Blood Changes Induced by Venesection in Women with Toxemia of Late Pregnancy.

The beneficial effect of blood letting in the toxemias of late pregnancy is well recognized, but little or no accurate information is available concerning the method of its action. During the course of investigations on the water concentration and the acid-base balance in a series of patients with various clinical types of toxemia (1), certain observations were made at different times in the same individual in the hope of determining the physico-chemical effects of venesection. The methods employed were those previously described (2, 3), except that the pH was determined colorimetrically and corrected to the electrometric value by subtracting a determined factor, 0.34. In each case the pH of the two samples (the first and last portions of the venesection) was compared with the same standard and then one was compared with the other. The clinical data on the patients mentioned are available in Tables I, II, and III of the communication mentioned above (1). Venesection was introduced into the therapy of the toxemias on an empirical basis in the belief that it would remove from the body some of the hypothetical "toxin" supposedly responsible for the condition. More recently, there has been a tendency to view its action as largely physical in nature. It is known that toxemic women with well defined clinical edema usually respond to therapy which invokes the mobilization of tissue water. The removal of large volumes (300 to 600 cc.) of blood increases the water content of the plasma and decreases the cell volume of the whole blood by drawing tissue water into the blood stream. This sequence of events is evidently based upon two physiologic facts: (1) the volume of circulating blood tends to remain constant, and (2) deficiencies in its volume are made up promptly by the withdrawal of tissue fluid when other external sources are unavailable. The fluid which is thus brought into the blood stream can then be eliminated by the kidneys, with the establishment of a mild diuresis. In all probability it is the extracellular tissue fluid which is first mobilized for this purpose. Assuming the correctness of these observations, it would then appear that study of the first and last portions of a slowly performed venesection might give some indication of the composition of the tissue fluids. One normal male control (a professional blood donor) and six toxemic patients (one hypertensive, three non-convulsive toxemics, and two eclamptics) were studied in this fashion, the amount of blood taken varying from 275 to 600 cc. and the time of withdrawal from 10 to 15 minutes. In certain instances a third specimen