Ventilator Management of Adult Patients in the Emergency Department

Table of Contents

 

Placing a patient on a ventilator in the ED presents an emergency clinician with an array of decisions regarding the initial approach and ventilator settings. While ventilation can be a life-saving intervention, there are primary principles involving pressure settings, PEEP, flow rate, tidal volume, and blood gas.

Volume assist-control ventilation versus pressure-regulated volume control ventilation: what are the circumstances for each?

How does predicted body weight dictate the tidal volume?

How will adjusting the inspirator-expiratory ratio (I:E) affect patient comfort?

Based on current evidence, what are the circumstances where patients should not be given supplemental oxygen?

How will the obstructive physiology of COPD and asthma affect ventilator settings? What are the particular concerns you should watch for?

For patients with acute respiratory distress syndrome, what does the evidence say on higher-PEEP or lower-PEEP strategies, and what are the indications for paralytics, recruitment maneuvers, and proning?

How is ARDS in patients with coronavirus disease infection different from what has been seen before? Is there good evidence on how to manage these patients?

What are the best ways to monitor and manage ventilated patients: pulse oximetry, waveform capnography, assessing for breath-stacking?

1. Abstract
2. Case Presentations
3. Introduction
4. Critical Appraisal of the Literature
5. Prehospital Care
6. Approach to Initial Ventilator Settings
   1. Modes of Ventilation
      1. Volume Assist-Control Mode
      2. Pressure-Regulated Volume Control
         • Tidal Volume
         • Inspiratory Peak Flow Rate (Inspiratory Time)
         • Respiratory Rate
         • Positive End-Expiratory Pressure
         • Fraction of Inspired Oxygen
         • Inspiratory to Expiratory Time (I:E Ratio)
   2. Other Modes of Ventilation
      1. Synchronous Intermittent Mandatory Ventilation With Pressure Support
      2. Airway Pressure Release Ventilation
   3. Oxygen Delivery
7. Approach to Specific Types of Patients Requiring Mechanical Ventilation
   1. Obstructive Physiology (Asthma and Chronic Obstructive Pulmonary Disease)
   2. Acute Respiratory Distress Syndrome
      1. Use of Paralytic Agents in ARDS
      2. Recruitment Maneuvers in ARDS
      3. Prone Positioning in ARDS
      4. Nontraditional Ventilator Settings in ARDS
   3. ARDS and Coronavirus Disease Infection
   4. Severe Metabolic Acidosis
8. Monitoring and Making Changes to the Ventilator Settings
   1. Arterial Blood Gas
   2. Pulse Oximetry
   3. Waveform Capnography
   4. Ventilator Pressures
   5. Assessing for Breath-Stacking
9. Special Populations
   1. Obese Patients
10. Controversies and Cutting Edge
    1. Extracorporeal Membrane Oxygenation
    2. Esophageal Pressure Monitoring
11. Summary
12. Risk Management Pitfalls in Mechanical Ventilation in the Emergency Department
13. Case Conclusions
14. Clinical Pathway for Ventilator Management in the Emergency Department
15. Tables and Figures
    1. Table 1. Predicted Body Weight for Females of Various Heights and Associated Tidal Volumes
    2. Table 2. Predicted Body Weight for Males of Various Heights and Associated Tidal Volumes
    3. Table 3. Examples of Initial Ventilator Settings for Obstructive Physiology (Asthma/COPD), Volume Assist-Control Mode
    4. Table 4. Examples of Initial Ventilator Settings for ARDS Patients, Volume Assist-Control Mode
    5. Table 5. ARDSNet Trial FiO2/PEEP (cm H2O) Protocol, Lower Versus Higher Strategy
    6. Table 6. Example of Initial Ventilator Settings for Patients With a Severe Metabolic Acidosis, Volume Assist-Control Mode
    7. Table 7. Scenarios and Their Associated Peak Pressure and Plateau Pressure Changes
    8. Figure 1. Normal Output of Waveform Capnography
    9. Figure 2. Waveform Capnography Demonstrating Bronchospasm
    10. Figure 3. Peak Versus Plateau Pressure
    11. Figure 4. Graph of Flow Versus Time
    12. Figure 5. An Expiratory Hold Demonstrating Auto-PEEP (Pressure Above the Set PEEP)
16. References

Abstract

There are a variety of ventilator options available to the emergency clinician, and decisions on choosing optimal settings will depend on the clinical circumstances. Understanding the latest literature in ventilator management can improve patient outcomes by ensuring optimal oxygenation and ventilation and reducing the potential for ventilator-induced lung injury. This article reviews the most appropriate ventilator settings for a variety of conditions in intubated adult patients presenting to the emergency department, and gives recommendations on monitoring the ventilated patient and making ventilator adjustments. An update on managing COVID-19-associated acute respiratory distress syndrome is also included.

Case Presentations

Your very first patient is wheeled into the resuscitation bay as you are walking through the doors to start your shift. A 30-year-old woman (5’3” tall, 120 kg) is in respiratory failure from an acute asthma exacerbation and requires a crash airway despite your best efforts to avoid endotracheal intubation. After intubation, the respiratory therapist asks for initial ventilator settings. You recall that these patients are at risk for breath-stacking and you start to devise your ventilator strategy...

Halfway into your shift, a 21-year-old man with type 1 diabetes mellitus presents, obtunded, with Kussmaul breathing. You start your standard resuscitation, but the patient requires endotracheal intubation, as he is unresponsive to all stimuli. You consider whether you should use the bag-valve mask during the apneic period during rapid sequence intubation...

At the end of your shift, a 50-year-old man who was seen 2 days ago at an outside hospital for pneumonia now presents in severe hypoxemic respiratory failure. The patient is intubated, but is difficult to oxygenate. A chest x-ray demonstrates good endotracheal tube placement, but bilateral diffuse infiltrates. You suspect acute respiratory distress syndrome and start thinking about the strategies you will use if your initial approach is ineffective in oxygenating the patient...

Introduction

When it becomes necessary to place a patient on a ventilator in the emergency department (ED), there are many options regarding ventilator settings, and understanding the strategies for each clinical scenario can improve patient outcomes.^1,2 A pre/post study on a multifaceted ED-based mechanical ventilator protocol found that initiating best ventilator management practice in the ED decreased mortality, duration of ventilation, and hospital length of stay.³

Fundamental to successful airway management is the optimization of oxygenation and perfusion prior to intubation and placement on a ventilator, if possible; failure to do this has been associated with an increased risk of peri-intubation cardiac arrest.^4,5 Most cases of intubation-related cardiac arrest occur within 10 minutes of intubation.⁶

Because patients require mechanical ventilation for a wide variety of conditions, the considerations and initial approach to ventilator management could be substantially different in different scenarios. This issue of Emergency Medicine Practice reviews general approaches to ventilator management, with a focus on specific conditions where a different approach to mechanical ventilation would be advantageous.

Critical Appraisal of the Literature

A literature search was performed using the PubMed Medical Subject Headings (MeSH) with key words respiratory distress syndrome (432 articles); ventilator-induced lung injury (72 articles); respiration, artificial (2528 articles); and ventilators, mechanical (66 articles) restricted to adults and trials in the past 10 years. Literature on randomized trials specific to the ED is relatively uncommon, as most are longitudinal studies performed in the intensive care unit (ICU). Many of the studies included patients who were enrolled in the ED, with the majority of the interventions carried out in the ICU. Nonetheless, there are supportive quasi-experimental (pre/post) and observational data with outcomes that mirror the randomized ICU-conducted trials. Therefore, it is reasonable to assume that the benefits found in the ICU ventilator trials are applicable to the ED population. Specific trials analyzing most individual components of ventilator management are lacking, except for trials regarding acute respiratory distress syndrome (ARDS), where literature is robust. All major trials on ventilator management were reviewed, as well as expert opinion articles regarding ED ventilator management.

Prehospital Care

If mechanical ventilation is within the scope of practice of the prehospital provider, the guidelines in this article apply. Most recent data show that hyperoxia in acutely ill medical patients is harmful, and expert recommendations advise following the same oxygenation guidelines in the prehospital setting as in the ED/inpatient setting by generally avoiding hyperoxia. (See the “Oxygen Delivery” section.)

If using bag-valve mask (BVM) ventilation for hypoxia during transport, utilize a positive end-expiratory pressure (PEEP) valve to provide PEEP where it is necessary, as adjusting PEEP on a ventilator. A PEEP valve may be integrated with the BVM or it may be an optional add-on, and it typically allows for the application of 0 to 20 cm H₂O of PEEP. PEEP provides pressure to the airways at the end of expiration, which can increase alveolar patency and improve oxygenation, especially in areas of shunting. Shunting refers to areas where alveoli are being perfused but not being ventilated (eg, shunting due to alveolar fluid accumulation in pulmonary edema, alveolar hemorrhage, pneumonia, etc). PEEP can keep these alveoli patent and participating in gas exchange. Following the same recommendations for PEEP as discussed in ventilated patients in the following sections is appropriate.

Risk Management Pitfalls in Mechanical Ventilation in the Emergency Department

1. “The patient with ARDS had difficulty oxygenating, so I increased the tidal volume to 12 mL/ kg as my first intervention.”

Increased tidal volumes have been shown to increase mortality in ARDS. Using lung-protective lower tidal volume strategies is preferred, using the FiO₂ and PEEP to maintain appropriate oxygenation. If this fails, prone positioning and/or APRV should be considered.

4. “This patient with severe DKA coded 5 minutes after I intubated him. I don’t understand why, since I used normal ventilator settings.”

Patients with severe metabolic acidosis need adequate respiratory compensation by using a high minute ventilation. Patients who receive longer-acting paralytics (such as rocuronium), are initially unable to over-breathe the ventilator since they are still paralyzed. Taking away their respiratory compensation with a lower minute ventilation after intubation can cause a precipitous decline in pH and lead to cardiac arrest.

10. “My patient with asthma was intubated, and the PaCO₂ was 70 mm Hg, so I increased the respiratory rate to increase his minute ventilation to ‘blow off’ some CO₂.”

Patients with asthma are at high risk for breath-stacking, and the high PaCO₂ reflects poor air movement from severe bronchospasm. Increasing the respiratory rate indiscriminately in this case is likely to lead to breath-stacking, which is dangerous. Monitoring the patient for breath-stacking is critical prior to any increases in respiratory rate, and hypercapnia in this situation should be tolerated as long as the pH remains above 7.20 (permissive hypercapnia).

Tables and Figures

References

Evidence-based medicine requires a critical appraisal of the literature based upon study methodology and number of subjects. Not all references are equally robust. The findings of a large, prospective, randomized, and blinded trial should carry more weight than a case report.

To help the reader judge the strength of each reference, pertinent information about the study, such as the type of study and the number of patients in the study is included in bold type following the references, where available. In addition, the most informative references cited in this paper, as determined by the author, are highlighted.

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