A Simple Microtonometric Method for Whole Blood Oxygen Dissociation Curve and a Critical Evaluation of the "Single Point" Procedure for Blood P₅₀

Abstract

We devised a rapid and simple method to obtain oxygen dissociation curve (ODC) for a small amount of blood with simple equipment. This system achieved the gas-blood equilibrium within 3min. Oxygen saturation of the equilibrated blood was measured spectrophotometrically while the pH, P_CO2, and PO2 was measured with a Radiometer blood gas analyzer system. Whole procedures to construct ODC from the 6 point measurements could be performed within 1hr. The standard ODC for 25 normal Japanese adults showed a mean P50 of 27.6±1.1Torr (pH 7.40, P_CO2 40Torr, 37°C), a slightly higher value than previously reported. The discrepancy, however, can be eliminated when corrected for a slightly lower S_O2 by the present procedure. The standard curves for the adult blood at pH 7.20 and 7.60 and for the cord blood at pH 7.40 were also described. The "single point" procedure, a much quicker approach to measure the P₅₀ (ABERMAN et al., 1975), was scrutinized by comparing with the "whole curve" method. The P₅₀'s by the two methods were not significantly different, mean±S.D. of the differences being 0.4±2.5 Torr (n=126) for the adult blood at pH 7.40, P_CO2 40Torr and 37°C. Similar results were obtained for the adult blood at pH 7.20 and 7.60 and for the cord blood at 7.40. We concluded that the "single point" method was sufficiently accurate and reliable.