Acute respiratory distress syndrome (ARDS): who’s at risk and ED-relevant management

Authors: Lucy Luu (EM Resident Physician, UT McGovern Medical School) and Hilary Fairbrother (Visiting Associate Professor of Emergency Medicine, Director of UME, UT McGovern Medical School) // Edited by: Alex Koyfman, MD (@EMHighAK) and Brit Long, MD (@long_brit)

Case

A 21-year-old male with no past medical history presents to the ED with shortness of breath that worsens with exertion. His symptoms started about one week ago but have worsened today. The patient was seen in the ED last week after being involved in a bicycle accident. He suffered multiple left-sided rib fractures without a pneumothorax and was discharged home with an incentive spirometer and multimodal pain meds. He has mild left-sided chest pain but no fever or cough. The patient is afebrile, tachypneic, tachycardic, diaphoretic, and hypoxic (69% O2 sat on room air and 88% on nonrebreather). He has bilateral diffuse crackles on exam.


Background

Acute respiratory distress syndrome (ARDS) is a condition of acute inflammatory lung injury that causes non-cardiogenic pulmonary edema by increasing alveolar capillary permeability. The thickened diffusion barrier leads to decreased lung compliance, inefficient gas exchange, increased physiological dead space, and subsequently hypoxemia.1,2

Diagnosis criteria for ARDS – Berlin definition (all 4 components must be present):1

  1. Acute onset (1 week or less)
  2. Hypoxemia (PF ratio* < 200 mmHg with a minimum of 5 cmH2O PEEP (or CPAP))
  3. Pulmonary edema (bilateral opacities on CXR)
  4. Non-cardiogenic (not caused by cardiac failure)

*PF (PaO2/FiO2) ratio is the ratio of arterial oxygen partial pressure to fractional inspired oxygen. PaO2 value can be obtained from ABG, and FiO2 is 0.21 at sea level (room air) or depends on supplemental O2.1

ARDS severity (mortality) can be categorized into mild, moderate, severe based on PaO2/FiO2 ratio.1

Who’s at Risk

Common risk factors (direct and indirect) of ARDS:2

  • Direct lung injury: pneumonia, gastric aspiration, pulmonary contusion, near drowning, inhalation injury
  • Indirect lung injury: sepsis, shock, acute pancreatitis, burns, crush injury, fat embolism, and massive transfusion

When Do We See These Patients in the ED?

Most of the times, ARDS does not develop or is not identified until patients are mechanically ventilated in the ICU. However, we may still encounter ARDS in the ED in critical patients who have been boarded in the ED for a long period, in patients who have bounced back from a recent observation period, in patients who have been discharged after a trauma, or in patients who failed to seek healthcare earlier in their disease course.

Potential Mimics

ARDS can be misdiagnosed since there are many conditions that may present as acute hypoxemic respiratory failure with bilateral alveolar infiltrates. The differential diagnoses for ARDS include cardiogenic pulmonary edema, severe multilobar pneumonia, acute exacerbation of pulmonary fibrosis, diffuse alveolar hemorrhage, idiopathic acute eosinophilic pneumonia, dissemination of lymphoma/leukemia, and several others. Since ARDS is a diagnosis of exclusion, aside from history and exam findings, certain diagnostic tests may be required before the correct diagnosis is reached. This may include ECHO, right heart catherization, flexible bronchoscopy, and/or lung biopsy, completed in the ICU.3

ED Management

In the ED, the primary focus is supportive care, with several other treatments:

  • Supplemental O2
  • Treat the underlying condition (pneumonia, sepsis, etc.)
  • Tempered diuresis – non-cardiogenic pulmonary edema takes much longer to respond to treatment than cardiogenic CHF, so avoid being overly aggressive with diuresis, as this may worsen underlying shock and increase likelihood of multi-organ failure4
  • Conservative fluid management strategy – for ARDS patients not in shock, the goal to obtain zero fluid balance4
  • Be cautious when using non-invasive positive pressure ventilation – the benefit of NIPPV in the initial management of ARDS remains controversial. An observational cohort study by Dr. Rana has shown that there is a high failure rate of the initial NIPPV therapy in medical critically ill patients (underlying shock, metabolic acidosis and severe hypoxemia) with ARDS/ALI, and it shows that NIPPV is associated with twice the mortality rate5,6
  • Consider intubation

Mechanical ventilation7,8,9

  • Use low tidal volume (6-8 mL/kg)* to avoid barotrauma
  • Avoid excessive oxygen exposure (clinical goals: FiO2 < 0.40, SpO2 > 88-90%, PaO2 > 55-60 mmHg)
  • Maintain head of bed elevation while mechanically ventilated to reduce the risk of developing pneumonia

* Ideal body weight (not actual body weight) should be used to calculate ventilator tidal volume.

 

Next Steps for the ICU

Critical steps and standards of care have been identified when treating patients with ARDS.

There is a focus on how these patients are ventilated including low tidal lung volumes, volume/pressure controlled ventilation, prone positioning, sedation, and neuromuscular blockade. There is research being done on respiratory rate and longer I:E ratios. PEEP is also used for alveolar recruitment, though this is controversial.

Early and extensive infection control is also indicated for patients with ARDS. Focused imaging may be used along with laboratory hematologic and urinary testing to attempt to identify a source of infection. Endocarditis must also be considered as a potential source of infection and ruled out with a transesophageal echo. Bronchoalveolar lavage should be performed to look for infection.

Finally, tight control of fluid administration along with the use of furosemide also seems to improve lung function, though it has not improved 60-day mortality.10

Currently, research done on various pharmacotherapies (activated protein C, beta-2 adrenergics, inhaled vasodilators, corticosteroids, etc.) has not demonstrated improved outcomes, with no improvement in mortality.11

Initial ventilator settings:

Back to the Case

CXR was obtained and showed diffuse bilateral patchy airspace opacities.

The patient was placed on BiPAP with FiO2 50% with SpO2 99%. His ABG returned with pH 7.36, PaCO2 34, PaO2 89, HCO3 19. The PF ratio was calculated to be 175, placing the patient in moderate severity for ARDS. After calling MICU for admission, the ICU fellow requested the patient to be intubated for ARDS protocol ventilation. Patient was eventually extubated and discharged after 6 days of hospitalization.

We do not encounter patients with ARDS often in the emergency room. However, it is important to recognize and diagnose this condition early in order to provide life-saving interventions before patients deteriorate.            


 Take Home Points

  • Know the accepted Berlin definition of ARDS
  • Recognize risk factors
  • Treat underlying causes
  • Gentle diuresis and conservative fluid therapy approach may improve survival
  • Use NIPPV with caution
  • Use low tidal volume (based on ideal body weight) in mechanical ventilation to minimize the risks of ventilation-induced lung injury

 References/Further Reading

  1. “Acute Respiratory Distress Syndrome (ARDS)”. https://lifeinthefastlane.com/ccc/acute-respiratory-distress-syndrome-ards/
  2. Siegel, M. “Acute respiratory distress syndrome: Epidemiology, pathophysiology, pathology, and etiology in adults.” UpToDate
  3. Siegel, M. “Acute respiratory distress syndrome: Clinical features and diagnosis in adults.” UpToDate
  4. Roch et al. “Fluid management in acute lung injury and ARDS.” Annals of Intensive Care 2011; 1:16.
  5. Garpestad E, Hill N. “Noninvasive ventilation for acute lung injury: how often should we try, how often should we fail?” Crit Care 2016; 10(4): 147-148.
  6. Rana et al. “Failure of noninvasive ventilation in patients with acute lung injury: observational cohort study.” Crit Care. 2016; 10(R79): 1-5.
  7. Fuller et al. “Mechanical Ventilation and ARDS in the ED”. CHEST 2015; 148 (2): 365-374.
  8. Hodder, R. “Critical care in the ED: potentially fatal asthma and acute lung injury syndrome.” Open Access Emergency Medicine 2012:4 53-68.
  9. The ARDS Network. “Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome.” N Engl J Med 2000; 342 (18): 1301-8.
  10. Bein, T. et. al. “The standard of care of patients with ARDS: ventilatory settings and rescue therapies for refractory hypoxemia.” Intensive Care Med.2016; 42:699-711.
  11. Calfee and Matthay, MDs. “Nonventilatory Treatments for Acute Lung Injury and ARDS”. CHEST 2007; 131: 913-920.

Leave a Reply

Your email address will not be published. Required fields are marked *