Intraoperative use of remifentanil and opioid induced hyperalgesia/acute opioid tolerance: systematic review

Intravenous Opioid Administration During Mechanical Ventilation and Use After Hospital Discharge

Importance

Guidelines recommend an analgesia-first strategy for sedation during mechanical ventilation, but associations between opioids provided during mechanical ventilation and posthospitalization opioid-related outcomes are unclear.

Objective

To evaluate associations between an intravenous opioid dose received during mechanical ventilation and postdischarge opioid-related outcomes in medical (nonsurgical) patients.

Design, Setting, and Participants

This retrospective cohort study evaluated adults receiving mechanical ventilation lasting 24 hours or more for acute respiratory failure and surviving hospitalization. Participants from 21 Kaiser Permanente Northern California hospitals from January 1, 2012, to December 31, 2019, were included. Data were analyzed from October 1, 2020, to October 31, 2023.

Exposures

Terciles of median daily intravenous fentanyl equivalents during mechanical ventilation.

Main Outcomes and Measures

The primary outcome was the first filled opioid prescription in 1 year after discharge. Secondary outcomes included persistent opioid use and opioid-associated complications. Secondary analyses tested for interaction between opioid doses during mechanical ventilation, prior opioid use, and posthospitalization opioid use. Estimates were based on multivariable-adjusted time-to-event analyses, with death as a competing risk, and censored for hospice or palliative care referral, rehospitalization with receipt of opioid, or loss of Kaiser Permanente plan membership.

Results

The study included 6746 patients across 21 hospitals (median age, 67 years [IQR, 57-76 years]; 53.0% male). Of the participants, 3114 (46.2%) filled an opioid prescription in the year prior to admission. The median daily fentanyl equivalent during mechanical ventilation was 200 μg (IQR, 40-1000 μg), with terciles of 0 to 67 μg, more than 67 to 700 μg, and more than 700 μg. Compared with patients who did not receive opioids during mechanical ventilation (n = 1013), a higher daily opioid dose was associated with opioid prescriptions in the year after discharge (n = 2942 outcomes; tercile 1: adjusted hazard ratio [AHR], 1.00 [95% CI, 0.85-1.17], tercile 2: AHR, 1.20 [95% CI, 1.03-1.40], and tercile 3: AHR, 1.25 [95% CI, 1.07-1.47]). Higher doses of opioids during mechanical ventilation were also associated with persistent opioid use after hospitalization (n = 1410 outcomes; tercile 3 vs no opioids: odds ratio, 1.44 [95% CI, 1.14-1.83]). No interaction was observed between opioid dose during mechanical ventilation, prior opioid use, and posthospitalization opioid use.

Conclusions and Relevance

In this retrospective cohort study of patients receiving mechanical ventilation, opioids administered during mechanical ventilation were associated with opioid prescriptions following hospital discharge. Additional studies to evaluate risks and benefits of strategies using lower opioid doses are warranted.

Erector spinae plane block reduces opioid consumption and improves incentive spirometry volume after cardiac surgery: A retrospective cohort study

BACKGROUND

Effective postoperative pain management is vital in cardiac surgery to prevent opioid dependency and respiratory complications. Previous studies on the erector spinae plane (ESP) block have focused on single-shot applications or immediate postoperative outcomes. This study evaluates the efficacy of continuous ESP block vs conventional care in reducing opioid consumption and enhancing respiratory function recovery postcardiac surgery over 72 hours.

METHODS

A retrospective study at a tertiary hospital (January 2021-July 2022) included 262 elective cardiac surgery patients. Fifty-three received a preoperative ESP block, matched 1:1 with a control group (n = 53). The ESP group received 0.5% ropivacaine intraoperatively and 0.16% ropivacaine every 4 hours postoperatively. Outcomes measured were cumulative oral morphine equivalent (OME) dose within 72 hours postextubation, daily maximum numerical rating scale (NRS) ≥3, incentive spirometry volume, and %baseline performance, stratified by surgery type (sternotomy or thoracotomy).

RESULTS

Significant OME reduction was observed in the ESP group (sternotomy: median decrease of 113 mg, 95% CI: 60-157.5 mg, p < 0.001; thoracotomy: 172.5 mg, 95% CI: 45-285 mg, p = 0.010). The ESP group also had a lower risk of daily maximum NRS ≥3 (adjusted OR sternotomy: 0.22, p < 0.001; thoracotomy: 0.07, p < 0.001), a higher incentive spirometry volumes (sternotomy: mean increase of 149 mL, p = 0.019; thoracotomy: 521 mL, p = 0.017), and enhanced spirometry %baseline (sternotomy: mean increase of 11.5%, p = 0.014; thoracotomy: 26.5%, p < 0.001).

CONCLUSION

Continuous ESP block was associated with a reduction of postoperative opioid requirements, lower instances of pain scores ≥3, and improve incentive spirometry performance following cardiac surgery. These benefits appear particularly prominent in thoracotomy patients. Further prospective studies with larger sample size are required to validate these findings.

Remifentanil-induced hyperalgesia in healthy volunteers: a systematic review and meta-analysis of randomized controlled trials

ABSTRACT

Recent literature suggests that the withdrawal of remifentanil (RF) infusion can be associated with hyperalgesia in clinical and nonclinical settings. We performed a systematic review and a meta-analysis of randomized controlled trials with cross-over design, to assess the effect of discontinuing RF infusion on pain intensity and areas of hyperalgesia and allodynia in healthy volunteers. Nine studies were included. The intervention treatment consisted in RF infusion that was compared with placebo (saline solution). The primary outcome was pain intensity assessment at 30 ± 15 minutes after RF or placebo discontinuation, assessed by any pain scale and using any quantitative sensory testing. Moreover, postwithdrawal pain scores were compared with baseline scores in each treatment. Secondary outcomes included the areas (% of basal values) of hyperalgesia and allodynia. Subjects during RF treatment reported higher pain scores after discontinuation than during treatment with placebo [standardized mean difference (SMD): 0.50, 95% confidence interval (CI): 0.03-0.97; P = 0.04, I 2 = 71%]. A significant decrease in pain scores, compared with baseline values, was found in the placebo treatment (SMD: -0.87, 95% CI: -1.61 to -0.13; P = 0.02, I 2 = 87%), but not in the RF treatment (SMD: -0.28, 95% CI: -1.18 to 0.62; P = 0.54, I 2 = 91%). The area of hyperalgesia was larger after RF withdrawal (SMD: 0.55; 95% CI: 0.27-0.84; P = 0.001; I 2 = 0%). The area of allodynia did not vary between treatments. These findings suggest that the withdrawal of RF induces a mild but nonclinically relevant degree of hyperalgesia in HVs, likely linked to a reduced pain threshold.

Buprenorphine Facilitates Rapid Weaning From Very-High-Dose Intrathecal Hydromorphone

Pain management in patients on chronic opioid therapy is a common clinical challenge. The phenomena of opioid-induced hyperalgesia and tolerance are important contributors to that challenge. There are multiple strategies described to wean opioid doses and/or transition patients off opioids altogether. However, there is very little data to guide transitions off chronic intrathecal opioids. Here, we report on two patients with intractable post-laminectomy pain syndrome, resulting in severe functional limitation in the setting of opioid escalation culminating in the intrathecal delivery of hydromorphone to daily doses as high as 20 mg/day. We describe their rapid successful weaning off opioids using low-dose buprenorphine, which resulted in a dramatic improvement in pain and function.

Traumatic Brain Injury and Opioids: Twin Plagues of the Twenty-First Century

Traumatic brain injury (TBI) and opioid use disorder (OUD) comprise twin plagues causing considerable morbidity and mortality worldwide. As interactions between TBI and OUD are to our knowledge uncharted, we review the possible mechanisms by which TBI may stimulate the development of OUD and discuss the interaction or crosstalk between these two processes. Central nervous system damage due to TBI appears to drive adverse effects of subsequent OUD and opioid use/misuse affecting several molecular pathways. Pain, a neurological consequence of TBI, is a risk factor that increases the likelihood of opioid use/misuse after TBI. Other comorbidities including depression, anxiety, posttraumatic stress disorder, and sleep disturbances are also associated with deleterious outcomes. We examine the hypothesis that a TBI "first hit" induces a neuroinflammatory process involving microglial priming, which, on a second hit related to opioid exposure, exacerbates neuroinflammation, modifies synaptic plasticity, and spreads tau aggregates to promote neurodegeneration. As TBI also impairs myelin repair by oligodendrocytes, it may reduce or degrade white matter integrity in the reward circuit resulting in behavioral changes. Along with approaches focused on specific patient symptoms, understanding the CNS effects following TBI offers a promise of improved management for individuals with OUD.

Comparative Effectiveness of Dual- Versus Mono-Sedative Therapy on Opioid Administration, Sedative Administration, and Sedation Level in Mechanically Ventilated, Critically Ill Children

OBJECTIVE

We estimated the effect of early initiation of dual therapy vs monotherapy on drug administration and related outcomes in mechanically ventilated, critically ill children.

METHODS

We used the electronic medical record at a single tertiary medical center to conduct an active comparator, new user cohort study. We included children <18 years of age who were exposed to a sedative or analgesic within 6 hours of intubation. We used stabilized inverse probability of treatment weighting to account for confounding at baseline. We estimated the average effect of initial dual therapy vs monotherapy on outcomes including cumulative opioid, benzodiazepine, and dexmedetomidine dosing; sedation scores; time to double the opioid or benzodiazepine infusion rate; initiation of neuromuscular blockade within the first 7 days of follow-up; time to extubation; and 7-day all-cause in-hospital death.

RESULTS

The cohort included 640 patients. Children receiving dual therapy received 0.03 mg/kg (95% CI, 0.02-0.04) more dexmedetomidine over the first 7 days after initiation of mechanical ventilation than did monotherapy patients. Dual therapy patients had similar sedation scores, time to double therapy, initiation of neuromuscular blockade, and time to extubation as monotherapy patients. Dual therapy patients had a lower incidence of death.

CONCLUSIONS

In this study, initial dual therapy compared with monotherapy does not reduce overall drug administration during mechanical ventilation. The identified effect of dual therapy on mortality deserves further investigation.

Analgesic efficacy of the inferior alveolar nerve block for maxillofacial cancer surgery under general anaesthesia - A randomised controlled study

Background and Aims

Mandibular resection during maxillofacial cancer surgery evokes a strong sympathetic response requiring high doses of opioids. We studied the effect of the inferior alveolar nerve block (IANB) for analgesia in maxillofacial cancer surgeries.

Methods

This randomised controlled study was conducted over five months in a tertiary care cancer hospital following Institutional Ethics approval and trial registration. Fifty consenting adult patients belonging to the American Society of Anesthesiologists (ASA) physical status I and II requiring maxillofacial cancer surgery with unilateral mandibular resection were recruited. Twenty-five patients in the study arm received ipsilateral IANB; a mock injection was given to the control group. Fentanyl requirement and haemodynamic parameters during primary tumour excision were the primary and secondary endpoints. Student's t-test was applied to compare primary and secondary endpoints.

Results

Forty-nine patients completed the study. Both arms were comparable with respect to age, gender distribution, ASA physical status and baseline heart rate (HR) and blood pressure (BP). The mean (standard deviation) intravenous fentanyl requirement during primary tumour excision in the IANB arm was 70(32) µg, significantly lower than 183(48) µg in the control arm, P < 0.001. The mean maximum HR during primary tumour excision was 82 and 99 per minute in the IANB and control arms, respectively (P < 0.001) whereas the maximum mean BP was 88 and 101 mm Hg, respectively (P < 0.001).

Conclusion

IANB significantly reduced intraoperative fentanyl requirement and caused fewer haemodynamic changes during maxillofacial cancer surgery requiring unilateral mandibular excision.

Demographics and Clinical Characteristics of Patients With Opioid Use Disorder and Offered Medication-Assisted Treatment in the Emergency Department

Background and objective The opioid use disorder (OUD) epidemic is a persistent public health crisis in the United States. Medication-assisted treatment (MAT) with opioid agonists, including buprenorphine, is an effective treatment and is commonly initiated in the emergency department (ED). This study describes the demographics and clinical characteristics of OUD patients presenting to the ED and evaluated for MAT. Methodology A retrospective, single-center descriptive study of 129 adult patients presenting to the ED between July 2018 and July 2020 with OUD and evaluated for MAT. Results A total of 129 patients were assessed for MAT. About half (53%) received MAT; the remaining received only a referral (35%) or declined any intervention (12%). The median age was 36 years interquartile range (IQR, 28-46 years) and predominantly male (73%), single (65%), white (73%), unemployed (57%) with public insurance (55%), and without a primary care physician (58%). Majority of the patients presented with opioid withdrawal (62%) or intoxication (15%), while 23% presented with other complaints. About half of the patients (51%) were discharged with a naloxone kit. The majority of the patients were induced with buprenorphine with 4 mg or less (54%) and only 6% of patients received repeat dosing. Conclusions Male, white patients who are unmarried and unemployed, lack primary care follow-up, and rely on public insurance are more likely to be candidates for MAT. Providers should always maintain a high suspicion of opioid misuse and optimize treatment for those in withdrawal. Understanding these characteristics in conjunction with recent health policy changes will hopefully guide and encourage ED-initiated interventions in combating the opioid crisis.

Association between intraoperative remifentanil use and postoperative hyperalgesia in adolescent idiopathic scoliosis surgery: a retrospective study

BACKGROUND

The liberal use of remifentanil in spine surgery has been associated with an increased incidence of postoperative hyperalgesia. Nevertheless, controversies remain as the existing evidence is inconclusive to determine the relationship between remifentanil use and the development of opioid-induced hyperalgesia. We hypothesized that intraoperative infusion of higher dose remifentanil during scoliosis surgery is associated with postoperative hyperalgesia, manifesting clinically as greater postoperative morphine consumption and pain scores.

METHODS

Ninety-seven patients with adolescent idiopathic scoliosis (AIS) who underwent posterior spinal fusion surgery at a single tertiary institution from March 2019 until June 2020 were enrolled in this retrospective study. Anesthesia was maintained using a target-controlled infusion of remifentanil combined with volatile anesthetic desflurane in 92 patients, while five patients received it as part of total intravenous anesthesia. Intravenous ketamine, paracetamol, and fentanyl were administered as multimodal analgesia. All patients received patient-controlled analgesia (PCA) morphine postoperatively. Pain scores at rest and on movement, assessed using the numerical rating scale, and the cumulative PCA morphine consumption were collected at a six-hourly interval for up to 48 h. According to the median intraoperative remifentanil dose usage of 0.215 µg/kg/min, patients were divided into two groups: low dose and high dose group.

RESULTS

There were no significant differences in the pain score and cumulative PCA morphine consumption between the low and high dose remifentanil group. The mean duration of remifentanil infusion was 134.9 ± 22.0 and 123.4 ± 23.7 min, respectively.

CONCLUSION

Intraoperative use of remifentanil as an adjuvant in AIS patients undergoing posterior spinal fusion surgery was not associated with postoperative hyperalgesia.

Distinct Profiles of Desensitization of µ-Opioid Receptors Caused by Remifentanil or Fentanyl: In Vitro Assay with Cells and Three-Dimensional Structural Analyses

Remifentanil (REM) and fentanyl (FEN) are commonly used analgesics that act by activating a µ-opioid receptor (MOR). Although optimal concentrations of REM can be easily maintained during surgery, it is sometimes switched to FEN for optimal pain regulation. However, standards for this switching protocol remain unclear. Opioid anesthetic efficacy is decided in part by MOR desensitization; thus, in this study, we investigated the desensitization profiles of REM and FEN to MOR. The efficacy and potency during the 1st administration of REM or FEN in activating the MOR were almost equal. Similarly, in β arrestin recruitment, which determines desensitization processes, they showed no significant differences. In contrast, the 2nd administration of FEN resulted in a stronger MOR desensitization potency than that of REM, whereas REM showed a higher internalization potency than FEN. These results suggest that different β arrestin-mediated signaling caused by FEN or REM led to their distinct desensitization and internalization processes. Our three-dimensional analysis, with in silico binding of REM and FEN to MOR models, highlighted that REM and FEN bound to similar but distinct sites of MOR and led to distinct β arrestin-mediated profiles, suggesting that distinct binding profiles to MOR may alter β arrestin activity, which accounts for MOR desensitization and internalization.

Amygdala Metabotropic Glutamate Receptor 1 Influences Synaptic Transmission to Participate in Fentanyl-Induced Hyperalgesia in Rats

The underlying mechanisms of opioid-induced hyperalgesia (OIH) remain unclear. Herein, we found that the protein expression of metabotropic glutamate receptor 1 (mGluR1) was significantly increased in the right but not in the left laterocapsular division of central nucleus of the amygdala (CeLC) in OIH rats. In CeLC neurons, the frequency and the amplitude of mini-excitatory postsynaptic currents (mEPSCs) were significantly increased in fentanyl group which were decreased by acute application of a mGluR1 antagonist, A841720. Finally, the behavioral hypersensitivity could be reversed by A841720 microinjection into the right CeLC. These results show that the right CeLC mGluR1 is an important factor associated with OIH that enhances synaptic transmission and could be a potential drug target to alleviate fentanyl-induced hyperalgesia.

Multimodal Pain Control Reduces Narcotic Use after Outpatient Abdominoplasty: Retrospective Analysis in an Ambulatory Surgery Practice

Despite dominating fewer headlines, the opioid epidemic continues to plague society. Surgeons have the responsibility to change their opioid prescribing habits while maintaining adequate patient comfort. This study examines the transition to a multimodal, perioperative protocol in an ambulatory surgery setting for abdominoplasty patients. We hypothesized that using multimodal analgesia could significantly reduce narcotic consumption.

Methods

The authors retrospectively compared one surgeon's consecutive abdominoplasty patients over 24 months. The control group received primarily narcotic medications to manage pain, and the treatment cohort was given a multimodal protocol for perioperative analgesia.

Results

Demographic data, surgical time, and postanesthesia care unit time between the groups were similar. Although the mean intravenous narcotic decreased in the operating room and postanesthesia care unit for the treatment group, it failed to achieve statistical significance. The treatment cohort was prescribed two-thirds less oral narcotic than the control (251 versus 787 mean morphine milligram equivalents P < 0.001). Ten patients in the treatment cohort used no oral narcotics compared to one in the control (P = 0.002), and only four narcotic refills were given in the treatment group compared to 36 in the control (P < 0.001), suggesting that the treatment group had better pain control despite taking fewer narcotics.

Conclusions

Optimally utilizing multimodal medications effectively reduces narcotic consumption while effectively managing postoperative pain from abdominoplasty in a private practice, ambulatory surgery setting. Surgeons must change their prescribing habits if we are going to make progress in the war against the opioid crisis.

Spinal NLRP3 inflammasome activation mediates IL-1β release and contributes to remifentanil-induced postoperative hyperalgesia by regulating NMDA receptor NR1 subunit phosphorylation and GLT-1 expression in rats

BACKGROUND

Trafficking and activation of N-methyl-D-aspartate (NMDA) receptors play an important role in initiating and maintaining postoperative remifentanil-induced hyperalgesia (RIH). Activation of the NOD-like receptor protein 3 (NLRP3) inflammasome has been linked to the development of inflammatory and neuropathic pain. We hypothesized that activation of NLRP3 inflammasome mediates IL-1β release and contributes to RIH in rats by increasing NMDA receptor NR1 (NR1) subunit phosphorylation and decreasing glutamate transporter-1 (GLT-1) expression.

METHODS

Acute exposure to remifentanil (1.2 μg/kg/min for 60 min) was used to establish RIH in rats. Thermal and mechanical hyperalgesia were tested at baseline (24 h before remifentanil infusion) and 2, 6, 24, and 48 h after remifentanil infusion. The levels of IL-1β, GLT-1, phosphorylated NR1 (phospho-NR1), and NLRP3 inflammasome activation indicators [NLRP3, Toll-like receptor 4 (TLR4), P2X purinoceptor 7 (P2X7R), and caspase-1] were measured after the last behavioral test. A selective IL-1β inhibitor (IL-1β inhibitor antagonist; IL-1ra) or three different selective NLRP3 inflammasome activation inhibitors [(+)-naloxone (a TLR4 inhibitor), A438079 (a P2X7R inhibitor), or ac-YVADcmk (a caspase-1 inhibitor)] were intrathecally administered immediately before remifentanil infusion into rats.

RESULTS

Remifentanil induced significant postoperative hyperalgesia, increased IL-1β and phospho-NR1 levels and activated the NLRP3 inflammasome by increasing TLR4, P2X7R, NLRP3, and caspase-1 expression, but it decreased GLT-1 expression in the L4-L6 spinal cord segments of rats, which was markedly improved by intrathecal administration of IL-1ra, (+)-naloxone, A438079, or ac-YVADcmk.

CONCLUSION

NLRP3 inflammasome activation mediates IL-1β release and contributes to RIH in rats by inducing NMDA receptor NR1 subunit phosphorylation and decreasing GLT-1 expression. Inhibiting the activation of the NLRP3 inflammasome may be an effective treatment for RIH.

Spinal orexin A attenuates opioid-induced mechanical hypersensitivity in the rat

Background

Repeated administration of opioid analgesics for pain treatment can produce paradoxical hyperalgesia via peripheral and/or central mechanisms. Thus, this study investigated whether spinally (centrally) administered orexin A attenuates opioid-induced hyperalgesia (OIH).

Methods

[D-Ala2, N-Me-Phe4, Gly5-ol]-enkephalin (DAMGO), a selective μ-opioid receptor agonist, was used to induce mechanical hypersensitivity and was administered intradermally (4 times, 1-hour intervals) on the rat hind paw dorsum. To determine whether post- or pretreatments with spinal orexin A, dynorphin A, and anti-dynorphin A were effective in OIH, the drugs were injected through an intrathecal catheter whose tip was positioned dorsally at the L3 segment of the spinal cord (5 μg for all). Mechanical hypersensitivity was assessed using von Frey monofilaments.

Results

Repeated intradermal injections of DAMGO resulted in mechanical hypersensitivity in rats, lasting more than 8 days. Although the first intrathecal treatment of orexin A on the 6th day after DAMGO exposure did not show any significant effect on the mechanical threshold, the second (on the 8th day) significantly attenuated the DAMGO-induced mechanical hypersensitivity, which disappeared when the type 1 orexin receptor (OX1R) was blocked. However, intrathecal administration of dynorphin or an anti-dynorphin antibody (dynorphin antagonists) had no effect on DAMGO-induced hypersensitivity. Lastly, pretreatment with orexin A, dynorphin, or anti-dynorphin did not prevent DAMGO-induced mechanical hypersensitivity.

Conclusions

Spinal orexin A attenuates mechanical hyperalgesia induced by repetitive intradermal injections of DAMGO through OX1R. These data suggest that OIH can be potentially treated by activating the orexin A-OX1R pathway in the spinal dorsal horn.

The Lack of Analgesic Efficacy of Nefopam after Video-Assisted Thoracoscopic Surgery for Lung Cancer: A Randomized, Single-Blinded, Controlled Trial

Nefopam is a centrally acting non-opioid analgesic, and its efficacy in multimodal analgesia has been reported. This study aimed to assess the analgesic efficacy of intraoperative nefopam on postoperative pain after video-assisted thoracoscopic surgery (VATS) for lung cancer. Participants were randomly assigned to either the nefopam or the control group. The nefopam group received 20 mg of nefopam after induction and 15 min before the end of surgery. The control group received saline. The primary outcome was cumulative opioid consumption during the 6 h postoperatively. Pain intensities, the time to first request for rescue analgesia, adverse events during the 72 h postoperatively, and the incidence of chronic pain 3 months after surgery were evaluated. Ninety-nine patients were included in the analysis. Total opioid consumption during the 6 h postoperatively was comparable between the groups (nefopam group [n = 50] vs. control group [n = 49], 19.8 [13.5–25.3] mg vs. 20.3 [13.9–27.0] mg; median difference: −1.55, 95% CI: −6.64 to 3.69; p = 0.356). Pain intensity during the 72 h postoperatively and the incidence of chronic pain 3 months after surgery did not differ between the groups. Intraoperative nefopam did not decrease acute postoperative opioid consumption or pain intensity, nor did it reduce the incidence of chronic pain after VATS.

Effect of remifentanil on post-operative analgesic consumption in patients undergoing shoulder arthroplasty after interscalene brachial plexus block: a randomized controlled trial

PURPOSE

Remifentanil is useful in balanced anesthesia; however, there is concern regarding opioid-induced hyperalgesia. The effect of remifentanil on rebound pain, characterized by hyperalgesia after peripheral nerve block has rarely been studied. This study evaluated whether intraoperative remifentanil infusion may increase postoperative analgesic requirement in patients receiving preoperative interscalene brachial plexus block (IBP).

METHODS

Sixty-eight patients undergoing arthroscopic shoulder surgery under general anesthesia were randomly allocated to remifentanil (R) or control (C) group. Preoperative IBP with 0.5% ropivacaine 15 mL was performed in all patients. Intraoperative remifentanil was administered only in the R group. Postoperative pain was controlled using intravenous patient-controlled analgesia (IV-PCA) and rescue analgesics. The primary outcome was the dosage of fentanyl-nefopam IV-PCA infused over 24 h postoperatively. The secondary outcomes included the numeric rating scale (NRS) score recorded at 4-h intervals over 24 h, amount of rescue analgesics and total postoperative analgesics used over 24 h, occurrence of intraoperative hypotension, postoperative nausea and vomiting (PONV) and delirium.

RESULTS

The dosage of fentanyl-nefopam IV-PCA was significantly less in C group than R group for postoperative 24 h. Fentanyl 101 [63-158] (median [interquartile range]) µg was used in the C group, while fentanyl 161 [103-285] µg was used in the R group (median difference 64 µg, 95% CI 10-121 µg, P = 0.02). Nefopam 8.1 [5.0-12.6] mg was used in the C group, while nefopam 12.9 [8.2-22.8] mg was used in the R group (median difference 5.1 mg, 95% CI 0.8-9.7 mg, P = 0.02). The total analgesic consumption: the sum of PCA consumption and administered rescue analgesic dose, converted to morphine milligram equivalents, was higher in the R group than C group (median difference 10.9 mg, 95% CI 3.0-19.0 mg, P = 0.01). The average NRS score, the incidence of PONV and delirium, were similar in both groups. The incidence of intraoperative hypotension was higher in R group than C group (47.1% vs. 20.6%, P = 0.005).

CONCLUSIONS

Remifentanil administration during arthroscopic shoulder surgery in patients undergoing preoperative IBP increased postoperative analgesic consumption.

Guidelines for Perioperative Care in Elective Abdominal and Pelvic Surgery at Primary and Secondary Hospitals in Low-Middle-Income Countries (LMIC's): Enhanced Recovery After Surgery (ERAS) Society Recommendation

Background

This is the first Enhanced Recovery After Surgery (ERAS®) Society guideline for primary and secondary hospitals in low–middle-income countries (LMIC’s) for elective abdominal and gynecologic care.

Methods

The ERAS LMIC Guidelines group was established by the ERAS® Society in collaboration with different representatives of perioperative care from LMIC’s. The group consisted of seven members from the ERAS® Society and eight members from LMIC’s. An updated systematic literature search and evaluation of evidence from previous ERAS® guidelines was performed by the leading authors of the Colorectal (2018) and Gynecologic (2019) surgery guidelines (Gustafsson et al in World J Surg 43:6592–695, Nelson et al in Int J Gynecol Cancer 29(4):651–668). Meta-analyses randomized controlled trials (RCTs), prospective and retrospective cohort studies from both HIC’s and LMIC’s were considered for each perioperative item. The members in the LMIC group then applied the current evidence and adapted the recommendations for each intervention as well as identifying possible new items relevant to LMIC’s. The Grading of Recommendations, Assessment, Development and Evaluation system (GRADE) methodology was used to determine the quality of the published evidence. The strength of the recommendations was based on importance of the problem, quality of evidence, balance between desirable and undesirable effects, acceptability to key stakeholders, cost of implementation and specifically the feasibility of implementing in LMIC’s and determined through discussions and consensus.

Results

In addition to previously described ERAS® Society interventions, the following items were included, revised or discussed: the Surgical Safety Checklist (SSC), preoperative routine human immunodeficiency virus (HIV) testing in countries with a high prevalence of HIV/AIDS (CD4 and viral load for those patients that are HIV positive), delirium screening and prevention, COVID 19 screening, VTE prophylaxis, immuno-nutrition, prehabilitation, minimally invasive surgery (MIS) and a standardized postoperative monitoring guideline.

Conclusions

These guidelines are seen as a starting point to address the urgent need to improve perioperative care and to effect data-driven, evidence-based care in LMIC’s.

Effects of subanesthesia dose S-ketamine induction on postoperative psychiatric complications after gynecological surgery

Ketamine may become an important drug for multimodal analgesia regime again because of its strong analgesic effects and retaining the advantage of spontaneous breathing. The present study was designed to explore the influences of different dosages of S-ketamine anesthesia induction regimes on psychiatric complications and postoperative prognosis in patients undergoing gynecological operations. In this prospective, triple-blinded, randomized, controlled study, patients undergoing elective gynecological surgery were randomized to one of three treatment groups: low-dose S-ketamine (LDSK) group (a 0.3 mg/kg bolus for anesthesia induction), minimal-dose S-ketamine (MDSK) group (a 0.2 mg/kg bolus for anesthesia induction), and placebo (CON) group (a saline bolus for anesthesia induction). The main outcome measures were as follows: intraoperative vital signs, extubation time, anesthesia recovery time and postanesthesia care unit (PACU) stay duration, incidence of psychiatric complications, Ramsay sedation scale (RSS) 1, 2, 24, and 48 h, postoperatively, and overall prognosis. One hundred and eighty female participants were finally included in this study from April 2021 to December 2021. Significant differences were not observed in age, height, weight, American Society of Anesthesiologists physical status classification, or history of mental illness between the groups. No statistically significant differences were discovered with regard to intraoperative vital signs, extubation time and PACU stay duration, incidence of psychiatric complications, and RSS scores at 1, 2, 24, and 48 h postoperatively in the three groups. However, the visual analog scale (VAS) scores of the CON group at 10 min after extubation and at the time point leaving PACU were much higher than that of the LDSK and MDSK groups. The VAS scores at 48 h after surgery in the MDSK group were also lower than that of the CON group and the CON group had received more analgesic drug treatment in the surgical wards consequently. Postoperative nausea and vomiting (PONV) occurrence at 24 and 48 h, postoperatively, increased sharply in the CON group than in the other two experimental groups, which led to an increase in the use of postoperative antiemetic drugs in this group. According to the postoperative satisfaction survey, patients in the CON group had lower medical satisfaction. Our data demonstrate that a small dosage of S-ketamine anesthesia induction can reduce postoperative pain and the incidence of PONV without increasing hemodynamic fluctuations or psychiatric complications.

Effect of opioid-free anesthesia on postoperative analgesia after laparoscopic gynecologic surgery

BACKGROUND

We performed this randomised controlled trial to evaluate the effect of opioid-free anesthesia (OFA) on postoperative analgesia after laparoscopic gynecologic surgery.

METHODS

78 patients undergoing laparoscopic gynecologic surgery were randomized to receive either OFA (Group OF) or opioid-inclusive anesthesia (Group C). Postoperative sufentanil consumption within the first 24 h, visual analogue scale (VAS) for pain, postoperative equivalent milligrams of morphine (EMM), severity of postoperative nausea (PN) and vomiting (PV), prevalence of PONV, use of antiemetics, time to first passage of flatus were compared by a two-tailed Student's t test, Wilcoxon rank-sum tests or Fisher's exact tests. Repeated measures ANOVA was used to assess the effect of allocation of groups over time.

RESULTS

The median [IQR] sufentanil consumption within 24 h was lower in Group OF (4[4.5]) than in Group C (6[8], mean difference [MD]=-2, 95% confidence interval [CI] [-4 to 0], P=0.029). The VAS scores at rest and during coughing at 6 h (P=0.009 at rest; P=0.002 during coughing), VAS scores during coughing at 2h (P=0.013) and 4 h (P=0.008), EMM (P=0.026), severities of PN (P=0.003) and PV (P=0.003), and the mean time to first passage of flatus (P=0.017) was significantly less in Group OF than that in Group C. The prevalence of PONV (26.3% [Group OF], 68.4% [Group C], OR=0.31, 95% CI [0.158 to 0.589], P <0.001), use of antiemetics (5.3% [Group OF], 28.9% [Group C], OR=0.136, 95% CI[0.028 to 0.667], P=0.012) was also significantly different between groups.

CONCLUSIONS

Compared to opioid-inclusive anesthesia during laparoscopic gynecologic surgery, OFA was associated with significant improvement in postoperative analgesia, reduced PONV incidenceprevalence and severity, and faster first passage of flatus.

fNIRS brain measures of ongoing nociception during surgical incisions under anesthesia

Significance: Functional near-infrared spectroscopy (fNIRS) has evaluated pain in awake and anesthetized states. Aim: We evaluated fNIRS signals under general anesthesia in patients undergoing knee surgery for anterior cruciate ligament repair. Approach: Patients were split into groups: those with regional nerve block (NB) and those without (non-NB). Continuous fNIRS measures came from three regions: the primary somatosensory cortex (S1), known to be involved in evaluation of nociception, the lateral prefrontal cortex (BA9), and the polar frontal cortex (BA10), both involved in higher cortical functions (such as cognition and emotion). Results: Our results show three significant differences in fNIRS signals to incision procedures between groups: (1) NB compared with non-NB was associated with a greater net positive hemodynamic response to pain procedures in S1; (2) dynamic correlation between the prefrontal cortex (PreFC) and S1 within 1 min of painful procedures are anticorrelated in NB while positively correlated in non-NB; and (3) hemodynamic measures of activation were similar at two separate time points during surgery (i.e., first and last incisions) in PreFC and S1 but showed significant differences in their overlap. Comparing pain levels immediately after surgery and during discharge from postoperative care revealed no significant differences in the pain levels between NB and non-NB. Conclusion: Our data suggest multiple pain events that occur during surgery using devised algorithms could potentially give a measure of "pain load." This may allow for evaluation of central sensitization (i.e., a heightened state of the nervous system where noxious and non-noxious stimuli is perceived as painful) to postoperative pain levels and the resulting analgesic consumption. This evaluation could potentially predict postsurgical chronic neuropathic pain.

Preoperative multimodal protocol reduced postoperative nausea and vomiting in patients undergoing mastectomy with reconstruction

BACKGROUND

Mastectomy with immediate reconstruction is a high-risk cohort for postoperative nausea and vomiting (PONV). Known risk factors for PONV include female gender, prior PONV history, nonsmoker, age < 50, and postoperative opioid exposure. The objective of this observational, cohort analysis was to determine whether a standardized preoperative protocol with nonopioid and anti-nausea multimodal medications would reduce the odds of PONV.

METHODS

After IRB approval, retrospective data were collected for patients undergoing mastectomy with or without a nodal resection, and immediate subpectoral tissue expander or implant reconstruction. Patients were grouped based on treatment: those receiving the protocol - oral acetaminophen, pregabalin, celecoxib, and transdermal scopolamine (APCS); those receiving none (NONE), and those receiving partial protocol (OTHER). Logistic regression models were used to compare PONV among treatment groups, adjusting for patient and procedural variables.

MAIN FINDINGS

Among 305 cases, the mean age was 47 years (21-74), with 64% undergoing a bilateral procedure and 85% having had a concomitant nodal procedure. A total of 44.6% received APCS, 30.8% received OTHER, and 24.6% received NONE. The APCS group had the lowest rate of PONV (40%), followed by OTHER (47%), and NONE (59%). Adjusting for known preoperative variables, the odds of PONV were significantly lower in the APCS group versus the NONE group (OR=0.42, 95% CI: 0.20, 0.88 p = 0.016).

CONCLUSIONS

Premedication with a relatively inexpensive combination of oral non-opioids and an anti-nausea medication was associated with a significant reduction in PONV in a high-risk cohort. Use of a standardized protocol can lead to improved care while optimizing the patient experience.

Comparison of the effects of dexmedetomidine and remifentanil on perioperative hemodynamics and recovery profile of patients undergoing laryngeal microsurgery: A prospective randomized double-blinded study

BACKGROUND

Laryngeal microsurgery (LMS) causes hemodynamic instability and postoperative agitation, cough, pain, nausea, and vomiting. Moreover, because of a short operation time, it is associated with challenging anesthetic management. The aim of this study was to compare the usefulness of continuous administration of dexmedetomidine and remifentanil in inducing general anesthesia in patients undergoing LMS.

METHODS

This is a prospective randomized control design. Continuous intravenous infusion of dexmedetomidine (group D) or remifentanil (group R) was administered from 10 minutes before the induction of anesthesia to the end of surgery. In both groups, 1.5 mg/kg propofol and 0.5 mg/kg rocuronium were administered for the induction of anesthesia, and desflurane were titrated during the measurement of the bispectral index. We recorded hemodynamic data, recovery time, grade of cough, pain score, and analgesic requirements during the perioperative period.

RESULTS

61 patients were finally analyzed (30 for group D, 31 for group R). The incidence of moderate to severe postoperative sore throat was higher in group R than in group D (42% vs 10%, P = .008), and the quantity of rescue fentanyl used in post-anesthesia care unit was significantly higher in group R than in group D (23.2 ± 24.7 mg vs 3.3 ± 8.6 mg; P < .001); however, the time required for eye opening was significantly longer in group D than in group R (599.4 ± 177.9 seconds vs 493.5 ± 103.6 seconds; P = .006). The proportion of patients with no cough or single cough during extubation was comparable between the 2 groups (group D vs group R: 73% vs 70%) as was the incidence of hemodynamic instability.

CONCLUSION

Although there was a transient delay in emergence time, dexmedetomidine reduced postoperative opioid use and the incidence of sore throat. Dexmedetomidine may be used as an alternative agent to opioids in patients undergoing LMS.

A Role for Transmembrane Protein 16C/Slack Impairment in Excitatory Nociceptive Synaptic Plasticity in the Pathogenesis of Remifentanil-induced Hyperalgesia in Rats

Remifentanil is widely used to control intraoperative pain. However, its analgesic effect is limited by the generation of postoperative hyperalgesia. In this study, we investigated whether the impairment of transmembrane protein 16C (TMEM16C)/Slack is required for α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic receptor (AMPAR) activation in remifentanil-induced postoperative hyperalgesia. Remifentanil anesthesia reduced the paw withdrawal threshold from 2 h to 48 h postoperatively, with a decrease in the expression of TMEM16C and Slack in the dorsal root ganglia (DRG) and spinal cord. Knockdown of TMEM16C in the DRG reduced the expression of Slack and elevated the basal peripheral sensitivity and AMPAR expression and function. Overexpression of TMEM16C in the DRG impaired remifentanil-induced ERK1/2 phosphorylation and behavioral hyperalgesia. AMPAR-mediated current and neuronal excitability were downregulated by TMEM16C overexpression in the spinal cord. Taken together, these findings suggest that TMEM16C/Slack regulation of excitatory synaptic plasticity via GluA1-containing AMPARs is critical in the pathogenesis of remifentanil-induced postoperative hyperalgesia in rats.

A Prospective Randomized Comparison of Postoperative Pain and Complications after Thyroidectomy under Different Anesthetic Techniques: Volatile Anesthesia versus Total Intravenous Anesthesia

While the postoperative outcome is favorable, post-thyroidectomy pain is considerable. Reducing the postoperative acute pain, therefore, is considered important. This study investigated whether the pain intensity and need for rescue analgesics during the immediate postoperative period after thyroidectomy differ according to the methods of anesthesia. Seventy-two patients undergoing total thyroidectomy under general anesthesia were examined. Patients were randomly assigned to undergo either total intravenous anesthesia with remifentanil and propofol (TIVA, n = 35) or propofol induction and maintenance with desflurane and nitrous oxide (volatile anesthesia [VA], n = 37). The mean administered dose of remifentanil was 1977.7 ± 722.5 μg in the TIVA group, which was approximately 0.268 ± 0.118 μg/min/kg during surgery. Pain scores based on a numeric rating scale (NRS) and the need for rescue analgesics were compared between groups at the postoperative anesthetic care unit (PACU). The immediate postoperative NRS values of the TIVA and VA groups were 5.7 ± 1.7 and 4.7 ± 2.3, respectively (P = 0.034). Postoperative morphine equianalgesic doses in the PACU were higher in the TIVA group than in the VA group (16.7 ± 3.8 mg vs. 14.1 ± 5.9 mg, P = 0.027). The incidence of immediate postanesthetic complications did not differ significantly between groups. In conclusion, more rescue analgesics were required in the TIVA group than in the VA group to adequately manage postoperative pain while staying in the PACU after thyroidectomy.

Evaluation of the Efficacy of Low-Dose Naloxone for the Prevention of Acute Remifentanil-Induced Hyperalgesia in Patients Undergoing General Anesthesia for Laparotomy

Background: Hyperalgesia is a major complication of continuous or intermittent opioid administration. The evidence suggests that concomitant administration of low-dose naloxone could prevent the development of acute opioid-induced hyperalgesia, with no effect on pain control. Objectives: The current study aimed to assess the effects of intraoperative low-dose naloxone, adding to remifentanil infusion on preventing acute postoperative hyperalgesia in patients undergoing general anesthesia for laparotomy. Methods: In this randomized clinical trial, patients undergoing general anesthesia for laparotomic hysterectomy in a tertiary referral teaching hospital from February to December 2019 were randomly assigned to one of three groups of remifentanil-naloxone (remifentanil 0.3 μg/ kg/min with low-dose naloxone 0.25μg/kg /h prepared in 50 mL of normal saline), remifentanil (0.3 μg/kg/min), and control (receiving 50 mL saline infusion), intraoperatively. Patients and researchers were blinded to the type of intervention. The severity of hyperalgesia, as the main outcome, was evaluated by the static Tactile test. The severity of pain was assessed by visual analogous scale 0.5, 2, 6, 12, and 24 hours after surgery. Results: In total, 75 patients were evaluated. The results showed no difference concerning the independent variables (age, body mass index, hypertension, surgery duration, anesthesia duration, and American Society of Anesthesiologists (ASA) class) between the three groups. Heart rate was significantly different in all study time points between the three groups (P < 0.001), but mean arterial pressure and systolic and diastolic blood pressure showed no significant difference (P > 0.05) throughout the study. Assessment of hyperalgesia using the tactile test revealed a higher incidence of hyperalgesia in the remifentanil group in 0.5, 2, 6, 12, and 24 hours after surgery compared to the other two groups, which was statistically significant between the groups at 0.5, 2, and 6 hours after surgery (P < 0.05). Shivering incidence, Morphine dose in 24 hours post-surgery, morphine dose in the recovery room, and VAS for pain were significantly different during the study between the three groups (P < 0.05). Conclusions: This study demonstrated the efficacy of intraoperative low-dose naloxone (0.25 μg/kg/h) added to remifentanil infusion on reducing the frequency and severity of acute postoperative hyperalgesia in patients undergoing general anesthesia for laparotomy hysterectomy.

Pharmacological Chaperones Attenuate the Development of Opioid Tolerance

Opioids are potent analgesics widely used to control acute and chronic pain, but long-term use induces tolerance that reduces their effectiveness. Opioids such as morphine bind to mu opioid receptors (MORs), and several downstream signaling pathways are capable of inducing tolerance. We previously reported that signaling from the endoplasmic reticulum (ER) contributed to the development of morphine tolerance. Accumulation of misfolded proteins in the ER induced the unfolded protein response (UPR) that causes diverse pathological conditions. We examined the effects of pharmacological chaperones that alleviate ER stress on opioid tolerance development by assessing thermal nociception in mice. Pharmacological chaperones such as tauroursodeoxycholic acid and 4-phenylbutyrate suppressed the development of morphine tolerance and restored analgesia. Chaperones alone did not cause analgesia. Although morphine administration induced analgesia when glycogen synthase kinase 3β (GSK3β) was in an inactive state due to serine 9 phosphorylation, repeated morphine administration suppressed this phosphorylation event. Co-administration of chaperones maintained the inactive state of GSK3β. These results suggest that ER stress may facilitate morphine tolerance due to intracellular crosstalk between the UPR and MOR signaling. Pharmacological chaperones may be useful in the management of opioid misuse.

The Opioid Wars-CON: The Risks of Opioids for Pain Management Outweigh the Benefits

The entire field of medicine, not just anesthesiology, has grown comfortable with the risks posed by opioids; but these risks are unacceptably high. It is time for a dramatic paradigm shift. If used at all for acute or chronic pain management, they should be used only after consideration and maximizing the use of nonopioid pharmacologic agents, regional analgesia techniques, and nonpharmacologic methods. Opioids poorly control pain, their intraoperative use may increase the risk of recurrence of some types of cancer, and they have a large number of both minor and serious side effects. Furthermore, there are a myriad of alternative analgesic strategies that provide superior analgesia, decrease recovery time, and have fewer side effects and risks associated with their use. In this article the negative consequences of opioid use for pain, appropriate alternatives to opioids for analgesia, and the available evidence in pediatric populations for both are described.

Preemptive Nalbuphine Attenuates Remifentanil-Induced Postoperative Hyperalgesia After Laparoscopic Cholecystectomy: A Prospective Randomized Double-Blind Clinical Trial

Background

Remifentanil-induced hyperalgesia (RIH) is a paradoxical phenomenon that may increase sensitivity to painful stimuli. Nalbuphine, which is both a μ-receptor antagonist and κ-receptor agonist, may affect RIH. The aim of this study was to evaluate the effects of nalbuphine on RIH during laparoscopic cholecystectomy.

Methods

A total of 96 patients were divided into the following four groups: 0.4 μg/kg/min of remifentanil with 0.2 mg/kg of nalbuphine (HRNA), 0.4 μg/kg/min of remifentanil with saline (HRSA), 0.1 μg/kg/min of remifentanil with 0.2 mg/kg of nalbuphine (LRNA), and 0.1 μg/kg/min of remifentanil with saline (LRSA). The pain thresholds of postoperative mechanical hyperalgesia were measured with von Frey filaments. Pain intensity and analgesic consumption were recorded up to 48 h after surgery.

Results

Pain thresholds on the inner forearm decreased in the HRSA group compared with the HRNA (P = 0.0167), LRNA (P = 0.0027), and LRSA (P = 0.0318) groups at 24 h after surgery. Pain thresholds on the peri-incisional area decreased in the HRSA group compared with HRNA, LRNA, and LRSA (all P < 0.0001) groups at 24 h after surgery. Patients in the HRNA group showed lower numeric rating scale scores at 1 h (P = 0.0159), 3 h (P = 0.0118), 6 h (P = 0.0213), and 12 h (P = 0.0118) than those in the HRSA group. Postoperative requirement for sufentanil was greater in the HRSA group than the HRNA group during the first 3 h (P = 0.0321) and second 3 h (P = 0.0040). Postoperative sufentanil consumption was also greater in the LRSA group than in the LRNA group during the first 3 h (P = 0.0321) and second 3 h (P = 0.0416).

Conclusion

Preemptive nalbuphine can ameliorate postoperative hyperalgesia induced by high-dose remifentanil in patients undergoing laparoscopic cholecystectomy.

NMDA Receptor Modulates Spinal Iron Accumulation Via Activating DMT1(-)IRE in Remifentanil-Induced Hyperalgesia

N-methyl-D-aspartate (NMDA) receptor activation is known to be critical in remifentanil-induced hyperalgesia. Evidence indicates that iron accumulation participates in NMDA neurotoxicity. This study aims to investigate the role of iron accumulation in remifentanil-induced hyperalgesia. Remifentanil was delivered intravenously in rats to induce hyperalgesia. The NMDA receptor antagonist MK-801 was intrathecally administrated. The levels of divalent metal transporter 1 without iron-responsive element [DMT1(-)IRE] and iron were detected. Behavior testing was performed in DMT1(-)IRE knockdown rats and rats treated with iron chelator DFO. Meanwhile, the spinal dorsal horn neurons were cultured and transfected with DMT1(-)IRE siRNA, and then respectively incubated with remifentanil and MK-801. The levels of intracellular Ca²⁺ and iron were assessed by fluorescence imaging. Our data revealed that spinal DMT1(-)IRE and iron content significantly increased in remifentanil-treated rats, and MK-801 inhibited the enhancements. DMT1(-)IRE knockdown and DFO prevented against remifentanil-induced hyperalgesia. Notably, the levels of Ca²⁺ and iron increased in remifentanil-incubated neurons, and these growths can be blocked by MK-801. DMT1(-)IRE knockdown attenuated iron accumulation but did not influence Ca²⁺ influx. This study suggests that DMT1(-)IRE-mediated iron accumulation is likely to be the downstream event following NMDA receptor activation and Ca²⁺ influx, contributing to remifentanil-induced hyperalgesia. PERSPECTIVE: Remifentanil-induced hyperalgesia is common even when used within clinical accepted doses. This study presents that aberrant iron accumulation is involved in the development of remifentanil-induced hyperalgesia in vivo and in vitro. Iron chelation may be a potential therapeutic strategy for the prevention of hyperalgesia in populations at high risk.

Opioid Induced Hyperalgesia, a Research Phenomenon or a Clinical Reality? Results of a Canadian Survey

BACKGROUND

Very little is known regarding the prevalence of opioid induced hyperalgesia (OIH) in day to day medical practice. The aim of this study was to evaluate the physician's perception of the prevalence of OIH within their practice, and to assess the level of physician's knowledge with respect to the identification and treatment of this problem.

METHODS

An electronic questionnaire was distributed to physicians who work in anesthesiology, chronic pain, and/or palliative care in Canada.

RESULTS

Of the 462 responses received, most were from male (69%) anesthesiologists (89.6%), in the age range of 36 to 64 years old (79.8%). In this study, the suspected prevalence of OIH using the average number of patients treated per year with opioids was 0.002% per patient per physician practice year for acute pain, and 0.01% per patient per physician practice year for chronic pain. Most physicians (70.2%) did not use clinical tests to help make a diagnosis of OIH. The treatment modalities most frequently used were the addition of an NMDA antagonist, combined with lowering the opioid doses and using opioid rotation.

CONCLUSIONS

The perceived prevalence of OIH in clinical practice is a relatively rare phenomenon. Furthermore, more than half of physicians did not use a clinical test to confirm the diagnosis of OIH. The two main treatment modalities used were NMDA antagonists and opioid rotation. The criteria for the diagnosis of OIH still need to be accurately defined.

Oxycodone preemptive analgesia after endoscopic plasma total adenotonsillectomy in children: A randomized controlled trial

BACKGROUND

Endoscopic tonsillectomy is associated with postoperative pain. Postoperative pain management remains to be improved in children. We aimed to investigate oxycodone preemptive analgesia in children undergoing endoscopic plasma total adenotonsillectomy.

METHODS

166 children with adenotonsillar hypertrophy were recruited at Wuhan Children's Hospital between 08/2016 and 03/2017. They were randomly assigned to receive SPOA (postoperative sufentanil), SPEA+SPOA (preemptive sufentanil and postoperative sufentanil), and OPEA+SPOA (preemptive oxycodone and postoperative sufentanil). The primary endpoint was serum c-fos levels. The secondary endpoints were the response entropy (RE) value, Pediatric Anesthesia Emergence Delirium (PAED) score, FLACC score, and adverse events.

RESULTS

c-fos mRNA levels were increased significantly after surgery in the SPOA and SPEA+SPOA groups (P < .05). Postoperatively, c-fos mRNA levels were higher in the SPOA group compared with the OPEA+SPOA group (P = .044). The RE values increased in all groups after surgery (P < .05). At extubation, RE values were higher in the SPOA group compared with the SPEA+SPOA and OPEA+SPOA groups (P < .05). The PAED scores were higher in the SPOA group compared with the OPEA+SPOA group (P = .045). In the SPOA group, the FLACC scores were decreased at 24 h after surgery vs 4 hours (P = .044). Prediction probability (Pk) values indicated that RE and c-fos mRNA levels were quantitative predictors for early postoperative stress reaction after surgery.

CONCLUSIONS

The subanalgesic dose of oxycodone (0.1 mg/kg) as preemptive analgesia could improve pain after endoscopic plasma total adenotonsillectomy in children.

[The effects of remifentanil used during cesarean section on oxidative stress markers in correlation with maternal hemodynamics and neonatal outcome: a randomized controlled trial]

BACKGROUND AND OBJECTIVE

Remifentanil is used to attenuate maternal hemodynamic response to intubation and surgical stress during Induction-Delivery period of cesarean section. The goal was to compare the effects of two remifentanil dosing regimens on oxidative stress level, in correlation with its hemodynamic and neonatal effects.

METHODS

Fifty-one patients, 17 per group, enrolled for elective cesarean section were randomly divided by computer-generated codes into three parallel groups: (A) patients received a 1μg.kg^-1 remifentanil bolus immediately before induction, followed by 0.15μg.kg^-1.min^-1 infusion, that was stopped after skin incision; (B) patients received a 1μg.kg^-1 remifentanil bolus immediately before induction; (C) (control), patients did not receive remifentanil until delivery. Maternal venous blood samples were taken at basal time, at extraction and 30minutes after the end of operation for spectrophotometrical determination of malondialdehyde and advanced oxidation protein products concentration. The same was conducted for umbilical venous sample.

RESULTS

Systolic blood pressure and heart rate remained significantly lower in group A compared to B and C during entire Induction-Delivery period (p<0.001, p=0.02 after intubation; p=0.006, p=0.03 after skin incision; p=0.029, p=0.04 after extraction; respectively). Malondialdehyde concentration was lower at time of extraction in maternal blood in group A compared to B and C (p=0.026). All neonatal Apgar scores were ≥ 8 and umbilical acid-base values within normal range.

CONCLUSIONS

The remifentanil dosing regimen applied in group A significantly attenuated lipid peroxidation and maternal hemodynamic response during entire I-D period, without compromising neonatal outcome.

Determination of acute tolerance and hyperalgesia to remifentanil constant rate infusion in dogs undergoing sevoflurane anaesthesia

OBJECTIVE

To determine if acute opioid tolerance (AOT) or opioid-induced hyperalgesia (OIH) could develop and limit the remifentanil-induced reduction in the sevoflurane minimum alveolar concentration (MAC). The response to mechanical nociceptive threshold (MNT) was evaluated and related to OIH.

STUDY DESIGN

A crossover, randomized, experimental animal study.

ANIMALS

A total of nine Beagle dogs.

METHODS

The dogs were anaesthetized with sevoflurane in 50% oxygen. Baseline sevoflurane MAC was measured (MACb1). Remifentanil (0.3 μg kg^-1 minute^-1) or 0.9% saline constant rate infusion (CRI) was administered intravenously (IV). Sevoflurane MAC was determined 20 minutes after CRI was initiated (MACpostdrug1), 30 minutes after MACpostdrug1 determination (MACpostdrug2) and after 1 week (MACb2). The MNT was determined at baseline (before anaesthesia), 3 and 7 days after anaesthesia. An increase of MACpostdrug2 ≥0.25% compared to MACpostdrug1 was considered evidence of AOT. A decrease in MNT at 3 and 7 days or an increase in MACb2 or both with respect to MACb1 were considered evidence of OIH.

RESULTS

Remifentanil CRI reduced sevoflurane MACpostdrug1 by 43.7% with respect to MACb1. MACpostdrug2 was no different from MACpostdrug1 with the saline (p = 0.62) or remifentanil (p = 0.78) treatments. No significant differences were observed in the saline (p = 0.99) or remifentanil (p = 0.99) treatments between MACb1 and MACb2, or for MNT values between baseline, 3 and 7 days.

CONCLUSION AND CLINICAL RELEVANCE

In dogs, under the study conditions, remifentanil efficacy in reducing sevoflurane MAC did not diminish in the short term, suggesting remifentanil did not induce AOT. Hyperalgesia was not detected 3 or 7 days after the administration of remifentanil. Contrary to data from humans and rodents, development of AOT or OIH in dogs is not supported by the findings of this study.

Remifentanil-Induced Secondary Hyperalgesia Is Not Prevented By Preoperative Acetazolamide Administration In Patients Undergoing Total Thyroidectomy: A Randomized Controlled Trial

Purpose

Acute administration of remifentanil may lead to opioid-induced hyperalgesia (OIH). Studies in mice suggest that OIH is mediated by impaired anionic homeostasis in spinal lamina I neurons due to a down-regulation of the K⁺-Cl⁻ co-transporter KCC2, which was reverted using acetazolamide (ACTZ), a carbonic anhydrase inhibitor. We propose that ACTZ prevents remifentanil-mediated OIH in humans.

Patients and methods

We conducted a randomized, double-blind, placebo-controlled clinical trial between December 2016 and September 2018. Patients were randomly allocated to receive ACTZ (250 mg of ACTZ 2 h before surgery) or placebo. To detect hyperalgesia, mechanical pain threshold (MPT) were measured before and after surgery using hand-held von Frey filaments in the forearm. Anesthesia was maintained with remifentanil at a target effect site of 4.5 ± 0.5 ng/mL, and sevoflurane at an end-tidal concentration of 0.8 MAC corrected for age.

Results

In total, 47 patients completed the study. Both groups were comparable in the baseline characteristics and intraoperative variables. Baseline MPT were similar in both groups. However, MPT in the forearm significantly diminished in the time in both groups. Finally, postoperative pain and morphine consumption were similar between groups.

Conclusion

Both groups developed remifentanil-mediated OIH at 12–18 h after surgery. However, ACTZ did not prevent the MPT reduction in patients undergoing total thyroidectomy.

Opioid-Mediated Modulation of Acid-Sensing Ion Channel Currents in Adult Rat Sensory Neurons

Muscle ischemia, associated with peripheral artery disease (PAD), leads to the release of proinflammatory mediators that decrease extracellular pH and trigger the activation of proton-activated acid-sensing ion channels (ASIC). Claudication pain, linked with low blood flow, can be partially relieved by endogenous opioid peptide release. However, we previously reported that sustained ASIC currents in dorsal root ganglion (DRG) neurons were enhanced by naturally occurring endomorphin-1 and -2 opioid peptides, indicating a role of opioid involvement in hyperalgesia. The present study examined whether clinically employed synthetic (fentanyl, remifentanil) and the semisynthetic opioid (oxycodone) would also potentiate sustained ASIC currents, which arise from ASIC3 channel isoforms. Here, we show that exposure of each opioid to DRG neurons resulted in potentiation of the sustained ASIC currents. On the other hand, the potentiation was not observed in DRG neurons from ASIC3 knockout rats. Further, the enhancement of the ASIC currents was resistant to pertussis toxin treatment, suggesting that Gα _i/Gα _o G-proteins are not involved. Additionally, the potentiation of sustained ASIC currents was greater in DRG neurons isolated from rats with ligated femoral arteries (a model of PAD). The effect of all three opioids on the transient ASIC peak current was mixed (increase, decrease, no effect). The inhibitory action appears to be mediated by the presence of ASIC1 isoform, while the potentiating effect is primarily due to ASIC3 isoform expression. These findings reveal that, under certain conditions, these three opioids can increase ASIC channel activity, possibly giving rise to opioid-induced hyperalgesia.

When pain gets stuck: the evolution of pain chronification and treatment resistance

It is well-recognized that, despite similar pain characteristics, some people with chronic pain recover, whereas others do not. In this review, we discuss possible contributions and interactions of biological, social, and psychological perturbations that underlie the evolution of treatment-resistant chronic pain. Behavior and brain are intimately implicated in the production and maintenance of perception. Our understandings of potential mechanisms that produce or exacerbate persistent pain remain relatively unclear. We provide an overview of these interactions and how differences in relative contribution of dimensions such as stress, age, genetics, environment, and immune responsivity may produce different risk profiles for disease development, pain severity, and chronicity. We propose the concept of "stickiness" as a soubriquet for capturing the multiple influences on the persistence of pain and pain behavior, and their stubborn resistance to therapeutic intervention. We then focus on the neurobiology of reward and aversion to address how alterations in synaptic complexity, neural networks, and systems (eg, opioidergic and dopaminergic) may contribute to pain stickiness. Finally, we propose an integration of the neurobiological with what is known about environmental and social demands on pain behavior and explore treatment approaches based on the nature of the individual's vulnerability to or protection from allostatic load.

Electroacupuncture Treatment Alleviates the Remifentanil-Induced Hyperalgesia by Regulating the Activities of the Ventral Posterior Lateral Nucleus of the Thalamus Neurons in Rats

Mechanisms underlying remifentanil- (RF-) induced hyperalgesia, a phenomenon that is generally named as opioid-induced hyperalgesia (OIH), still remain elusive. The ventral posterior lateral nucleus (VPL) of the thalamus, a key relay station for the transmission of nociceptive information to the cerebral cortex, is activated by RF infusion. Electroacupuncture (EA) is an effective method for the treatment of pain. This study aimed to explore the role of VPL in the development of OIH and the effect of EA treatment on OIH in rats. RF was administered to rats via the tail vein for OIH induction. Paw withdrawal threshold (PWT) in response to mechanical stimuli and paw withdrawal latency (PWL) to thermal stimulation were tested in rats for the assessment of mechanical allodynia and thermal hyperalgesia, respectively. Spontaneous neuronal activity and local field potential (LFP) in VPL were recorded in freely moving rats using the in vivo multichannel recording technique. EA at 2 Hz frequency (pulse width 0.6 ms, 1-3 mA) was applied to the bilateral acupoints "Zusanli" (ST.36) and "Sanyinjiao" (SP.6) in rats. The results showed that both the PWT and PWL were significantly decreased after RF infusion to rats. Meanwhile, both the spontaneous neuronal firing rate and the theta band oscillation in VPL LFP were increased on day 3 post-RF infusion, indicating that the VPL may promote the development of RF-induced hyperalgesia by regulating the pain-related cortical activity. Moreover, 2 Hz-EA reversed the RF-induced decrease both in PWT and PWL of rats and also abrogated the RF-induced augmentation of the spontaneous neuronal activity and the power spectral density (PSD) of the theta band oscillation in VPL LFP. These results suggested that 2 Hz-EA attenuates the remifentanil-induced hyperalgesia via reducing the excitability of VPL neurons and the low-frequency (theta band) oscillation in VPL LFP.

The Effect of Ondansetron on Acute Opioid Tolerance in Patients Receiving Intrathecal Opioids Prior to Cesarean Delivery

BACKGROUND

Multiple animal studies suggest that ondansetron ameliorates opioid-induced hyperalgesia and tolerance. In this study, we aimed to determine if the administration of ondansetron prior to spinal anesthesia would have an effect on intrathecal opioid-induced acute opioid tolerance, postoperative pain, and analgesic requirements in patients undergoing cesarean delivery with spinal anesthesia.

METHODS

Eighty-six patients undergoing elective cesarean delivery were recruited and randomly allocated to receive either 8 mg intravenous ondansetron (n = 44) or placebo (n = 42) in a prospective, double-blind design. All patients received spinal anesthesia consisting of 15 mg bupivacaine, 20 μg of fentanyl, and 100 μg of preservative-free morphine. We used linear mixed-effects models to assess the difference in pain and opioid consumption in the first 24 hours after surgery between the 2 groups.

RESULTS

No differences between the 2 groups were found in age, body mass index, American Society of Anesthesiologists physical status scores, duration of surgery, or sensory and motor block characteristics. There was no difference between the 2 groups in postoperative pain scores (P = 0.95) or opioid consumption (P = 0.68).

CONCLUSIONS

In patients undergoing cesarean delivery under spinal anesthesia with intrathecal opioids, the administration of ondansetron prior to spinal anesthesia did not significantly affect postoperative pain scores or opioid consumption. Thus, the administration of ondansetron did not have an effect on acute opioid tolerance in our study.

Effects of Ketamine on Postoperative Pain After Remifentanil-Based Anesthesia for Major and Minor Surgery in Adults: A Systematic Review and Meta-Analysis

Ketamine, an N-methyl-D-aspartate (NMDA) receptor antagonist, has been postulated as an adjuvant analgesic for preventing remifentanil-induced hyperalgesia after surgery. This systematic review and meta-analysis aims to assess the effectiveness of ketamine [racemic mixture and S-(+)-ketamine] in reducing morphine consumption and pain intensity scores after remifentanil-based general anesthesia. We performed a literature search of the PubMed, Web of Science, Scopus, Cochrane, and EMBASE databases in June 2017 and selected randomized controlled trials using predefined inclusion and exclusion criteria. To minimize confounding and heterogeneity, studies of NMDA receptor antagonists other than ketamine were excluded and the selected studies were grouped into those assessing minor or major surgery. Methodological quality was evaluated with the PEDro and JADA scales. The data were extracted and meta-analyses were performed where possible. Twelve RCTs involving 156 adults who underwent minor surgery and 413 adults who underwent major surgery were included in the meta-analysis. When used as an adjuvant to morphine, ketamine reduced postoperative morphine consumption in the first 24 h and postoperative pain intensity in the first 2 h in the minor and major surgery groups. It was also associated with significantly reduced pain intensity in the first 24 h in the minor surgery group. Time to the first rescue analgesia was longer in patients who received ketamine and underwent major surgery. No significant differences in the incidence of ketamine-related adverse effects were observed among patients in the intervention group and controls. This systematic review and meta-analysis show that low-dose (≤0.5 mg/kg for iv bolus or ≤5 μg/kg/min for iv perfusion) of ketamine reduces postoperative morphine consumption and pain intensity without increasing the incidence of adverse effects.

Perioperative Management of Patients with Addiction to Opioid and Non-opioid Medications

PURPOSE OF REVIEW

With the rise of the opioid epidemic, anesthesiologists will find themselves faced with opioid-addicted patients more frequently. Addiction to opioids may also occur concurrently with abuse of other non-opioid medications. Our review article seeks to outline an armamentarium of pain management strategies in the perioperative period for these patients with addiction to opioid and non-opioid medications.

RECENT FINDINGS

Statistics from the CDC demonstrate a shocking increase in opioid prescription rates and opioid-related deaths. Furthermore, opioid-addicted patients have notoriously undertreated pain in the perioperative period. A multitude of strategies are available in the perioperative period to treat pain in these patients. Formulating treatment plans for opioid and non-opioid-addicted patients undergoing surgery should include considerations in the pre-, intra-, and post-operative period. Our review article outlines several non-opioid modalities which may be employed to treat pain in these patients; however, particularly in the opioid-addicted population, the practitioner must be aware that non-opioids alone may not suffice to treat post-surgical pain. Consultation with pain management may be warranted to optimize opioid and non-opioid treatment for these patients.

Opioid-induced hyperalgesia in clinical anesthesia practice: what has remained from theoretical concepts and experimental studies?

PURPOSE OF REVIEW

This article reviews the phenomenon of opioid-induced hyperalgesia (OIH) and its implications for clinical anesthesia. The goal of this review is to give an update on perioperative prevention and treatment strategies, based on findings in preclinical and clinical research.

RECENT FINDINGS

Several systems have been suggested to be involved in the pathophysiology of OIH with a focus on the glutaminergic system. Very recently preclinical data revealed that peripheral μ-opioid receptors (MORs) are key players in the development of OIH and acute opioid tolerance (AOT). Peripheral MOR antagonists could, thus, become a new prevention/treatment option of OIH in the perioperative setting. Although the impact of OIH on postoperative pain seems to be moderate, recent evidence suggests that increased hyperalgesia following opioid treatment correlates with the risk of developing persistent pain after surgery. In clinical practice, distinction among OIH, AOT and acute opioid withdrawal remains difficult, especially because a specific quantitative sensory test to diagnose OIH has not been validated yet.

SUMMARY

Since the immediate postoperative period is not ideal to initiate long-term treatment for OIH, the best strategy is to prevent its occurrence. A multimodal approach, including choice of opioid, dose limitations and addition of nonopioid analgesics, is recommended.