
if the clinical indicators warrant. The remainder of
treatment is supportive and involves hyperventilation
with 100% oxygen, fluid administration and active cooling
if temperature is elevated. One should be prepared
to treat hyperkalemia and cardiac dysrhythmias. The
surgical procedure should be terminated as quickly as
is feasible after which the patient is transferred to the
intensive care unit. Dantrolene should be continued in
1-2 mg/kg doses, every four hours for at least 24 hours.
Patients should be monitored for recrudescence of the
reaction as well as for complications such as myoglobinuria,
renal failure and disseminated intravascular
coagulation (DIC).
A very important component of care for the patient
who has had an unexpected MH reaction is counseling
and education for both patient and family. While the
patient himself is known to be MH susceptible, his family
members must be assumed to be MH susceptible until
it is proven otherwise. A diagnosis of MH has implications
for employment, life insurance premiums and
for future anesthetic management. Specialists at “MH
clinics” are best able to advise the patient and his family;
it is the duty of the attending anesthesiologist to
make that referral. At the MH clinic, the appropriateness
of muscle biopsy will be discussed. Muscle biopsy
can rule out (or in) MH susceptibility in a family member
but is painful and requires an anesthetic. It is expected
that in the near future, the development of a genetic
blood test will obviate the need for the invasive
muscle biopsy in the majority of patients.
The anesthetic management of a patient known to be
MH-susceptible is straightforward. Dantrolene prophylaxis
may (rarely) be given preoperatively to high risk
patients. Intra-operatively, standard monitoring is used
with an emphasis on end-tidal CO2, O2 saturation and
temperature measurement. Triggers are avoided by using
a “trigger-free” anesthetic machine which is free of
vapourizers, and has been flushed clear of residual
volatile gases. An anesthetic technique which does not
involve the use of succinylcholine or volatile anesthetic
gases is chosen. Post-operatively, the patient is usually
observed in the post-anesthetic care unit for an extended
period of time (e.g. 4 hours). If no suspicious
signs (such as fever or unexplained tachycardia) are detected,
routine post-operative care follows. The patient
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