BACKGROUND: Early exercise has been recommended in critically ill patients, but its impact on subject-ventilator interaction is still unclear. Therefore, the aim of this study was to evaluate the occurrence of subject-ventilator asynchrony during passive exercise in mechanically ventilated subjects. METHODS: This study included deeply sedated subjects who were under mechanical ventilation for < 72 h. Subjects were coupled to a cycle ergometer and maintained at rest for 5 min (baseline period). After this period, they started 20 min of passive exercise, followed by 10 min of rest (recovery period). The occurrence of asynchrony was monitored by the analysis of flow and airway pressure waveforms, registered throughout the protocol during the baseline, exercise, and recovery periods. Hemodynamic and respiratory parameters were registered at the end of each period. Finally, arterial blood gas analysis was performed twice, at the end of the baseline period and at the end of the recovery period. RESULTS: 8 subjects were enrolled (63.3 6 16.7 y old, 50% male). The asynchrony index increased during exercise (median 32.1% [interquartile range (IQR) 18.6-47.6%]), compared to baseline (median 6.6% [IQR 3.9-10.4%]), returning to initial levels during the recovery period (median 2.7% [IQR 0-12.2%]). The most frequent types of asynchrony were ineffective triggering (index of 11.8% [IQR 1.2-22.5%] during exercise, compared to 2.0% [IQR 1.4-4.4%] at baseline), and insufficient flow (index of 11.7% [IQR 4.7-19.3%] during exercise, compared to 2.0% [IQR 1.1 to 3.3%] at baseline). There were no significant changes in the hemodynamic and respiratory variables. CONCLUSIONS: Early cycle ergometer passive exercise in deeply sedated subjects can worsen subject-ventilator interaction, due to ineffective triggering and insufficient flow. Adjustments in the ventilatory parameters may be necessary to avoid asynchrony during exercise.

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