Effects of thoracic epidural anesthesia and adrenoceptor blockade on the cardiovascular response to dopamine in the dog

Abstract

The cardiovascular effects of dopamine are different before and during thoracic epidural anesthesia (TEA). To evaluate underlying adrenoceptor-mediated mechanisms, dopamine effects were investigated in nine chloralose-anesthetized dogs. The circulatory response to dopamine (0-40 micrograms.kg-1.min-1) was studied before and during TEA, and during TEA after introducing the alpha 1-antagonist prazosin (0.3 mg.kg-1), the alpha 2-antagonist rauwolscine (0.3 mg.kg-1), and the beta 1-antagonist metoprolol (0.5 mg.kg-1). TEA decreased mean arterial pressure (MAP) by 29%, cardiac output (CO) by 36%, heart rate (HR) by 27%, and the maximum rate of change of left ventricular pressure (LVdP/dt) by 52%. Systemic vascular resistance, pulmonary vascular resistance and mean pulmonary artery pressure (MPAP) remained unaltered by TEA. Dopamine-induced increases in MAP and HR were augmented by TEA. Both MAP and LVdP/dt increased above pre-TEA levels at 10 micrograms.kg-1.min-1. Prazosin attenuated the increases in MAP and MPAP by dopamine. Adding rauwolscine almost abolished the dopamine response in MAP and MPAP. Metoprolol almost eliminated the dopamine effects on CO and LVdP/dt. Only minor alterations in cardiac filling pressures were observed during the study. Plasma norepinephrine (NE) concentration was lower during than before TEA at corresponding dopamine infusion rates. NE was reduced by the beta 1-blockade. During TEA, the plasma dopamine levels were generally higher, and they were further increased by adding beta 1-blockade. In conclusion, myocardial contractility and arterial pressure were restored to pre-TEA values by dopamine at 5-10 micrograms.kg-1.min-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Are the cardiovascular actions of dopamine altered by isoflurane?

“…Thc underlying mechanism for this altered vascular responsiveness of dopamine by isoflurane anesthesia is obscure. In this context it is, however, noteworthy that dopamine-induced systemic vasoconstriction was potentiated after thoracic epidural sympathetic blockade in the dog (33). Similar observations have been made in man (34).…”

“…Similar observations have been made in man (34). Seemingly, the decrease in sympathetic adrenergic outflow, induced by epidural blockade (33,34) may facilitate the vawular responsivencss to exogenous dopamine. Recent data demonstrate that isoflurane anesthesia is associated with decreases in sympathetic nervous dischargc in man (35).…”

Comparison of Feasibility and Safety of Epidural Catheterization between Cranial and Caudal Lumbar Vertebral Segments in Dogs

“…Although experimental studies on thoracic epidural analgesia have been reported [6][7][8]13], epidural neuroaxial blocks in the thoracic or cranial lumbar area have rarely been used in the clinical setting. However, a paper documented an easy access at T13-L1 and L1-L2 levels for the injection of a contrast medium for myelography [15]; therefore, we believe that needle insertion and epidural catheterization should be feasible through the cranial lumbar intervertebral spaces.…”

The use of epidural anesthesia in coronary surgery: pro and contra. Review

“…При введении местного анестетика в эпидуральное пространство происходит блокада импульсов симпатических нервов на уровне соответствующих дерматомов. По данным экспериментальных исследований на животных, эффекты выключения влияния симпатической нервной системы на сосудистый тонус могут варьировать -от отсутствия влияния [29] до значимого снижения сосудистого сопротивления [30,31]. При исследовании динамики сосудистого сопротивления у пациентов во время кардиохирургических вмешательств с использованием эпидуральной анестезии было показано, что блокада кардиальных дер-матомов снижает сосудистое сопротивление [32].…”