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Anesth Analg 2003;96:28-32
© 2003 International Anesthesia Research Society

CARDIOVASCULAR ANESTHESIA

Hemodilution Does Not Alter Arterial Baroreflex Control of Heart Rate in Anesthetized Dogs

Makoto Tanaka, MD, and Toshiaki Nishikawa, MD

Department of Anesthesia, Akita University School of Medicine, Japan

Address correspondence and reprint requests to Makoto Tanaka, MD, Department of Anesthesia, Akita University School of Medicine, Hondo 1–1-1, Akita-City, 010–8543, Japan. Address e-mail to mtanaka{at}med.akita-u.ac.jp

The cardiovascular effects of acute normovolemic hemodilution (ANH) are characterized by increased cardiac output and decreased systemic vascular resistance. However, whether arterial baroreflex function is altered by ANH remains undetermined. We assigned 23 anesthetized, mechanically ventilated dogs to mild ANH (hemoglobin, 7–8 g/dL; n = 11) or profound ANH (hemoglobin, 4–5 g/dL; n = 12) achieved by phlebotomy and simultaneous exchange with lactated Ringer’s solution at 1:3 ratio to maintain constant central venous pressure and pulmonary artery occluded pressure. Baroreflex sensitivity was assessed by measurements of RR intervals of the electrocardiogram and mean arterial blood pressure (MAP) through a femoral artery catheter. Baroreflex responses were triggered by bolus IV injections of phenylephrine (25–75 µg) and nitroprusside (50–100 µg). The linear portion of the baroreflex curves relating RR intervals and MAP were used to determine baroreflex sensitivities. Compared with the predilution period, both ANH groups had significant increases in cardiac output and decreases in systemic vascular resistance (P < 0.01), whereas MAP and heart rate (HR) remained unchanged. However, no significant difference was detected between pre-ANH and post-ANH baroreflex sensitivities in either group. Our results indicate that arterial baroreflex control of HR is preserved during ANH to a hemoglobin concentration of 4–5 g/dL in anesthetized dogs.

IMPLICATIONS: Acute normovolemic hemodilution may be preoperatively used to minimize the requirement of allogeneic blood products during major surgery. We found that baroreflex function is preserved during mild (hemoglobin concentration, 7–8 g/dL) and profound hemodilution (hemoglobin concentration, 4–5 g/dL) in pentobarbital-anesthetized dogs.






Lippincott, Williams & Wilkins 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 HighWire Press
Copyright © 2003 by the International Anesthesia Research Society.