Awake prone positioning in acute hypoxaemic respiratory failure

Abstract

Awake prone positioning (APP) of patients with acute hypoxaemic respiratory failure gained considerable attention during the early phases of the coronavirus disease 2019 (COVID-19) pandemic. Prior to the pandemic, reports of APP were limited to case series in patients with influenza and in immunocompromised patients, with encouraging results in terms of tolerance and oxygenation improvement. Prone positioning of awake patients with acute hypoxaemic respiratory failure appears to result in many of the same physiological changes improving oxygenation seen in invasively ventilated patients with moderate-severe acute respiratory distress syndrome. A number of randomised controlled studies published on patients with varying severity of COVID-19 have reported apparently contrasting outcomes. However, there is consistent evidence that more hypoxaemic patients requiring advanced respiratory support, who are managed in higher care environments and who can be prone for several hours, benefit most from APP use. We review the physiological basis by which prone positioning results in changes in lung mechanics and gas exchange and summarise the latest evidence base for APP primarily in COVID-19. We examine the key factors that influence the success of APP, the optimal target populations for APP and the key unknowns that will shape future research.

FIGURE 1

Physiological effects of awake prone positioning (APP). When supine, the dependent lung is compressed by the lung weight, the pleural pressure gradient and the weight of the heart. When prone, these dorso-ventral lung regions are relieved of these pressures, with functional residual capacity increasing from the dorsal to ventral direction. Alveolar inflation from the dorsal to the ventral direction becomes more homogenous and ventilation/perfusion ratio matching is improved. Improved diaphragmatic movement and enhanced secretion removal also contribute beneficially. In the cardiovascular system, APP increases cardiac output due to increased lung recruitment and reduction in hypoxic pulmonary vasoconstriction as well as increased systemic venous return related to increased intra-abdominal pressure, resulting in increases in right ventricular pre-load and decreased right ventricular afterload. In the abdomen, APP improves diaphragmatic function, as it moves caudally, reducing pressure on the lung, while a moderate increase in intra-abdominal pressure improves venous return to the heart. Scans reproduced from [81] with permission.

FIGURE 2

Images from two male patients with coronavirus disease 2019 pneumonitis enrolled in the awake prone positioning (APP) trial conducted in Mexico: a) and b) APP group patient; c) and d) control group patient. Both were males in their 50s, admitted 10 days from initial symptoms and thorax computed tomography (CT) was performed at days 1 and 5 after admission. In the proned patient there is a progressive improvement from a) to b) over the 5-day period; in the patient remaining supine, there is a worsening in lung consolidation from c) to d), especially at right lung base, and the second CT was taken right after commencement of invasive ventilation on day 5. Courtesy of Miguel Ibarra-Estrada.

FIGURE 3

Forest plots of randomised controlled trials with a subgroup analysis of intubation based on a) advanced versus conventional oxygen respiratory support and b) intensive care unit (ICU) versus non-ICU. APP: awake prone positioning. Reproduced and modified from [43] with permission.

FIGURE 4

Technique for placing patients in awake prone position. a) Explain to the patient the potential benefit of the technique. b) Remove electrodes from the anterior thorax. c) Move the patient horizontally to a side of the bed. d) Slowly place the patient in full lateral position. e) Move the patient to a full prone position. f) Replace the electrodes on the back. g) Awake prone positioning (APP) can be used under high-flow nasal cannula (HFNC) but also under noninvasive ventilation (NIV) with a facial mask. h) APP can be used under HFNC but also under NIV with a helmet.

FIGURE 5

Approaches to optimising prone positioning in awake patients receiving advanced respiratory support. a–c) Different positions of the arms can be tried depending on the patient's preferences (swimmer's position). d) and e) Pillows can be placed under the thorax or the legs to improve comfort. f) A smartphone can help to distract/relax the patient.