Inspiratory Musclse Activity as a Non-invasive, Continuous, Complementary Marker of Dyspnea During Mechanical Ventilation

RATIONALE: Dyspnea is common during invasive mechanical ventilation but is difficult to assess in non-communicative patients. The Mechanical Ventilation-Respiratory Distress Observation Scale (MV-RDOS) is validated for observational assessment in this population but is intermittently applied and observer-dependent. OBJECTIVES: Evaluate whether inspiratory muscle activity, quantified as the pressure-time product of inspiratory muscle pressure (PmusPTP) and derived continuously and noninvasively from ventilator waveforms, is associated with intermittently applied MV-RDOS assessments. METHODS: Two-center prospective observational study in 45 adults receiving invasive mechanical ventilation unable to self-report dyspnea. MV-RDOS was assessed at least twice daily for up to five days. Airway flow and pressure were recorded continuously, and PmusPTP was computed for sequential 131-second airway waveform epochs and time-matched to MV-RDOS assessments. We evaluated discrimination of MV-RDOS-defined respiratory distress (MV-RDOS > 2.6) using receiver-operating-characteristic analysis and described the association between PmusPTP and MV-RDOS. MEASUREMENTS AND MAIN RESULTS: Among 281 time-matched MV-RDOS-PmusPTP pairs, PmusPTP showed discrimination for MV-RDOS > 2.6 with an area under the curve of 0.741 (95% CI 0.663-0.820). Youden-optimal operating point was PmusPTP = 20 cmH2O·s·min-1 (sensitivity 0.59; specificity 0.88). The linear association between MV-RDOS and PmusPTP was moderate (R2 = 0.36; P < .001), with substantial dispersion. CONCLUSIONS: Continuous noninvasive estimation of inspiratory PmusPTP from ventilator waveforms yields a physiological index moderately associated with MV-RDOS determinations in non-communicative mechanically ventilated adults. These findings support the feasibility of continuous inspiratory muscle activity monitoring and suggest further studies to determine how such measures may complement observational and patient-reported dyspnea assessments.