Dead space analysis at different levels of positive end-expiratory pressure in acute respiratory distress syndrome patients

Abstract

PurposeTo analyze the effects of positive end-expiratory pressure (PEEP) on Bohr's dead space (VDBohr/VT) in patients with acute respiratory distress syndrome (ARDS). Material and methodsFourteen ARDS patients under lung protective ventilation settings were submitted to 4 different levels of PEEP (0, 6, 10, 16 cmH2O). Respiratory mechanics, hemodynamics and volumetric capnography were recorded at each protocol step. ResultsTwo groups of patients responded differently to PEEP when comparing baseline with 16-PEEP: those in which driving pressure increased > 15% (∆P˃15%, n = 7, p = .016) and those in which the change was ≤15% (∆P≤15%, n = 7, p = .700). VDBohr/VT was higher in ∆P≤15% than in ∆P≤15% patients at baseline ventilation [0.58 (0.49–0.60) vs 0.46 (0.43–0.46) p = .018], at 0-PEEP [0.50 (0.47–0.54) vs 0.41 (0.40–0.43) p = .012], at 6-PEEP [0.55 (0.49–0.57) vs 0.44 (0.42–0.45) p = .008], at 10-PEEP [0.59 (0.51–0.59) vs 0.45 (0.44–0.46) p = .006] and at 16-PEEP [0.61 (0.56–0.65) vs 0.47 (0.45–0.48) p = .001]. We found a good correlation between ∆P and VDBohr/VT only in the ∆P˃15% group (r = 0.74, p < .001). ConclusionsIncreases in PEEP result in higher VDBohr/VT only when associated with an increase in driving pressure.