Abstract

Strenuous respiratory effort has been proposed as a second hit, introducing the concepts of "patient self-inflicted lung injury" (P-SILI) and underassistance myotrauma. We investigated the effects of continuous positive airway pressure (CPAP) and high-flow nasal oxygen (HFNO) on inspiratory and expiratory effort, lung injury, and myotrauma of obligatory and accessory respiratory muscles in experimental P-SILI. In rats, lung injury was induced through surfactant depletion, followed by 3 h of standard oxygen therapy (2 L/min, positive control) or supported ventilation (CPAP 6 cmH2O, HFNO 4 L/min, and protective mechanical ventilation [MV, negative control] groups). Subjects were assessed through esophageal manometry, surface electromyography on the abdominal wall, thoracic ultrasound, plasma multiplex analysis, and histology on the lungs, diaphragm, and accessory inspiratory and expiratory muscles. Compared against standard oxygen therapy, the MV and CPAP groups resulted in lower inspiratory and expiratory efforts and diaphragm excursion. Furthermore, intragroup analysis showed that CPAP also reduced respiratory rate and prevented the loss of lung aeration. All support therapies prevented lung, diaphragm, and accessory muscle injuries, but with nuances. In lungs and accessory muscles, MV showed the highest injury protection and HFNO the lowest, while CPAP was the most protective for the diaphragm. Only MV resulted in a lower plasma GRO-alpha concentration than standard oxygen therapy. Invasive and non-invasive respiratory support therapies are effective in protecting the lungs and respiratory muscles, but the effect is stepped in the lung and varies between obligatory and accessory respiratory muscles.