Dehydration is divided into dehydration in general and terminal dehydration. Dehydration in general is a lack of body water due to a disturbance of the equilibrium between intake and excretion of water resulting from a reduced fluid intake, an increased loss of fluid or a combination of the two. A decreased sodium level can lead to hypotonic dehydration, elevated sodium levels result in hypertonic dehydration. In isotonic dehydration the fluid and sodium levels are balanced. Terminal dehydration is the dehydration in the dying who are no longer able to drink sufficient amounts. It is the final phase before death. Dehydration occurs due to increased losses from vomiting, diarrhoea, impaired renal function and losses through the skin. Dehydration can also occur due to fluid accumulation such as ascites, oedema and bleeding. Symptoms of dehydration include: decreased urinary output, dry skin and mucosa, weight changes - ascites leads to weight gain - decreased skin turgor, constipation, altered mental state, apathy and a reduced level of consciousness. Pain is not a symptom of dehydration; in fact dehydration can be an analgesic. To the patient's carers, thirst is often the most worrying symptom requiring treatment. Thirst is often confused with a dry mouth.
Dehydration is diagnosed using history and symptoms. Laboratory tests have limited additional value. When dehydration has been determined, the decision whether to rehydrate using intravenous fluid, a feeding tube or hypodermoclysis should be made.