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Isoflurane causes more severe regional myocardial dysfunction than halothane in dogs with a critical coronary artery
1Department of Anesthesia, University of Basel/Kantonsspital, Switzerland.
Abstract:
The effects of 1) isoflurane (ISO)- and halothane (HAL)-induced hypotension to a mean aortic pressure (AoP) of 55 mmHg, and 2) of substituting ISO and HAL for each other at a mean AoP of 55 mmHg on global and regional left ventricular performance (ultrasonic dimension technique) and on coronary hemodynamics (electromagnetic flow probes) were studied in eight open-chest dogs (anesthetized and paralyzed by continuous infusions of fentanyl and pancuronium) with a critical coronary artery stenosis (micrometer-controlled snare) of the left anterior descending coronary artery (LAD). The stenosis reduced resting coronary blood flow by 5% (P less than 0.05) without affecting global or regional myocardial performance. HAL- and ISO-induced hypotension caused comparable decreases in global cardiac function, but regional myocardial dysfunction in the area of stenosis and the reduction in coronary flow through the stenosed LAD were more pronounced during ISO. Substitution of HAL for ISO at constant mean AoP, heart rate, end-diastolic dimensions and pressures, and stroke volume resulted in significant (P less than or equal to 0.05) amelioration of regional myocardial dysfunction (improvement in contraction amplitude, disappearance of paradoxical systolic lengthening and akinesis), a 20% increase in flow through the stenosed LAD, and a 20% decrease in flow through the unobstructed left circumflex coronary artery. These data suggest that, in the presence of a critical coronary artery stenosis: 1) ISO- and HAL-associated hypotension result in comparable decreases in global cardiac function, 2) ISO-associated hypotension is more likely to cause severe regional myocardial dysfunction suggestive of ischemia than equal degrees of HAL-associated hypotension, and 3) the different effects of HAL and ISO on ischemic myocardial segments at equally reduced coronary perfusion pressure are primarily related to their different effects on coronary vasomotor tone.