Invasive Mechanical Ventilation

Patients With or Under Investigation for COVID-19

Background

• Mechanical ventilation is required up to 10% of all patients with COVID-19. The ARDS picture of COVID-19 is unique. Many patients will present with “silent hypoxemia”; i.e. degree of hypoxemia is out of proportion to lung compliance. Because lung compliance is relatively preserved, the work of breathing may initially appear normal.

• In patients on nasal cannula, keeping SpO2 90 – 92% will facilitate early detection of worsening oxygenation, since oxyhemoglobin curve is steepest in this range

Indications

• Acute hypoxemic respiratory failure requiring > 6 L/min nasal cannula

• Acute hypercarbic respiratory failure

• Other conventional indications for mechanical ventilation

Contraindications

• Absolute: DNI

• Relative: None

Team & Equipment

• Respiratory Therapist

• CCRN

• Staff Intensivist

• Ventilator 

PPE

• ACE for aerosol-generative procedures

• Whenever possible, the ventilator controller/servo should be detached from the machine manifold and placed outside of the patient room (see photo below). This reduces entry/re-entry and utilization of PPE for routine ventilator management.

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Lung-Protective Ventilation

• All patients should receive mechanical ventilation with non-injurious tidal volumes (≤ 6 cc/kg ideal body weight) according to existing NIH ARDSNet protocols, using the High PEEP ladder (see below)

• Patients with COVID-19-ARDS appear to have a prompt and sustained response to PEEP, indicating the alveoli may be partially drowned but durably recruitable if an “open lung” approach of high PEEP is initiated early

• Checklist for Lung Protection (best outcomes when all 4 are met)

  • VT ≤ 6 cc/kg IBW

  • Plateau pressure ≤ 30

  • Driving pressure (Pplat – PEEP) ≤ 18

  • Minimal or no asynchrony  

• Staff intensivist will prescribe and actively manage ventilator settings to achieve desired clinical and physiologic outcomes

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Special Considerations

• ARDS with superimposed expiratory airflow limitation (asthma, COPD, CF)

  • Lung protective ventilation remains the priority

  • Higher risk of global overdistention/barotrauma due to incomplete lung emptying. Higher risk of regional overdistention/barotrauma due to heterogeneous lung emptying

  • Attention to expiratory waveform and periodic assessment for auto-PEEP

  • See protocol for Respiratory Treatment: Bronchodilators (Section ##). In general, bronchodilator treatments should be given as metered dose inhaler (MDI) puffs delivered in-line with the ventilator to minimize aerosolization. In some cases of severe bronchospasm, intravenous bronchodilators may be used.

  • Corticosteroids generally avoided for COVID-19-ARDS, but may be used in cases of acute, severe, and reversible airflow limitation

• ARDS with acute cor pulmonale (ACP)

  • ACP = acute right ventricular failure due to hypoxemic lung disease

  • Clues pointing to ACP: hemodynamic dysfunction with evidence of LV underfilling (high pulse pressure variation), high dead space fraction (wide discrepancy between etCO2 and pCO2), TTE shows RV dilatation

  • ACP occurs in 20% of ARDS cases and requires specific RV protective priorities. Failure to unload the RV is independently associated with mortality.

  • RV protective ventilation checklist

    • Keep pCO2 ≤ 48 (respiratory acidosis causes pulmonary vasoconstriction)

    • Decreased alveolar distending pressure (keep Pplat < 27) by lowering VT or PEEP

    • Decrease hypoxic pulmonary vasoconstriction

  • These patients will most likely improve with proning (see Prone Ventilation protocol)

• ARDS with severe refractory hypoxemia

  • Severe hypoxemia is usually due to lung derecruitment owing to worsening ARDS. However, a significant fraction of patients with COVID-19 may have hypoxemia due to decreased lung perfusion in the setting of cardiogenic shock or acute cor pulmonale.

    • Limited TTE (can be at point of care) to evaluate cardiac function

  • Prone Ventilation

    • Initiate when P/F < 150 on FIO2 = 60% and PEEP = 10

    • Follow Prone Ventilation protocol (here) for further guidance

  • Airway Pressure Release Ventilation (APRV)

    • Initial settings – PHigh = 30, THigh = 5 sec, PLow = 0, PLow = 0 - 1 sec

    • Staff intensivist will prescribe and titrate APRV settings

    • Follow APRV protocol (here) for further guidance

  • Referral for ECMO if possible ​

Prophylaxis

• Nutrition: early enteric trophic feeding with escalation as tolerated

• Peptic Ulcer Disease: H2 receptor antagonist

• VAP: AVAMC ICU VAP bundle

  • Daily sedation holiday and weaning assessment as soon as feasible

  • Oral hygiene with chlorhexidine q4 hours

  • HOB > 30°

  • Continuous aspiration of subglottic secretions (CASS) if available

• DVT: AVAMC ICU standard thromboprophylaxis

  • Low dose unfractionated heparins (LDUH) q8 – q12 hours OR

  • Low dose low molecular weight heparins (LMWH) q24 hours OR

  • Fondaparinux

  • SCD if excessive bleeding risk precludes anticoagulation

Detached and externalized ventilator display/servo

High PEEP ladder and ARDSNet protocol