Background There is on-going controversy regarding the potential for increased respiratory effort to generate patient self-inflicted lung injury (P-SILI) in spontaneously breathing patients with COVID-19 acute hypoxaemic respiratory failure. However, direct clinical evidence linking increased inspiratory effort to lung injury is scarce. We adapted a computational simulator of cardiopulmonary pathophysiology to quantify the mechanical forces that could lead to P-SILI at different levels of respiratory effort. In accordance with recent data, the simulator parameters were manually adjusted to generate a population of 10 patients that recapitulate clinical features exhibited by certain COVID-19 patients, i.e., severe hypoxaemia combined with relatively well-preserved lung mechanics, being treated with supplemental oxygen. Results Simulations were conducted at tidal volumes (VT) and respiratory rates (RR) of 7 ml/kg and 14 breaths/min (representing normal respiratory effort) and at VT/RR of 7/20, 7/30, 10/14, 10/20 and 10/30 ml/kg / breaths/min. While oxygenation improved with higher respiratory efforts, significant increases in multiple indicators of the potential for lung injury were observed at all higher VT/RR combinations tested. Pleural pressure swing increased from 12.0 ± 0.3 cmH2O at baseline to 33.8 ± 0.4 cmH2O at VT/RR of 7 ml/kg/30 breaths/min and to 46.2 ± 0.5 cmH2O at 10 ml/kg/30 breaths/min. Transpulmonary pressure swing increased from 4.7 ± 0.1 cmH2O at baseline to 17.9 ± 0.3 cmH2O at VT/RR of 7 ml/kg/30 breaths/min and to 24.2 ± 0.3 cmH2O at 10 ml/kg/30 breaths/min. Total lung strain increased from 0.29 ± 0.006 at baseline to 0.65 ± 0.016 at 10 ml/kg/30 breaths/min. Mechanical power increased from 1.6 ± 0.1 J/min at baseline to 12.9 ± 0.2 J/min at VT/RR of 7 ml/kg/30 breaths/min, and to 24.9 ± 0.3 J/min at 10 ml/kg/30 breaths/min. Driving pressure increased from 7.7 ± 0.2 cmH2O at baseline to 19.6 ± 0.2 cmH2O at VT/RR of 7 ml/kg/30 breaths/min, and to 26.9 ± 0.3 cmH2O at 10 ml/kg/30 breaths/min. Conclusions Our results suggest that the forces generated by increased inspiratory effort commonly seen in COVID-19 acute hypoxaemic respiratory failure are comparable with those that have been associated with ventilator-induced lung injury during mechanical ventilation. Respiratory efforts in these patients should be carefully monitored and controlled to minimise the risk of lung injury.

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There is ongoing controversy regarding the potential for increased respiratory effort to generate patient self-inflicted lung injury (P-SILI) in spontaneously breathing patients with COVID-19 acute respiratory failure. However, direct clinical evidence linking increased inspiratory effort to lung injury is scarce. We adapted a recently developed computational simulator that replicates distinctive features of COVID-19 pathophysiology to quantify the mechanical forces that could lead to P-SILI at different levels of respiratory effort. In accordance with recent data, the simulator was calibrated to represent a spontaneously breathing COVID-19 patient with severe hypoxaemia (SaO2 80.6%) and relatively well-preserved lung mechanics (lung compliance of 47.5 ml/cmH2O), being treated with supplemental oxygen (FiO2 = 100%). Simulations were conducted at tidal volumes (VT) and respiratory rates (RR) of 7 ml/kg and 14 breaths/min (representing normal respiratory effort) and at VT/RR of 15/14, 7/20, 15/20, 10/30, 12/30, 10/35, 12/35, 10/40, 12/40 ml/kg / breaths/min. Lung compliance was unaffected by increased VT but decreased significantly at higher RR. While oxygenation improved, significant increases in multiple indicators of the potential for lung injury were observed at all higher VT/RR combinations tested. Pleural pressure swing increased from 10.1 cmH2O at baseline to 30 cmH2O at VT/RR of 15 ml/kg / 20 breaths/min and to 54.6 cmH2O at 12 ml/kg / 40 breaths/min. Dynamic strain increased from 0.3 to 0.49 at VT/RR of 12 ml/kg / 30 breaths/min, and to 0.6 at 15 ml/kg / 20 breaths/min. Mechanical power increased from 7.83 J/min to 17.7 J/min at VT/RR of 7 ml/kg / 20 breaths/min, and to 240.5 7 J/min at 12 ml/kg / 40 breaths/min. Our results suggest that the forces generated during increased inspiratory effort in severe COVID-19 are compatible with the development of P-SILI. If conventional oxygen therapy or non-invasive ventilation is ineffective in reducing respiratory effort, control of driving and transpulmonary pressures with invasive ventilation may reduce the risk of P-SILI and allow time for the resolution of the underlying condition.