malignant hyperthermia barbara robertson, md, frcpc dept of anesthesia, pah
TRANSCRIPT
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Malignant Hyperthermia
Barbara Robertson, MD, FRCPCDept of Anesthesia, PAH
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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?
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1960 First case described
1962 Inherited component suggested
1960’s Toronto and Wisconsin MH families identified / similarity to PSS recognized
1971 International symposium Toronto
1971 CHCT muscle biopsy described
1975 Dantrolene found to be specific treatment (FDA approved 1979)
1981-82 Patient advocacy groups formed
1980’s Use of intraoperative capnography helps early detection
1990’s RYR1 gene mutation discovered (100% PSS, 50% MH)
2000’s Genetic testing available
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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)
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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
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Why is it?
• It’s complicated!• Uncontrolled release of calcium by
the ryanodine receptor in the terminal cisternae of the sarcoplasmic reticulum
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Intracellular hypercalcemia
• Increased calcium release• Decreased calcium uptake• Defect in the muscle membrane• Altered function / structure of
proteins & fatty acids
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Trigger agents
• Volatile anesthetic gases (sevo, des, etc)
• Succinylcholine
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Safe drugs in MH
• N20• Nondepolarizing relaxants (roc,
vec, atracurium etc)• Local anesthetics• Narcotics • Sedative hypnotics (midaz,
propofol etc)
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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
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Conditions associated with MH
• Central core disease• Myotonia flutuans• King or King-Denborough
myopathy• Osteogenesis imperfecta• Heat / exercise syndromes?
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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)
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How to recognize it?
• Classically presents in OR• Tachycardia• Tachypnea• Hypertension• Arrhythmias• Rigidity• Hyperthermia
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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
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Later…..
• Myoglobinuric renal failure• DIC• Death
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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
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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)
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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
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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
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MH treatment memory aid
• Some • Hot• Dude• Better• Give• Iced• Fluids• Fast
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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
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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
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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
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Afterwards, monitor for….
• Recrudescence (25% of patients)• DIC• Myoglobinuric renal failure
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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
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ICU care (cont’d)
• Refer patient & family to MH centre for testing
• Recommend registry in MHAUS data base
• Recommend Medic Alert bracelet
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ABC’s
• A: • Aware of recrudescence • Ask relatives anesthesia / neuromusc
disease history• B:• Biopsy• C: • Contact MHAUS
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ABC’s + D
• D:• Dantrolene 1 mg/kg IV q6h x 24 -
36 hrs• Documentation to MHAUS registry
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Management of MH susceptible patient
• Refer to anesthesia consult clinic• Prophylaxis with dantrolene?• Hospital setting vs private clinic?• GA vs local / regional?
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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
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MH cart
• Dantrolene• Sterile water (in warming
cupboard?)• Bicarb, dextrose, CaCl2, lidocaine• Insulin (in fridge)• NS IV bags (in fridge)• Other stuff
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PAR care for MH susceptible
• Observe for 4 – 6 hours • May be appropriate for day surgery
if GA was uneventful
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Thank you!Thank you!