Isobolographic analysis of the interaction between epidural sufentanil and bupivacaine in rats

Use of high-resolution thermography as a validation measure to confirm epidural anesthesia in mice: a cross-over study

BACKGROUND

Effective epidural anesthesia is confirmed in humans by sensory assessments but these tests are not feasible in mice. We hypothesized that, in mice, infrared thermography would demonstrate selective segmental warming of lower extremities following epidural anesthesia.

METHODS

We anesthetized 10 C57BL/6 mice with isoflurane and then inserted a PU-10 epidural catheter under direct surgical microscopy at T11-12. A thermal camera (thermal sensitivity ±0.05°C, pixel resolution 320x240 pixels, and spatial resolution 200 μm) recorded baseline temperature of front and rear paws, tail and ears. Thermography was assessed at baseline and 2, 5, 10, and 15 min after an epidural bolus dose of 50 μL bupivacaine 0.25% or 50 μL saline (control) using a cross-over design with dose order randomized and investigators blinded to study drug. Thermal images were recorded from video and analyzed using FLIR software. Effect over time and maximal effect (E_max) were assessed by repeated measures ANOVA and paired t-tests. Comparisons were between bupivacaine and control, and between lower vs upper extremities.

RESULTS

Epidural bupivacaine caused progressive warming of lower compared with upper extremities (P <0.001), typically returning to baseline by 15 min after administration. Mean (±SD) E_max was +3.73 (±1.56) °C for lower extremities compared with 0.56 (±0.68) °C (P=0.03) for upper extremities. Following epidural saline, there was no effect over time (E_max for lower extremities -0.88 (±0.28) °C compared with the upper extremities -0.88 (±0.19) °C (P >0.99).

CONCLUSIONS

Thermography is a useful tool to confirm epidural catheter placement in animals for which subjective, non-noxious, sensory measures are impossible.

Effect of Addition of Fentanyl and Clonidine to Local Anesthetic Solution in Peribulbar Block

Objective:

To compare the effect of addition of fentanyl and clonidine as adjuvants to bupivacaine and lignocaine in peribulbar block.

Methods:

The study was conducted on 105 adult patients of either sex, of ASA grade I and II undergoing ophthalmic surgeries. Patients were randomly divided into 3 groups of 35 each. All the patients were given peribulbuar block with 5ml lignocaine 2% +3 ml bupivacaine 0.5% +1 ml hyaluronidase (250 IU). In addition to this 1 ml normal saline was added to Group S, 25 μg fentanyl to Group F and 25 μg clonidine to Group C. Onset and duration of globe and lid akinesia, duration of sensory blockage and analgesia, hemodynamic parameters, number of rescue analgesic and visual analogue score were recorded.

Results:

The mean time of onset of globe and lid akinesia was significantly faster in group F and group C compared to group S, mean duration of globe and lid akinesia was longer in Group F (207.71 + 13.54 and 143.14 + 7.86 min) and group C (213.52 + 14.52 and 162.06 + 17.1 min) compared to group S (117.78 + 10.42 and 87.64 + 9.76 min). The mean duration of analgesia was significantly longer in group F (217.71 + 12.67) and C (258.82 + 14.50 min) as compared to group S (131.39 + 9.63 min).

Conclusion:

Addition of fentanyl or clonidine as adjuvant to local anaesthetic in peribulbar block provides faster onset and prolonged analgesia compared to local anaesthetic alone.

Comparison between the intravenous and caudal routes of sufentanil in children undergoing orchidopexy and further evaluation of the association of caudal adrenaline and neostigmine

Background:

The aim of this study was to compare the intravenous (IV) and caudal routes of administration of sufentanil for children undergoing orchidopexy and also to evaluate the effects on addition of caudal adrenaline and neostigmine.

Materials and Methods:

Sixty patients scheduled for orchidopexy were divided into the following groups: 1) Group IVSu received IV 0.5 μg/kg sufentanil and caudal saline; 2) Group CSu received caudal 0.5 μg/kg sufentanil and IV saline; 3) Group CSuAdr received caudal sufentanil plus adrenaline 5 μg/ml (1:200,000) and IV saline; 4) Group CSuNeo received caudal sufentanil plus neostigmine, and IV saline; and 5) Group CSuNeoAdr received caudal sufentanil plus neostigmine plus adrenaline, and IV saline. Heart rate and mean blood pressure >15% was treated with increasing isoflurane concentration. Consumption of isoflurane, side effects, quality of sleep, time to first administration of analgesic, and number of doses of 24-h rescue analgesic were recorded.

Results:

Groups were demographically similar. Isoflurane consumption showed the following association: Group IVSu = Group CSuNeo = Group CSuNeoAdr < Group CSu = Group CSuAdr (P < 0.02). VAS for sedation on reversal of anesthesia showed the following association: Group CSuNeo = Group CSuNeoAdr < Group CSu = Group CSuAdr = Group IVSu (P < 0.005). Time to the first administration of dipyrone showed the following association: Group IVSu = Group CSu = Group CSuAdr (3-4 h) < Group CSuNeo = Group CSuNeoAdr (10-11 h) (P < 0.05). Number of doses of rescue analgesic showed the following association: Group IVSu = Group CSu = Group CSuAdr > Group CSuNeo = Group CSuNeoAdr (P < 0.005). Incidence of adverse effects was similar among groups.

Conclusion:

Caudal sufentanil alone was no better than when administered in the IV route, and would just be justified by the association of neostigmine, but not adrenaline. Neostigmine association resulted in better perioperative analgesia.

Advances in labor analgesia

The pain of childbirth is arguably the most severe pain most women will endure in their lifetimes. The pain of the early first stage of labor arises from dilation of the lower uterine segment and cervix. Pain from the late first stage and second stage of labor arises from descent of the fetus in the birth canal, resulting in distension and tearing of tissues in the vagina and perineum. An array of regional nerve blocks, systemic analgesic, and nonpharmacologic techniques are currently used for labor analgesia. Nonpharmacologic methods are commonly used, but the effectiveness of these techniques generally lacks rigorous scientific study. Continuous labor support has been shown to decrease the use of pharmacologic analgesia and shorten labor. Intradermal water injections decrease back labor pain. Neuraxial labor analgesia (most commonly epidural or combined spinal-epidural) is the most effective method of pain relief during childbirth, and the only method that provides complete analgesia without maternal or fetal sedation. Current techniques commonly combine a low dose of local anesthetic (bupivacaine or ropivacaine) with a lipid soluble opioid (fentanyl or sufentanil). Neuraxial analgesia does not increase the rate of cesarean delivery compared to systemic opioid analgesia; however, dense neuraxial analgesia may increase the risk of instrumental vaginal delivery.

Comparison of three doses of epidural fentanyl followed by bupivacaine and fentanyl for labor analgesia

BACKGROUND

Epidural fentanyl 100 microg after lidocaine-epinephrine test dose has been shown to provide adequate analgesia in early labor. This investigation determines the effect of three different bolus doses of epidural fentanyl on duration and quality of analgesia during early first stage of labor.

METHODS

In this prospective, double-blind study, 103 laboring nulliparous at cervical dilation <5 cm were enrolled. After an epidural test dose of lidocaine (60 mg) with epinephrine (15 microg), parturients received, randomly, bolus of epidural fentanyl 50, 75, or 100 microg, followed by a continuous infusion of epidural bupivacaine 0.0625% and fentanyl 3 microg/ml at a rate of 10 ml/h. Pain scores and maternal sedation, pruritus, nausea, and vomiting were recorded 10, 20, and 30 min after fentanyl, and every 30 min thereafter until first request for additional analgesia.

RESULTS

Adequate analgesia was achieved in 87% (28/32), 94% (35/38), and 94% (31/33) in the fentanyl 50, 75, and 100 microg groups within 20 min. Mean duration of analgesia before re-dosing was significantly longer in fentanyl 100 and 75 microg groups (185.6+/-82.9 and 188.5+/-82.2 min, respectively) as compared with fentanyl 50 microg group (133.6+/-46.2 min, P<0.016). There was no difference in the incidence of maternal side effects or neonatal Apgar scores among the three groups.

CONCLUSION

After a test dose of lidocaine-epinephrine, the three epidural fentanyl doses produced similar effective labor analgesia. However, epidural fentanyl 75 microg followed by epidural infusion of dilute bupivacaine and fentanyl produced longer duration of analgesia than fentanyl 50 microg followed by the same infusion, with no further prolongation when the dose of fentanyl was increased up to 100 microg.

Epidural Fentanyl Speeds the Onset of Sensory and Motor Blocks During Epidural Ropivacaine Anesthesia

In this study we examined the onset times of sensory and motor block during epidural ropivacaine anesthesia with and without the addition of fentanyl to the epidural solution. Forty-five young male patients undergoing knee arthroscopic surgery were randomly allocated into 3 groups of 15 patients each: epidural fentanyl (EF; epidural administration of 15 mL of 1% ropivacaine plus 100 mug fentanyl followed by IV injection of 2 mL of normal saline); IV fentanyl (IF; epidural administration of 15 mL of 1% ropivacaine plus 2 mL of normal saline followed by IV injection of 100 mug fentanyl); and control (C; epidural administration of 15 mL of 1% ropivacaine plus 2 mL of normal saline followed by IV injection of 2 mL of normal saline). The sensory and motor blocks were assessed by pinprick and modified Bromage scale, respectively. The hemodynamic changes, postepidural shivering, and side effects of epidural fentanyl were also recorded. There was no difference in the distribution of age, weight, and height among the 3 groups. The onset time of sensory block to the T10 dermatome was significantly more rapid in the EF group (13.0 +/- 3.0 min) than in the IF group (16.2 +/- 3.5 min, P < 0.05) or C group (17.7 +/- 3.6 min, P < 0.05). The onset times of motor block up to Bromage scale 1 and 2 were significantly more rapid in the EF group (11.9 +/- 4.6 and 24.4 +/- 5.9 min) than in the IF group (16.9 +/- 4.7 and 30.8 +/- 5.6 min, P < 0.05) or C group (18.3 +/- 4.9 and 32.7 +/- 5.7 min, P < 0.05). There was no difference in the incidence of shivering among the three groups. Pruritus was observed in three patients of the EF group and one patient of the IF group. No nausea, vomiting, respiratory depression, urinary retention, or hypotension was observed in any patient. We conclude that epidural administration of the mixture of 100 mug fentanyl and 1% ropivacaine solution accelerated the onset of sensory and motor blocks during epidural ropivacaine anesthesia without significant fentanyl-related side effects.

The Site of Action of Epidural Fentanyl Infusions in the Presence of Local Anesthetics: A Minimum Local Analgesic Concentration Infusion Study in Nulliparous Labor

We have previously demonstrated that continuous epidural infusions of fentanyl without local anesthetics elicit analgesia by a systemic mechanism. In this study, we examined the hypothesis that, in the presence of epidural bupivacaine, continuous infusions of epidural fentanyl elicit analgesia by a spinal mechanism. Forty-eight nulliparous women in active labor participated in this prospective, randomized, double-blinded study. Women received lumbar epidural analgesia with 20-30 mL bupivacaine 0.125% until pain free. Subjects were then randomized to either IV or epidural (EPI) fentanyl infusion groups. Each infusion delivered fentanyl 30 microg/h. All women received an epidural infusion of bupivacaine at a rate of 20 mL/h, the concentration of which was determined by the response of the previous woman in the same group to the analgesic regimen used. Unlike previous studies that assessed the minimum local analgesic concentration (MLAC) for bolus administration at the initiation of analgesia, this study assessed MLAC(infusion) for the maintenance of analgesia throughout the first stage of labor. MLAC(infusion) was determined using the up-down sequential analysis described by Dixon and Massey. The MLAC(infusion) of epidural bupivacaine was 0.063% (95% confidence interval, 0.058-0.068) and 0.019% (95% confidence interval, 0.000-0.038) in the IV and EPI groups respectively. A continuous infusion of fentanyl was more than three times as potent when administered by the epidural than by the IV route. This marked increase in potency for the epidural route is highly suggestive for a predominantly spinal mechanism of action for infused epidural fentanyl under the conditions of this study.

IMPLICATIONS

This study determined the median effective concentration for epidural infusions of bupivacaine during labor analgesia. Coadministered epidural fentanyl infusions were more than three times more potent than IV fentanyl infusions, suggesting a predominantly spinal mechanism of opioid action under these study conditions.

Spinal Mechanisms Contribute to Analgesia Produced by Epidural Sufentanil Combined with Bupivacaine for Postoperative Analgesia

When used alone, lipid-soluble epidural opioids are thought to produce analgesia supraspinally via systemic absorption. However, spinal opioids and local anesthetics have been shown to act synergistically at the spinal level in animal studies. We, therefore, tested the hypothesis that sufentanil requirements will be less when given epidurally than IV in patients simultaneously given epidural bupivacaine after major abdominal surgery. Forty patients were anesthetized with isoflurane and epidural bupivacaine for major abdominal surgery. After surgery, each was given a continuous epidural infusion of bupivacaine at a rate of 5 mg/h and sufentanil patient-controlled analgesia (PCA). In a randomized, double-blinded fashion, the sufentanil was given either epidurally or IV. PCA settings were the same in each group. For 60 hrs after surgery, the following variables were measured: pain scores at rest, during mobilization, and during coughing; extension of sensory block; side effects; and sufentanil consumption. Pain scores, extension of sensory block, and the incidence of side effects did not differ between the two groups. Consumption of sufentanil in the epidural group was half that of the IV group (48 h after surgery: 107 +/- 57 microg versus 207 +/- 100 microg for the epidural and IV groups, respectively; P < 0.05). We conclude that spinal mechanisms contribute to the analgesia produced by epidural sufentanil in combination with a local anesthetic.

IMPLICATIONS

When combined with epidural bupivacaine, the sufentanil requirement was 50% less when given epidurally than IV. Epidural sufentanil thus appears to have a spinal mechanism of action.

Epidural ketamine potentiates epidural morphine but not fentanyl in acute nociception in rats

Epidural opioids have been reported to provide superior analgesia in acute pain management. Despite the fact that the required doses are low, major side effects such as respiratory depression may still occur. In an effort to maximize analgesia and to minimize the rate of side effects, epidural NMDA receptor antagonists, especially ketamine, may be co-administered with opioids. This study investigated whether ketamine had beneficial effects on fentanyl- or morphine-induced antinociception in an acute pain model in rats. In male Wistar rats, an epidural catheter was placed under general anaesthesia. After 1 week the animals were subjected to the tail withdrawal reaction (TWR) test. After determination of the basal reaction latencies, fentanyl, morphine, ketamine or combinations of an opioid with ketamine were administered epidurally. TWR latencies were measured for up to 2h after treatment. Both opioids showed a dose related antinociceptive effect. Fentanyl had a fast onset and a short duration of action whereas the reverse was true for morphine. Ketamine exhibited only limited antinociceptive properties. In the combinations, ketamine improved morphine-induced antinociception both in terms of maximal possible effect (MPE) as well as in duration of action. The combination of fentanyl with ketamine did not result in any improvement, neither in terms of MPE nor in duration of action. Moreover, increasing doses of ketamine tended to decrease the MPE of various doses of fentanyl. These data confirm that ketamine, contrary to opioids, does not possess important antinociceptive properties in an acute test such as the TWR test. Furthermore, these data indicate that additive drugs such as ketamine may have different effects on different opioids.