Proceedings

Hemoglobin P₅₀ Dynamics During Hypothermic Cardiopulmonary Bypass

¹ Extracorporeal Technologies, Inc., Indianapolis, Indiana
² Emory University Clinic and Hospital, Atlanta, Georgia

^* Direct communications to: J. B. Riley, 3380 Founders Road, Indianapolis, IN 46268.

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.