Hemoglobin P50 Dynamics During Hypothermic Cardiopulmonary Bypass

Abstract

The hemoglobin P50 was ascertained prior to anesthesia and CPB and calculated during hypothermic CPB to track the change in hemoglobin affinity in fifty randomly selected cardiac disease patients. The AMINCO Hem-0-Scan standardized P50 averaged 32.1 +/− 6.8 (1 SD) mmHg in the awake, slightly sedated CPB candidate. The awake patients were distributed into three significantly different (p < .05) groups: left-shifted oxyhemoglobin dissociation curve (ODC), P50 = 23.1 ±/− 1.4, n = 5; normal ODC, P50 = 27.2 ±/− 1.3, n = 13; and right-shifted ODC, P50 = 35.4 ±/− 6.1, n = 32. The three groups converged at the termination of hypothermic CPB to a single group calculated, mean P50 = 30.7 ±/− 4.7 mmHg. Unlike the previous studies of Woodson2 (1970) and Wilkinson (1979), the Hem-O-Scan pre-CPB P50 demonstrated a weak inverse correlation to ejection fraction, cardiac index and hemoglobin flow index in this patient group. The position of the ODC prior to and during CPB may not be accurately predicted. Therefore, direct measurement of pO2 and O2 saturation of hemoglobin is recommended and calculator prediction of hemoglobin O2 saturation from pO2 assuming a beginning P50 = 27 mmHg may not be trusted in cardiac diseased patients.