Arterial blood gases during exercise: Validity of transcutaneous measurements

Objective: To investigate the validity of transcutaneous measurements of bl ood gas tensions for the assessment of partial arterial pressure of oxygen (Pao(2)) and carbon dioxide (Paco(2)) during treadmill exercise. Design: Experimental, self-controlled against a reference standard. Setting: Lung function laboratory. Patients: Eighty-one patients with various lung diseases. Interventions: At rest and at symptom-limited peak exercise, puncture of th e radial artery with concurrent transcutaneous measures of blood gases. Main Outcomes Measures: Arterial blood samples were analyzed with a radiome ter to measure Pao(2) and Paco(2). A microgas apparatus was used to measure gas tensions transcutaneously. Values obtained transcutaneously (TcPo2, Tc Pco(2)) were compared with those obtained by blood sample. TcPo2 was adjust ed as close as possible to the Pao(2) obtained in the same conditions, with the correction factor of the apparatus. Values obtained transcutaneously w ere compared with those obtained by blood sample to establish the sensitivi ty and specificity of the noninvasive method. Results: Mean differences standard deviation between transcutaneous and art erial tension at peak exercise were 0.4 +/- 7.0mmHg and 2.1 +/- 3.3mmHg for Pao(2) and Paco(2), respectively. The transcutaneous device enabled us to predict a decrease in Pao2 (greater than or equal to 2mmHg) from rest to ex ercise with a sensitivity of 92.1% and a specificity of 90% and an increase in Paco(2) with a sensitivity of 88% and a specificity of 58.9%. Conclusions: Although transcutaneous measurement are sufficiently sensitive and specific to detect patients whose Pao(2) decreases during exercise, it s precision is not sufficient for gas exchange calculations.