Critical Care Alert: Mechanical Ventilator Protocol

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A Quasi-Experimental, Before-After Trial Examining the Impact of an Emergency Department Mechanical Ventilator Protocol on Clinical Outcomes and Lung-Protective Ventilation in Acute Respiratory Distress Syndrome

A 48-year-old male presents to the emergency department (ED) after being found unresponsive on a park bench with a bottle of alcohol nearby. By the time he arrives in the ED, he is moaning but does not follow commands. Vital signs show a temperature of 101.4 degrees Fahrenheit, heart rate of 127 beats per minute, blood pressure of 101/68 mmHg, respiratory rate of 18 breaths per minute, and an oxygen saturation of 82% on room air. A bedside glucose check is normal and portable chest X-ray is notable for diffuse infiltrates. He only improves to 86% on a facemask with a nasal trumpet in place and he remains lethargic, so the decision is made to intubate. Intubation is successful, and you turn over management of the ventilator to the respiratory therapist while you see another patient and call the ICU for admission. During your discussion with the intensivist, she asks, “Can you make sure the ventilator is set up appropriately for his ARDS?”

Article
Fuller BM, Ferguson IT, Mohr NM, et al. A Quasi-Experimental, Before-After Trial Examining the Impact of an Emergency Department Mechanical Ventilator Protocol on Clinical Outcomes and Lung-Protective Ventilation in Acute Respiratory Distress Syndrome. Crit Care Med. 2017;45(4):645-652.

Objective
To evaluate the impact of an ED mechanical ventilation protocol on clinical outcomes and adherence to lung-protective ventilation (LPV) in patients with acute respiratory distress syndrome (ARDS).

Background
ARDS is most commonly defined by the Berlin definition where a chest X-ray shows “bilateral opacities consistent with pulmonary edema that are not fully explained by effusions, lobar/lung collapse, or nodules/masses” and there is a decrease ratio of arterial oxygen content (PaO2) to the fraction of inhaled oxygen (FiO2), called the P/F ratio. Mild ARDS is defined by a P/F ratio between 200mmHg and 300mHg. Moderate ARDS ranges from 100mmHg to 200mmHg and severe ARDS has a P/F ratio less than 100mmHg.

It has been well-established that LPV can lessen ventilator-associated lung injury (VALI) and decrease mortality in ARDS thanks to ARDSNet. Despite this, compliance to LPV remains relatively low. According to the authors, VALI can occur very early after initiation of mechanical ventilation, making the ED the first site in prevention of ARDS in many intubated patients. ED boarding times are often sufficient to begin the process of developing ARDS, and the ventilator settings used immediately after intubation often influence the initial settings in the ICU. Studies have shown that LPV is under-utilized in the ED and that mechanical ventilation in the ED is associated with the development of ARDS.

Hypothesis
Implementing an ED-based mechanical ventilation protocol would reduce mortality in ARDS patients and increase use of LPV in both the ED and intensive care unit (ICU).

Design
▸ Quasi-experimental, before-after trial with implementation of ED LPV protocol at a single tertiary academic center
▸ Ventilation protocol, performed by ED staff:

  • Set tidal volume to ~6mL/kg predicted body weight (PBW) based on measured height
  • Limit plateau pressure to less than 30cm H2O
  • Set PEEP to at least 5cm H2O (greater for higher BMI)
  • Initial FiO2 of 0.30 to 0.40, titrated to a PaO2 of 55-60mmHg
  • Respiratory rate of 20-30 breaths per minute
  • Elevate head of bed to greater than 30 degrees and place naso- or oro-gastric tube

▸ Measured ventilator settings, airway pressures, pulmonary mechanics, and gas exchange variables in the ED and twice daily in the ICU for 2 weeks or duration of ARDS
▸ LPV defined as tidal volume less than or equal to 6.5mL/kg PBW

Inclusion criteria: Adult patients intubated and placed on mechanical ventilation in the ED who developed ARDS within 7 days of initial presentation

Exclusion criteria: Patients who were extubated or died within 24 hours, on chronic mechanical ventilation, had a tracheostomy, or were transferred to another hospital.

Primary outcome: In-hospital mortality

Secondary outcomes: Ventilator, ICU, and hospital-free days

Results:
▸ 229 patients included in final analysis
• 186 in pre-intervention group
• 43 in intervention group
• Majority of excluded patients did not develop ARDS

▸ Mean time to develop ARDS was 1.8 days
• 65 patients developed ARDS while in the ED
• 164 patients were diagnosed with ARDS after ICU admission

 

Comparison of Emergency Department Ventilator Settings

VARIABLEPRE-INTERVENTION GROUPINTERVENTION GROUPP VALUE
Tidal volume PBW (mL/kg)8.16.4<0.01
Lung Protective Ventilation (%)11.161.5<0.01
PEEP (cmH2O)58<0.01
Respiratory rate (bpm)16.520.7<0.01
FiO2 (%)10070<0.01
Elevated head of bed (%)37.191.8<0.01
PaO2 (mmHg)11385<0.01
Peak pressure (cmH2O)33.928.9<0.01
Plateau pressure (cmH2O)22.322.40.98

Outcomes
▸ Lung protective ventilation in the ED was the only predictor of receiving LPV in the ICU
▸ Ventilator settings were overall less likely to be lung protective in the ICU than in the ED in both groups
▸ Tidal volumes were 1.2mL/kg lower in the intervention group throughout the ICU course

Outcomes

OUTCOMEPRE-INTERVENTIONINTERVENTIONADJUSTED ODDS RATIOp
Mortality54.839.50.360.02
Ventilator-free days7.711.64.00.03
ICU-free days7.29.11.90.23
Hospital-free days4.05.71.60.20

Authors’ Conclusion and Limitations

  • Implementing a LPV protocol in the ED is feasible and associated with improved mortality in ARDS patients.
  • Initiating LPV in the ED likely decreased early VALI which lead to observed outcomes.
  • Observed benefit may have been greater if compliance with LPV had been greater in the ICU.
  • ARDS is not an ICU-specific process and focus on ventilator settings in the ED is critical.
  • Benefit (or harms) of LPV in patients without ARDS not addressed in this study.
  • Single-center study and small sample size limits external validity.
  • Protocol addressed several variables at once, which makes it impossible to know where the observed benefit is exactly coming from.

Our Conclusions and Applications for the Emergency Department

  • Standardizing ventilator settings with lung-protective protocols may be a reasonable practice to implement in the Emergency Department with significant potential benefits for ARDS patients.
  • Ideas behind protocols are not new; they just need to be implemented consistently.
  • Ventilator settings started in the ED tend to be carried over into the ICU.
  • Given that compliance with LPV was poor in both the ED and the ICU prior to the implementation of the protocol, it is difficult to know if ED LPV caused the decreased mortality or if ED LPV caused improved adherence in the ICU, which led to the observed benefit.
  • Improved adherence to LPV in the ICU may be an important target moving forward.
  • More data is needed on the effects of this protocol on patients who did not develop ARDS (and is being reported on in other papers by this author group).
  • Applying protocols such as the one described may not be appropriate for all patients, such as asthma patients, but more data is needed.
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