Rare postoperative delayed malignant hyperthermia after off-pump coronary bypass surgery and brief review of literature

68 years old gentleman with severe triple vessel coronary artery disease was scheduled for CABG surgery.No history of antipsychotic medications, any medical illness, previous anesthesia exposure or muscle disorders in his family.

Anesthesia induction was done uneventfully and OPCAB was done successfully. No evidence of MH intraoperatively. EtCO2 and temperature started rising ,generalized muscle rigidity was observed including masseter muscle spasm despite using vecuronium.ABG showed mixed respiratory and metabolic acidosis with raised lactate level of 5 mmol/L and hyperkalemia of 4.9 mEq/L.

Considering clinical suspicion of MH, IV dantrolene 1 mg/kg was administered within 30 min of noticing the symptoms. Patient’s limb rigidity decreased and temperature dropped to 38.2°C. Oral dantrolene 50 mg qid was started due to nonavailability of IV dantrolene.

Patient was extubated on the 3rd postoperative day.


Malignant hyperthermia (MH) is pharmacogenetic syndrome inherited in an autosomal dominant way. Mutations in genes coding for calcium channel proteins (RYR1) and receptors (dihydropyridine) are responsible for MH susceptibility in 30–50% of the cases.

MH susceptible (MHS) patient when exposed to triggering anesthetic agents  causes uncontrolled intracellular release of calcium in skeletal muscle with resultant sustained muscle contraction. Such muscular hypermetabolic state produces rigidity, hyperthermia, and acidosis.

In the present case, we managed to administer dantrolene in 30 min after diagnosing the symptoms. Dantrolene is recommended in the dose of 2.5 mg/kg every 5 min until a clinical improvement is seen and maintenance doses (1 mg/kg IV every 4–6 h) for 24–48 h .

Cardiac surgical patients are generally prone to develop an acute renal injury. Rhabdomyolysis in untreated MH can cause myoglobininduced kidney damage.Aggressive fluid replacement with crystalloids and adequate diuresis can decrease the risk of myoglobin precipitation in renal tubules. Rapid and exaggerated rewarming during CPB can be a potential risk factor. Slow rewarming till 36°C is advisable.

MH triggering agents are inhalational halogenated anesthetics (e.g., sevoflurane, desflurane, isoflurane, enflurane, and halothane) and depolarizing muscle relaxant like succinylcholine.

Safe agents in MHS patients include all IV sedatives and anesthetic including propofol, dexmedetomidine, ketamine, etomidate, and barbiturates. All local anesthetics (e.g., ropivacaine, lidocaine, and bupivacaine), nondepolarizing neuromuscular blockers (e.g., atracurium, vecuronium, and rocuronium), analgesics and anxiolytics (opioids and benzodiazepines), and inhalational agents limited to nitrous oxide and xenon .

Rare postoperative delayed malignant hyperthermia after off-pump coronary bypass surgery and brief review of literature

Read full Article at : Annals of Cardiac Anesthesia