Do you recommend fluid restriction in addition to other management strategies for patients with hyponatremia due to SIADH?

Fluid restriction is the mainstay of therapy in patients with SIADH. To correct hyponatremia due to SIADH, electrolyte-free water intake must be less than urinary electrolyte-free water excretion assuming no significant non-renal fluid losses. The degree of fluid restriction may be lessened by the use of salt tablets alone, salt tablets and a loop diuretic or urea to increase urinary electrolyte-free water clearance.

Fluid restriction is not needed in patients with a brisk aquaresis induced by a...

In short no, or not much. I hyperbolically call fluid restriction "torture". You are relying on insensible losses to raise your P Na. In SIADH, the UNa tends to be high and your urinary electrolyte-free water (once you add the UK) is going to be very little. I prefer to try to decrease UOSM or increase solute intake or both.

In hospitalized patients with asymptomatic mild to moderate hyponatremia due to SIADH, I focus on the removal of an offending agent if possible (SSRI, etc), fluid restriction, and increase in solute intake. For outpatients with chronic mild hyponatremia due to SIADH who have had intermittent moderate to severe hyponatremia, I typically prescribe urea supplements in addition to recommending fluid restriction and an increase in other solutes.

Fluid restriction is torture, and typically, the UNa + U K is so high in SIADH that the urine is not electrolyte-free water. I prefer to tell or drink to this but not extra, stop offering agents, try to increase solute intake, and if tolvaptan can be approved, it may take as little as 7.5 3X a week to 15-39 a day (quite variable can test response in hospital). See Dosing in SIADH: A Tale of Two Tolvaptans.

Typically not covered, so urea is the other option; many formulations out there. Typical d...

This depends on the Urine Osmolality (a surrogate for ADH activity). If > 500, fluid restriction alone will likely fail and the patient will need other therapies (salt tablets, urea, tolvaptan). If lower urine osmolality, fluid restriction to 800 mL to 1L can work.

Fluid restriction as monotherapy fails to increase serum sodium by 5 mEq/L in half of the patients with hyponatremia. Therefore, I see it mostly as an adjunct as opposed to the main treatment.

As others have pointed out, a high urinary osmolality (>500 mOsm/Kg H2O) along with the sum of urinary sodium and potassium being greater than serum sodium, a urinary volume less than <1.5L/d, and an increase in serum sodium <2 mEq/L in 24-48 hours on fluid restriction <1L/d, have all been predictors of a ...