Capillary blood gases in acute exacerbations of COPD

Summary Objectives To assess the correlation and agreement between measurements of P O 2 , P CO 2 , H + and HCO 3 − in arterial and capillary blood in patients with acute exacerbations of COPD. To assess the repeatability of capillary measurements. Design Method comparison study. Setting Accident and emergency department in a university teaching hospital. Main outcome measures Measurements of P O 2 , P CO 2 , H + and HCO 3 − in one arterial and two capillary samples taken from consecutive patients with acute exacerbations of COPD. Results The agreement between measurements of P CO 2 , H + and HCO 3 − in arterial and capillary blood was good with mean differences of 0.087kPa, 1.044nmol/l and 0.513mmol/l, respectively. The corresponding 95% limits of agreement were narrow. The agreement between measurements of P O 2 was poor with a mean difference of 1.256kPa and wide 95% limits of agreement. There was good repeatability between capillary samples with mean differences of 0.094kPa, 0.674nmol/l and 0.028mmol/l for measurements of P CO 2 , H + and HCO 3 respectively and narrow coefficients of repeatability. Conclusions Capillary blood gas measurements provide an accurate assessment of P CO 2 , H + and HCO 3 − and can be used to reliably measure the ventilatory status of patients. Combined with continuous pulse oximetry they can be used as an alternative to arterial blood gas measurements in patients with acute exacerbations of COPD.