Oxygen-Air Mixture Does Not Differ from Oxygen-Nitrous Oxide Mixture in Influencing PF Ratio in Healthy Patients Undergoing Laparoscopic Cholecystectomy

Objective: This randomized single-blind study was designed to evaluate the effects of oxygen administration in air versus in N2O to the PaO2 / FiO(2) (PF ratio) in healthy patients undergoing laparoscopic cholecystectomy. Method: Sixteen patients with ASA I and II, age of less than 65 years and BMI of less than 40 were randomly recruited into two groups to receive either O-2 in air gas mixture (Group 1) or O-2 in N2O gas mixture (Group 2). All patients received midazolam 7.5 mg po and 3 minutes preoxygenation with 100% O-2 prior to the induction of anaesthesia. Anaesthesia was induced with IV fentanyl 2 mcg/kg, propofol 2 mg/kg and paralyzed with IV rocuronium 0.6-0.8 mg/kg. All patients were maintained with FiO(2) of 0.35, sevoflurane with MAC of 1.0-1.2 and end CO2 of 30-35 mmHg. Result: The peritoneal insufflations pressures were documented. A series of blood gases were taken prior to preoxygenation, at 30, 60 and 90 minutes post intubation. There was no overall difference between the two groups in terms of the PF ratio (p = 0.142), over time (p = 0.515) and time interaction within groups (p = 0.806) despite lower overall PF ratio in Group 2. Conclusion: There was no significant difference in the partial pressure of oxygen to the fractional inspired oxygen ratio (PF Ratio) in healthy patients ventilated with oxygen-Air or oxygen-nitrous oxide mixtures during laparoscopic cholecyctectomy.