Pb840

We assessed adult patients within 24 h after receiving invasive mechanical ventilation, which was anticipated to be continued for more than 48 h. The exclusion criteria were as follows: patients aged below 18 years, with trauma or chest tube insertion at the measurement point, receiving treatment with continuous neuromuscular blocking agent (NMBA) infusion, and diagnosed with esophageal disease.
Throughout the study period, all patients received pressure assist-control ventilation using the same ICU ventilator (PB840 or PB980) (Covidien, Mansfield, Massachusetts). The inspiratory pressure was set to obtain a tidal volume of 6–8 mL/kg ideal body weight. Parameters such as positive end-expiratory pressure, fraction of inspired oxygen, respiratory frequency, inspiratory time and flow trigger sensitivity were adjusted by bedside physicians. Other patient management strategies were performed by the bedside physicians and nurses according to the critical care guidelines and the analgesia-sedation protocol of our institution.

All exercise tests were made using the same bedside cycle ergometer (Fig. 1) (MOTOmed Letto 2, RECK-Technik GmbH and Co. Betzenweiler, Germany). Patients randomized to PSV/PAV+ were ventilated with a PB 840 ventilator (Covidien, Mansfield, MA, USA). Patients randomized to PSV/NAVA were ventilated with a Servo-i ventilator (Maquet, Solna, Sweden). An indirect calorimetry apparatus was used to measure oxygen uptake (Quark RMR ICU; Cosmed, Rome, Italy).Fig. 1

Example of a patient ventilated with Neurally Adjusted Ventilator Assist (NAVA) while performing exercise with the cycle ergometer (MOTOmed Letto 2, RECK-Technik GmbH and Co. Betzenweiler, Germany). Oxygen consumption is measured through indirect calorimetry

Airway flow and pressure sensors were connected to the respiratory circuit, proximal to the Y-piece. The flow was measured through a pneumotachograph (Fleish No. 2; Metabo; Epalinges, Switzerland). Proximal airway pressure was measured using a differential pressure transducer (Validyne MP45 ±80cmH₂O; Northridge, CA, USA). Signals were acquired with an analogue–digital converter (MP100; Biopac systems, Goleta, CA, USA), sampled at 200 Hz and stored in a laptop computer for subsequent off-line analysis (Acqknowledge 3.7.3, Biopac Systems).