By Asmaa M. Idres

 Pharmacogenic disorder, inherited clinical myopathic syndrome affecting the skeletal muscles causing acute hypermetabolic state Mode of inheritance:  Autosomal dominant with variable expression and reduced penetrance (main).  Autosomal recessive, multi-factorial, unclassified pattern.

 Pathogenesis: Ca is released from sarcoplasmic reticulum on exposure to triggering agents leading to:  Irreversible myofibrillar contracture  Hypermetabolic state  Anerobic glycolysis  Muscle tissue damage and hyperkalemia

 Unexplained tachycardia (earliest).  Rise in end-tidal CO2.  Peculiar rigidity, even after nondepolarizing relaxants have been administered.  Metabolic acidosis, respiratory acidosis.  Hypoxemia, hyperthermia, rhabdomyolysis, hyperkalemia,hypercalcemia,hyperphosphate mia.  Myoglobinuria, acute renal failure, cardiac dysrhythmias.  DIC.

 Drug toxicity or abuse  Environmental heat gain more than loss  Equipment malfunction with increased carbon dioxide  Exercise hyperthermia  Heat stroke  Hyperthyroidism  Hypokalemic periodic paralysis  Muscular dystrophies (Duchenne’s, Becker’s)  Myotonias  Neuroleptic malignant syndrome  Pheochromocytoma  Rhabdomyolysis  Sepsis

Malignant Hyperthermia–Associated Syndromes: Masseter Spasm (“Thiopental- Succinylcholine or Halothane- Succinylcholine Rigidity”).  Jaw muscle rigidity in association with limb muscle flaccidity after the administration of succinylcholine.  It may occur even after pretreatment with a“defasciculating” dose of a nondepolarizing relaxant.  Anesthesia should be halted especially with (jaw of steel), start treatment of MH.  80% of patients may show trismus but no rigidity of other muscles, variant in normal patients.

 Past history: Previous uneventful halothane anesthesia does not exclude patient′s susceptibilty to MH  Family history is positive in 25% of cases.  Presence of musculoskeletal disorders.  King – Denborough sydrome is the only sydrome that always involves MH.

 CPK : Screening unreliable test  Caffiene contracture test: Gold standard test. Reliable in 95% of cases.  Other tests: not diagnostic eg EMG Motor unit counting  Recently micro-dialysis to detect increase in CO2 after im. Injection of caffiene in vivo

 Preoperative: previous episodes of MH and their documentation.  Family history.  Monitoring.  Premedications : safe in appropriate doses;  Phenothiazines are not recommended.

 Anesthesia machine, prepared by draining, removing, disabling anesthetic vaporizers, changing tubing, CO2 absorbent, flowing oxygen at 10 L/min for 20 minutes.  Modern anesthesia workstation requires longer time.  Iced solutions and adequate supplies of dantrolene must be available.

Choice of anesthesia  Regional, local anesthesia If possible, If not iv induction of anesthesia followed by nitrous oxide, oxygen, and a nondepolarizing relaxant with opioid supplementation is recommended.  Reversal of nondepolarizing relaxants with anticholinesterase and anticholinergic agents is recommended.  Even under the most controlled circumstances, the anesthesiologist should be alert to the early signs of MH.

 Stop all inhalation agents and succinylcholine and call for help.  Hyperventilation with 100% oxygen  Dantrolene sodium:  vial (20 mg) mixed with 50 mL of distilled water, dissolve faster at temperature 20 to 40°C.  2.5 mg/kg,repeat as needed up to 10 mg/kg.  If significant metabolic acidosis give mEq/kg bicarbonate.  Large volumes of fluid to maintain urinary output

 Dysrhythmia control follows, avoid Calcium channel blockers, lidocaine can be given safely during an MH crisis.  Ice packs, gastric, wound, rectal lavage for increased temperature up to cardiopulmonary bypass.  Glucose, insulin, bicarbonate for hyperkalemia.

 In ICU for close monitoring, continuing dantrolene, treatment of complications.  Notify patient and his family.