Closed-circuit anesthesia prolongs the neuromuscular blockade of rocuronium.

BACKGROUND Volatile anesthetics are known to potentiate the neuromuscular blocking effect of nondepolarizing muscle relaxants. The influences of anesthetic techniques, closed-circuit anesthesia (CCA) and high flow semi-closed anesthesia (SCA), on the neuromuscular blockade of rocuronium has not yet been studied in detail. This study was purposed to compare the effects of isoflurane conveyed in minimal flow (CCA) and in high flow (SCA) on the neuromuscular blockade of rocuronium. METHODS Fifty females scheduled for elective laparoscopic gynecological surgery were enrolled for study and randomly assigned to receive either CCA (n = 25) or SCA (n = 25). Anesthesia was induced with fentanyl 2 micrograms/kg, thiopental 5 mg/kg and rocuronium 0.6 mg/kg. Two percent isoflurane in high O2 flow (3 l/min) was given for 10 min to all patients initially to wash isoflurane in the functional residual capacity of both lungs and the breathing circuit. After the wash in, for CCA group, the O2 flow was reduced to 300 ml/min with isoflurane vaporizer setting adjusted to 3-5% for anesthesia maintenance, while for SCA group, anesthesia was maintained with 1.5-2% isoflurane in 3 l/min O2 flow throughout the surgery. Electromyogram was used to determine neuromuscular blockade. Rocuronium (0.15 mg/kg) was given to maintain muscle relaxation when T1 reached 25% of control. We maintained the anesthetic depth until the recordings of T1 twitch response which reached 75% was completed. Onset time, duration, recovery index and intubating conditions were recorded. The hemodynamic parameters and the inhaled/exhaled concentrations were also measured every 15 min after skin incision in both groups. RESULTS The onset time and intubating conditions were similar in both groups. In comparison with SCA group, longer clinical durations (54.1 +/- 14.4 vs. 45.4 +/- 9.2 min, P < 0.05), longer durations of maintained dose (41.1 +/- 11.1 vs. 30.2 +/- 8.6 min, P < 0.01) and longer recovery index (34.2 +/- 10.7 vs. 20.9 +/- 5.4 min, P < 0.0001) were observed in CCA group. CONCLUSIONS We conclude that CCA may further prolong the neuromuscular blocking effect of rocuronium than SCA.