title: Body salt and water balances in cardiothoracic surgery patients with intensive care unit-acquired hyponatremia.
abstract: OBJECTIVE
  Hyponatremia is frequently observed in intensive care unit (ICU) patients, but there is still lack information on the physiological mechanisms of development.
  
  
  METHODS
  In this retrospective analysis we performed tonicity balances in 54 patients with ICU acquired hyponatremia. We calculated fluid and solute in and outputs during 24 hours in 106 patient days with decreasing serum-sodium levels.
  
  
  RESULTS
  We could observe a positive fluid balance as a single reason for hyponatremia in 25% of patients and a negative solute balance in 57%. In 18% both factors contributed to the decrease in serum-sodium. Hyponatremic patients had renal water retention, measured by electrolyte free water clearance calculation in 79% and positive input of free water in 67% as reasons for decline of serum-sodium. The theoretical change of serum sodium during 24 hours according to the calculations of measured balances correlated well with the real change of serum sodium (r = 0.78, P < .01).
  
  
  CONCLUSIONS
  Balance studies showed that renal water retention together with renal sodium loss and high electrolyte free water input are the major contributors to the development of hyponatremia. Control of renal water and sodium handling by urine analysis may contribute to a better fluid management in the ICU population.
authors.affiliation: Department of Nephrology, Krankenhaus der Elisabethinen, Linz, Austria.
authors.forename: Sandra
authors.initials: S
authors.lastname: Stieglmair
authors.forename: Gregor
authors.initials: G
authors.lastname: Lindner
authors.forename: Andrea
authors.initials: A
authors.lastname: Lassnigg
authors.forename: Mohamed
authors.initials: M
authors.lastname: Mouhieddine
authors.forename: Michael
authors.initials: M
authors.lastname: Hiesmayr
authors.forename: Christoph
authors.initials: C
authors.lastname: Schwarz
mesh_terms: D000328:Adult; D006348:Cardiac Surgical Procedures; D005260:Female; D006801:Humans; D007010:Hyponatremia / Q000503:physiopathology*; D007362:Intensive Care Units; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D012307:Risk Factors; D014883:Water-Electrolyte Imbalance / Q000503:physiopathology*
keywords: Cardiothoracic surgery; Electrolyte free water clearance; Fractional excretion sodium; Hyponatremia; Intensive care unit; Tonicity balance