Hyponatremia is common after surgery for traumatic hip fracture, according to a new retrospective review.

“This study provides evidence that an average post-operative drop in serum sodium concentration should be expected in this patient group,” Dr. James Edward Rudge and Dr. Daniel Kim of City Hospital, Sandwell and West Birmingham Hospitals NHS Trust write in their report, published online June 7 in Age and Ageing.

From 15% to 30% of hospital inpatients develop moderate hyponatremia (130-135 mmol/l), while the electrolyte disorder can also be a late complication of surgery, the researchers write. Hyponatremia is also common after orthopedic surgery, they add.
To examine the incidence of hyponatremia after hip fracture surgery as well as risk factors for the disorder, Dr. Rudge and Dr. Kim looked at 254 patients who underwent hip surgery after trauma in their unit in 2012. Mean serum sodium dropped by 1.8 mmol after surgery. Twenty-seven percent of patients developed moderate hyponatremia, while 9% developed severe hyponatremia (< 130 mmol/l).

Patients on selective serotonin reuptake inhibitors, those on proton pump inhibitors, and those on an increasing number of medications were all significantly more likely to develop hyponatremia, the researchers found. There was no association between gender, operative procedure, fracture type, ethnicity, or American Society of Anesthesiologists’ grade. Average hospital stay was 30 days for the hyponatremic patients, versus 21 days for the normonatremic patients.

The rate of postoperative hyponatremia in the current study was higher than seen in past studies, the researchers note; one study found a 6% risk in orthopedic surgery patients for the first six days after surgery, while another found 3% in the first three days after surgery. The second study, they note, also found most cases of hyponatremia occurred in hip fracture patients. “The current study provides evidence that this subset of orthopedic patients is at greater risk of post-operative hyponatremia,” the authors write.

“The operative process itself may be a risk factor and all patients should be considered at risk of developing the condition,” they conclude.