Plasmatic ions influence the oxyhemoglobin dissociation curve of patients with chronic obstructive lung disease

Chronic hypoxemia, carboxyhemoglobin and ionic disorders as induced by drug intake may a priori influence the oxyhemoglobin dissociation curve (ODC) of patients suffering from chronic obstructive lung disease (COLD). We have traced the ODC and related indices on whole blood of 54 normal non smoking subjects and of 54 ambulatory smokers or ex-smokers COLD patients whose the FEV(1) was 1.17 +/- 0.45 litres (mean and SD) and the resting PaO2 63.3 +/- 7.7 Torr. In COLD patients HbCO induces a le shift of the ODC according to the following equation : P-50 (Torr) = 27.6 - 0.4 (HbCO - 1) where P-50 is the PO2 necessary to saturate hemoglobin at 50 %. When normalized for HbCO level of 1 % there was no difference in the ODC of the two groups. In contrast, the dispersion around the mean was significantly more important in patients than in control subjects from 20 to 90 % SO2. We attributed this fact to ionic disorders that were present in 51 out of the 54 patients and were presumably due to drug intake. The P-50 (Torr) = -35.55 + 0.325 (Na+) + 0.096(Cl-) + 0.27 (total CO2), r = 0.73, where Na +, Cl- and total CO2 were expressed in mEq/l. We concluded that : 1) hypoxemia was not deep enough in our patients to shift their ODC to the right; 2) plasmatic ions influenced their ODC; 3) and when possible, it is important to correct ionic disorders either by a curative or a preventive approach.