When tracheal intubation is required for a short procedure, can one avoid the myalgias associated with succinylcholine?
Until the development of mivacurium, a short-acting nondepolarizing agent, patients who required tracheal intubation for surgical procedures less than 20 minutes in duration could be managed only by the administration of a bolus dose of succinylcholine to facilitate intubation followed by a continuous infusion for maintenance of neuromuscular blockade. Alternatively, after administering succinylcholine for intubation high concentrations of isoflurane could be administered to provide a satisfactory degree of muscle relaxation. Isoflurane could also be used to facilitate the action of small doses of a short-acting nondepolarizing muscle relaxant. However, the use of high concentrations of a volatile anesthetic can result in delayed awakening, an undesirable consequence in the setting of ambulatory surgery.
Disadvantages of succinylcholine include postoperative myalgias and the potential triggering of malignant hyperther-mia. At times, myalgias, which occur 5 times more commonly after ambulatory surgery than in the inpatient population, may far outlast the discomforts associated with the surgical procedure itself. These muscle pains may vary in intensity from mild to incapacitating in nature and often develop on the first postoperative day.
Mivacurium, like succinylcholine, is degraded by plasma cholinesterase. In the patient with atypical pseudo-cholinesterase, the effective duration of action is markedly prolonged. However, it may still be possible to antagonize the drug. Ordinarily, the majority of the mivacurium is rapidly hydrolyzed to inactive metabolites. The recom-mended intubating dose is 0.2–0.25 mg/kg in adults. When employing the 0.25 mg/kg dose, an initial dose of 0.15 mg/ kg should be followed 30 seconds later by 0.10 mg/kg. In children, a dose of 0.2–0.3 mg/kg is often used. Satisfactory intubating conditions are usually achieved in approximately 1.5–2.5 minutes. The duration of neuromus-cular blockade is 15–20 minutes in adults but only 9–11 minutes in children. Unfortunately, mivacurium is not free of side-effects. The drug may cause histamine release, which may cause cutaneous flushing and even bronchospasm and hypotension in some patients. Hypotension has not been a problem when dosage guidelines are not exceeded and the drug is administered slowly. Antagonism can be easily accomplished by conventional dosages of edrophonium or neostigmine administered in conjunction with the appro-priate anticholinergic agent. Twenty minutes after a single bolus dose, it may be unnecessary to antagonize the block when the train-of-four has returned to normal and fade is not present to a tetanic stimulus.