Determinants of hyponatremia following a traumatic brain injury

Hyponatremia is common in patients with central nervous system disease. It may prolong hospitalization and increase morbidity and mortality. However, the incidence and risks factors remain largely unknown in traumatic brain injury (TBI). The objectives of this study are to characterize hyponatremia in TBI patients and find its main risk factors.

All patients admitted with a diagnosis of acute TBI over a 1-year period were included, except patients with known chronic hyponatremia, those who died within 72 h, and those receiving hyperosmolar therapy to treat their intracranial hypertension. Sodium levels throughout hospitalization were collected. Post-traumatic hyponatremia was defined as follows: borderline (1-2 points below normal and 1-2 days duration) and significant (more than 2 points below normal and/or more than 2 days duration). Demographic data, GCS, mechanism of injury, and CT findings were collected. These factors were correlated to the incidence of hyponatremia.

Hyponatremia was found in 29% of the 283 included patients and was significant in 2/3 of the cases. Significant hyponatremia had a narrower peak, between 7 and 11 days, while borderline hyponatremia started earlier and was more distributed in time. Factors associated with hyponatremia were greater age (p = 0.004), worse ISS (p = 0.017), worse Marshall Grade on CT (p = 0.007), and a diffuse pattern of injury on CT (p < 0.001). Significant hyponatremia was associated with: a diffuse pattern of injury on CT (p = 0.032), the presence of intracerebral hemorrhage (p = 0.027), and multiple lesions on CT (p = 0.043).

Post-traumatic hyponatremia is common and can lead to serious consequences in TBI patients. Adequate monitoring and treatment are therefore important. Older patients and those with more significant injury on CT are more at risk.