Rethinking Ventilation For COVID-19
We are rethinking ventilation for COVID-19 in Italy and the United States.
Front-line physicians in Italy and now New York are telling us we are approaching the use of ventilators incorrectly and it could be causing harm. I am hoping spreading their concerns and their solutions will help practitioners working with these patients consider these ideas, watch what is taking place with their COVID-19 patients and consider that we may need to rethink ventilation protocol for COVID-19. Once our hospitals have a protocol set, it takes a lot to get them to change protocol even if the old protocol is not in the patients best interest.
COVID-19 was originally thought to act like an acute respiratory distress syndrome, but it actually acts more like high-altitude pulmonary edema (HAPE) or "the bends". This means the current use of ventilators may be causing lung injury in COVID-19 patients and practitioners are reconsidering the need for lung-protective strategies that utilize lower pressure settings for some patients, instead of high positive end-expiratory pressure for everyone. Physicians should consider the lowest possible positive end-expiratory pressure and gentle ventilation for paitents initially until if and when they need the higher pressure.
Dr. Kyle-Sidell, A New York physician says the patients are presenting oddly and he decided to figure out exactly what the clinical syndrome looked like. He eventually decided the patients look similar to someone who has the bends - when divers are diving and come up too quickly. He does not know if the pathophysiology is similar but he says the clinical presentation is similar. They look more like high-altitude sickness than they do pneumonia. He said it is a high-compliance (indicating a pliable lung with low elastic recoil) condition. Lung compliance is highest at moderate lung volumes.
Dr. Luciano Gattinoni in Italy agrees. He recently said they are seeing relatively high lung compliance with well preserved lung gas volume but severe hypoxemia when many patients first present to them. He thinks this is due to loss of lung perfusion regulation and hypoxic vasoconstriction. He said, "If we operate under a paradigm whereby we are treating ARDS in these high-compliant patients, we may not be operating under the right paradigm."
His suggestions are as follows:
- Patients treated with Continuous Positive Airway Pressure or Non Invasive Ventilation, presenting with clinical signs of excessive inspiratory efforts, intubation should be prioritized to avoid excessive intrathoracic negative pressures and self-inflicted lung injury.
- High PEEP in a poorly recruitable lung tends to result in severe hemodynamic impairment and fluid retention.
- Prone positioning of patients with relatively high compliance results in a modest benefit at the price of a high demand for stressed human resources.After considering that, all we can do ventilating these patients is “buying time” with minimum additional damage: the lowest possible PEEP and gentle ventilation.
Dr. Kyle-Sedell says there appear to be two phenotypes:"one in which the lungs display what you call high compliance, low elastance; and one in which they have low compliance and high elastance. "
In the beginning Dr. Gattinoni says they have high compliance. They suffer from lack of oxygen but they are not having trouble inflating their lungs. The new treatment needs to be changed over to high oxygen levels with the lowest pressures in the beginning to try and get the oxygen levels high. This Dr. Gattinoni says should be continued as long as the patient has low elastance and high-compliance disease.
Later there is low compliance and high elastance. There is lack of oxygen and the presssure needed to expand the lungs becomes greater. Their respiratory muscles get tired and it becomes hard to breath. These patients need more pressure from the ventilator at this point as has been being given to everyone, not just these later stage patients.
An additional interview by Medcape UK with Dr Nathalie Stevenson, a consultant in intensive care and anaesthetics, Royal Free London NHS Foundation Trust has the following to say: "Most COVID-19 patients are hypoxaemic with type 1 respiratory failure and so the application of oxygen and recruitment of the small airways in the lungs is the best intervention. To do this, one administers oxygen, and considers the application of less-invasive devices such as CPAP (continuous positive airway pressure). We’ve been seeing anecdotally that those patients started on CPAP and kept on CPAP can do better than those who are intubated early on. Once intubated, the chance of surviving is sadly much lower. "
"The change in thinking has largely come about after acknowledging that there is a lower survival rate for those patients who end up being intubated, and seeing that some patients can perhaps avoid intubation through application of less-invasive respiratory support such as CPAP."
Currently it is unknown if the CPAP is any better than simply supplyiing high flow nasal oxygen. Dr. Stevensons thinks it depends on the individual presenting. With a very compliant lung on CPAP there’s a worry of over-inflation. Unfortunately, it is hard to measure the degree of lung compliance when a patient is not on a ventilator.
Dr. Stevenson also pointed out that fluid restriction usually undertaken with ARDS and that has been used with COVID-19 patients may not be the best idea in early stages of COVID-19 as they are seeing many patients develop acute kidney inury.
Newer Data and Contrary Information
On 4-21-2020 Medscape came out with a new article whre Dr. Luanne Freer points out that the comparison between high altitude pulmonary edema (HAPE) and VOID-19 is potentially risky. She says, "With COVID, we don't understand everything that's going on, but we know for sure it's an inflammatory process – not a pressure-related problem," Dr. Freer said. "I thought ... this could be so dangerous to load the medicines that we use when we're treating HAPE onto patients with COVID-19. HAPE is a noncardiogenic form of pulmonary edema, as are ARDS due to bacteria or viral pneumonia, re-expansion pulmonary edema, immersion pulmonary edema, negative pressure pulmonary edema, and neurogenic pulmonary edema. Importantly, in all of these cases, edema accumulates in the interstitial and alveolar spaces of the lung as a result of imbalance in Starling forces. HAPE, is a fundamentally different phenomenon than what is seen in COVID-19-related ARDS, which involves viral-mediated inflammatory responses as the primary pathophysiological mechanism."
It was pointed out that supplemental oxygen can be enough in HAPE, whereas in COVID-19 it may improve hypoxemia but not resolve the inflammation and injury. Dr. Freer said, "only good supportive care including mechanical ventilation, quite often for long periods of time, allows some patients to survive until their disease resolves."
Luciano Gattinoni, MD, of the Medical University of Göttingen in Germany published a letter to the editor in the American Journal of Respiratory and Critical Care Medicine stressing that the ARDS presentation in COVID-19 patients is not typical and requires a patient physiology–driven treatment approach, rather than a standard protocol–driven approach. Dr. Gattinoni and colleagues suggested that instead of high positive end-expiratory pressure (PEEP), physicians should consider the lowest possible PEEP and gentle ventilation. Ultimately, this is the crux of the situation. Each patient needs to be evaluated for how they are presenting. Something that should always be done in any patient presentation.