title: Masking of syndrome of inappropriate antidiuretic hormone secretion: the isonatremic syndrome.
abstract: OBJECTIVE
  To determine whether the administration of isotonic saline in patients undergoing spinal fusion surgery prevents the development of hyponatremia, thus masking the detection of syndrome of inappropriate antidiuretic hormone secretion (SIADH).
  
  
  METHODS
  Prospective observational cohort study conducted in pediatric patients undergoing spinal fusion surgery. Using established criteria for diagnosing SIADH with the exception of serum sodium as a criterion, we separated patients into those with and without masked SIADH. Random cortisol levels were measured in the perioperative period to test for adrenal insufficiency to exclude it as a cause for natriuresis and hyponatremia.
  
  
  RESULTS
  Of the 40 patients included in the study, 13 (32%; 95% CI, 19%-49%) met study criteria for masked SIADH. The serum sodium levels between the 2 groups were not different throughout the postoperative period. The antidiuretic hormone levels were increased at 24-48 hours after surgery (20.4 pg/mL in masked SIADH group vs 6.6 pg/mL in no masked SIADH group, P = .04). Subjects with masked SIADH demonstrated a tendency for weight gain (3.9 kg vs 2.5 kg, P = .058), which was maximal on postoperative day 2. Cortisol levels were similar between the groups.
  
  
  CONCLUSIONS
  Masked SIADH (SIADH-like state without hyponatremia) commonly occurs in the postoperative period in children and young adults undergoing spinal fusion surgery. Early postoperative evaluation and recognition may result in appropriate management of patient's fluid balance.
authors.affiliation: Division of Pediatric Critical Care, Presbyterian Hospital, Albuquerque, NM.
authors.forename: Irfan
authors.initials: I
authors.lastname: Khan
authors.affiliation: Department of Biostatistics at the University of Iowa, Iowa City, IA.
authors.forename: Bridget
authors.initials: B
authors.lastname: Zimmerman
authors.affiliation: Department of Pediatric Nephrology, University of Iowa Children's Hospital, Iowa City, IA.
authors.forename: Patrick
authors.initials: P
authors.lastname: Brophy
authors.affiliation: Division of Pediatric Critical Care, University of Iowa Children's Hospital, Iowa City, IA. Electronic address: sameer-kamath@uiowa.edu.
authors.forename: Sameer
authors.initials: S
authors.lastname: Kamath
mesh_terms: D000293:Adolescent; D002648:Child; D005260:Female; D006454:Hemoglobins / Q000096:biosynthesis; D006801:Humans; D006854:Hydrocortisone / Q000097:blood; D007010:Hyponatremia / Q000517:prevention & control*; D007177:Inappropriate ADH Syndrome / Q000175:diagnosis* / Q000628:therapy*; D016014:Linear Models; D008297:Male; D059035:Perioperative Period; D011446:Prospective Studies; D012965:Sodium Chloride / Q000737:chemistry*; D013123:Spinal Fusion / Q000379:methods; D013997:Time Factors; D055815:Young Adult
chemical_list: D006454:Hemoglobins; D012965:Sodium Chloride; D006854:Hydrocortisone