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 protects animals from clinical sepsis after direct acute lung injury with Pseudomonas aeruginosa as compared with high "stretch" ventilation.


METHODS
Prospective study.


METHODS
Experimental animal laboratory.


METHODS
Twenty-seven anesthetized and paralyzed rabbits.


METHODS
P. aeruginosa (109 colony forming units) was instilled into 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 were 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-expiratory pressure of 3-5 cm H2O was used for all experiments. Radiolabeled albumin was used as a marker of alveolar epithelial permeability.


RESULTS
Hemodynamics, arterial blood gas determination, alveolar permeability, wet-to-dry ratios on lungs, and time course of bacteremia were determined. When final values were compared with the values at the beginning of the experiment, there were significant decreases in mean arterial pressure (from 104 +/- 15 to 57 +/- 20 mm Hg), pH (from 7.46 +/- 0.04 to 7.24 +/- 15), Pao2 (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 degrees C) in the high tidal volume group, whereas no significant differences were found in the low tidal volume group. Decreased alveolar permeability was shown in the low tidal volume group, as was decreased extravascular 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 noted in the time course of bacteremia, although there was a trend toward earlier 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, hemodynamic status, and acid-base status as well as decreased alveolar permeability and contralateral extravascular lung water.
Savel
R H
RH
Department of Anesthesia and Perioperative Care, University of California-San Francisco, San Francisco, CA 94143-0624, USA.
Yao
E C
EC
Gropper
M A
MA
D000818:Animals; D015415:Biomarkers / Q000032:analysis; D001784:Blood Gas Analysis; D001794:Blood Pressure; D002199:Capillary Permeability; D002985:Clinical Protocols; D004195:Disease Models, Animal; D015633:Extravascular Lung Water / Q000737:chemistry / Q000382:microbiology; D006439:Hemodynamics; D008297:Male; D011175:Positive-Pressure Respiration / Q000379:methods*; D011446:Prospective Studies; D011552:Pseudomonas Infections / Q000150:complications*; D011550:Pseudomonas aeruginosa; D011650:Pulmonary Alveoli / Q000098:blood supply; D011817:Rabbits; D012128:Respiratory Distress Syndrome / Q000382:microbiology* / Q000503:physiopathology / Q000628:therapy*; D013990:Tidal Volume; D013997:Time Factors
D015415:Biomarkers