Invasive Mechanical Ventilation
Patients With or Under Investigation for COVID-19
Background
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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.
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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
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Acute hypoxemic respiratory failure requiring > 6 L/min nasal cannula
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Acute hypercarbic respiratory failure
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Other conventional indications for mechanical ventilation
Contraindications
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Absolute: DNI
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Relative: None
Team & Equipment
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Respiratory Therapist
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CCRN
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Staff Intensivist
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Ventilator
PPE
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ACE for aerosol-generative procedures
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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.
Lung-Protective Ventilation
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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)
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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
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Checklist for Lung Protection (best outcomes when all 4 are met)
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VT ≤ 6 cc/kg IBW
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Plateau pressure ≤ 30
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Driving pressure (Pplat – PEEP) ≤ 18
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Minimal or no asynchrony
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Staff intensivist will prescribe and actively manage ventilator settings to achieve desired clinical and physiologic outcomes
Special Considerations
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ARDS with superimposed expiratory airflow limitation (asthma, COPD, CF)
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Lung protective ventilation remains the priority
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Higher risk of global overdistention/barotrauma due to incomplete lung emptying. Higher risk of regional overdistention/barotrauma due to heterogeneous lung emptying
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Attention to expiratory waveform and periodic assessment for auto-PEEP
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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.
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Corticosteroids generally avoided for COVID-19-ARDS, but may be used in cases of acute, severe, and reversible airflow limitation
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ARDS with acute cor pulmonale (ACP)
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ACP = acute right ventricular failure due to hypoxemic lung disease
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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
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ACP occurs in 20% of ARDS cases and requires specific RV protective priorities. Failure to unload the RV is independently associated with mortality.
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RV protective ventilation checklist
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Keep pCO2 ≤ 48 (respiratory acidosis causes pulmonary vasoconstriction)
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Decreased alveolar distending pressure (keep Pplat < 27) by lowering VT or PEEP
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Decrease hypoxic pulmonary vasoconstriction
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These patients will most likely improve with proning (see Prone Ventilation protocol)
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ARDS with severe refractory hypoxemia
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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.
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Limited TTE (can be at point of care) to evaluate cardiac function
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Prone Ventilation
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Initiate when P/F < 150 on FIO2 = 60% and PEEP = 10
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Follow Prone Ventilation protocol (here) for further guidance
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Airway Pressure Release Ventilation (APRV)
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Initial settings – PHigh = 30, THigh = 5 sec, PLow = 0, PLow = 0 - 1 sec
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Staff intensivist will prescribe and titrate APRV settings
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Follow APRV protocol (here) for further guidance
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Referral for ECMO if possible
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Prophylaxis
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Nutrition: early enteric trophic feeding with escalation as tolerated
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Peptic Ulcer Disease: H2 receptor antagonist
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VAP: AVAMC ICU VAP bundle
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Daily sedation holiday and weaning assessment as soon as feasible
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Oral hygiene with chlorhexidine q4 hours
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HOB > 30°
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Continuous aspiration of subglottic secretions (CASS) if available
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DVT: AVAMC ICU standard thromboprophylaxis
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Low dose unfractionated heparins (LDUH) q8 – q12 hours OR
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Low dose low molecular weight heparins (LMWH) q24 hours OR
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Fondaparinux
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SCD if excessive bleeding risk precludes anticoagulation
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Detached and externalized ventilator display/servo
High PEEP ladder and ARDSNet protocol