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Malignant Hyperthermia Catherine Maw 24/10/2012. OUTLINE Define and discuss aetiology of thermal disorders Relevance to ICU Clinical Presentation of MH.

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Presentation on theme: "Malignant Hyperthermia Catherine Maw 24/10/2012. OUTLINE Define and discuss aetiology of thermal disorders Relevance to ICU Clinical Presentation of MH."— Presentation transcript:

1 Malignant Hyperthermia Catherine Maw 24/10/2012

2 OUTLINE Define and discuss aetiology of thermal disorders Relevance to ICU Clinical Presentation of MH Differential diagnosis and pitfalls Treatment in theatre and ICU Subsequent management

3 Thermoregulation Balance between heat production and loss Hypothalamic thermoregulatory centre “Pyrexia” = resetting of thermoregulatory set point to a higher level by activation of heat conserving mechanisms “Hyperthermia” = failure of effector mechanisms to maintain the normal set point


5 Fever in the ICU Regulated hyperthermia Endogenous pyrogens (IL6 and PGE2) act on the hypothalamus Reset the thermoregulatory set point to higher temp Effector organs prevent heat loss May be protective When pyrogens decrease, set point decreases Deleterious effects (↑CO, O2 consumption, CO2 production)

6 Hyperthermia Failure of effector mechanisms to maintain the hypothalamic set point (core ≥ 40°C) Heat stroke Drug induced hyperthermias (MH, NMS, Serotonin syndrome, sympathomimetic syndrome, anticholinergic syndrome) Heat injury is the insult Protein denaturation and lipid dissolution at 42°C (core)

7 Why is it fatal? Direct cellular damage Increases membrane permeability Activation of Na-K-ATPase pump ATP depletion Tissue oedema Cytokine activation, coagulation cascade activation Cellular death (lactate, hyperkalaemia, acidosis) Similar picture to sepsis

8 Why? Metabolic acidosis Hyperkalaemia Rhabdomyolysis Renal failure DIC Liver failure Death

9 Australian History 1960: Dr Jim Villiers at Royal Melbourne Hospital Patient with 10 family members who died under GA Patient had malignant hyperthermia (MH) Villiers presented the successful anaesthetic outcome 1972: Lancet. Denborough and Lovell. Royal Melbourne (one of 3) centres for MH

10 Definition and Aetiology Pharmacological disease of skeletal muscle Hypermetabolic crisis Induced by exposure to volatile anaesthetic agents or Suxamethonium Loss of normal calcium homeostasis Unregulated release of Calcium form the sarcoplasmic reticulum Myocyte hypermetabolism

11 Relevance Anaesthetic complication Ongoing patient care will always involve ICU Insidious versus acute True MH rare Hyperthermia differentials more common

12 Epidemiology 1 in 10,000 to 1 in 30,000 anaesthetics Young adults (45-55% of cases in <19 years) More frequent in minor ops Male > Female 2:1 Mortality previously 70-80% Reduced to 2-3% now


14 Genetics of MH Majority of MH susceptible patients have mutations on RYR1 or DHP genes Inherited or spontaneous 50% Autosomal Dominant 200 mutations identified 29 have causality

15 Pathophysiology ctd Sustained muscle contraction due to high levels of myoplasmic calcium Heat generated (initial insult) Cascade similar to sepsis/systemic inflammation Initial aerobic metabolism generating CO2 and → cellular acidosis Then Oxygen and ATP depletion → worsening acidosis and lactate production Depleted energy → muscle death and rhabdomyolysis

16 Risk Factors Positive family history Previous exposure to Suxamethonium or volatiles Exertional heat stroke Exercise induced rhabdomyolysis Central core disease Scoliosis Strabismus surgery

17 Diagnosis

18 Early Prolonged masseter muscle spasm after Suxamethonium Inappropriately ↑ ETCO2 or tachypnoea during spontaneous respiration (ETCO2 >60) Inappropriately ↑ ETCO2 (ETCO2 >55) during controlled ventilation Inappropriate tachycardia Cardiac arrhythmias, especially ventricular ectopics

19 Developing Developing rise in temperature (0.5 ◦C per 15 mins) Progressive respiratory and later metabolic acidosis Hyperkalaemia Profuse sweating Cardiovascular instability Desaturation Generalised muscle rigidity

20 Late Myoglobinuria Myalgia Grossly elevated CK Coagulopathy Cardiac arrest

21 Differential diagnosis Inadequate anaesthesia / machine issue / patient factor Sepsis Intracerebral infection or bleed Recreational drugs Neuroleptic malignant syndrome Thyroid storm Phaeochromocytoma

22 Management ANZCA suggest MH Resource kit Link to mhanz Task cards based on the aviation safety model If diagnosis is suspected: Declare Emergency Call for HELP and send for MH resource kit Turn off the volatile and remove vaporisers Hyperventilate on >15l/min fresh gas flows with 100% O2 TIVA









31 Ongoing Care ICU for ventilatory support, haemodynamic monitoring, renal support CK peaks at 14 hours Dantrolene does not effect cardiac or smooth muscle Recrudescence in 25% 1mg/kg Dantrolene every 6 hours for 48 hours

32 MH Susceptibility Testing Gold standard is the contracture test In vitro response of a fresh sample of muscle tissue to Caffeine or Halothane Muscle strip in physiological solution is attached to a strain gauge and electrically stimulated to measure baseline tension Repeat in Halothane and Caffeine High sensitivity and specificity Expensive and specialist referral needed Genetic testing cheaper but sensitivity 30-50%

33 ?


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