Association of preoperative hyponatremia with surgical outcomes: a systematic review and meta-analysis of 32 observational studies.

BACKGROUND
Preoperative hyponatremia is prevalent in patients undergoing surgical procedures, but it is uncertain if hyponatremia will lead to increased risk of surgical mortality and morbidity.


METHODS
A systematic search of Medline (PubMed), Embase and Cochrane Library from inception till 2 July 2021 was performed. Full length articles that reported on the association between surgical outcomes among adults ≥18 years with documented preoperative hyponatremia were included.


FINDINGS
We identified 32 observational studies comprising 1,301,346 participants. All studies had low risk of bias. When adjusted for covariates, patients with hyponatremia had significantly higher odds of developing major complications (defined as a composite measure of 9 major complications) compared to patients with normal sodium concentrations (aOR =  1.37, 95%CI = 1.23-1.53, I2 = 78%. N = 10). Additionally, patients with preoperative hyponatremia also significantly higher hazards of early mortality (<90 days) compared to patients with normonatremia (aHR = 1.27, 95%CI = 1.13-1.43, I2 = 97%. N = 10) after adjustment for covariates. Preoperative hyponatremia also had significant associations with respiratory, renal and septic complications. In terms of prognostic performance, preoperative hyponatremia performed adequately in predicting major complications in surgical patients (AUC = 0.70, LR- 0.90) with a specificity of 88% and a sensitivity of 25%.


INTERPRETATION
Our meta-analysis suggests that preoperative hyponatremia is associated with poorer early mortality and major morbidity outcomes in surgical patients. Hyponatremia is also a specific prognosticator for major complications in surgical patients, reiterating its potential use as a clinical indicator of poor outcomes.