Malignant Hyperthermia CCC
OVERVIEW
- Malignant Hyperthermia = pharmacogenetic disease of skeletal muscle induced by exposure to certain anaesthetic agents
- incidence 1:5,000 -> 1:65,000 anaesthetics (suspected)
- mutation in the gene coding for the ryanodine receptor
- autosomal dominant
- gene on chromosome 19
- thymidine instead of cytosine
- produces a cysteine for arginine substitution at position 615 of the receptor.
PATHOPHYSIOLOGY
- excess Ca2+ release during muscle contraction -> increased musle metabolism + heat production.
- prolonged and intensified interation between actin and myosin.
- enhanced aerobic metabolism -> lactic acidosis -> accumulation of intra-mitochondrial calicum -> deconjugation of oxidative phosphorylation -> cytolysis.
TRIGGERS
- stress (in pigs)
- all volatile agents (except N2O)
- suxamethonium
-> these all either enhance Ca2+ influx or slowing its efflux
- some may have tolerated the same agents previously
- rare in barbiturate-N2O-opiate-tranquiliser-non-depolarising muscle relaxant anaesthesia
- sux potent trigger (first exposure)
- volatiles (median exposure till fulminant -> 3)
CLINICAL
- in lower North Island of NZ trigger names = Harvey, Harwere & Cook
- history of Central Core Disease
(1) increased ETCO2
(2) tachycardia
(3) tachypnoea
(4) masseter spasm (if develops this convert to a MH safe anaesthetic)
(5) muscle rigidity
(6) temp increase (late) – 1 C\15min
- intra-op & 4\24 post op
- tachyarrhythmia
- difficulty ventilation
- hypertension
- sweating
- DIC
- hyperkalaemia
- cardiac arrest
INVESTIGATIONS
- PaCO2 >60mmHg
- PvCO2 >90mmHg and increasing
- BE -5 and falling
- metabolic acidosis
- CK >50,000 IU/L
- K+ increases
- Na+ increases
- myoglobinuria
ACUTE MANAGEMENT
- call for help
- discontinue all anesthetic agents
- maintain anaesthesia with hypnotics and opioids.
- muscle relaxation with NDNMBD
- terminate surgery
- hyperventilate
- 100% O2
- cool (N/S stomach lavage)
- maintain urine output
- inotropes as needed
- HCO3 2-4mEq/kg
- Dantrolene 2.5mg/kg every 5min (total dose 10mg/kg/day – continuous infusion or treat recurrence (25%))
- cardiac arrhythmias -> beta blockers & lignocaine.
- high K+ -> glucose-insulin & frusemide
- watch for DICCK Q6hrly
PROGNOSIS
- mortality without dantrolene = 70%
- mortality with dantrolene = 5%
LONG-TERM MANAGEMENT
- referral to an MH centre
- warn patient and family of impending consequences
- if uncertain about diagnosis -> must screen
- IVCT
- subsequent gene mutations studies if positive + family screening
- if blood test negative -> must have a muscle biopsy
- medic alert and appropriate documentation
PROPHYLACTIC MANAGEMENT
- take history
- decrease anxiety with midazolam
- machine -> remove vapourisers, flush with O2 @ 10 L\min for 20min
- new circuit and airway devices
- ETCO2 monitoring
- nasal temp probe
- dantrolene available
OBSTETRIC PATIENTS
- baby = 50% chance of having MH
- planned delivery with early anaesthetic advice
- anticipate airway problems -> AFOI
- RA safe and preferred
- MH safe drugs
- sux doesn’t cross the placenta
References and Links
- Cadogan M. Michael Denborough (1929-2014). Eponymictionary
[cite]
Critical Care
Compendium
Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.
After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.
He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE. He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.
His one great achievement is being the father of three amazing children.
On Twitter, he is @precordialthump.
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