Background
Hyponatraemia in hospitalised patients has been associated with increased mortality. The syndrome of inappropriate anti-diuretic hormone (SIADH) is a common cause of hyponatraemia. Recent European and American guidelines gave conflicting advice regarding the role of urea in the treatment of SIADH. We hypothesised that urea would be a more effective treatment of hyponatraemia than fluid restriction in this setting.
Methods
Review of urea use for the treatment of hyponatraemia in patients admitted to a tertiary hospital during 2016-17. Primary endpoint: Proportion of patients achieving a serum sodium ≥130mmol/L at 72h.
Results
Urea was used on 75 occasions in 66 patients. The median age was 67 (IQR 52-76), 41% were female. Sixty-seven (89.3%) had hyponatraemia due to SIADH of which CNS pathology (62.7%) was the most common underlying cause. The median nadir serum sodium was 122mmol/L (IQR 118-126). Fluid restriction was first line treatment in 62.2%. Urea was first line treatment in 23% and second line in 77%. In fifty three patients who received other treatment prior to commencement of urea, the mean sodium change in the 72h following urea initiation (7.0±4.9mmol/L) was significantly greater than with the preceding treatments (-1.0±4.8mmol/L; p<0.001). Thirty-two (62.7%) achieved serum sodium ≥130mmol/L at 72h post-initiation of urea, and 13 (25.5%) ≥135mmol/L. The initial urea dose range was 15-90g daily (mode 30g, 54.7%), and median treatment duration 6 days (IQR 4-8). Seventeen patients (22.7%) had side effects, distaste the most common (7), followed by nausea (6) and hypokalaemia (4). None were severe. No patients developed hypernatraemia, over-correction (>10mmol/L in 24h or >18mmol/L in 48h), or died.
Conclusion
Urea is a safe, effective treatment for moderate-severe hyponatraemia in patients who failed or were unable to have fluid restriction with a tolerable side effect profile.