Malignant Hyperthermia Flashcards
What is MH?
Hypermetabolic disorder, triggered by anesthetic medication: succs & all gases except N20. Related to receptor dysfunction w/i myocyte, rayanodine receptor. Near unlimited calcium influx into myocyte causing sustained contraction leading to skeletal muscle necrosis.
Describe process of calcium release for muscle contraction in MH
Rayanodine receptor in sarco retic mediates calcium rls into cytoplasm, usually re-sequesters back into sarco retic p/ contraction. In MH release is cont and re-sequester does not happen resulting in greatly elevated myoplasmic calcium levels leading to uncontrolled muscle tetany.
Areas where Calcium is involved in skeletal muscle contraction
Termed “excitation-contraction coupling”. Requires both ATP and calcium for contraction. Calcium influx to TTubule, stims Ca rls from sarco retic into cytoplasm, Ca + ATP open trop complex for myosin cross bridge binding to move filaments (contraction). ATP req for cross bridge and Calcium re-sequestration.
What are the metab products of excessive muscle contraction in MH (x4 per diagram)
Rigor / Heat / CO2 / Lactate
What are the effects of MH hypermetabolic state?
Glycogen depletion/hypoglycemia leads to anaerobic metabolism / incr O2 requirements for muscle, attempts to remove Ca from myocyte leads to anaerobic metabolism / excess CO2 production leads to resp acidosis / extreme heat production leads to sz risk / contributing factors leading to anaerobic metab leads to metabolic acidosis. Kidney damage from broken down cell products of myoglobin, CK, potassium excess.
What is the cause of MH?
Triggered by exposure to anesthetic/succs causes altered muscle receptor function. Not necessarily occurs with first exposure. It is an autosomal dominant disorder, carrier’s child has 50% chance of having deficit.
How to diagnose MH pre-op
Gold standard is caffeine halothane contracture test, requires muscle biopsy. Serum genetic testing is less accurate. Must have preop assess with questions regarding personal/family hx of MH, temp post op?? muscle soreness post op? ICU post op??
What are the conditions assoc with MH?
central core disease. Muscular dystrophies: duchenne!!!! (major one), King-den, Becker, Myopathic, Sarco Retic ATP deficiency. Don’t always produce MH, but at much greater risk. Dont give them the drug Melissa.
What Rx triggers MH?
Succinylcholine, all gas anesthetics expect N20
What are the pathophysiologic features of MH?
increased/sustained skeletal muscle contraction / incr O2 consumption / incr CO2 production / depletion of cell energy stores / lactic acidosis / muscle destruction / rls of myoglobin/k+/CK leads to renal damage.
What are the clinical signs of MH?
Rise in EtCO2 (most reliable) / incr HR (first sign) / incr temp (slow or fast, 1-2*C per min / masseter muscle rigidity (25% with succs mass musc rigidity assoc w/ MH) / arrhythmias (from k, acidosis, hypoxia) / myoglobinuria (?hematuria) / mottled/cyanotic skin (shock) / decr Sa02 / muscle rigidity
Affect of MH on EtCO2
Very abnormal to have increasing CO2 when clinician is increasing minute ventilation to manage prev elevated EtCO2, can’t catch up to CO2 production. We would be consistently incr RR (r/o CO2 absorbent problem, exp valve dysfxn)
Treatment of MH
Remember, all vital/labs that are in derangement are result of uncontrolled muscle contraction. All tx are palliative until you treat cause with Dantrolene. Dose of 2.5 mg/kg bolus, up to 10 mg/kg, q6 hours x 24 hours. Vial is 20mg mix with 50ml STERILE WATER!! 70 kg pt = 175 mg = 9 vials. Rule keep 36 vials in stock/cart.
What do to when recognize MH?
Call help, surgeon to finish ASAP, MH protocol/cart, d/c anesth agent, hypervent w/ 100% O2, dantrolene 2.5mg/kg up to 10mg/kg as bolus. Cooling measures and palliative tx for other symptoms. Early dantrolene admin is vital in reducing mortality. Get clean 2nd machine with anesth washed out.
Mechanism of action of Dantrolene
skeletal muscle relaxant dantrolene inhibits the release of Ca2+ from the sarcoplasmic reticulum during excitation-contraction coupling and suppresses the uncontrolled Ca2+ release that underlies the skeletal muscle pharmacogenetic disorder malignant hyperthermia.
