P062 Agreement between arterial and capillary CO2 level in patients undergoing sleep study for suspected hypoventilation

BACKGROUND: Measurement of arterial CO2 (PaCO2) is the gold standard for diagnosis of sleep hypoventilation during polysomnography. However, arterial PaCO2 measurement is a labour-intensive and painful. Previous audit in our unit demonstrated ABGs are often delayed or omitted when requested. Continuous monitoring of transcutaneous carbon dioxide (TcCO2) is often used as a surrogate marker of PaCO2, however caution should be applied in interpreting TcCO2 due to the “sensor drift” phenomenon. Arterialized capillary blood gas (CBG) measurement has been described in various settings and is used in many respiratory units. Concordance with ABG and TcCO2, however, is poorly described in the literature. A retrospective review was performed to assess concordance of arterialized capillary CO2 level (PcCO2) with TcCO2 measured during routine polysomnography. METHODS: This is a retrospective audit of patients with provisional diagnosis of sleep-related hypoventilation syndrome who attended Sunshine Coast University Hospital Sleep Disorders Centre for overnight sleep studies. Continuous TcCO2 was monitored and arterialized PcCO2 measured at the outset and completion of study. CO2 results will be compared to assess concordance. Where an ABG was performed simultaneously with a CBG the concordance will be reported. PROGRESS TO DATE: Full results to follow. It is anticipated that 30-40 patients will be included. Few ABGs were performed. ANTICIPATED OUTCOME: Initial evaluation suggests PcCO2 may be a viable alternative to ABG based on concordance with limited ABG data. PcCO2 may be superior to TcCO2 due to the common phenomenon of TcCO2 “drift”. A prospective study, utilising ABG, CBG and TcCO2 is needed.