Determinants of Transcutaneous Ear Lobe CO2 Tension (PtCO2) at 37°C During On-Pump Cardiac Surgery.

ABSTRACT

OBJECTIVE: There are no available criteria for determining the optimal flow rate and mean arterial pressure level in patients undergoing cardiopulmonary bypass (CPB). Transcutaneous carbon dioxide tension (PtCO2) has been proposed for microcirculation monitoring and it could be useful for guiding hemodynamic optimization under CPB. The goal of this exploratory study was to determine the factors that influence PtCO2 variations during CPB. DESIGN: Cutaneous ear lobe CO2 tension was monitored along with hemodynamic parameters every 10 minutes during CPB, until aortic unclamping. SETTING: French university teaching hospital. PARTICIPANTS: Patients scheduled for cardiac surgery requiring CPB were prospectively included. INTERVENTION None. MEASUREMENTS AND MAIN RESULTS: A total of 41 patients were included (520 observations). There was a statistically significant association between PaCO2 and PtCO2 (beta = 0.493 [0.154-0.832], p = 0.043), mostly when PaCO2 was outside the normal range. When PaCO2 was normal, PtCO2 was inversely correlated with mean arterial pressure (after adjustment for PaCO2 and body temperature Beta -0.245, SE = 0.037, p<0.001) but not with CPB flow rate (p = 0.11). CONCLUSION: The factors that influence PtCO2 during CPB cardiac surgery are PaCO2, body temperature, and mean arterial pressure. When PaCO2 is normal, a PtCO2 elevation might be explained by insufficient mean arterial pressure. Whether low PtCO2 values during CPB should trigger the administration of vasoconstrictors remains to be evaluated.