DHM COVID-19 Clinical Dispatch
Bite-sized, weekly clinical updates
Issue #7: ARDS - Everything Old is New Again
This week, in a special edition, we bring you an interview with Dr. Carolyn Calfee, Professor of Medicine in the division of Pulmonary and Critical Care at UCSF.
In this issue we discuss the controversy around Acute Respiratory Distress Syndrome in COVID-19 (is it even ARDS?!) and highlight best practices for management of patients with COVID related respiratory failure.
And finally we give all the stomach-sleepers out there something to talk about in our Paper-of-the-Week on awake proning!
- The COVID Clinical Working Group
Spaced Learning Corner: Quiz Yourself!
In the Duan et al study of patients with severe COVID-19 treated with convalescent plasma therapy, which of the following showed a trend toward improvement after treatment with convalescent plasma?
a) SARS-COV2 viral load
b) Lymphocyte count
c) C-reactive protein
d) SpO2
e) All of the above
ARDS and its Coat of Many Colors
Early on in the pandemic a theory emerged regarding respiratory failure associated with COVID-19. Promoted primarily by Luciano Gattinoni in Italy, and picked up on social media and in the lay press, was an idea that COVID-19 associated ARDS was not “typical” ARDS (characterized by non-cardiogenic pulmonary edema, low compliance, and shunt-related hypoxia), most notably differentiated by high lung compliance. Based on a small handful of cases, advocates for this theory argued that old strategies for managing ARDS may be inappropriate in COVID-19.
In order to understand this topic, Avromi and Peter interviewed Dr. Carolyn Calfee, a Professor of Medicine and specialist in Pulmonary and Critical Care.
The interview below has been edited for clarity and length. Questions appear in bold.
Carolyn - thanks so much for giving us the time. To start off, is ARDS the correct model to think about COVID-related lung injury?
Yes, COVID-19 related ARDS is ARDS. We have known since ARDS was initially described in the Lancet in 1967 that it is a heterogeneous syndrome. If you read the initial case series by Ashbaugh and Petty of 12 patients, some of them had severe trauma, some had pancreatitis and some had viral pneumonia. One of the challenges of trying to understand the physiology and biology of ARDS is that it is a heterogeneous syndrome.
Some prominent physicians have argued there is a categorical difference between COVID-related ARDS and “typical” ARDS. Is there any truth to this?
I think that article, while well intentioned, has generated a lot of problems with a complete absence of data. We know there is a lot of heterogeneity in ARDS, and that heterogeneity is in-part physiologic. Wide ranges of lung compliance are seen, for example, in the large trial cohorts. If you intubate someone very early in their course of COVID-19 (as was done in many places early in the pandemic), compliance is going to look much closer to normal.
It’s not a different type of ARDS. We know the compliance varies widely within ARDS. A recent case series of 66 patients with COVID-19 in Boston revealed a wide spectrum of lung compliance, seeming to refute this theory. While there may be something biologically unique about COVID-19 related ARDS, we still need large data sets to truly support this theory.
What differences have you seen with COVID-related ARDS?
The thing that has stood out to me is really how long these patients require mechanical ventilation. Even without neuromuscular blockade these patients are at risk of critical illness myopathy and neuropathy. You add in neuromuscular blockade and possibly steroids and that risk goes up substantially.
Does standard ARDS management (like low tidal volume ventilation) work for all causes of ARDS? Should we expect it to be beneficial in COVID-19?
Yes exactly - if you look at the original LPV [lung protective ventilation] trial you have patients with trauma, TRALI [transfusion-related lung injury], pancreatitis, pneumonia, urosepsis. Lung protective ventilation seems to work for all those cases because, we think, we’re avoiding additional ventilator related lung injury. So I think it’s critically important to adhere to that as closely as possible for these patients.
Might there be things about COVID-19 that are unique? Absolutely. But people have been studying questions about how to subphenotype different types of ARDS for decades and it is critically important to stick to what we know improves outcomes in ARDS, the most common cause of which is pneumonia (and viral pneumonia), which is lung-protective, low tidal volume ventilation.
Have you been using awake proning? [see below for our paper of the week!]
I have not, though I just reviewed an article for a general medicine journal on awake proning, which reported an improvement in oxygenation for those patients who were able to tolerate it. I think that’s all we have evidence for at the moment. Whether that translates into meaningful clinical outcomes is unknown. For example in the ARMA trial, oxygenation improved in the high tidal volume group, but those patients died more!
It’s going to require testing and RCTs. But in the setting of a resource-crunched environment, it makes so much sense to improve someone’s oxygenation and potentially stave off intubation. It’s a really creative solution, and it’ll be interesting to see what ongoing RCTs show.
Thank you so much for your time, we really appreciate it.
Back to Basics - ARDS Management
The table above is a summary of guidelines supported by the British Thoracic Society (2019) and are similar to those of the American Thoracic Society (2017).
Quick Lit - Awake Proning!
Prone positioning is thought to reduce the collapse of gravity-dependent areas of the lung and to allow for more evenly distributed perfusion – together improving lung recruitment and ventilation-perfusion matching. Though prone positioning has not been found to benefit all patients with acute hypoxemic respiratory failure, prone ventilation does seem to improve outcomes in those with severe hypoxemia. Most notably, the 2013 PROSEVA trial found that early, prolonged prone
ventilation in patients with severe ARDS significantly decreased mortality.
More recently proning has been studied in spontaneously breathing, non-intubated patients. During the COVID-19 pandemic, awake prone positioning has gained popularity as a potential strategy to manage hypoxemia in non-intubated patients and to preserve limited ICU resources. In this paper, we examine whether this strategy is feasible and effective in patients with severe COVID-19.
Links
Questions, thoughts, insights? Share them on our Clinical Knowledge Portal!
Prior Dispatches:
Issue 1: GI symptoms in COVID
Issue 2: Predictors of Severe COVID Disease
Issue 3: Hypercoagulability in COVID-19
Issue 4: SARS-CoV-2 and the Inflammatory Response
Issue 5: Remdesivir for COVID-19
Issue 6: Convalescent Plasma
