Chest wall loading in the ICU: pushes, weights, and positions

Abstract

Clinicians monitor mechanical ventilatory support using airway pressures—primarily the plateau and driving pressure, which are considered by many to determine the safety of the applied tidal volume. These airway pressures are influenced not only by the ventilator prescription, but also by the mechanical properties of the respiratory system, which consists of the series-coupled lung and chest wall. Actively limiting chest wall expansion through external compression of the rib cage or abdomen is seldom performed in the ICU. Recent literature describing the respiratory mechanics of patients with late-stage, unresolving, ARDS, however, has raised awareness of the potential diagnostic (and perhaps therapeutic) value of this unfamiliar and somewhat counterintuitive practice. In these patients, interventions that reduce resting lung volume, such as loading the chest wall through application of external weights or manual pressure, or placing the torso in a more horizontal position, have unexpectedly improved tidal compliance of the lung and integrated respiratory system by reducing previously undetected end-tidal hyperinflation. In this interpretive review, we first describe underappreciated lung and chest wall interactions that are clinically relevant to both normal individuals and to the acutely ill who receive ventilatory support. We then apply these physiologic principles, in addition to published clinical observation, to illustrate the utility of chest wall modification for the purposes of detecting end-tidal hyperinflation in everyday practice.

PEEP Titration Is Markedly Affected by Trunk Inclination in Mechanically Ventilated Patients with COVID-19 ARDS: A Physiologic, Cross-Over Study

“…In other words, in the same patients, the “best” PEEP in the semi-recumbent position was associated with a lower percentage of overdistended and collapsed lung parenchyma. This finding might be explained by a greater tendency towards alveolar collapse in the supine-flat position, due, once again, to the lower starting EELV and to the possible role of the pressure exerted by the abdominal content on the dorsal, dependent lung regions [ 12 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ].…”

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

“…As a consequence, respiratory system compliance is not expected to improve during external compression. With this principle in mind, assessing respiratory system compliance in response to brief but sustained chest wall compression (lasting < 15 s) has gained attention as another simple method for detecting net end-tidal hyperinflation during the COVID-19 pandemic [58]. Manual compression sustained for several breathing cycles produces effects which are immediate, quickly reversed, and universally available (Figure 5).…”

The place of positive end expiratory pressure in ventilator-induced lung injury generation

“…An imbalance of these competing actions that favors end-tidal hyperinflation may be detected by simple, noninvasive bedside maneuvers that reduce absolute lung volume [24 ▪ ,25 ▪ ]. For example, in patients with severe COVID-19 associated ARDS, external pressure applied to the abdomen or rib cage often produced a ‘mechanical paradox’.…”

“…This phenomenon is characterized by lower plateau pressure during chest wall compression for a given tidal volume, despite reduced chest wall flexibility. Detection of paradox during such maneuvers suggests relief of end-inspiratory alveolar hyperinflation that responds to the lower lung volumes consequent to PEEP reduction [24 ▪ ]. Less end-tidal hyperinflation improves lung protective tidal mechanics, reduces maximal tissue strain and may beneficially redistribute pulmonary blood flow.…”