Halothane, but Not Isoflurane or Enflurane, Protects Against Spontaneous and Epinephrine-Exacerbated Acute Thrombus Formations in Stenosed Dog Coronary Arteries

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Abstract
Occlusive platelet thrombi periodically form in mechanically stenosed dog coronary arteries producing cyclical blood flow reductions occurring over 4-7 min. Cyclical coronary flow reductions are exacerbated by IV epinephrine 0.4 .mu.g .cntdot. kg-1 .cntdot. min-1 for 15 min. These flow reductions can be abolished by known inhibitors of platelet function. This study assess the effect of halothane, isoflurane, and enflurane on spontaneous- and epinephrine-exacerbated cyclical coronary flow reductions. Twenty-three open-chest dogs [1% halothane (n = 5), 0.5% halothane (n = 5%), 0.25% halothane (n = 3), 1.5% isoflurane (n = 5), and 2.0% enflurane (n = 5)] with a mechanically stenosed coronary artery showed cyclical blood flow reductions. With 1.0% halothane administration, spontaneous cyclical blood flow reductions were abolished (n = 5), whereas during administration of isoflurane 1.5% (n = 5) and enflurane 2.0% (n = 5) cyclical flow reductions and myocardial ischemia continued. Subsequent administration of halothane in the isoflurane and enflurane groups showed abolition of coronary flow reductions in all animals (n = 10). In eight animals a 15-min epinephrine infusion (0.4 .mu.g .cntdot. kg-1 .cntdot. min-1) was given following a control period and again following abolition of coronary flow reductions by halothane 0.5% (n = 5) and halothane 0.25% (n = 3). The magnitude of cyclical blood flow reductions (difference between initial and final coronary flow level of each flow reduction) changed from 52 .+-. 11 to 61 .+-. 12 ml/min (NS), and frequency increased from 0.37 to 0.57/min (P < 0.05, n = 8) during epinephrine infusion. Halothane abolishes spontaneously occurring cyclical blood flow reductions and prevents epinephrine-induced cyclical blood flow reductions, whereas isoflurane and enflurane do not inhibit spontaneous cyclical coronary blood flow reductions. The effects of halothane on coronary artery thrombus formation in humans are unknown, but additional studies are needed to investigate the effect of halothane and other anesthetic agents on coronary thrombus formation and platelet function in humans.