Circulatory changes during high thoracic epidural anaesthesia--influence of sympathetic block and of systemic effect of the local anaesthetic.

Circulatory changes during high thoracic epidural anaesthesia (TEA) were studied in nine healthy volunteers by means of echocardiography and systolic time intervals. The subjects also underwent a physical work test with bicycle ergometry. To evaluate the systemic effect of the local anaesthetic (bupivacaine), the same subjects were investigated 3 weeks later when a corresponding dose of the local anaesthetic was injected intramuscularly instead of epidurally. On the first occasion, after baseline measurements an epidural catheter was inserted at T4 level and 5 ml of 0.5% bupivacaine were injected. This volume led to sensory block within dermatomes T1-T5. On the second occasion all subjects received 8 ml of 0.5% bupivacaine intramuscularly. Heart rate (HR) and systolic blood pressure decreased during TEA, both at rest and during exercise. Following i.m. injection, HR decreased at rest but remained unchanged during exercise. The systolic blood pressure was not affected but the diastolic blood pressure increased during the exercise test. After administration of TEA, stroke volume (SV) decreased 22% and cardiac output (CO) 33%. Following i.m. injection of bupivacaine, SV decreased 8% and CO 20%. The pre-ejection period/left ventricular ejection time ratio increased 23% during TEA and 16% after i.m. injection. The results indicate that the circulatory changes did not seem to be caused entirely by the cardiac sympathetic block, but were due partly to the systemic effect of bupivacaine.