What should you know about effects of severe dehydration?

When the body loses more fluid than it replaces, blood volume falls and circulation becomes less effective. Water and mineral salts are needed for the brain, muscles, heart and kidneys, so imbalance can cause dizziness, headache, weakness, confusion, muscle cramps or a fast heartbeat. Urine may become dark and less frequent.

Vomiting or diarrhoea from gastroenteritis, heavy sweating during heat exhaustion, fever and difficulty drinking can all contribute. Severe dehydration may lead to fainting, kidney injury, shock or dangerous changes in salts. Older adults, young children and people with kidney or heart problems can worsen quickly.

If the person is awake and able to swallow, offer frequent small sips of water or an oral rehydration drink. Pause briefly if nausea worsens, then try again. Rest in a cool place and avoid alcohol. Do not force fluids into someone who is drowsy, confused or vomiting repeatedly.

Medical care may be needed for fluid through a vein and checks of kidney function or salts. Do not rely on urine colour alone: cloudy or dark urine can have several causes, including infection or stones.

Get urgent medical help for confusion, fainting, inability to keep fluids down, severe weakness, very little urine, a fast or irregular heartbeat, breathing difficulty or worsening dizziness. Seek prompt assessment when dehydration follows persistent vomiting, diarrhoea, heat exposure or a suspected infection. A person who cannot drink safely should not be managed at home.

What caused the fluid loss? Do I need blood tests, kidney checks or intravenous fluids? Which drinks are suitable, how should medicines be adjusted while I am dehydrated, and what warning sign means I should return immediately?