Malignant Hyperthermia Flashcards
What is malignant hyperthermia?
It is a rare, life-threatening, hypermetabolic skeletal muscle disorder.
How does malignant hyperthermia occur?
Triggering agents induce significantly increased calcium concentrations in the skeletal muscle cells. Sustained muscle contraction occurs. Energy-dependent calcium channels try to
remove the excess calcium which increases the metabolism of the skeletal muscles. The increased metabolism depletes ATP stores and causes lactic acidosis. The acidosis and increased temperature destroys the sarcolemma which releases creatine
kinase, myoglobin, and potassium.
What is the mortality rate of malignant hyperthermia?
1-5%
What is the earliest sign of malignant hyperthermia?
A rise in the ETCO2 level is the earliest sign. In the absence of capnography, an elevated heart rate would most likely be the first symptom.
How long after induction of general anesthesia does
malignant hyperthermia usually occur?
Most episodes occur within 1 hour of exposure.
What intravenous anesthetics trigger malignant
hyperthermia?
No intravenous anesthetics are known to trigger malignant hyperthermia.
Is masseter spasm after administration of
succinylcholine diagnostic of malignant
hyperthermia?
No, but it may be the first indication that a patient has malignant hyperthermia. Many clinicians advocate observing closely for any signs of hypermetabolism after a patient exhibits masseter
spasm on administration of succinylcholine. Some studies indicate that up to 50% of children who exhibit masseter spasm with succinylcholine have malignant hyperthermia.
What are the triggering agents for malignant
hyperthermia?
The volatile agents (halothane, sevoflurane, isoflurane, and desflurane) as well as succinylcholine trigger malignant
hyperthermia in susceptible individuals.
How early an indicator of malignant hyperthermia is
an increase in temperature?
An increase in temperature is typically a late sign, but the temperature may increase as much as 0.5 degrees Celsius every 15 minutes up to temperatures of 46 degrees Celsius.
How is malignant hyperthermia transmitted
genetically?
It is an autosomal dominant genetic disorder.
How does delayed onset malignant hyperthermia
occur?
Delayed onset malignant hyperthermia has been reported to occur with desflurane and sevoflurane. Episodes have been noted to occur as much as 6 hours after exposure.
How does cardiac irritability result from malignant
hyperthermia?
The presence of hyperkalemia, acidosis, and increased body temperature results in an increased susceptibility to potentially
lethal cardiac arrhythmias.
Can regional anesthesia be used in patients with
malignant hyperthermia?
Yes. Both amide and ester local anesthetics may be used for regional anesthesia in patients with malignant hyperthermia.
Should patients with malignant hyperthermia receive a prophylactic dose of dantrolene prior to receiving an anesthetic?
Dantrolene prophylaxis is not necessary as long as the patient receives a non-triggering anesthetic.
What are the laboratory signs of malignant
hyperthermia?
Increased PaCO2, metabolic and respiratory acidosis, hyperkalemia, elevated creatine kinase, myoglobinemia, and myoglobinuria.
What is the treatment for malignant hyperthermia?
1) Discontinue any volatile agents and hyperventilate the patient with 100% oxygen
2) Dantrolene should be administered
3) Active cooling using stomach lavage with cold
water, surface cooling, and infusion of cold saline in the bladdermay be performed
4) Sodium bicarbonate may be administered
to treat hyperkalemia and acidosis
5) Saline should be administered to maintain a urine output of at least 2 mL/kg/hour
and
6) Osmotic or tubular diuretics should be administered
How is dantrolene packaged?
It is packaged as a lyophilized (freeze dried) powder that must be mixed with 60 cc of sterile water prior to injection.
How does dantrolene work to treat malignant
hyperthermia?
Dantrolene works directly on the ryanodine type 1 receptor to inhibit the efflux of calcium from the sarcoplasmic reticulum.
What is the dose of dantrolene in the treatment of
malignant hyperthermia?
Treatment of acute episodes is 2.5 mg/kg IV every 5-10 minutes to a maximum dose of 10 mg/kg. Even if the episode is under control, dantrolene may have to be repeated at a dose of 1-2
mg/kg every 6 hours for a 24 hour period to prevent recurrence.
What are the side effects of large doses of
dantrolene?
Nausea, vomiting, skeletal muscle weakness, and blurred vision.
What receptor has been linked to malignant
hyperthermia and where is this receptor found?
The ryanodine receptor, which is a major calcium release trigger located in the sarcoplasmic reticulum
What are some of the hypermetabolic conditions that can mimic malignant hyperthermia under general anesthesia?
Sepsis, thyrotoxicosis, pheochromocytoma, CNS injury, light anesthesia, and release of a lower extremity tourniquet or aortic cross-clamp
What is neuroleptic malignant syndrome and how
does it compare to malignant hyperthermia?
NMS is similar to malignant hyperthermia in that it is associated with fever, rhabdomyolysis, hypertension, tachycardia, muscle rigidity, and acidosis. It differs from MH in that it is related to the administration of haloperidol and the atypical antipsychotic medications. Dantrolene, benzodiazepines, and bromocriptine have proved useful in the treatment of NMS. Also, MH occurs
acutely with exposure while NMS occurs after long-term therapy with its triggering agents. Sudden discontinuation of drugs used
to treat Parkinson’s disease can cause NMS.
When does myoglobin appear in the plasma after the onset of malignant hyperthermia?
Myoglobin appears in the plasma within minutes.
