40 Paul Fourman and Patricia M. Leeson 



generally assumed ; and a good urinary output does not neces- 

 sarily mean there is no deficit of water, for it may represent 

 failure of conservation. In the unconscious or helpless patient 

 the intake depends on the physician's instructions and the 

 nurses' care. If the intake is less than the combined losses from 

 the skin, the lungs and the bowels, there must be a deficit of 

 water in the body and the plasma [Na] will eventually rise. 



Some cerebral lesions are associated with a high fever, or 

 with excessive sweating, or with an abnormally rapid respira- 

 tion. With any of these the insensible losses of water may 

 increase from the normal value of some 800 ml. They have 

 rarely been measured, but in one patient they were thought 

 to be as much as five litres a day (Gordon and Goldner, 1957). 



One expects the volume of urine to be small in water de- 

 ficiency, and its concentration high. But there are three ways 

 in which untoward renal losses of water may contribute to 

 water deficiency: diabetes insipidus from a failure of the 

 pituitary-hypothalamic mechanism; defective renal func- 

 tion; and osmotic diuresis. Neither the first nor the second 

 has always been excluded in cases reported as cerebral hyper- 

 natraemia. Diabetes insipidus possibly explains cases 1 and 3 

 of Cooper and Crevier (1952) and one case of Natelson and 

 Alexander (1955). The force of this explanation is emphas- 

 ized by a patient reported by Peters (1948), a young woman 

 whose serum [Na] rose from 140 to 171 m-equiv./l. in 24 hours 

 following an operation for craniopharyngioma which was com- 

 plicated by diabetes insipidus. In an incontinent patient a low 

 concentration of the urine may be the only clue to diabetes 

 insipidus, and the effect of pitressin should be tried in all 

 patients with hypernatraemia in whom this possibility exists. 



The excretion of a large amount of solutes produces an 

 osmotic diuresis (McCance, 1945; Hervey, McCance and Tayler 

 1946; Rapoport et al., 1949). This happens in spite of a water 

 deficiency (McCance, Young and Black, 1944) and may even 

 be the cause of it. 



Urea, sodium and chloride are the main osmotically active 

 constituents of the urine. The excretion of urea may be 



