Malignant Hyperthermia
Barbara Robertson, MD, FRCPC
Dept of Anesthesia, PAH
Overview
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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?
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
Resources at hand
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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)
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
Why is it?
• It’s complicated!
• Uncontrolled release of calcium
by the ryanodine receptor in the
terminal cisternae of the
sarcoplasmic reticulum
Intracellular
hypercalcemia
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Increased calcium release
Decreased calcium uptake
Defect in the muscle membrane
Altered function / structure of
proteins & fatty acids
Trigger agents
• Volatile anesthetic gases (sevo,
des, etc)
• Succinylcholine
Safe drugs in MH
• N20
• Nondepolarizing relaxants (roc,
vec, atracurium etc)
• Local anesthetics
• Narcotics
• Sedative hypnotics (midaz,
propofol etc)
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
Conditions associated
with MH
• Central core disease
• Myotonia flutuans
• King or King-Denborough
myopathy
• Osteogenesis imperfecta
• Heat / exercise syndromes?
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)
How to recognize it?
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Classically presents in OR
Tachycardia
Tachypnea
Hypertension
Arrhythmias
Rigidity
Hyperthermia
As the crisis develops….
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Rising ET CO2
CO2 absorbent gets hot
Skin colour mottled or cyanotic
Sweating
Mixed respiratory & metabolic
acidosis
• Elevated K, lactate, myoglobin,
CK
Later…..
• Myoglobinuric renal failure
• DIC
• Death
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
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)
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
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
MH treatment memory aid
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Some
Hot
Dude
Better
Give
Iced
Fluids
Fast
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
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
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
Afterwards, monitor
for….
• Recrudescence (25% of
patients)
• DIC
• Myoglobinuric renal failure
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
ICU care (cont’d)
• Refer patient & family to MH
centre for testing
• Recommend registry in MHAUS
data base
• Recommend Medic Alert
bracelet
ABC’s
• A:
• Aware of recrudescence
• Ask relatives anesthesia /
neuromusc disease history
• B:
• Biopsy
• C:
• Contact MHAUS
ABC’s + D
• D:
• Dantrolene 1 mg/kg IV q6h x 24 36 hrs
• Documentation to MHAUS
registry
Management of MH
susceptible patient
• Refer to anesthesia consult
clinic
• Prophylaxis with dantrolene?
• Hospital setting vs private
clinic?
• GA vs local / regional?
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
MH cart
• Dantrolene
• Sterile water (in warming
cupboard?)
• Bicarb, dextrose, CaCl2,
lidocaine
• Insulin (in fridge)
• NS IV bags (in fridge)
• Other stuff
PAR care for MH
susceptible
• Observe for 4 – 6 hours
• May be appropriate for day
surgery if GA was uneventful
Thank you!