A 70 year old man presents feeling unwell. His blood tests show:Severe hypernatraemia with renal failure
Osmolality = 332.9+Glucose ie very high
Predominant increase in Urea, likely indicating severe dehydration requiring fluid replacement orally(water) or iv (5% dextrose) to correct fluid/ Na /osmolality over 1-2 days to prevent complications.
Free water deficit Calculation:
TBW % X (Na-140)/140
TBW 50% males and 40% females
Approach to 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) or less commonly excess salt which causes a rise in serum osmolality.
Decreased water intake (with normal fluid loss)
- Disordered thirst perception 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
Aim of treatment:
- 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)