Mechanical Ventilation Practices and Low Tidal Volume Ventilation in Air Medical Transport Patients: The AIR-VENT Study

BACKGROUND: The management of mechanical ventilation critically impacts outcome for patients with acute respiratory failure. Ventilator settings in the early post-intubation period may be especially influential on outcome. Low tidal volume ventilation in the prehospital setting has been shown to impact the provision of low tidal volume after admission and influence out-come. However, there is an overall paucity of data on mechanical ventilation for air medical transport patients. The objectives of this study were to characterize air medical transport ventilation practices and assess variables associated with nonprotective ventilation. METHODS: This was a multi-center, nationwide (approximately 130 bases) retrospective cohort study conducted on consecutive, adult mechanically ventilated air medical transport patients treated in the preho-spital environment. Descriptive statistics were used to assess the cohort; the chi-square test compared categorical variables, and continuous variables were compared using independent samples t test or Mann-Whitney U test. To assess for predictors of nonprotective ventilation, a multivari-able logistic regression model was constructed to adjust for potentially confounding variables. Low tidal volume ventilation was defined as a tidal volume of ≤ 8 mL/kg predicted body weight (PBW). RESULTS: A total of 68,365 subjects were studied. Height was documented in only 4,186 (6.1%) subjects. Significantly higher tidal volume/PBW (8.6 [8.3–9.2] mL vs 6.5 [6.1–7.0] mL) and plateau pressure (20.0 [16.5–25.0] cm H₂O vs 18.0 [15.0–22.0] cm H₂O) were seen in the nonpro-tective ventilation group (P < .001 for both). According to sex, females received higher tidal volume/PBW compared to males (7.4 [6.6–8.0] mL vs 6.4 [6.0–6.8] mL, P < .001) and composed 75% of those subjects with nonprotective ventilation compared to 25% male, P < .001. After multivariable logistic regression, female sex was an independent predictor of nonprotective ventilation (adjusted odds ratio 6.79 [95% CI 5.47–8.43], P < .001). CONCLUSIONS: The overwhelming majority of air medical transport subjects had tidal volume set empirically, which may be exposing patients to nonprotective ventilator settings. Given a lack of PBW assessments, the frequency of low tidal volume use remains unknown. Performance improvement initiatives aimed at indexing tidal volume to PBW are easy targets to improve the delivery of mechanical ventilation in the prehospi-tal arena, especially for females.