Influence of vasopressin level on osmotic pressure and sodium concentration in plasma and cerebrospinal fluid in patients with intracranial lesions.

To study the influence of the vasopressin level on osmotic pressure and sodium concentration in plasma and cerebrospinal fluid (CSF), plasma and CSF were sampled simultaneously in 27 patients with central nervous system lesions. A significant elevation of arginine vasopressin (AVP) levels in plasma and CSF and a significant increase in the osmotic pressure gradients of plasma and CSF were observed in hyponatremic patients. The significant increases in the osmotic pressure gradients may be attributable to hemodilution and CSF concentration resulting from the elevated AVP level, because the sodium concentration gradients of plasma and CSF did not significantly increase. The elevated AVP levels in plasma and CSF and the increased osmotic pressure gradients of plasma and CSF normalized in parallel with improvement of consciousness. These findings suggest that the increased osmotic pressure gradients of plasma and CSF, derived from increased AVP secretion into blood and CSF, exacerbates brain edema induced by the primary lesion and may contribute to the clinical deterioration of some patients with intracranial lesions.