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