Atelectasis, Shunt, and Worsening Oxygenation Following Reduction of Respiratory Rate in Healthy Pigs Undergoing ECMO: An Experimental Lung Imaging Study

Abstract

Rationale: Reducing the respiratory rate during extracorporeal membrane oxygenation (ECMO) decreases the mechanical power, but it might induce alveolar de-recruitment. Dissecting de-recruitment due to lung edema vs. the fraction due to hypoventilation may be challenging in injured lungs.Objectives: We characterized changes in lung physiology (primary endpoint: development of atelectasis) associated with progressive reduction of the respiratory rate in healthy animals on ECMO.Methods: Six female pigs underwent general anesthesia and volume control ventilation (Baseline: PEEP 5 cmH2O, Vt 10 ml/kg, I:E = 1:2, FiO2 0.5, rate 24 bpm). Veno-venous ECMO was started and respiratory rate was progressively reduced to 18, 12, and 6 breaths per minute (6-h steps), while all other settings remained unchanged. ECMO blood flow was kept constant while gas flow was increased to maintain stable PaCO2.Measurements and Main Results: At Baseline (without ECMO) and toward the end of each step, data from quantitative CT scan, electrical impedance tomography, and gas exchange were collected. Increasing ECMO gas flow while lowering the respiratory rate was associated with an increase in the fraction of non-aerated tissue (i.e., atelectasis) and with a decrease of tidal ventilation reaching the gravitationally dependent lung regions (p = 0.009 and p = 0.018). Intrapulmonary shunt increased (p < 0.001) and arterial PaO2 decreased (p < 0.001) at lower rates. The fraction of non-aerated lung was correlated with longer expiratory time spent at zero flow (r = 0.555, p = 0.011).Conclusions: Progressive decrease of respiratory rate coupled with increasing CO2 removal in mechanically ventilated healthy pigs is associated with development of lung atelectasis, higher shunt, and poorer oxygenation.

Impact of obesity on outcomes of extracorporeal membrane oxygenation support: a systematic review and meta-analysis

“…For instance, in obese individuals, changes in chest wall resistance and lung compliance can complicate respiratory function [ 32 ]. With respect to ECMO, oxygenation challenges may arise due to ventilation-perfusion mismatch and atelectasis [ 33 ]. The removal of CO2 is impeded by these altered mechanics, potentially resulting in hypercapnia.…”

Determining Extracorporeal Membrane Oxygenation Outcomes in Obese Patients with ARDS

“…Altered respiratory mechanics in obese patients, such as decreased compliance, ventilation-perfusion mismatch, and atelectasis, affect the ECMO's ability to provide adequate oxygenation and CO2 removal. This can lead to hypoxemia and inadequate organ support (Spinelli et al, 2021).…”

Interactions between extracorporeal support and the cardiopulmonary system

“…Right ventricular function may become an important factor in future strategies for VV ECMO initiation and weaning. Importantly, the level of support during ECMO therapy may also impact RV function: Total transfer of gas exchange and absolute lung rest may promote atelectasis with associated RV-strain while support at an inadequate level may risk exacerbation of lung injury caused by mechanical ventilation ( Spinelli et al, 2021 ). Optimal settings should be chosen considering both RV strain and the mechanical power applied to the lung.…”