Lung Compliance

The ability of the lung to expand and recoil is compliance. When comparing traditional ARDS to COVID-19 ARDS, lung compliance is very important. Compliance can be divided into two types:

• Static compliance – lungs not moving and at rest (pressure is the only variable)
• Dynamic compliance – lungs moving during breathing

Certain disease processes affect lung compliance, by either decreasing or increasing compliance:

• Low lung compliance
  • Pulmonary fibrosis, due to collagen build-up which decreases lung elasticity
  • ARDS, due to atelectasis in dependent areas of the lung
• High lung compliance
  • Chronic obstructive pulmonary disease and emphysema, due to elastic recoil damage
  • COVID-19 ARDS (Gattinoni et. al., 2020)

Interventions for COVID-19 ARDS

Follow the Surviving Sepsis Campaign: Guidelines on the Management of Critically Ill Adults with Coronavirus Disease 2019 (COVID-19) and the First Update (January 2021).

*Perfusion is equally as important as ventilation.

• Intubate and extubate in a negative pressure room; staff should don appropriate personal protective equipment (PPE), preferably Powered Air Purifying Respirators (PAPRs); minimize number of staff in room.
• Use a low tidal volume (Vt) strategy; Vt 4-8 mL/kg of predicted body weight (most common 6 mL/kg).
• Target plateau pressure of less than 30 cm H₂O; higher levels significantly increase the risk of barotrauma.
  • If plateau pressure is greater than 30 cm H₂O, decrease PEEP or decrease Vt.
• Use PEEP and Vt needed to oxygenate the blood and ventilate the patient.
  • In mild ARDS, can start with lower PEEP.
  • In moderate to severe ARDS, consider higher PEEP strategy (10 cm H₂O or greater).
• Maintain SpO₂ no higher than 96%.
• Consider alternative modes of ventilation, such as pressure-limited modes or volume targeted pressure-controlled ventilation (remember, compliant lungs need less pressure).
• Use recruitment maneuvers; avoid using staircase (incremental PEEP) recruitment maneuvers.
• Proning for mechanically ventilated adults with COVID-19 and ARDS
  • Consider 12-16 hours/day.
  • Watch for hemodynamic and ventilation/perfusion instability for 1^st hour post proning and placing patient supine.
  • Proning results take longer to see than typical ARDS; results are more due to redistribution of perfusion and gravitational forces (Gattinoni, et. al., 2020).
  • Put cables and intravenous lines on one side, when possible.
  • If available, use a proning team.
• Avoid the use of inhaled nitric oxide.
• For patients who remain hypoxemic despite optimizing ventilation and other rescue strategies, attempt a trial of inhaled pulmonary vasodilator as a rescue therapy. If no rapid improvement in oxygenation, taper the treatment.
• Sedation
  • When proning, patients may require additional sedation to tolerate the prone position.
  • If patients continue to have ventilator dyssynchony despite optimizing ventilator settings and sedation, consider paralyzing the patient.
• Patients decompensate quickly, especially during weaning; use a very, very slow weaning process even if patient appears comfortable on low pressure support (PS) settings.
• Patients are coagulopathic; if using continuous renal replacement therapy (CRRT), consider frequent boluses of heparin versus infusion, or administration of argatroban pre-circuit.
• Consider tracheostomy if the patient is anticipated to be on the ventilator for over 14 days.  This is a highly aerosolized procedure so perform it in a negative pressure room. Consider trach teams if the volume of tracheostomies is high.
• In mechanically ventilated patients with COVID-19 and refractory hypoxemia despite optimizing ventilation, use of rescue therapies, and proning, attempt veno-venous extracorporeal membrane oxygenation (ECMO), if available, or refer the patient to an ECMO center. ECMO should only be considered for select patients with COVID-19 and severe ARDS.
• Pharmacotherapy (Alhazzani et. al, 2021)
  • Strong recommendations
    • Avoid using hydroxychloroquine.
    • Use a short course of systemic corticosteroids over not using corticosteroids.
    • Administer pharmacologic VTE prophylaxis.
  • Weak recommendations
    • For patients considered for corticosteroids, use dexamethasone over other corticosteroids.
    • For adults with severe COVID-19 who do not require mechanical ventilation, IV remdesivir is suggested and should be started within 72 hours of positive PCR or antigen test.
    • For adults who require mechanical ventilation for critical COVID-19, IV remdesivir is not suggested.
    • For adults with severe or critical COVID-19, it is suggested that convalescent plasma not be used outside of clinical trials.