Suspected ventilator-associated respiratory infection in severely ill patients: a prospective observational study

Abstract

Introduction: Ventilator-associated respiratory infection (VARI) is an important cause of morbidity in critically-ill patients. Clinical trials performed in heterogeneous populations have suggested there are limited benefits from invasive diagnostic testing to identify patients at risk or to target antimicrobial therapy. However, multiple patient subgroups (for example, immunocompromised, antibiotic-treated) have traditionally been excluded from randomization. We hypothesized that a prospective surveillance study would better identify patients with suspected VARI (sVARI) at high risk for adverse clinical outcomes, and who might be specifically targeted in future trials.

Methods: We performed a prospective observational study in all patients ventilated for greater than 48 hours. sVARI was identified by surveillance for changes in white blood cell count, temperature, sputum, and/or new chest X-ray infiltrates. Indices of disease co-morbidity, as well as mortality, duration of mechanical ventilation, and length of hospital or ICU stay were correlated with sVARI.

Results: Of 1806 patients admitted to the ICU over 14 months, 267 were ventilated for greater than 48 hours, and 77 developed sVARI. Incidence of sVARI was associated with iatrogenic immunosuppression or admission for respiratory illness. Any sVARI, whether suspected ventilator-associated pneumonia (sVAP) or ventilator-associated tracheobronchitis (sVAT), was associated with increased length of stay and duration of mechanical ventilation.

Conclusions: Clinical surveillance for sVARI identifies patients at risk for increased morbidity. Iatrogenically immunosuppressed patients, a subgroup previously excluded from randomized clinical trials, represent a growing proportion of the critically-ill at risk for sVARI who might be targeted for future investigations on diagnostic or therapeutic modalities.

Figure 1

Patient flow. A flow diagram for patients at risk for suspected ventilator-associated pneumonia, and identification of patients with suspected ventilator-associated tracheobronchitis (sVAT) or suspected ventilator-associated pneumonia (sVAP), are shown.

Figure 2

ICU or hospital length of stay in patients with sVAP or sVAT. For patients with no suspected infection, sVAT or sVAP, median values ± interquartile range (IQR) are shown for A) ICU length of stay (days) or B) hospital length of stay (days). P <0.003 for sVAT or sVAP versus no infection by Wilcoxon rank sum test. sVAP, suspected ventilator-associated pneumonia; sVAT, suspected ventilator-associated tracheobronchitis.