title: Sleep apnoea is a risk factor for acute kidney injury after coronary artery bypass grafting.
abstract: OBJECTIVE
  Acute kidney injury (AKI) is a common complication in patients who undergo coronary artery bypass grafting (CABG). Sleep apnoea is associated with sympathetic activation, inflammatory reaction and plaque burden. The possible status of sleep apnoea as a risk factor for AKI after CABG has not been studied.
  
  
  METHODS
  We recruited 169 patients for an overnight sleep study using a Food and Drug Administration-approved portable device before they underwent elective CABG. AKI after CABG was defined as a relative increase of greater than 25% or an absolute increase of greater than 0.5 mg/dl in the serum creatinine level from baseline within 5 days after CABG. A generalized structural equation model (gSEM) was then applied to ascertain whether sleep apnoea, defined as an Apnoea-Hypopnoea index (AHI) of 15 or higher, was associated with AKI after CABG after adjusting for the effects of confounding variables.
  
  
  RESULTS
  Of the 150 patients (88.8%) who completed the study, the incidence of AKI after CABG was 22.7%. The mean AHI was higher in the AKI group (27.4 ± 19.8) than that in the non-AKI group (18.3 ± 16.5; P < 0.01). The prevalence of sleep apnoea was higher in the AKI group (64.7%) than that in the non-AKI group (45.7%; P = 0.05). The patients in the AKI group were older (P < 0.01) and shorter (P = 0.03) and had higher systolic blood pressures (P = 0.01), greater waist circumferences (P = 0.04) and larger left atrial diameters (P < 0.01) than those in the non-AKI group. The patients in the AKI group had higher serum haemoglobin levels (P = 0.04) and lower glucose levels (P < 0.01) than those in the non-AKI group. A gSEM based on binomial distributions showed that sleep apnoea was an independent predictor of AKI after CABG (adjusted odds ratio, 2.89; confidence interval, 1.09-7.09; P = 0.03) after adjustment for the effects of haemoglobin, glucose levels, the left atrial diameter and systolic blood pressure.
  
  
  CONCLUSIONS
  Sleep apnoea is prevalent and is associated with AKI after CABG. The data presented here provide the first insights into the potential of treating sleep apnoea to attenuate the risk of AKI after CABG.
authors.affiliation: Department of Cardiology, National University Heart Centre Singapore, Singapore.
authors.forename: Jieli
authors.initials: J
authors.lastname: Kua
authors.affiliation: Department of Cardiology, National University Heart Centre Singapore, Singapore.
authors.forename: Liang-Ping
authors.initials: LP
authors.lastname: Zhao
authors.affiliation: Yong Loo Lin School of Medicine, National University of Singapore, Singapore Department of Cardiac, Thoracic and Vascular Surgery, National University Heart Centre Singapore, Singapore.
authors.forename: Theodoros
authors.initials: T
authors.lastname: Kofidis
authors.affiliation: Yong Loo Lin School of Medicine, National University of Singapore, Singapore Cardiovascular Research Institute, National University Heart Centre Singapore, Singapore Department of Mathematics and Statistics, La Trobe University, Melbourne, VIC, Australia.
authors.forename: Siew-Pang
authors.initials: SP
authors.lastname: Chan
authors.affiliation: Department of Cardiology, National University Heart Centre Singapore, Singapore.
authors.forename: Tiong-Cheng
authors.initials: TC
authors.lastname: Yeo
authors.affiliation: Department of Cardiology, National University Heart Centre Singapore, Singapore.
authors.forename: Huay-Cheem
authors.initials: HC
authors.lastname: Tan
authors.affiliation: Department of Cardiology, National University Heart Centre Singapore, Singapore Yong Loo Lin School of Medicine, National University of Singapore, Singapore mdclchr@nus.edu.sg.
authors.forename: Chi-Hang
authors.initials: CH
authors.lastname: Lee
mesh_terms: D058186:Acute Kidney Injury / Q000453:epidemiology* / Q000209:etiology; D000368:Aged; D001026:Coronary Artery Bypass / Q000009:adverse effects* / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011183:Postoperative Complications / Q000453:epidemiology* / Q000209:etiology; D011446:Prospective Studies; D012307:Risk Factors; D012891:Sleep Apnea Syndromes / Q000453:epidemiology*
keywords: Complication; Coronary artery; Renal failure; Risk factor; Sleep-disordered breathing