Original contribution
Sevoflurane-N2O versus propofol/isoflurane-N2O during elective surgery using the laryngeal mask airway in adults

Presented in part at the American Society of Anesthesiologists’ Annual Meeting, September, 1998, Orlando. Supported by the MetroHealth Foundation, Chester Summer Scholar Program. Gensia, Inc. donated three laryngeal mask airways. No other financial support was provided.
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Abstract

Study Objectives: To compare a sevoflurane-nitrous oxide (N2O) general anesthetic technique with a standard technique of propofol for induction, and isoflurane-N2O for maintenance.

Design: Prospective, randomized study.

Setting: University-affiliated tertiary-care hospital.

Patients: 62 adults undergoing elective surgery using the laryngeal mask airway (LMA).

Interventions: Patients received either the standard technique of propofol for induction and isoflurane-N2O for maintenance (controls) or sevoflurane-N2O for both induction and maintenance of general anesthesia.

Measurements: Induction and emergence times, heart rate, blood pressure, oxygen saturation, and end-tidal carbon dioxide were recorded.

Main Results: Time to loss of consciousness was faster after propofol (mean ± SEM: 51 ± 3 sec) than after sevoflurane-N2O (85 ± 10 sec; p < 0.05). Ready for surgery times, were however, similar between groups (10 ± 1 vs. 11 ± 1 min, respectively). All patients in the control group had apnea after LMA insertion compared with 4 patients in the sevoflurane-N2O group (p < 0.05). Heart rate was lower 5 and 10 minutes after LMA insertion in the sevoflurane-N2O group (69 ± 3 and 66 ± 3 bpm) versus the control group (81 ± 3 bpm and 74 ± 3 bpm, p < 0.05). After cessation of anesthetic gases, there were no differences in time to LMA removal, eye opening, or exiting the operating room (OR) between the control group (7, 8, and 10 min) and sevoflurane-N2O groups (7, 8, and 12 min, respectively). The majority of patients in both groups (92% to 97%) rated their anesthetic experience as excellent or good.

Conclusions: Sevoflurane-N2O and propofol provided comparable conditions for LMA insertion. Sevoflurane-N2O was not associated with a faster return of consciousness or faster time to exit the OR compared with isoflurane-N2O.

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.

Section snippets

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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