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Hyperoxic ventilation at the critical hematocrit: Effects on myocardial perfusion and function
Author(s) -
Kemming G. I.,
Meisner F. G.,
Meier J.,
Tillmanns J.,
Thein E.,
Eriskat J.,
Habler O. P.
Publication year - 2004
Publication title -
acta anaesthesiologica scandinavica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.738
H-Index - 107
eISSN - 1399-6576
pISSN - 0001-5172
DOI - 10.1111/j.0001-5172.2004.00460.x
Subject(s) - medicine , hematocrit , cardiology , hypoxic pulmonary vasoconstriction , ventilation (architecture) , oxygenation , anesthesia , perfusion , blood flow , coronary perfusion pressure , cardiac output , coronary circulation , vascular resistance , vasoconstriction , ischemia , cardiac function curve , hemodynamics , heart failure , cardiopulmonary resuscitation , resuscitation , mechanical engineering , engineering
Background: Hemodilution reduces hematocrit (Hct) and blood oxygen content. Tissue oxygenation is mainly preserved by increased cardiac output. As myocardial O 2 ‐demands increase, coronary vasodilatation becomes necessary to increase myocardial blood flow. Myocardial ischemia occurs at a critical Hct‐value (Hct crit ), 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 Hct crit , defined as onset of myocardial ischemia (ECG changes). At Hct crit , hyperoxic ventilation was started. Measurements were performed at baseline, at Hct crit , and after 15 min of hyperoxic ventilation. We determined myocardial blood flow (microsphere method), arterial O 2 ‐content, subendocardial O 2 ‐delivery and myocardial function (left ventricular pressure increase). Results: At Hctcrit 7 (6;8)%, O 2 ‐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 −1 100 g −1 ], all pigs displayed myocardial ischemia and compromised myocardial function ( P < 0.05). Hyperoxic ventilation produced increased coronary vascular resistance secondary to vasoconstriction, and reduced myocardial blood flow [426 (404;464), ml min −1 100 g −1 ; P < 0.05]. Myocardial oxygenation was found to be maintained by increased O 2 ‐content [4.4 (4.2;4.8), ml dl −1 ; P < 0.05], the contribution of dissolved O 2 to subendocardial O 2 ‐delivery increased (32 vs. 8%; P < 0.05), which preserved myocardial function. Conclusion: Hyperoxic ventilation at Hct crit is followed by coronary vasoconstriction and reduction of coronary blood flow. However, myocardial oxygenation and function is maintained, as increased O 2 ‐content (in particular dissolved O 2 ) preserves myocardial oxygenation.