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Myocardial Blood Flow and Oxygen Consumption during Isovolemic Hemodilution Alone and in Combination with Adenosine-Induced Controlled Hypotension

Received from the Department of Anesthesiology, Illinois Masonic Medical Center, and the Departments of Anesthesiology and of Physiology and Biophysics, University of Illinois College of Medicine, Chicago, Illinois.

Abstract

Recent reports have proposed combining isovolemic hemodilution and controlled hypotension tolimit blood loss during surgery. Before such a technique can be considered for clinical use, it must be demonstrated that it does not endanger maintenance of adequate myocardial oxygenation. Accordingly, measurements of left ventricular myocardial blood flow and oxygen consumption were obtained during isovolemic hemodilution alone and in combination with adenosine-induced controlled hypotension in ten pentobar-bital-anesthetized, open chest dogs with normal coronay circulation. Hemodilution to a hematocrit of 21.7% was produced by isovolemic exchange of whole blood for 5% dextran. In the presence of hemodilution, adenosine was infused intravenously at a rate sufficient to decrease mean aortic pressure to 51 mm Hg. Myocardial blood flow was measured with radioactive microspheres and used to calculate global left ventricular myocardial oxygen consumptionand oxygen supply. Hemodilution alone increased aortic blood flow (+43%) but had no effect on aortic pressure, left atrial pressure, heart rate, or left ventricular dP/dt_max an increase in myocardial blood flow (+130%) maintained oxygen supply and consumption at the baseline level. Adenosine-induced hypotension during hemodilution decreased heart rate (–35%), left ventricular dP/dt max (–28%), and aortic blood flow (–14%). These systemic responses were accompanied byreduced myocardial oxygen consumption (–29%) and increased myocardial blood flow (+54%) and myocardial oxygen supply (+72%). These latter effects resulted in reduction in the coronary arterio-venous oxygen content difference and in an attendant rise in coronary sinus Po₂ (+66%), which are signs of luxuriant myocardial perfusion. The present study demonstrated in anesthetized dogs that 1) myocardial oxygenation is well maintained during isovolemic hemodilution alone and, 2) myocardial oxygenation is influenced favorably when isovolemic hemodilution is combined with adenosine-induced controlled hypotension. Further studies are required to evaluate the safetyof the latter condition in hearts with stenotic coronary arteries.

Key Words: ANESTHETIC TECHNIQUES—hypotensive • HEART—myocardial oxygenation • BLOOD—hemodilution

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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