Local Spinal Cord Blood Flow and Glucose Utilization during Spinal Anesthesia with Bupivacaine in Conscious Rats

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Abstract
The author studied in conscious rats the local spinal blood flow (SCBF) and metabolic effects on intrathecally administered bupivacaine. Fourteen rats received 0.75% bupivacaine, 15 .mu.l, through a chronically implanted lumbar subarachnoid catheter; 12 control animals were treated identically, except that they received only an equal volume of saline intrathecally; 10 min after intrathecal drug injection, either local SCBF or glucose utilization was measured in the lumbar spinal cord of 7 experimental and 6 control animals with the quantitative autoradiographic iodo-[14C]antipyrine or 2-[14C]deoxyglucose methods, respectively. Intrathecal bupivacaine produced a limp tail, absent hindlimb withdrawal to pinch and 25-30 min of analgesia on the tail-flick test. Mean arterial blood pressure decreased 14% (P < 0.01) after bupivacaine was administered, but there was no change in arterial blood gases, pH or rectal temperature. Subarachnoid bupivacaine reduced both local SCBF and glucose utilization, but the SCBF effect was larger. Local SCBF decreased 27-34% (P < 0.01) in all 5 spinal gray and 3 white matter areas measured; there was little regional variability in the response. The reduction in spinal glucose utilization was regionally selective and less marked. For example, glucose utilization decreased 15% (P < 0.05) and 21% (P < 0.05) in lateral and anterior spinal white matter, respectively, but only decreased approximately 3% in laminae I-III and dorsal white matter (P > 0.1). A trend toward metabolic depression was also evident in laminae VIII (-15%, P = 0.06), VII (-13%, P = 0.09), and IV-VI (-11%, P > 0.1). Regardless of whether it acts on the spinal cord itself or on extraspinal cord sites (e.g., spinal roots) to produce anesthesia, intrathecal bupivacaine evidently alters the circulatory and metabolic state of the spinal cord.