The syndrome of inappropriate antidiuretic hormone secretion and its effect on blood indices following spinal fusion.

Red blood cell indices in four adolescent and preadolescent patients with documented inappropriate antidiuretic hormone secretion (SIADH) following spinal fusion were examined for evidence of dilution. The blood indices in these preoperative patients demonstrated evidence of dilution on both the intracellular and extracellular levels. The major factors causing these dilutional effects were elevated ADH, intravenous fluid overloading, and mobilization of "third space" fluids. It appears that extracellular dilution secondary to these factors results in spuriously low blood indices (namely, hemoglobin, hematocrit, and red blood cells) during the postoperative period. These findings suggest that an awareness of SIADH and avoiding intravenous fluid overloads by accurately managing intraoperative and postoperative fluids will decrease the dilutional effects observed on blood indices and perhaps save patients from unwarranted transfusions.