Changes in the plasma sodium concentration after minor, moderate and major surgery.

The plasma sodium concentration, [Na]P, falls following major surgery and this fall is exacerbated by the administration of sodium-free or sodium-low intravenous fluids in the postoperative period. As a prelude to prospective, but controlled, studies we observed the range of [Na]P on admission for surgery in 477 patients. In 309 patients the extent of the change in [Na]P by the first postoperative day (delta [Na]) was related to the severity of the operation undergone (minor, moderate or major) and the volume of potentially hypo-osmolar intravenous fluid given. The mean admission [Na]P was significantly lower with increasing severity of proposed operation. A highly significant fall occurred in [Na]P following surgery of every grade; such falls in [Na]P were seen even when no potentially hypo-osmolar fluids were administered. A significant inverse relationship between admission [Na]P and delta [Na] was demonstrated. We conclude that [Na]P falls following surgery of any severity and that such falls occur even when exogenous dilution cannot be implicated as a cause.

Water, sodium, potassium, and chloride content of skeletal muscle in fit and ill subjucts.

Biopsies of deltoid, gastrocnemius, or rectus abdominis taken under general anaesthesia from each of 15 subjects have been analysed for fat, water, sodium, potassium, and chloride. Some 110 samples were analysed for each muscle, and all the estimations were made on each sample. Standards have been constructed for the normal composition of these three muscles, and their reliability is discussed. Data from subjects with peptic ulcer, hyponatraemia, and sustained weight loss must be excluded from standards. It seems likely that standards could be improved by taking age and sex into account.