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Review
. 2024 Mar 22;13(7):1833.
doi: 10.3390/jcm13071833.

The Respiratory Mechanics of COVID-19 Acute Respiratory Distress Syndrome-Lessons Learned?

Rebecca L Kummer  1 , John J Marini  2
Affiliations
Review

The Respiratory Mechanics of COVID-19 Acute Respiratory Distress Syndrome-Lessons Learned?

Rebecca L Kummer et al. J Clin Med. .

Abstract

Acute respiratory distress syndrome (ARDS) is a well-defined clinical entity characterized by the acute onset of diffuse pulmonary injury and hypoxemia not explained by fluid overload. The COVID-19 pandemic brought about an unprecedented volume of patients with ARDS and challenged our understanding and clinical approach to treatment of this clinical syndrome. Unique to COVID-19 ARDS is the disruption and dysregulation of the pulmonary vascular compartment caused by the SARS-CoV-2 virus, which is a significant cause of hypoxemia in these patients. As a result, gas exchange does not necessarily correlate with respiratory system compliance and mechanics in COVID-19 ARDS as it does with other etiologies. The purpose of this review is to relate the mechanics of COVID-19 ARDS to its underlying pathophysiologic mechanisms and outline the lessons we have learned in the management of this clinic syndrome.

Keywords: ARDS; COVID-19; PEEP; PSILI; VILI.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Changing time course of the underlying characteristics of COVID-19 ARDS. Early on in the disease course, lung compliance may be relatively well preserved, leading to atypical responses to recruitment maneuvers and PEEP titration. As time passes, the more typical features of ARDS physiology may develop including poor compliance and worsening shunting.
Figure 2
Figure 2
Mechanisms of gas exchange impairment in COVID-19 ARDS versus traditional ARDS. On the left, typical ARDS is depicted by a large area of dense consolidation (dark blue) representing shunt and a small area of less densely consolidated lung (light blue) representing V/Q mismatch. The white area represents unaffected lung (the baby lung). In COVID-19 ARDS, there is a relatively larger portion of V/Q mismatch distributed throughout much of the lung (checkered pattern). On the right side of the figure, a similar concept is demonstrated in a bar graph.
Figure 3
Figure 3
Benefits and consequences of raising PEEP in early COVID-19 ARDS. The goal of raising the PEEP is to open collapsed lung units (dark grey) that may participate in gas exchange and improve V/Q matching (depicted by the upwards arrow to the lungs with reduced consolidation). However, raising the PEEP may instead redirect blood flow to collapsed lung units and increase stress on the baby lung without the desired benefit of improved V/Q matching (depicted by the blue arrow). As the disease progresses, responses to the PEEP may change.
Figure 4
Figure 4
Effects of prone positioning on the distributions of ventilation (blue shading) and perfusion (red shading), contrasting COVID-19 ARDS versus traditional ARDS. Ventilating patterns are affected similarly by prone positioning in both categories of ARDS. However, while regional perfusion remains relatively unaltered by prone positioning in traditional ARDS, gravitational forces combined with impaired homeostatic Vaso regulation alter regional perfusion in C-ARDS.
Figure 5
Figure 5
Paradoxical effects of loading via horizontal positioning or external abdominal pressure on respiratory system compliance, as exemplified by plateau pressure with an unchanging tidal volume and PEEP. Constant manual pressure is applied to the abdomen with enough force to raise the plateau pressure by two centimeters of water (green arrows). Upon resumption of tidal breathing, three to five breath cycles (vertical blue lines) are delivered under loaded conditions (shaded) with the same constant force applied to the abdomen, and a new plateau pressure is measured. If it is observed to be lower than the original plateau pressure while under the load, this is consistent with mechanical paradox. The red arrows depict the difference in plateau pressure between pre-loaded and loaded conditions (A: Pplat, B: Pload). Note that loading can also be applied without the need for compression maneuvers via the simple transition from upright to horizontal positioning of the thorax.
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This research received no external funding.