Circulatory effects of short-term hypercapnia during thoracolumbar epidural anaesthesia.

In ten elderly patients subjected to extensive thoracolumbar epidural anaesthesia, circulatory changes were studied before and during sympathetic stimulation. Induced hypercapnia was used as a sympathetic stimulus. After establishment of the epidural anaesthesia, which extended from T1 to L2, there were decreases in heart rate, mean arterial blood pressure, cardiac output and systemic vascular resistance. Hypercapnia before the epidural block increased heart rate, arterial blood pressure and cardiac output, while hypercapnia after established epidural block induced only a slight increase in arterial blood pressure. The results indicate that in spite of an extensive epidural block, there are some "escaped" sympathetic nerve fibres that can be mobilized during sympathetic stimulation.