Acute dehydration

Vomiting, diarrhoea, fever, heavy sweating, hot conditions, or difficulty drinking can deplete both water and body salts. The circulation then has less fluid available, which may cause a racing pulse, light-headedness on standing, headache, weakness, and reduced concentration.

Dark urine and passing urine less often can accompany dehydration, although urine changes can have other causes. Babies, older adults, pregnant people, and anyone with kidney, heart, or metabolic illness may become unwell more readily and need earlier assessment.

If the person is alert and can swallow, offer frequent small sips. An oral rehydration solution is useful when vomiting or diarrhoea has also caused salt loss; prepare it exactly as the packet directs. Continue normal feeds for babies and offer familiar, easy-to-tolerate food when appetite returns.

Avoid forcing large drinks at once because this may provoke vomiting. Monitor alertness, urination, dizziness, and whether fluids stay down. People who have been given fluid restrictions for heart or kidney disease should contact their clinician for tailored advice rather than substantially increasing intake on their own.

Get emergency help for collapse, severe confusion, extreme drowsiness, seizures, absent or abnormal breathing, blue or grey lips, or inability to wake normally. These findings indicate serious illness regardless of the suspected cause.

Arrange urgent assessment when fluids cannot be kept down, urine becomes very scarce, dizziness prevents standing, there is blood in vomit or stool, severe abdominal pain develops, or a child has markedly fewer wet nappies, no tears, a sunken soft spot, or unusual lethargy.

Tell the clinician about fluid losses, heat exposure, recent illness, urine output, medicines, and existing conditions. Ask whether blood or urine tests are needed, which rehydration drink suits you, and how to adjust fluids safely during future episodes.