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Concise Critical Appraisal: Early Self-Proning in Awake, Nonintubated Patients in the ED

Severe hypoxemia is one of the most serious problems in COVID-19. In some patients it is discordant with the degree of respiratory distress. Many patients with severe hypoxemia require supplemental oxygen, but the degree of shunt can render nonrebreather face masks and nasal cannulas inadequate, with many patients continuing to have refractory hypoxemia. Those with refractory hypoxemia who are not responsive to supplemental oxygen are often intubated to avoid the use of noninvasive ventilation (NIV) and high-flow nasal cannula (HFNC) because of the concern of exposure from aerosolization of viral particles. Intubated patients have exceptionally high rates of mortality, and the number of COVID-19 patients being intubated has caused a strain on critical care capacity in some regions. Some patients with severe COVID-19 remain hypoxemic despite supplemental oxygenation but do not appear in extremis and do not require immediate intubation. Many of these hypoxemic patients with COVID-19 have chest radiography consistent with acute respiratory distress syndrome (ARDS). Proning has been found to be helpful in ARDS (Guérin et al. N Engl J Med. 2013;368:2159-2168), so perhaps the latter group of hypoxemic COVID-19 patients not in extremis might benefit from proning as well.

Caputo et al (Acad Emerg Med. 2020;27:375-378) investigated proning awake patients with COVID-19 and its effect on the degree of hypoxemia as measured by pulse oximetry (Spo2). This was an observational cohort study that examined a convenience sample of 50 adult patients who were hypoxemic (Spo2 < 90%) on presentation to the emergency department (ED) and who did not respond to supplemental oxygen (persistent Spo2 < 93%). This sample was collected during the early stages of the COVID-19 pandemic, from March 2020 through April 2020.

Patients were confirmed to have COVID-19 with a positive severe acute respiratory syndrome coronavirus 2 polymerase chain reaction. Patients in this study needed to be able to self-prone. Patients were excluded if they had a do-not-resuscitate or do-not-intubate order on file, were in cardiac arrest, were on NIV, or were intubated in the prehospital setting. The primary outcomes were change in Spo2 on supplemental oxygen before proning and Spo2 on the same amount of supplemental oxygen after proning for 5 minutes. The secondary outcome was the number of patients who were proned but required intubation within 24 hours.

The median Spo2 was 80% initially and 84% after supplemental oxygen. After 5 minutes of proning, the median Spo2 increased to 94%. Thirteen patients required intubation within the first 24 hours for respiratory failure. Respiratory failure was defined as persistent Spo2 < 90% in the setting of worsening or unresolved tachypnea with either accessory muscle use, altered mental status or hypercarbia on blood gas analysis.

This trial showed that self-proning improved Spo2 in COVID-19 patients. However, the study had some limitations. First, this was a small observational study based on a convenience sample. Conclusions may be confounded by other variables. Additionally, the patients were from a single hospital, which raises concern about the external validity of this trial and its application to the general population. Recent studies from France and Italy (Elharrar et al. JAMA. 2020;e208255; Sartini et al. JAMA. 2020;e207861) show similar improvement in Spo2, albeit less pronounced in the Elharrar et al cohort. Further work needs to be done in a prospective manner.

Proning can help optimize shunt physiology by allowing improved perfusion to well-ventilated lung tissue and assist with recruitment of atelectatic lung units and sputum clearance. When combined with higher levels of inspired oxygen and positive pressure such as HFNC or NIV, proning may help delay intubation or prevent intubation entirely.

While the degree that proning improves hypoxemia in these patients is promising, other more important patient-centered outcomes need to be further elucidated in self-proning. Namely, rates of intubation, length of mechanical ventilation, length of hospital stay, patient safety, and mortality are ultimately more important than Spo2. Further studies investigating HFNC and bilevel positive airway pressure in conjunction with proning and its effect on these patient-centered outcomes may provide valuable insight for managing an important subset of severely hypoxemic patients.

Authors of this installment of Concise Critical Appraisal:

Arman Sobhani, MD, is a clinical assistant instructor and advanced resuscitation fellow in the Department of Emergency Medicine at Stony Brook Medicine.

Brian J. Wright, MD, MPH, is a clinical associate professor and the program director for the Advanced Resuscitation Training Program in the Department of Emergency Medicine at Stony Brook Medicine. Dr. Wright is an editor of Concise Critical Appraisal.

Posted: 6/10/2020 | 2 comments

Professor Gattinoni proposed an interesting mechanism by which prone positioning improves oxygenation in type 1 patients with COVID-19 pneumonia who have near-normal compliance with only minimal lung recruitability. According to Professor Gattinoni, prone positioning (and high PEEP) does not improve oxygenation by recruitment of collapsed areas, but through redistribution of pulmonary perfusion and improvement of V/Q matching. The physiologic mechanism underlying oxygenation improvement in prone-positioned patients who have non-recruitable lung is gravity-dependent reduction in perfusion of the basal (non-dependent) regions such that perfusion becomes more properly matched with ventilation. However, for this mechanism to act there must be a “baseline” increase in pulmonary perfusion relative to alveolar ventilation such as might result from loss of hypoxic pulmonary vasoconstriction and/or AT2 receptor-mediated vasodilatation (dysregulated pulmonary perfusion). Obviously, when the "baseline" V/Q abnormality is increased shunt due to increased pulmonary blood flow, measures that reduce blood flow such as prone positioning (and high PEEP) would be expected to improve V/Q ratio and arterial oxygenation—regardless of alveolar recruitment. However, this is unlikely to occur if dead space ventilation (resulting from pulmonary micro-thrombi, right heart failure or AT1 receptor-mediated pulmonary vasoconstriction) is the main mechanism of hypoxemia. By further decreasing pulmonary perfusion, prone positioning (and high PEEP) may actually worsen dead space ventilation and pulmonary gas exchange. The effect of prone positioning (and high PEEP) on arterial oxygenation in type 1 patients is probably determined by which type of V/Q mismatch is present at baseline—shunt vs dead space ventilation. Thus, it is likely that prone positioning (and high PEEP) is not a “one-size-fits-all” strategy for patients with type 1 disease, and that careful evaluation of the underlying physiologic abnormality is mandatory before considering prone positioning (and high PEEP) in these patients.
6/12/2020 3:26:20 PM

Thank you,

We have been very proactively turning our awake patients prone with COVID. We have used it with CPAP and NIV and found it very successful in some patients while others required mechanical ventilation. The drive is to turn any patient with refractory hypoxaemia prone on our ICU. There should be more data coming out soon.
6/11/2020 5:40:07 PM

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