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Hyperoxic ventilation at the critical hematocrit: Effects on myocardial perfusion and function

Background:  Hemodilution reduces hematocrit (Hct) and blood oxygen content. Tissue oxygenation is mainly preserved by increased cardiac output. As myocardial O2‐demands increase, coronary vasodilatation becomes necessary to increase myocardial blood flow. Myocardial ischemia occurs at a critical Hc...

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Published in:Acta anaesthesiologica Scandinavica 2004-09, Vol.48 (8), p.951-959
Main Authors: Kemming, G. I., Meisner, F. G., Meier, J., Tillmanns, J., Thein, E., Eriskat, J., Habler, O. P.
Format: Article
Language:English
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Summary:Background:  Hemodilution reduces hematocrit (Hct) and blood oxygen content. Tissue oxygenation is mainly preserved by increased cardiac output. As myocardial O2‐demands increase, coronary vasodilatation becomes necessary to increase myocardial blood flow. Myocardial ischemia occurs at a critical Hct‐value (Hctcrit), with accompanying exhaustion of coronary reserve. Hyperoxic ventilation is known to both reverse peripheral tissue hypoxia at Hctcrit and also to induce coronary vasoconstriction. This study aimed to determine whether hyperoxic ventilation at Hctcrit further exacerbates myocardial ischemia and dysfunction. Methods:  Nine anesthetized pigs ventilated on room air were hemodiluted by 1 : 1 exchange of blood with pentastarch (6%HES) to Hctcrit , defined as onset of myocardial ischemia (ECG changes). At Hctcrit , hyperoxic ventilation was started. Measurements were performed at baseline, at Hctcrit, and after 15 min of hyperoxic ventilation. We determined myocardial blood flow (microsphere method), arterial O2‐content, subendocardial O2‐delivery and myocardial function (left ventricular pressure increase). Results:  At Hctcrit 7 (6;8)%, O2‐content was reduced [3.7 (3.1;3.9) ml dl−1]. Despite a compensatory increase of myocardial blood flow [531 (449;573), ml min−1100 g−1], all pigs displayed myocardial ischemia and compromised myocardial function (P 
ISSN:0001-5172
1399-6576
DOI:10.1111/j.0001-5172.2004.00460.x