Hypernatremia and mortality in patients with severe traumatic brain injury

Introduction

Hypernatremia (HyperNa) carries on an increased risk of death in critically ill patients [1]. It is not known, however, whether this is true also in patients with severe traumatic brain injury (TBI).

Methods

We analyzed prospective data from all patients admitted for severe TBI (GCS < 8) to a trauma ICU over a 3-year time period. We collected demographics, clinical variables, complications, and the available laboratory data for each day of ICU stay. Major outcomes were ICU and hospital mortality, and ICU length of stay (LOS). We used Cox proportional-hazards regression models with time-dependent variates designed to reflect the exposure to the varying sodium (Na) levels over time during the ICU stay. The same models were adjusted for age, gender, and Na levels at admission as baseline covariates.

Results

We included in the study 130 TBI patients (mean age 52 years, SD 23, range 18–96; males 74%; median GCS 3, range 3–8; mean SAPS II 50, SD 14, range 9–84; all mechanically ventilated; tracheostomy in 64/130, 49%). ICU mortality was 36/130 (27.7%), hospital mortality was 42/130 (32.3%). Follow-up included a total of 1,334 patient-days (average of 2.9 measurements of serum Na/day). Serum Na values were computed as the daily average, which was 140 mmol/l (range 133–153); the patient average of the daily maximum Na levels was 143 mmol/l (range 131–164). Twenty-six percent of the days in the ICU were complicated by HyperNa (that is, at least one value of Na > 145 mmol/l), with 70% of the patients showing this abnormality. The average time of first occurrence of HyperNa was 5 days from ICU admission, while only five patients had HyperNa at ICU admission. A daily increase from the cumulative patient-average by 1 SD unit (about 2.4 mmol/l Na) was associated with a 2.15 times increase hazard of death (95% CI = 1.28–3.59; P = 0.004). Adjustment for the daily use of hypertonic solutions did not change our findings. HyperNa was slightly associated with increased ICU LOS.

Conclusion

Our study suggests a strong relation between increased Na levels and mortality in patients with severe TBI. Although these results do not prove a causal relation between increased Na levels and death, we urge for interventional studies to ascertain the safety of treatment strategies that might increase serum Na levels in patients with severe TBI.