The Effect of Epidural Fentanyl on the Minimum Local Analgesic Concentration of Epidural Chloroprocaine in Labor

A multicenter study of the analgesic effects of epidural chloroprocaine after lower limb orthopedic surgery

STUDY OBJECTIVE

To investigate the effects and optimal concentration of chloroprocaine for epidural analgesia after lower limb orthopedic surgery.

DESIGN

Prospective, randomized, observational, multicenter clinical study.

SETTING

Operating room, postoperative recovery area, university hospital.

PATIENTS

One hundred and twenty patients from 4 hospitals were enrolled and randomized into 5 groups after lower limb orthopedic surgery under epidural anesthesia with lidocaine.

INTERVENTIONS

Epidural chloroprocaine mixed with 0.4μg/mL fentanyl was administered via a patient-controlled analgesia pump at the concentration of 0.6%, 0.8%, 1.0%, 1.2%, or 1.4% after the surgery.

MEASUREMENTS

Systolic blood pressure, heart rate, visual analog score at rest and during activity, as well as the Bromage score at 0 minute, 30 minutes, 1 hour, 2 hours, 4 hours, 8 hours, 24 hours, and 48 hours after the surgery were recorded and compared. Use of morphine and incidence of adverse effects were also recorded.

MAIN RESULTS

Patients given 1.2% chloroprocaine showed the lowest visual analog score compared with other groups. There was no significant difference in the Bromage score among 5 groups. The Bromage score returned to 0 in 89.7% of the patients 48 hours after surgery. No difference in postoperative morphine usage, blood pressure, or heart rate was found among 5 groups.

CONCLUSIONS

Epidural 1.2% chloroprocaine with 0.4μg/mL fentanyl could generate proper analgesic effects with little influence on mobility in patients undergoing lower limb orthopedic surgery. In addition, it could generate a good sense and movement separation, facilitating the early functional training.

Sparing effects of sufentanil on epidural ropivacaine in elderly patients undergoing transurethral resection of prostate surgery

PURPOSE

This study examined the sparing effect of sufentanil on the median effective concentration (EC₅₀) of epidural ropivacaine in elderly patients undergoing elective transurethral resection of prostate (TURP).

MATERIALS AND METHODS

This was a prospective randomized double-blind dose-response study. Fifty eight elderly patients with American Society of Anesthesiologists physical status I-II who were scheduled for TURP surgery under epidural anesthesia were randomly allocated to a group receiving 15 mL of ropivacaine (group R) or a group receiving ropivacaine plus 5 μg of sufentanil (group RS). The concentration of ropivacaine was determined by a Dixon's up-and-down sequential allocation. The first participant received 0.3% of ropivacaine in both groups and subsequent concentrations were determined by the response of the previous patient in the same group. The EC₅₀ of epidural ropivacaine was analyzed using the Dixon and Massey method.

RESULTS

The EC₅₀ of ropivacaine during TURP surgery was 0.186% (95% confidence interval, 0.173-0.200%) in group R, and 0.136% (95% confidence interval, 0.127-0.144%) in group RS (p<0.01). No differences in Bromage scale of motor block examination and the onset time of sensory block were observed.

CONCLUSION

Administration of 5 μg of epidural sufentanil caused a 37% reduction in the EC₅₀ of epidural ropivacaine in elderly patients who underwent TURP surgery. Thus, sufentanil addition during surgery of TURP can decrease the dose of ropivacaine anesthesia required.

Addition of Adrenaline to Chloroprocaine Provides a Moderate Duration Time for Epidural Anaesthesia in Elective Caesarean Section

OBJECTIVE: Epidural anaesthesia using chloroprocaine with or without adrenaline and lidocaine with adrenaline were compared. METHODS: Sixty parturients undergoing elective caesarean section under epidural anaesthesia were randomized to receive 3% chloroprocaine (group C), 3% chloroprocaine with adrenaline (group CA) or 2% lidocaine with adrenaline (group LA). Onset time, duration time and various maternal, fetal and neonatal parameters were monitored. Pain was assessed using a visual analogue scale. RESULTS: The onset time of analgesia in group CA was similar to that in group C but was shorter than that in group LA. Duration of analgesia, loss of cold sensation and motor blockade in group CA were prolonged compared with group C, but were shorter than those in group LA. No differences in maternal, fetal or neonatal effects were seen. A higher pain score was reported in group C than in groups CA or LA at the end of surgery. CONCLUSIONS: Epidural anaesthesia using chloroprocaine with adrenaline has a quick onset and moderate duration and is an attractive alternative to lidocaine and adrenaline or chloroprocaine alone for caesarean section.

Adding sufentanil to levobupivacaine or ropivacaine intrathecal anaesthesia affects the minimum local anaesthetic dose required

BACKGROUND

We carried out this prospective, randomized, double-blind study in order to evaluate whether the intrathecal addition of sufentanil 3.3 mcg affects both the minimum local anaesthetic dose (MLAD) of spinal levobupivacaine and ropivacaine for a caesarean section and enhances the spinal block characteristics.

METHODS

One hundred and eighty women were randomly allocated into four groups: levobupivacaine (Group L), levobupivacaine plus sufentanil (Group L+S), ropivacaine (Group R) and ropivacaine plus sufentanil (Group R+S). Each received 3 ml of the study solution intrathecally as part of a combined spinal/epidural technique. The initial dose was 12 mg for Groups L and L+S, and 15 mg for Groups R and R+S. The test solution was required to achieve a visual analogue pain score (VAPS) of 30 mm or less to be considered effective at skin incision, uterine incision, birth, peritoneal closure and at the conclusion of surgery. Effective or ineffective responses determined a 0.5 mg decrease or increase of the same drug, respectively, for the next patient in the same group, using an up-down sequential allocation.

RESULTS

Using the Dixon and Massey formula, the MLAD was 10.65 mg [confidence interval (CI) 95%: 10.14-11.56] in Group L, 4.73 mg (CI 95%: 4.39-5.07) in Group L+S, 14.12 mg (CI 95%: 13.50-14.60) in Group R and 6.44 mg (CI 95%: 5.86-7.02) in Group R+S.

CONCLUSIONS

The addition of sufentanil reduced the MLAD of both the local anaesthetics. It did not affect their potency ratio significantly and resulted in enhanced spinal anaesthesia.

Genetic variability of the mu-opioid receptor influences intrathecal fentanyl analgesia requirements in laboring women

Labor initiates one of the most intensely painful episodes in a woman's life. Opioids are used to provide analgesia with substantial interindividual variability in efficacy. mu-Opioid receptor (muOR, OPRM1) genetic variants may explain differences in response to opioid analgesia. We hypothesized that OPRM1 304A/G polymorphism influences the median effective dose (ED(50)) of intrathecal fentanyl via combined spinal-epidural for labor analgesia. Nulliparous women were prospectively recruited around 35 weeks gestation (n=224), and genotyped for 304A/G polymorphism. Those requesting neuraxial labor analgesia were enrolled in one of the two double-blinded trials: up-down sequential allocation (SA, n=50) and a separate confirmatory random-dose allocation trial (RA, n=97). Effective analgesia from intrathecal fentanyl was defined by >or=60 min analgesia with verbal rating score <or=1 (scale 0-10) and was compared between mu OR 304A homozygotes (Group A) and women carrying at least one 304G allele (Group G). OPRM1 304G allele frequency f(-) was 0.18. Using SA, intrathecal fentanyl ED(50) was 26.8 microg (95% CI 22.7-30.9) in Group A and 17.7 microg (95% CI 13.4-21.9) in Group G (p<0.001; 304A homozygosity increased the ED(50) 1.5-fold). RA confirmed that 304A homozygosity significantly increases intrathecal fentanyl ED(50) (27.4 microg in Group A and 12.8 microg in Group G [p<0.002; 2.1-fold]). We demonstrate for the first time that the muOR 304G variant significantly reduces intrathecal fentanyl ED(50) for labor analgesia, suggesting women with the G variant may be more responsive to opioids and require less analgesic drugs. These findings for intrathecal fentanyl pharmacogenetics may have implications for patients receiving opioids in other settings.

Effect of sufentanil on minimum local analgesic concentrations of epidural bupivacaine, ropivacaine and levobupivacaine in nullipara in early labour

BACKGROUND

The aim was to assess the effect of epidural sufentanil on relative analgesic potencies of epidural bupivacaine, ropivacaine and levobupivacaine by determining the minimum local analgesic concentrations during labour.

METHODS

In a randomised, double-blind study, 171 parturients were allocated to one of six groups receiving a 10-mL bolus of bupivacaine, ropivacaine or levobupivacaine alone or with sufentanil 0.75 microg/mL. The concentration of local anaesthetic was determined by the response of the previous parturient using up-down sequential allocation starting at a concentration of 0.13% wt/vol with a testing interval of 0.01%. Effective analgesia was defined as a visual analogue pain score < or = 15/100 mm within 30 min and lasting for 30 min. Median effective concentrations were estimated and two-sided P < 0.05 was significant.

RESULTS

Local anaesthetic concentration, use of sufentanil and local anaesthetic drug were independent significant predictors of effective and ineffective analgesia. Bupivacaine was significantly more potent than levobupivacaine and ropivacaine. The relative potency ratios without sufentanil of 0.77:0.83:1.00 were reduced to 0.36:0.38:1.00 by the addition of sufentanil. The major factor influencing local anaesthetic requirements was the addition of sufentanil, which reduced overall requirements by a factor of 4.2 (95% CI 3.6-4.8); this effect was proportionately more enhanced for bupivacaine.

CONCLUSIONS

Local anaesthetic requirements for bupivacaine, levobupivacaine and ropivacaine follow an analgesic potency hierarchy. Any potency differences are small when compared to the effect of sufentanil, which resulted in a four-fold reduction in local anaesthetic requirements. Sufentanil may also enhance the potency differences between bupivacaine and the two S-enantiomer agents.

Chloroprocaine may not affect epidural morphine for postcesarean delivery analgesia

STUDY OBJECTIVE

The purpose of this study is to assess the independent effect of epidural chloroprocaine on morphine used for pain relief after cesarean delivery.

DESIGN

We used a randomized, double blind, placebo-controlled trial.

SETTING

The study took place at the labor and delivery ward of an academic medical center.

PATIENTS

Forty pregnant women undergoing elective cesarean delivery under spinal-epidural anesthesia.

INTERVENTIONS

Patients were randomized to receive either 150 mg of 3% chloroprocaine or placebo, followed by 3 mg of epidural morphine.

MEASUREMENTS

The primary outcome for this investigation was the duration of pain relief after morphine administration, defined as the time at first use of supplemental opioids for analgesia. Secondary outcomes included pain scores, blood pressure, heart rate, respiratory rate, anesthetic sensory level, nausea and vomiting, pruritus, supplemental use of nonsteroidal anti-inflammatory medications, and satisfaction.

MAIN RESULTS

The groups were similar in demographics and duration of spinal anesthesia. Using Kaplan-Meier survival analysis of the duration of morphine analgesia, we found no difference between the groups (chloroprocaine, 1191 minutes, vs placebo, 1267 minutes, P = 0.52). There was no difference in pain scores or the need for supplemental analgesics. Side effects of epidural morphine were similar between the groups.

CONCLUSIONS

We found that epidural chloroprocaine did not reduce the duration or effectiveness of postoperative analgesia from epidural morphine.

Obese parturients have lower epidural local anaesthetic requirements for analgesia in labour †

BACKGROUND

There are no studies comparing local anaesthetic requirements for obese and normal parturients. Obesity has been associated with a higher incidence of Caesarean section and higher levels of epidural block have also been found in obese obstetric patients, suggesting they may require less local anaesthetic. The aim of our study was to estimate the minimum local analgesic concentration (MLAC) of bupivacaine for obese and non-obese parturients.

METHODS

Otherwise healthy parturients (n=32) requesting epidural analgesia were enrolled in this up-down sequential allocation study. Women were in active labour (3-6 cm cervical dilatation) with visual analogue pain scores (VAPS) >40/100 mm. Subjects with BMI >30 kg m(-2) were allocated to the obese group and BMI < or = 30 kg m(-2) were allocated to the normal group. The initial epidural dose for both groups was 20 ml 0.1% w/v bupivacaine (20 mg), with a dosing increment of 0.01% w/v VAPS < or = 10/100 mm defined effective analgesia. The MLAC was estimated using up-down reversals and probit regression with P<0.05 as significant.

RESULTS

Groups were similar except for BMI and weight (P<0.001). Local anaesthetic requirements were significantly (P<0.001) reduced by a factor of 1.68 (95% CI 1.32-2.29) in the obese group, with significantly higher initial level of block (P<0.001).

CONCLUSION

We found obese parturients to have significantly decreased epidural bupivacaine analgesic requirements. A contributing factor to obese patients having more difficult labours may be that relatively larger doses of local anaesthetic are administered than actually required. It may be worth considering lowering the concentrations and doses with which we initiate analgesia in obese parturients.

Current status and clinical relevance of studies of minimum local-anaesthetic concentration (MLAC)

PURPOSE OF REVIEW

Studies comparing the effects of epidural local anaesthetics have been limited by the lack of knowledge of their relative potencies. In 1995 the concept of the minimum local-anaesthetic concentration (MLAC) was introduced, this has been defined primarily as the median effective analgesic concentration in the first stage of labour. Pharmacologically, this model aims to determine equipotent analgesic concentrations of local anaesthetics, to compare motor effects and to evaluate the relative toxicity during labour. However, results of recent MLAC studies are not uniform and rather confusing, and thus, the basic validity of the MLAC concept for determining local-anaesthetic potency is increasingly discussed.

RECENT FINDINGS

MLAC studies have postulated that ropivacaine is up to 40% less potent than bupivacaine, but as potent as levo-bupivacaine. Intriguingly, bupivacaine has been shown to be as effective as levo-bupivacaine in identical experimental protocols. Modified MLAC studies resulted additionally in local anaesthetic-sparing effects of epidural/intrathecal opioids, clonidine and epinephrine. MLAC studies have also been applied to compare the relative analgesic as well as relative motor-blocking potency of local anaesthetics.

SUMMARY

Relative differences in local anaesthetics' potencies derived from MLAC examinations are meaningful and correct from the pharmacological point of view, but they cannot simply be transferred to daily clinical practice. Thus, MLAC values should not be misinterpreted as these data are not suggested to be suitable to define and quantify the pharmacodynamics of local anaesthetics, nor to unequivocally predict their toxicological profile in clinically relevant concentrations.

Anaesthetic Agents for Advanced Regional Anaesthesia

Interest in the use of regional anaesthesia, particularly peripheral nerve blocks (PNBs) and continuous PNBs, has increased in recent years. Accompanying this resurgence in interest has been the development of new local anaesthetics and additives designed to enhance block duration and quality. This manuscript provides a literature-based review on accepted uses of local anaesthetics and adjuncts for a variety of regional anaesthesia techniques. A brief review of local anaesthetic pharmacodynamics describes the action of these drugs in preventing nerve depolarisation, thus blocking nerve impulses. Toxic adverse effects of local anaesthetics, specifically CNS and cardiac manifestations of excessive local anaesthetic blood concentrations and the direct neurotoxic properties of local anaesthetics, are discussed generally and specifically for many commonly used local anaesthetics. Clinically useful ester and amide local anaesthetics are evaluated individually in terms of their physical properties and toxic potential. How these properties impact on the clinical uses of each local anaesthetic is explored. Particular emphasis is placed on the long-acting local anaesthetic toxic potential of racemic bupivacaine compared with levobupivacaine and ropivacaine, which are both levorotatory stereoisomers. Guidelines for using ropivacaine and mepivacaine, based on the authors' experience using advanced regional anaesthesia in a busy practice, is provided. Finally, epinephrine (adrenaline), clonidine and other local anaesthetic additives and their rationale for use is covered along with other future possibilities.

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.

The effect of clonidine on the minimum local analgesic concentration of epidural ropivacaine during labor

On the basis of the determination of minimum local analgesic concentration (MLAC), ropivacaine has been demonstrated to be less potent than bupivacaine during the first stage of labor. In this study we assessed the effect of clonidine on the MLAC of ropivacaine. Seventy-seven parturients of mixed parity requesting epidural analgesia for labor (cervical dilation, 3-7 cm) were included in the study. They received an epidural bolus of either ropivacaine (n = 30), ropivacaine plus clonidine 30 microg (n = 28), or ropivacaine plus clonidine 60 microg (n = 19) in the second part of the study. The concentration of the ropivacaine solution was determined by the response of the previous parturient in that group by using an up-down sequential allocation. A visual analog pain score of < or =10 mm within 30 min after the epidural bolus (20 mL) was considered an effective response. An effective result directed a 0.01% wt/vol decrement for the next patient. An ineffective result directed a 0.01% wt/vol increment. The MLAC of ropivacaine was 0.097% wt/vol (95% confidence interval, 0.085%-0.108%). It was unaffected by a 30-microg dose of epidural clonidine (0.081% [0.045%-0.117%]) but was significantly decreased by a 60-microg clonidine dose (0.035% [0.024%-0.046%]) (P < 0.001). This study documents a decrease in the MLAC of ropivacaine by clonidine, significant for a 60- microg dose.

IMPLICATIONS

Epidural ropivacaine potency in labor can be increased by the addition of epidural clonidine. This study demonstrates that 60 microg of epidural clonidine significantly decreases the minimum local analgesic concentration of ropivacaine during the first stage of labor but is associated with sedation.