Educational draft · awaiting clinical reviewUse Rapid for revision, not patient-care decisions. Check current national and local guidance and the BNF or BNFC before acting.
2 min synopsisUK scopeSources checked 27 Aug 2026Clinical review pending
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Loss of thirst removes the defence against hypernatraemia
Adipsia with AVP deficiency can produce profound hypernatraemic dehydration without the expected complaint of thirst. Compulsive or hypothalamic excess drinking can instead cause acute hyponatraemia, cerebral oedema and seizure. Altered consciousness, major sodium disturbance, hypothermia or hyperthermia requires acute monitored care.
Action: Assess ABCDE, bedside glucose, temperature, volume status, measured sodium and osmolality, urine output and urine osmolality. Correct water and sodium at a controlled syndrome-specific rate, protect cortisol physiology when pituitary disease is possible, and involve endocrinology and neuroscience services early.
Synopsis
Distinguish impaired thirst, primary polydipsia and broader hypothalamic dysfunction, then build supervised water, endocrine and neurobehavioural safety plans.
Thirst and AVP secretion are separate hypothalamic responses to tonicity; losing one but not the other creates distinctive risk.
Adipsia means absent or inadequate thirst despite a physiological stimulus and is particularly dangerous when central AVP deficiency coexists.
Primary polydipsia suppresses AVP appropriately and produces very dilute urine; chronic excess intake can blur dynamic testing by reducing renal concentrating capacity.
Investigation priorities
01
Fluid and urine-volume diaryFirst step
Quantify drinking, nocturia and urine output against timing of symptoms, medicines and caregiver support.
Management branches
Water phenotypeDefine what drives drinking and urine
Thirst, high intake, urinary frequency or recurrent dysnatraemia lacks a clear cause.
Measure true urine volume and construct a timed intake-output history with family or carers where insight or memory may be limited.
Check paired plasma and urine tonicity plus glucose, calcium, potassium, kidney function and relevant medicines before imposing fluid change.
Key medicines
Desmopressin in adipsic AVP deficiencyUse the formulation-specific fixed regimen designed by the specialist centre, coordinated with a prescribed daily water intake and weight or sodium adjustment rule rather than unsupervised symptom dosing.
National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.