Bedside detection of end-tidal overdistention: an exploratory comparison of loading maneuvers

Paradoxical improvement in respiratory system compliance with chest wall loading ('mechanical paradox') has been well described in adult respiratory distress syndrome (ARDS), especially in the setting of severe Covid-19 pneumonia. A standardized bedside technique of chest wall loading to elicit this paradoxical response has not been fully developed.

In two community ICUs, adult patients who were passively ventilated with volume control for diverse conditions underwent a series of stepwise compression maneuvers: first, manual compressions of the chest and abdomen in the semi-Fowler and supine positions; then, compressions of the chest and abdomen with 2, 6, and 10 kg saline bags in the supine position. These maneuvers were conducted with small and large surface 'footprints'. Under each loading condition, three breath cycles were allowed to pass before tidal volume, PEEP, peak, and plateau pressures were recorded.

Ten patients were included in the case series. Only one of ten patients demonstrated mechanical paradox, which was elicited both by chest wall loading and by moving the patient from the semi-Fowler to the horizontal position. In all patients, abdominal compression elicited a larger change in plateau pressure than did sternal compression. At least 6 kg of weighting force was needed to detect a meaningful change in plateau pressure.

Mechanical paradox occurs infrequently outside of very severe, unresolving ARDS. Apart from compression over the upper abdomen, a simple bedside maneuver for detection of mechanical paradox may be moving the patient from the semi-upright to the supine position.