Hypernatraemia and Hyponatraemia 39 



nexion it may be recalled that two of Allott's patients had 

 had an alimentary haemorrhage. 



It is partly through neglect of this phenomenon that some 

 authors have been led to place cases of hypernatraemia with a 

 low urinary sodium in a separate group. 



Symptoms of water deficiency. There are several reasons 

 why authors describing neurogenic or cerebral hypernatraemia 

 may have overlooked a water deficiency. Though they often 

 state that there is no cUnical evidence of dehydration in their 

 patients (e.g. Cooper and Crevier, 1952), this does not in fact 

 mean very much. The word dehydration is used for two 

 clinical states : one of water deficiency alone, and the other of 

 salt deficiency which generally also entails a loss of water. 

 This usage implies that these deficiencies produce a similar 

 clinical picture, though it was made clear long ago that this 

 is not so (Kerpel-Fronius, 1935 ; Nadal, Pedersen and Maddock, 

 1941). Water deficiency is not clinically obvious unless it is 

 extreme, because the deficit is distributed throughout the 

 body water. In salt deficiency, on the other hand, the extra- 

 cellular fluid, though but a third of the total in volume, bears 

 the whole of the deficit; it is patients with the latter who have 

 the haggard look, the sunken eyes, the small pulse and low 

 blood pressure of dehydration. Patients with simple water 

 deficiency are ill, but there are no specific signs of the defici- 

 ency, the tongue may even be moist, and it is not obvious it is 

 water they lack. If in addition, as a result of a craniotomy 

 their faces are oedematous, it may even be mistakenly as- 

 sumed that they have accumulated water in excess. The 

 diagnostic difficulties are increased because, particularly in 

 older patients, some of the most striking symptoms of water 

 deficiency are cerebral rather than vascular, for instance 

 drowsiness and confusion, and disturbances of behaviour, 

 which can mimic a lesion of the frontal lobes. These symptoms 

 make it more difficult to give water; but they can be com- 

 pletely reversed with water. 



Losses of water. Abnormally large losses of water may 

 go unrecognized. Extrarenal losses may be larger than is 



