The importance of the circuit capacity in the administration of CPAP.

The effectiveness of Continuous positive airway pressure (CPAP) administration in improving blood oxygenation and the importance of the circuit capacity, by checking two different volumes of balloon reservoirs (a 3 l versus 23 l balloon), in reducing the work of breathing is presented. Twenty-five postoperative patients, after major gastrointestinal interventions were included in this study. Each patient being studied under three different conditions: Phase I: spontaneous breathing, Phase II: CPAP - 11 cmH2O, 3 l balloon reservoir; Phase III: CPAP - 11 cmH2O, 23 l balloon reservoir. All patients were intubated and were breathing room air. The results obtained clearly show a significant improvement in blood oxygenation due to CPAP, p less than 0.001. In addition, the work of breathing was considerably reduced utilizing a large capacity system with significant lower flow rates, p less than 0.001 and p less than 0.0001 respectively. Furthermore, rebreathing was prevented by maintaining continuous bubbling in the exit chamber and proved by having no change in PaCO2.