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Evaluation of the effect of diagnostic methodology on the reported incidence of ventilator-associated pneumonia
  1. A Conway Morris1,
  2. K Kefala1,2,
  3. A J Simpson1,
  4. T S Wilkinson1,
  5. K Everingham2,
  6. D Kerslake2,
  7. S Raby2,
  8. I F Laurenson3,
  9. D G Swann2,
  10. T S Walsh2
  1. 1
    MRC Centre for Inflammation Research, University of Edinburgh, Scotland, UK
  2. 2
    Critical Care, Royal Infirmary of Edinburgh, Scotland, UK
  3. 3
    Department of Clinical Microbiology, Royal Infirmary of Edinburgh, Scotland, UK
  1. Dr A Conway Morris, Room C2.17, MRC Centre for Inflammation Research, Queen’s Medical Research Institute, University of Edinburgh, Little France Crescent, Edinburgh EH16 4TJ, UK; mozza{at}doctors.org.uk

Abstract

Background: The optimal method for diagnosing ventilator-associated pneumonia (VAP) is controversial and its effect on reported incidence uncertain. This study aimed to model the impact of using either endotracheal aspirate or bronchoalveolar lavage on the reported incidence of pneumonia and then to test effects suggested from theoretical modelling in clinical practice.

Methods: A three-part single-centre study was undertaken. First, diagnostic performance of aspirate and lavage were compared using paired samples from 53 patients with suspected VAP. Secondly, infection surveillance data were used to model the potential effect on pneumonia incidence and antibiotic use of using exclusively aspirate or lavage to investigate suspected pneumonia (643 patients; 110 clinically suspected pneumonia episodes). Thirdly, a practice change initiative was undertaken to increase lavage use; pneumonia incidence and antibiotic use were compared for the 12 months before and after the change.

Results: Aspirate overdiagnosed VAP compared with lavage (89% vs 21% of clinically suspected cases, p<0.0001). Modelling suggested that changing from exclusive aspirate to lavage diagnosis would decrease reported pneumonia incidence by 76% (95% CI 67% to 87%) and antibiotic use by 30% (95% CI 20% to 42%). After the practice change initiative, lavage use increased from 37% to 58%. Although clinically suspected pneumonia incidence was unchanged, microbiologically confirmed VAP decreased from 18 to 9 cases per 1000 ventilator days (p = 0.001; relative risk reduction 0.61 (95% CI 0.46 to 0.82)), and mean antibiotic use fell from 9.1 to 7.2 antibiotic days (21% decrease, p = 0.08).

Conclusions: Diagnostic technique impacts significantly on reported VAP incidence and potentially on antibiotic use.

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Footnotes

  • Competing interests: AJS has received expenses from Astra Zeneca and Glaxo Smith Kline (for travel and accommodation) to attend international educational conferences. IFL has received expenses from Astra Zeneca (for travel and accommodation) to attend international educational conferences. TSW is the recipient of an unrestricted educational grant from Wyeth pharmaceuticals for work concerning epidemiology of ICU-acquired infection. All other authors have no conflicts of interest to declare.

  • Funding: This work was supported by a grant from the Sir Jules Thorn Charitable Trust, an unrestricted educational grant from Wyeth Pharmaceuticals and the Edinburgh Critical Care Research Group Trials fund.

  • Patient consent: The study was approved by the Research Ethics Committee.

  • See Editorial, p 463

  • ▸ Additional details of the methodology are published online only at http://thorax.bmj.com/content/vol64/issue6

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