title: Does preoperative hyponatremia potentiate the effects of left ventricular dysfunction on mortality after cardiac surgery?
abstract: OBJECTIVE
  Left ventricular dysfunction and preoperative hyponatremia are associated with adverse outcomes after cardiac surgery. However, the interactions between them are unknown. Thus, we evaluated the interaction of low left ventricular ejection fraction (<40%) and preoperative hyponatremia (Na <135 mEq/L) with morbidity and mortality after cardiac surgery.
  
  
  METHODS
  The interaction of hyponatremia and ejection fraction with hospital complications, length of stay, and mortality was analyzed using logistic and Cox regression analysis in 2247 patients who underwent cardiac surgery between 2005 and 2008 at The Ohio State University Wexner Medical Center.
  
  
  RESULTS
  Of the patients, 68.5% had normal ejection fraction. Hyponatremia was present in 18% of patients with normal ejection fraction and 35% of patients with low ejection fraction. Hyponatremic patients had higher rates of New York Heart Association class III and IV, more comorbidities, and higher Society of Thoracic Surgeons score and European System for Cardiac Operative Risk Evaluation irrespectively of their ejection fraction. The correlation between preoperative sodium and ejection fraction was weak (r(2) = 0.04). Hyponatremia increased the rate of postoperative complications and hospital stay, and decreased 1- and 3-year survivals in patients with both normal and low ejection fraction. Hyponatremia was independently associated with longer hospital stay for normal ejection fraction (multiplier, 1.18; confidence interval, 1.09-1.27; P < .001) and low ejection fraction (multiplier, 1.10; confidence interval, 1.0-1.21; P = .05), increased need for dialysis for normal ejection fraction (odds ratio, 2.16; confidence interval, 1.08-4.32; P = .03), and increased risk of mortality for normal ejection fraction (hazard ratio, 1.56; confidence interval, 1.20-2.05; P = .001), but not for patients with low ejection fraction (hazard ratio, 1.21; confidence interval, 0.89-1.65; P = .21).
  
  
  CONCLUSIONS
  Hyponatremia is more common in patients with low ejection fraction. Although preoperative hyponatremia is independently associated with adverse outcomes in patients with normal ejection fraction, an association with adverse outcomes in patients with low ejection fraction was not demonstrated.
authors.affiliation: Division of Cardiac Surgery, The Ohio State University Medical Center, Columbus, Ohio, USA. juan.crestanello@osumc.edu
authors.forename: Juan A
authors.initials: JA
authors.lastname: Crestanello
authors.forename: Gary
authors.initials: G
authors.lastname: Phillips
authors.forename: Michael S
authors.initials: MS
authors.lastname: Firstenberg
authors.forename: Chittoor
authors.initials: C
authors.lastname: Sai-Sudhakar
authors.forename: John
authors.initials: J
authors.lastname: Sirak
authors.forename: Robert
authors.initials: R
authors.lastname: Higgins
authors.forename: William T
authors.initials: WT
authors.lastname: Abraham
mesh_terms: D006348:Cardiac Surgical Procedures; D015897:Comorbidity; D005260:Female; D006801:Humans; D007010:Hyponatremia / Q000150:complications* / Q000401:mortality*; D007902:Length of Stay / Q000706:statistics & numerical data; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D011183:Postoperative Complications; D016016:Proportional Hazards Models; D013318:Stroke Volume; D015996:Survival Rate; D018487:Ventricular Dysfunction, Left / Q000150:complications* / Q000401:mortality*