Alarm raised over preoperative hyponatremia

By Eleanor McDermid, Senior medwireNews Reporter

Preoperative hyponatremia is common and, even when mild, carries a risk for perioperative complications and mortality, shows a large cohort study.

In a commentary accompanying the article in the Archives of Internal Medicine, Joseph Vassalotti and Erin DuPree, both from Mount Sinai Medical Center in New York, USA, caution that clinicians should not order extra preoperative tests unless really necessary, as it has been shown that few results actually affect management.

But they say: "Previous hyponatremia and conditions commonly associated with hyponatremia are reasonable indications to perform serum sodium assessment in a subpopulation of preoperative patients."

In the study, a total of 75,423 major surgery patients in the American College of Surgeons National Surgical Quality Improvement Program database had preoperative hyponatremia (sodium level <135 mEq/L). During the first 30 days after surgery, 5.2% of these patients died, compared with just 1.3% of 888,840 patients with normal preoperative sodium levels.

After accounting for confounders, mortality risk remained a significant 44% higher in patients with hyponatremia than in those without, report David Bates (Brigham and Women's Hospital, Boston, Massachusetts, USA) and team.

Vassalotti and DuPree observe that severe hyponatremia warrants immediate investigation and possible postponement of surgery to allow for treatment. However, most cases reported by Bates et al were mild, with just 8546 of the 75,423 patients with hyponatremia having sodium levels below 130 mEq/L.

Moreover, the mortality risk was particularly marked in patients scheduled for elective (nonemergent) surgery, at a 59% increase, and in relatively healthy patients (American Society of Anesthesiologists class 1 or 2), at a 93% increase.

"Increased risk in patients scheduled for elective surgery with mild and almost certainly asymptomatic hyponatremia presents an important opportunity for the internist performing preoperative medical consultation," say Vassalotti and DuPree.

They add that the high prevalence of mild, and presumably asymptomatic, hyponatremia highlights the importance of identifying the underlying etiology.

Hyponatremia also raised the risk for perioperative complications. Patients with the condition had a 21% increased risk for major coronary events, a 24% increased risk for wound infections, and a 17% rise in the risk for developing pneumonia.

"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," say Vassalotti and DuPree.

They note "that the impact of preoperative medical consultation may not be the consult recommendations alone but, more important, perioperative co-management with anesthesia and surgical colleagues."

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