Emulsified Isoflurane Local Anesthetic Effects Research

Background: Studies have shown that local use of volatile anesthetics produce cutaneous anesthesia (in rats and humans) and spinal anesthesia (in dogs). However, there is still no report on the epidural anesthetic effects of volatile anesthetics. The aim of the present study was to evaluate the epidural anesthetic effects of the 8% emulsified isofluane in rabbitsMethods: With the approval of Animal Research Committee, male adult New Zealand white rabbits were used in the following studies. Pharmacodynamic study: twenty-four hours after successful epidural catheterization, forty rabbits were randomly assigned in 4 groups of 10 each, respectively receiving epidural administration (in a blinded manner) of emulsified isoflurane (8%, v/v) 1ml (E-isoflurane group), 1% lidocaine 1ml (Lidocaine group), 30% Intralipid^? lml (Lipid group), or normal saline 1ml (NS group). Sensory and motor functions and state of consciousness were determined at baseline and at predetermined regular intervals until at least 1 hour after total recovery. Long-term neurologic complications were daily observed for two weeks after the experiment. Histopathologic study: 12 successfully epidural catheterized rabbits were randomly divided into 2 groups of 6 each respectively receiving 8%isoflurane 1ml (E-isoflurane group) or NS 1ml (NS group). The animals were killed 20 minites and 6 hours after the epidural drug administration respectively (three in each group for each time), and the spinal cord, nerve roots, and ganglia were removed for histopathologic examination by light microscopy. Results: Phamacodynamic study: Sensory blockade onset time, motor blockade onset time and motor blockade duration of E-isoflurane group (1.4±0.7min, 1.6±0.7min and 33.5±10min respectively) were similar to that of Lidocaine group (1.3±0.5min, 1.7±0.8min and 37.8±8min respectively). Sensory blockade duration of E-isoflurane group was longer than that of Lidocaine group (68±13min vs. 49±13min, p<0.01). No epidural anesthesia effects were presented in both NS group and Lipid group. None of the rabbits of the four groups showed any decrease in consciousness level after the epidural drug administration. None of the rabbits showed any long-term neurologic deficits during a two-week-observation. Histopathologic study: None of the rabbits in the two studied groups showed obvious histopathologic abnormities.Conclusion: The present study demonstrates for the first time that epidural administration of 8% emulsified isofurane produces totally reversible epidural anesthetic effects without any signs of neurotoxicity or decrease in consciousness in rabbits. Objective To facilitate the evaluation of intravenous regional anesthesia, we developed this rat model of IVRA.Methods Thirty adult male SD rats (BW 200-250g) were randomly assigned into three groups with 10 in each, respectively receiving l%lidocaine 0.5ml (Lid group), 0.5%bupivacaine 0.5ml (Bup group) and normal saline 0.5ml (NS group) for tail IVRA. The IVRA procedures were performed as follows: Rats were placed in restrainers wich allows free movement of the tail and slightly restricted movement of the body. After a 24 gauge intravenous cannula was inserted and kept into the tail vein of the rat, the tail was exsanguinated with rubber strips made of surgical gloves. Then an elastic rubber tourniquet (valve core sleeve of bicycle) was applied between the proximal third and mid third of the tail and 0.5 ml of studied drug was injected into the tail vein via the pre-inserted cannula. Ten minutes after drug administration, the tourniquet was released. Tail flick latency (TFL) was measured with a tail-flick unit (Ugo Basile 7360) at 1, 3, 5, 10, 15, 20 min after drug administration and at 10-min intervals afterwards, until 60 minutes after TFL had returned to its baseline or the observation was lasted at least for 120 minutes. TFL increase was standardized by calculating the percentage of maximum possible effect (%MPE) as follows: %MPE = (TFL post-treatment -TFL pre-treatment) / (cut-off time - TFL pre-treatment)×100%. With %MPE calculation, the onset-time and recovery time of analgesia were determined. Onset-time of analgesia was defined as the time needed between drug administration and %MPE reaching 50% for the first time; Recovery time of analgesia was defined as the time elapsed from tourniquet release to %MPE less than 50% for the first time. Anesthetic effect was evaluated by tail-clamping test with an alligator clip (the cut-off time is 10 seconds) at the same time course as that of the tail-flick test. Lacking of aversive reactions (jerk, flinch, squeak, and evasive movement) to the tail-clamping stimulus was considered as the presentation of anesthesia effect. With tail-clamping test, the onset time and recovery of anesthetic effect were detected (Onset time of anesthesia: time needed between drug administration and absence of aversive reactions to tail clamping stimulus for the first time; Recovery time of anesthesia: time from tourniquet release to reappearance of aversive reactions to the tail clamping for the first time). Besides the study mentioned above, the present experiments also observed the enfluences of tourniquet duration and environmental temperature on the tail-flick test and tail-clamping test during tourniquet period in other groups of rats.Results: The onset-time of analgesia and anesthesia were 1±0min and 1±0min in Lid group and 1±0min and 1.4±0.8min in Bup group. There were no differences between groups. The recovery time of analgesia in Bup group were 56±22min(10-90min) and 31±19min (20-70min) respectively, which were much longer than those of Lid group [26±17min (10-60min) and 16±12min (5-40min) respectively] (P<0.01). No analgesia or anesthesia effect was observed in NS group. With other groups of rats, we found that both the TFL and the animal's responses to the tail clamping were not significantly enfluenced by the tourniquet application while the tourniquet duration was within 20 min, and so did the environmental temperature while it was kept between 25℃and 37℃. Conclusions The rat' tail IVRA model is a simple and reliable animal model for the evaluation of intravenous regional anesthesia. However, the enfluences of the tourniquet duration and the environmental temperature on the sensory function of rat's tail ought to be taken into consideration while using this animal model in studies. Objective To observe the intravenous regional anesthetic effects of the 8% emulsified isoflurane in a rat model of IVRA.Methods Fourty adult male SD rats (BW 200-250g) were randomly assigned into four groups with 10 in each, respectively receiving 8% emulsified isoflurane 0.5ml (E-iso group), 1%lidocaine 0.5ml (Lid group), 30% Intralipid(?) 0.5ml (Lipid group) and normal saline 0.5ml (NS group) for tail IVRA. The IVRA procedures were performed as follows: Rats were placed in restrainers wich allows free movement of the tail and slightly restricted movement of the body. After a 24 gauge intravenous cannula was inserted and kept into the tail vein of the rat, the tail was exsanguinated with rubber strips made of surgical gloves. Then an elastic rubber tourniquet (valve core sleeve of bicycle) was applied between the proximal third and mid third of the tail and 0.5 ml of studied drug was injected into the tail vein via the pre-inserted cannula. Ten minutes after drug administration, the tourniquet was released. Tail flick latency (TFL) was measured with a tail-flick unit (Ugo Basile 7360) at 1, 3, 5, 10, 15, 20min after drug administration and at 10-min intervals afterwards, until 60 minutes after TFL had returned to its baseline or at least for 120 minutes. TFL increase was standardized by calculating the percentage of maximum possible effect (%MPE) as follows: %MPE = (TFL post-drug - TFL pre-drug) / (cut-off time - TFL pre-drug)×100%. With %MPE calculation, the onset-time and recovery time of analgesia were determined. Onset-time of analgesia was defined as the time needed between drug administration and %MPE reaching 50% for the first time; Recovery time of analgesia was defined as the time elapsed from tourniquet release to %MPE less than 50% for the first time. Anesthetic effect was evaluated by tail-clamping test with an alligator clip (the cut-off time is 10 seconds) at the same time course as that of the tail-flick test. Lacking of aversive reactions (jerk, flinch, squeak, and evasive movement) to the tail-clamping stimulus was considered as the presentation of anesthesia effect. With tail-clamping test, the onset time and recovery of anesthetic effect were detected (Onset time of anesthesia: time needed between drug administration and absence of aversive reactions to tail clamping stimulus for the first time; Recovery time of anesthesia: time from tourniquet release to reappearance of aversive reactions to the tail clamping for the first time). The consciousness of the rat was also observed during the experiment period. Complications of the tail skin (ulcer, abscess, or necrosis) were observed for two days after the experiment.Results: After drug administration, local anesthesia occurred in 8 rats in E-iso group (n=10) whereas 10 rats in Lid group. The onset-time of analgesia and anesthesia were 1±0min and 1.5±0.9min in E- iso group and 1±0min and 1.0±0min in Lid group. There were no differences between drugs. The recovery time of analgesia and anesthesia in E-iso group were 28±14min(10-40min) and 15±9min(5-40min, n=8) respectively, which were also similar to those in Lid group [30±12min (10-50min) and 18±12min (5-50min) respectively] (P>0.05). Although the 2 rats in E-iso group showed no local anesthesia effect after drug administration, their pain thresholds were increased obviously (their highest %MEP of TFL at the tail site distal to the tourniquet were 67% and 87% respectively). No analgesia or anesthesia effect was occurred in either Lipid group or NS group. The TFL and rat's responses to the tail-clamping test at the proximal-third tail showed no changes during the observation period in all the four groups. No animal showed an abnormal consciousness level during the experiment. All rats in both E-iso group and Lid group recovered completely from IVRA after the experiment. No complications occurred during a two-day observation in the four groups.Conclusions: The present study shows that the 8% emulsified isoflurane produces reversible intravenous regional anesthesia /analgesia effect in rats. However, its anesthesia potency in IVRA is lower than that of 0.5% lidocaine. Objective To develop an animal model of peripheral nerve blocking anesthesia in consciousness rats.Methods Adult male SD rats (BW 200-300g) were selected to perform the present studies. (1) Tail-nerve block techniques: Rat was placed in restrainer with its tail outside for tail-nerve injections. To localize the injected drug in injection site during injection, two elastic rubber tourniquets were applied in advance to the base of the tail and 4cm distally to the base of tail respectively. Tail nerve injections were performed on the two sides of tail between two tourniquets. With a 26 gauge needle connected to a microsyringe (100ul), 0.1ml of the studied drug was infiltrated near to the lateral surface of the caudal spinous process in each injection and each side of the tail received two injections with an interval of about 1cm along the axis of the tail. Two minutes after tail-nerve injections were completed, the tourniquets were unlaced and observations were made in regular intervals. (1) Observation of effective power and recovery rate of the tail-nerve block techniques: Sixty adult male SD rats randomly assigned into two groups with 30 in each, respectively receiving 2%lidocaine (Lid group) and normal saline (NS group) for tail-nerve injections in a blind manner. To evaluate the changes of sensory function in the rat tail, the tail-flick test and tail clamping test were performed at 15 min and 6 hours after tail nerve injections. Tail flick latency (TFL) reached 10 seconds (cut-off time) or animal showed no aversive reactions to the tail clamping test (cutoff time is 10 seconds) was considered to be the sign of total blockade. TFL recovered to less than 4 seconds or animal regained a response to tail clamping test was thought to be a sign of total recovery from anesthesia. With these methods, the effective power and recovery rate of anesthesia were determined. (2) Comparison of tail-nerve block effect of lidcaine and bupivacaine: 30 adult male SD rats randomly assigned into three groups with 10 in each, respectively receiving 2%lidocaine (Lid group), 0.5% bupivacaine (Bup group) and normal saline (NS group) for tail-nerve injections in a blind manner. Analgesia effect of the drug was evaluated by tail-flick test and the results were expressed as tail flick latency (TFL). TFL was measured with a tail-flick unit (Ugo Basile 7360) at 5, 10min after drug administration and at 10-min intervals afterwards, until 60 minutes after TFL returned to its baseline or the observations were lasted at least for 240 minutes. TFL increase was standardized by calculating the percentage of maximum possible effect (%MPE) as follows: %MPE = (TFL post-intervention - TFL pre-intervention) / (cut-off time - TFL pre-intervention)×100%. With %MPE calculation, the onset-time and duration of analgesia were determined. Onset-time of analgesia was defined as the time elapsed between drug administration and %MPE reaching 50% for the first time; Duration of analgesia was defined as the time during which %MPE was kept above 50% after drug administration. Anesthetic effect was evaluated by tail-clamping test with an alligator clip (52mm) at the same time course as that of the tail-flick test. Lacking of aversive reactions (jerk, flinch, squeak, and evasive movement) to the tail-clamping stimulus (the cut-off time is 10 seconds) was considered as the presentation of anesthesia effect. Otherwise, there was no anesthetic effect. With tail-clamping test, the onset time and duration of anesthetic effect were detected. Onset time of anesthesia: time needed between drug administration and absence of aversive reactions to tail clamping stimulus for the first time; Duration of anesthesia: time during which the rat presented no aversive reactions to the tail clamping. The pain threshold of the paws was also measured with the tail-flick unit and act as self control.Results (1) In Lid group, both the effective power and recovery rate of anesthesia were 100% (either by tail flick test or by tail clamping test). None of the rats in NS group showed any tail-nerve blockade effects. (2) All the animals in both Lid group and Bup group showed total tail-nerve blocking effects after tail-nerve injections of the drugs. The onset-times of analgesia and anesthesia were 5±0min and 6±2min in Lid group and 5±0min and 7±3min in Bup group. There were no differences between the two groups. The durations of analgesia and anesthesia in Bup group were 137±16 min (110-160 min) and 102±18 min (70-130min) respectively, which were much longer than those of Lid group [58±15min (40-80min) and 89±19min (70-110min) respectively] (P<0.01). No analgesia or anesthesia effect was observed in NS group. The pain threshold of paws showed no changes during the observation period in all the three groups.Conclusions This rat model of tail-nerve block is a simple and reliable animal model for the evaluation of peripheral nerve blocking anesthesia. Objective To observe the peripheral nerve blocking effects of 8% emulsified isoflurane in a rat model of tail-nerve block.Methods Forty adult male SD rats (BW 200-300g) were randomly assigned into four groups with 10 in each, respectively receiving 8% emulsified isoflurane(E-iso group), 1%lidocaine (Lid group), 30% Intralipid^? (Lipid group), and normal saline (NS group) for tail-nerve block. Tail-nerve block were performed as follows: Rat was placed in restrainer with its tail outside for tail-nerve injections. To localize the injected drug in injection site during injection, two elastic rubber tourniquets were applied in advance to the base of the tail and 4cm distally to the base of tail respectively. In each animal, the tail-nerve injections were performed on the two sides of the rat's tail between two tourniquets. With a 26 gauge needle connected to a microsyringe (100ul), 0.1ml of the studied drug was infiltrated near to the lateral surface of the caudal spinous process in each injection, and each side of the tail received two injections (0.1ml×2) with an interval of about 1cm along the axis of tail. Two minutes after tail-nerve injections (both of the two sides), the tourniquets were unlaced and observations were made in regular intervals. Analgesia effect of the drug was evaluated by tail flick test and the results were expressed as tail flick latency (TFL). TFL was measured with a tail-flick unit (Ugo Basile 7360) at 5, 10, 15, 20 min after drug administration and at 10-min intervals afterwards, until 60 minutes after TFL returned to its baseline or the observations were lasted at least for 240 minutes in total. TFL increase was standardized by calculating the percentage of maximum possible effect (%MPE) as follows: %MPE = (TFL post-intervention - TFL pre-intervention) / (cut-off time - TFL pre-intervention)×100%. With %MPE calculation, the onset-time and duration of analgesia were determined. Onset-time of analgesia was defined as the time elapsed between drug administration and %MPE reaching 50% for the first time; Duration of analgesia was defined as the time during which %MPE was kept above 50% after drug administration. Anesthetic effect was evaluated by tail-clamping test with an alligator clip (52mm) at the same time course as that of the tail-flick test. Lacking of aversive reactions (jerk, flinch, squeak, and evasive movement) to the tail-clamping stimulus (the cut-off time is 10 seconds) was considered as the presentation of anesthesia effect. Otherwise, there was no anesthetic effect. With tail-clamping test, the onset time and duration of anesthetic effect were detected. Onset time of anesthesia: time needed between drug administration and absence of aversive reactions to tail clamping stimulus for the first time; Duration of anesthesia: time during which the rat presented no aversive reactions to the tail clamping. The pain threshold of the paws was also measured with the tail-flick unit and act as a self control.Results After tail-nerve injections, local anesthesia occurred in 7 of 10 rats in E-iso group whereas in 10 of 10 rats in Lid group. The onset-time of analgesia and anesthesia were 5±0min and 6.4±2.4min (n=7) in E-iso group and 5±0min and 5.0±0min in Lid group. There were no differences between the two groups. The durations of analgesia and anesthesia in E-iso group were 113±22 min (90-150 min) and 86±13 min (70-120min, n=7) respectively, which were more longer than those of the Lid group [76±13min (60-100min) and 43±13min (30-70min) respectively] (P<0.01). Although the 3 rats of E-iso group showed no local anesthesia effect after tail-nerve injections, their pain thresholds were increased obviously (their highest %MEP of TFL was 78%, 81%, and 88% respectively). All rats in both E-iso group and Lid group recovered completely from tail-nerve block after the experiment. No analgesia or anesthesia effect was found in either Lipid group or NS group. In all the four groups, the pain threshold of paws showed no changes and no animal showed an abnormal consciousness level during the observation period. No complications occurred in the four groups during a two-day observation.Conclusions This study shows that the 8% emulsified isoflurane produces tail-nerve blocking effects without affecting the level of consciousness in rats.