The clinical utility of arterialized earlobe capillary blood in the assessment of patients for long-term oxygen therapy

The prescription of long-term oxygen (LTOT) is underpinned by the measureme nt of arterial PO2, generally obtained by radial artery puncture. This test is commonly associated with patient discomfort and a test that is reliable , well-tolerated and non-invasive would be advantageous Cutaneous oximetry has not proved sufficiently accurate. Arterialized earlobe capillary sampli ng has been proposed, with some authors stating that it is under-utilized. However, to date studies have yielded conflicting results and the clinical utility remains uncertain. Our regional oxygen service based at a specialis t respiratory hospital undertook a prospective! study of consecutive patien ts with chronic respiratory disease undergoing assessment for LTOT. Simulta neous radial artery and arterialized earlobe sampling was performed. Rigoro us steps were taken to ensure optimal arterialization of the earlobe sample s. Agreement between arterial and arterialized PO2 and PCO2 was compared us ing the Bland-Altman method. One hundred patients were studied. Procedural difficulties (insufficient sample or air in sample) were similar for both p rocedures, however clotting occurred more frequently in arterialized earlob e samples. Sixty-four sample pairs were available for comparison. The bias and limits of agreement between arterialized and arterial PO2 were wide, me an (+/- 2 SD), -048 (-2.05-1.09) kPa. The bias and limits of agreement for PCO2 were smaller. Using the absolute criterion (arterial PO2 < 7.3 kPa), 9 /55 (16%) patients would receive oxygen inappropriately based on the arteri alized earlobe sample. Conversely, no patients would have been denied LTOT. Radial artery puncture gave rise to significantly greater ciscomfort (P < 0.0001) and level of concern (P < 0.0001). Patient preference strongly favo ured arterialized earlobe samp ing. However, despite rigorous attention to arterialization earlobe sampling was insufficiently accurate to replace rad ial artery puncture in the prescription of LTOT. (C) 2001 Harcourt Publishe rs Ltd.