Hypernatraemia in the neurointensive care unit: central diabetes insipidus and noncentral diabetes insipidus

Introduction

Hypernatraemia is a prognostically serious complication in the neurointensive care unit. A typical, well-known syndrome associated with acute brain disease is central diabetes insipidus (cDI). However, cDI is not a frequent reason of hypernatraemia in neurointensive care. There are other causes of hypernatraemia, most frequently osmotherapy by mannitol or renal failure [1]. The purpose of our study was to evaluate retrospectively all hypernatraemias in patients with acute brain diseases admitted to our neurologic-neurosurgical care unit (NNICU) over a period of 5 years.

Methods

We analysed all patients with acute brain disease and serum sodium above 150 mmol/l. Firstly we diagnosed cDI according to serum and urine osmolality, hourly diuresis, renal function parameters and response to desmopressin. The remaining hypernatraemias were categorised as non-cDI. Patients without measured serum osmolality were excluded.

Results

There were 75 hypernatraemic patients (mean age 56.8 years; 41 male) with the following diagnoses: stroke 43, tumour 20, trauma 7, hydrocephalus 4 and epilepsy 1. The mean Glasgow coma scale (GCS) on onset of hypernatraemia was 12 ± 3.4, the mean Glasgow outcome scale (GOS) upon discharge from the NNICU was 3.3 ± 1.4. We found cDI only in eight patients (altogether 15 days). We classified 59 patients as non-cDI hypernatraemia (163 days). The remaining patients were not evaluated because they had no serum osmolality measurements. Between the two groups there were no differences in GCS (P = 0.631), GOS (P = 0.857), serum sodium (P = 0.736), and serum osmolality (P = 0.476), but patients with cDI had low urine osmolality (P = 0.001). On the other hand, the non-cDI group received more antioedematic therapy (P = 0.013) and diuretics (P = 0.019). In this group, mannitol was received in 48 (81.4%) patients and six (10.2%) had creatinine clearance below the reference range (range <1.15 ml/s).

Conclusion

In neurointensive care cDI is not the most common type of hypernatraemia. Most hypernatraemias are non-cDI due to anti-oedematic therapy and kidney dysfunction.