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.

Benefits and harm of paracetamol and ibuprofen in combination for post-operative pain: Pre-planned subgroup analyses of the multicenter, randomized PANSAID trial.

BACKGROUND: The "Paracetamol and Ibuprofen in Combination" (PANSAID) trial showed that combining paracetamol and ibuprofen resulted in lower opioid consumption than each drug alone and we did not find an increase in risk of harm when using ibuprofen vs paracetamol. The aim of this subgroup analysis was to investigate the differences in benefits and harms of the interventions in different subgroups. We hypothesized that the intervention effects would differ in subgroups with different risk of pain or adverse events. METHODS: In these pre-planned subgroup analyses of the PANSAID trial population, we assessed subgroup heterogeneity in intervention effects between (a) subgroups (sex, age, use of analgesics, American Society of Anesthesiologists (ASA) score, and type of anesthesia) and morphine consumption, and (b) subgroups (sex, age, use of non-steroidal anti-inflammatory drugs (NSAIDs), and ASA score) and serious adverse events. RESULTS: Test of interaction between age and the pairwise comparison between paracetamol 1 g vs paracetamol 0.5 g + ibuprofen 200 mg (P = .009) suggested lower morphine consumption in patients >65 years. However, post hoc analyses of related outcomes showed no interaction for this pairwise comparison. All other tests of interaction regarding both benefit and harm were not statistically significant. CONCLUSION: These pre-planned subgroup analyses did not suggest that patients in the investigated subgroups benefitted differently from a basic non-opioid analgesic regimen consisting of paracetamol and ibuprofen. Further, there was no evidence of subgroup heterogeneity regarding harm and use of ibuprofen. Because of reduced statistical power in subgroup analyses, we cannot exclude clinically relevant subgroup heterogeneity.

Pain management after total hip arthroplasty at five different Danish hospitals: A prospective, observational cohort study of 501 patients.

BACKGROUND: The available literature does not present a "gold standard" for post-operative pain treatment after total hip arthroplasty (THA). The aim of this prospective observational study was to explore and document post-operative pain treatment, including outcomes, in a large cohort of patients undergoing THA at five different Danish hospitals. METHODS: This prospective, multicentre, observational cohort study of 501 THA patients was performed at five different hospitals in the Capital Region and at the Region Zealand in Denmark, from April 2014 to April 2016. The study had two co-primary outcomes: Pain during mobilisation at 6 hours post-operatively (numeric rating scale [NRS] [0-10]) and morphine consumption 0-24 hours post-operatively. RESULTS: A large variety of analgesic treatments were used at the included hospitals and none of the hospitals used the same non-opioid basic analgesic regimen. For all patients at all hospitals, the NRS-pain level during mobilisation at 6 hours was 5 (3-6), (median [interquartile range]) and the 24-hour intravenous morphine (eqv) consumption was 25 mg (18-35). Although some statistically significant differences between hospitals were found for morphine use, no non-opioid analgesic regimen demonstrated consistent clinically relevant superior efficacy. In general, pain levels at rest were low to moderate and pain during mobilisation was moderate. CONCLUSIONS: Analgesic treatment routines differed between hospitals. Pain levels, however, did not differ substantially and were in general low at rest and moderate during mobilisation. No non-opioid analgesic treatment demonstrated consistent analgesic superiority.

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.

The association between areas of secondary hyperalgesia and volumes of the caudate nuclei and other pain relevant brain structures-A 3-tesla MRI study of healthy men.

INTRODUCTION: Central sensitization plays a pivotal role in maintenance of pain and is believed to be intricately involved in several chronic pain conditions. One clinical manifestation of central sensitization is secondary hyperalgesia. The degree of secondary hyperalgesia presumably reflects individual levels of central sensitization. The objective of this study was to investigate the association between areas of secondary hyperalgesia and volumes of the caudate nuclei and other brain structures involved in pain processing. MATERIALS AND METHODS: We recruited 121 healthy male participants; 118 were included in the final analysis. All participants underwent whole brain magnetic resonance imaging (MRI). Prior to MRI, all participants underwent pain testing. Secondary hyperalgesia was induced by brief thermal sensitization. Additionally, we recorded heat pain detection thresholds (HPDT), pain during one minute thermal stimulation (p-TS) and results of the Pain Catastrophizing Scale (PCS) and Hospital Anxiety and Depression score (HADS). RESULTS: We found no significant associations between the size of the area of secondary hyperalgesia and the volume of the caudate nuclei or of the following structures: primary somatosensory cortex, anterior and mid cingulate cortex, putamen, nucleus accumbens, globus pallidus, insula and the cerebellum. Likewise, we found no significant associations between the volume of the caudate nuclei and HPDTs, p-TS, PCS and HADS. CONCLUSIONS: Our findings indicate that the size of the secondary hyperalgesia area is not associated with the volume of brain structures relevant for pain processing, suggesting that the propensity to develop central sensitization, assessed as secondary hyperalgesia, is not correlated to brain structure volume.

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.

Heterogenic control groups in randomized, controlled, analgesic trials of total hip and knee arthroplasty.

INTRODUCTION: Postoperative analgesic interventions are often tested adjunct to basic non-opioid analgesics in randomized controlled trials (RCTs). Consequently, treatment in control groups, and possible assay sensitivity, differs between trials. We hypothesized that postoperative opioid requirements and pain intensities vary between different control groups in analgesic trials. EVIDENCE ACQUISITION: Control groups from RCTs investigating analgesic interventions after total hip and knee arthroplasty were categorized based on standardized basic analgesic treatment. Morphine consumption 0 to 24 hours postoperatively, and resting pain scores at 6 and 24 hours for subgroups of basic treatments, were compared with ANOVA. In an additional analysis, we compared pain and opioid requirements in trials where a non-steroidal anti-inflammatory drug (NSAID) was administered as an intervention with trial where NSAID was administered in a control group. EVIDENCE SYNTHESIS: We included 171 RCTs employing 28 different control groups with large variability in pain scores and opioid requirements. Four types of control groups (comprising 78 trials) were eligible for subgroup comparisons. These subgroups received "opioid" alone, "NSAID + opioid", "acetaminophen + opioid", or "NSAID + acetaminophen + opioid", respectively. Morphine consumption and pain scores varied substantially between these groups, with no consistent superior efficacy in any subgroup. Additionally, trials administering NSAID as an intervention demonstrated lower pain scores and opioid requirements than trials where NSAID was administered in a control group. CONCLUSIONS: Analgesic treatment in RCT control groups varies considerably. Control groups receiving various combinations of opioid, NSAID and acetaminophen did not differ consistently in pain and opioid requirements. Pain and opioid requirements were lower in trials administering NSAID as an intervention compared with trials administering NSAID in a control group.

Dose-related beneficial and harmful effects of gabapentin in postoperative pain management - post hoc analyses from a systematic review with meta-analyses and trial sequential analyses.

BACKGROUND: During the last 15 years, gabapentin has become an established component of postoperative pain treatment. Gabapentin has been employed in a wide range of doses, but little is known about the optimal dose, providing the best balance between benefit and harm. This systematic review with meta-analyses aimed to explore the beneficial and harmful effects of various doses of gabapentin administered to surgical patients. MATERIALS AND METHODS: Data in this paper were derived from an original review, and the subgroup analyses were predefined in an International Prospective Register of Systematic Reviews published protocol: PROSPERO (ID: CRD42013006538). The methods followed Cochrane guidelines. The Cochrane Library's CENTRAL, PubMed, EMBASE, Science Citation Index Expanded, Google Scholar, and FDA database were searched for relevant trials. Randomized clinical trials comparing gabapentin versus placebo were included. Four different dose intervals were investigated: 0-350, 351-700, 701-1050, and >1050 mg. Primary co-outcomes were 24-hour morphine consumption and serious adverse events (SAEs), with emphasis put on trials with low risk of bias. RESULTS: One hundred and twenty-two randomized clinical trials, with 8466 patients, were included. Sixteen were overall low risk of bias. No consistent increase in morphine-sparing effect was observed with increasing doses of gabapentin from the trials with low risk of bias. Analyzing all trials, the smallest and the highest dose subgroups demonstrated numerically the most prominent reduction in morphine consumption. Twenty-seven trials reported 72 SAEs, of which 83% were reported in the >1050 mg subgroup. No systematic increase in SAEs was observed with increasing doses of gabapentin. CONCLUSION: Data were sparse, and the small number of trials with low risk of bias is a major limitation for firm conclusions. Taking these limitations into account, we were not able to demonstrate a clear relationship between the dosage of gabapentin and opioid-sparing or harmful effects. These subgroup analyses are exploratory and hypothesis-generating for future trialists.

Postoperative pain treatment after total knee arthroplasty: A systematic review.

INTRODUCTION: The aim of this systematic review was to document efficacy, safety and quality of evidence of analgesic interventions after total knee arthroplasty (TKA). METHODS: This PRISMA-compliant and PROSPERO-registered review includes all-language randomized controlled trials of medication-based analgesic interventions after TKA. Bias was evaluated according to Cochrane methodology. Outcomes were opioid consumption (primary), pain scores at rest and during mobilization, adverse events, and length of stay. Interventions investigated in three or more trials were meta-analysed. Outcomes were evaluated using forest plots, Grading of Recommendations Assessment, Development and Evaluation (GRADE), L'Abbe Plots and trial sequential analysis. RESULTS: The included 113 trials, investigating 37 different analgesic interventions, were characterized by unclear/high risk of bias, low assay sensitivity and considerable differences in pain assessment tools, basic analgesic regimens, and reporting of adverse events. In meta-analyses single and continuous femoral nerve block (FNB), intrathecal morphine, local infiltration analgesia, intraarticular injection of local anaesthetics, non-steroidal anti-inflammatory drugs, and gabapentinoids demonstrated significant analgesic effects. The 24-hour morphine-sparing effects ranged from 4.2 mg (CI: 1.3, 7.2; intraarticular local anaesthetics), to 16.6 mg (CI: 11.2, 22; single FNB). Pain relieving effects at rest at 6 hours ranged from 4 mm (CI: -10, 2; gabapentinoids), to 19 mm (CI: 8, 31; single FNB), and at 24 hours from 3 mm (CI: -2, 8; gabapentinoids), to 16 mm (CI: 8, 23; continuous FNB). GRADE-rated quality of evidence was generally low. CONCLUSION: A low quality of evidence, small sample sizes and heterogeneity of trial designs prohibit designation of an optimal procedure-specific analgesic regimen after TKA.

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.

Transversus abdominis plane block after laparoscopic colonic resection in cancer patients: A randomised clinical trial.

BACKGROUND: A key point in pathways for optimal rehabilitation and enhanced recovery is an effective postoperative multimodal pain treatment regimen. OBJECTIVE: To investigate the analgesic effects of transversus abdominis plane (TAP) block in conjunction with paracetamol and ibuprofen in patients undergoing laparoscopic colonic resection. DESIGN: Randomised placebo-controlled double-blind study. SETTING: Herlev University Hospital, Copenhagen, Denmark, from March 2010 to February 2013. PATIENTS: Eighty adult patients scheduled for elective laparoscopic colectomy. INTERVENTIONS: Bilateral TAP block with 20 ml of either ropivacaine or isotonic saline. MAIN OUTCOME MEASURES: Visual analogue scale (VAS) pain scores (0 to 100 mm) while coughing at 6 h after surgery (primary outcome). Secondary outcomes were area under the curve pain scores (2 to 24 h) at rest and while coughing, 24-h morphine consumption and incidence of nausea and vomiting. RESULTS: VAS pain scores at 6 h while coughing was not different between groups (median, interquartile range), TAP, 27 (11 to 45) mm vs. placebo, 33 (20 to 49) mm (P = 0.20). Total 24-h morphine consumption was reduced in the TAP block group vs. placebo group, 30 (15 to 41) mg vs. 43 (30 to 67) mg, respectively (P = 0.008). This difference was most pronounced in the first postoperative hours. The remaining outcomes did not differ between groups. CONCLUSION: TAP block used in combination with paracetamol and ibuprofen did not reduce pain after laparoscopic colonic surgery. However, we found a 30% reduction in opioid use, most marked in the early postoperative period. TRIAL REGISTRATION: www.clinicaltrials.gov (NCT01418144).

Postoperative Treatment of Pain after Hip Fracture in Elderly Patients with Dementia.

BACKGROUND/AIMS: Prior studies have shown that patients with dementia are at risk of receiving insufficient treatment for pain after a hip fracture. We therefore hypothesized that elderly hip fracture patients with dementia received less postoperative pain treatment than those without dementia. METHOD: All patients (age ≥65 years) who had been operated on for a hip fracture in the Copenhagen University Hospital region in 2009 were included. Data about analgesic use for the first 72 h after surgery were acquired from the hospitals' electronic medication system and linked with information about dementia, comorbidity, and prior drug use. RESULTS: A total of 1,507 patients were included, of which 296 (19.6%) suffered from dementia. Both groups were equally likely to receive paracetamol and opioids. Patients with dementia received lower doses of oral morphine equivalents during the first [dementia vs. no dementia: 29.0 (26.4-31.8) vs. 34.7 (33.1-36.4) mg, p = 0.001] and second [27.8 (25.4-30.5) vs. 31.2 (29.9-32.4) mg, p = 0.019] but not on the third postoperative day (p = 0.10). CONCLUSION: The lower doses of opioids may reflect uncertainty about how to treat pain patients with dementia. Further guidance is needed, as inadequate treatment of pain may have adverse consequences.

Preoperative dexamethasone reduces acute but not sustained pain after lumbar disk surgery: a randomized, blinded, placebo-controlled trial.

Glucocorticoids have attracted increasing attention as adjuvants in the treatment of acute postoperative pain. Furthermore, anecdotal reports may support glucocorticoids for preventing sustained postoperative pain. We explored preoperative dexamethasone combined with paracetamol and ibuprofen on acute and sustained pain after lumbar disk surgery. In this blinded study, 160 patients undergoing lumbar disk surgery were randomly assigned to 16 mg IV dexamethasone or placebo. All patients received perioperative paracetamol and ibuprofen, and postoperative IV patient-controlled analgesia with morphine. Primary outcome was pain during mobilization (visual analog scale) 2 to 24 hours postoperatively. Secondary outcomes were acute pain at rest, morphine consumption, nausea, vomiting, ondansetron consumption, sedation, and quality of sleep. Patients were followed up by written questionnaire 3 months postoperatively. Acute pain during mobilization (weighted average area under the curve, 2-24 hours) was significantly reduced in the dexamethasone group: 33 (22) mm vs placebo 43 (18) mm, (95% confidence interval [CI] 3-16) P = 0.005. Vomiting 0 to 24 hours postoperatively was reduced in the dexamethasone group (17 episodes) vs placebo (51 episodes) P = 0.036. No other differences were observed. However, 6.5% (95% CI 2-15) in the dexamethasone group vs placebo 0% had an antibiotically treated wound infection (P = 0.13). Sixteen percent (95% CI 7-26) vs 8% (95% CI 0-17) reported new weakness/paralysis of the legs in the dexamethasone and placebo groups, respectively, 3 months postoperatively (P = 0.20). In conclusion, preoperative dexamethasone significantly reduced pain during mobilization and vomiting, after lumbar disk surgery. No significant effects were observed 3 months postoperatively.

Endogenous Opioid-Masked Latent Pain Sensitization: Studies from Mouse to Human.

UNLABELLED: Following the resolution of a severe inflammatory injury in rodents, administration of mu-opioid receptor inverse agonists leads to reinstatement of pain hypersensitivity. The mechanisms underlying this form of latent pain sensitization (LS) likely contribute to the development of chronic pain, but LS has not yet been demonstrated in humans. Using a C57BL/6 mouse model of cutaneous mild heat injury (MHI) we demonstrated a dose-dependent reinstatement of pain sensitization, assessed as primary (P < 0.001) and secondary hyperalgesia (P < 0.001) by naloxone (0.3­10 mg/kg), 168 hrs after the induction of MHI. Forward-translating the dose data to a human MHI model (n = 12) we could show that LS does indeed occur after naloxone 2 mg/kg, 168 hrs after a MHI. Our previous unsuccessful efforts to demonstrate unmasking of LS in humans are thus likely explained by an insufficient naloxone dose (0.021 mg/kg). However, while LS was consistently demonstrated in 21/24 mice, LS was only seen in 4/12 subjects. This difference is likely due to selection bias since the C57BL/6 mouse strain exhibits markedly enhanced pain sensitivity in assays of acute thermal nociception. Future exploratory studies in humans should prioritize inclusion of "high-sensitizers" prone to develop LS and use post-surgical models to elucidate markers of vulnerability to chronic postsurgical pain. TRIAL REGISTRATION: EudraCT 2012-005663-27.

Adductor Canal Block With 10 mL Versus 30 mL Local Anesthetics and Quadriceps Strength: A Paired, Blinded, Randomized Study in Healthy Volunteers.

BACKGROUND AND OBJECTIVES: Adductor canal block (ACB) is predominantly a sensory nerve block, but excess volume may spread to the femoral triangle and reduce quadriceps strength. We hypothesized that reducing the local anesthetic volume from 30 to 10 mL may lead to fewer subjects with quadriceps weakness. METHODS: We performed a paired, blinded, randomized trial including healthy men. All subjects received bilateral ACBs with ropivacaine 0.1%; 10 mL in 1 leg and 30 mL in the other leg. The primary outcome was the difference in number of subjects with quadriceps strength reduced by more than 25% from baseline in 2 consecutive assessments. Secondary outcomes were quadriceps strength as a percentage of baseline at predefined time points, functional outcome assessed by the 30-Second Chair Stand Test (1 leg at a time), and sensory block. Clinicaltrials.gov Identifier: NCT01981746. RESULTS: We included and analyzed 26 subjects. For either volume, 2 subjects had a reduction in quadriceps strength by more than 25% from baseline (difference, 0%; 95% confidence interval, -13 to 13; P > 0.999). Similarly, we found no significant differences between volumes in quadriceps strength at any of the predefined time points or in sensory block. The only statistically significant difference between volumes was found in the 30-Second Chair Stand Test at 2 hours (P = 0.02), but this difference had disappeared at 4 hours (P = 0.06). CONCLUSIONS: Varying the volume of ropivacaine 0.1% used for ACB between 10 and 30 mL did not have a statistically significant or clinically relevant impact on quadriceps strength.

Endogenous opioid antagonism in physiological experimental pain models: a systematic review.

Opioid antagonists are pharmacological tools applied as an indirect measure to detect activation of the endogenous opioid system (EOS) in experimental pain models. The objective of this systematic review was to examine the effect of mu-opioid-receptor (MOR) antagonists in placebo-controlled, double-blind studies using 'inhibitory' or 'sensitizing', physiological test paradigms in healthy human subjects. The databases PubMed and Embase were searched according to predefined criteria. Out of a total of 2,142 records, 63 studies (1,477 subjects [male/female ratio = 1.5]) were considered relevant. Twenty-five studies utilized 'inhibitory' test paradigms (ITP) and 38 studies utilized 'sensitizing' test paradigms (STP). The ITP-studies were characterized as conditioning modulation models (22 studies) and repetitive transcranial magnetic stimulation models (rTMS; 3 studies), and, the STP-studies as secondary hyperalgesia models (6 studies), 'pain' models (25 studies), summation models (2 studies), nociceptive reflex models (3 studies) and miscellaneous models (2 studies). A consistent reversal of analgesia by a MOR-antagonist was demonstrated in 10 of the 25 ITP-studies, including stress-induced analgesia and rTMS. In the remaining 14 conditioning modulation studies either absence of effects or ambiguous effects by MOR-antagonists, were observed. In the STP-studies, no effect of the opioid-blockade could be demonstrated in 5 out of 6 secondary hyperalgesia studies. The direction of MOR-antagonist dependent effects upon pain ratings, threshold assessments and somatosensory evoked potentials (SSEP), did not appear consistent in 28 out of 32 'pain' model studies. In conclusion, only in 2 experimental human pain models, i.e., stress-induced analgesia and rTMS, administration of MOR-antagonist demonstrated a consistent effect, presumably mediated by an EOS-dependent mechanisms of analgesia and hyperalgesia.

Postoperative pain treatment after total hip arthroplasty: a systematic review.

Treatment of postoperative pain should rely on results from randomized controlled trials and meta-analyses of high scientific quality. The efficacy of a particular intervention may depend on the type of surgical procedure, which supports the reporting of "procedure-specific" interventions. The aim of this systematic review was to document the procedure-specific evidence for analgesic interventions after total hip arthroplasty (THA). This PRISMA-compliant and PROSPERO-registered review includes randomized placebo-controlled trials (RCTs) of medication-based analgesic interventions after THA. Endpoints were postoperative opioid consumption, pain scores (rest and during mobilization), adverse events, and length of hospital stay. Fifty-eight trials with 19 different interventions were retrieved. High risk of bias, substantial differences in assessment-tools and criteria for pain, irregular reporting of adverse events, considerable differences in supplemental analgesic consumption, and basic analgesic regimens generally characterized trials. Meta-analyses of non-steroidal anti-inflammatory drugs, local infiltration analgesia, intrathecal opioids, and lumbar plexus block provided a 24-hour intravenous morphine-sparing effect of 14.1 (95 % confidence interval: 8.0-20.2) mg, 7.5 (3.7-11.3) mg, 19.8 (14.9-24.7) mg, and 11.9 (6.4-17.3) mg, respectively. Non-steroidal anti-inflammatory drugs and lumbar plexus block were demonstrated to provide reductions in postoperative pain scores. Intrathecal opioids increased pruritus, and lumbar plexus block reduced nausea and pruritus. The GRADE-rated quality of evidence ranged from low to very low throughout the analyses. This review demonstrated, that some analgesic interventions may have the capacity to reduce mean opioid requirements and/or mean pain intensity compared with controls, but the available randomized placebo-controlled trials does not allow a designation of a "best proven intervention" for THA.

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.