Reestimation of the effects of inorganic phosphates on the equilibrium between oxygen and hemoglobin

Abstract

In a previous paper, published in this journal, we showed that the data obtained in patients with severe ketoacidosis suggest that inorganic phosphates (K₂HPO₄) can increase their P 50 and therefore enhance tissue oxygenation without concomitant alteration of the 2,3 diphosphoglycerate (DPG) [1]. In order to test the hypothesis that K₂HPO₄ could influence the oxyhemoglobin dissociation curve (ODC) by a mecanism which was not DPG mediated we have measured the total ODC on whole blood with and without addition of 13–80 mmol/1 of inorganic phosphates. On average, the level of DPG remained unchanged when the P 50 with K₂HPO₄ was significantly higher (p>0.001) (P 50=29.9±3.7 mmHg) than when phosphates were not administered (P 50=25.5±2.8 mmHg). The relationship between P 50 (mmHg) and K₂HPO₄ (=X mmol/1) was ΔP 50=−2.97 10⁻³(X)²+0.26(X)−0.42 (r=0.78).

Seeing that phosphates have an immediate action on the ODC, we calculated in our ketoacidosis patients, the relationship between the P 50, the inorganic phosphates (P_i in mg%) and the DPG in μmol/gHb. Both factors exert a highly significant effect (p<0.001) on the P 50, according to the following equation: P 50=0.35 DPG+0.26 P_i+18.92 (r=0.73). Our data are important in two points. First it is useful to add inorganic phosphates to the treatment of patients with severe ketoacidosis in order to enhance their tissue oxygenation. Second they recall that the ODC is not only determined by the classical effects of temperature, pH and DPG byt also by inorganic anions, like phosphates as described by Benesh and Benesh in their pioneering work [2].