The Surviving Sepsis Campaign panel recently recommended that “mechanically ventilated patients with COVID-19 should be managed similarly to other patients with acute respiratory failure in the ICU.”
Yet, COVID-19 pneumonia, despite falling in most of the circumstances under the Berlin definition of ARDS, is a specific disease, whose distinctive features are severe hypoxemia often associated with near normal respiratory system compliance (more than 50% of the 150 patients measured by the authors and further confirmed by several colleagues in Northern Italy). This remarkable combination is almost never seen in severe ARDS.
These severely hypoxemic patients despite sharing a single etiology (SARS-CoV-2) may present quite differently from one another: normally breathing (“silent” hypoxemia) or remarkably dyspneic; quite responsive to nitric oxide or not; deeply hypocapnic or normo/ hypercapnic; and either responsive to prone position or not. Therefore, the same disease actually presents itself with impressive non-uniformity.
Based on detailed observation of several cases and discussions with colleagues treating these patients, we hypothesize that the different COVID-19 patterns found at presentation in the emergency department depend on the interaction between three factors:
- the severity of the infection, the host response, physiological reserve and comorbidities
- the ventilatory responsiveness of the patient to hypoxemia
- the time elapsed between the onset of the disease and the observation in the hospital
The interaction between these factors leads to the development of a time-related disease spectrum within two primary “phenotypes”:
Type L, characterized by:
- LOW elastance (i.e., high compliance)
- LOW ventilation to perfusion ratio
- LOW lung weight
- LOW recruitability
Type H, characterized by:
- HIGH elastance
- HIGH right-to-left shunt
- HIGH lung weight
- HIGH recruitability
Editor’s note: see the original editorial (below) for treatment recommendations based on phenotype L vs H. These recommendations are being received with curiosity / intrigue (e.g., does COVID-19 act more like high-altitude pulmonary edema (HAPE) rather than ARDS?) as well as potential resistance (e.g., as experienced by the physician in this video).
SOURCE: Intensive Care Medicine
VIDEO: HAPE not ARDS?
Physicians in the COVID-19 trenches are beginning to question whether standard respiratory therapy protocols for acute respiratory distress syndrome (ARDS) are the best approach for treating patients with COVID-19 pneumonia.
At issue is the standard use of ventilators for a virus whose presentation has not followed the standard for ARDS, but is looking more like high-altitude pulmonary edema (HAPE) in some patients.
In a letter to the editor published in the American Journal of Respiratory and Critical Care Medicine on March 30, and in an editorial accepted for publication in Intensive Care Medicine, Luciano Gattinoni, MD, of the Medical University of Göttingen in Germany and colleagues make the case that protocol-driven ventilator use for patients with COVID-19 could be doing more harm than good.
Dr. Gattinoni noted that COVID-19 patients in ICUs in northern Italy had an atypical ARDS presentation with severe hypoxemia and well-preserved lung gas volume. He and colleagues suggested that instead of high positive end-expiratory pressure (PEEP), physicians should consider the lowest possible PEEP and gentle ventilation–practicing patience to “buy time with minimum additional damage.”
SOURCE: The Hospitalist
I’ll describe what Gattinoni was saying, which is that really what we’re seeing in ARDS are two different phenotypes: one in which the lungs display what you call high compliance, low elastics; and one in which they have low elasticity and high compliance.
To say it simply for people who are not pulmonologists, if you think of the lungs as a balloon, typically when people have ARDS or pneumonia, the balloon gets thicker. So not only do you lack oxygen, but the pressure and the work to blow up the balloon becomes greater. So one’s respiratory muscles become tired as they struggle to breathe. And patients need pressure.
What Gattinoni is saying is that there are essentially two different phenotypes, one in which the balloon is thicker, which is a low-compliance disease. But in the beginning they display high compliance. Imagine if the balloon is not actually thicker but thinner, so they’d suffer from a lack of oxygen. But it is not that they suffer from too much work to blow up the balloon.
As far as how we’re going to switch, we’re going to take our approach differently from the traditional ARDSnet protocol in that we are going to do an oxygen-first strategy: We’re going to leave the oxygen levels as high as possible and we’re going to try to use the lowest pressures possible to try to keep the oxygen levels high. That’s the approach we’re going to do, so long as the patients continue to display the physiology of a low elastance, high-compliance disease.
GATTINONI LETTER: Am J Resp + Crit Care Med
GATTINONI EDITORIAL: Intensive Care Medicine
Mortality in COVID-19 vs other viruses (UK). Mortality in ICU patients with COVID-19 (n=690) as compared to pneumonia caused by other viruses (2017-2019, n=4434). ‘Resp’ = non-invasive support, including oxygen 50%+ or mask BiPAP. ‘Vent+’ = endotracheal ventilation or ECMO.
The recruitment:inflation ratio (R:I). (COVID-19). Orange lines denote patients who were prone at least once x 24 hr; thicker lines (3) went on to ECMO. R:I > 0.5 suggests high recruitability.
DATASOURCE: Am J Respir Crit Care Med.
R:I CALCULATOR: https://crec.coemv.ca/