Ten adolescent and preadolescent patients who underwent posterior spinal
fusion for idiopathic scoliosis or spondylolisthesis were examined for the
presence or absence of the postoperative syndrome of inappropriate
antidiuretic-hormone secretion. For each patient, levels of serum sodium,
serum osmolality, urine sodium, urine osmolality, and serum antidiuretic
hormone were obtained preoperatively and postoperatively. The investigation
clearly showed that the syndrome occurred in each patient, with the level
of serum antidiuretic hormone being highest within a few hours
postoperatively. This resulted in a reduction of urinary output, the
reduction being maximum on the day of operation and the output gradually
rising to normal over the next three days. This syndrome and its associated
low postoperative urinary output is common after spinal fusion and should
be treated with restriction of fluids rather than administration of
increased amounts of fluid.