Ropivacaine in ultrasound-guided femoral nerve block: what is the minimal effective anaesthetic concentration (EC90)?

Comparative analysis of the analgesic effects of intercostal nerve block, ultrasound-guided paravertebral nerve block, and epidural block following single-port thoracoscopic lung surgery

OBJECTIVE

In this study, we compared the analgesic effects of intercostal nerve block (ICNB), ultrasound-guided paravertebral nerve block (PVB), and epidural block (EB) following single-port thoracoscopic lung surgery.

METHOD

A total of 120 patients who underwent single-hole thoracoscopic lung surgery were randomly and equally divided into three groups: ICNB group, the PVB group, and the EB group. ICNB was performed under direct thoracoscopic visualization before the conclusion of the surgery in the ICNB group, while PVB and EB were performed after general anesthesia in the PVB and EB groups, respectively. Patient-controlled intravenous analgesia (PCIA) was used following the surgery in all the groups. The following indicators were recorded: Intraoperative sufentanil dosage, anesthesia awakening time, postoperative intubation time, nerve block operation time, postoperative visual analog scale (VAS) pain scores during resting and coughing at regular intervals of 0, 2, 4, 8, 24, and 48 h, the time until first PCIA, number of effective compressions within 24 h postoperatively, number of rescue analgesia interventions, and the side effects.

RESULTS

In comparison to the ICNB group, the PVB and EB groups had a lower intraoperative sufentanil dosage, significantly shorter anesthesia awakening time, and postoperative intubation time, but longer nerve block operation time, lower VAS scores when resting and coughing within 24 h postoperatively (all p-values less than 0.05). Conversely, there were no statistically significant differences in VAS scores during resting and coughing after 24 h (all p-values greater than 0.05). Time to first PCIA, number of effective compressions and number of rescue analgesia at the 24-hour mark postoperatively were significantly better in the PVB and EB groups than that in the ICNB group (P < 0.05). However, there was a higher incidence of side effects observed in the EB group (P < 0.05).

CONCLUSION

The analgesic effect of PVB and EB following single-port thoracoscopic lung surgery is better than that of ICNB. PVB causes fewer side effects and complications and is safer and more effective.

Ultrasound-guided caudal anaesthesia combined with epidural anaesthesia for caesarean section: a randomized controlled clinical trial

BACKGROUND

Although epidural anaesthesia and spinal anaesthesia are currently the general choices for patients undergoing caesarean section, these two neuraxial anaesthesia methods still have drawbacks. Caudal anaesthesia has been considered to be more appropriate for gynaecological surgery. The purpose of this study was to compare epidural anaesthesia combined with caudal anaesthesia, spinal anaesthesia and single-space epidural anaesthesia for caesarean section with respect to postoperative comfort and intraoperative anaesthesia quality.

METHODS

In this clinical trial, 150 patients undergoing elective caesarean section were recruited and randomized into three groups according to a ratio of 1:1:1to receive epidural anaesthesia only, spinal anaesthesia only or epidural anaesthesia combined with caudal anaesthesia. The primary outcome was postoperative comfort in the three groups. Secondary outcomes included intraoperative anaesthesia quality and the incidences of nausea, vomiting, postdural puncture headache, maternal bradycardia, or hypotension.

RESULTS

More patients were satisfied with the intraoperative anaesthesia quality in the EAC group than in the EA group (P = 0.001). The obstetrician was more significantly satisfied with the intraoperative anaesthesia quality in the SA and EAC groups than in the EA group (P = 0.004 and 0.020, respectively). The parturients felt more comfortable after surgery in the EA and EAC groups (P = 0.007). The incidence of maternal hypotension during caesarean section was higher in the SA group than in the EA and EAC groups (P = 0.001 and 0.019, respectively).

CONCLUSIONS

Epidural anaesthesia combined with caudal anaesthesia may be a better choice for elective caesarean section. Compared with epidural anaesthesia and spinal anaesthesia, it has a higher quality of postoperative comfort and intraoperative anaesthesia.

Differential blockade, comparative study of different ropivacaine concentrations (0.75%; 0.2%; 0.12%) for ultrasound guided sciatic and femoral nerve blocks in calves: Prospective cross-over study

Pharmacodynamic understanding of the different local anesthetic concentrations allows adapting their use to diverse clinical/surgical procedures, such as intraoperative and/or postoperative analgesia. A crossover study was performed, where 6 calves (5 male and 1 female), weighing 120 ± 28 Kg, were subjected to combined sciatic and femoral nerve block using three ropivacaine concentrations. The treatments were: R0.75, using 0.75% ropivacaine; R0.2, 0.2% ropivacaine; and R0.12%, 0.12% ropivacaine. All treatments were performed with ultrasound and neurostimulation assistance, and a volume of 0.1 mL/kg of the respective local anesthetic solution was administered in each block point. The sites of mechanical nociceptive threshold (MNT) evaluation were based on the calf pelvic limb dermatomes. The proportion between desensitized areas, MNT elevation time and level of ataxia were registered. Elevation of MNT occurred in 100% of the tested areas in the R0.75 and R0.2 treatments, and in 82% of the R0.12 treatment. Mean MNT elevation times were 9.5 ± 0.7 h for R0.75, 6 ± 0.8 for R.02, and 2.4 ± 2.3 for R0.12, differing significantly between all treatments. No difference was observed between MNT elevation time and ataxia duration time, in each treatment. It is concluded that the duration of sensory-motor effects is dose-dependent, but there was not possible to detect block selectivity as the concentrations was reduced. More desensitized areas and extension were obtained with the use of higher concentrations.

The postoperative analgesia of retrolaminar block in patients undergoing surgery with general anesthesia: a systematic review

INTRODUCTION

Postoperative pain has always been a difficult problem in anesthesia management. The neurological block technique has been used for postoperative analgesia management, but compared with the traditional block method, the effect of postoperative analgesia after layer block is still controversial, and a clear literature review is needed. This systematic review's goal was to investigate RLB's impact on postoperative analgesia.

EVIDENCE ACQUISITION

The literature search was performed using the PubMed, Web of Science, Embase, and Cochrane Central Register of Controlled Trials (CENTRAL) databases. Patients aged 18 years who underwent retrolaminar block were considered eligible. The article must report the results of the original study related to postoperative analgesia. The characteristics of the study sample and evaluating the RLB for postoperative analgesia were extracted from each included article and concluded.

EVIDENCE SYNTHESIS

Eleven randomized controlled trials (726 patients) were included. After summarizing the analysis of the results of RLB on changing postoperative analgesia indexes in different surgeries, we concluded that PVB is better used for postoperative analgesia compared with RLB. The analgesic effect of RLB provides advantages compared with EPSB, SCPB, etc.

CONCLUSIONS

Based on the results of this review, RLB can be applied to thoracic surgery, abdominal surgery and parotid surgery, but its analgesic effect is not significant enough, and further research is needed in the future to provide stronger evidence for postoperative analgesia in surgical patients.

Femoral nerve block using lower concentration ropivacaine preserves quadriceps strength while providing similar analgesic effects after knee arthroscopy

PURPOSE

Femoral nerve block (FNB) is widely used in patients undergoing knee arthroscopy. However, the most commonly used concentration of ropivacaine (0.2% or above) may cause an unexpected decrease in the muscle strength of the quadriceps. Therefore, a lower concentration of ropivacaine (0.1%) for FNB was administered to investigate the effect on quadriceps strength and postoperative pain after knee arthroscopy.

METHODS

This was a double-blind, randomized, controlled trial (ChiCTR2000041404). A total of 83 patients scheduled for elective knee arthroscopy were randomized to receive 0.1% or 0.2% ropivacaine for FNB under ultrasound guidance. The primary outcomes were quadriceps strength and numerical rating scale (NRS) pain score. Quadriceps strength was measured before surgery and 6 h and 24 h after surgery, while NRS score was recorded before surgery, at the postanaesthesia care unit (PACU), and 6 h and 24 h after surgery. Multiple linear regression tests were used to compare the differences in quadriceps strength and NRS score between the two groups. Two-factor analysis of variance, using the factors group and time of measurement, was used for repeated NRS scores. Secondary outcomes included knee mobility, side effects, patient satisfaction, and length of hospital stay.

RESULTS

The mean (SD) quadriceps strength at 6 h after surgery was 7.5 (5.7) kg for the 0.1% ropivacaine group and 3.0 (4.4) kg for the 0.2% ropivacaine group. The mean difference adjusted for baseline characteristics was - 5.2 (95% CI - 7.2 to - 3.1) kg (P < 0.001). There was no significant difference between the two groups in quadriceps strength at 24 h after surgery. The mean differences in the average NRS score and maximum NRS score in the PACU were - 0.6 (P = 0.008) and - 1.0 (P < 0.001), respectively. There was no significant difference in NRS score at 6 h or 24 h after surgery. Two-factor analysis of variance showed no significant difference in the interaction factors of time and group for average NRS score and maximum NRS score.

CONCLUSIONS

Compared with 0.2% ropivacaine, 0.1% ropivacaine for FNB preserved quadriceps strength at 6 h after knee arthroscopy while providing similar analgesic effects.

LEVEL OF EVIDENCE

I.

The Median Effective Analgesic Concentration of Ropivacaine in Sciatic Nerve Block Guided by Ultrasound After Arthroscopic Anterior Cruciate Ligament Reconstruction: A Double-Blind Up-Down Concentration-Finding Study

Background

The median effective analgesic concentration (MEAC; EC50 = effective concentration in 50% patients) of ropivacaine in sciatic nerve block guided by ultrasound (US) required for effective postoperative analgesia following arthroscopic anterior cruciate ligament (ACL) reconstruction has not yet been found. This study aimed to determine the effectiveness of MEAC of 20 ml ropivacaine of postoperative anesthesia for patients after ACL reconstruction.

Methods

In total, 29 patients who underwent elective arthroscopic ACL reconstruction were enrolled in this study. All the subjects were given 20 ml of 0.2% ropivacaine for femoral nerve block. A concentration of 20 ml ropivacaine administered to the sciatic nerve was measured by applying the up-and-down sequential method (UDM). The starting concentration was 0.2% in the first patient, and the next patient received decremented 0.025% ropivacaine if the prior patient's postoperative visual analog pain score was <4 in the initial 8 h. Otherwise, the participant was given an incremental dose of 0.025% ropivacaine. The EC50 of ropivacaine was determined by using centered isotonic, linear-logarithmic, exponential regressions, and linear regression. The “goodness of fit” was compared among various models by calculating the residual standard errors.

Results

The concentration of ropivacaine administered ranged from 0.1 to 0.2%. The EC50 [95% confidence interval (CI)] determined by four statistical methods (centered isotonic, exponential regressions, linear-logarithmic, and linear regression) was 0.115, 0.113% (0.108, 0.343%), 0.142% (0.112, 0.347%), and 0.129% (0.103, 0.359%), respectively. Among all models, the residual standard error was the smallest for the exponential regression (0.2243).

Conclusion

The EC50 of ropivacaine in US-guided sciatic nerve block was 0.113–0.142%, and exponential regression model best matched the data.

Comparison of the analgesic effect of ultrasound-guided paravertebral block and ultrasound-guided retrolaminar block in Uniportal video-assisted Thoracoscopic surgery: a prospective, randomized study

Background

The optimal modality for postoperative analgesia after uniportal video-assisted thoracoscopic surgery (UVATS) for the treatment of lung cancer has not yet been determined. Both ultrasound-guided paravertebral block (PVB) and retrolaminar block (RLB) have been reported to be successful in providing analgesia after UVATS. However, which block technique provides superior analgesia after UVATS is still unclear. This randomized study was designed to compare the postoperative analgesic effects and adverse events associated with ultrasound-guided PVB and RLB after UVATS.

Methods

Sixty patients with lung cancer were randomized to undergo ultrasound-guided PVB (group P) or ultrasound-guided RLB (group R). In group P, 30 mL of 0.5% ropivacaine was injected at the T3 and T5 levels via ultrasound-guided PVB (15 mL at each level on the operative side). In group R, 30 mL of 0.5% ropivacaine was injected at the T3 and T5 levels via ultrasound-guided RLB (15 mL at each level on the operative side). The primary outcome was the numerical rating scale (NRS) score within 48 h after surgery. The secondary outcomes were total postoperative sufentanil consumption, time to first analgesic request and adverse events.

Results

At 3, 6, 12, 24, 36 and 48 h postoperatively, the NRS score at rest in group P was lower than that in group R (p < 0.05). At 3, 6, 12, 24 and 36 h postoperatively, the NRS score while coughing in group P was lower than that in group R (p < 0.05). The total postoperative sufentanil consumption in group P was significantly lower than that in group R (p < 0.001). Additionally, the time to first analgesic request was longer in group R than in group P (p < 0.0001). The incidence of nausea in group R was higher than that in group P (p < 0.05).

Conclusions

In patients with lung cancer undergoing UVATS, ultrasound-guided PVB with 0.5% ropivacaine provides better analgesia and results in less nausea than ultrasound-guided RLB. Compared with ultrasound-guided RLB, ultrasound-guided PVB seems to be a better technique for analgesia in UVATS.

Trial registration

The name of this study is the Effect And Mechanism Of Ultrasound-guided Multimodal Regional Nerve Block On Acute And Chronic Pain After Thoracic Surgery. This study was registered in the Chinese Clinical Trial Registry (ChiCTR2100044060). The date of registration was March 9, 2021.

What is the minimum effective anesthetic volume (MEAV90) of 0.2% ropivacaine required for ultrasound-guided popliteal-sciatic nerve block?

Background and Aims:

Popliteal-Sciatic nerve block under Ultrasound Guidance (USG) using a local anesthetic agent like Ropivacaine is an established technique for providing analgesia and muscle relaxation for lower limb surgeries with minimal untoward events. Establishing the minimal volume of 0.2% ropivacaine required to provide intraoperative and postoperative analgesia will further reduce the drug requirements and adverse effects toward the patient.

Material and Methods:

This randomized prospective observational blinded study was done in a tertiary care referral hospital in South India over 9 months from August 2017 till April 2018. The block was performed on all recruited patients under ultrasound guidance with a starting volume of 16 ml 0.2% ropivacaine. Duration of time for loss of pin-prick sensation around the sole of the foot (tibial nerve) and the lateral malleolus (common peroneal nerve) was noted. If successful, the volume of the drug for subsequent patients was randomized by lottery method to either be kept the same or reduced. If the block failed, the subsequent patient recruited would have an increased volume of drug injected.

Results:

By Probit regression analysis using the biased coin up-and-down method we found that 9.3 ml (MEAV90) of 0.2% ropivacaine was sufficient for providing adequate analgesia. Factors such as patient age or weight had no role in efficacy of the block. There were no adverse effects such as allergy to the drug or systemic toxicity noted in the studied patients.

Conclusion:

9.3 ml of 0.2% ropivacaine is sufficient to provide analgesia (assessed by pin-prick) in 90% of patients undergoing popliteal-sciatic block for lower limb surgeries.

Effects of adding a combined femoral and sciatic nerve block with levobupivacaine and clonidine to general anaesthesia in femoropopliteal bypass surgery: A randomised, double-blind, controlled trial

BACKGROUND

Adding a regional block to general anaesthesia can prevent postoperative pain and improve peripheral circulation.

OBJECTIVE

To seek improved postoperative analgesia and care due to a long-acting combined femoral and sciatic nerve block in patients undergoing femoropopliteal bypass surgery.

DESIGN

A randomised, double-blind, controlled trial.

SETTING

Vascular surgery unit of a French university hospital.

PATIENTS

Forty-four adults scheduled for bypass surgery under general anaesthesia.

INTERVENTION

Patients were allocated to receive either an active nerve block with 20 ml of 0.375% levobupivacaine and clonidine 0.5 μg kg, or a simulated (sham) block only, but with local anaesthesia of the skin, before general anaesthesia. General anaesthesia was standardised with propofol, then sevoflurane and sufentanil adjusted according to clinical need. Postoperative analgesia was standardised with paracetamol 1 g every 6 h, and intravenous morphine, initially titrated in the postanaesthesia care unit and then patient-controlled. Oral analgesics were repeated up to day 3.

MAIN OUTCOME MEASURES

The primary outcome was morphine consumption during the first 24 postoperative hours. In a subgroup of postoperative patients distal tissue oxygen saturation was recorded at the lateral side of the blocked calf.

RESULTS

Patients in the active group received less intra-operative sufentanil (median dose 25 vs. 41 μg), needed less morphine during the first 24 h (15 vs. 27 mg) and 72 (20 vs. 35 mg) postoperative hours, than in the control group. They also had less pain on movement, but pain at rest, the tissue oxygen saturation and other rehabilitation outcomes were unaffected by the treatment. Tolerance outcomes were also similar between groups.

CONCLUSION

Combining the two regional blocks improves the quality of postoperative care in this frail population, probably by reducing the amount of peri-operative opioid.

TRIAL REGISTRATION

ClinicalTrials.gov (ref. NCT01785693).

A Randomized Controlled Trial of FNB versus FICB for Patients with Femoral Neck Fractures Before Spinal Anesthesia

Background and Objectives

Patients with femoral neck fractures often suffer severe pain. This randomized controlled clinical study compared the effect of femoral nerve block (FNB) and fascia iliaca compartment block (FICB) in this population.

Patients and Methods

Forty-six patients were randomly assigned to one of the two groups: FNB group (femoral nerve block, n=23) or FICB group (fascia iliaca compartment block, n=23). Before positioning for spinal anesthesia, patients received FNB with 15 mL of 0.5% ropivacaine or FICB with 40 mL of 0.5% ropivacaine. Pain was evaluated using a visual analogue scale (VAS) at rest and during hip flexion after admission to the operation room; at 3, 5, 8, and 10 min after analgesia intervention; and during positioning for spinal anesthesia. Positioning was attempted after 10 min of analgesia intervention in each group. Time required to perform spinal anesthesia, quality of positioning, and patient satisfaction were documented.

Results

The VAS scores in the FNB group were significantly lower than those in FICB group at 3 and 5 min after analgesia intervention (P=0.000). However, there were no significant differences in VAS between groups at 8 or 10 min or during positioning.

Conclusion

FNB and FICB produce similar analgesic effects in patients with femoral neck fractures, but FNB has a more rapid onset of pain relief.

Evaluation of Pectoral Nerve Block in Modified Radical Mastectomy: Comparison of Three Concentrations of Ropivacaine

Background

Pectoral nerve block type I (PECS I Block) and type II (PECS II Block) with ropivacaine are relatively new analgesic methods for breast-cancer surgery. We evaluated the safety and efficacy of different concentrations of ropivacaine given in the same volume for the PECS II Block in patients undergoing modified radical mastectomy (MRM).

Patients and Methods

One hundred and twenty women undergoing elective MRM who met inclusion criteria were divided randomly into four groups of 30: control group without PECS II Block and R_0.2%, R_0.3%, and R_0.4% groups, who received general anesthesia plus the PECS II Block with ropivacaine at 0.2%, 0.3%, and 0.4%, respectively, in a volume of 40 mL.

Results

The postoperative numerical rating scale (NRS) pain score at rest and active was significantly higher in the control group than that in the three ropivacaine groups (P<0.05 for all), and the postoperative NRS score in the R_0.3% group and R_0.4% group at 12, 24, and 48 h postoperatively were significantly lower than that in the R_0.2% group (P<0.05 for all); there was no significant difference between the R_0.3% group and R_0.4% group. The time when pain was first felt after MRM, the total number of complaints during 3, 6, 12, 24, and 48 h after MRM, and the total analgesic requirement (tramadol consumption) during the first 24 h postoperatively in the R_0.3% group and R_0.4% group were significantly lower than those in the control group and R_0.2% group (P<0.05 for all); there was no significant difference between the R_0.3% group and R_0.4% group.

Conclusion

A dose of 0.3% ropivacaine was the optimal concentration for a PECS II Block for patients undergoing MRM because it provided efficacious analgesia during and >48 h after MRM. Increasing the ropivacaine concentration did not improve the analgesia of the PECS II Block significantly.

The Feasibility of the Ultrasound-Guided Femoral Nerve Block Procedure with Low-Dose Local Anesthetic in Intracapsular and Extracapsular Hip Fractures

BACKGROUND

The local anesthetic dosages used in the current literature in regional applications of local anesthetics are frequently high for surgical purposes, and there are no sufficient dosage studies for emergency department (ED) management.

OBJECTIVES

The aim of this study was to determine the success of lower local anesthetic dosages capable of reducing costs and excessive exposure to drugs in pain control in patients with femoral neck fractures (FNFs) in the ED.

METHODS

Patients ≥65 years of age with FNFs and reporting Wong-Baker Pain Rating Scales scores ≥8 were included in this prospective, interventional study. Patients underwent ultrasound-guided regional femoral block with 5 mL 2% prilocaine. Pain scores before the procedure and at 30 min and 2 h postprocedure were compared with the Friedman test and Wilcoxon test with Bonferroni correction.

RESULTS

Forty patients, 20 with intracapsular and 20 with extracapsular FNFs, were enrolled. The initial pain scores of patients with both intra- and extracapsular fractures were 8 (range 8-10). A statistically significant 50% decrease in pain scores was observed in both groups 30 min after the regional block procedure (p < 0.001). A statistically significant 75% decrease in pain scores was observed in both groups 2 h after the regional block procedure (p < 0.001). No statistically significant difference was determined in the change in 30-min and 2-h pain scores between the groups.

CONCLUSIONS

The administration of 5 mL 2% prilocaine for pain control in FNFs in elderly patients in the ED can reduce systemic analgesic requirements by establishing effective analgesia in both intracapsular and extracapsular fractures.

Ultrasound-guided ankle block. History revisited

Following forefoot surgery, compared to the traditional multimodal approach, regional anesthesia and analgesia provides high quality pain relief, decreases opioids consumption and leads to very high satisfaction scores. Traditional regional techniques relied either on wound infiltration, landmark technique ankle blocks or popliteal sciatic nerve block. Numerous anatomic variations of the different nerves might lead to failure following a blind technique. The current evolution towards ambulatory care will push surgical teams to favor techniques that simplify postoperative treatment and encourages immediate ambulation. The development of Ultrasound Guided Blocks has enabled us to perform very selective and precise nerve blocks. Ankle blocks provide excellent intraoperative anesthesia as well as long postoperative pain relief. Complications are rare using regional anesthesia for postoperative analgesia even after extensive foot surgery. Revival of ankle blocks is a perfect example of the high impact of new technological advances in improving ambulatory surgical care after foot surgery.

Lower extremity regional anesthesia: essentials of our current understanding

The advent of ultrasound guidance has led to a renewed interest in regional anesthesia of the lower limb. In keeping with the American Society of Regional Anesthesia and Pain Medicine's ongoing commitment to provide intensive evidence-based education, this article presents a complete update of the 2005 comprehensive review on lower extremity peripheral nerve blocks. The current review article strives to (1) summarize the pertinent anatomy of the lumbar and sacral plexuses, (2) discuss the optimal approaches and techniques for lower limb regional anesthesia, (3) present evidence to guide the selection of pharmacological agents and adjuvants, (4) describe potential complications associated with lower extremity nerve blocks, and (5) identify informational gaps pertaining to outcomes, which warrant further investigation.

Local Anesthetic Injection Speed and Common Peroneal Nerve Block Duration: A Randomized Controlled Trial in Healthy Volunteers

BACKGROUND AND OBJECTIVES

The speed of local anesthetic (LA) injections in peripheral regional anesthesia ranges from slow continuous infusions (3-12 mL/h) to rapid manual injections (>7500 mL/h). Optimizing injection speed could augment the spread of LA toward the targeted nerves and influence nerve block characteristics. The objective of this study was to investigate whether injection speed of a single dose of LA affects peripheral nerve block duration.

METHODS

After approval from the Danish Regional Scientific Ethics Committee, we enrolled 60 healthy adult volunteers. We used an ultrasound-guided catheter-based technique to perform a common peroneal nerve block. Participants were randomized to receive 4.0 mL of ropivacaine 0.2% with 1 of 5 injection speeds: 12, 60, 300, 600, or 1800 mL/h. Investigators and participants were blinded to group assignment and intervention. Primary outcome was duration of sensory nerve block defined by insensitivity toward cold. Secondary outcomes were duration of motor nerve block, time to onset of sensory nerve block, and grades of sensory and motor nerve block.Intergroup differences were tested by one-way analysis of variance.

RESULTS

We found no differences in sensory block duration between the 5 groups. Durations were median [range]: 11 [6-14], 12 [9-14], 10.5 [2-15], 11 [8-17], and 12 [9-18] hours, respectively (P = 0.294). In addition, we found no differences in secondary outcomes.

CONCLUSIONS

Injection speed of LA in the range of 12 to 1800 mL/h did not affect common peroneal nerve block duration.

CLINICAL TRIAL REGISTRATION

This study was registered at ClinicalTrials.gov, identifier NCT02801799.

Sequential allocation trial design in anesthesia: an introduction to methods, modeling, and clinical applications

Estimation of the dose-response curve for new anesthetic protocols typically focuses on identifying minimum effective doses. The application of a sequential experimental method is appropriate, as it minimizes sample size requirements by updating dose assignments based on information accrued from successive subjects. One approach is the up-and-down method for estimating the median effective dose in a patient population (ED₅₀ ). Designs better suited for achieving greater than 50% effectiveness, include the biased coin approach, and continual reassessment method. In this review we introduce different sequential design methods, provide examples of their use, and show through simulation how the method employed influences sample size and the accuracy of the estimated dose. Simulation studies are presented to illustrate the effects of dose parameter and stopping rule choice for up-and-down method and biased coin approach. For continual reassessment method, the effects of assumed dose-response model, prior guess, and cohort size are simulated. A binary response regression curve was fit to the data in Saidman and Eger's endtidal halothane dose-finding study to provide a dose-response curve for generating simulations. A range of options exist when designing a study using sequential allocation with biased coin approach or continual reassessment method. Method choice influences the required sample size and confidence in estimated effect. In the halothane example, up-and-down method decreases the required sample size by 20-30% when the choice of design parameters is optimal. For both up-and-down method and biased coin approach designs, greater sample sizes, arising from adjusted stopping criteria, might be required to achieve reliable estimates. The continual reassessment method is only efficient if a limited range of doses can be chosen a priori. In conclusion the up-and-down method can be more efficient than nonsequential designs for the estimation of the median dose/intervention level for a given intervention (ED₅₀ ). The biased coin approach or continual reassessment method are preferred for the estimation of higher or lower tail quantiles such as ED₉₀ or ED₁₀ . Continual reassessment method may be superior if knowledge of the dose-response relationship is available for the drug of interest.

The Utility of Peripheral Nerve Blocks in Interventional Radiology

OBJECTIVE

The aim of this article is to provide an overview of peripheral nerve blocks, the use of peripheral nerve block within and outside interventional radiology, and the complications of peripheral nerve block.

CONCLUSION

Interventional radiologists are often responsible for sedation and pain management in the majority of interventional radiology procedures. Peripheral nerve block is increasingly being used in interventional radiology.