Protective effects of low tidal volume ventilation in a rabbit model of Pseudomonas aeruginosa-induced acute lung injury

Objective: To determine whether low "stretch" mechanical ventilation protec ts animals from clinical sepsis after direct acute lung injury with Pseudom onas aeruginosa as compared with high "stretch" ventilation. Design: Prospective study. Setting: Experimental animal laboratory. Subjects: Twenty-seven anesthetized and paralyzed rabbits. Interventions: P. aeruginosa (10(9) colony forming units) was instilled int o the right lungs of rabbits that were then ventilated at a tidal volume of either 15 mL/kg (n = 11) or 6 mL/kg (n = 7) for 8 hrs.: Control animals we re ventilated at a tidal volume of either 15 mL/kg (n = 4) or 6 mL/kg (n = 5) for 8 hrs, but an instillate without bacteria was used. A positive end-e xpiratory pressure of 3-5 cm H2O was used for all experiments. Radiolabeled albumin was used as a marker of alveolar epithelial permeability. Measurements and Main Results: Hemodynamics, arterial blood-gas determinati on, alveolar permeability, wet-to-dry ratios on lungs, and time course of b acteremia were determined. When final: values were compared with the values at the beginning of the experiment, there were significant decreases in me an arterial pressure (from 104 +/- 15 to 57 +/- 20 mm Hg), pH (from 7.46 +/ - 0.04 to 7.24 +/- 15), Pao(2) (from 528 +/- 35 to 129 +/- 104 torr [70.4 /- 4.7 to 17.2 +/- 13.9 kPa]), and temperature (from 38.2 +/- 1 to 36.2 +/- 1.2 degreesC) in the high tidal volume group, whereas no significant diffe rences were found in the low tidal volume group. Decreased alveolar permeab ility was shown in the low tidal volume group, as was decreased extravascul ar lung water in the uninstilled lung in the low tidal volume group (12.7 /- 2.5 vs. 4.3 +/- 0.45 g H2O/g dry lung). No noteworthy difference was not ed in the time course of bacteremia, although there was a trend toward earl ier bacteremia in the high tidal volume group. Conclusions: In our animal model of P. aeruginosa-induced acute lung injury , low tidal volume ventilation was correlated with improved oxygenation, he modynamic status, and acid-base status as well as decreased alveolar permea bility and contralateral extravascular lung water.