49 Lung Protective Ventilation is Uncommon During Aeromedical Transport: An Observational Study

Abstract

Mechanical ventilation is common during aeromedical transport, and emerging data suggests that routine application of low-tidal volume lung protective ventilation may decrease complications of critical illness. This study was designed to describe mechanical ventilation practices for intubated patients transported by air ambulance and to assess the effect of mechanical ventilation strategy on clinical outcomes. Our hypotheses were (1) lung protective ventilation would be uncommon in the out-of-hospital setting, (2) out-of-hospital ventilation practices would influence initial ventilator management in the hospital, and (3) non-lung protective ventilation would increase the incidence of acute respiratory distress syndrome (ARDS). Retrospective, observational cohort study of all adult patients transported by a university-affiliated aeromedical transport service to a 711-bed tertiary academic medical center (July 2011 to May 2013). Patients were excluded for (1) death within 72 hours of hospital arrival or (2) admission to an outside hospital prior to transfer. Data was collected on ventilator settings and clinical outcomes from the electronic medical record. Univariate descriptive analyses were performed and linear regression was used to test the hypothesis that hospital ventilation strategy was influenced by out-of-hospital ventilation settings. The association between lung protective ventilation and clinical outcomes was measured with a logistic regression model. Lung protective ventilation was defined a priori as ≤ 8 mL/kg predicted body weight (PBW). The Institutional Review Board approved the study under waiver of informed consent. A total of 235 patients were included in the analysis. The majority of patients (57%) were ventilated solely with bag-valve ventilation during transport. The mean tidal volume of mechanically ventilated patients was 8.6 mL/kg PBW (SD 1.7 ml/kg PBW). Lung-protective ventilation was used in 13% of patients (n= 31). Patients receiving non-protective ventilation during aeromedical transport were significantly more likely to be exposed to non-protective ventilation in the emergency department (P<0.001) and intensive care unit (P=0.015). Out-of-hospital lung-protective ventilation was associated with a decrease in mechanical ventilation days (2.1 versus 3.6 day, P=0.027), but there was no association with the incidence of ARDS, length of stay, or mortality. Low tidal volume ventilation was rare during aeromedical transport and was associated with a “therapeutic momentum” of non-lung protective ventilation during early in-hospital care. Prehospital tidal volumes were associated with a decrease in mechanical ventilation days, but not associated with development of ARDS or mortality. The out-of-hospital aeromedical environment offers a unique opportunity to study the impact of early prophylactic therapies on complications of critical illness, and further study is needed to better characterize the role of lung protective ventilation on ARDS prevention.