Abstract
To investigate the effect of positive end-expiratory pressure (PEEP) guided by transpulmonary pressure or with maximum oxygenation-directed PEEP on lung injury in a porcine model of acute respiratory distress syndrome (ARDS). The porcine model of ARDS was induced in 12 standard pigs by intratracheal infusion with normal saline. The pigs were then randomly divided into two groups who were ventilated with the lung-protective strategy of low tidal volume (VT) (6 ml/kg), using different methods to titrate PEEP level: transpulmonary pressure (TP group; n = 6) or maximum oxygenation (MO group; n = 6). Gas exchange, pulmonary mechanics, and hemodynamics were determined and pulmonary inflammatory response indices were measured after 4 h of ventilation. The titrated PEEP level in the TP group (6.12 ± 0.89 cmH2O) was significantly lower than that in the MO group (11.33 ± 2.07 cmH2O) (P < 0.05). The PaO2/FiO2 (P/F) after PEEP titration both improved in the TP and MO groups as compared with that at T0 (when the criteria for ARDS were obtained). The P/F in the TP group did not differ significantly from that in the MO group during the 4 h of ventilation (P > 0.05). Respiratory system compliance and lung compliance were significantly improved in the TP group compared to the MO group (P < 0.05). The VD/VT in the TP group was significantly lower than that in the MO group after 4 h of ventilation (P < 0.05). Central venous pressure increased and the cardiac index decreased significantly in the MO group as compared with the TP group (P < 0.05), whereas oxygen delivery did not differ significantly between the groups (P > 0.05). The pulmonary vascular permeability index and the extravascular lung water index in the TP group were significantly lower than those in the MO group (P < 0.05). The TP group had a lower lung wet to dry weight ratio, lung injury score, and MPO, TNF-, and IL-8 concentrations than the MO group (P < 0.05). In summary, in a pig model of ARDS, ventilation with low VT and transpulmonary pressure-guided PEEP adjustment was associated with improved compliance, reduced dead space ventilation, increased cardiac output, and relieved lung injury, as compared to maximum oxygenation-guide PEEP adjustment.
Highlights
Mechanical ventilation has improved survival in patients with acute respiratory distress syndrome (ARDS), it can cause further lung injury
Lung recruitment maneuver (LRM) were performed with 40 cmH2O Positive end-expiratory pressure (PEEP) for 30 s in the continuous positive airway pressure mode, followed by return to baseline ventilation, except that PEEP was maintained at 20 cmH2O.Arterial blood gas was measured after 5 min
In a porcine model of ARDS ventilated with low VT and with Ptp at end- inspiration limited to 25 cmH2O, Ptp-guided PEEP adjustment was associated with improved compliance, reduced dead space ventilation, increased cardiac output (CO), and relieved lung injury, as compared to optimal oxygenation-guided PEEP adjustment
Summary
Mechanical ventilation has improved survival in patients with acute respiratory distress syndrome (ARDS), it can cause further lung injury. The mortality rate of patients with ARDS, has remained high over the last two decades, despite the implementation of lung-protective ventilation. One reason for this may be that such global parameters (a fixed tidal volume, airway pressure, etc.) reflect distension of the whole lung and the chest wall, rather than the transpulmonary pressure (Ptp), the actual distending pressure of the lung [9,10,11]. We conducted a randomized controlled pilot study to test the hypothesis that PEEP titration based on Ptp would relieve lung injury better than that based on maximum oxygenation in an ARDS model
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