Fluid Restriction Therapy for Chronic Siad; Results of a Prospective Randomised Controlled Trial.

Context Fluid restriction (FR) is the recommended first-line treatment for syndrome of inappropriate antidiuresis (SIAD), despite the lack of prospective data to support its efficacy. Design A prospective non-blinded randomised controlled trial of FR versus no treatment in chronic SIAD. Interventions and outcome 46 patients with chronic asymptomatic SIAD were randomised to either FR (1 liter/day) or no specific hyponatremia treatment (NoTx) for one month. The primary endpoints were change in plasma sodium concentration (pNa) at days 4 and 30. Results Median baseline pNa was similar in the two groups [127 mmol/L (IQR 126-129) FR and 128 mmol/L (IQR 126-129) NoTx, p=0.36]. pNa rose by 3 mmol/L (IQR 2-4) after three days FR, compared with 1 mmol/L (IQR 0-3) NoTx, p=0.005. There was minimal additional rise in pNa by day 30; median pNa increased from baseline by 4 mmol/L (IQR 2-6) in FR, compared with 1 mmol/L (IQR 0-1) NoTx, p=0.04. 17% of FR had a rise in pNa of ≥5 mmol/L after three days, compared with 4% NoTx, RR 4.0 (95% CI 0.66-25.69), p=0.35. 61% of FR corrected pNa to ≥130 mmol/L after three days, compared with 39% of NoTx, RR 1.56 (95% CI 0.87-2.94), p=0.24. Conclusion FR induces a modest early rise in pNa in patients with chronic SIAD, with minimal additional rise thereafter, and is well-tolerated. More than one third of patients fail to reach a pNa ≥130 mmol/L after three days of FR, emphasising the clinical need for additional therapies for SIAD, in some patients.