Inadequate assessment of patient-ventilator interaction due to suboptimal diaphragm electrical activity signal filtering

Introduction: Monitoring diaphragm electrical activity (EAdi) allows evaluation of patient-ventilator interaction and effort, but EAdi reliability is challenged due to possible signal artefacts. Notably, expiratory EAdi peaks \u003e1 µV are often classified as ineffective efforts. We reason that such small peaks could reflect cardiac artefacts. In-depth signal analysis was performed to explain how incorrect EAdi filtering affects interpretation of patient effort. Methods: EAdi, raw diaphragm electromyography, diaphragm pressure, flow and airway pressure (Paw) were measured in two patients under pressure support ventilation. Also, waveform data (EAdi, esophageal pressure (Pes), flow and Paw) from 15 patients ventilated with continuous positive airway pressure (10-min/patient) were analyzed to assess incidence of expiratory EAdi peaks \u003e1 µV. Results: Expiratory EAdi peaks did not reflect patient effort, but coincided with cardiac activity (F1). Also, 4063 breaths from 15 patients showed presence of 240 expiratory EAdi peaks in 12 patients (median % of total breaths; 6.8% (min-max: 0.6-23.6%)). Only 8.8% of the peaks were true ineffective efforts (confirmed with Pes). Discussion: Patient-ventilator interaction can be misinterpreted due to suboptimal EAdi filtering. This affects EAdi reliability and highlights the need for proper understanding of monitoring signals used for research and patient care.