Abstract PR532

Abstract

Background & Objectives: Preoxygenation is used to maximise alveolar oxygen reserves prior to induction of anaesthesia thus allowing a longer safe apnoea time prior to securing the airway. A barrier to routine preoxygenation is the delay that such practice might incur in the time to induction of anaesthesia1. Optimal preoxygenation is defined as FeO2≥0.9. However, this may predispose to alveolar absorption atelectasis and may be unachievable within an acceptable timeframe. Therefore, a FeO2≥0.8 is a compromise target. The purpose of this study was to determine whether Non-Invasive Ventilation (NIV) would achieve a targeted Fractional Expired Oxygen (FeO2) concentration faster than standard ventilation (SV) during preoxygenation prior to induction of anaesthesia. Materials & Methods: This was a cross-over study of 20 adult patients (age range 18-80) undergoing elective surgery. The patients were recruited via the Pre-Operative Assessment Clinic to undergo a controlled comparison of two preoxygenation techniques. SV consisted of 10L/min of 100% oxygen via tight fitting facemask. NIV consisted of 10L/min of 100% oxygen via tight fitting facemask, with 5cmH20 pressure support and 5cmH20 positive end expiratory pressure. Each patient was preoxygenated using both techniques. The sequence of preoxygenation was randomised, with sufficient time interval between techniques to allow alveolar gas composition to return to baseline. Patients were placed in the supine position and initial FeO2 after the first breath was recorded. The time the patient reached a FeO2 0.8 was recorded. An additional 2 minutes were allowed for the patient to reach 0.9. If this was not achieved the maximal FeO2 was recorded. At the end of the study patients were asked for their preferred technique. Results: Of the 20 patients recruited 14 were male and 6 female. The average age was 60 years. The mean time to achieve FeO20.8 using NIV (57 seconds: range 30 - 105 sec) was faster than SV (148 seconds: range 50 - 440 sec). The mean difference was 92 seconds faster for NIV (95% confidence interval: range 43.3 -142.6; P=0.0009). In addition, when subjected to NIV, 15/20 patients (75%) achieved FeO2 0.9 in a further 2 minutes, compared to only 6/20 patients (30%) in the standard preoxygenation group. 78% of patients preferred NIV to standard technique (P=0.0184).Conclusion: This study demonstrates that NIV is a technique that achieves a FeO2 0.8 faster and is better tolerated than standard preoxygenation.