• Chang-Yi Lin, Haibo Zhang, Kuo-Chen Cheng, and Arthur S Slutsky.
• Department of Medicine, Mackay Memorial Hospital, Taiwan.
• Crit. Care Med. 2003 May 1;31(5):1429-34.

ObjectiveWe examined the hypothesis that mechanical ventilation with a potentially injurious strategy would predispose animals to the detrimental effects of subsequent instillation of bacteria.DesignInterventional animal study.SettingA university hospital research laboratory.SubjectsFifty Sprague-Dawley male rats.InterventionsRats were anesthetized and randomized to receive a protective (tidal volume 7 mL/kg, positive end-expiratory pressure 5 cm H(2)O, n = 25) or an injurious ventilatory strategy (tidal volume 21 mL/kg, zero positive end-expiratory pressure, n = 25). Hemodynamics were similar during the 1-hr ventilation period in the two groups. Animals were then disconnected from the ventilator and Pseudomonas aeruginosa was instilled intratracheally before extubation. Thereafter, animals breathed spontaneously; mortality rate was assessed up to 48 hrs, at which time the animals were killed.Measurements And Main ResultsThe 48-hr mortality rate was 28% in the protective group and 40% in the injurious group (p = not significant). A positive bacterial culture from the lung was obtained in 56% of the surviving rats in the low tidal volume group and 67% in the high tidal volume group (p =.059). A positive blood bacterial culture was found in 11% of the low tidal volume group and 33% in the high tidal volume group (p <.05). The absolute bacterial count in the blood was lower in the low tidal volume group compared with the high tidal volume group (p <.05). Concentrations of blood tumor necrosis factor-alpha and macrophage inflammatory protein-2, and lung macrophage inflammatory protein-2 at 48 hrs were significantly higher in the low tidal volume group than in the high tidal volume group.ConclusionsAn injurious ventilatory strategy predisposes animals to subsequent bacteremia associated with an impaired host defense reflected by cytokine response.

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