Assessing the Impact of Routine Intervention for Perioperative Hyponatremia on Postoperative Outcomes

BACKGROUND: Preoperative hyponatremia is associated with poorer outcomes, including increased mortality, ICU admissions, prolonged hospital stays, and readmissions. Whether routine intervention improves outcomes remains unclear. OBJECTIVE: To assess an institutional protocol requiring internist referral and treatment for serum sodium < 130 mmol/L before surgery. DESIGN: Retrospective registry-based study using a quasi-experimental regression discontinuity design. Sharp, kink, and triangular kernel models estimated effects at the intervention threshold. Subgroup analyses included patients with cardiac disease, chronic kidney disease, moderate operative risk, and emergency surgery. PARTICIPANTS: Of 180,926 adult patients between 2013 and 2020, 24,846 had preoperative serum sodium 125-135 mmol/L. After excluding 43 with incomplete data, 24,803 remained. INTERVENTIONS: Protocolized internist referral and treatment for preoperative serum sodium < 130 mmol/L. MAIN MEASURES: The primary outcome was 30-day mortality. Secondary outcomes included 1-year mortality, ICU admissions, length of stay, and rapid postoperative sodium correction. KEY RESULTS: Compared with serum sodium 130-135 mmol/L, sodium < 130 mmol/L was associated with higher unadjusted 30-day mortality (3.32% vs 1.33%), 1-year mortality (21.25% vs 11.03%), ICU admission (18.65% vs 11.50%), and mean length of stay (20.64 ± 25.51 vs 13.42 ± 21.01 days; all p < 0.001). No significant threshold effects were seen for 30-day mortality (treatment effect = 1.22, p = 0.138), ICU admissions (0.014, p = 0.564), or length of stay (0.184, p = 0.943). Significant discontinuity was observed for 1-year mortality (0.081, p = 0.010), particularly among patients with cardiac disease (0.162, p < 0.001), with chronic kidney disease (0.071, p = 0.012), with moderate operative risk (0.779, p = 0.013), or undergoing emergent surgery (0.100, p = 0.001). Lower preoperative sodium predicted rapid postoperative correction (OR = 1.190, p < 0.001). CONCLUSIONS: Protocolized internist referral and treatment for preoperative serum sodium < 130 mmol/L did not affect short-term perioperative outcomes but may have reduced 1-year mortality, particularly in subgroups with cardiac and renal disease. Further studies are required to determine if this reflects treatment of underlying comorbidities rather than the effect of sodium normalization alone.