Spinal Cord and Cerebral Blood Flow Responses to Subarachnoid Injection of Local Anesthetics with and without Epinephrine

Abstract

Subarachnoid anesthesia with lidocaine, mepivacaine, or tetracaine with and without added epinephrine (1:100 000) produced no demonstrable changes in average cerebral (CBF) or segmental spinal cord blood flow (SCBF) in 38 cats anesthetized with pentobarbital. Blood flow was measured by the injection of radioactive microspheres. Seven groups of cats received either lidocaine 15 mg, lidocaine 15 mg with epinephrine, mepivacaine 10 mg, mepivacaine 10 mg with epinephrine, tetracaine 5 mg, tetracaine 5 mg with epinephrine, or saline with epinephrine 1:100 000. Mean arterial pressure (MAP) decreased significantly (P less than 0.05) in Groups I-VI. Added epinephrine had no effect on the decrease in MAP. Amplitude of the somatosensory cortical evoked response decreased significantly in Groups I-VI, but did not change from control in Group VII. No significant change in CBF or SCBF was demonstrated in any group at any time. Plasma lidocaine and mepivacaine levels were significantly less at 5 min after subarachnoid injection in the groups receiving epinephrine compared to those not receiving epinephrine (P less than 0.05). The data appear to support the hypothesis of a vasoconstrictive reduction in systemic absorption of intrathecal local anesthetics, but suggest that significant segmental spinal cord ischemia does not occur. Maintenance of total flow in the face of a decrease in MAP suggests that autoregulation in brain and spinal cord may be maintained. Changes in regional SCBF or CBF may have been present but were not examined in this study. Further studies of brain and spinal cord blood flow dynamics, regional flow changes, and regulation of flow after intrathecal agents are necessary.

Clinical Pharmacokinetics of Epidural and Spinal Anaesthesia

“…In several studies administration of lignocaine, mepivacaine and amethocaine (tetracaine) did not produce significant effects on either total or regional spinal cord blood flow in dogs and cats (De Rosayro et al 1983; Dohi et al 1984Dohi et al , 1987Porter et al 1985). However, in other studies in dogs, lignocaine and amethocaine increased both spinal cord and dural blood flows despite marked decreases in the mean arterial blood pressure (Kozodyet al 1985b,c).…”

“…In the study of Porter et al (1985) neither lignocaine nor mepivacaine (with or without adrenaline) altered the total or segmental spinal cord blood flow in cats, but plasma concentrations of both drugs were markedly lower after administration of adrenaline-containing solutions. Confounding factors between the above studies include dif-290 ferences in species, volumes and doses administered, methods used to determine blood flows, times of the observations and administration of general anaesthetics.…”

Effects of epinephrine in local anesthetics on the central and peripheral nervous systems: Neurotoxicity and neural blood flow

“…Plain intrathecal epinephrine (up to 0.5 mg) does not significantly alter SCBF in dogs or cats, whether measured by hydrogen clearance 34 or microspheres. 35,36 Its effects are more complex when admixed with local anesthetics. For instance, intrathecal lidocaine or tetracaine either increase 9,37 or have no effect on SCBF.…”

Effect of Tetracaine-induced Spinal Anesthesia on Pial Microcirculation in Pentobarbital Anesthetized Rats

“…Intrathecal administration of lidocaine, mepivacaine, and tetracaine did not cause any significant change of CBF in cats. 3 Our study showed that rCBF and the ID of pial arteriole did not change after T 10 and T 6 level of spinal anesthesia. Therefore, we conclude that spinal block at or below the T 6 level has no significant effects on cerebral circulation in the rat.…”

“…In the study of Porter et al, 3 the earliest measurement of CBF after spinal anesthesia was at 5 minutes. The spinal anesthesia induced in our studies resulted in systemic hypotension similar to that of previously reported by others.…”