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I am grateful to Laing and Wong for raising once again the issue of hypernatraemic dehydration in the first few days of life.1 However, I think it is important to remember that hypernatraemic dehydration, like anaemia, is a sign of disease and not a diagnosis in itself. A low haemoglobin concentration in blood can be caused by a large number of different pathological and physiological processes. Hypernatraemic dehydration should be seen in the same light.
Laing and Wong’s article describes two situations in which a child can be found to exhibit the typical biochemical and clinical features of hypernatraemic dehydration, that is—weight loss and hypernatraemia. The first mentioned is associated with gastroenteritis in a bottle fed infant, commonly a few weeks old and the second is seen in “breast fed” infants in the first few days of life. The hypernatraemia associated with these situations is caused by different problems with water balance—in neither is the problem an increased intake of sodium. In the infant with diarrhoea there is an excess loss of water and in the “breast fed” baby an insufficient intake of water.
In discussing hypernatraemic dehydration in association with diarrhoea in young infants, Laing and Wong refer to a paper by Chambers and Steel, where attention is drawn to the slightly increased concentration of sodium in artificial milk mixed incorrectly by parents.2 This is a red herring. The excess sodium concentration of the artificial milk mixed incorrectly by the mothers reached a maximum of 59 mmol/l with a mean of 37.2 mmol/l. Those who believe that this concentration of sodium could be responsible for hypernatraemic dehydration should remember that the concentration of sodium in the standard oral rehydration solutions in use in the UK is either 60 mmol/l (Dioralyte, Dioralyte rebel, Diocalm junior) or 50 mmol/l (Rehidrat, Electrolade) and that the WHO formulation for oral rehydration solution contains 90 mmol/l of sodium.
In fact the cause of this association of hypernatraemic dehydration with diarrhoea is the continued feeding with artificial milk after the onset of diarrhoea. The intestinal hurry associated with gastroenteritis results in the delivery of a solution rich in protein and complex carbohydrates to the colon which, after digestion by colonic bacteria, produces a considerable osmotic load in the colon, which in turn results in the production of voluminous stool low in sodium.3 The result is hypernatraemic dehydration due to excessive water loss. Those who require further discussion of this hypothesis are advised to read the excellent paper by Hirschhorn.3
The second situation relates to the title of the piece, namely hypernatraemic dehydration in the first few days of life in association with “breast feeding”. Though the breast milk produced, in very small quantities, by the mothers of these children is often found to contain a high concentration of sodium, this has nothing to do with their babies’ hypernatraemic state. As Jack Newman puts it so eloquently in his electronic response to Laing and Wong, these babies are not dehydrated because they are breast fed but because they are only pretending to breast feed. They are, in fact, starving. This is amply illustrated by the case described in Oddie et al of a “bottle fed” baby admitted at 6 days of age with hypernatraemic dehydration whose dehydration had nothing to do with the bottle milk being “fed” to her but was caused by the fact that she had oesophageal atresia.4 Hypernatraemic dehydration is frequently seen in the elderly and the mentally handicapped when their need for basic care, and presumably a regular intake of water, is neglected.5–7
Hypernatraemic dehydration is a sign of illness not a diagnosis. It is commonly caused by excess water loss or by insufficient water intake, either alone or in combination. It is almost never the result of excess sodium intake, which would result in retention of water and an increase in body weight, though this would obviously require intact thirst mechanisms and access to sufficient water.
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