Prediction of arterial blood gases by transcutaneous O2 and CO2 in critically ill hyperdynamic trauma patients.

Abstract

The management of severe adult respiratory distress syndrome in critically injured patients requires the frequent measurement of arterial blood gases for adjustment of cardiovascular and ventilatory support. Since these require blood withdrawal and laboratory determinations, a noninvasive method of assessment of arterial gas tensions would permit more frequent assessment of the patient as well as permitting rapid changes in the patient's ventilatory status to be detected earlier in the clinical course. The role of transcutaneous O2 and CO2 tension in providing these measurements was evaluated in 92 studies in 38 critically ill patients with ARDS due to trauma and/or sepsis. All patients were normodynamic or hyperdynamic at the time of study (cardiac index 2.5 to 7.6 L/min/m2) and were intubated and on increased inspired oxygen fractions (FIO2 = 30 to 100%) delivered by mechanical ventilation, had a range of body temperature from 35.0 to 39.5 degrees C and pH from 7.29 to 7.57 The data from a transcutaneous O2 and CO2 sensor applied to the skin of the anterior thorax were analyzed by multiple regression analysis of variances. Prediction of the arterial oxygen tension (PaO2) from 52 to 253 torr was possible from regression-corrected measurements of the transcutaneous O2 (TcO2): [PaO2 = 1.1 (TcO2) - 0.28 (FIO2) + 45.5]. The arterial carbon dioxide tension (PaCO2) from 26 to 57 torr was predicted from the transcutaneous CO2 (TcCO2):[PaCO2 = 0.76 (TcCO2) + 0.06 (FIO2) + 0.035 (TcO2) + 4.1]. With these corrections, a noninvasive Respiratory Index was computed for assessing ARDS severity, and dynamic changes in arterial gases could be followed in response to postural changes, ventilatory alterations, or cardiovascular perturbations. These data suggest that a reasonable estimate of the arterial blood gases can be obtained from a regression-corrected measurement of the transcutaneous O2 and CO2 tensions in critically injured normodynamic or hyperdynamic ARDS patients.