A novel non-invasive method to detect excessively high respiratory effort and dynamic transpulmonary driving pressure during mechanical ventilation

BACKGROUND: Excessive respiratory muscle effort during mechanical ventilation may cause patient self-inflicted lung injury and load-induced diaphragm myotrauma, but there are no non-invasive methods to reliably detect elevated transpulmonary driving pressure and elevated respiratory muscle effort during assisted ventilation. We hypothesized that the swing in airway pressure generated by respiratory muscle effort under assisted ventilation when the airway is briefly occluded (ΔP(occ)) could be used as a highly feasible non-invasive technique to screen for these conditions. METHODS: Respiratory muscle pressure (P(mus)), dynamic transpulmonary driving pressure (ΔP(L,dyn), the difference between peak and end-expiratory transpulmonary pressure), and ΔP(occ) were measured daily in mechanically ventilated patients in two ICUs in Toronto, Canada. A conversion factor to predict ΔP(L,dyn) and P(mus) from ΔP(occ) was derived and validated using cross-validation. External validity was assessed in an independent cohort (Nanjing, China). RESULTS: Fifty-two daily recordings were collected in 16 patients. In this sample, P(mus) and ΔP(L) were frequently excessively high: P(mus) exceeded 10 cm H(2)O on 84% of study days and ΔP(L,dyn) exceeded 15 cm H(2)O on 53% of study days. ΔP(occ) measurements accurately detected P(mus) > 10 cm H(2)O (AUROC 0.92, 95% CI 0.83–0.97) and ΔP(L,dyn) > 15 cm H(2)O (AUROC 0.93, 95% CI 0.86–0.99). In the external validation cohort (n = 12), estimating P(mus) and ΔP(L,dyn) from ΔP(occ) measurements detected excessively high P(mus) and ΔP(L,dyn) with similar accuracy (AUROC ≥ 0.94). CONCLUSIONS: Measuring ΔP(occ) enables accurate non-invasive detection of elevated respiratory muscle pressure and transpulmonary driving pressure. Excessive respiratory effort and transpulmonary driving pressure may be frequent in spontaneously breathing ventilated patients.