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Effects of pressure-support ventilation with different levels of positive end-expiratory in a mild model of acute respiratory distress syndrome
Intensive Care Medicine Experimentalvolume 3, Article number: A573 (2015)
Pressure-support ventilation improves lung mechanics, blood gas exchange, hemodynamics, and work of breathing (WOB) in mild acute respiratory distress syndrome (ARDS) [1, 2]. Nevertheless, those beneficial effects could be dependent of positive end-expiratory pressure (PEEP) applied during mechanical ventilation. So far, no study has compared pressure-support ventilation (PSV) with pressure controlled ventilation (PCV) in different PEEP levels.
To compare PSV and PCV target to protective tidal volume (VT=6ml/kg) using two PEEP levels (2 and 5 cmH2O) in a mild ARDS model.
Thirty-two male Wistar rats (310 ± 19 g) were submitted to intratracheal Escherichia coli lipopolysaccharide (200µg in 200µl of saline) instillation. After 24 hours, animals were anesthetized, tracheotomized, and their lungs were mechanically ventilated in PSV to achieve VT = 6 ml/kg. After baseline data collection, animals were randomly divided to four groups (n=8/group):
PCV + PEEP = 2 cmH2O (PCV-P2);
PCV + PEEP = 5 cmH2O (PCV-P5);
PSV + PEEP = 2 cmH2O (PSV-P2);
PSV + PEEP = 5 cmH2O (PSV-P5).
Animals were ventilated for 2 hours. Mean arterial pressure (MAP), arterial blood gases, peak airway (Ppeak,RS) and peak transpulmonary (Ppeak,L) pressures, and pressure-time product (PTP), as a surrogate of WOB, were evaluated.
All animals showed better oxygenation along time, regardless of ventilator strategy. Animals submitted to PCV, regardless of PEEP, received more colloids to keep MAP>70 mmHg. Ppeak,RS, and Ppeak,L were higher in animals submitted to PEEP = 5 cmH2O than PEEP = 2 cmH2O, independently of pressure-controlled, and pressure-support ventilator strategies. Nevertheless, at PEEP = 5 cmH2O, but not at PEEP = 2 cmH2O, animals submitted to PSV showed lower Ppeak,RS, and Ppeak,L compared to PCV animals (PSV-P5:11.2 ± 1.9 cmH2O vs PCV-P5:15.3 ± 1.4 cmH2O, p < 0.05). In accordance, PTP was lower in animals submitted to PEEP = 5 cmH2O compared to PEEP = 2 cmH2O during PSV (PSV-P5:0.08 ± 0.03 cmH2O.s vs PSV-P2:0.22 ± 0.09 cmH2O.s, p < 0.05).
In a mild ARDS model, pressure-support ventilation is associated to better hemodynamics, lung mechanics, and it seems to have a dependent effect of the adjusted PEEP level, as depicted by work of breathing.
CNPq, FAPERJ, CAPES, PRONEX, MS-DECIT
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