Hypernatraemia Nursing Guide

Definition & Classification

Hypernatraemia = serum sodium >145 mmol/L. It always represents a state of hyperosmolality — insufficient free water relative to sodium.

Severity	Na⁺ Level	Clinical Features
Mild	146–149 mmol/L	Thirst, irritability
Moderate	150–159 mmol/L	Confusion, neuromuscular irritability
Severe	≥160 mmol/L	Seizures, coma, cerebral haemorrhage (brain shrinkage), death

Symptoms (Brain Dehydration)

Intense thirst (if conscious and not impaired)
Lethargy, weakness, irritability
Confusion, restlessness
Seizures, coma (severe)
Dry mucous membranes, decreased skin turgor
Tachycardia, postural hypotension

Cerebral consequences: Rapid hypernatraemia causes brain cell shrinkage → bridging veins tear → subdural haemorrhage. Rapid correction causes brain oedema (cerebral cells swell as water rushes back in). Both extremes are dangerous.

Causes of Hypernatraemia

Water Loss (Most Common)

Insensible losses — sweating (GCC summer heat), fever, tachypnoea
Diabetes insipidus — central (ADH deficiency) or nephrogenic (ADH resistance)
Osmotic diuresis — glucose (DKA, HHS), mannitol, tube feeds
Lactulose-induced diarrhoea
Vomiting, diarrhoea

Inadequate Water Intake

Reduced access to water — elderly, intubated, infants, confused patients
Impaired thirst mechanism (adipsia, hypothalamic lesions)
Ramadan fasting with excessive heat exposure

Excess Sodium Intake (Rare)

Hypertonic saline iatrogenic
Sea water ingestion (drowning)
Sodium bicarbonate excess

Safe Fluid Correction

Correction rate — CRITICAL: Maximum correction rate 10–12 mmol/L per 24 hours (0.5 mmol/L/hour). Too rapid correction → cerebral oedema → seizures, herniation, death. Use hypotonic fluids: 5% dextrose, 0.45% NaCl (half-normal saline), or oral water.

Free Water Deficit Formula

Free Water Deficit (L) = 0.6 × Body weight (kg) × [(Actual Na / Target Na) − 1]
Example: 70 kg male, Na = 165, target Na = 145
Deficit = 0.6 × 70 × [(165/145) − 1] = 42 × 0.138 = 5.8 L
Replace over 48 hours minimum (approximately 120 mL/hr of 5% dextrose) + ongoing losses

Fluid Choice

Fluid	When Used
Oral water / water via NGT	First choice if patient can tolerate and is not vomiting
5% Dextrose IV	Patient nil-by-mouth; provides free water (glucose metabolised, leaving water)
0.45% NaCl (half-normal)	Haemodynamically unstable AND hypernatraemic; also replaces some sodium
0.9% NaCl	Initial resuscitation if profoundly hypovolaemic (shock) — then switch to hypotonic fluid

Ongoing losses: Must estimate and add daily insensible losses (sweat, fever, tachypnoea) to replacement calculations. GCC patients may have 500–2000 mL/day additional insensible losses in summer. Repeat Na every 4–6 hours during active correction.

Diabetes Insipidus (DI)

DI = inability to concentrate urine, causing massive diuresis of dilute urine → hypernatraemia if fluid intake cannot compensate.

Feature	Central DI	Nephrogenic DI
Mechanism	ADH (vasopressin) deficiency from posterior pituitary	Kidney unresponsive to ADH
Causes	Pituitary tumour/surgery, head injury, infiltrative disease (sarcoidosis), idiopathic	Lithium (most common drug), hypercalcaemia, hypokalaemia, inherited
Urine osmolality	Low (<300 mOsm/kg)	Low (<300 mOsm/kg)
Response to desmopressin (DDAVP)	YES — urine concentrates (confirms central)	NO — no concentration
Treatment	Intranasal/oral desmopressin (DDAVP)	Treat cause (stop lithium); thiazide + low-salt diet; NSAIDs (reduce GFR)

Water deprivation test: Patient deprived of water for 4–8 hours. Urine and serum osmolality measured every 1–2 hours. At maximum dehydration, DDAVP is given. Response confirms central vs nephrogenic DI. Performed under close medical supervision.

GCC Clinical Context

Lithium-induced nephrogenic DI is a significant issue in GCC patients with bipolar disorder on long-term lithium
Neurosurgical post-operative DI is common after pituitary surgery — abundant in GCC hospitals performing endoscopic transsphenoidal surgery
Dehydration/heat stroke can unmask subclinical DI
Elderly patients with hypothalamic disease (hypodipsia) do not feel thirst appropriately — hypernatraemia can develop silently in GCC summer heat

MCQ Practice — Hypernatraemia

Q1. A 75-year-old nursing home resident has serum Na⁺ of 162 mmol/L. She is confused and unable to drink. What is the MAXIMUM safe correction rate per 24 hours?

A) Correct fully to 140 mmol/L within 6 hours using 5% dextrose

B) 20 mmol/L per 24 hours

C) 10–12 mmol/L per 24 hours with 5% dextrose IV

D) 15 mmol/L per 12 hours

✅ C — Maximum safe correction rate for hypernatraemia is 10–12 mmol/L per 24 hours (0.5 mmol/L/hour). Rapid correction causes cerebral oedema as brain cells swell when water rapidly re-enters. Use 5% dextrose or oral water. Check serum Na every 4–6 hours during correction.

Q2. A patient produces 8 litres of urine per day with a urine osmolality of 60 mOsm/kg. Serum Na is 155 mmol/L. When desmopressin (DDAVP) is given, urine osmolality rises to 780 mOsm/kg. What is the diagnosis?

A) Nephrogenic diabetes insipidus

B) Central (cranial) diabetes insipidus

C) Psychogenic polydipsia

D) SIADH

✅ B — Response to DDAVP (urine concentrates) = central DI (ADH deficiency). In nephrogenic DI, DDAVP produces NO response. Central DI is treated with intranasal/oral desmopressin. Psychogenic polydipsia causes dilute urine but serum Na is usually normal or low.

Q3. Which IV fluid is MOST appropriate for correcting hypernatraemia in a haemodynamically stable patient?

A) 0.9% NaCl (normal saline)

B) Hartmann's solution

C) 5% Dextrose (provides free water)

D) 3% hypertonic saline

✅ C — 5% dextrose provides free water (glucose is metabolised, leaving water). This dilutes serum sodium. 0.9% NaCl provides no free water and will worsen hypernatraemia. Hypertonic saline is used for severe hyponatraemia, not hypernatraemia. 0.45% NaCl is an alternative for combined dehydration + hypernatraemia.

Q4. Which drug is the most common cause of nephrogenic diabetes insipidus?

A) Amiodarone

B) Furosemide

C) Lithium

D) ACE inhibitors

✅ C — Lithium is the most common drug cause of nephrogenic DI. It blocks ADH-stimulated water channel (AQP2) insertion in the collecting duct. Even after stopping lithium, DI may persist for years. Consider switching to valproate or lamotrigine for mood disorder if severe DI develops.

Hypernatraemia — Nursing Guide