A simple microtonometric method for whole blood oxygen dissociation curve and a critical evaluation of the "single point" procedure for blood P50.

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 3 min. Oxygen saturation of the equilibrated blood was measured spectrophotometrically while the pH, PCO2, 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 1 hr. The standard ODC for 25 normal Japanese adults showed a mean P50 of 27.6 +/- 1.1 Torr (pH 7.40, PCO2 40 Torr, 37 degrees C), a slightly higher value than previously reported. The discrepancy, however, can be eliminated when corrected for a slightly lower SO2 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, PCO2 40 Torr and 37 degrees 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.