Table 2.

The etiology, diagnosis and basic management of neurosurgical hyponatremia.

Diagnosis	Blood Volume Status	Diagnostic Criteria	Treatment
SIADH	Euvolaemic	See Table 3	Fluid restriction Vaptan therapy
Acute ACTH deficiency	Euvolaemic (may be hypotensive)	0900 h cortisol <300 nmol/L in stressed patient	Steroid replacement therapy
Hypovolaemia	Hypovolaemic	Negative fluid balance	IV fluids
CSWS	Hypovolaemic	Profound diuresis and natriuresis Low BP and CVP	Aggressive IV fluids
Mixed SIADH and CSWS	Variable/fluctuating	Usually SIADH initially, then progressing to CSWS	Depends on stage
Inappropriate IV fluids	Hypervolaemic	Positive fluid balance May have edema/LVF	Diuretics Stop IV fluids