Role of endothelial dysfunction on tolerance to supine position in patients with acute respiratory distress syndrome on mechanical ventilation
Authors:   ,   Pontificia Universidad Católica de Chile. Escuela de Medicina, Bachmann Barrón María Consuelo 
Published: August 2024

Introduction: The prone position is a maneuver frequently used to improve oxygenation inpatients with ARDS on mechanical ventilation. Physiologically, optimization of gas exchangeoccurs by recruiting the dorsal regions of the lung, improving the ventilation/perfusion (V/Q)ratio. Despite the benefits, this position presents complications. Therefore, it is important toclearly know its indications and duration time. Prolonged use of the prone position (more than16 hours) can be associated with severe muscle weakness among other complications, whileits use for short and repeated periods is associated with accidents, increase workload, and agreater number of days in IMV. Therefore, it is important to be able to precisely determine themoment in which the patient is ready to be supinated.Through EIT it has been shown that both in healthy and ARDS conditions, the distribution ofpulmonary ventilation is predominantly dorsal in prone, and ventral in supine position. Whileperfusion under normal and pathological conditions presents a dorsal predominance. Itwould be expected that, with adequate endothelial function, the presence of hypoxicpulmonary vasoconstriction allows the redistribution of pulmonary perfusion towardsnormally aerated regions, allowing optimal gas exchange. We hypothesized thatmechanically ventilated in prone position ARDS patients, with endothelial dysfunction are notcapable of regulate pulmonary perfusion and, therefore, increasing their V/Q imbalance, withthe position change worsening oxygenation.Methods: Observational quasi-experimental clinical study in patients admitted to the ICU ofthe UC-CHRISTUS Clinical Hospital, in Santiago, Chile. Patients with diagnosis of ARDSconnected to IMV in prone position were included. Endothelial function was assessed atbaseline through flow-mediated vasodilation and NIRS. Hemodynamic and ventilatoryparameters, ABG, and distribution of ventilation and perfusion through EIT were evaluated inprone and supine for analysis of shunt, dead space, and V/Q mismatch. Lung aeration wasevaluated with lung ultrasound and computed tomography. Supine position intolerance wasdefined as the need for a second prone cycle within the first 24 hours after the switch.Results: This analysis included 20 patients, of whom 13 tolerated the change in position. Nocorrelation was found between the V/Q ratio and tolerance to position change. There werealso no associations found between clinical (NIRS and FMD) and biochemical (bloodmarkers) assessments of endothelial dysfunction and V/Q ratio imbalance. However, othervariables were shown to play a relevant role in tolerance outcomes. The failed group exhibiteda more widespread distribution of lung injury assessed by CT compared to the successfulgroup (local injury). Additionally, the failed group showed significantly higher values of drivingpressure and PaCO2 than the successful group, and these differences were found during boththe prone and supine periods.Conclusions: No relation was observed between tolerance to position change and thepresence of endothelial dysfunction, and we have not been able to find the existence ofpredictive patterns of tolerance. Respiratory mechanics and pulmonary injury distributioncould be the determining factor.