The term proning (placing patients on their stomachs) has become common in journal articles and YouTube videos about the in-hospital ventilation of patients with COVID-19 disease. Because proning (and in particular awake proning) is becoming a familiar part of treatment protocols for COVID-19, we offer here a consideration of its origin and application. A caveat: like much else in the current outbreak, evidence to support awake proning in patients infected with SARS-CoV-2 is largely anecdotal at this time.
Why Prone a Patient?
Physical position affects the distribution and volume of air in the lungs, and can have direct effects on the expansion or collapse of the delicate alveoli that permit the exchange of oxygen and carbon dioxide in the blood. It has long been known that the supine position (lying on the back) can be detrimental to underlying pulmonary function, particularly for patients on mechanical ventilation. Like many in-hospital procedures, mechanical ventilation is typically administered to patients in the supine position.
In the 1970s, clinicians began investigating the potential of placing patients on their stomachs to treat acute respiratory distress syndrome (ARDS), a condition defined by diffuse bilateral alveolar damage and a severe mismatch between ventilation—the transfer of oxygen into and out of the alveoli during respiration—and perfusion, the flow of blood to the alveolar capillaries. Ventilation/perfusion mismatch results in elevated levels of carbon dioxide in the blood and oxygen deficiency (hypoxia). Hypoxia manifests as low oxygen saturation and cyanosis, a blue discoloration of the skin. ARDS is a cause of death in patients with COVID-19.
Why is the Supine Position an Issue for Hospitalized Patients on Ventilation?
In the supine position, the lungs are compressed by gravity and other forces (including the internal organs), which can cause hyperinflation of alveoli in the ventral (upward-facing) lung while causing alveolar collapse (atelectasis) in the dorsal part of the lung (lying closest the bed). Gravity complicates things by pushing blood downward toward the poorly oxygenated alveoli in the posterior lung, creating a ventilation/perfusion mismatch. This mismatch is thought to drive rapid deterioration of patients with ARDS and other conditions that compromise breathing.
Why is Proning Beneficial for Ventilated Patients?
Research has found that when proning is used in patients with severe ARDS and hypoxemia not improved by other means, it has the benefit of:
- better ventilation of the dorsal lung regions threatened by alveolar collapse;
- improvement in ventilation/perfusion matching; and
- potentially an improvement in mortality.
These benefits are the result of a more even distribution of ventilator volumes and pressures throughout the lung, which is thought to reduce the incidence and severity of ventilator-induced lung injury. 
Can Proning be Used in Non-Ventilated Patients?
Subsequent to studies in ventilated ARDS patients, clinicians discovered that proning may be beneficial in non-intubated (non-ventilated) patients – a practice of great potential benefit in COVID-19 disease, where intubation places healthcare professionals at greatly increased risk of infection.  A number of reports from the US, China, France and Italy, including case series and retrospective analyses, have recently appeared to support the use of monitored awake proning as a method of redressing COVID-associated ARDS while avoiding or forestalling intubation and ventilation. [2-3]
Proning may help avoid Mechanical Ventilation and Intubation in Patients with COVID-19
At Penn Medicine, averting the need for intubation and ICU care is among the objectives for proning in COVID-19 patients.
All intubations and ICU care (where patients are on mechanical ventilation) place providers at increased risk for infection by increasing the presence of infectious particles in the air. Awake proning has been shown in a consecutive series from New York City to successfully avoid intubation in 64% of hospitalized COVID-positive patients. 
“We like to avoid ventilation as much as possible, and though there’s not a lot of evidence to support proning, it has worked in the past,” says Kaytlena Stillman, MD, MPH, of Penn Emergency Medicine, adding that there is still a risk that mechanical ventilation will be necessary despite proning.
The indications for proning at Penn Medicine include vital sign and hemodynamic stability, an O2 saturation level of <92% on supplemental oxygen, and a conscious, oriented and responsive patient able to move in and out of the prone position with minimal or no assistance. Patients are in a negative pressure room, closely monitored (including telemetry and appropriate nursing ratios), and re-evaluated at regular intervals. Padding is provided to alleviate pressure point injuries.
“The patient must be re-evaluated at regular intervals, and we do remain in the room for the initial proning to see how they will respond,” says Zaffer Qasim, MD, of Penn Emergency Medicine. “If the patient cannot tolerate the prone position, or has worsening hypoxia, work of breathing or tachycardia, the patient is returned to the supine position and their head-of-bed elevated. At this point, it’s likely that intubation and mechanical ventilation will be necessary.”
Additional Resources from Penn Medicine
Dr. Qasim and colleagues at Penn Presbyterian Hospital have created a video on awake proning protocol during COVID-19.
Watch a video about ARDS mechanisms and therapies from Penn pulmonologist Nuala J. Myer, MD.
1. Caputo N, Strayer R, Levitan R. Early Self-Proning in Awake, Non-intubated Patients in the Emergency Department: A Single ED’s Experience during the COVID-19 Pandemic. Acad Emerg Med. April 2020. [doi:10.1111/acem.13994]
2. Elharrar X, Trigui Y, Dols A-M, et al. Use of Prone Positioning in Nonintubated Patients With COVID-19 and Hypoxemic Acute Respiratory Failure. JAMA Published online May 15, 2020. [doi:10.1001/jama.2020.8255]
3. Sartini C, Tresoldi M, Scarpellini P, et al. Respiratory Parameters in Patients With COVID-19 After Using Noninvasive Ventilation in the Prone Position Outside the Intensive Care Unit. JAMA. Published online May 15, 2020. [doi:10.1001/jama.2020.7861]
4. Caputo N, Strayer R, Levitan R. Early Self-Proning in Awake, Non-intubated Patients in the Emergency Department: A Single ED’s Experience during the COVID-19 Pandemic. Acad Emerg Med. April 2020. [doi:10.1111/acem.13994]