Spinal cord blood flow during spinal anesthesia in dogs: the effects of tetracaine, epinephrine, acute blood loss, and hypercapnia.

To examine the effects of subarachnoid tetracaine and epinephrine on spinal cord blood flow (SCBF), lumbar SCBF and cerebral blood flow (CBF) were measured simultaneously by the hydrogen clearance technique in dogs (n = 45) anesthetized with halothane. The lumbar subarachnoid administration of tetracaine, 5 mg dissolved in 1 ml of a 7.5% dextrose solution had no significant effect on either SCBF or CBF for 4 hr even though arterial blood pressure and heart rate decreased significantly. After subarachnoid epinephrine alone (100, 300, and 500 micrograms), SCBF varied widely but did not change significantly with any of the injections, nor did CBF. Responses of SCBF to hypercapnia and to acute blood loss during spinal anesthesia with tetracaine were also examined. Increased PaCO2 (from 35 to 57 mm Hg) increased both SCBF and CBF similarly before and after subarachnoid tetracaine; SCBF increased from 26.8 +/- 9.0 ml X 100 g-1 X min-1 (mean +/- SD) before to 34.2 +/- 13.6 ml X 100 g-1 X min-1 during hypercapnia during spinal anesthesia, which was almost identical to the increase (from 31.5 +/- 8.1 ml X 100 g-1 X min-1 to 39.9 +/- 6.0 ml X 100 g-1 X min-1) before spinal anesthesia. Whereas acute blood loss (approximately 20% of estimated blood volume) during spinal anesthesia with tetracaine caused a 23% reduction of SCBF (P less than 0.05), in the absence of tetracaine SCBF remained unchanged during hemorrhagic hypovolemia.(ABSTRACT TRUNCATED AT 250 WORDS)