Effect of positive airway pressure during pre-oxygenation and induction of anaesthesia upon safe duration of apnoea

BACKGROUND AND AIMS: Induction of general anaesthesia per se as also the use of 100% oxygen during induction of anaesthesia, results in the development of atelectasis in dependent lung regions within minutes of anaesthetic induction. We aimed to assess the effect of application of a continuous positive airway pressure (CPAP) of 5 cm H2O during pre-oxygenation and induction of anaesthesia on the period of apnoea before the occurrence of clinically significant desaturation. METHODS: In this prospective, randomised, and double-blind study, 40 patients posted for elective surgery were enrolled. Duration of apnoea was measured as the time from the administration of succinylcholine hydrochloride to the time when oxygen saturation fell to 93%. Student's t-test was used for comparing the duration of apnoea. RESULTS: The safe duration of apnoea was found to be significantly longer in patients receiving CPAP of 5 cm H2O (Group P; n = 16) compared to the group receiving no CPAP (Group Z; n = 20), that is, 496.56 ± 71.68 s versus 273.00 ± 69.31 s (P < 0.001). CONCLUSION: The application of CPAP of 5 cm H2O using a Mapleson A circuit with a fixed positive end-expiratory pressure device during 5 min of pre-oxygenation with 100% oxygen prior to the induction of anaesthesia provides a clearly longer duration of apnoea before clinically significant arterial desaturation occurs.