Potential for Lung Recruitment and Ventilation-Perfusion Mismatch in Patients With the Acute Respiratory Distress Syndrome From Coronavirus Disease 2019*

Abstract

Objectives: Severe cases of coronavirus disease 2019 develop the acute respiratory distress syndrome, requiring admission to the ICU. This study aimed to describe specific pathophysiological characteristics of acute respiratory distress syndrome from coronavirus disease 2019. Design: Prospective crossover physiologic study. Setting: ICU of a university-affiliated hospital from northern Italy dedicated to care of patients with confirmed diagnosis of coronavirus disease 2019. Patients: Ten intubated patients with acute respiratory distress syndrome and confirmed diagnosis of coronavirus disease 2019. Interventions: We performed a two-step positive end-expiratory pressure trial with change of 10 cm H 2 O in random order. Measurements and Main Results: At each positive end-expiratory pressure level, we assessed arterial blood gases, respiratory mechanics, ventilation inhomogeneity, and potential for lung recruitment by electrical impedance tomography. Potential for lung recruitment was assessed by the recently described recruitment to inflation ratio. In a subgroup of seven paralyzed patients, we also measured ventilation-perfusion mismatch at lower positive end-expiratory pressure by electrical impedance tomography. At higher positive end-expiratory pressure, respiratory mechanics did not change significantly: compliance remained relatively high with low driving pressure. Oxygenation and ventilation inhomogeneity improved but arterial co 2 increased despite unchanged respiratory rate and tidal volume. The recruitment to inflation ratio presented median value higher than previously reported in acute respiratory distress syndrome patients but with large variability (median, 0.79 [0.53-1.08]; range, 0.16-1.40). The Fio 2 needed to obtain viable oxygenation at lower positive endexpiratory pressure was significantly correlated with the recruitment to inflation ratio (r = 0.603; p = 0.05). The ventilation-perfusion mismatch was elevated (median, 34% [32-45%] of lung units) and, in six out of seven patients, ventilated nonperfused units represented a much larger proportion than perfused nonventilated ones. Conclusions: In patients with acute respiratory distress syndrome from coronavirus disease 2019, potential for lung recruitment presents large variability, while elevated dead space fraction may be a specific pathophysiological trait. These findings may guide selection of personalized mechanical ventilation settings. (Crit

Recruitability and effect of PEEP in SARS-Cov-2-associated acute respiratory distress syndrome

“…The present small cases series is the first to describe early and complete respiratory mechanics evaluation in SARS-Cov-2-associated ARDS consistent with the "2 phenotypes" model proposed by Gattinoni et al [16]. Our observations extend those initially reported in three small cases series showing essentially low or variable potentials of recruitment with PEEP [4][5][6]. In the recently reported Chinese series of 12 SARS-Cov-2-associated ARDS, all patients were initially considered as poorly recruitable based on the same method to measure R/I ratio [4].…”

“…Authors concluded that R/I ratio is feasible, even in the constrained Covid-19 environment and may allow to guide individual titration of PEEP to limit potential harmful effects expected with high PEEP in poorly recruitable patients. Most (75%) of these patients received NIV or HFNC before intubation for a median of 5 [IQR, [4][5][6][7] days. This could lead to patient self-inflicted lung injury [17] that may explain, at least in part, their low respiratory system compliance (around 20 mL/cmH 2 O) after intubation.…”

“…In a large series of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-Cov-2)-associated respiratory failure, the majority of intubated patients were ventilated with high level of positive endexpiratory pressure (PEEP) [1]. However, information about specific individual characteristics of respiratory mechanics of SARS-Cov-2-associated ARDS remains very limited [4][5][6]. Based on their experience during the crisis, some authors suggested that part of the SARS-Cov-2 associated ARDS may present relatively high respiratory system compliance (C RS ) and poor recruitability with PEEP, contrasting with severe hypoxemia.…”

Pulmonary and systemic involvement in COVID‐19 patients assessed with ultrasound‐guided minimally invasive autopsy

“…[27][28][29] Indeed, there is increasing evidence that thrombotic phenomena in patients with severe COVID-19 can involve the pulmonary and systemic arteries, leading to a severe ventilation-perfusion mismatch in the lungs and peripheral ischaemic events. 30,31 The mechanisms involved in the inflammatory and/or virus-induced endothelial cell dysfunction and in the increase in the density of alveolar megakaryocytes in COVID- 19 patients have yet to be determined. Previous studies have demonstrated that functional Toll-like receptor 3 is expressed in megakaryocytes and platelets, suggesting a role for this receptor in the megakaryopoiesis/thrombopoiesis alterations in viral infections.…”

Helmet CPAP to Treat Hypoxic Pneumonia Outside the ICU: An Observational Study During the COVID-19 Outbreak

“…PaO 2 /FiO 2 ratio doubled from about 100 to 200 mmHg (P<0.001); respiratory rate decreased from 28 [22-32] to 24 [20][21][22][23][24][25][26][27][28][29] breaths per minute, P<0.001). CPAP failure was independently associated with CRP, time to oxygen mask failure, age, PaO 2 /FiO 2 during CPAP, number of comorbidities.…”