[Efficacy of preoxygenation using tidal volume breathing: a comparison of Mapleson A, Bain's and Circle system]

Efficacy of preoxygenation depends upon inspired oxygen concentration, its flow rate, breathing system configuration and patient characteristics. We hypothesized that in actual clinical scenario, where breathing circuit is not primed with 100% oxygen, patients may need more time to achieve EtO₂≥90%, and this duration may be different among various breathing systems. We thus studied the efficacy of preoxygenation using unprimed Mapleson A, Bain's and Circle system with tidal volume breathing at oxygen flow rates of 5L.min^-1 and 10L.min^-1.

Patients were randomly allocated into one of the six groups, wherein they were preoxygenated using either Mapleson A, Bain's or Circle system at O₂ flow rate of either 5L.min^-1 or 10L.min^-1. The primary outcome measure of our study was the time taken to achieve EtO₂≥90% at 5 and 10L.min^-1 flow rates.

At oxygen flow rate of 5L.min^-1, time to reach EtO₂≥90% was significantly longer with Bain's system (3.7±0.67min) than Mapleson A and Circle system (2.9±0.6, 3.3±0.97min, respectively). However at oxygen flow rate of 10L.min^-1 this time was significantly shorter and comparable among all the three breathing systems (2.33±0.38min with Mapleson, 2.59±0.50min with Bain's and 2.60±0.47min with Circle system).

With spontaneous normal tidal volume breathing at oxygen flow rate of 5L.min^-1, Mapleson A can optimally preoxygenate patients within 3min while Bain's and Circle system require more time. However at O₂ flow rate of 10L.min^-1 all the three breathing systems are capable of optimally preoxygenating the patients in less than 3min.