title: Outcomes of post-cardiac surgery patients with persistent hyperlactatemia in the intensive care unit: a matched cohort study.
abstract: BACKGROUND
  Higher morbidity and mortality rates are seen amongst patients presenting with hyperlactatemia in the postoperative period. The purpose of this study was to determine the relationship between persistent elevations in lactate and poor ICU outcome in post-cardiac surgery patients.
  
  
  METHODS
  This was a retrospective matched cohort analysis of cardiac surgery patients undergoing bypass and/or valve surgery in a university hospital centre. Selection criteria were: cardiac bypass and/or valve surgery; admission to the ICU for > 24 h postoperatively; and peak lactate ≥ 3.0 mmol/L. Hyperlactatemic patients were matched to 2 normolactatemic patients. Multivariable conditional logistic regression was used to determine predictors of hyperlactatemia and mortality.
  
  
  RESULTS
  Four hundred sixty-nine post-cardiac surgery patients were admitted to the ICU for > 24 h. 144 of these patients had an arterial blood lactate ≥ 3.0 mmol/L. Amongst the mortalities, 78.9 % presented with hyperlactatemia. Independent risk factors predictive of a lactate ≥ 3.0 mmol/L were preoperative IABP insertion (RR 2.8, CI 1.1-7.2) and postoperative acute kidney injury (RR 3.2, CI 2.1-5.4). Patients whose lactate concentrations continued to increase >30 h postoperatively were more likely to die (RR 8.44 CI 2.50-28.53).
  
  
  CONCLUSIONS
  The persistence of hyperlactatemia is a more important determinant of postoperative outcome than the absolute value of the peak lactate concentration. A simple postoperative lactate washout does not sufficiently explain this lactate accumulation. Mortality is proposed to be secondary to a state of ongoing hypoperfusion.
authors.affiliation: Division of General Surgery, Vancouver General Hospital, 950 West 10th Avenue, Vancouver, Canada. nicole.mak@alumni.ubc.ca.
authors.forename: Nicole T J J
authors.initials: NT
authors.lastname: Mak
authors.affiliation: Department of Nephrology, McGill University Health Centre, Montréal, Canada. Sameena.iqbal@mcgill.ca.
authors.forename: Sameena
authors.initials: S
authors.lastname: Iqbal
authors.affiliation: Division of Cardiothoracic Surgery, McGill University Health Centre, Montréal, Canada. benoit.devarennes@muhc.mcgill.ca.
authors.forename: Benoit
authors.initials: B
authors.lastname: de Varennes
authors.affiliation: Departments of Surgery and Critical Care Medicine, McGill University Health Centre, 1650 Cedar Ave. L9.411, Montréal, QC, H3G 1A4, Canada. kosar.khwaja@mcgill.ca.
authors.forename: Kosar
authors.initials: K
authors.lastname: Khwaja
mesh_terms: D058186:Acute Kidney Injury / Q000209:etiology; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D006348:Cardiac Surgical Procedures / Q000009:adverse effects*; D005260:Female; D006801:Humans; D065906:Hyperlactatemia / Q000209:etiology*; D007362:Intensive Care Units; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D011184:Postoperative Period; D012189:Retrospective Studies; D012307:Risk Factors; D016896:Treatment Outcome