Effect of PEEP on Dead Space in an Experimental Model of ARDS

BACKGROUND: The difference between Bohr and Enghoff dead space are not well described in ARDS patients. We aimed to analyze the effect of PEEP on the Bohr and Enghoff dead spaces in a model of ARDS. METHODS: 10 pigs submitted to randomized PEEP steps of 0, 5, 10, 15, 20, 25 and 30 cm H2O were evaluated with the use of lung ultrasound images, alveolar-arterial oxygen difference (P(A-a)O2), transpulmonary mechanics, and volumetric capnography at each PEEP step. RESULTS: At PEEP >= 15 cm H2O, atelectasis and P(A-a)O2 progressively decreased while end-inspiratory transpulmonary pressure (P-L), end-expiratory P-L, and driving P-L increased (all P < .001). Bohr dead space (V-DBohr/V-T), airway dead space (V-Daw/V-T), and alveolar dead space (V-Dalv/V-Talv), reached their highest values at PEEP 30 cm H2O (0.69 +/- 0.10, 0.53 +/- 0.13 and 0.35 +/- 0.06, respectively). At PEEP