Hypernatraemia CCC

• CCC – Hypernatraemia
• CCC – Hypernatraemia Mind map (PDF)

Cause of HYPERnatraemia

• Water loss in excess of salt deficit
  • Hypernatremia is usually due to insufficient water (primarily in patients who either do not experience thirst normally, or cannot act on it)
  • Hypernatraemia occurs less commonly associated with excess salt
• Each litre of free water loss associated with 3-5mEq rise in sodium
• Problem associated with rise in serum osmolarity

Decreased water intake (with normal fluid loss)

• Disordered thirst perception (Normally increase of 2% osmolarity associated with increase in thirst) e.g. hypothalamic lesion
• Lack of environmental water
• Inability to communicate water needs e.g. Coma, CVA, Intubated patients and Kids

Hypotonic fluid loss (Water loss in excess of salt loss)

• Skin:
  • Sweat in hot climate or exercise (Heat stroke, Heat exhaustion)
  • Burns
• GI disturbances (especially with salt replacement)
  • Vomit, diarrhoea, fistula
• Renal disease Impaired renal concentrating ability
  • Diabetes Insipidus
    • Central, Nephrogenic or Drugs (alcohol, phenytoin, lithium, colchicine, Amphotericin, gentamicin)
  • Osmotic diuresis
    • CRF, mannitol, Hyperglycaemia, hypokalaemia
  • Renal disease
    • Nephropathy, myeloma, TIN, obstructive uropathy, PKD

Increased salt

• Acute salt poisoning
  • Ingestion of seawater or salt tablets, IV NaHCO3, hypertonic saline
• Increased mineralocorticoid
  • Primary hyperaldosteronism (Increased BP, decreased K, and alkalosis)
• Increased glucocorticoid (Cushings)
• Ectopic ACTH

Clinical

• HYPERnatremic dehydration
  • Increased serum osmolality, draws water into vascular space
  • Free water shift form interstitial to vascular space
  • Deceptively normal vital signs
  • Associated with brain cellular dehydration
• Symptoms worsen if change in Na is rapid
  • Increased risk of intracerebral haemorrhage secondary to rapid brain shrinkage
• Chronic hypernatremia has milder symptoms with adaptation

Clinical Signs/Symptoms

Signs manifest changes in serum osmolality. Brain shrinkage secondary to free water loss

• >350            Excessive thirst
• >375            Weakness and lethargy. Irritability
• >400            Ataxia, tremor
• >420            Focal neurological deficit; Hyperreflexia and Spasticity
• >430            Coma and seizures

Correction

• Stop ongoing losses
• Correct water deficit
• Correct sodium deficit if hypovolaemic
• Treat the underlying cause

Complications of treatment

• Intracerebral haemorrhage (especially in neonates: complication of NaHCO3 administration)
• Coma and seizures
• Cerebral oedema (if correction too rapid)

Calculation

Calculate Water deficit

Total body water x (serum Na-140)/ (140)

• TBW is usually 50% in males and 40% in females
• So male with Na of 160 has free water deficit of (0.5 x 70) x 20/140 = 5 Litres

• Aim to replace deficit plus maintenance and ongoing losses
• Replace with oral free water or 5% dextrose over 24-48 hours
• Rapid correction possible in acute cases
• Slow correction in chronic cases to avoid cerebral oedema

Correct Na slowly over 24-48 hours with a reduction of Na of 0.5-1.0mmol/hour (Maximum of 10-15 mEq in 24 hours)