Spontaneous Breathing and Pendelluft in Patients with Acute Lung Injury: A Narrative Review

Abstract

Acute respiratory distress syndrome (ARDS) is characterized by acute-onset rapid-deteriorating inflammatory lung injury. Although the preservation of spontaneous breathing may have physiological benefits in oxygenation, increasing evidence shows that vigorous spontaneous breathing may aggravate lung injury (i.e., patient self-inflicted lung injury). Increased lung stress and pendelluft, which is defined as intrapulmonary gas redistribution without a significant change in tidal volume, are important mechanisms of patient self-inflicted lung injury. The presence of pendelluft may be considered a surrogate marker of vigorous inspiratory effort, which can cause the dependent lung to overstretch. In this review, we summarized three major methods for electrical impedance tomography-based pendelluft monitoring. Future studies are warranted to compare and validate the different methods of pendelluft estimation in patients with ARDS.

Keywords: acute respiratory distress syndrome; pendelluft; spontaneous breathing.

Figure 1

The estimation of the regional lung inflation of spontaneous breathing by controlled ventilation. During the whole estimation process, the regional ventilation of the patient is monitored by the EIT system (Pulmovista 500^®, Draeger medical GmbH, Luebeck, Germany). At the beginning of spontaneous breathing, the strong inspiratory effort causes significant inflation and impedance change at the dependent lung region. After controlled breathing with neuromuscular blocking agents, the regional impedance changes at the dependent lung decreases. To estimate the regional lung inflation of the spontaneous breathing effort, incremental titration of the driving pressure is applied until the same regional impedance change at the dependent lung is achieved.

Figure 2

The quantitative analysis of pendelluft. The global impedance–time curve is presented in the bottom column and the timepoint of nadir impedance was recognized as the starting point of inspiration (black dash line). The impedance–time curve of each region of interest is presented in the upper column, and the timepoints of nadir impedance were also defined, including ventral (green dash line), mid-ventral (blue dash line), mid-dorsal (red dash line), and dorsal (brown dash line) parts. The impedance difference of each region between the global and regional nadir timepoints were calculated and summed as the pendelluft volume.

Figure 3

The estimation of pendelluft amplitude. The global impedance–time curve is presented in the upper column, and the timepoint of nadir impedance and peak impedance are recognized as the starting and ending points of inspiration (black dash line). The bottom column presents the impedance–time curve from two consecutive pixels. The regional impedance change of the pixel was defined by the impedance change in a breath cycle. Meanwhile, the global impedance change of the pixel was defined by the impedance difference in each pixel between the starting and ending timepoints of inspiration. The difference between regional and global impedance changes is summed as the pendelluft amplitude.