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

OBJECTIVEto 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. DESIGNAnimal experimental study. SETTINGAnimal experimental laboratory. SUBJECTSMixed-breed pigs (n = 18), aged 4 to 5 mos, weighing 25 to 30 kg. INTERVENTIONSThe 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 H2 O 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 RESULTSAt 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). CONCLUSIONSThe application of 10 cm H2 O of PEEP reduces EVLW in a time-dependent manner and maximum protective effect is achieved if it is applied immediately after lung injury production. (Crit Care Med 1999; 27:380-384)