title: Postoperative hyponatremia despite near-isotonic saline infusion: a phenomenon of desalination.
abstract: BACKGROUND
  It is widely presumed that the development of postoperative hyponatremia (which may be severe) results from administration of hypotonic fluids while antidiuretic hormone is acting.
  
  
  OBJECTIVE
  To show that hyponatremia would occur in patients 24 hours after surgery if only near-isotonic solutions are given and to evaluate the mechanisms responsible for hyponatremia in this setting.
  
  
  METHODS
  Prospective cohort study.
  
  
  METHODS
  University medical center.
  
  
  METHODS
  22 women who were having uncomplicated gynecologic surgery with infusion of near-isotonic solutions only (sodium chloride, 154 mmol/L, or Ringer lactate [sodium, 130 mmol/L, and potassium, 4 mmol/L]).
  
  
  METHODS
  Plasma electrolyte levels were measured at the time of induction of anesthesia and 24 hours later. Data on the balance of water and electrolytes were obtained for the same 24-hours period.
  
  
  RESULTS
  At the time of induction of anesthesia, the plasma sodium concentration was 140 +/- 1 mmol/L; 24 hours later, it decreased in 21 of 22 patients (mean decrease, 4.2 +/- 0.4 mmol/L [P < 0.001]; lowest level, 131 mmol/L in 2 patients). The urine remained hypertonic (peak sodium plus potassium concentration in urine, 294 +/- 9 mmol/L) in all patients for the first 16 hours after induction of anesthesia.
  
  
  CONCLUSIONS
  Postoperative hyponatremia occurred within 24 hours of induction of anesthesia when only near-isotonic fluids were infused. Hyponatremia was generally caused by generation of electrolyte-free water during excretion of hypertonic urine-a desalination process. This electrolyte-free water was retained in the body because of the actions of antidiuretic hormone. If the pathophysiology of this hyponatremic state is understood, recommendations for its prevention and treatment can be deduced.
authors.affiliation: St. Michael's Hospital, University of Toronto, Ontario, Canada.
authors.forename: A
authors.initials: A
authors.lastname: Steele
authors.forename: M
authors.initials: M
authors.lastname: Gowrishankar
authors.forename: S
authors.initials: S
authors.lastname: Abrahamson
authors.forename: C D
authors.initials: CD
authors.lastname: Mazer
authors.forename: R D
authors.initials: RD
authors.lastname: Feldman
authors.forename: M L
authors.initials: ML
authors.lastname: Halperin
mesh_terms: D000328:Adult; D004573:Electrolytes / Q000097:blood / Q000652:urine; D005260:Female; D005440:Fluid Therapy; D006801:Humans; D007010:Hyponatremia / Q000209:etiology* / Q000378:metabolism / Q000503:physiopathology; D007552:Isotonic Solutions / Q000627:therapeutic use; D011183:Postoperative Complications / Q000209:etiology* / Q000378:metabolism / Q000503:physiopathology; D011446:Prospective Studies; D000077325:Ringer's Lactate; D012965:Sodium Chloride / Q000627:therapeutic use*; D014599:Uterus / Q000601:surgery; D014882:Water-Electrolyte Balance
chemical_list: D004573:Electrolytes; D007552:Isotonic Solutions; D000077325:Ringer's Lactate; D012965:Sodium Chloride