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 (EVLW) whether the timing of positive-end expiratory pressure (PEEP) application 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 which a permeability pulmonary edema was instigated by infusing oleic acid (0.1/kg) into the central vein. All animals were then randomly divided into three groups. In group 1 (n = 5), 10 cm H2O of PEEP was applied immediately after the oleic acid infusion and maintained throughout the 6 hrs of the experiment. 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 without PEEP for the six hrs of the experiment. MEASUREMENTS AND MAIN RESULTS: At the end of the experiment, EVLW was calculated by gravimetric method. EVLW in group 1 (11.46+/-2.00 mL/kg) was significantly 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 Pao2/Fio2 ratio was significantly better 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-dependent manner and maximum protective effect is achieved if it is applied immediately after lung injury production.