Sodium (natremia) — hyponatremia and hypernatremia
Reference values and classification
- Normal adult natremia: 136 to 145 mmol/L (mEq/L)
- Mild hyponatremia 130–135 mmol/L + moderate: 125–129 mmol/L + severe: < 125 mmol/L + very severe with serious symptoms: < 120 mmol/L
- Mild hypernatremia 146–150 mmol/L + moderate: 151–159 mmol/L + severe: ≥ 160 mmol/L
- Pseudohyponatremia Artifactual hyponatremia in massive hypertriglyceridemia + significant paraproteinemia → water is diluted in a plasma rich in lipids or proteins → low natremia due to measurement artifact (flame method) → normal measured plasma osmolality → verify by direct method (potentiometry) or calculate osmolality
Hyponatremia — Causes and Diagnostic Approach
| Urine osmolality + Natriuresis | Cause | Mechanism + context |
|---|---|---|
| Urine osmolality < 100 mOsm/kg (dilute urine) = psychogenic polydipsia or excessive water intake | Potomania + primary polydipsia + excessive beer (beer potomania) + hypoosmolar infusions | Free water intake exceeding renal excretory capacity + normal but water-overloaded kidney + treatment: fluid restriction |
| Urinary osmolality > 100 mOsm/kg (concentrated urine) + Natriuresis < 30 mmol/L (kidney conserves Na) | True hypovolemia (extrarenal Na loss): diarrhea + vomiting + third-space sequestration + adrenal insufficiency + burns | Volume loss → ADH activation → water retention → dilutional hyponatremia + kidney reabsorbs Na (low natriuresis) + treatment: 0.9 NaCl % |
| Urinary osmolality > 100 mOsm/kg + Natriuresis > 30 mmol/L (kidney is losing Na) | SIADH (Syndrome of Inappropriate Antidiuresis) + adrenal insufficiency + hypothyroidism + thiazide diuretics | SIADH = most frequent cause of hyponatremia in hospitals → ADH secreted despite normal or low osmolality → water retention + volume expansion + Na loss in urine + causes of SIADH: bronchial cancer + pneumopathies + medications (SSRIs + carbamazepine + cyclophosphamide + NSAIDs) + neurological (SAH + meningitis + trauma) |
| Urinary osmolality > 100 mOsm/kg + variable urinary Na + hypervolemia (edema) | Heart failure + liver cirrhosis + nephrotic syndrome | Reduced circulating effective volume → ADH activation → water retention + increased total Na but low serum Na (dilution) + treatment: sodium and fluid restriction + diuretics |
Symptoms and urgencies of hyponatremia
- Mild to moderate symptoms: nausea + headaches + mild confusion + fatigue + irritability + muscle cramps
- Severe symptoms (hyponatremic encephalopathy - emergency): somnolence + stupor + vomiting + seizures + coma + respiratory arrest + cerebral herniation → natremia generally < 120–125 mmol/L + or sudden drop regardless of absolute value
- Severe symptomatic hyponatremia — urgent correction: sérum salé hypertonique (NaCl 3 %) 150 mL IV en 20 minutes → objectif : augmentation de la natrémie de 4 à 6 mmol/L dans la première heure pour stopper les symptômes cérébraux → puis correction lente à ne pas dépasser 10 à 12 mmol/L par 24 heures (risque de myélinolyse centropontine si correction trop rapide)
- Central Pontine Myelinolysis (CPM — Osmotic Demyelination Syndrome) irreversible demyelination of the brainstem (pons) if hyponatremia is corrected too rapidly → locked-in syndrome + quadriplegia + dysphagia + encephalopathy → maximal risk factors: hypokalemia + alcoholism + malnutrition + correction > 12 mmol/L/24 h
SIADH — Diagnostic Criteria and Treatment
- Diagnostic criteria for SIADH (Bartter and Schwartz): Hyponatremia (< 136 mmol/L) + low plasma osmolality ( 100 mOsm/kg → urine not maximally diluted) + natriuresis > 30 mmol/L + clinically normal blood volume (no edema + no dehydration) + normal renal, thyroid, and adrenal function
- Management of asymptomatic or mildly symptomatic chronic SIADH: Water restriction (500–1,000 mL/day) = first-line treatment + treatment of underlying cause + salt + oral urea (0.25–0.5 g/kg/day — increases free water excretion capacity) + or vaptans (tolvaptan — Samsca® + IV conivaptan) → ADH V2 receptor antagonists → selective aquaresis (free water excretion without Na) → very effective + but risk of overly rapid correction → cautious use under close monitoring of natremia
Hypernatremia — causes and treatment
| Mechanism | Main cause | Treatment |
|---|---|---|
| Free water loss (hypertonic dehydration) | Central diabetes insipidus (ADH deficiency – hypothalamic tumor + head trauma + post-surgery) or nephrogenic (kidneys insensitive to ADH – lithium + hypercalcemia + kidney disease) + insensible skin losses (fever + sweating + burns) + osmotic diarrhea | Oral free water if conscious + or NaCl 0.45 % IV or D5 % (IV free water) + careful correction: do not exceed a 10 mmol/L drop in natremia per 24 hours + free water deficit calculation: Deficit (L) = 0.6 × weight × (natremia/140 − 1) |
| Excessive sodium intake | Hypertonic saline perfusions + IV sodium bicarbonate + inappropriate oral NaCl + hyperosmolar enteral feeding | Stop sodium intake + free water compensation + furosemide if hypervolemia |
| Mixed water + sodium loss (water > sodium) | Osmotic diarrhea + significant renal losses (loop diuretics + hyperglycemia + mannitol) | Progressive replacement with hypo-osmolar solutions |
Call 911 or go to the emergency room immediately if severe hyponatremia ( 160 mmol/L) is discovered in an elderly person or an infant—intracellular dehydration can cause cerebral thrombosis and intracranial hemorrhage. Natremia should be measured quickly in any context of acute mental confusion or unexplained seizures.
For electrolytic balance including natremia and urinary osmolality, interpretation of hyponatremia or hypernatremia, and referral to the emergency room if necessary, Clinique Omicron offers consultations at its service points in Quebec and via telemedicine. To make an appointment, visit cliniqueomicron.ca.
Consult at Clinique Omicron
Clinique Omicron's nurse practitioners (NPs) prescribe and interpret natremia with plasma and urine osmolality and natriuresis to guide the etiology of dysnatremias, differentiate between hyponatremias due to excess water (SIADH + potomania + heart failure) and hyponatremias due to sodium loss (gastrointestinal losses + diuretics), initiate corrective measures (fluid restriction + NaCl if hypovolemic) according to safe correction guidelines, and refer severe or symptomatic abnormalities to the emergency department. Consultations are available at several service points across Quebec and via telemedicine. To book an appointment, visit cliniqueomicron.ca.
The content of this page is for informational purposes only and does not replace medical advice. Dysnatremias – particularly severe hyponatremia and hypernatremia – can be life-threatening and require careful and controlled correction under close medical supervision. Too rapid correction of hyponatremia can cause irreversible central pontine myelinolysis.
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