Preoperative hyponatremia and perioperative complications.

BACKGROUND: Although hyponatremia has been linked to increased morbidity and mortality in a variety of medical conditions, its association with perioperative outcomes remains uncertain.
METHODS: To determine whether preoperative hyponatremia is a predictor of 30-day perioperative morbidity and mortality, we conducted a cohort study using the American College of Surgeons National Surgical Quality Improvement Program database to identify 964 263 adults undergoing major surgery from more than 200 hospitals (from January 1, 2005, to December 31, 2010) and observed them for 30-day perioperative outcomes. We used multivariable logistic regression to estimate relative risks for death, major coronary events, wound infections, and pneumonia occurring within 30 days of surgery and quantile regression to estimate differences in average length of hospital stay.
RESULTS: A total of 75 423 patients with preoperative hyponatremia (sodium level <135 mEq/L [to convert to millimoles per liter, multiply by 1.0]) were compared with 888 840 patients with normal baseline sodium levels (135-144 mEq/L). Preoperative hyponatremia was associated with a higher risk of 30-day mortality (5.2% vs 1.3%; adjusted odds ratio [aOR], 1.44; 95% CI, 1.38-1.50), and this finding was consistent in all the subgroups. This association was particularly marked in patients undergoing nonemergency surgery (aOR, 1.59; 95% CI, 1.50-1.69; P < .001 for interaction) and American Society of Anesthesiologists class 1 and 2 patients (aOR, 1.93; 95% CI, 1.57-2.36; P < .001 for interaction). Furthermore, hyponatremia was associated with a greater risk of perioperative major coronary events (1.8% vs 0.7%; aOR, 1.21; 95% CI, 1.14-1.29), wound infections (7.4% vs 4.6%; 1.24; 1.20-1.28), and pneumonia (3.7% vs 1.5%; 1.17; 1.12-1.22) and prolonged median lengths of stay by approximately 1 day.
CONCLUSION: Preoperative hyponatremia is a prognostic marker for perioperative 30-day morbidity and mortality.