Is mild hypernatremia an independent predictor of poor clinical outcome in neurocritically ill patients?

Abstract Background: Hypernatremia is a common complication encountered during the treatment of neurocritically ill patients. However, it is unclear whether clinical outcomes correlate with the severity of hypernatremia in such patients. Therefore, we investigated the impact of hypernatremia on mortality of these patients, depending on the degree of hypernatremia.Methods: Among neurosurgical patients admitted to the intensive care unit (ICU) in a tertiary hospital from January 2013 to December 2019, patients who were hospitalized in the ICU for more than 5 days and whose serum sodium levels were obtained during ICU admission were included. Hypernatremia was defined as the highest serum sodium level exceeding 150 mEq/L observed. We classified the patients into four subgroups according to the severity of hypernatremia and performed propensity score matching analysis.Results: Among 1,146 patients, 353 patients (30.8%) showed hypernatremia. Based on propensity score matching, 290 pairs were included in the analysis. The hypernatremia group had higher rates of in-hospital mortality and 28-day mortality in both overall and matched population (both p < 0.001 and p = 0.001, respectively). In multivariable analysis of propensity score-matched population, moderate and severe hypernatremia were significantly associated with in-hospital mortality (adjusted odds ratio [OR]: 4.58, 95% confidence interval [CI]: 2.15 – 9.75 and adjusted OR: 6.93, 95% CI: 3.46 – 13.90, respectively) and 28-day mortality (adjusted OR: 3.51, 95% CI: 1.54 – 7.98 and adjusted OR: 10.60, 95% CI: 5.10 – 21.90, respectively) compared with the absence of hypernatremia. However, clinical outcomes, including in-hospital mortality and 28-day mortality, were not significantly different between the group without hypernatremia and the group with mild hypernatremia (p = 0.720 and p = 0.690, respectively). The mortality rates of patients with moderate and severe hypernatremia were significantly higher in both overall and matched population. Interestingly, the mild hypernatremia group of matched population showed the best survival rate.Conclusions: Moderate and severe hypernatremia were associated with poor clinical outcomes in neurocritically ill patients. However, the prognosis of patients with mild hypernatremia was similar with that of patients without hypernatremia. Therefore, mild hypernatremia may be allowed during treatment of intracranial hypertension using hyperosmolar therapy.