Over 20 years ago a group of hospitals in the WNY region collaborated with a local payer to see if we could predict outcomes in hospitalized patients based on readily available parameters such as lab test results (unpublished data). At the top of our list was serum sodium. Hyponatremia was a very good predictor of adverse outcomes in the hospitalized adult population. Subsequent published studies have demonstrated hyponatremia is a good predictor of mortality, length of stay and overall costs.
Now a new study (Leung 2012) shows that preoperative hyponatremia in patients undergoing surgery predicts higher 30-day mortality and more numerous complications, including wound infections, perioperative cardiovascular events, and pneumonia. After adjustment for confounding factors, length of stay in patients with preoperative hyponatremia is also about a day longer.
Perhaps the most interesting finding was that the risks were increased the most in patients undergoing nonemergent surgery and those in the lowest ASA classes, hence patients who would ordinarily be considered less risky.
The debate is around whether the hyponatremia is simply a marker of higher risk or is somehow causally related to the adverse outcomes. Most likely it is simply a marker of higher risk. Hyponatremia is commonly seen in patients with multiple comorbidities (including conditions like heart failure, chronic liver or kidney disease, cancer, etc.) and patients on multiple medications.
Of course, what is not known is whether correction of the hyponatremia preoperatively reduces these excess risks. That would require a randomized controlled trial of considerable magnitude and complexity (since the etiology and management of hyponatremia is quite diverse).
As we’ve pointed out on numerous occasions, screening for risk factors may be important from a prognostic standpoint but really adds little other than cost if you don’t have interventions that are shown to reduce that excess risk.
Leung AA, McAlister FA, Rogers SO, et al. Preoperative Hyponatremia and Perioperative Complications. Arch Intern Med 2012; Published online September 10, 2012