Purpose: Discharge is a critical time point in the care pathway of geriatric hospital patients, and post-acute care facilities often have less monitoring possibilities. Active medical issues such as electrolyte disturbances should be treated before transfer. We studied the impact of in-hospital hypernatremia of older hip fracture patients to mortality at 90 days.

Methods: A retrospective study population of 2240 hip fracture patients from 2015 to 2019 was collected from the Hospital District of Southwest Finland data pool. In the present study we included patients aged ≥65 years who were transferred from the operating hospital to primary health care wards after surgery (n = 1,125). Laboratory results were collected on admission and before discharge. The main outcome was mortality at 90 days.

Results: Hypernatremia, defined as serum sodium ≥144 mmol/l, was present in 6.8 % (n = 91) before discharge. For patients with hypernatremia the crude mortality at 90 days was 35.8 % (95 % CI 27.1 to 46.3) and for patients with normal serum sodium 9.6 % (95 % CI 8.0 to 11.6). The age- and sex-adjusted hazard ratio of hypernatremia compared to normal serum sodium was 3.91 (95 % CI 2.62 to 5.82).

Conclusion: In-hospital hypernatremia had predictive value for 90-day mortality. We recommend active screening for and prompt treatment of perioperative hypernatremia in hip fracture patients. Local guidelines and discharge checklists are recommended to secure the discharge period.