Evaluation of epidural sensory block by thermal stimulation, laser stimulation, and recording of somatosensory evoked potentials
Department of Anesthesiology, Orebro Medical Center Hospital, Sweden. Regional anesthesia
The existence of differential sensory block during epidural analgesia has been confirmed by some authors and disputed by others. This study attempts to elucidate this issue by using quantitative methods for evaluation of sensory block.
A single epidural injection of 20 mL 0.5% bupivacaine with epinephrine was administered at the L1-T12 level in 11 male volunteers. Sensory block was evaluated by two qualitative (pinprick and light touch) and two quantitative methods (thermal stimulation with Thermotest [Somedic, Stockholm, Sweden] and argon laser stimulation). For measurement of motor block in the lower extremities and in the rectus abdominis muscle, quantitative methods were used. Sensory block was also assessed by somatosensory evoked potentials recorded during electrical and laser stimulation at the most cranial analgesic dermatome (loss of sharpness in pinprick perception) and the anesthetic dermatome L2 (loss of light touch perception).
The zone of anesthesia was smaller than the zone of any other investigated variable. The cranial spread of analgesia and motor block was lower than that of laser-assessed block. Partial block of laser perception and thermal perception lasted longer than analgesia and motor block. No consistent segmental or temporal differences were found between the Thermotest and laser methods. During epidural block, prolongation of latencies and reduction in amplitudes of somatosensory evoked potentials produced at the most cranial analgesic dermatome did not differ significantly from those produced at the anesthetic dermatome.
No differential block of small nerve fibers was found during epidural analgesia by Thermotest and argon laser stimulation. Recording of somatosensory evoked potentials did not demonstrate significant difference between responses from the sites with most superficial and with most intense sensory block.
Available from: PubMed Central
- "Several mechanisms have been suggested to explain the extension of spinal blockade when administering an epidural top-up during CSE. Leakage of the epidural local anesthetic through the dural hole in the subarachnoid space [9,10] or perineural or transdural spread of epidural local anesthetic bringing "subclinical" analgesia to full analgesic strength [11,12] have been proposed. Local anesthetic administered in the epidural space may enter the subarachnoid space by diffusion through the sleeves of the dura mater that cover the spinal roots as they traverse it . "
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ABSTRACT: The purpose of the present study is to investigate the anesthetic effect of reduced doses of spinal bupivacaine with epidural top ups in comparison with those of spinal bupivacaine and to determine the adequate doses of drugs used during lower extremity surgeries.
SIXTY ADULT PATIENTS WERE RANDOMIZED TO THREE DIFFERENT TECHNIQUE GROUPS: S group (10 mg of spinal bupivacaine), SE1 group (7.5 mg of spinal bupivacaine + epidural 1.5% lidocaine 10 ml) or SE2 group (5 mg of spinal bupivacaine + epidural 1.5% lidocaine 10 ml). The level of sensory block, modified Bromage motor scores (MBS), systolic blood pressure and heart rate were recorded for 30 min following anesthesia. Peak sensory block height and MBS, time for sensory regression to L1 and motor recovery to MBS 1, side effects and operator's satisfaction were noted.
The levels of peak sensory block were similar among the groups (P > 0.05). For the SE2 group, the regression to the L1 dermatome was faster (P = 0.004) and the maximum MBS was lower (P = 0.001) than that of the other two groups. Motor block recovery to MBS 1 was faster for the SE1 and SE2 groups than for the S group (P < 0.001). The operator's satisfaction scores of the SE2 group were lower than those of the other two groups (P = 0.019).
During combined spinal-epidural anesthesia, 7.5 mg of spinal bupivacaine and epidural 1.5% lidocaine 10 ml produced faster motor recovery than did 10 mg of spinal bupivacaine in patients undergoing lower extremity surgeries.
Available from: Jeffrey Rushen
- "tests. According to Svensson et al. 1991 , Zaric et al. 1996 , and Jacobson et al. Ž . "
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ABSTRACT: We describe a method for measuring nociception in cattle using a CO2 laser aimed at the caudal aspect of the metatarsi. In Experiment 1, infrared thermography showed that calves responded by lifting their legs when skin temperatures reached 45-55°C. In Experiment 2a, the validity of the method was tested by comparing the response latencies of 14 calves to two power settings (2.25 W vs. 4.5 W) with each setting being applied six times. We found that both leg-lift latencies and tail-flick latencies were lower at the higher power setting, and the calves were more likely to respond by kicking than by simply moving the leg. The standard deviations between and within calves were smaller at the higher power setting, and the large within-calf variation means that at least three tests were required to obtain reliable measures that could differentiate between calves. In Experiment 2b, application of the laser at a range of power settings (2.0, 3.0, 4.0, 4.5, 5.0 and 5.5 W) on 16 calves showed that response latencies decreased as power increased up to 4.5 W, after which no further change occurred. In Experiment 3, the repeatability of the method was evaluated on nine measures with the high power setting (4.5 W). The coefficient of variation associated with repetition of the measures was 36%. In general, we found little change in response latencies with repeated use of the laser, except that responses on the second test tended to be shorter. Experiment 4 showed that ambient temperatures between 16°C and 27°C did not affect response latencies, but these were longer at temperatures of 7°C. We suggest that the method is a useful way of measuring cattle's sensitivity to nociception as the animals need not be restrained and the distance to the animal need not be closely controlled. However, to obtain accurate, valid and reliable measures it is necessary to use a high power setting (4.5 W) and take at least three consecutive measures of the response latency.
Available from: Dusanka Zaric
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ABSTRACT: In animal studies, ropivacaine has shown more pronounced sensory block than motor block, which makes it an interesting drug for postoperative pain relief. The aim of this study was to investigate the dose response of sensory and motor block during continuous epidural infusion of 0.1, 0.2, or 0.3% ropivacaine in volunteers in a double-blind manner. Bupivacaine 0.25% and isotonic saline were used as reference and control, respectively.
Each treatment group consisted of eight healthy men. After a bolus dose of 10 mL at the L2-L3 interspace, the solution in question was infused at 10 mL/h for 21 hours. Sensory block was evaluated by the pinprick, light touch, and Thermotest methods. Motor block was measured by the Bromage scale, by average rectified electromyography in abdominal muscles, and by mechanical measurement of isometric muscle force in the lower extremities. Mobilization of the subjects was attempted throughout the investigation.
The number of blocked dermatomes (evaluated by pinprick) with 0.1% ropivacaine was significantly smaller than with the other test solutions (P = .002-.0008). Motor block was minimal with 0.1% ropivacaine, so that all subjects could be mobilized; it was moderate with 0.2 and 0.3% ropivacaine and most intense with 0.25% bupivacaine. The regression phase was significantly shorter with all three concentrations of ropivacaine than with bupivacaine (P < .01).
Ropivacaine 0.1% produced limited analgesia and minimal motor block, so that ambulation was possible throughout the investigation. With 0.2 and 0.3% ropivacaine, analgesia was more extensive, and motor block was considered moderate. Ropivacaine 0.2% should be evaluated for future postoperative pain treatment.
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