Agreement between arterial and non-arterialised fingertip capillary blood gas and acid-base values

Background: Arterial puncture is considered the gold standard for obtaining blood gas and acid-base values and facilitates the assessment of acutely and critically ill patients, as well as control of patients in long-term oxygen therapy (LTOT). Substitutional capillary sampling has been proposed, as researchers cite lower complication rates, physician independence, lower degree of invasiveness and higher degree of patient comfort. An arterialised earlobe is considered the method of choice to obtain capillary blood sampling, but in an acute setting, the need for vasodilating pastes may be time-consuming and impractical. The aim of this study is to examine whether accurate blood gas and acid-base measurements can be obtained using non-arterialised fingertip blood. Materials and methods: Consecutive arterial punctures and non-arterialised capillary blood samples were drawn from 62 patients with stable-phase chronic obstructive pulmonary disease (COPD), and subsequently analysed. Agreement between arterial and capillary blood gas values was compared using the method recommended by Bland and Altman. Results: Results show that limits of agreement (LoA) regarding PO₂ (LoA: -1.27-4.45 kPa); Base Excess (LoA: -1.35-0.55); lactate (LoA: -0.77-0.20 mmol/l) and SO₂ (LoA: -0.02-0.06) are wider than what would be applicable for clinical use. However, clinically acceptable LoA were obtained regarding PCO₂ (LoA: -0.64-0.38 kPa); pH (LoA: -0.02-0.03), and HCO₃ ^- (LoA: -1.06-0.55 mmol/l). Conclusion: LoA for PCO₂, pH and HCO₃ ^- indicate that measurement of these parameters in non-arterialised capillary blood may be useful in clinical practice/an acute setting. What this paper adds: Capillary blood sampling provides a fast, non-invasive means of obtaining blood gas-values;Traditionally, capillary blood sampling for blood gas analysis is obtained from the earlobe using arterialisation;The present study presents accurate measurements of PCO₂, HCO₃ ^- and pH using non-arterialised fingertip capillary blood;The present study is the first to show this in a population of stable-phase COPD patients.