The patient-ventilator breath contribution (PVBC) index estimates the relative contribution of the patient to total tidal volume (Vt_insp) during mechanical ventilation in neurally adjusted ventilator assist mode and has been used to titrate ventilator support. The reliability of this index in ventilated patients is unknown and was investigated in this study. PVBC was calculated by comparing tidal volume (Vt_insp) and diaphragm electrical activity (EAdi) during assisted breaths (Vt_insp/EAdi)_assist and during unassisted breaths (Vt_insp/EAdi)_no-assist. Vt_insp was normalized to peak EAdi (EAdi_peak) using 1) one assisted breath, 2) five consecutive assisted breaths, or 3) five assisted breaths with matching EAdi preceding the unassisted breath (^N1PVBC², ^X5PVBC², and PX5VBCEAdi-matching2 , respectively). In addition, PVBC was calculated by comparing only Vt_insp for breaths with matching EAdi (PVBCβ²). Test-retest reliability of the different PVBC calculation methods was evaluated with the intraclass correlation coefficient (ICC) using five repeated PVBC maneuvers performed with a 1-min interval. In total, 125 PVBC maneuvers were analyzed in 25 patients. ICC [95% confidence interval] values were 0.46 [0.23-0.66], 0.51 [0.33-0.70], and 0.42 [0.14-0.69] for ^N1PVBC², ^X5PVBC², PX5VBCEAdi-matching2 , respectively. Complex waveform analyses showed that insufficient EAdi filtering by the ventilator software affects reliability of PVBC calculation. With our new EAdi-matching techniques reliability improved (PVBCβ² ICC: 0.78 [0.60-0.90]). We conclude that current techniques to calculate PVBC exhibit low reliability and that our newly developed criteria and estimation of PVBC-using Vt_insp of assisted breaths and unassisted breaths with matching EAdi-improves reliability. This may help implementation of PVBC in clinical practice. NEW & NOTEWORTHY The patient-ventilator breath contribution (PVBC) index estimates the relative contribution of the patient to tidal volume generated by the patient and the mechanical ventilator during mechanical ventilation in neurally adjusted ventilator assist mode. It could be used to titrate ventilator support and thus to limit development of diaphragm dysfunction in intensive care unit patients. Currently available methods for bedside assessment of PVBC are unreliable. Our newly developed criteria and estimation of PVBC largely improve reliability and help to quantify patient contribution to total inspiratory effort.

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