Isonatremic dehydration

Dehydration can follow vomiting, diarrhoea, fever, heavy sweating, reduced drinking, or medicines that increase fluid loss. In the isonatremic type, water and dissolved salts are lost together, so the sodium concentration may not look greatly changed even though the total fluid volume has fallen.

Possible signs include thirst, a dry mouth, headache, tiredness, dizziness when standing, reduced urination, and dark urine. The underlying cause matters: gastroenteritis and heat exhaustion can both remove fluid quickly, while kidney problems may alter how the body handles water and salt.

If you are alert and able to drink, take frequent small sips of water or an oral rehydration drink, particularly after fluid loss from vomiting or diarrhoea. Continue suitable food as tolerated. Avoid relying on alcohol, and do not use salt tablets or concentrated homemade mixtures without medical advice.

A clinician may assess pulse, blood pressure, urine output, weight, and blood tests. People with kidney, heart, or endocrine conditions may need an individual fluid plan. Children, older adults, and anyone who cannot keep fluids down can become unwell more quickly.

Get urgent medical help for confusion, fainting, severe weakness, very little or no urine, inability to drink, persistent vomiting, blood in vomit or stool, or severe abdominal pain. Seek prompt care after heat exposure if the person is worsening, unusually drowsy, or has a high body temperature. These features can indicate a serious fluid deficit or another illness.

Ask what caused the fluid loss, whether blood or urine tests are needed, which rehydration drink is suitable, and how much to take while symptoms continue. Discuss whether your regular medicines need review during vomiting, diarrhoea, or poor intake.