• Clotilde Schilte, Pierre Bouzat, Anne Millet, Perrine Boucheix, Karin Pernet-Gallay, Benjamin Lemasson, Emmanuel L Barbier, and Jean-François Payen.
• 1Pôle Anesthésie Réanimation, Hôpital Michallon, CHU de Grenoble, Grenoble, France. 2INSERM, U836, Grenoble, France. 3Grenoble Institut des Neurosciences, Université Grenoble Alpes, Grenoble, France. 4Département de Réanimation Pédiatrique et Néonatale, Hôpital Couple Enfant, Grenoble, France.
• Crit. Care Med. 2015 Oct 1;43(10):2212-8.

ObjectivesBased on evidence supporting a potential relation between posttraumatic brain hypoxia and microcirculatory derangements with cell edema, we investigated the effects of the antiedematous agent mannitol on brain tissue oxygenation in a model of diffuse traumatic brain injury.DesignExperimental study.SettingNeurosciences and physiology laboratories.SubjectsAdult male Wistar rats.InterventionsThirty minutes after diffuse traumatic brain injury (impact-acceleration model), rats were IV administered with either a saline solution (traumatic brain injury-saline group) or 20% mannitol (1 g/kg) (traumatic brain injury-mannitol group). Sham-saline and sham-mannitol groups received no insult.Measurements And Main ResultsTwo series of experiments were conducted 2 hours after traumatic brain injury (or equivalent) to investigate 1) the effect of mannitol on brain edema and oxygenation, using a multiparametric magnetic resonance-based approach (n = 10 rats per group) to measure the apparent diffusion coefficient, tissue oxygen saturation, mean transit time, and blood volume fraction in the cortex and caudoputamen; 2) the effect of mannitol on brain tissue PO2 and on venous oxygen saturation of the superior sagittal sinus (n = 5 rats per group); and 3) the cortical ultrastructural changes after treatment (n = 1 per group, taken from the first experiment). Compared with the sham-saline group, the traumatic brain injury-saline group had significantly lower tissue oxygen saturation, brain tissue PO2, and venous oxygen saturation of the superior sagittal sinus values concomitant with diffuse brain edema. These effects were associated with microcirculatory collapse due to astrocyte swelling. Treatment with mannitol after traumatic brain injury reversed all these effects. In the absence of traumatic brain injury, mannitol had no effect on brain oxygenation. Mean transit time and blood volume fraction were comparable between the four groups of rats.ConclusionThe development of posttraumatic brain edema can limit the oxygen utilization by brain tissue without evidence of brain ischemia. Our findings indicate that an antiedematous agent such as mannitol can improve brain tissue oxygenation, possibly by limiting astrocyte swelling and restoring capillary perfusion.

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