Capillary blood gases in acute exacerbations of COPD

SummaryObjectivesTo assess the correlation and agreement between measurements of PO2, PCO2, H+ and HCO3− in arterial and capillary blood in patients with acute exacerbations of COPD. To assess the repeatability of capillary measurements.DesignMethod comparison study.SettingAccident and emergency department in a university teaching hospital.Main outcome measuresMeasurements of PO2, PCO2, H+ and HCO3− in one arterial and two capillary samples taken from consecutive patients with acute exacerbations of COPD.ResultsThe agreement between measurements of PCO2, H+ and HCO3− in arterial and capillary blood was good with mean differences of 0.087 kPa, 1.044 nmol/l and 0.513 mmol/l, respectively. The corresponding 95% limits of agreement were narrow. The agreement between measurements of PO2 was poor with a mean difference of 1.256 kPa and wide 95% limits of agreement. There was good repeatability between capillary samples with mean differences of 0.094 kPa, 0.674 nmol/l and 0.028 mmol/l for measurements of PCO2, H+ and HCO3 respectively and narrow coefficients of repeatability.ConclusionsCapillary blood gas measurements provide an accurate assessment of PCO2, H+ and HCO3− 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.