Hyponatremia linked to risk for mortality, complications 30 days after surgery

Thirty days after surgery, patients with preoperative hyponatremia were at greater risk for mortality compared with patients whose baseline sodium levels were normal. Additionally, patients with preoperative hyponatremia were also at greater risk for perioperative coronary events and other complications, according to data from a study published in the Archives of Internal Medicine.

Researchers conducted a cohort study using the American College of Surgeons National Surgical Quality Improvement Program (ACS NSQIP), a program designed to improve the quality of surgical care for adults in the United States via 300 academic and community hospitals. Patients were aged 18 years or older and had undergone any major surgery between 2005 and 2010. After exclusions, the final cohort consisted of 964,263 patients.

Of the patients involved, preoperative hyponatremia was reported in 75,423 (7.8%) patients. However, the greatest prevalence of preoperative hyponatremia was evident in patients who underwent cardiac surgery (11.8%) and vascular surgery (11.2%). This was followed by general (7.5%), orthopedic (7.1%) and other (6.1%) procedures, according to data. During the study, 15,630 patients died within 30 days of surgery.

Patients with hyponatremia were typically older men with greater comorbidity and more likely to be inpatients or patients who underwent emergency surgery, according to researchers.

In primary outcomes, patients with mild hyponatremia (4.6% deaths; adjusted OR=1.38; 95% CI, 1.32-1.45) and moderate-to-severe hyponatremia (9.6% deaths; OR=1.72; 95% CI, 1.58-1.88) displayed greater mortality rates compared with patients with normal preoperative sodium levels (1.3% deaths), according to data (P<.001).

Secondary outcome data indicated the presence of preoperative hyponatremia was also linked to a greater risk for major coronary events compared with patients with normal sodium levels (OR=1.21; 95% CI, 1.14-1.29), wound infections (OR=1.24; 95% CI, 1.20-1.28) and pneumonia (OR=1.17; 95% CI, 1.12-1.22).

Once the researchers adjusted for all covariates, hyponatremia was linked to longer median lengths of hospital stay by roughly 1 day for most surgeries during the study, researchers wrote. For patients who were initially excluded from the cohort (n=1,197,311), researchers repeated their analyses and found the risk for mortality remained elevated.

Researchers suggest further research is needed to determine whether correcting preoperative hyponatremia will reduce risks.

In an accompanying editorial, Joseph A. Vassalotti, MD, and Erin DuPree, MD, of the division of nephrology and the department of medicine at Mount Sinai Medical Center, said the findings from this study are not surprising due to underlying comorbidities.

“An individualized approach considering hyponatremia in the context of the patient’s comorbidities and the planned surgical procedure can be the only guide to the sequence of interventions,” Vassalotti and DuPree wrote.

For more information:

Leung AA. Arch Intern Med. 2012;doi:10.1001/archinternmed.2012.3992.

Vassalotti JA. DuPree E. Arch Intern Med. 2012;doi:10.1001/2013.jamainternmed.2.

Disclosure: The researchers report no relevant financial disclosures.