Inspiratory Pressure Support Prevents Diaphragmatic Fatigue during Weaning from Mechanical Ventilation

TLDR

Persistent weaning failure is common in patients recovering from acute respiratory failure. The study aimed to evaluate whether inspiratory pressure support could prevent diaphragmatic fatigue in patients failing weaning. The authors applied varying levels of inspiratory pressure support to eight weaning‑unsuccessful patients, monitoring diaphragmatic electromyography and respiratory muscle oxygen consumption. Inspiratory pressure support decreased work of breathing and respiratory muscle oxygen consumption, eliminated diaphragmatic fatigue signs, and enabled identification of an optimal support level (up to 20 cm H₂O) that prevented fatigue while avoiding hyperinflation, with sternocleidomastoid activity serving as a useful monitor.

Abstract

Persistent inability to tolerate discontinuation from mechanical ventilation is frequently encountered in patients recovering from acute respiratory failure. We studied the ability of inspiratory pressure support, a new mode of ventilatory assistance, to promote a nonfatiguing respiratory muscle activity in eight patients unsuccessful at weaning from mechanical ventilation. During spontaneous breathing, seven of the eight patients demonstrated electromyographic signs of incipient diaphragmatic fatigue. During ventilation with pressure support at increasing levels, the work of breathing gradually decreased (p < 0.02) as well as the oxygen consumption of the respiratory muscles (p < 0.01), and electrical signs suggestive of diaphragmatic fatigue were no longer present. In addition, intrinsic positive end-expiratory pressure was progressively reduced. For each patient an optimal level of pressure support was found (as much as 20 cm H2O), identified as the lowest level maintaining diaphragmatic activity without fatigue. Above this level, diaphragmatic activity was further reduced and untoward effects such as hyperinflation and apnea occurred. When electrical diaphragmatic fatigue occurred, the activity of the sternocleidomastoid muscle was markedly increased, whereas it was minimal when the optimal level was reached.We conclude that in patients demonstrating difficulties in weaning from the ventilator: (1) pressure support ventilation can assist spontaneous breathing and avoid diaphragmatic fatigue (pressure support allows adjustment of the work of each breath to provide an optimal muscle load); (2) clinical monitoring of sternocleidomastoid muscle activity allows the required level of pressure support to be determined to prevent fatigue.