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CRITICAL CARE AND TRAUMA

Low Tidal Volume Ventilation in a Porcine Model of Acute Lung Injury Improves Cerebral Tissue Oxygenation

Johannes Bickenbach, MD^*, Norbert Zoremba, MD, Michael Fries, MD, Rolf Dembinski, MD, PhD^*, Robert Doering, Eileen Ogawa, MD^*, Rolf Rossaint, MD, PhD^*, and Ralf Kuhlen, MD, PhD

From the *Department of Surgical Intensive Care; Department of Anesthesiology, RWTH University Hospital, Aachen, Germany; and Department of Intensive Care Medicine, Helios Hospital Berlin Buch, Berlin, Germany.

Address correspondence and reprint requests to Johannes Bickenbach, Department of Surgical Intensive Care, RWTH University Hospital, Pauwelsstr. 30, D-52074 Aachen, Germany. Address e-mail to jbickenbach{at}ukaachen.de.

BACKGROUND: In study, we investigated the effects of different tidal volumes on cerebral tissue oxygenation and cerebral metabolism in a porcine model of acute lung injury (ALI). We hypothesized that mechanical ventilation with low tidal (LT) volumes improves cerebral tissue oxygenation and metabolism after experimentally induced ALI.

METHODS: After inducing experimental ALI by surfactant depletion, we studied two conditions in 10 female pigs: 1) LT volume ventilation with 6 mL/kg body weight, and 2) high tidal (HT) volume ventilation with 12 mL/kg body weight. Variables of gas exchange, hemodynamic, continuous cerebral tissue oxygen tension (p_tiO₂), cerebral microdialysis, and systemic cytokines were analyzed. After induction of ALI, data were collected at 2, 4, and 8 h. The primary end point was the change in p_tiO₂. For group comparisons, a t-test was used. A value of <0.05 was considered to indicate statistical significance.

RESULTS: At baseline and after induction of ALI, no differences between groups were found in p_tiO₂; however, p_tiO₂ was significantly lower in the HT group after 4 and 8 h. Pao₂ and Paco₂ showed no significant differences between the groups at all timepoints. Regarding cerebral microdialysis, a significantly higher level of extracellular lactate could be demonstrated after 2, 4, and 8 h in the HT group. The release of cytokines resulted in higher values for interleukin-6 and interleukin-8 in the HT group.

CONCLUSION: Protective ventilation with LT yielded a significant improvement in cerebral tissue oxygenation and metabolism compared to HT ventilation in a porcine model of ALI. There was dissociation between arterial and cerebral tissue oxygenation. Cerebral oxygenation and metabolism might have possibly been impaired by a more distinctive inflammatory response in the HT group.