Patient selection: hyponatremia from SIADH secretion vs hypovolemia. Patients with other causes of hyponatremia were excluded (hypthyroidism, hypocorticolism, hypopituitarism, beer potomania, chronic renal disease, nephrotic syndrome, cirrhosis, congestive heart failure, polydipsia).
Parameters:
(1) urine sodium concentration in mmol/L
(2) serum BUN in mg/dL
(3) ratio of urine sodium to serum BUN
|
Parameter
|
Probably Hypovolemia
|
Overlap
|
Probably SIADH
|
|
urine sodium
|
< 30
|
30 to 50
|
> 50
|
|
serum BUN
|
> 20
|
10 to 20
|
< 10
|
|
ratio urine sodium to serum BUN
|
< 2
|
2 to 5.5
|
> 5.5
|
where:
• SIADH secretion is associated with euvolemia if salt and water intake are normal but can show signs of hypovolemia if there is significant fluid and salt restriction.
• Hypovolemia may be associated with decreased skin turgor, hypotension, tachycardia, and/or dry mucous membranes.
• The urine sodium value was higher for a patient with hypovolemia if s/he were receiving diuretics.
The authors found that an infusion of isotonic saline had a beneficial effect on patients with a urine sodium up to 50 mmol/L. The increase in serum sodium was around 12 mmol/L vs 5 mmol/L for a patient with SIADH secretion.
