Effects of Thoracic Epidural Block and the Beta‐1 ‐Adrenoreceptor Agonist Prenalterol on the Cardiovascular Response to Infrarenal Aortic Cross‐Clamping in Man

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Abstract
Sixteen patients scheduled for abdominal aortic resection and grafting were randomly assigned to two groups to study the cardiovascular effects of infrarenal aortic cross‐clamping. The patients in the first group had received a thoracic. epidural block followed by intravenous administration of the selective beta‐l‐adrenoreceptor agonist prenalterol prior to induction of general anaesthesia. The patients in the second group served as controls and received no specific treatment prior to general anaesthesia. In both groups, aortic cross‐clamping was followed by an equal rise in pulmonary artery diastolic pressure and mean systemic arterial pressure. There was a significant difference in systemic vascular resistance, as the control group had a 46% increase 30 s after cross‐clamping, while the pretreated patients had only a 7% increase at the same time. Moreover, the patients given the thoracic epidural block followed by prenalterol increased their stroke volume and cardiac indices, as compared to the patients in the control group who showed a significant decrease in these parameters. Possible mechanisms for the mode of action of the combined thoracic epidural block and beta‐l‐adrenoreceptor agonist pretreatment are discussed.