The Association Between Tidal Volume and Ventilator-Associated Events in Adult ICU Patients Open Access

Abstract

Objective: Ventilator-associated events (VAE) are associated with an increased risk for mortality in adult ICU patients; however, there is still limited data regarding modifiable risk factors. Mechanical ventilation with a high tidal volume is associated with an increased risk for developing the acute respiratory distress syndrome and pneumonia which are both common causes of VAEs. The primary purpose of this study was to evaluate the association between tidal volume and VAE in adult ICU patients receiving invasive mechanical ventilation. In addition, the association between tidal volume and two broad categories of VAEs (infection-related and non-infection related VAEs) was also examined.

Study design : Nested matched case-control study

Study setting: Medical, surgical, coronary care and neurointensive care units at two academic teaching hospitals

Methods: Patients who received conventional invasive mechanical ventilation for more than 2 days were screened for VAE. VAE cases were matched to up to five controls based on admission ICU and the cases' duration of mechanical ventilation prior to VAE onset. Conditional logistic regression was used to estimate the association between mean tidal volume and VAE. Additional models examined the association between mean tidal volume and both infection-related and non-infection related VAEs independent of additional patient and clinical characteristics.

Results: A total of 190 VAE cases were identified and were successfully matched to 931 controls. Mean tidal volume was independently associated with the occurrence of ventilator-associated events when adjusted for the matching variables (adjusted OR, 1.21 per 1 ml/kg PBW; 95% CI, 1.11 - 1.33) and after controlling for 16 additional patient characteristics (adjusted OR, 1.23; 95% CI, 1.11 - 1.35). This association remained significant for non-infection-related VAEs (adjusted OR, 1.23; 95% CI, 1.09 - 1.38) and there was a trend towards significance for infection-related VAEs (adjusted OR, 1.22; 95% CI, 0.99 - 1.50). In the multivariable model, male sex and black race were also independent risk factors for VAE.

Conclusion: Invasive mechanical ventilation with a high tidal volume is independently associated with an increased risk of developing a VAE in adult ICU patients. More research is needed to determine if the use of low tidal volume ventilation decreases VAE rates.

Table of Contents

INTRODUCTION.................................................................................................1

BACKROUND......................................................................................................3

METHODS..........................................................................................................6

RESULTS...........................................................................................................12

DISCUSSION.....................................................................................................15

REFERENCES....................................................................................................20

TABLES AND FIGURES.......................................................................................22

Table 1. Characteristics of ventilator-associated event cases and matched controls

Table 2. Distribution of mean tidal volume quintiles in the study population

Table 3. Multivariable model of the association between mean tidal volume and

ventilator-associated events

Table 4. Multivariable model of the association between mean tidal volume and

non-infection-related ventilator-associated events

Table 5. Multivariable model of the association between tidal volume and

infection-related ventilator-associated events

Figure 1. Surveillance definitions of ventilator-associated events

Figure 2. Classification of ventilator-associated events

Figure 3. Flow diagram showing the selection of VAE cases and controls

Figure 4. The association between tidal volume (quintiles) and ventilator-associated events adjusted for matching variables

Figure 5. The association between tidal volume (quintiles) and ventilator-associated events

adjusted for matching variables and 16 pre-specified patient characteristics

About this Master's Thesis

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School	Laney Graduate School
Department	Clinical Research Curriculum Program
Degree	MS
Submission	Master's Thesis
Language	English
Research Field	Health Sciences, Medicine and Surgery
Keyword	Ventilator-associated events Mechanical ventilation Intensive care unit Tidal volume Quality metrics
Committee Chair / Thesis Advisor	Martin, Greg, Emory University Murphy, David J, Emory University
Committee Members	McGowan Jr., John E, Emory University Manatunga, Amita, Emory University

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