Clinical utility of arterialised capillary earlobe sampling in the critical care setting

Introduction

The purpose of this study was to determine whether earlobe capillary blood gas sampling, performed by nonmedical staff, provides a clinically acceptable estimate of the pH, pCO₂ and pO₂ in critically ill adults.

Methods

Paired samples (arterial and capillary) were obtained from patients aged 16 years and over admitted to the general intensive therapy unit who had an arterial line in situ. Details of the severity of illness, use of vasoactive agents and complications were recorded.

Results

One hundred and thirty-one paired independent samples were obtained from 142 patients. Mean age 60 (18–87) years, mean APACHE II score 20 (5–44). Bland–Altman analysis was used to compare arterial and capillary pH, pCO₂ and pO₂, respectively. See Table 1. The use of vasoconstricting drugs had no significant effect on the mean differences between arterial and capillary values for pH, pCO₂ or pO₂ (P = 0.4, 0.8 and 0.7, respectively). For high arterial pCO₂ tensions (>6.5 kPa), capillary measurements showed a mean bias of 0.95 kPa with limits of agreement of -0.22 to 2.12 kPa. For hypoxic patients (PaO₂ < 10 kPa), capillary sampling had a mean bias of 0.05 kPa with limits of agreement of -1.08 to 1.17 kPa. There were no complications of capillary sampling in terms of bruising, bleeding or infection. It took significantly longer to obtain capillary samples than arterial ones (35 s, P < 0.001).

Table 1

Conclusion

Capillary earlobe sampling provides a reliable estimation of the arterial pH and pCO₂ in critically ill patients. For estimation, the technique has a higher level of agreement pO₂ when the arterial PO₂ is below 10 kPa. Capillary earlobe blood sampling would be a reliable method of monitoring for patients who do not have an arterial line in situ and can be performed without complications by nonmedical personnel.