Patterns of Nerve Conduction Blockade by Different Combinations of Lidocaine-bupivacaine Mixture / 대한마취과학회지

BACKGROUND: A mixture of local anesthetics such as lidocaine and bupivacaine has frequently been used in clinical practice. The rationale behind this is to take advantage of lidocaine's rapid onset and bupivacaine's perpetuation in anesthesia. The purpose of this study was to examine the changes in the onset and recovery of nerve blocking action exerted by the different combinations of these two in the mixture. METHODS: Isolated sciatic nerve preparations obtained from adult male Sprague-Dawley rats were used in this study. Recordings of A-fiber compound action potentials (A-CAPs) were made at the end of the isolated nerve while single pulse stimuli (0.5 msec, supramaximal intensity, 2 Hz) were applied to the opposite end of the nerve. Seven different composition of lidocaine-bupivacaine mixtures were prepared (0 : 6, 1 : 5, 2 : 4, 3 : 3, 4 : 2, 5 : 1, 6 : 0 vol./vol.), where basal concentrations of lidocaine and bupivacaine were 0.2% and 0.05%, respectively. Amplitudes of A-CAPs were measured before, during and after perfusion of mixture solution. The time needed for A-CAPs amplitude to decrease to 10% of the basal value after starting perfusion (onset time) and that needed to reach to 50% of the basal value after ceasing the perfusion (recovery time) were measured. RESULTS: With increasing concentration ratios of lidocaine to bupivacaine in the mixture as mentioned above, the following onset and recovery times were obtained (6.0 +/- 0.3, 5.6 +/- 0.3, 6.0 +/- 0.5, 8.3 +/- 0.5, 7.3 +/- 0.6, 7.8 +/- 0.3, and 10.8 +/- 0.8, minutes; 38 +/- 4, 63 +/- 12, 87 +/- 19, 100 +/- 13, 104 +/- 18, 137 +/- 27, and 157 +/- 18 minutes, respectively). CONCLUSION: Onset times were, in general, exponentially decreased with the increase in the lidocaine concentration. However, recovery times were lineary increased with the increase in the bupivacaine concentration. So, it should be kept in mind that rapid onset can only be obtained with the expense of substantial reduction in the duration of local anesthetic effect of the mixture, and vice versa.

Effects of Substance P Antagonist, D-Arg, D-Phe, D-Trp, Leu- Substance P on the Mechanical Hyperalgesia of Inflammation Induced by Freund's Complete Adjuvant in Rat Paw / 대한마취과학회지

BACKGROUND: The effect of substance P (SP) on the hyperalgesia induced by inflammation is controversial, and as SP remains in the periphery just for a short period of time after release from the nerve ending, the contribution of SP on the development of sustained mechanical hyperalgesia in rats with inflammation is questionable. The purpose of this experiment is to evaluate the effect of SP on the development of mechanical hyperalgesia induced by Freund's complete adjuvant (FCA) using SP antagonist [D-Arg, D-Phe, D-Trp, Leu]-substance P (SPA). METHODS: Male Sprague Dawley rats were divided into four groups; control (normal saline) and three different doses of SPA (0.25 microgram, 2.5 microgram, 25 microgram/0.1 ml). Inflammation was induced in rats by injecting 0.15 ml of FCA intraplantarly. Rats showed typical hyperalgesia within 12 hours after injection and maintained it for about one week. To test the effect of SPA on the developement of inflammation, either SPA or saline was injected at 1 h before and at the time of FCA injection under light halothane anesthesia after a baseline test. The effect of SPA on hyperalgesia was assessed by measuring mechanical hyperalgesia at 2, 6, 12, 24 hrs and 4 days after injection of the drug. To test the effect of SPA on fully developed inflammation, tests were done 2 days after injection of FCA. Mechanical hyperalgesias were assessed at 15, 30, 60, 90, 120 min after the drug injections. RESULTS: SPA injected to suppress the initial SP spill over decreased the mechanical hyperalgesia in a dose dependent manner. SPA injected after the full development of inflammation also decreased mechanical hyperalgesia. CONCLUSIONS: SP released at the initial phase of inflammation as well as SP released after the development of inflammation are all important for the maintainance of mechanical hyperalgesia.