Original contributionSevoflurane-N2O versus propofol/isoflurane-N2O during elective surgery using the laryngeal mask airway in adults
Introduction
Unlike most inhalational anesthetics that cause airway irritation, inhaled sevoflurane provides smooth induction of general anesthesia with little or no apnea or airway irritation.1 Moreover, the low blood:gas partition coefficient of sevoflurane (0.63–0.66) has been associated with a rapid offset of clinical effect compared with other inhalational drugs of greater solubility such as halothane (blood:gas partition coefficient = 2.5) or isoflurane (coefficient = 1.43).2, 3, 4 A faster offset of clinical effect might result in a more rapid return to consciousness and a shorter emergence time at the conclusion of surgery. For example, in unpremedicated female patients undergoing major gynecologic procedures for which neuromuscular blockade, tracheal intubation, and controlled mechanical ventilation were required, time to emergence was approximately 2.7 minutes shorter with sevoflurane-nitrous oxide (N2O) compared with isoflurane-N2O.2
The purpose of this prospective, randomized study was to evaluate the use of sevoflurane-N2O for induction and maintenance of general anesthesia in patients undergoing elective surgeries for which spontaneous ventilation via the laryngeal mask airway (LMA) was desired. The study was designed to test the following hypotheses: 1) compared with IV propofol, inhaled sevoflurane-N2O induction is associated with faster loss of consciousness (LOC), faster “anesthesia ready time,” satisfactory conditions for LMA insertion, and reduced apnea episodes (≥20 sec) after LMA insertion; and 2) compared with isoflurane-N2O, maintenance of anesthesia with sevoflurane-N2O is associated with faster return of consciousness and faster time to exit the operating room (OR) after the conclusion of surgery.
The present study differs from a previous evaluation of induction, maintenance, and emergence characteristics of sevoflurane-N2O2 with respect to higher sevoflurane concentration during induction, use of a voluntary maximal vital capacity breathing method for inhalation induction, midazolam premedication, use of the LMA, absence of neuromuscular relaxants, spontaneous ventilation during the procedure, and nonrequirement for reversal of neuromuscular block at the conclusion of surgery.
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Materials and methods
The study was approved by the MetroHealth Medical Center Institutional Review Board, and written informed consent was obtained from 62 ASA physical status I, II, and III patients undergoing elective surgery. Exclusion criteria were age <18 years, pregnancy, renal failure, ASA physical status <III, and conditions predisposing to risk of aspiration. Patients were randomized to one of two groups using a table of random numbers: group 1: propofol/isoflurane-N2O, n = 32 and group 2: sevoflurane-N2O,
Results
Demographics were similar between groups (Table 1). One patient in the control group required thiopental, succinylcholine, and tracheal intubation because of persistent coughing after LMA insertion. Data for this patient are reported up to time of intubation. One patient in each group required succinylcholine (10 mg and 20 mg) for treatment of laryngospasm after LMA insertion (Table 2). Compared with baseline, BP was decreased and ETCO2 was increased in both groups after LMA insertion (Table 3)
Discussion
The results of the present study indicated that both sevoflurane-N2O and propofol were effective in inducing general anesthesia and providing adequate conditions for LMA insertion. Despite the longer time to LOC with sevoflurane-N2O, there were no intergroup differences in “ready for surgery time.” Thus, use of an inhalation induction technique does not delay start of surgery when compared with IV induction drugs. Induction time with sevoflurane-N2O in the present study was nearly twice as fast
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Associate Professor of Anesthesia
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Chester Scholar
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Assistant Professor of Anesthesia
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Research Associate