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Malignant Hyperthermia | Quick Review | Causes | Signs | Symptoms | Onset | Treatment | Halothane Contracture Test | Ryanodine Receptor | Anesthetic Management | Dantrolene Sodium

What is malignant hyperthermia?

-It is a rare life threatening hyper-metabolic skeletal muscle disorder.

How does malignant hyperthermia occur? 

-Triggering agents induce significantly calcium concentration in the skeletal muscle cells.

-Sustained muscle contraction occurs.

-Energy dependent calcium channel try to remove the excess calcium which increase 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? 

  • The mortality rate of malignant hyperthermia is 1 – 5 % .

What is the earliest sign of malignant hyperthermia?

  • A rise in ETCo2 level is the earliest sign.

  • In the absence of capnography , an elevated heart rate would most likely to be the first symptom.

How long after induction of general anesthesia does malignant hyperthemia occur?

  • Most episodes occur within 1 hour of exposure to the induction of general anesthesia.

What intravenous anesthetic trigger malignant hyperthermia?

  • No intravenous anesthetic agents 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 sign of hyper-metabolism after a patient exhibit masseter on administration of succinylcholine .

  • Some studies indicates that upto 50% of children who exhibit masseter spasm with succinylcholine have malignant hyperthermia.

What are the triggering agents for malignant hyperthermia?

  • The volatile anesthetic agents (halothane, Sevoflurane, Isoflurane and desflurane ) as well as succinylcholine trigger malignant hyperthermia in susceptible individuals.

  • But nitrous oxide does not trigger malignant hyperthermia.

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 degree celsius every 15 minute upto temperature of 46 degree celsius .

How is malignant hyperthermia transmitted genetically?

  • It is an autosomal dominant genetic disorder.

How does delayed onset of malignant hyperthermia occur ?

  • Delayed of of malignant hyperthemia has been reported to occur with desflurane and sevoflurane. Episode has been noted to occur as much as 6 hour after the 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?

  • Both amide and ester local anesthetics may be used in patients with malignant hyperthermia.

Should patients with malignant hyperthemia receive a prophylactic dose of Dantrolene prior to receiving an anesthetic?

  • Dantrolene prophylaxis is not necessary as long as the patient receives the non triggering anesthetic.

    What are the laboratory signs of malignant hyperthermia?

  • Increased paCO2, metabolic and respiratory acidosis , hyperkalemia , elevated Creatine kinase , myglobinemia and myglobinuria.

What is the treatment of malignant hyperthermia?

  • Discontinue any volatile agents and hyperventilate the patient with 100% oxygen.

  • Dantrolene sodium should be administered (Dose 1mg/kg body weight )

  • Active cooling using stomach lavage with cold water, surface cooling and infusion of cold saline in the bladder may be performed.

  • Sodium bicarbonate may be administered to treat hyperkalemia and acidosis.

  • Saline should be administered to maintain a urine output of  at least 2mL/kg/hr and osmotic or tubular diuretics should be administered.

How is Dantrolene packaged?

  • It is packed as a lyophilized (freeze dried) powder that must be mixed with 60cc 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 from calcium from the sarcoplasmic reticulum.

What is the dose of dantrolene in the treatment of malignant hyperthermia?

  • Treatment of acute episodes is 2.5mg /kg/iv every 5-10 minute to a maximum dose of 10mg/kg.

  • Even if the episode is under control, dantrolene may have to be repeated at the dose of 1-2mg/kg every 6 hours for a 24 hour period to prevent recurrence.

What are the side effects of large doses of dantrolene ?

The side effects of large doses of dantrolene are

  • Nausea

  • Vomiting

  • Skeletal muscle disorder

  • 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 scarcoplasmic reticulum.

What are some of hyper metabolic conditions that can mimic malignant hyperthermia under general anesthesia?

Hypermetablic conditions are as follows.

  • Sepsis

  • Thyrotoxiocosis

  • Pheochromocytoma

  • CNS injury

  • Light anesthesia

  • Release of 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, hypotension , 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 drug used to treat Parkinson’s disease can cause NMS.

Why does myoglobin appear in the plasma after the onset of malignant hyperthermia?

  • Myoglobin appears in the plasma within a minute after the onset of malignant hyperthermia.

How does the anesthesia induced rhabdomyolysis associated with Duchenne’s muscular dystrophy compared to malignant hyperthermia ?

  • Duchenne’s muscular dystrophy was once thought to be associated with MH , but is now accepted that it is completely separate condition .

  • The anesthesia induced rhabdomyolysis associated with Duchenne’s is triggered by the same agents and clinically exhibits most of the same symptoms.

  • The difference is that dantrolene does not treat anesthesia induced  rhabdomyolysis and may produce marked skeletal muscle weakness which is of particular concern for these patients.

Is there a test to diagnose malignant hyperthermia ?

  • In North America , the caffeine Halothane contracture testcan diagnose malignant hyperthermia.

How does the caffeine Halothane contracture test work ?

  • A muscle biopsy is obtained .

  • High dose of caffeine release calcium from the Sarcolemma.

  • This effect is enhanced by halothane.

  • The muscle tissue in patients with malignant hyperthermia contracts abnormally when exposed to these two patients,Confirming the diagnosis of malignant hyperthermia .

Are there any other tests for malignant hyperthermia other than the Halothane contracture test ?

  • Yes, there is molecular genetic test that examine the gene coding for theRYR1 (Ryanodine receptor) that has a low sensitivity, but is much invasive than the contracture test.

 

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