No significant change in urinary sodium excretion within 48h after Roux-en-Y gastric bypass surgery: the weight LUSER study

Introduction Metabolic and bariatric surgery is effective in achieving remission of hypertension and metabolic disease. It is unclear whether metabolic changes within the first 48h after surgery can potentially explain underlying mechanisms of hypertension control. We aimed to assess changes in urinary sodium excretion early after Roux-en-Y gastric bypass (RYGB) as a potential weight-loss-independent mechanism of hypertension remission. Methods All patients undergoing primary RYGB provided a 24-h urine collection, blood pressure (BP) measurement, and blood sampling both preoperatively and 48h postoperatively. The dietary sodium content was similar at both time points. Results Twenty patients were included, of whom 16 met the minimum output urine volume criteria for 24-h urine samples. Mean patient age was 55.2 ± 7.7 years and median body mass index was 48kg/m 2 with 13 patients (65%) diagnosed with hypertension and 7 (35%) with obstructive sleep apnoea. Twenty-four-hour urine sodium excretion was similar immediately prior to surgery and 48h postoperatively (72.1 ± 44.0 vs 74.5 ± 65.2mmol/24h, p = 0.45). There was no significant difference in systolic or diastolic BP immediately prior to surgery compared with 48h postoperatively (143.3 ± 15.1 vs 135.9 ± 16.3mmHg, p = 0.09 and 79.8 ± 9.2 vs 79.9 ± 5.8mmHg, p = 0.47). Both findings were confirmed on further sensitivity analysis. Conclusion No significant change in urinary sodium excretion or BP was detected in the first 48h post RYGB in normotensive patients or those with well-controlled hypertension.