Notes:
• Hypernatraemia is relatively rare in primary care

• More common in hospital, especially in critically ill patients

• Generally occurs when thirst or independent access to water is impaired

• Basic causes:

o Pure free water loss (dehydration). Inadequate water intake; diabetes insipidus; thirst impairment.
o Hypotonic fluid loss (dehydration + hypovolaemia). Dermal losses; gastrointestinal losses; urinary losses.
o Hypertonic sodium gain (may cause hypervolaemia). Iatrogenic; excess salt ingestion; hyperaldosteronism.
o Intracellular shift of water (rare). Very strenuous exercise.