Hyponatremia after spinal fusion caused by inappropriate secretion of antidiuretic hormone (SIADH).

The Syndrome of Inappropriate Secretion of Antidiuretic Hormone (SIADH) was found to occur in at least 5% of patients recovering from a spinal fusion operation. A retrospective review was undertaken for all patients who had had a spinal fusion in 1981. The author applied strict criteria for the diagnosis of SIADH and found that at least eight of 161 patients suffered this complication. A factor analysis revealed that SIADH was most likely to develop in patients with large spinal deformities and greater than usual intraoperative blood loss. There was no correlation with age, sex, type of fusion, or cause of spinal deformity. The diagnosis, treatment, and pathogenesis of SIADH suggest that an extensive spinal fusion operation is a previously unrecognized predisposing condition.