Early Physiologic Effects of Prone Positioning in COVID-19 Acute Respiratory Distress Syndrome

Abstract

Background. The mechanisms underlying oxygenation improvement after prone positioning in COVID-19 ARDS have not been fully elucidated yet. We hypothesized that the oxygenation increase with prone positioning is secondary to the improvement of ventilation-perfusion matching. Methods. In a series of consecutive intubated COVID-19 ARDS patients receiving volume-controlled ventilation, we prospectively assessed the percent variation of ventilation-perfusion matching by electrical impedance tomography (EIT) before and 90 minutes after the first cycle of prone positioning (primary endpoint). We also assessed changes in the distribution and homogeneity of lung ventilation and perfusion, lung overdistention and collapse, respiratory system compliance, driving pressure, optimal positive end-expiratory pressure (PEEP), as assessed by EIT, and the ratio of partial pressure to fractional inspired oxygen (PaO2/FiO2) (secondary endpoints). Data are reported as medians [25th - 75th] or percentages. Results. We enrolled 30 consecutive patients, all analyzed without missing data. Compared to supine position, prone positioning overall improved ventilation-perfusion matching from 58 [43-69] % to 68 [56-75] % (p=0.042), with a median difference of 8.0% (95% Confidence Interval 0.1 to 16.0%) . Dorsal ventilation increased from 39 [31-43] % to 52 [44-62] % (p<0.001), while dorsal perfusion did not significantly vary. Prone positioning also reduced lung overdistension from 9 [4-11] % to 4 [2-6] % (p=0.025), while it did not significantly affect ventilation and perfusion homogeneity, lung collapse, static respiratory system compliance, driving pressure, and optimal PEEP. PaO2/FiO2 overall improved from 141 [104-182] mmHg to 235 [164-267] mmHg (p=0.019). However, 9 (30%) patients were non-responders, experiencing an increase in PaO2/FiO2 <20% with respect to baseline. Conclusions. In COVID-19 ARDS patients, prone positioning overall produced an early increase in ventilation-perfusion matching and dorsal ventilation. These effects were, however, heterogeneous among patients.

Effect of prone positioning on end-expiratory lung volume, strain and oxygenation change over time in COVID-19 acute respiratory distress syndrome: A prospective physiological study

“…As previously demonstrated, PP reduces non-aerated and over-aerated lung regions immediately and the inflated gas is more evenly distributed (31, 37). Furthermore, as recently reported by Zarantonello and co-workers, the ventilation-perfusion matching is improved early after PP (16). Consequently, the strain on the alveoli is reduced during the entire PP period as confirmed in our study.…”

“…This provides a strong rationale for its use in this scenario (15). Furthermore, Zarantonello and co-workers observed that PP induced an improvement of ventilation-perfusion matching and dorsal ventilation within the first 90 min (16). Another study established the positive role of PP on outcomes, in which shorter time to PP was associated with a decrease in mortality (17).…”

Advanced Point-of-care Bedside Monitoring for Acute Respiratory Failure

“…Perfusion electrical impedance tomography could be an adjunctive bedside tool to identify patients with pulmonary embolism 69 or to assess the modification of the ventilation/perfusion mismatch after PEEP changes 8 or prone positioning. 9 From this perspective, in a small cohort of ARDS patients subjected to invasive mechanical ventilation, the percentage of lung units with an unmatched ventilation-to-perfusion ratio was an independent risk factor for mortality, having been higher in nonsurvivors compared to survivors. 70 lung properties among lung regions increases the regional ventilation delay; when optimal positive end-expiratory pressure is applied to a recruitable lung, regional ventilation delay decreases Electrical impedance tomography parameters in the setting of the acute respiratory failure along with advantages and limitations of the technology compared to conventional monitoring are reported.…”

Prone Positioning in COVID-19 ARDS: Comment

“…We read with interest the recent article by Zarantonello et al . 1 on the physiologic effects of prone positioning on ventilation and perfusion distribution, oxygenation, and lung mechanics in COVID-19 acute respiratory distress syndrome patients. We would like to first congratulate the authors for the nicely conducted study that once again proved the clinical applicability of electrical impedance tomography for the assessment of ventilation–perfusion matching at the bedside.…”