JMIR Publications

ABSTRACT

Background:

Hyponatremia and hypernatremia as defined conventionally (<135 mEq/L and >145 mEq/L, respectively) are associated with increased perioperative morbidity and mortality. However, the effects of subtle deviations in serum sodium concentration within the normal range are not well characterized.

Objective:

This analysis sought to determine the association between borderline hyponatremia (135-137 mEq/L) and hypernatremia (143-145 mEq/L) on perioperative morbidity and mortality.

Methods:

The American College of Surgeons National Surgical Quality Improvement Program (NSQIP) database was queried to extract all patients undergoing elective, non-cardiac surgery from 2015 to 2019. The primary predictor variable was preoperative serum sodium concentration measured less than five days before the index surgery. The two primary outcomes were the odds of morbidity and mortality occurring within 30 days of surgery. Both outcomes were modeled using weighted generalized additive models to minimize the effect of selection bias while controlling for covariates.

Results:

In the overall cohort, 1,003,956 of 4,551,726 available patients had a serum sodium concentration drawn within five days of their index surgery. The odds of morbidity and mortality across sodium levels 130-150 mEq/L relative to a sodium level of 140 mEq/L followed a U-shaped curve. Preoperative serum sodium concentrations of less than 139 mEq/L and greater than 144 mEq/L were independently associated with increased morbidity probability. Serum sodium concentrations of less than 138 and greater than 142 mEq/L were associated with increased mortality probability. Hypernatremia was associated with higher odds of both morbidity and mortality than corresponding degrees of hyponatremia.

Conclusions:

Among patients undergoing elective, non-cardiac surgery, preoperative serum sodium levels less than 138 and greater than 142 are associated with increased morbidity and mortality, even within currently accepted “normal” ranges. The current definition of perioperative eunatremia may need to be revisited in future prospective investigations.