Effect of mechanical ventilation strategy on dissemination of intratracheally instilled Escherichia coli in dogs

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Abstract
To test the effect of different mechanical ventilation strategies on dissemination of intratracheally instilled Escherichia coli in dogs and to determine the extent and distribution of lung damage. Prospective, randomized study. Experimental animal laboratory. Eighteen anesthetized and paralyzed dogs. We studied the effect of three ventilatory strategies based on two variables: transpulmonary pressure and positive end-expiratory pressure (PEEP). Group 1 animals (n = 6) were ventilated with a PEEP of 3 cm H2 O and a tidal volume of 15 mL/kg, which generated an end-inspiratory transpulmonary pressure of 2 We measured the pressure-volume relationship (pressure-volume curve) of the respiratory system before and 6 hrs after bacterial instillation. We obtained blood cultures before and 0.5, 1, 2, 3, 4, 5, and 6 hrs after bacterial instillation. After 6 hrs, the lungs were removed for histologic (histologic score) and gravimetric (wet-to-dry weight ratio, WW/DW) analysis. During the experiment 0, 5, and 1 dogs developed positive blood cultures in groups 1, 2, and 3, respectively. The number of dogs that developed bacteremia in group 2 was significantly greater than in the other two groups (p We conclude that the ventilatory strategy most likely to overdistend the lungs while allowing repetitive opening and closure of alveoli (group 2) facilitated bacterial translocation from the alveoli to the bloodstream and increased lung injury, as determined by histologic and gravimetric analysis. PEEP ameliorated these effects, despite lung overdistention, but increased histologic and gravimetric indices of lung injury in dependent as compared with the nondependent regions. (Crit Care Med 1997; 25:1733-1743)