title: Postoperative intubation time is associated with acute kidney injury in cardiac surgical patients.
abstract: BACKGROUND
  Acute kidney injury (AKI) is a frequent complication after cardiac surgery and is associated with a poor prognosis. Mechanical ventilation is an important risk factor for developing AKI in critically ill patients. Ventilation with high tidal volumes has been associated with postoperative organ dysfunction in cardiac surgical patients. No data are available about the effects of the duration of postoperative respiratory support in the immediate postoperative period on the incidence of AKI in patients after cardiac surgery.
  
  
  METHODS
  We performed a secondary analysis of 584 elective cardiac surgical patients enrolled in an observational trial on the association between preoperative cerebral oxygen saturation and postoperative organ dysfunction and analyzed the incidence of AKI in patients with different times to extubation. The latter variable was graded in 4 h intervals (if below 16 h) or equal to or greater than 16 h. AKI was staged according to the AKI Network criteria.
  
  
  RESULTS
  Overall, 165 (28.3%) patients developed AKI (any stage), 43 (7.4%) patients needed renal replacement therapy. Patients developing AKI had a significantly (P <0.001) lower renal perfusion pressure (RPP) in the first 8 hours after surgery (57.4 mmHg (95% CI: 56.0 to 59.0 mmHg)) than patients with a postoperatively preserved renal function (60.5 mmHg ((95% CI: 59.9 to 61.4 mmHg). The rate of AKI increased from 17.0% in patients extubated within 4 h postoperatively to 62.3% in patients ventilated for more than 16 h (P <0.001). Multivariate logistic regression analysis of variables significantly associated with AKI in the univariate analysis revealed that the time to the first extubation (OR: 1.024/hour, 95% CI: 1.011 to 1.044/hour; P <0.001) and RPP (OR: 0.963/mmHg; 95% CI: 0.934 to 0.992; P <0.001) were independently associated with AKI.
  
  
  CONCLUSIONS
  Without taking into account potentially unmeasured confounders, these findings are suggestive that the duration of postoperative positive pressure ventilation is an important and previously unrecognized risk factor for AKI in cardiac surgical patients, independent from low RPP as an established AKI trigger, and that even a moderate delay of extubation increases AKI risk. If replicated independently, these findings may have relevant implications for clinical care and for further studies aiming at the prevention of cardiac surgery associated AKI.
authors.forename: Matthias
authors.initials: M
authors.lastname: Heringlake
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Nowak
authors.forename: Julika
authors.initials: J
authors.lastname: Schön
authors.forename: Jens
authors.initials: J
authors.lastname: Trautmann
authors.forename: Astrid Ellen
authors.initials: AE
authors.lastname: Berggreen
authors.forename: Efstratios I
authors.initials: EI
authors.lastname: Charitos
authors.forename: Hauke
authors.initials: H
authors.lastname: Paarmann
mesh_terms: D058186:Acute Kidney Injury / Q000209:etiology*; D000368:Aged; D001921:Brain / Q000098:blood supply; D006348:Cardiac Surgical Procedures; D017558:Elective Surgical Procedures; D005260:Female; D006801:Humans; D015994:Incidence; D007442:Intubation, Intratracheal / Q000009:adverse effects*; D008297:Male; D008875:Middle Aged; D011175:Positive-Pressure Respiration / Q000009:adverse effects*; D011183:Postoperative Complications / Q000209:etiology*; D012044:Regression Analysis; D012307:Risk Factors; D013997:Time Factors