Pressure support ventilation in intensive care patients receiving prolonged invasive ventilation

Background: To our knowledge, the use and management of pressure support ventilation (PSV) in patients receiving prolonged (≥ 7 days) invasive mechanical ventilation has not previously been described. Objective: To collect and analyse data on the use and management of PSV in critically ill patients receiving prolonged ventilation. Design, setting and participants: We performed a multicentre retrospective observational study in Australia, with a focus on PSV in patients ventilated for ≥ 7 days. Main outcome measures: We obtained detailed data on ventilator management twice daily (8am and 8pm moments) for the first 7 days of ventilation. Results: Among 143 consecutive patients, 90/142 (63.4%) had received PSV by Day 7, and PSV accounted for 40.5% (784/1935) of ventilation moments. The most common pressure support level was 10 cmH(2)O (352/780) observations [45.1%]) with little variation over time, and 37 of 114 patients (32.4%) had no change in pressure support. Mean tidal volume during PSV was 8.3 (7.0–9.5) mL/kg predicted bodyweight (PBW) compared with 7.5 (7.0–8.3) mL/kg PBW during mandatory ventilation (P < 0.001). For 74.6% (247/331) of moments, despite a tidal volume of more than 8 mL/kg PBW, the pressure support level was not changed. Among 122 patients exposed to PSV, 97 (79.5%) received likely over-assistance according to rapid shallow breathing index criteria. Of 784 PSV moments, 411 (52.4%) were also likely over-assisted according to rapid shallow breathing index criteria, and 269/346 (77.7%) having no subsequent adjustment of pressure support. Conclusions: In patients receiving prolonged ventilation, almost two-thirds received PSV, which accounted for 40.5% of mechanical ventilation time. Half of the PSV-treated patients were exposed to high tidal volume and two-thirds to likely over-assistance. These observations provide evidence that can be used to inform interventional studies of PSV management.