I have spent more than 20 years in academic critical care and have begun to attend every three to four weeks in our ICU where COVID-19 cases are ever increasing. As of today, we have no prospective randomized studies to demonstrate critical care techniques that improve outcomes in patients with COVID-19. Here is a bit of what I’ve seen in the area of respiratory management.
Permissive hypoxia: A common observation is that patients with COVID-19 can exhibit profound hypoxemia, that historically would have led to escalation of therapies and intubation, without presenting with the typical distress. If a patient is not working excessively hard to breathe, but exhibits very low oxygen levels, trials of high-flow oxygen by nasal cannula or non-invasive ventilation, and proning (when feasible) should be considered first. Intubation may be reserved for patients with signs of tissue hypoxia (lactic acidosis) or hyperventilation likely to eventuate in fatigue or cardiopulmonary collapse.
High-flow oxygen and non-invasive ventilation: To date, healthcare systems have been reluctant to provide patients with COVID-19 high-flow oxygen due to worries that high-flow increases aerosolization of the pathogen. Some institutions have taken to intubating patients if they fail nasal cannula up to five-six liters/minute; without attempting the normal sequence to trial high-flow oxygen or noninvasive ventilation. Mortality associated with invasive ventilation is very high (80 percent in China, roughly 40-50 percent in the U.S.). There is no data to indicate whether ALL excess mortality with intubation is related to such patients simply being more ill, or because some are intubated who could be supported with non-invasive techniques thereby exposing them unnecessarily to the higher risks of invasive ventilation. I advocate treating patients with COVID-19 the same as other patients, including trials of high-flow oxygen and/or non-invasive ventilation, before resorting to intubation. Also, these patients have very high respiratory rates that can remain stable (either have high dead space or high VCO2); we need to recalibrate what constitutes criteria for intubation for “work of breathing.” Here, non-invasive ventilation is very helpful (and I’ve noticed high respiratory rates with high tidal volumes without intubating). Healthcare workers should be safe if we practice compulsive, careful hygienic contact techniques. During my last rotation, we clearly averted intubation in several patients who would otherwise have been intubated.
Proning: There is rapidly accruing anecdotal data that proning before intubation: 1) improves oxygenation and 2) averts the need for intubation in patients who otherwise would have been intubated. These have been mentioned in newspaper articles and shared anecdotes; but so far there have not been peer-reviewed papers available for review. Rotational therapy helps re-recruit dependent, atelectatic segments and redirects more blood to well ventilated segments. There are a number of approved research protocols for attempting proning of non-intubated patients before resorting to intubation.
It is critical to note that ARDSnet principles have been applied empirically to patients with COVID-19 with no data demonstrating efficacy. The underlying assumption is that COVID-19 is diffuse acute lung injury, but that does NOT appear to be the case.
Naturally, clinicians have approached this unknown using therapies that have been tested for other diseases in the past. And because some patients with COVID-19 pneumonia have diffuse, relatively homogenous lung lesions, it was assumed that ARDSnet ventilator techniques (and adjunct measures like proning and neuromuscular blockade) was the best starting point. But it is possible that these techniques are harmful in some patients.
I recently had a patient, transferred from a center that is overwhelmed with COVID-19 cases who arrived on assist control 20 bpm/Vt 400 ml/80% FiO2/14 PEEP. Within 10 minutes of case review and careful bedside titrations, his oxygenation remained the same on 10 bpm/500 ml/50% FiO2/5 PEEP. He passed a pressure support trial and was successfully extubated the following day. For him, the ARDSnet approach had trapped him on the ventilator.
Several similar cases also didn’t conform to typical acute lung injury features. Their infiltrates were patchy, not bilateral/homogenous. Despite severe shunt, their lung compliance was near normal and bedside PEEP escalation trials worsened hypoxemia. Little is known about pathology of COVID-19 pneumonia, but CT studies show that patchy infiltrates are typical in many, if not a majority, of patients. Application of PEEP in focal lung shunt (pneumonia) can markedly worsen shunt by redistributing blood flow away from alveoli where PEEP is acting to compress capillaries, to flooded/collapsed segments that are not impacted by PEEP. Since the radiographic features of many COVID-19 pneumonitis patients are not diffuse/homogenous but rather patchy/focal, it explains why PEEP and ARDSnet aren’t appropriate for every case. Finally, notwithstanding the very high mortality of Chinese ventilated patients, it was found that, “In Wuhan, patients with acute hypoxemic respiratory failure due to COVID-19 have a poor tolerance to high PEEP, likely as the result of the direct and severe lung damage by the virus and inflammatory reactions”. While this observation does not discount the utility of ARDSnet for appropriate patients, it is consistent with the concepts presented above.
Primary considerations for respiratory management of patients with COVID-19 pneumonia:
- While proning results have not been published, all anecdotes suggest that many patients — before and after intubation — experience improved oxygenation with rotational therapy.
- In light of the very high morbidity and mortality associated with intubation, consider intubation as a last resort. Consider both proning and tolerating lower-than-normal oxygenation if the patients is tolerating it well. Consider a trial of high-flow oxygen or non-invasive ventilation (with extra attention to staff safety). All in an attempt to temporize and prevent intubation when possible.
- While ARDSnet ventilator settings may be appropriate for patients with diffuse lung lesions, consider circumspection if not more conventional ventilation in patients with patchy, heterogenous disease.
- There is accruing evidence that COVID-19 is a clotting disease and early, full-dose anticoagulation should be considered.