key: cord-0979753-o2wcf6nd
authors: Bahloul, Mabrouk; Kharrat, Sana; Chtara, Kamilia; Chelly, Hedi; Hamida, Chokri Ben; Bouaziz, Mounir
title: Gravity-induced ischemia in the brain and prone positioning for COVID-19 patients breathing spontaneously: still far from the truth!
date: 2022-02-28
journal: Acute Crit Care
DOI: 10.4266/acc.2022.00199
sha: b1490faf3a1c1f3e5623af74c4e0a43d3598868e
doc_id: 979753
cord_uid: o2wcf6nd

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Moreover, as suggested by Jaster and Ottaviani [3] , an upright head position (or at least partially upright), is usually used for all these patients. In fact, this position improves oxygenation in ARDS patients and was proposed as an alternative to the prone position [2] .

Second, the application of the prone position leads to an increase in lung recruitability and alveolar recruitment, which causes ventilation-perfusion enhancement. As a consequence, early application of the prone position can improve severe hypoxemia and respiratory failure in COVID-19 patients with spontaneous breathing [1, 2] . This improves brain oxygenation and can prevent brain ischemia. A prospectively designed, multicenter, international, randomized, open-label meta-trial with a large sample size (1,121 patients) [2] established that awake prone positioning application leads to a significant reduction in the incidence of treatment failure within 28 days of enrollment in patients with respiratory failure due to COVID-19. In this study, a longer mean daily duration of awake prone positioning (> 8 hours/day) was associated with treatment success at day 28 (prevention of intubation or death). For patients with acute respiratory distress requiring invasive mechanical ventilation with a partial pressure of oxygen in arterial blood/fractional percentage of inspired oxygen (PaO 2 /FIO 2 ) ratio < 150 mm Hg, it was established that the application of prone positioning was associated with a significant reduction of mortality [4] . According to formal guidelines [4] , prone positioning is recommended for at least 16 consecutive hours in ARDS patients with a PaO 2 /FIO 2 ratio < 150 mm Hg to reduce mortality (grade 1+).

Third, it has been well established that the prone position improves heart function [5] . The application of the prone position leads to an increase in the cardiac preload and decreases the right ventricular afterload in patients with ARDS [5] . This results in an increase in cardiac output in patients with preload reserve, leading to positive macrocirculatory effects with enhanced organ blood flow (in particular to the brain) and oxygen delivery to the body. All these phenomena can prevent brain ischemia. Finally, it has been well established that severe hypoxia leads to endothelial dysfunction and thrombosis formation. The major improvement of hypoxemia following application of the prone position can prevent this dysfunction and, as a consequence, thrombosis formation and brain ischemia.

In conclusion, as summarized in Figure 1 , the early application of prone positioning can improve severe hypoxemia and outcomes in COVID-19 patients with spontaneous breathing. By substantially improving hypoxemia and cardiac output, the prone position can prevent endothelial dysfunction and, as a consequence, thrombosis formation and brain ischemia.

Impact of prone position on outcomes of COVID-19 patients with spontaneous breathing

Awake prone positioning for COVID-19 acute hypoxaemic respiratory failure: a randomised, controlled, multinational, open-label meta-trial

Gravity-induced ischemia in the brainand prone positioning for COVID-19 patients breathing spontaneously

Formal guidelines: management of acute respiratory distress syndrome

Optimizing the circulation in the prone patient

No potential conflict of interest relevant to this article was reported.