Measurement of plasma antidiuretic hormone and its significance in subarachnoid hemorrhage

Abstract

The syndrome of inappropriate secretion of antidiuretic hormone (SIADH) occasionally follows subarachnoid hemorrhage (SAH). Plasma ADH level in patients with SAH mainly due to cerebral aneurysms was studied, and the risk for developing SIADH following SAH was discussed. Plasma ADH was measured using radio immunoassay in 25 control subjects and in 36 patients with SAH. Repeated plasma ADH measurements were made preoperatively in cases with SAH until 4 weeks after SAH. The mean (±SD) plasma level of ADH in control subjects was 3.8±1.2 pgml. Plasma ADH levels in cases with SIADH were 6.4±2.9 pgl, inappropriately elevated for the corresponding serum osmolarities and significantly higher than that of control subjects (P<0.001). The majority of cases with SIADH were Grade III or IV after Hunt & Hess. Even though the mean value of serum sodium or osmolarity was not significantly different from the controls, the mean plasma level of ADH in cases with Grade III or IV was significantly higher than the controls. The mean (±SD ) plasma level of ADH in cases with Grade III or IV measured within 14 days following SAH was, 7.8±2.8 pgml, significantly elevated (P<0.001). When compared with control subjects, cases with SAH did not show any significant increase of plasma aldosterone, blood urea nitrogen, and hematocrit which would have suggested blood volume depletion. Therefore, it was suggested that the excessive release of ADH recognized in the present study was due to non-physiological (inappropriate) release of ADH caused by non-osmotic factors other than blood volume depletion. From the present study, it was concluded that patients with Grade III or IV, especially in an acute stage following SAH, were unable to suppress ADH release properly and to excrete a water load normally. Therefore, these patients were susceptible to SIADH in spite of usually normal serum sodium. Thus, fluid intakes and electrolytes should be closely observed.