Comparison of CPAP preoxygenation versus conventional preoxygenation on duration of safe apnoea time in patients undergoing elective surgery under general anaesthesia

Anesthesia induction usually leads to apnoea, during apnoea, oxygenation depends on the oxygen reserves stored within the body .While breathing room air these stores are quantitatively low.As we cannot perfectly predict the difficulty in airway management, desirability of maximal preoxygenation is theoretically present for all patients.Induction of general anaesthesia per se as also the use of 100% oxygen during preoxygenation results in the development of atelectasis in dependent lung regions within minutes of anaesthetic induction.Therefore this randomized, controlled study was undertaken to compare the effect of CPAP (continuous positive airway pressure) preoxygenationvs conventional preoxygenation on duration of safe apnoea time in patients posted for elective surgery under general anaesthesia.After obtaining approval from the institutional review board and institutional ethics committee and prior consent from participants, 60 adult patients scheduled for elective surgery under general anaesthesia were randomized into two groups-PEEP group and ZEEP group.Patients in PEEP group were preoxygenated with CPAP of 5 cm of H2O with 100% oxygen for five minutes and in ZEEP group no CPAP was used.Duration of safe apnoea time (taken as till Spo2 reached 94%) and ABG analysis at various time intervals was done for each group.The comparison of normally distributed continuous variables between the groups was performed using Student's t test.Nominal categorical data between the groups were compared using Chi-squared test or Fisher's exact test as appropriate.P value less than 0.05 was considered statistically significant.We found out that the duration of safe apnoea time was significantly longer in PEEP group (408.90 ± 32.73) as compared to ZEEP group (257.70 ± 12.79 s) ( P value less than 0.001).PaO2 after preoxygenation was also significantly higher in PEEP group (416.62 ± 28.72 mmHg) as compared to ZEEP group (367.02 ± 14.29 mmHg) ( P value less than 0.001).We concluded that the application of continuous positive airway pressure during preoxygenation is a simple, well tolerated technique that may have advantages especially in those patients in whom difficulty in airway management is anticipated, those who are at increased risk of desaturation such as morbidly obese patients and when assisted ventilation is not applied such as during rapid sequence induction.