Alpha2 -receptor agonists as adjuvants for brachial plexus nerve blocks-A systematic review with meta-analyses.

BACKGROUND: We review the efficacy and safety of dexmedetomidine and clonidine as perineural or systemic adjuvants for brachial plexus blocks (BPB). METHODS: We included randomised controlled trials on upper limb surgery with BPBs in adults, comparing dexmedetomidine with clonidine or either drug with placebo. The primary outcome was duration of analgesia. Secondary outcomes included adverse and serious adverse events. The review was conducted using Cochrane standards, trial sequential analyses (TSA) and Grading of Recommendations Assessment, Development and Evaluation (GRADE). RESULTS: We included 101 trials with 6248 patients. Overall, duration of analgesia was prolonged with both clonidine (176 min [TSA adj. 95% CI: 118, 205, p < .00001; 33 trials]) and dexmedetomidine (292 min [TSA adj. 95% CI: 245 329, p < .00001; 53 trials]), but was longer for dexmedetomidine than clonidine (205 min [TSA adj. 95% CI: 157, 254, p < .00001; 19 trials]). Compared with placebo, dexmedetomidine was associated with bradycardia (RR 4.2 [95% CI 2.2, 8.3]), and both clonidine (RR 4.5 [95% CI 1.1, 18.3]) and dexmedetomidine (RR 3.9 [95% CI 2.0, 7.5]) were associated with hypotension. Serious adverse events were mostly related to block technique. GRADE-rated quality of evidence was low or very low. CONCLUSION: Alpha2-receptor agonists used as adjuvants for BPBs lead to a prolonged duration of analgesia, with dexmedetomidine as the most efficient. Alpha2-receptor agonists were associated with increased risk of cardiovascular adverse events. The quality of evidence was low to very low.

Adductor canal block with a suture-method catheter - A parallel or perpendicular approach?

BACKGROUND: We performed a randomised blinded pilot study in 16 healthy volunteers to assess whether placing a suture-method catheter in the adductor canal is feasible with two different insertion techniques. METHODS: Each volunteer had a suture-method catheter placed approximately halfway between the superior anterior iliac spine and base of the patella in both legs. Catheters were placed using a parallel technique in one leg and a perpendicular technique in the other leg, according to randomisation. 15 mL lidocaine 1% was injected in each catheter. Successful placement was defined as loss of cold sensation in the saphenous area 30 min after injection. Volunteers were sent home and returned the following day and another dose of lidocaine (15 mL, 1%) was injected through the catheters. Catheter displacement distance was assessed by ultrasound and cold sensation was assessed. In case of preserved cold sensation, we attempted to reposition the catheter with a subsequent injection of lidocaine and reassessment of cold sensation. RESULTS: All primary placements were successful using the perpendicular approach (100%; 95% CI 81%-100%) whereas one placement failed using the parallel approach (94%; 95% CI 72%-99%). Three catheters placed using the perpendicular approach were displaced on day 2, compared to one catheter placed with the parallel approach. Displacement distance was highly variable. All catheters, except one, could be repositioned. Three volunteers reported transient sensory deficits lasting approximately 6-8 weeks. CONCLUSION: The suture-method catheter can be placed in the adductor canal with high success rates for initial placement with both techniques.

Adductor Canal Block With Continuous Infusion Versus Intermittent Boluses and Morphine Consumption: A Randomized, Blinded, Controlled Clinical Trial.

BACKGROUND: Based on the assumption that relatively large volumes of local anesthetic optimize an adductor canal block (ACB), we theorized that an ACB administered as repeated boluses would improve analgesia without compromising mobility, compared with a continuous infusion. METHODS: We performed a randomized, blinded, controlled study, including patients scheduled for total knee arthroplasty with spinal anesthesia. Patients received 0.2% ropivacaine via a catheter in the adductor canal administered as either repeated intermittent boluses (21 mL/3 h) or continuous infusion (7 mL/h). The primary outcome was total (postoperative day [POD], 0-2) opioid consumption (mg), administered as patient-controlled analgesia. Pain, ambulation, and quadriceps muscle strength were secondary outcomes. RESULTS: We randomized 110 patients, of whom 107 were analyzed. Total opioid consumption (POD, 0-2) was a median (range) of 23 mg (0-139) in the bolus group and 26 mg (3-120) in the infusion group (estimated median difference, 4 mg; 95% confidence interval [CI], -13 to 5; P = .29). Linear mixed-model analyses revealed no difference in pain during knee flexion (mean difference, 2.6 mm; 95% CI, -2.9 to 8.0) or at rest (mean difference, 1.7 mm; 95% CI, -1.5 to 4.9). Patients in the bolus group had improved quadriceps sparing on POD 2 (median difference, 7.4%; 95% CI, 0.5%-15.5%). However, this difference was not present on POD 1 or reflected in the ambulation tests (P > .05). CONCLUSIONS: Changing the mode of administration for an ACB from continuous infusion to repeated intermittent boluses did not decrease opioid consumption, pain, nor mobility.

Ultrasound guided repositioning of a new suture-method catheter for adductor canal block - a randomized pilot study in healthy volunteers.

BACKGROUND: We performed a randomized, blinded pilot study in 12 volunteers to assess the feasibility to reposition an intentionally displaced suture-method catheter for two different insertion techniques for adductor canal block. METHODS: Each volunteer had an ultrasound-guided suture-method catheter placed in the adductor canal (AC) in both legs. The catheters were placed using a perpendicular technique in one leg and a parallel technique in the other leg, according to randomization. 15 mL lidocaine 1% (LA) was injected in each catheter. Successful primary placement was defined as combined LA spread within the AC and loss of cold sensation 15 min after injection. All catheters were intentionally displaced, and subsequently repositioned using ultrasound. Another dose of lidocaine (15 mL 1%) was injected through the catheters and assessed for successful repositioning. RESULTS: Successful primary placement was achieved in 83% (95% CI 55-95%) of catheters placed perpendicular to the AC, and in 75% (95% CI 47-91%) of catheters placed parallel to the AC. Of those with successful primary placement, 100% (95% CI 72-100%) of catheters placed perpendicular to the AC, and 67% (95% CI 35-88%)) placed parallel to the AC could be repositioned. CONCLUSIONS: Placement and secondary repositioning after displacement of a suture-method catheter within the adductor canal is achievable. A perpendicular technique seems more reliable. TRIAL REGISTRATION: NCT03315481 clinicaltrials.gov . The study was submitted on March 1, 2017. Due to clerical error, the study was posted on October 20, 2017.

Does Dexmedetomidine Have a Perineural Mechanism of Action When Used as an Adjuvant to Ropivacaine?: A Paired, Blinded, Randomized Trial in Healthy Volunteers.

BACKGROUND: Dexmedetomidine used as an adjuvant to local anesthetics may prolong the duration of peripheral nerve blocks. Whether this is mediated by a perineural or systemic mechanism remains unknown. The authors hypothesized that dexmedetomidine has a peripheral mechanism of action. METHODS: The authors conducted a randomized, paired, triple-blind trial in healthy volunteers. All received bilateral saphenous nerve blocks with 20 ml ropivacaine, 0.5%, plus 1 ml dexmedetomidine, 100 µg/ml, in one thigh and 20 ml ropivacaine 0.5% plus 1 ml saline in the other thigh. The primary outcome measure was the duration of block assessed by temperature sensation (alcohol swab). The secondary outcome measure was the duration of block assessed by pinprick, pain during tonic heat stimulation, warmth detection threshold, and heat pain detection threshold. RESULTS: All 21 enrolled volunteers completed the trial. The mean duration of block assessed by temperature sensation in the leg receiving ropivacaine plus dexmedetomidine was 22 h (95% CI, 21 to 24) compared to 20 h (95% CI, 19 to 21) in the leg receiving ropivacaine plus placebo with a mean difference of 2 h (95% CI, 1 to 3; P = 0.001). The duration of block was also significantly longer in the leg receiving dexmedetomidine when assessed by pinprick, pain during tonic heat stimulation, and warmth detection threshold but not heat pain detection threshold. One participant experienced numbness in an area in the leg receiving dexmedetomidine. CONCLUSIONS: Dexmedetomidine prolongs the duration of a saphenous nerve block by a peripheral mechanism when controlling for systemic effects but not necessarily to a clinically relevant extent.

The Effect of Local Anesthetic Volume Within the Adductor Canal on Quadriceps Femoris Function Evaluated by Electromyography: A Randomized, Observer- and Subject-Blinded, Placebo-Controlled Study in Volunteers.

BACKGROUND: Single-injection adductor canal block (ACB) provides analgesia after knee surgery. Which nerves that are blocked by an ACB and what influence-if any-local anesthetic volume has on the effects remain undetermined. We hypothesized that effects on the nerve to the vastus medialis muscle (which besides being a motor nerve innervates portions of the knee) are volume-dependent. METHODS: In this assessor- and subject-blinded randomized trial, 20 volunteers were included. On 3 separate days, subjects received an ACB with different volumes (10, 20, and 30 mL) of lidocaine 1%. In addition, they received a femoral nerve block and a placebo ACB. The effect on the vastus medialis (primary endpoint) and the vastus lateralis was evaluated using noninvasive electromyography (EMG). Quadriceps femoris muscle strength was evaluated using a dynamometer. RESULTS: There was a statistically significant difference in EMG response from the vastus medialis, dependent on volume. Thirty-five percent (95% confidence interval [CI], 18-57) of the subjects had an affected vastus medialis after an ACB with 10 mL compared with 84% (95% CI, 62-94) following 20 mL (P = 0.03) and 100% (95% CI, 84-100) when 30 mL was used (P = 0.0001). No statistically significant differences were found between volume and effect on the vastus lateralis (P = 0.81) or in muscle strength (P = 0.15). CONCLUSIONS: For ACB, there is a positive correlation between local anesthetic volume and effect on the vastus medialis muscle. Despite the rather large differences in EMG recordings, there were no statistically significant differences in quadriceps femoris muscle strength. Subsequent clinical studies comparing different volumes in a surgical setting, powered to show differences not only in analgesic efficacy, but also in adverse events, are required.

The Isolated Effect of Adductor Canal Block on Quadriceps Femoris Muscle Strength After Total Knee Arthroplasty: A Triple-Blinded, Randomized, Placebo-Controlled Trial with Individual Patient Analysis.

BACKGROUND: Using peripheral nerve block after total knee arthroplasty (TKA), without impeding mobility, is challenging. We hypothesized that the analgesic effect of adductor canal block (ACB) could increase the maximum voluntary isometric contraction (MVIC) of the quadriceps femoris muscle after TKA. METHODS: We included 64 patients on the first postoperative day. Group A received an ACB with 30 mL ropivacaine 0.75% at t0 and with 30 mL saline 60 minutes later (t60). Group B received the treatment in the opposite order. The primary end point was the difference between groups in MVIC at t60, expressed as a percentage of postoperative preblock values. In this manner, the effect of the ACB could be isolated from the detrimental effect on muscle strength caused by the surgery. Secondary end points were differences between groups in mobility and pain scores. We planned a subgroup analysis dividing patients according to preblock pain scores during knee flexion. RESULTS: At t60, MVIC was higher in group A, with a median of 170% (95% confidence interval [CI], 147-231) of preblock values compared with 93% (95% CI, 82-98) in group B (P < 0.0001). No statistically significant differences were found in the Timed Up and Go (TUG) test. Three patients lost the ability to perform the TUG test in group A. At t60, differences in visual analog scale pain were in favor of group A; 12 mm (95% CI, 6-18) at rest, 14 mm (95% CI, 5-22) during knee flexion, and 18 mm (95% CI, 10-26) during the TUG test. CONCLUSIONS: ACB improves quadriceps femoris muscle strength, but whether this translates into enhanced mobility is not clearly supported by this study.

Effect of Total Dose of Lidocaine on Duration of Adductor Canal Block, Assessed by Different Test Methods: A Report of Two Blinded, Randomized, Crossover Studies in Healthy Volunteers.

BACKGROUND: The binary aims of this study were to investigate the effect of total dose of lidocaine on duration of an adductor canal block (ACB) and to validate different methods used to assess nerve blocks. METHODS: We performed 2 blinded, randomized, controlled crossover trials, including healthy, young men. In study 1, 14 subjects received 4 ACBs with saline and 40, 80, and 160 mg lidocaine. In study 2, 14 new subjects received 2 ACBs with 100 and 300 mg lidocaine. We kept volume constant at 20 mL for all blocks, only altering concentration. ACB duration was assessed every hour postblock using mechanical (primary outcome) and temperature discrimination; warmth and heat pain detection thresholds; pain during heat stimulation; and tolerance to electrical current in the saphenous distribution. Finally, we measured quadriceps femoris muscle strength (clinical trial registration: NCT02172729). RESULTS: In study 1, block duration assessed by mechanical discrimination differed significantly when comparing the 40-mg dose with the 80-mg dose (mean difference, 1.15 hours; 99% confidence interval [CI], 0.38-2.09 hours) and with the 160-mg dose (mean difference, 0.92 ours; 99% CI, 0.17-1.62). However, there was no difference between the 80-mg and 160-mg doses (mean difference, -0.23 hour; 99% CI, -1.12 to 0.46 hours). Neither for the secondary outcomes were there any differences between the 80- and 160-mg doses (99% CI including 0). Because of 38% (5/13) failed blocks in the 40-mg group, we decided to perform study 2. In study 2, all but 1 test showed no difference in duration despite a 3-fold increase in dose. The temperature discrimination test showed 100% sensitivity and specificity for differentiating between the presence and absence of block and was the only test with scores >90% for both parameters. CONCLUSIONS: We did not find evidence that increasing the total dose of lidocaine may prolong duration of an ACB. The temperature discrimination test was the only test with scores >90% for both specificity and sensitivity.

Effects of popliteal plexus block after total knee arthroplasty: a randomized clinical trial.

BACKGROUND AND OBJECTIVES: Motor-sparing peripheral nerve blocks enhance multimodal opioid-sparing strategies after total knee arthroplasty. We hypothesized that adding a popliteal plexus block to a femoral triangle block could reduce 24-hour opioid consumption after total knee arthroplasty, compared with standalone femoral triangle block or adductor canal block. METHODS: This patient- and assessor-blinded, randomized controlled trial allocated 165 patients into three equally sized parallel groups, receiving either 1) popliteal plexus block+femoral triangle block, 2) femoral triangle block, or 3) adductor canal block. Intravenous oxycodone was administered via patient-controlled analgesia pumps. The primary outcome was 24-hour postoperative opioid consumption. Secondary outcomes were preoperative maximum voluntary isometric contraction and manual muscle tests of knee and ankle movement assessed before and after the nerve block procedure together with postoperative pain scores, mobilization, and 12-hour opioid consumption. RESULTS: 24-hour postoperative intravenous oxycodone consumption varied significantly between groups (p<0.01), with medians (IQR) of 6 mg (2-12) in the popliteal plexus block+femoral triangle block group, 10 mg (8-16) in the femoral triangle block group, and 12 mg (6-18) in the adductor canal block group. Median consumption in the popliteal plexus block+femoral triangle block group was reduced by -4 mg (95% CI -7.4 to -1.0, p<0.01) and -6 mg (95% CI -8.3 to -1.3, p=0.01) compared with groups of femoral triangle block and adductor canal block, respectively. No differences were found in pain scores, mobilization, or changes in preoperative muscle strength. Post hoc analysis revealed successful 24-hour opioid-free postoperative care among 12 patients with popliteal plexus block+femoral triangle block, as compared with two with femoral triangle block and six with adductor canal block. CONCLUSION: Adding a popliteal plexus block to a femoral triangle block resulted in a statistically significant reduction of 24-hour postoperative opioid consumption after total knee arthroplasty. However, no differences were found in pain scores. Popliteal plexus block did not impair the lower leg muscles.

Systemic dexmedetomidine is not as efficient as perineural dexmedetomidine in prolonging an ulnar nerve block.

BACKGROUND: We tested the joint hypotheses that both perineural and systemic dexmedetomidine prolong the duration of an ulnar nerve block (UNB) compared with ropivacaine alone and that systemic dexmedetomidine is noninferior compared with perineural dexmedetomidine in block prolongation. METHODS: We performed bilateral UNBs in 22 healthy volunteers on two separate days. On the first day, each arm was randomized to either 4 mL ropivacaine 5 mg/mL+1 mL dexmedetomidine 100 µg/mL (Perineural) or 4 mL ropivacaine 5 mg/mL+1 mL saline (Systemic). On the subsequent treatment day, each arm was randomized to 1 mL of saline plus 4 mL of ropivacaine at either 7.5 mg/mL(HiRopi) or 5 mg/mL (NoDex). The primary outcome measure was the duration of sensory block assessed by mechanical discrimination. RESULTS: Mean sensory block duration was longer in both the Perineural (14.4 hours, 95% CI 13.1 to 15.6) and Systemic treatments (9.2 hours, 95% CI 8.6 to 9.8) compared with the NoDex treatment (7.1 hours, 95% CI 6.6 to 7.6) (p<0.0001 for both). Systemic dexmedetomidine was inferior (not noninferior) compared with perineural dexmedetomidine, as the 95% CI of the difference (mean difference 5.2 hour, 95% CI 4.2 to 6.1) exceeded the noninferiority limit of 3.6 hour. Onset time did not differ among the groups. The other test modalities demonstrated similar block durations as the primary outcome. CONCLUSIONS: Adding dexmedetomidine perineurally to ropivacaine doubles the duration of an UNB. Systemic dexmedetomidine also prolongs the duration of UNB, but has less of an effect compared with the perineural route. TRIAL REGISTRATION NUMBER: NCT03222323.

Clonidine used as a perineural adjuvant to ropivacaine, does not prolong the duration of sensory block when controlling for systemic effects: A paired, blinded, randomized trial in healthy volunteers.

BACKGROUND: Clonidine used as an adjuvant to ropivacaine have been shown to prolong the duration of peripheral nerve blocks. The mechanism of action remains unclear. We hypothesized, that clonidine used as an adjuvant to ropivacaine extends the duration of an adductor canal block (ACB) by a peripheral mechanism, compared to ropivacaine alone when controlling for systemic effects. METHODS: We conducted a paired, blinded, randomized trial in healthy volunteers. Participants received bilateral ACBs containing 20 ml ropivacaine 0.5% + 1 ml clonidine 150µg/ml in one leg and 20 ml ropivacaine 0.5% + 1 ml saline in the other leg. The primary outcome measure was duration of sensory block assessed by temperature sensation (alcohol swab). Secondary outcome measures were duration of sensory block assessed by: pinprick, maximum pain during tonic heat stimulation, warmth detection threshold and heat pain detection threshold. RESULTS: We enrolled 21 volunteers and all completed the trial. There was no difference in duration of sensory block assessed with an alcohol swab: Mean duration in the leg receiving ropivacaine + clonidine was 19.4h (SD 2.7) compared to 19.3h (SD 2.4) in the leg receiving ropivacaine + placebo with a mean difference of 0.1h (95% CI: -1.0 to 1.3), P = 0.83. No differences in block duration were detected when assessed by: Pinprick, mean difference 0.0 h (95% CI: -1.3 to 1.3), maximum pain during tonic heat stimulation, mean difference -0.7 h (95% CI: -2.1 to 0.8), warmth detection threshold, mean difference -0.1 h (95% CI: -1.8 to 1.6) or heat pain detection threshold, mean difference -0.2 h (95% CI: -1.7 to 1.4). CONCLUSIONS: Administering clonidine perineurally as an adjuvant to ropivacaine in an ACB did not prolong the duration of sensory block in a setup controlling for systemic effects of clonidine.

Effect of adductor canal block versus femoral nerve block on quadriceps strength, mobilization, and pain after total knee arthroplasty: a randomized, blinded study.

BACKGROUND AND OBJECTIVES: Total knee arthroplasty (TKA) is often associated with severe pain. Different regional anesthetic techniques exist, all with varying degrees of motor blockade. We hypothesized that pain relief provided by the adductor canal block (ACB) could increase functional muscle strength. METHODS: We included 50 TKA patients with severe movement-related pain; defined as having visual analog scale pain score of greater than 60 mm during active flexion of the knee. The ACB group received an ACB with ropivacaine 0.2% 30 mL and a femoral nerve block (FNB) with 30 mL saline. The FNB group received an ACB with 30 mL saline and an FNB with ropivacaine 0.2% 30 mL. We compared the effect of the ACB versus FNB on maximum voluntary isometric contraction of the quadriceps muscle relative to a postoperative baseline value. Secondary end points were differences between groups in ability to ambulate and changes in pain scores (Clinicaltrials.gov identifier NCT01922596). RESULTS: After block, the quadriceps maximum voluntary isometric contraction increased to 193% (95% confidence interval [CI], 143-288) of the baseline value in the ACB group and decreased to 16% (95% CI, 3-33) in the FNB group with an estimated difference of 178% (95% CI, 136-226), P < 0.0001. Pain scores were similar between groups. Before block, 2 of 25 patients in each group were unable to perform the Timed-Up-and-Go test; after block, this number increased to 7 of 25 in the FNB group and decreased to 0 of 25 in the ACB group. CONCLUSION: Adductor canal block provides a clinically relevant and statistically significant increase in quadriceps muscle strength for patients in severe pain after TKA.