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BackgroundWe tested the hypothesis that, following unicompartment knee arthroplasty, a continuous adductor canal block decreases the time to reach 4 discharge criteria compared with a continuous femoral nerve block.MethodsSubjects were randomized to either an adductor canal or femoral perineural catheter (2-day ropivacaine 0.2% infusion) in an unmasked fashion. The primary outcome was the time to attain 4 discharge criteria: (1) adequate analgesia; (2) intravenous opioid independence; (3) ability to independently stand, walk 3 m, return, and sit down; and (4) ambulate 30 m.ResultsSubjects with an adductor canal catheter (n = 15) reached all 4 criteria in a median of 35 hours (interquartile range, 24-43 hours), compared with 40 hours (interquartile range, 27-69 hours) for those with a femoral catheter (n = 15; Wilcoxon rank sum test: P = 0.46; log-rank test: P = 0.16). However, the percentages of subjects (adductor canal: femoral) who reached the 2 mobilization criteria were 27%:0% on postoperative day (POD) 0, 93%:53% on POD 1, and 100%:73% on POD 2. Of adductor canal subjects, 100% were discharge ready by POD 2, compared with only 73% of femoral subjects (P < 0.001).ConclusionsCompared with a continuous femoral nerve block, a continuous adductor canal block did not appreciably decrease the median number of hours to overall discharge readiness, yet did decrease the number of discrete days until discharge readiness. These results are applicable to only unicompartment knee arthroplasty and must be considered preliminary because of the limited sample size of this pilot study.

Introduction: Complex Regional Pain Syndrome (CRPS) is a debilitating neuropathic condition often refractory to conventional treatments. N-methyl-D-aspartate (NMDA) receptor antagonists have a well-established role in the development and modulation of chronic neuropathic pain. Nitrous oxide is widely used and generally safe anesthetic gas with NMDA receptor antagonist activity. We therefore tested the hypothesis that brief periods of nitrous oxide exposure reduce pain in patients with CRPS., Methods: Patients with a diagnosis of CRPS were randomized to either 2 hours of nitrous oxide exposure on three alternating days (Nitrous Oxide) versus a placebo air/oxygen mixture (Air-Oxygen). Our primary outcome was patient-reported pain scores at 1 week and 1 month. Secondary and exploratory outcomes were physical and mental health (PRMOIS-29 v2 survey), specific neuropathic pain symptoms (McGill short-form questionnaire), and opioid consumption., Results: 44 patients participated in the study; 20 were randomized to Nitrous Oxide and 24 were assigned to Air-Oxygen. Pain scores did not differ significantly, with the estimated difference in means (Nitrous Oxide-Air-Oxygen) of -0.57 (95% CI: -1.42 to 0.28) points, p=0.19. There were also no differences detected in secondary outcomes, with the estimated difference in mean Z-scores for physical health (Nitrous Oxide-Air-Oxygen) of 0.13 (95% CI: -0.16 to 0.43), mental health 0.087 (95% CI: -0.31 to 0.48), and Patient Global Impression of Change score -0.7 (95% CI: -1.85 to 0.46)., Conclusions: Compared with air/oxygen, 2 hours of nitrous oxide/oxygen exposure for three sessions did not provide meaningful therapeutic potential for patients with chronic CRPS. Our results do not support using nitrous oxide for the treatment of CRPS., Competing Interests: Competing interests: DIS is a consultant for Edwards Lifesciences, Sensifree, and Perceptive Medical. None of the conflicts are related to the submitted study. AT was a speaker for Pfizer and consultant for Consentric Medical. None of the conflicts are related to the submitted study. None of the other authors declare competing interests., (© American Society of Regional Anesthesia & Pain Medicine 2024. No commercial re-use. See rights and permissions. Published by BMJ.)

Introduction: We previously reported that a 6-day continuous peripheral nerve block reduces established postamputation phantom pain. To provide patients and providers with the information to best inform treatment decisions, here we reanalyze the data and present the results in a more patient-centered format. We also provide information on patient-defined clinically relevant benefits to facilitate evaluation of available studies and guide future trial design., Methods: The original trial enrolled participants with a limb amputation and phantom pain who were randomized to receive a 6-day continuous peripheral nerve block(s) of either ropivacaine (n=71) or saline (n=73) in a double-masked fashion. Here we calculate the percentage of each treatment group that experienced a clinically relevant improvement as defined by previous studies as well as present what the participants of our study defined as small, medium, and large analgesic improvements using the 7-point ordinal Patient Global Impression of Change scale., Results: Among patients who were given a 6-day ropivacaine infusion, 57% experienced at least a 2-point improvement on the 11-point numeric rating scale in their average and worst phantom pain 4 weeks postbaseline as compared with 26% (p<0.001) for average and 25% (p<0.001) for worst pain in patients given a placebo infusion. At 4 weeks, the percentage of participants rating their pain as improved was 53% for the active vs 30% for the placebo groups (95% CI 1.7 (1.1, 2.7), p = 0.008). For all patients combined, the median (IQR) phantom pain Numeric Rating Scale improvements at 4 weeks considered small, medium, and large were 2 (0-2), 3 (2-5), and 5 (3-7), respectively. The median improvements in the Brief Pain Inventory interference subscale (0-70) associated with small, medium, and large analgesic changes were 8 (1-18), 22 (14-31), and 39 (26-47)., Conclusions: Among patients with postamputation phantom pain, a continuous peripheral nerve block more than doubles the chance of a clinically relevant improvement in pain intensity. Amputees with phantom and/or residual limb pain rate analgesic improvements as clinically relevant similarly to other chronic pain etiologies, although their smallest relevant improvement in the Brief Pain Inventory was significantly larger than previously published values., Trial Registration Number: NCT01824082., Competing Interests: Competing interests: BMI and BK: The University of California has received funding and/or equipment for other research projects from Epimed International (Dallas, TX), Infutronics (Natick, MA), Avanos (Irvine, CA), and SPR Therapeutics (Cleveland, OH). DIS: Chair Data and Safety Monitoring Board, Neuros Medical QUEST trial. Consultant for Pacira Pharmaceuticals (Parsippany, NJ), and this company funds trials in the Department of Outcomes Research. SPC: receives research funding (paid to the institution) from Avanos (Irvine, CA), and research funding (paid to the institution) from Scilex (San Diego, CA). He serves as a consultant for SPR Therapeutics (Cleveland, OH). AT: Pacira Pharmaceuticals (Parsippany, NJ) funds trials in the Department of Outcomes Research., (© American Society of Regional Anesthesia & Pain Medicine 2023. Re-use permitted under CC BY-NC. No commercial re-use. Published by BMJ.)

Introduction: The risk of bleeding during regional anesthesia implementation in patients on antithrombotic therapy remains poorly characterized. We; therefore, analyzed bloody tap rates and adjusted ORs comparing patients who take antithrombotic medications with those who do not., Methods: 65,814 qualifying regional anesthetics (2007-2019) from the Network for Safety in Regional Anesthesia and Acute Pain Therapy registry were included in a retrospective cohort analysis. Procedures in patients who took antithrombotic drugs were compared with procedures in patients who did not. The primary outcome was bloody puncture, defined as any kind of blood aspiration during placement. Secondarily, we considered timely discontinuation of thromboprophylaxis and the impact of various drug classes. As a sensitivity analysis, we used propensity matched groups., Results: Patients on antithrombotic therapy were more likely to have a bloody puncture during peripheral nerve block implementation (adjusted OR 1.60; 95% CI 1.33 to 1.93; p<0.001) irrespective of whether therapy was discontinued. In contrast, bloody neuraxial blocks were no more common in patients who took antithrombotic medications (adjusted OR 0.95; 95% CI 0.82 to 1.10; p=0.523) so long as they were paused per guideline. Across both peripheral and neuraxial blocks, concurrent use of more than one platelet and/or coagulation cascade inhibitor nearly doubled the odds (adjusted OR, 1.89; 95% CI 1.48 to 2.40; p<0.001)., Discussion: Patients on antithrombotic therapy receiving peripheral blocks are at increased risk for bloody punctures irrespective of discontinuation practice. Patients having neuraxial blocks are not at increased risk so long as antithrombotics are stopped per guidelines. Patients who take combined medications are at especially high risk. Guidelines for discontinuing antithrombotic treatments for neuraxial anesthesia appear to be effective and should possibly be extended to high-risk peripheral blocks., Competing Interests: Competing interests: DIS is a consultant for Pacira and his department conducts funded research for the company. Thomas Volk received honoraria for lectures from CSL Behring and Pajunk. CK, CAG and GW declare no competing interests., (© American Society of Regional Anesthesia & Pain Medicine 2022. No commercial re-use. See rights and permissions. Published by BMJ.)