Effect of Sampling on Erythrocyte, Dye and Protein Concentrations of Venous Blood of Dogs

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Abstract
The change in hematocrit values of successive blood samples was studied in normal and splenectomized dogs under various conditions. The initial decrease was not an artifact due to centrifuging differences, stasis or cell size changes. It was statistically significant whether the dogs were accustomed to the procedure or not, and was augmented under anesthesia. The magnitude of the change was reduced when activity before drawing each sample was comparable, when withdrawal was through indwelling tubing, or when the spleen was removed. Combining these 3 conditions abolished the response. Sample volumes up to 4% of the total blood volume resulted in approximately the same hematocrit decrease as did removal of small volumes (4 ml). In normal dogs after erythrol tetranitrate the decrease was not significant. After Mecholyl (acetyl-beta-methylcholine bromide) it was enhanced in normal dogs and was not significant after splenectomy.