Daniel Kolinsky MD, Nicholas M Mohr, MD MS & Brian M Fuller, MD, MSCI
‘Not again,’ you think to yourself as you listen to the dispatch report. “Call for inter-hospital transport. The patient is a 58 year-old male with a recent diagnosis of pneumonia, in the ED with acute respiratory failure, and is now intubated. Needs transport to the ICU.” This presentation is all too familiar. You remember transporting a similar patient two hours ago. How could you forget? He was hypoxic in the 80’s from his pneumonia.
On arrival to the ED, you get report from the nurses. During sign out you notice that the patient’s ventilator settings are different, specifically the tidal volume is substantially higher than the previous patient’s. You remember that lung-protective ventilation improves outcome in patients with ARDS. You wonder if the same lung-protective strategy should be used in patients at risk for ARDS?
Does the early use of lung-protective ventilation reduce the incidence of ARDS?
Pre-hospital care of the critically ill and injured patient often requires airway management and subsequent mechanical ventilation. Modern transport ventilators can support critically ill patients across the spectrum of illness severity, and also provide more reliable tidal volume and respiratory rates than manual bag-valve positive pressure ventilation.  Furthermore, they also free up the advanced care medic to perform other necessary patient care activities. 
Although portable mechanical ventilators have advanced critical care transport capabilities, they are not without risk. Ventilator associated lung injury (VALI) is a general term that refers to how a ventilator can propagate injury in already damaged lungs, or initiate injury in at-risk lungs.  Lung-protective ventilation aims to mitigate VALI by reducing the mechanical power applied to the lungs.  In patients with established ARDS, lung-protective ventilation with low tidal volume and effective PEEP is standard of care. [5-6] There is also a growing body of evidence from critically ill patients in the ICU and operating room demonstrating that low tidal volume ventilation [6-8 mL/kg predicted ideal body weight (PBW)] is associated with improved outcomes in mechanically ventilated patients without ARDS. [7-12] Although the data are not definitive, the current body of evidence suggests that using lung-protective ventilation strategies can mitigate VALI and prevent progression to ARDS.
Pre-hospital transport and the emergency department (ED) are the common entry points into the hospital for critically ill patients, yet only recently has research been devoted to mechanical ventilation in these arenas. Low tidal volume ventilation initiated in the ED is more likely to be continued in the ICU. [13-14] Additionally, it has been demonstrated that the mechanical ventilation strategy started in the pre-hospital setting is often continued in the ED and in the ICU.15 Together, these studies demonstrate that “ventilator inertia” is real and reinforce the importance of initiating lung protective ventilator strategies from the outset. Unfortunately, compliance with lung protective ventilation strategies in the pre-hospital setting (13%) and ED (range 27.1%-55.7%) leaves much room for improvement. [13-15]
As more studies show that earlier diagnoses with commensurate time-sensitive interventions for the critically ill improves outcomes, pre-hospital personnel will be expected to implement these new standards into practice.  Among these interventions, ventilator management is paramount as mechanical ventilation is one of the most common indications for intensive care. [17-18] Providers transporting these patients in the post-intubation period must think about the potential for VALI, as ARDS develops early in the course of critical illness. 
Setting the Ventilator
In order to determine the appropriate tidal volume for lung protective ventilation, one needs to know the patient’s gender and height in order to calculate the PBW. PBW can then be derived from a table for low tidal volume ventilation.
Other ventilator parameters to monitor when using lung protective ventilation are positive end-expiratory pressure (PEEP) and the plateau pressure. PEEP can be used to keep diseased alveoli open and limit physiologic shunting thus reducing hypoxemia. Setting the PEEP to 5 cm H2O and titrating PEEP and fraction of inspired oxygen (FiO2) combinations using a PEEP table is a simple way to maintain alveolar recruitment and limit derecruitment injury (i.e. atelectrauma). Targeting oxygen saturations of 88% or greater can limit the dangers of hyperoxia as well. Additionally, maintaining plateau pressures less than 30 cm H2O helps to limit alveolar stretch.
Take Home Points
Acknowledgement that the pre-hospital period is part of the continuum of critical care has led to a focus on implementing best care practices early. In the intubated patient, this includes ventilator management and institution of lung-protective ventilation. Currently, there is a growing body of evidence for using lung-protective ventilation to reduce VALI and to prevent to ARDS. Several large studies testing prophylactic lung protective ventilation are underway. [20-21] Their results will provide further insight into the use of early lung-protective ventilation to improve outcomes.
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