[Significance of plasma atrial natriuretic peptide measurement during the management of hyponatremia in neurosurgical patients].

We have examined the total number of admitted cases to clarify the pathogenesis of hyponatremia during the management of neurosurgical patients. We experienced 32 cases of hyponatremia during the past year by measuring the sodium balance and atrial natriuretic peptide (ANP) level. According to these two factors, we divided the cases into three groups. The first group shows normal ANP levels in spite of hyponatremia. Low administration of the sodium was thought to be the cause in these cases. The second group shows the elevated ANP levels with a positive sodium balance. Elevated circulatory volume due to the inadequate level of antidiuretic hormone and mild heart and/or kidney failures cause these conditions. Water restriction and/or diuresis were effective methods in the management of the cases. The last group shows the elevated ANP levels with a negative sodium balance. There is a statistically significant negative correlation between sodium balance and the ANP level. Marked natriuresis due to the elevated ANP causes the decrement of the circulatory volume in these cases. Pathogenesis of the last group is very important in the management of neurosurgical patients in an acute state, especially in subarachnoid hemorrhage cases. The decrement of the systemic circulatory volume would jeopardize the patient's neurological condition. In this group, water restriction that has been commonly recommended is contraindicated. Satisfactory water and sodium replenishment seems to be the best recommended treatment for this group.