P027 Predictors of CPAP failure in severe obstructive sleep apnoea and obesity hypoventilation syndrome patients

There are mixed findings regarding predictors of failing continuous positive airway pressure in the obstructive sleep apnoea and obesity hypoventilation population, with duration of time under 90% oxygen saturation independently associated with treatment failure. Our study examined predictors of CPAP failure in severe OSA and OHS patients using baseline characteristics, diagnostic polysomnography, arterial blood gases and TcCO2 oximetry data. An observational review of patients in an accredited sleep laboratory from 2016 to 2021 was performed. Patients with treatment studies demonstrating CPAP failure were compared to patients controlled on CPAP therapy via pressure determination study. Independent t-test compared group characteristics and multivariate logistic regression was performed to assess predictors of CPAP failure. Data is presented as mean unless otherwise stated. Twenty patients who required bilevel support ventilation were compared to thirty-five patients controlled by CPAP. Total sleep time (266vs328minutes, p=0.007) and sleep efficiency (62% vs 75%, p=0.028) was lower in the BSV group. Patients who failed CPAP spent a greater percentage of T<88% on their diagnostic study (T<88%, 46.4%vs9.66%, p=0.001). Percentage of T<88% oxygen saturations were significant in being able to predict CPAP failure (p<0.001) using a model including arterial blood gas PaCO2 and TcCO2 data. TcCO2, blood gases and baseline demographic data were not significant in determining CPAP failure. Our study strengthens the duration of time spent hypoxic or T<88% as a significant predictor of CPAP failure. Surprisingly, TcCO2 data and paired arterial blood gas data was not able to predict who would require bilevel ventilation in our cohort.