Subarachnoid bupivacaine decreases spinal cord blood flow in dogs

Eighteen mongrel dogs were randomized into two equal groups. Cervical, thoracic and lumbosacral spinal cord and spinal dural blood flows were measured using the radioactive microsphere technique. Blood flow determinations were made prior to, and 20 and 40 minutes following lumbar subarachnoid injection of: (1) 0.4 per cent bupivacaine (20 mg), or (2) 0.4 per cent bupivacaine (20 mg) with 1/25,000 epinephrine (200 micrograms). In dogs given subarachnoid bupivacaine or bupivacaine with epinephrine, the maximum decrease in mean arterial blood pressure (33 per cent) occurred at 40 minutes post-injection. Cardiac index decreased in dogs given subarachnoid bupivacaine (197 +/- 11 ml X kg-1 X min-1 control vs. 141 +/- 19 ml X kg-1 X min-1 at 40 minutes), while it increased in dogs given bupivacaine with epinephrine (201 +/- 11 ml X kg-1 X min-1 - control vs. 252 +/- 15 ml X kg-1 X min-1 at 40 minutes). Dogs receiving subarachnoid bupivacaine demonstrated a significant decrease in spinal cord blood flow to all regions. Dogs receiving subarachnoid bupivacaine with epinephrine demonstrated a significant decrease in thoracic and lumbosacral spinal cord blood flow; however, cervical cord blood flow remained unchanged. Thoracic and lumbosacral dural blood flows were significantly decreased in both groups following subarachnoid injection. Subarachnoid bupivacaine 0.4 per cent (20 mg) and 0.4 per cent with epinephrine 1/25,000 (200 micrograms) decrease spinal cord and spinal dural blood flow in dogs.