Variation of early auditory evoked potentials (EAEP) in severe hyponatremia

Full text

Severe hyponatremia induces neurological symptoms in connection with its rate of appearance. The aim of this study was to measure the variations of EAEP during hyponatremia and to determine its prognostic interest.

Patients and method

65 patients (44 women and 21 men, mean age 67.3± 15.7 years) with hyponatremia <125 mmol/l at their admission to the emergency room or intensive care unit, were included. The EAEP (monaural stimulation by alternative clicks of 0.1 ms at 90 Db) were recorded daily until hyponatremia correction was achieved (250 records). EAEP parameters (I, III and V peaks latency, I-III, III-V and I-V intervals) were studied according to the level and the mechanism of hyponatremia, and according to the neurological symptomatology and survival of the patients.

Results

The mean value of the initial natremia was 118± 7 mmol/l, by dilution in 78% of cases, with neurological signs in 69%. Correction speed was 4.8± 2.2 days. Fifteen patients died but no cases of centropontine myelinolysis occurred. There was a linear correlation between natremia decrease and brainstem conduction lengthening (III and V peaks, intervals, P<10^-4). These variations were corrected by the normalization of natremia (P<10^-5). Hyponatremia was associated with a lengthening of the I-V interval in 74.5% of patients. The mechanism of the hyponatremia, the presence of neurological signs or the patient outcome had no effect on EAEP parameters.

Conclusion

Severe hyponatremia must be considered a cause of EAEP lengthening. EAEP evaluation does not constitute a prognostic factor of hyponatremia.