Mechanical Ventilation & Extubation

Background

Principles of mechanical ventilation are generally unchanged and should generally follow ARDS guidelines.

Helpful Commentaries/Articles

Fan E, Beitler JR, Brochard L, Calfee CS, Ferguson ND, Slutsky AS, Brodie D. COVID-19-associated acute respiratory distress syndrome:
is a different approach to management warranted? Lancet Respir Med 2020;8:816–821.

Gattinoni L, Coppola S, Cressoni M, Busana M, Rossi S, Chiumello D. COVID-19 does not lead to a “typical” acute respiratory distress syndrome. Critical Care Med 2020;201(10):1299-1300.

Brochard L, Slutsky A, Pesenti A. Mechanical ventilation to minimize progression of lung injury in acute respiratory failure. Am J Resp Crit Care Med 2017;195(4):438-442.

Gattinoni L, Chiumello D, Caironi P, Busana M, Romitti F, Brazzi L, Camporota L. COVID-19 pneumonia: different respiratory treatments for different phenotypes? Intensive Care Medicine 2020;46:1099-1102.

Marini JJ, Gattinoni L. Management of COVID-19 Respiratory Distress. JAMA 2020;323(22):2329-2330.

Tobin MJ, Laghi F, Jubran A. Caution about early intubation and mechanical ventilation in COVID-19. Annals of Intensive Care 2020;78(10).

Kallet RH. A comprehensive review of prone position in ARDS. Resp Care 2015;60(11):1660-1687.

General Principles

After intubation, while the patient is still paralyzed, we recommend setting PEEP 10, measuring height and setting the tidal volume to 6 ml/kg/PBW, then measuring generated P_plat, compliance and driving pressure (ΔP=P_plat-PEEP).
- Driving pressure should be kept less than 14.
- P_plat should be less than 30.
- Do not ventilate to normalize ABGs (pH, P_aCO₂). Permit hypercarbia.
Special consideration is recommended for unique situations observed in the COVID patient which appear to uncouple respiratory drive, compliance and oxygenation in a manner not seen in the classic ARDS patient. For example:
- Normal compliance with moderate to severe hypoxemia
- High respiratory drive with mild to moderate hypoxemia
In the spontaneously breathing patient with high respiratory drive, consider the risks of self-injurious negative intra-pleural pressure in decision making around sedation and ventilation strategies.
In patients with normal lung compliance (greater than 40), or ΔP less than 14, consider liberalizing the guideline tidal volume target of 6ml/kg/PBW target and allow tidal volumes of 8ml/kg/PBW if this allows the patient to remain more awake and on less sedation.
Patients who will not benefit from invasive ventilation/critical care should not be offered or initiated on mechanical ventilation. This decision rests with the specialist physician, not the patient or family/SDM.
Duration of ventilation tends to be prolonged and many patients require tracheostomy.

Considerations in setting PEEP

PEEP tables and default high PEEP strategies for hypoxemia may not be optimal in COVID-19 patients, particularly in the early phase (where compliance is relatively normal).
PEEP should be titrated to individual patient physiology and lung mechanics.
In patients with normal (greater than 40) or near-normal compliance, care should be taken in setting PEEP.
- While higher PEEP settings may improve oxygenation, if compliance drops as a result of increased PEEP (driving pressure increases), this may be injurious.
- In addition, this can impact cardiac output due to increased pressure on the RV.
Consider the need for higher PEEP in the obese patient.
High PEEP titration tables or decremental PEEP titration studies may be appropriate in the classic ARDS patient with recruitable dependent lung areas. See ARDS guidelines.

Sedation and Paralysis

Sedation is not required in all patients.
Depth of sedation should be tailored to patient and mechanical ventilation requirements.
Routine paralysis for hypoxemia is not recommended but paralysis may be required to facilitate optimal mechanical ventilation.
If paralysis is required, we recommend attempting to stop paralysis daily where possible and restarting only if necessary.
Shortages of sedative and paralytic medications are expected. Local strategies are recommended for conservation and substitution.

Proning Considerations

When to initiate proning:
- If compliance is acceptable, marked by P_plat less than 25-30 and ΔP less than 12-14, use prone position for refractory hypoxemia (P/F <100) after optimization of PEEP and sedation.
- If compliance is low, use the prone position as per ARDS guidelines (P/F <150) after optimization of PEEP and sedation.
  - In these patients, proning is expected to improve oxygenation as well as lung mechanics thus reducing injurious ventilation.
Optimal PEEP should be reassessed once the patient is stabilized in the prone position.
Prone positioning does not always require paralysis.
The depth of sedation is patient-specific.
Consider stopping proning when:
- PF ratio above 150 for 6 hrs in the supine position AND PEEP is less than or equal to 12;
- Ventilation in the supine condition is possible with safe lung mechanics (ΔP < 14, Pplat < 30).
- A repeated attempt at proning results in minimal or no improvement in PF (many clinicians use 20% improvement).

Inhaled Pulmonary Vasodilators (Flolan, iNO)

In the classic ARDS patient, if available, inhaled Flolan/iNO may be used as a rescue strategy for refractory hypoxemia in patients who have optimal sedation and mechanical ventilation and have been trialled in the prone position (unless contraindicated).
Additional considerations could include documented right heart failure or intra-cardiac R to L shunt with associated hypoxemia.

Extracorporeal Membrane Oxygenation (ECMO)

ECMO is a limited resource.
ECMO specialists at Toronto General Hospital (ON) are available for consultation through Criticall and are happy to discuss any case. TGH has the capacity to manage the increasing volume of calls for consultations.
In general, an earlier referral for ECMO based on the patient trajectory is preferred by the ECMO program in order to allow safe patient transfer to the ECMO centre without cannulation.
Mechanical ventilation should be optimized per the ARDS order set utilizing:
- Deep sedation, paralysis
- Prone positioning
- Trial of recruitment maneuver and high PEEP
- Trial of inhaled flolan/iNO (if available)

Indications for ECMO Consultation

Severe and refractory hypoxemia (P/F <100 AND FiO2 above 80%) OR
P_plat above 30 despite optimization OR
Refractory hypercarbia (PaCO2 > 60 and pH < 7.15 for > 6 hrs).

Relative Contraindications for ECMO

These criteria are general guidance and reflect those who are unlikely to benefit from ECMO with COVID pneumonia / ARDS. Expert consultation is advised in cases where the intensivist thinks the patient may benefit from ECMO.

BMI above 40 kg/m2 or weight above 125 kg
Age above 55 particularly with significant comorbidities
*each patient should be considered individually
Cardiogenic shock as part of the late evolution of COVID-19 infection
Refractory shock
Significant comorbidity burden

Extubation

Once a patient meets extubation criteria, we are planning to follow this protocol.
Move the patient into a negative pressure room or bring HEPA-filter into the room.
Staff in the room in airborne precautions (extubation is considered AGMP).
1 hour after extubation, resume droplet contact precautions.
If the patient fails and requires re-intubation, follow the COVID intubation process.
For post-extubation stridor, a short trial of heliox with a Tavish mask (<2 hrs) would be an acceptable alternative to CPAP. No good evidence exists to recommend this but it makes physiologic sense and may be used if clinically appropriate.

Tracheostomy

Tracheostomy for COVID-19 positive patients failing to wean from mechanical ventilation will be performed once the patient has had 2 endotracheal aspirates at least 24 hours apart.

*Tracheostomy document link*

Palliation of the ventilated patient with COVID

We recognize that some patients with COVID will die.

Once a decision has been made to transition to comfort care, this protocol will be instituted.
If out of isolation in ICU (not COVID+ or PUI), the patient would receive typical palliation including extubation and does not require additional isolation precautions.
Administer appropriate dosage of either morphine or fentanyl targeted to the relief of air hunger or dyspnea and relief of pain.
Give adjunctive medications if required (e.g. midazolam, haloperidol)
When the patient is comfortable and the respiratory rate has slowed, turn the ventilator onto SBT settings at FiO2 0.21.
If the patient remains comfortable, without evidence of pain, awareness or respiratory distress perform the following steps, use COVID extubation protocol (above).
Continue to monitor patients and provide bolus doses of opiates and benzodiazepines as needed.

Care of the Deceased Patient Under Investigation or with confirmed COVID

Legend
PEEP: positive end-expiratory pressure
P_plat: plateau pressure
Driving Pressure (ΔP) = P_plat – PEEP
PBW: predicted body weight
PF Ratio: ratio of partial pressure of arterial oxygen (PaO2) to fraction of inspired oxygen (FiO2)