In most cases, the first signs and symptoms of the disorder are evident in the operating room. However, MH can also occur in the recovery room or even after the patient has been transferred to the patient floor. It is important to remember that none of the signs and symptoms occur in all cases. Initial signs usually include tachycardia (90% of cases) and tachypnea (80% of cases) due to the sympathetic nervous system response to the underlying hypermetabolism and hypercarbia (80% of cases). In the paralyzed patient under general anesthesia, the first sign of MH can be hypercarbia that is resistant to adjustments in the ventilator setting. Next, an increase in blood pressure, cardiac dysrhythmias, and muscle rigidity (80% of cases) are often seen. Patients may then become hyperthermic (70% of cases), with a rise of 1 to 2 degrees Celsius every 5 minutes. An arterial blood gas will usually show respiratory and metabolic acidosis. Other lab abnormalities include hyperkalemia, hypercalcemia, lactic acidemia and myoglobinuria. Creatinine kinase levels rise to 20,000 or more within 12 to
24 hours, putting the patient at risk for myoglobinuric renal failure. Isolated myoglobinuria in the early postoperative period should make the anesthesiologist and surgical team suspicious for MH. Masseter muscle rigidity shortly after the administration of succinylcholine has also been associated with MH as well.