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Malignant Hyperthermia

Malignant Hyperthermia. Barbara Robertson, MD, FRCPC Dept of Anesthesia, PAH. Overview. What is it? Why is it? Who gets it? How do you recognize it? How do you treat it? What to do if patient is susceptible?. Resources at hand. MH hotline: 1-800-644-9737 Outside USA: +1-303-389-1647

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Malignant Hyperthermia

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  1. Malignant Hyperthermia Barbara Robertson, MD, FRCPC Dept of Anesthesia, PAH

  2. Overview • What is it? • Why is it? • Who gets it? • How do you recognize it? • How do you treat it? • What to do if patient is susceptible?

  3. Resources at hand • MH hotline: 1-800-644-9737 • Outside USA: +1-303-389-1647 • Website: www.mhaus.org • Wall flow chart from MHAUS • There’s an app for that (ePocrates, Gas Guide, MHapp)

  4. What is MH? • Potentially fatal inherited disease • Fever, rigidity, acidosis • Hypermetabolic state of skeletal muscles with high intracellular calcium levels • Triggered by exposure to volatile anesthetics and / or succinylcholine

  5. Why is it? • It’s complicated! • Uncontrolled release of calcium by the ryanodine receptor in the terminal cisternae of the sarcoplasmic reticulum

  6. Intracellular hypercalcemia • Increased calcium release • Decreased calcium uptake • Defect in the muscle membrane • Altered function / structure of proteins & fatty acids

  7. Trigger agents • Volatile anesthetic gases (sevo, des, etc) • Succinylcholine

  8. Safe drugs in MH • N20 • Nondepolarizing relaxants (roc, vec, atracurium etc) • Local anesthetics • Narcotics • Sedative hypnotics (midaz, propofol etc)

  9. Who gets it? • 1:50,000 adult GAs • 1:15,000 pediatric GAs • Incidence rising due to better awareness but mortality declining (overall 10%) • Inherited as autosomal dominant with variable penetrance

  10. Conditions associated with MH • Central core disease • Myotonia flutuans • King or King-Denborough myopathy • Osteogenesis imperfecta • Heat / exercise syndromes?

  11. Other conditions • Muscular dystrophy (hyperkalemia after sux but not MH) • Pheochromocytoma & thyrotoxicosis show hypermetabolism but not MH • Neuroleptic malignant syndrome (related to phenothiazine exposure over long term causing dopamine depletion)

  12. How to recognize it? • Classically presents in OR • Tachycardia • Tachypnea • Hypertension • Arrhythmias • Rigidity • Hyperthermia

  13. As the crisis develops…. • Rising ET CO2 • CO2 absorbent gets hot • Skin colour mottled or cyanotic • Sweating • Mixed respiratory & metabolic acidosis • Elevated K, lactate, myoglobin, CK

  14. Later….. • Myoglobinuric renal failure • DIC • Death

  15. Variable presentations • Delay in onset until emergence, PAR or ward • Masseter muscle rigidity • Several uneventful GA’s in the past, then MH occurs during current GA

  16. Diagnostic tests • Caffeine halothane contracture test is the gold standard (muscle biopsy) • 5 centres in North America perform the accepted protocol (Toronto is only one in Canada listed on MHAUS website) • Genetic testing (2 centres in USA listed on MHAUS website)

  17. Problems with testing • False negative (had MH after testing negative) • More than one gene mutation may cause MH because only 50% to 80% of MH susceptible patients have RYR 1 variant or mutation

  18. How to treat? • Early diagnosis and treatment result in very low mortality • Any location where anesthetics are administered should have MH plan & sufficient dantrolene • MH cart, practice drills, wall chart with hotline number

  19. MH treatment memory aid • Some • Hot • Dude • Better • Give • Iced • Fluids • Fast

  20. Acute phase • Call for help & get the MH cart / crash cart • Declare an emergency • Stop the triggering agents • Hyperventilate with high flow 100% O2 • Switch to non triggering anesthesia to finish the surgery if needed / change circuit? • Dantrolene

  21. Dantrolene • Need help to mix • Initial dose 2.5 mg/kg (175 mg) • Each bottle is 20 mg = 9 bottles for first dose • Each bottle mixed with 60 ml H2O = 540 ml water for 9 bottles • Acts by reducing intracellular calcium in skeletal muscles

  22. Acute Episode (cont’d) • Cool patient (goal = 38) • ABG, lytes results guide further treatment for metab & resp acidosis, hyperkalemia • Arrhythmias respond to correction of hypercapnia, hyperkalemia & acidosis • CK level, myoglobin

  23. Afterwards, monitor for…. • Recrudescence (25% of patients) • DIC • Myoglobinuric renal failure

  24. In ICU: • Dantrolene 1mg/kg q6hr x 24-36 hours then orally? • EKG, art line, urinary catheter, temperature, 2nd IV line • CVC?, capnography? • Monitor & treatment for specific abnormalities

  25. ICU care (cont’d) • Refer patient & family to MH centre for testing • Recommend registry in MHAUS data base • Recommend Medic Alert bracelet

  26. ABC’s • A: • Aware of recrudescence • Ask relatives anesthesia / neuromusc disease history • B: • Biopsy • C: • Contact MHAUS

  27. ABC’s + D • D: • Dantrolene 1 mg/kg IV q6h x 24 -36 hrs • Documentation to MHAUS registry

  28. Management of MH susceptible patient • Refer to anesthesia consult clinic • Prophylaxis with dantrolene? • Hospital setting vs private clinic? • GA vs local / regional?

  29. GA in MH susceptible • Flush gas machine / remove vaporizers / new circuit & CO2 absorber • Monitor ETCO2 & temp • MH cart ready & nearby • TIVA with propofol +/- N2O +/-nondepolarizing NMB + narcotics = non trigger anesthesia • Use high fresh gas flow

  30. MH cart • Dantrolene • Sterile water (in warming cupboard?) • Bicarb, dextrose, CaCl2, lidocaine • Insulin (in fridge) • NS IV bags (in fridge) • Other stuff

  31. PAR care for MH susceptible • Observe for 4 – 6 hours • May be appropriate for day surgery if GA was uneventful

  32. Thank you!

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