Distribution of the Intensity of Spontaneous Breathing Effort During Mechanical Ventilation

Rationale:Both insufficient and excessive respiratory effort during mechanical ventilation are associated with lung and diaphragm injury, and poor outcome. The characteristics of respiratory effort under MV has not been systematically described. The expiratory occlusion pressure (Pocc) is a non-invasive technique to estimate effort and lung-distending pressure from spontaneous breathing during MV. We set out to describe the frequency and magnitude of effort and lung-distending pressure in patients receiving MV. Methods:In a retrospective cohort study, we collected data from charts of patients receiving invasive MV at Toronto General Hospital from July 2019 to June 2021. Pocc is routinely measured once daily in every patient on MV. Data on patient demographic characteristics and ventilator settings was collected in a registry of ventilated patients in Toronto. For each day, we calculated the proportion of patients in whom effort was absent (Pocc = 0), low (Pocc -1 to -5 cm H2O), moderate (-5 to -15 cm H2O), high (-16 to -30 cm H2O), and very high (< -30 cm H2O). Excessive dynamic transpulmonary driving pressure was defined as estimated ΔPL,dyn was >20 cm H2O. Results:We included 854 patients who received invasive MV for at least 1 day. Of 577 patients in whom Pocc was measured on day 1 (within 24 hours of initiation of MV), effort was absent in 434 (75%) patients, moderate in 70 (12%), and high or very high 43 (7%). Of 328 patients in whom Pocc was measured on day 5, effort was absent in 127 (39%) patients, moderate in 80 (24%) patients and high or very high in 91 (28%). Among spontaneously breathing patients (Pocc <0 cm H2O), estimated dynamic transpulmonary driving pressure exceeded 20 cm H2O in 49/116 (42%) on day 1 and 77/150 (51%) on day 5. On patient-days on which estimated dynamic transpulmonary driving pressure exceeded 20 cm H2O, on average the ventilator contributed 62% (SD 24%) of total lung-distending pressure and the patient contributed 38% (SD 24%) of total lung-distending pressure. Over days 1 through 10, respiratory efforts were more vigorous in patients with COVID-19 pneumonia compared to those without (mean Pocc -12 cm H2O vs -7 cm H2O, p= <0.01). Conclusions:Respiratory effort is frequently absent or excessive during MV. Patients frequently exhibited excessive lung-distending pressures during spontaneous breathing. COVID-19 pneumonia was associated with higher respiratory effort. (Figure Presented).