The effect of storage on the P50 of feline blood

Objective: To determine the effect of storage on the P-50 of feline hemoglobin. Design: Prospective, in vitro, laboratory study. Subjects: Venous blood from 4 clinically healthy cats. Measurements: Blood was collected into CPDA-l anticoagulant /preservative and maintained at 4 degrees C for 5 weeks. Measurements were made on Days 0, 2, 4, 7,14, 21, 28, and 35. The blood samples were equilibrated in a tonometer to gas mixtures containing 2.5%, 4%, 5%, or 8% oxygen, with 5% carbon dioxide balance nitrogen; pH was adjusted to 7.4. Chloride, partial pressure of oxygen, and hemoglobin saturation were measured; P,90 was calculated. Results: Chloride decreased from 124.3 +/- 2.1 to 88.5 +/- 1.9 mEq/L immediately after dilution with CPDA-1, and did not change for the 5 weeks thereafter. The P-50 decreased from an average of 35.0 +/- 1.2 to between 31 and 32 mmHg after 7 days, and did not change further for 4 weeks thereafter. Conclusions: The decrease in P50 of feline hemoglobin was minor compared with that of blood from species in which 2,3-diphosphoglycerate (2,3-DPG) is a major modifier of hemoglobin affinity for oxygen. The decrease in P50 in the present study was attributed to an initial decrease in chloride and a subsequent loss of modest quantities of red cell 2,3-DPG.