Does Inhalational Nitrous Oxide Affect Induction Dose of Propofol and Haemodynamic

Abstract

Background: Propofol is a commonly used induction agent. Propofol does not possess any strong analgesic effect, when used alone for induction of anaesthesia. In dose of more than 2 mg/kg bolus known to cause hypotension even requiring vasopressors. Nitrous oxide (N2O) has been in use for more than 150 years. Although N2O reduces the requirement of propofol for induction and maintenance, the effects of both the drugs on overall haemodynamic remain controversial. The aim of this study was to evaluate the efficacy and safety of induction dose of propofol when N2O was concurrently administered and haemodynamic alteration with addition of N2O to therapeutic dose of propofol. Materials and Methods: This was a prospective, randomized and double blinded comparison study that was conducted after obtaining institutional ethical approval. The study population consisted of eighty patients aged between 18 to 60 years from either sex and classified as American Society of Anaesthesiologists (ASA) physical status I or II which were scheduled for various elective surgical procedures under general anaesthesias. Participants were randomly allocated into two groups comprising 40 subjects each. Group PN received breathed 67% N2O (4 L/min) + 33% O2 (2L/min) and propofol. Group PO: breathed 100 % O2 (6L/min) and propofol. Changes in heart rate (HR), systolic blood pressure (SBP), mean arterial pressure (MAP) and Oxygen saturation (SpO2) were measured Preoperatively (baseline T0), After 3minutes of premedication (T1), After 1minute of inhalation of 100% O2 before induction of anesthesia (T2), After induction (T3), At 2, 5 and 10 minutes after induction (T4), (T5), and (T6). Results: Induction time and dose of propofol in PN group were significantly less. As 42.5% of the patients were induced in less than 100 sec, 57.5% in less than 200 sec and none of the patients required more than 200 sec for induction as compare to group PO where 77.5% required more than 200 sec, 22.5% in less than 200 sec and none of the patients were induced in less than 100 sec. The mean ± SD of induction time in groups PN and PO were 113.38±35.93 and 258.00±59.43 seconds respectively with p < 0.001. In group PN, 57.5% required 0.5-1.0mg/kg, 40% required less than 0.5mg/kg unlike group PO where 77.5% required 1-2mg/kg. The mean ± SD induction dose required for induction of anesthesia were 0.58±0.19 mg/kg and 1.43±0.40 mg/kg with and without 67% N2O in O2. Increase in HR in groups PN and PO 16.38% and 6.42% respectively. Conclusions: Co-administration of N2O during induction of anaesthesia achieves significant reduction in induction dose as well as induction time of propofol. It provides significant stability in SBP, and MAP, without affecting arterial oxygen saturation. N2O causes significant increase in HR.