Recovery from mivacurium-induced neuromuscular blockade after neurosurgical procedures of long duration.

Abstract

To determine if recovery following prolonged (5 hours in length or greater) infusions of mivacurium is different from recovery after single bolus administration. open-labelled, controlled study. Inpatient neurosurgical service at a university hospital. 36 patients between the ages of 18 to 65 without significant history of renal, hepatic, cardiac, or metabolic disease undergoing neurosurgical procedures. 21 patients had craniotomies or skull base procedures of an estimated length of 5 hours or greater; 15 patients (control) underwent short neurosurgical operations (two hours or less). Intravenous (IV) mivacurium 0.15 mg/kg was given with stable general anesthesia with 70% nitrous oxide in oxygen, 0.2% to 0.3% end-tidal isoflurane, and continuous infusion of fentanyl. The control group was allowed to recover spontaneously after single bolus administration while neuromuscular blockade was maintained in the study group with a continuous infusion of mivacurium until 30 minutes before completion of surgery, at which time the infusion was discontinued and neuromuscular function was allowed to recover spontaneously. The evoked compound electromyogram of the adductor pollicis brevis muscle was measured during stimulation of the ulnar nerve at 2 Hz for 2 seconds at 10-second intervals. Measurements included time to 50% and 90% depression of twitch (T1 of the TOF response), time to T1 equal to 25% (T1(25)), 50% (T1(50)), and 75% (T1(75)) of baseline, and TOF ratio (TR) at 10%, 25%, 50%, and 75% recovery. Recovery index (RI), which is T1(75) minus T1(25), was also determined. All mivacurium infusion rates decreased during surgery. Recovery rates were significantly longer in the long infusion (LI) group than the control group. RI was also increased in the LI group compared with the single bolus control (11.3 +/- 1.2 minutes vs. 7.1 +/- 0.8 minutes p < 0.05). Recovery following mivacurium by prolonged continuous infusion was slower than that observed after single bolus administration in this patient population. Clinically, this increased time to recovery may be insignificant.