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CRITICAL CARE AND TRAUMA

Increased Cerebral Tissue Oxygen Tension After Extensive Hemodilution with a Hemoglobin-Based Oxygen Carrier

Gregory M. T. Hare, MD PhD, FRCPC^*, Kathryn M. Hum^*, Steve Y. Kim^*, Aiala Barr, PhD, Andrew J. Baker, MD FRCPC^*, and C. David Mazer, MD FRCPC^*

Departments of *Anesthesia and Public Health, University of Toronto, St. Michael’s Hospital, Toronto, Ontario, Canada

Address correspondence and reprint requests to C. David Mazer, MD, FRCPC, Department of Anesthesia, University of Toronto, St. Michael’s Hospital, 30 Bond St., Toronto, Ontario, M5B 1W8, Canada. Address e-mail to mazerd{at}smh.toronto.on.ca

Transfusion of anemic patients with hemoglobin-based oxygen carriers (HBOCs) may improve cerebral oxygen delivery. Conversely, cerebral vasoconstriction, associated with HBOC transfusion, could limit optimal cerebral tissue oxygenation. We hypothesized that hemodilution with a HBOC would maintain cerebral tissue oxygenation, despite the occurrence of cerebral vasoconstriction. Isoflurane-anesthetized rats (100% oxygen) underwent direct measurement of mean arterial blood pressure (MAP), caudate tissue oxygen tension (P_BrO₂), and regional cortical cerebral blood flow (rCBF) before and after 50% of the estimated blood volume (30 mL/kg) was exchanged with either an HBOC (hemoglobin raffimer; Hemolink^TM) or pentastarch (n = 6). Hemodilution with hemoglobin raffimer caused a transient increase in P_BrO₂ from 24.9 ± 13.3 mm Hg to 32.2 ± 19.1 mm Hg (P < 0.05), a sustained increase in MAP, and no change in rCBF. Arterial blood oxygen content was maintained despite an increase in methemoglobin and reduced oxygen saturation. Hemodilution with pentastarch caused a transient increase in MAP, no change in P_BrO₂, and a sustained increase in rCBF (P < 0.05), whereas the hemoglobin concentration and oxygen content were significantly reduced. Hemodilution with hemoglobin raffimer augmented P_BrO₂ and prevented the increase in rCBF observed after similar hemodilution with pentastarch. These data suggest that transfusion with hemoglobin raffimer may help to maintain cerebral oxygenation during severe anemia.

IMPLICATIONS: This study demonstrates that cerebral tissue oxygen tension is increased after exchange transfusion with a hemoglobin-based oxygen carrier (hemoglobin raffimer), despite evidence of cerebral vasoconstriction and an increase in methemoglobin concentration in isoflurane-anesthetized rats.

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Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999