P50 values determined by tonometry and by simplified techniques

Actual determination of the position of the oxygen hemoglobin dissociation curve (P50) was compared to three methods of estimating P50 in 39 patients with various diseases. There was a significant correlation between determined and estimated P50 values (P less than 0,001) for each of the methods studied. The data suggest that calculating P50 is reliable and may replace the need for actual measurement.