Incidence and Risk Factors for Hyponatremia in Postoperative Spinal Surgery Patients.

Introduction: The incidence of hyponatremia after orthopedic surgery is high. Hyponatremia may prolong hospitalization and increase mortality, but few reports have identified risk factors for hyponatremia after spinal surgery. This study aims to determine the incidence and risk factors for hyponatremia after spinal surgery.

Methods: A total of 200 patients aged 20 years or older who underwent spinal surgery at our hospital from 2020-2021 were recruited. Data on age, sex, height, weight, body mass index, operation duration, blood loss, albumin level, the geriatric nutritional risk index (GNRI), potassium level, the estimated glomerular filtration rate (eGFR), sodium level, length of hospital stay, history of hypertension, dialysis status, the occurrence of delirium during hospital stay, and oral medication use were collected. Comparisons between the postoperative hyponatremia group and the postoperative normonatremia group were conducted to evaluate the impact of hyponatremia on clinical outcomes.

Results: Postoperative hyponatremia was observed in 56 (28%) of the 200 patients after spinal surgery. Comparison between the postoperative hyponatremia group with the postoperative normonatremia group revealed that the patients in the postoperative hyponatremia group were significantly older (72 versus 68.5 years, p<0.01). Postoperative hyponatremia was significantly associated with low GNRI values (100.8 versus 109.3, p<0.01), low eGFR values (59.2 versus 70.8 mL/min/1.73 m², p<0.01), preoperative hyponatremia (138.5 vs. 141 mEq/L, p<0.01), and a high incidence of delirium (12.5% versus 2.7%, p=0.01). Older age (odds ratio=1.04, p=0.01) and preoperative hyponatremia (odds ratio=0.66, p value<0.01) were risk factors for postoperative hyponatremia.

Conclusions: In addition to older age and preoperative hyponatremia, the study identified new risk factors for postoperative hyponatremia, which are preoperative undernutrition and impaired renal function. The incidence of delirium was significantly higher in the postoperative hyponatremia group, suggesting that correcting preoperative hyponatremia and ensuring good nutrition may prevent delirium and thereby shorten hospital stays.