WINNING ABSTRACT: Supplemental O 2 is frequently added to bi-level non-invasive ventilation circuits to maintain Sa,O2 .90%. Oxygen can be added at several points & in the presence of different inspiratory pressures. The effect of varying entrainment sites and inspiratory pressures (IPAP) on PO2, PCO2, Fio2, inspiratory triggering and expiratory triggering in COPD patients is unknown. 18 patients with stable COPD (mean FEV1 47%) participated in the study. Oxygen was added at 4 sites in the

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... latory circuit (site 1: between mask and exhalation port; site 2: just distal to exhalation port; site 3: at ventilator outlet; site 4: directly into the mask via an inlet). The effect of varying entrainment sites and inspiratory pressures on arterial PO2, PCO2, FIO2, was recorded at 3 mins. The same full face mask (Respironics, Image 3) & ventilator (Respironics, BIPAP ST 30) was used. Results for PO2 are shown at IPAP 10/EPAP 4 [table 1 ]. Anova was used to analyse the data. Site 4 (via mask) was associated with a significantly higher PO2 at all flow rates compared with sites 1, 2 and 3 (P,0.001). Site 3 (at ventilator outlet) was associated with the lowest PO2 at all flow rates, particularly at 15 L min (P,0.001). Adding oxygen to the mask at lower IPAPs result in higher oxygen delivery.