P103 Utility of Capillary Blood Gases (CBGs) for measuring gas exchange in the Sleep Laboratory.

INTRODUCTION: Arterial Blood Gases (ABGs) are used for assessing respiratory failure in clinical practice. ABGs also provide a useful verification tool for nocturnal Transcutaneous Carbon Dioxide (TcCO2) measurements. However, there are known complications to collecting ABGs. Conversely, CBG is less invasive and more accessible to clinical practice. We assessed CBGs as an alternative to ABGs to measure pCO2 and pO2, and its suitability for verifying TcCO2. We hypothesised that CBG sampling would be suitable for TcCO2 verification and would be a suitable ABG surrogate. METHODS: ABGs were sampled by Resident Medical Officers (RMOs) and CBGs were sampled by Sleep Scientists to validate TcCO2 at awake. Correlation between measures was assessed via Pearson and Spearman coefficients. ρ > 0.6 demonstrate a moderate positive correlation, with strengthening correlation as ρ approaches 1. Agreement between measurements was assessed via Bland-Altman plots. RESULTS: There was a moderately strong correlation between CBG vs TcCO2 (n=125) (ρ = 0.694, p < 0.001) and CBG vs ABG (pCO2) (n=29) (ρ = 0.725, p < 0.001), with a strong correlation for ABG vs TcCO2 (n=81) (ρ = 0.847, p < 0.001). Bland-Altman plots showed agreement between CBG, ABG and TcCO2. CONCLUSIONS: There were strong positive correlations observed, with agreement seen across all measures of pCO2. This analysis demonstrates both the accuracy of nocturnal TcCO2 and the utility of CBG to verify TcCO2. Surrogate CO2 measures support positive patient outcomes and verification of gas exchange.