Role of the oxygen supply position in the circuit during continuous positive airway pressure therapy: a randomized cross-over simulation study

PURPOSE: Continuous Positive Airway Pressure (CPAP) is the main treatment for patients with obstructive sleep apnoea (OSA). Hypoxemic patients with sleep-disordered breathing may require CPAP and additional low-flow oxygen. However, specific recommendations on where to attach the oxygen bleed-in connector are lacking. METHODS: This randomised cross-over trial assessed the fraction of inspired oxygen (FIO₂) in a simulated OSA patient’s lung resulting from different rates of low-flow oxygen (1, 2 and 3 l/min) added via three different bleed-in connector locations under different levels of either fixed pressure (5, 9 and 12 cmH2O) or constant flow (5, 10 and 15 l/min) (repeated 3x in random order). The three locations tested in a single-limb circuit with a vented full-face mask were: (1) near the CPAP mask between the mask and tubing, (2) at the tube outlet of the device, and (3) directly connected to the oxygen-port of the device. RESULTS: The bleed-in connector positioned near the tube outlet generally produced the highest and near the CPAP mask the lowest FiO₂. At the highest pressure and flow, FiO₂ remained more stable across the locations and oxygen flows of 1–3 l/min, compared to lower pressure and lower flow. FiO₂ differences between locations were notably more pronounced under different flows, ranging from 0 to 22% relative change, compared to a more limited range of 0 to 8.3% under varying CPAP pressures. CONCLUSION: We recommend positioning the oxygen bleed-in connector at the device tube outlet for CPAP devices without an oxygen port, particularly when using lower pressures.