COVID-19 Pneumonia: Severe Adult Respiratory Distress Syndrome (ARDS)

Does COVID-19 pneumonia may fall under the definition of adult respiratory distress syndrome (ARDS)?

APRIL 18, 2020 -- More details on the "remarkable combination" of distinctive features seen in patients with COVID-19 pneumonia are outlined by the Italian clinicians who warned that protocol-driven ventilator use could be doing more harm than good in some patients.

Luciano Gattinoni, MD, from Medical University of Göttingen, Germany, and colleagues first raised these concerns in a letter to the American Journal of Respiratory and Critical Care Medicine.

Now they have taken their observations further, writing in an editorial in Intensive Care Medicine on April 14. They argue that although COVID-19 pneumonia may fall under the definition of adult respiratory distress syndrome (ARDS), it is a "specific disease" with distinctive features.

They report that, in their series of 150 patients, only 20% to 30% showed disease that was similar to severe ARDS.

They also identified two distinct phenotypes (Type L and Type H), which they argue require different treatment approaches.

This runs counter to current guidance. The European Society of Intensive Care Medicine, which issued one of the first international guidelines on the management of critically ill patients with the disease, states that patients with COVID-19 receiving mechanical ventilation "should be managed similarly to other patients with acute respiratory failure in the intensive care unit (ICU)".

Other groups have also questioned this guidance and the current protocols for mechanical ventilation in COVID-19 pneumonia patients.

In a Medscape commentary, Barbara A. McLean, MN, RN, CCRN, a critical care clinical specialist at Grady Health System, Atlanta, Georgia, said that their experience also points to COVID-19 pneumonia as having two different lung pathologies, which need two separate ventilator protocols.

A frontline clinician in New York has also questioned current ventilator protocols, pointing out that some patients were presenting with symptoms that looked like high-altitude sickness, with hypoxia, but were still able to talk.

This was echoed in comments made recently by Massimiliano Sorbello, MD, AOU Policlinico San Marco University Hospital, Catania, Italy, who has observed a "dissociation" between clinical signs and laboratory results in COVID-19 patients.

Speaking in a webinar hosted by the European Society of Anaesthesiology (ESA) April 9, he noted that, based on what the numbers say, one would think the patient would be "gasping or almost in a coma."

"But when you go and see the patient, he is awake, he is speaking to you, he doesn't look as bad" as his data would suggest, and "you are really starting to ask yourself why you should intubate such a patient," Massimiliano said.

He added that that, "at least at the beginning, it is not the ARDS we used to's a different respiratory failure." But he warned that COVID-19 patients can "suddenly deteriorate."

Report on 150 Patients With COVID-19

In their latest study, Gattinoni and colleagues report on 150 patients with COVID-19 pneumonia. More than half of these patients had near-normal respiratory system compliance despite having severe hypoxemia, a finding that was corroborated by other colleagues working in Northern Italy.

Analyzing the cases further, they determined that there were different patterns of COVID-19, depending on the interaction of three factors:

• The severity of the infection, the host response, the physiologic reserve, and comorbidities

• The ventilatory responsiveness to hypoxemia

• The length of time between symptom onset and presenting to the hospital

Gattinoni and collegues say that consideration of these factors led them to develop the view that there are two distinct COVID-19 phenotypes, Type L and Type H.

Type L was characterized by:

• Low elastane (high compliance)

• A low ventilation-to-perfusion ratio, with a near-normal pulmonary artery pressure

• A low lung weight on computed tomography (CT)

• Low lung recruitability, with a very low proportion of non-aerated lung tissue

These Type L patients may stay in this phenotype for a period of time and then either improve or worsen, in which case they shift to the opposite end of the phenotypic spectrum and develop Type H disease, the team notes.

Type H patients were found to have:

• High elastane, linked to increased edema

• High right-to-left shunt

• High lung weight, with a >1.5 kg increase on CT

• High lung recruitability

"The transition from Type L to Type H may be due to the evolution of the COVID-19 pneumonia," the authors write, but they suggest that this transition could also be a result of the "the injury attributable to high-stress ventilation." In other words, the mechanical ventilation may be doing more harm than good in these cases.

They set out a series of recommendations that emphasize the need to take into account the patient's clinical condition and minimize the risk of lung injury while they have Type L disease.

The authors add that Type H COVID-19 pneumonia accounts for 20% to 30% of patients in their series, and "fully fits" the criteria for severe ARDS.

These Type H patients "should be treated as severe ARDS," including mechanical ventilation with higher positive end-expiratory pressure.

The researchers conclude that, while CT scan is the best way to distinguish patients with the two phenotypes, if that is not available, "signs which are implicit in Type L and Type H definition could be used as surrogates: respiratory system elastance and recruitability."

"Understanding the correct pathophysiology is crucial to establishing the basis for appropriate treatment," the authors stress. They have previously outlined the different treatment approaches for the distinct physiologies.

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Sources: Am J Respir Crit Care Med. Published online. LetterIntensive Care Med. Published online. Editorial

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