In a new study of patients with severe COVID-19 (SARS-CoV-2) hospitalized on ventilators, researchers found that lying face down was better for the lungs.
The research letter was published online in the American Thoracic Society’s American Journal of Respiratory and Critical Care Medicine.
In “Lung Recruitability in SARS—CoV-2 Associated Acute Respiratory Distress Syndrome: A Single-Center, Observational Study,” Haibo Qiu, MD, Chun Pan, MD, and co-authors report on a retrospective study of the treatment of 12 patients in Wuhan Jinyintan Hospital, China, with severe COVID-19 infection-related acute respiratory distress syndrome (ARDS) who were assisted by mechanical ventilation. Drs. Qiu and Pan were in charge of the treatment of these patients, who were transferred from other treatment centers to Jinyintan Hospital.
A majority of patients admitted to the ICU with confirmed COVID-19 developed ARDS.
The observational study took place during a six-day period the week of Feb. 18, 2020.
“This study is the first description of the behavior of the lungs in patients with severe COVID-19 requiring mechanical ventilation and receiving positive pressure,” said Dr. Qiu, professor, Department of Critical Care Medicine, Zhangda Hospital, School of Medicine, Southeast University, Nanjing, China.
“It indicates that some patients do not respond well to high positive pressure and respond better to prone positioning in bed (facing downward).”
The clinicians in Wuhan used an index, the Recruitment-to-Inflation ratio, that measures the response of lungs to pressure (lung recruitability).
Members of the research team, Lu Chen, Ph.D., and Laurent Brochard, Ph.D., HDR, from the University of Toronto, developed this index prior to this study.
The researchers assessed the effect of body positioning.
Prone positioning was performed for 24-hour periods in which patients had persistently low levels of blood oxygenation.
Oxygen flow, lung volume and airway pressure were measured by devices on patients’ ventilators. Other measurements were taken, including the aeration of their airway passages and calculations were done to measure recruitability.
Seven patients received at least one session of prone positioning. Three patients received both prone positioning and ECMO (life support, replacing the function of heart and lungs). Three patients died.
Patients who did not receive prone positioning had poor lung recruitability, while alternating supine (face upward) and prone positioning was associated with increased lung recruitability.
“It is only a small number of patients, but our study shows that many patients did not re-open their lungs under high positive pressure and may be exposed to more harm than benefit in trying to increase the pressure,” said Chun Pan, MD, also a professor with Zhongda Hospital, School of Medicine, Southeast University. “By contrast, the lung improves when the patient is in the prone position.
Considering this can be done, it is important for the management of patients with severe COVID-19 requiring mechanical ventilation.”
The team consisted of scientists and clinicians affiliated with four Chinese and two Canadian hospitals, medical schools and universities.
Earlier trials could not demonstrate a mortality benefit of prone-position over supine position ventilation [Table 1]. The swing in evidence supporting prone-position ventilation can largely be credited to the PROSEVA (Proning Severe ARDS Patients) trial. 
This was a multicentre, prospective, randomized controlled trial (RCT) where 466 severe ARDS patients were assigned to undergo either 16 h prone-positioning sessions or to be left in the supine position. The 28-day mortality was 16.0% in the prone group and 32.8% in the supine group (P < 0.001).
The 90-day mortality was 23.6% in the prone group versus 41.0% in the supine group (P < 0.001).
These results may, however, be confounded by the fact that the supine position group were a sicker group with a slightly higher SOFA score and were receiving more pressors and neuromuscular blockers.
Also, the list of exclusion criteria was lengthy suggesting that the beneficial outcome may be restricted to a minority of ARDS patients. Furthermore, the PROSEVA staff was highly trained and experienced in the procedure of prone-positioning, so the same results may not apply to settings with untrained staff.
The earliest of meta-analysis done in 2008 did not show any mortality benefit of prone-positioning, but two meta analyses performed in 2010 by Sud etal. and Gattinoni etal. respectively showed that cases of severe ARDS do benefit from prone-positioning.
In December 2013, Lee et al. conducted a meta-analysis of 11 RCTs and concluded that along with severe ARDS, longer durations of prone-positioning is also beneficial.
The meta-analysis done in January 2014 by Beitler etal. have shown a survival benefit with low tidal volume and prone-position ventilation. 
The largest of the meta-meta analyses published in March 2014 by Tonelli et al. where they included 159 RCTs and 29 meta analyses to see the effect of various modalities in cases of ARDS, also suggested that prone-position ventilation has survival benefit in cases of severe ARDS [Table 2].
The mechanics of prone-position ventilation can be explained as follows: In a normal lung, the alveolar density is more posteriorly. 
In supine position, these posterior alveoli get compressed due to various reasons such as:
(1) Action of gravity,
(2) shape of the chest wall: The anterior lung parenchyma is more conical than the posterior lung parenchyma. The anterior alveoli thus have a greater volume of intra-thoracic cavity available to expand and are thus more distended than the posterior alveoli and
(3) the heart and diaphragm further act under gravity to compress posterior alveoli.
The total recruitment of alveoli is more in prone-position than in supine position because the posterior lung parenchyma comes in non-dependent position and hence their compression due to gravity is prevented and also because the heart and diaphragm no longer act under gravity to compress alveoli.
The ARDS lung is characterized by infiltrates that tend to accumulate in the dependent alveoli. In supine position, the infiltrates accumulate and compromise the posterior alveoli and thus prevent ventilation. The anterior alveoli, which are fewer than posterior alveoli, are only available to maintain ventilation. [Figure 1]
In prone-position, the infiltrates rapidly shift to accumulate and compromise the anterior alveoli (dependent part). The posterior alveoli (non-dependent), which are far greater in number than anterior alveoli, are thus released to maintain a better perfusion. 
The same amount of infiltrates has more posterior alveoli to compromise in the supine position as compared to anterior alveoli in prone-position. This helps in more alveolar recruitment in a homogeneous manner.  Apart from this, the perfusion also is maintained homogeneously.  The pre-load on the heart decreases and cardiac index improves. The end result is better oxygenation. 
Prone-position ventilation is not free from complications. Those related to the mechanics of manoeuvre are a transient desaturation, transient hypotension, accidental extubation, and catheter displacements.
Those related to duration of proning are pressure ulcers, vomiting and need for excessive sedation. Harmful complications like compression of nerves and retinal vessels, facial oedema, difficulty in instituting cardiopulmonary resuscitation have also been seen. Most of these can be prevented by an experienced team and use of special devices and beds that facilitate the mechanics of safe proning.
Patient can be turned into prone-position either manually or through automated beds designed for this purpose. Manual method is cheaper than the automated one but requires highly skilled staff and integrated work of the nursing staff with the respiratory therapist.
The respiratory therapist ensures the stability of the endotracheal tube, one nurse is needed to secure the vascular lines and at least two or three nurses to turn the patient prone. Automated prone-positioning needs one nurse, minimises risk during turning and provides continuous rotation if required.
- Prone positioning can be used in mechanically ventilated patients with severe hypoxic respiratory failure to optimise oxygenation
- most studied in patients with acute respiratory distress syndrome (ARDS) where short lived improvements in oxygenation are common (70%) and sometimes dramatic (e.g. Gattinoni et al, 2001). Some patients have no effect and others have a long lasting effect, persisting well after rolling supine again.
- the recent PROSEVA trial found a marked mortality benefit in patients with severe ARDS (PF ratio <150)
- severe ARDS with life threatening, refractory hypoxaemia
- prone positioning may also be used for patients with posterior wounds, burns and skin flaps
- untrained staff
- increased intracranial pressure
- increased abdominal pressure
- abdominal and chest wounds
- C-spine precautions
- extreme obesity
- haemodynamic instability
- assemble sufficient trained staff to coordinate positioning safely
- provide padding and support for potential pressure areas (face, upper chest, pelvis, knees)
- turn patient prone
- abdomen should hang between two pillows/ supports
- duration varies among protocols (e.g. 6-16 hours a day for up to 10 days)
See this video from the PROSEVA trial paper in NEJM:
- reduction in VC
- reduction FRC
- optimisation of V/Q matching (increased blood flow to the dependent lung)
- increase in FRC
- reduced atelectasis
- facilitates secretion drainage
- less lung deformation in the prone position (increased homogeneity) -> increased ventilation
- abdomen is less likely to distend when in prone position -> increase in FRC
- heart sits against sternum (rather than left lung) -> lung is less compressed
- decreased transpleural pressure gradient between dependent and non-dependent lung in the prone position
- plateau pressure is more uniformly distributed when prone -> more uniform alveolar ventilation
- recruitment manoeuvres have been shown to be more effective in the prone position
- alterations in chest wall mechanics -> allowing lungs to inflate at lower pressures
- dorsoventral orientation of large airways
- decreased enteral nutrition
- ETT obstruction or dislodgement;
- chest tube and abdominal drain dislodgement
- increased intrabdominal pressure
- increased intracranial pressure
- difficulty monitoring (e.g. ECG lead placement)
- labour intensive
- difficult to perform procedures or reintubate
- may delay referral to other potentially life-saving measures such as ECMO
- facial oedema
- pressure trauma:
- -> ocular
- -> blindness, orbital skin necrosis
- -> bridge of nose
- -> mentum
- -> humeral head
- -> breast implants
- -> ASIS
- -> male genitals
- -> knees
- there have been multiple conflicting RCTs but the weight of evidence now suggests prone ventilation is beneficial in selected severe ARDS patients
- Gattinoni et al 2001 was the original study showing improvement in oxygenation of most patients with ALI /ARDS by proning
- Recent meta-analyses suggest a mortality benefit for patients with severe ARDS (PF ratio <100), with an NNT of 11
- Subsequent to the above meta-analyses, the PROSEVA trial by Guerin et al 2013 showed a marked mortality benefit (NNT = 6) for prone ventilation in severe ARDS (28-day mortality 16% prone versus 32.8% supine)
References and Links
Journal articles and textbooks
- Abroug F, Ouanes-Besbes L, Dachraoui F, Ouanes I, Brochard L. An updated study-level meta-analysis of randomised controlled trials on proning in ARDS and acute lung injury. Crit Care. 2011;15(1):R6. PMC3222033.
- Fessler HE, Talmor DS. Should prone positioning be routinely used for lung protection during mechanical ventilation? Respir Care. 2010 Jan;55(1):88-99. PMID: 20040127.
- Gattinoni L, Tognoni G, Pesenti A, Taccone P, Mascheroni D, Labarta V, Malacrida R, Di Giulio P, Fumagalli R, Pelosi P, Brazzi L, Latini R; Prone-Supine Study Group. Effect of prone positioning on the survival of patients with acute respiratory failure. N Engl J Med. 2001 Aug 23;345(8):568-73. PMID: 11529210.
- Gattinoni L, Carlesso E, Taccone P, Polli F, Guérin C, Mancebo J. Prone positioning improves survival in severe ARDS: a pathophysiologic review and individual patient meta-analysis. Minerva Anestesiol. 2010 Jun;76(6):448-54. PMID: 20473258.
- Guérin C, et al; PROSEVA Study Group. Prone positioning in severe acute respiratory distress syndrome. N Engl J Med. 2013 Jun 6;368(23):2159-68. PMID: 23688302.
- Soo Hoo. In Prone Ventilation, One Good Turn Deserves Another. New Engl J Med 2013; epublished May 20th
- Messerole E, Peine P, Wittkopp S, Marini JJ, Albert RK. The pragmatics of prone positioning. Am J Respir Crit Care Med. 2002 May 15;165(10):1359-63. PMID: 12016096.
- Pelosi P, Brazzi L, Gattinoni L. Prone position in acute respiratory distress syndrome. Eur Respir J. 2002 Oct;20(4):1017-28. PMID: 12412699.
- Sud S, Friedrich JO, Taccone P, Polli F, Adhikari NK, Latini R, Pesenti A, Guérin C, Mancebo J, Curley MA, Fernandez R, Chan MC, Beuret P, Voggenreiter G, Sud M, Tognoni G, Gattinoni L. Prone ventilation reduces mortality in patients with acute respiratory failure and severe hypoxemia: systematic review and meta-analysis. Intensive Care Med. 2010 Apr;36(4):585-99. PMID: 20130832.
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