Reasoning GP · Algorithm · 1-page summary
Hypernatraemia in adults
For: adults with serum sodium >145 mmol/L, in hours or OOH. Not for: infants and children (hypernatraemic dehydration → 999 / urgent paediatric admission; full algorithm, steps 1 and 7); hospital fluid and desmopressin treatment (full algorithm, step 6).
Core rule: hypernatraemia is usually a water deficit — ask why this person cannot get, or keep, water. Symptoms and tempo override the number. Unknown duration = chronic: sodium should fall no faster than about 0.5 mmol/L per hour and 10–12 mmol/L in 24 hours — too-rapid correction causes cerebral oedema.
0Stop — call 999 now — emergency transfer
- Any sodium with confusion, reduced consciousness, seizures, shock or severe dehydration → 999
- Na⁺ ≥160 mmol/L (severe) and drowsy, unable to drink, deteriorating or cannot be transferred safely → 999; otherwise immediate senior/specialist input → Same-day admission
- Polyuria after head injury, neurosurgery, pituitary surgery, meningitis or encephalitis (acute central DI) → 999 / Same-day with endocrinology or acute medicine. Suspected HHS (hyperglycaemia, hyperosmolality, reduced consciousness) → 999
- Focal neurology is a separate emergency (stroke, haemorrhage, venous sinus thrombosis). Correction is a hospital task with sodium monitoring.
1Triage by sodium — mmol/L; ≥160 severe, block 0
| Na⁺ | Action |
|---|---|
| 155–159 | Urgent hospital assessment/admission; sooner if unstable. |
| 150–154 | Same-day acute medical assessment in most; immediate if symptomatic, dehydrated, not drinking, polyuric, or DI/HHS suspected. |
| 146–149, at risk | Same-day if new, persistent, rising, unexplained or polyuric; or elderly, frail, symptomatic, confused, unable to drink or cause unclear. |
| 146–149, well | May start at home (block 5) only if clinically well, cognitively intact, cause clear and a named person will provide drinks; urgent repeat. |
2Screen — one row is enough
- Polyuria (>50 mL/kg/day, about >3 L/day) + thirst + dilute urine + rising sodium → possible DI → Same-day acute medicine; urgent endocrinology discussion.
- On lithium and hypernatraemic, dehydrated, confused or not drinking → Same-day; 12-hour lithium level.
- Dehydration with AKI (rising creatinine) → Same-day acute medical assessment.
- Dependent adult, recurrent or with poor care → possible neglect → Same-day safeguarding concern to the local authority, alongside treatment (Care Act 2014); also salt poisoning.
3Assess — face to face; not by telephone
☐ GCS, orientation, focal neurology ☐ Hydration, lying and standing BP, pulse, temperature, urine output, weight ☐ Capillary glucose and ketones ☐ Swallow; access to water — who gives the drinks? ☐ U&E, glucose, HbA1c, calcium; paired serum and urine osmolality with urine sodium; 12-hour lithium level if on lithium ☐ Drugs: lithium, diuretics, lactulose, effervescent medicines
Not in primary care: water-deprivation or copeptin testing; IV fluids.
4Classify — only once urgency is settled
- Inadequate intake (commonest) — access, cognition, swallow, impaired thirst; concentrated urine (e.g. >600 mOsm/kg).
- Extrarenal loss — fever, sweating, diarrhoea (incl. lactulose), vomiting, burns.
- DI — dilute urine, high serum osmolality; central (head injury, pituitary) or nephrogenic (lithium, hypercalcaemia, hypokalaemia, CKD).
- HHS — sodium may look normal and rise as glucose falls → emergency admission (JBDS).
- Sodium gain (rare) — saline, bicarbonate, feeds, enemas, effervescent medicines, deliberate salt.
- Uncertain — say so; osmolalities, same-day advice.
5Treat today — mild, well, can drink
- Fluids: plain water (not sports drinks or saline); ORS for diarrhoea. A named person gives measured drinks — if nobody can, same-day assessment.
- Drugs: review diuretics, lactulose; stop effervescent medicines where possible. Lithium: no abrupt stop without urgent specialist advice unless toxic; no amiloride or thiazide without it. Doses: NICE/SPC, BNF, local formulary.
- Never fluid-restrict. Urgent repeat U&E at an interval set by the laboratory and context. On desmopressin: vomiting, nil by mouth or no water access is an emergency.
6Refer routinely
- Pituitary or hypothalamic cause, recurrent or chronic DI → endocrinology.
- NDI from CKD, or lithium DI with renal impairment → nephrology; lithium changes are specialist.
- Care home: documented daily fluid target, monitored intake, thickened fluids for dysphagia.
7Never reassure by — symptoms, tempo and who gives the drinks matter more than the number
- "Not thirsty" — thirst is impaired in older people and absent with altered consciousness.
- "Encourage fluids" when nobody can bring, hold or help with a drink.
- "Poor intake" when the urine is dilute — think DI or osmotic diuresis.
- A normal-looking sodium with high glucose — HHS; sodium rises as glucose falls.
- A fast fall because the number is high — cerebral oedema and seizures.
- A sodium that settles in a dependent adult — the safeguarding question remains.
8Safety-net — say it to the patient and carer, then document it
999 “Call 999 for new confusion, drowsiness, a fit, collapse or being unable to drink.” Same day: “Contact us or NHS 111 today for vomiting, drinking less, passing much less urine, or passing large volumes of urine with thirst.”
Remote or OOH: hydration, cognition and access to drinks cannot be judged by phone — raised sodium with drowsiness or confusion, vomiting, reduced drinking, living alone or depending on carers → face to face the same day.
✓Safe to manage in primary care only if — all five, documented
Na⁺ 146–149; no block 0–2 row; not rising
Clinically well, cognitively intact, not polyuric
Can drink; named person provides measured drinks
Glucose, calcium, U&E checked; drugs reviewed
Urgent repeat booked; safeguarding considered; safety-net
Summary of the full Reasoning GP hypernatraemia algorithm, which holds the detail, cause classifier, DI and HHS management and evidence. Sources: NICE CG174, NG29, CG185; JBDS-IP HHS in adults (2022); Society for Endocrinology cranial DI guidance (2018); local lithium shared-care protocol; CQC regulation 14. Clinical reference — follow local acute-transfer, safeguarding and prescribing policies and check doses: NICE/SPC, BNF.