Читать книгу Understanding Anatomy and Physiology in Nursing - John Knight - Страница 32

Water intoxication can be thought of as the opposite of dehydration and is caused by consuming too much water. It is frequently seen in endurance athletes such as cyclists and marathon runners who may routinely consume large quantities of water at drinking stations along the routes of their races. Occasionally it occurs following the use of recreational drugs such as ecstasy (MDMA), which can induce thirst and also upset the normal water balance of the body by reducing urine output. Young babies who are fed on formula milk may also be at risk, particularly in poorer households where the milk powder may be over-diluted to make it last longer.

Consuming large quantities of water dilutes the blood, in effect making it hypotonic and at a lower concentration to the cytosol within cells. The dilution of blood in these patients will also lead to hyponatraemia (low blood sodium). Water will gradually move from the blood into the cells by osmosis, causing the cells to swell. Since all the tissues of the body are composed of cells, during water intoxication all the soft tissues will begin to swell and internal organs will enlarge. Early signs of water intoxication will include headache, nausea and vomiting. In more serious cases, the patient may experience confusion, visual disturbances, drowsiness, breathing difficulties, muscle weakness and cramping.

Since the brain is enclosed within the cranium of the skull, there is minimal space available to accommodate cerebral enlargement, and the intracranial pressure will increase restricting blood flow and reduce cerebral perfusion. As a result, the patient will gradually lose consciousness, commonly slipping into a coma and, unless quickly treated, they will suffer permanent brain damage and may die.

Treatment will be determined by the cause and severity of water intoxication. Firstly, the amount of fluid taken on board must be reduced and excess water expelled. This can be achieved by the administration of diuretics to increase urine output. If the condition has been caused by medication, the patient’s medication must be reviewed and the drug causing the problem should be discontinued.

The importance of following the manufacturer’s instructions when mixing infant formula must be reinforced and where financial hardship is a contributing factor, parents should be advised on appropriate support networks and benefits that might be available. Sodium levels should be corrected by careful administration of intravenous fluids with a relatively high concentration of sodium. Diuretics will also help increase sodium levels as excess fluid is excreted; however, these have to be used with care as some can cause significant loss of potassium, leading to hypokalaemia (low blood potassium).