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1                            Malignant hyperthermiaMalignant hyperthermia is a life-threatening elevation in body temperat...
2      6. shock, and      7. hyperthermia. Temperature is usually ≥ 40° C and may be extremely high (ie,         > 43° C)....
3      3. Benzodiazepines given IV, often in high doses, can be used to control         agitation.      4. Malignant hyper...
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Malignant hyperthermia


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Malignant hyperthermia

  1. 1. 1 Malignant hyperthermiaMalignant hyperthermia is a life-threatening elevation in body temperature usuallyresulting from a hypermetabolic response to concurrent use of a depolarizing musclerelaxant and a potent, volatile inhalational general anesthetic.Manifestations can include muscle rigidity, hyperthermia, tachycardia, tachypnea,rhabdomyolysis, and respiratory and metabolic acidosis.Diagnosis is clinical; patients at risk can be tested for their susceptibility. The highestpriority treatments are rapid cooling and aggressive supportive measures.The muscle relaxant involved is usually succinylcholine; the inhalational anesthetic ismost often halothane, but other anesthetics (eg, isoflurane, sevoflurane, desflurane)may also be involved. This drug combination causes a similar reaction in somepatients with muscular dystrophy and myotonia.PathophysiologyMalignant hyperthermia affects about 1/20,000 people.Susceptibility is inherited, with autosomal dominant inheritance and variablepenetrance. Most often, the causative mutation affects the ryanodine receptor ofskeletal muscle; however, > 22 other causative mutations have been identified. In susceptible patients. ↓Anesthetic-induced potentiation of ca exit from the sarcoplasmic reticulum of skeletal muscle ↓ Ca-induced biochemical reactions are accelerated ↓ Causing severe muscle contractions & elevation of the metabolic rate.Complications 1. K↑ 2. Respiratory and metabolic acidosis, 3. Ca↓ 4. Rhabdomyolysis with CK elevation and myoglobinemia may occur, 5. Coagulation abnormalities (particularly DIC). In older patients and patients with comorbidities, DIC may increase the risk of death.Symptoms and SignsMalignant hyperthermia may develop during anesthesia or the early postoperativeperiod. Clinical presentation varies, depending on the drugs used and the patientssusceptibility. 1. Muscular rigidity, especially in the jaw, is often the first sign, followed by 2. tachycardia, 3. other arrhythmias, 4. tachypnea, 5. acidosis,Yapa Wijeratne
  2. 2. 2 6. shock, and 7. hyperthermia. Temperature is usually ≥ 40° C and may be extremely high (ie, > 43° C). 8. Urine may appear brown or bloody if rhabdomyolysis and myoglobinuria have occurred.Diagnosis o Clinical evaluation o Testing for complications o Susceptibility testing for people at riskThe diagnosis is suspected by the appearance of typical symptoms and signs within 10min to, occasionally, several hours after inhalational anesthesia is begun. Earlydiagnosis can be facilitated by prompt recognition of jaw rigidity, tachypnea,tachycardia, and increased end-tidal CO2.There are no immediately confirmatory tests, but patients should have testing forcomplications, including ECG, blood tests (CBC with platelets, electrolytes, BUN,creatinine, CK, Ca, PT, PTT, fibrinogen, d-dimer), and urine testing formyoglobinuria.Other diagnoses must be excluded. Perioperative sepsis may cause hyperthermia butrarely as soon after induction. Inadequate anesthesia can cause increased muscle toneand tachycardia but not elevated temperature. Thyroid storm and pheochromocytomararely manifest immediately after anesthetic induction.Susceptibility testingRecommended for people at risk based on a o Family history of the disorder o Personal history of a severe or incompletely characterized previous adverse reaction to general anesthesia.The caffeine halothane contracture test (CHCT) is the most accurate. It measures theresponse of a muscle tissue sample to caffeine and halothane. This test can be doneonly at certain referral centers and requires excision of about 2 g of muscle tissue.Genetic testing has limited sensitivity (about 30%) but is quite specific; patients inwhom a mutation is identified do not require the CHCT.Treatment 1. Rapid cooling and supportive measures It is critical to cool patients as quickly and effectively as possible to prevent damage to the CNS and also to give patients supportive treatment to correct metabolic abnormalities. Outcome is best when treatment begins before muscular rigidity becomes generalized and before development of rhabdomyolysis, severe hyperthermia, and DIC. 2. Dantrolene; (a muscle relaxant) (2.5 mg/kg IV q 5 min as needed, up to a total dose of 10 mg/kg) should be given in addition to the usual physical cooling measures. In some patients, tracheal intubation, paralysis, and induced coma are required to control symptoms and provide support.Yapa Wijeratne
  3. 3. 3 3. Benzodiazepines given IV, often in high doses, can be used to control agitation. 4. Malignant hyperthermia has a high mortality and may not respond to even early and aggressive therapy.Prevention 1. Local or regional anesthesia is preferred to general anesthesia when possible. 2. Potent inhalational anesthetics and depolarizing muscular relaxants should be avoided in patients who are susceptible. 3. Nondepolarizing muscular blockers are the preferred preanesthetic drugs. Preferred anesthetics include barbiturates (eg, thiopental), etomidate, and propofol. 4. Dantrolene should be available at the bedside.Yapa Wijeratne