Loading...
Please wait while the page loadsNursing · Fluid & Electrolyte Balance
What dehydration actually is, how to assess it in children and adults, which signs mean a patient is shocked, and how to plan safe fluid replacement.
Save for later
Student note
Perfusion means blood flow reaching tissues. Capillary refill time (CRT) is the time taken for colour to return after pressing the skin: prolonged means slow. Isotonic, hypotonic, and hypertonic describe the sodium level alongside the water loss, not just the amount of fluid lost. ORS stands for oral rehydration solution. AKI is acute kidney injury. Maintenance fluids are the ongoing daily fluid requirements, separate from any deficit you are replacing.
Read the whole patient
Dehydration is a clinical diagnosis, not a single blood test. Always combine history, observations, urine output, and how the patient looks.
Children compensate
Heart rate, urine output, and capillary refill change before blood pressure falls. Waiting for hypotension is waiting too long.
Older adults hide it
Confusion, falls, "off legs", and reduced appetite can be the only signs. Always check fluid intake, observations, and bloods.
Fluids are a drug
Wrong type, rate, or volume can cause harm. Document, reassess, recheck U&Es, and escalate if no improvement.
What is happening in the body, and why does it matter?
The basic idea
Why losses happen
Why it matters
Children and adults compared
Red flags
Clinical pearl
Dehydration is not just "needing a drink". It is a whole-body problem with cardiovascular, renal, and neurological consequences. By the time blood pressure falls in a child, they have usually been compensating for some time and need urgent fluid resuscitation.
Why does the sodium level change the picture?
Isotonic
Hypotonic
Hypertonic
Why this matters
Red flags
Clinical pearl
Hypertonic and hypotonic dehydration are not just lab labels. They change how fluid replacement is planned, because sodium correction that is too fast can cause cerebral oedema or osmotic demyelination. This is why senior review and slower correction are essential.
How do you grade dehydration in a child at the bedside?
No clinical dehydration
Clinical dehydration
Clinical shock
Useful extras
Red flags
Clinical pearl
Hypotension is a late and serious sign in children. They compensate by increasing heart rate and constricting peripherally, so a child with cold hands, fast heart rate, and prolonged capillary refill is already in trouble, even before blood pressure changes.
What changes in older or adult patients?
Common signs
Older adults are different
Useful measures
When to worry
Red flags
Clinical pearl
In adults, especially older ones, dehydration often hides behind other labels: a fall, confusion, weakness, a "UTI". Always check fluid intake, observations, urine output, and bloods. Rehydration can be the single most important treatment in a deteriorating older patient.
How do you correct dehydration safely?
Mild to moderate (children)
When to use IV fluids
Resuscitation fluids
Maintenance fluids
Red flags
Clinical pearl
Fluids are a drug, not just hydration. The wrong type, rate, or volume can cause harm. Always document weight, type of fluid, rate, total volume given, and response. Reassess regularly: the plan should change if the patient changes.
Why does dehydration affect so many systems, and how can it be prevented?
Cardiovascular
Renal
Neurological
Prevention
Red flags
Clinical pearl
A dehydrated patient is rarely just dehydrated. They may have an AKI, electrolyte problem, infection, or new neurological picture brewing alongside. Treat the fluid deficit, but always look for the cause and reassess everything else too.
| Category | What you see | What you do |
|---|---|---|
| No clinical dehydration | Alert, normal observations, moist mucous membranes, normal urine output. | Encourage usual fluids, monitor at home with safety-net advice. |
| Clinical dehydration | Unwell or behaviour change, reduced output, dry mucous membranes, tachycardia, sunken eyes. | Start ORS, reassess regularly, consider hospital review if not improving. |
| Clinical shock | Decreased consciousness, pale or mottled, cold peripheries, prolonged CRT, weak pulses, hypotension (late). | A–E approach, oxygen as needed, IV access, fluid bolus, urgent senior review. |
Children: easy to miss
Older adults: easy to miss
| Link | What connects them | Bedside meaning |
|---|---|---|
| Fluid + cardiovascular | Reduced circulating volume lowers stroke volume and triggers compensation. | Tachycardia, prolonged CRT, and cool peripheries are early warnings. Hypotension is late. |
| Fluid + renal | Poor renal perfusion drops filtration and can cause pre-renal AKI. | Falling urine output and rising creatinine point to perfusion problems, not just kidney disease. |
| Fluid + neurological | Sodium and water shifts affect brain cells. | Confusion, irritability, drowsiness, and (in severe cases) seizures can appear with dehydration. |
| Fluid + GI | Vomiting and diarrhoea both cause and worsen dehydration. | Always think upstream: treat the cause as well as replacing fluid losses. |
Definition
Types
Assessment
Treatment
Sources & References
NICE (2009, updated 2024) — Diarrhoea and vomiting caused by gastroenteritis in under 5s (CG84)NICE (2015, updated 2020) — Intravenous fluid therapy in children and young people (NG29)NICE (2013, updated 2017) — Intravenous fluid therapy in adults in hospital (CG174)Resuscitation Council UK — Paediatric and adult advanced life support guidelinesAlso practise with
One useful next step beats opening twelve new tabs.
Practise next
You have already done the reading. The best next move is a short practice block or one related guide, while the details are still fresh.
