The prevalence and risk factors of the Syndrome of Inappropriate Anti-Diuretic Hormone secretion (SIADH) following spinal surgery

The Syndrome of Inappropriate Anti-Diuretic Hormone (SIADH) secretion is the most common etiology of normovolemic hyponatremia, which occurs following non-physiologic release of antidiuretic hormone (ADH) from the posterior pituitary, or an ectopic source. SIADH has been reported as a complication of cardiothoracic, brain, and spinal surgeries. This study was conducted to assess the prevalence of SIADH following spinal surgeries and to identify the underlying risk factors. Samples were patients undergoing any spinal surgery at the Hospitals of Shafa Yahyaian and Rasoul Akram, Tehran, Iran in a 2-year period. Blood and urine sodium concentrations and osmolarity were measured before and after surgery. The amount of hemorrhage, as well as the patients'' fluid input and output during surgery were recorded. Fluid input and output was also recorded on the first postoperative day. The prevalence of SIADH following spinal surgeries was 60.3%. Mean duration of surgery in SIADH patients was longer than in others. Mean amount of hemorrhage and total fluid loss during surgery were significantly higher in SIADH patients than in healthy individuals. SIADH is the principal cause of hyponatremia following spinal surgeries; the reported prevalence rates vary widely from 5 to 100%. SIADH following surgery has been attributed to stress, and in spinal or neurological surgeries to dural damage or traction of neuronal pathways. Time is of the essence in the treatment of hyponatremia and prevention of complications that may increase the mortality and morbidity of spinal surgeries.