Ability of dynamic airway pressure curve profile and elastance for positive end-expiratory pressure titration
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To evaluate the ability of three indices derived from the airway pressure curve for titrating positive end-expiratory pressure (PEEP) to minimize mechanical stress while improving lung aeration assessed by computed tomography (CT).
Prospective, experimental study.
University research facilities.
Animals were anesthetized and mechanically ventilated with tidal volume of 7 ml kg−1. In non-injured lungs (n = 6), PEEP was set at 16 cmH2O and stepwise decreased until zero. Acute lung injury was then induced either with oleic acid (n = 6) or surfactant depletion (n = 6). A recruitment maneuver was performed, the PEEP set at 26 cmH2O and decreased stepwise until zero. CT scans were obtained at end-expiratory and end-inspiratory pauses. The elastance of the respiratory system (Ers), the stress index and the percentage of volume-dependent elastance (%E 2) were estimated.
Measurements and main results
In non-injured and injured lungs, the PEEP at which Ers was lowest (8–4 and 16–12 cmH2O, respectively) corresponded to the best compromise between recruitment/hyperinflation. In non-injured lungs, stress index and %E 2 correlated with tidal recruitment and hyperinflation. In injured lungs, stress index and %E 2 suggested overdistension at all PEEP levels, whereas the CT scans evidenced tidal recruitment and hyperinflation simultaneously.
During ventilation with low tidal volumes, Ers seems to be useful for guiding PEEP titration in non-injured and injured lungs, while stress index and %E 2 are useful in non-injured lungs only. Our results suggest that Ers can be superior to the stress index and %E 2 to guide PEEP titration in focal loss of lung aeration.
KeywordsAcute lung injury Lung protective strategy Ventilator-induced lung injury
This work was supported by grants from the Brazilian Agencies CNPq and FAPERJ, the Clinic of Anesthesiology of the University Hospital Carl Gustav Carus, Technical University Dresden, Germany and by grant no. HL-086827 from the National Institutes of Health, Bethesda, MA, USA.
Dynamic CT-scan. Tidal inflation-related changes at the hilus region with a PEEP of 0 cmH2O (WMV 6123 kb)
Dynamic CT-scan. Tidal inflation-related changes at the hilus region with a PEEP of 12 cmH2O (WMV 6123 kb)
Dynamic CT-scan. Tidal inflation-related changes at the hilus region with a PEEP of 26 cmH2O (WMV 6123 kb)
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