A randomized prospective study of BIS guided low-flow sevoflurane anesthesia; is air safer than nitrous oxide?

  • Hulya Celebi Professor of Anesthesiology & Reanimation Department of Anesthesiology and Reanimation, Faculty of Medicine, Gazi University, 06500-Besevler, Ankara, (Turkey)
  • Gozde Inan Consultant, Department of Anesthesiology and Reanimation, Faculty of Medicine, Gazi University, 06500-Besevler, Ankara, (Turkey)

Abstract

Objective: This prospective randomized BIS controlled study was conducted to compare low-flow anesthesia (LFA) techniques with or without nitrous oxide (N2O) using remifentanil and sevoflurane, with respect to ventilation parameters and sevoflurane consumption.

Methodology: Forty-five, ASA I/II women younger than 65-year-old, scheduled for gynecological surgery lasting nearly two hour under general anesthesia were enrolled. Electrocardiogram (ECG), pulse oximetry, non-invasive arterial pressure, train-of-four (TOF) and bispectral index (BIS) were monitored. Anesthesia was induced by inj propofol 2 mg/kg with increments of 10 mg until BIS was under 60 and rocuronium 0.6 mg/kg. Patients were randomized to one of three groups, 15 patients in each, to receive either N2O (Group N) or N2O-free anesthesia (Groups R I and R II). All groups received bolus remifentanil 0.5 µg/kg and then infusions @ 0.2 µg/kg/min (Group R I), or 0.05 µg/kg/min (Group R II) as maintenance. Anesthesia was maintained with sevoflurane in O2 + N2O or air. Signs indicating adequate depth of anesthesia during maintenance phase of anesthesia were HR, arterial blood pressure and BIS. The goal was to obtain a BIS value between 40 and 60 and hemodynamic parameters within 20% of baseline values. Opioid infusions were constant as sevoflurane vaporizer dial setting was adjusted in ± 0.5% volumes to maintain this goal. Systolic, diastolic and mean arterial pressures, HR, SpO2, the inspired and expired gas partial pressure measurements of O2, sevoflurane, N2O, and CO2, BIS values sevoflurane vaporizer dial settings, and recovery times were recorded. Measuring points were at every 5 min during surgery. A minimum inspired oxygen concentration (FiO2) of 0.3 was maintained. Consumption and costs for sevoflurane were calculated.

Results: Demographic data, duration of surgery and anesthesia were similar between the groups. A significant decrease was observed in FiO2 by time in all groups. For all recording times FiO2 was statistically greater in Group N. The difference between delivered Oand FiO2 was the lowest in Group N. The difference between inspired and expired fractions of sevoflurane (Fisevo and Fetsevo) reduced by time during the low flow period. It was lower in Group N than in remifentanil groups. Total sevoflurane consumption was significantly greater in Group R II than Group N but there was no significant difference in sevoflurane consumption and costs per patient per minute between groups. Recovery times were comparable between the groups.

Conclusions: We concluded that risk of hypoxia and volatile anesthetic consumption did not differ with or without N2O in remifentanil-sevoflurane, low flow anesthesia. Monitoring FiO2 is essential in both air/O2 and N2O/O2 mixtures. Both are safe to administer unless FiO2 is lower than 30%. BIS-guided sevoflurane with its low solubility feature successfully adapts quickly to variable anesthetic depth levels during low-flow anesthesia.

Key words: Anesthesia; Closed Circuit, Anesthesia; Rebreathing; Nitrous oxide; Consciousness Monitors; Bispectral Index Monitor

Citation: Inan G, Celebi H. A randomized prospective study of BIS guided low-flow sevoflurane anesthesia; is air safer than nitrous oxide? Anaesth Pain & Intensive Care 2016;20(3):266-272

Received: 31 January 2016; Reviewed: 27 March 2016; Corrected: August 2016; Accepted; 9 September 2016

Published
05-10-2019
How to Cite
Celebi, H., & Inan, G. (2019). A randomized prospective study of BIS guided low-flow sevoflurane anesthesia; is air safer than nitrous oxide?. Anaesthesia, Pain & Intensive Care. Retrieved from https://apicareonline.com/index.php/APIC/article/view/635
Section
Original Articles