Effects of thoracic vs. lumbar epidural anaesthesia on systemic haemodynamics and coronary circulation in sevoflurane anaesthetized dogs.

BACKGROUND

Although many investigators reported changes in coronary circulation during thoracic epidural anaesthesia (TEA), no previous studies have attempted to compare it with lumbar epidural anaesthesia (LEA) concerning coronary circulation. Our aim was to compare effects of TEA on systemic haemodynamics and coronary circulation with those of LEA in anaesthetized dogs.

METHODS

In dogs receiving 1.5% sevoflurane, 2% lidocaine (0.1 ml kg-1) was injected into the epidural space via an epidural catheter inserted at either the T7-T8 (TEA group, n = 8) or L5-L6 (LEA group, n = 8) interspace, and the same dose was repeated again 30 min later.

RESULTS

Heart rate and maximum left ventricular dP/dt decreased in the TEA group but were unchanged in the LEA group. Decreases in mean arterial pressure were found for both groups, and they were more substantial in the TEA than in the LEA group. Decreases in left ventricular minute work index were found for both groups, and they tended to be more substantial in the TEA than in the LEA group. Coronary perfusion pressure and blood flow decreased in both groups. Calculated coronary vascular resistance increased in the TEA group but was unchanged in the LEA group.

CONCLUSION

The most significant difference between TEA and LEA concerning coronary circulation was characterized by an increase in coronary vascular resistance in the TEA group, which was not present in the LEA group. The increase in coronary vascular resistance caused by TEA may be explained by a coronary vasoconstriction caused by a lower myocardial oxygen demand.