Immediate application of positive-end expiratory pressure is more effective than delayed positive-end expiratory pressure to reduce extravascular lung water

Objective: to determine by the measurement of extravascular lung water (EVL W) whether the timing of positive end expiratory pressure (PEEP) applicatio n influences the intensity of lung injury. Design: Animal experimental study. Setting: Animal experimental laboratory. Subjects: Mixed-breed pigs (n = 18), aged 4 to 5 mos, weighing 25 to 30 kg, Interventions: The animals were anesthetized and tracheotomized, after whic h a permeability pulmonary edema was instigated by infusing oleic acid (0.1 /kg) into the central vein, All animals were then randomly divided into th ree groups, In group 1 (n = 5), 10 cm H2O of PEEP was applied immediately a fter the oleic acid infusion and maintained throughout the 6 hrs of the exp eriment, Group 2 (n = 7) received the same level of PEEP 120 mins after the insult for 4 hrs, Group 3 (n = 6), the control group, was ventilated witho ut PEEP for the six hrs of the experiment, Measurements and Main Results: At the end of the experiment, EVLW was calcu lated by gravimetric method. EVLW in group 1 (11.46 +/- 2.00 mL/kg) was sig nificantly less than in group 2 (19.12 +/- 2.62 mL/kg) and group 3 (25.81 /- 1.57 mL/kg), (p<.0001). Oxygenation also showed important differences by the end of the experiment when the Pao(2)/Flo(2) ratio was significantly b etter in group 1 (467 +/- 73) than in group 2(180 +/- 82) and group 3 (39 /- 9), (p<.0001), Conclusions: The application of 10 cm H2O of PEEP reduces EVLW in a time de pendent manner and maximum protective effect is achieved if it is applied i mmediately after lung injury production.