Lung-Distending Pressure During Spontaneous Breathing Under Mechanical Ventilation Assessed Using Diaphragm Electrical Activity

Abstract Introduction Ventilator-delivered pressures and patient efforts during assisted mechanical ventilation leave patients at risk of lung injury. Electrical diaphragm activity can provide continuous diaphragm monitoring because it provides an electromyographic measure of diaphragmatic effort. However, it is uncertain whether this can be used to assess respiratory effort of lung distending pressure during spontaneous breathing. Objectives Our primary objective was to establish the validity of using electrical diaphragm activity (Edi) to total lung-distending pressure (ΔPL,dyn). We then applied this method to a longitudinal cohort study to describe the distribution and magnitude of ΔPL,dyn during assisted mechanical ventilation. Methods We performed a secondary analysis based on two published studies. Pocc and Edi were measured in 16 mechanically ventilated patients. ΔPes was measured and observed ΔPL,dyn was computed. Similarly, ΔPes, ΔPL,dyn, Pocc, Edi,occ, and Edi,open were measured in an additional 12 mechanically ventilated patients.Estimated ΔPL,dyn for non-occluded breaths was computed as ΔPaw – Pocc/Edi,occ [asterisk] 2/3 [asterisk] Edi,open. The estimated ΔPL,dyn was validated against observed ΔPL,dyn via Pearson's correlation and Bland-Altman analysis. This method was then applied to 45 patients where ΔPaw, Edi,open, and Pocc were measured. Results The validation analysis was performed using 98 recordings obtained in 28 subjects. We found that the median ΔPL,dyn was 19cm H2O (15-23 cm H2O) and estimated ΔPL,dyn had a median of 20 cm H2O (IQR 16-25 cm H2O). The measured and predicted ΔPL,dyn, showed a moderate correlation (R2=0.70, p<0.0001) with a bias of 6% and limits of agreement approximating 28% – 40%. In the longitudinal cohort with 45 patients and 4508 study-hours, we computed the distribution of estimated ΔPL,dyn during assisted ventilation. Estimated ΔPL,dyn was elevated ( >25 cm H2O) in 21% of hours with spontaneous breathing and 35 patients had ≥1 hour of ΔPL,dyn >25 cm H2O. When estimated ΔPL,dyn exceeded 25 cm H2O, the contribution of respiratory effort to total lung-distending pressure was a median of 71% (IQR 58-82%). Conclusion Dynamic transpulmonary driving pressure, a measure of lung stress during spontaneous breathing, can be estimated by monitoring Edi and Pocc. Excessive respiratory effort may be an important and frequent contributor to excess lung stress and strain during mechanical ventilation.

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