Remifentanil-acute opioid tolerance and opioid-induced hyperalgesia: a systematic review. Am J Ther. 2015;22:e62-e74. [PMID: 25830866 DOI: 10.1097/mjt.0000000000000019]

Remifentanil-induced inflammation in microglial cells: Activation of the PAK4-mediated NF-κB/NLRP3 pathway and onset of hyperalgesia

BACKGROUND

The perioperative use of remifentanil is associated with postoperative hyperalgesia, which can impair recovery and extend hospitalization. Recent studies have revealed that microglia-mediated activation of the NLRP3 inflammasome plays a critical role in opioid-induced hyperalgesia, with NF-κB acting as a pivotal activation point for NLRP3. Despite these findings, the specific molecular mechanisms underlying remifentanil-induced postoperative hyperalgesia remain unclear. This study aims to develop a model of remifentanil-induced hyperalgesia and investigate the molecular mechanisms, focusing on the NF-κB/NLRP3 pathway, using both in vitro and in vivo approaches.

METHOD

We established a remifentanil-induced hyperalgesia model and performed proteomic analysis to identify differential protein expression in the spinal cord tissue of rats. NLRP3 or PAK4 antagonists were administered intrathecally in vivo, and mechanical pain thresholds in the hind paws were measured using Von Frey testing. In vitro, we applied NLRP3 or PAK4 inhibitors or used lentivirus infection to silence PAK4, NF-κB, and NLRP3 genes. Protein expression was assessed through immunohistochemistry, immunofluorescence, and Western blotting. Additionally, ELISA was performed to measure IL-1β and IL-18 levels, and RT-qPCR was conducted to evaluate the transcription of target genes.

RESULTS

Proteomic analysis revealed that remifentanil upregulates PAK4 protein in spinal cord tissue two hours after the surgery. In addition, remifentanil induces morphological changes in the spinal cord dorsal horn, characterized by increased expression of PAK4, p-p65, NLRP3 and Iba-1 proteins, which in turn leads to elevated IL-1β and IL-18 levels and an inflammatory response. Intrathecal injection of NLRP3 or PAK4 inhibitors mitigates remifentanil-induced hyperalgesia and associated changes. In vitro, downregulation of PAK4 inhibits the increase in PAK4, p-p65, NLRP3 and Caspase-1 induced by LPS. Conversely, the downregulation of NLRP3 does not impact the levels of PAK4 and p-p65 proteins, aligning with the in vivo results and suggesting that PAK4 acts as an upstream signaling molecule of NLRP3.

CONCLUSION

Remifentanil can increase PAK4 expression in spinal cord dorsal horn cells by activating the NF-κB/NLRP3 pathway and mediating microglial activation, thereby contributing to postoperative hyperalgesia.

Peri-operative pain management in adults: a multidisciplinary consensus statement from the Association of Anaesthetists and the British Pain Society

BACKGROUND

Nearly half of adult patients undergoing surgery experience moderate or severe postoperative pain. Inadequate pain management hampers postoperative recovery and function and may be associated with adverse outcomes. This multidisciplinary consensus statement provides principles that might aid postoperative recovery, and which should be applied throughout the entire peri-operative pathway by healthcare professionals, institutions and patients.

METHODS

We conducted a directed literature review followed by a four-round modified Delphi process to formulate recommendations for organisations and individuals.

RESULTS

We make recommendations for the entire peri-operative period, covering pre-admission; admission; intra-operative; post-anaesthetic care unit; ward; intensive care unit; preparation for discharge; and post-discharge phases of care. We also provide generic principles of peri-operative pain management that clinicians should consider throughout the peri-operative pathway, including: assessing pain to facilitate function; use of multimodal analgesia, including regional anaesthesia; non-pharmacological strategies; safe use of opioids; and use of protocols and training for staff in caring for patients with postoperative pain.

CONCLUSIONS

We hope that with attention to these principles and their implementation, outcomes for adult patients having surgery might be improved.

Optimizing Pediatric Sedation: Evaluating Remimazolam and Dexmedetomidine for Safety and Efficacy in Clinical Practice

Daily, children undergo countless investigations and interventions, which require sedation and immobilization to ensure safety and accuracy. This remains associated with a persistent risk of sedation-induced life-threatening events as children are particularly vulnerable to adverse medical events and complications. Consequently, there is an urgent need to increase the safety of pediatric sedation and anesthesia. An ideal approach involves the use of drugs with fewer intrinsic side effects. In this context, on the basis of their pharmacokinetic properties, remimazolam (RMZ) and dexmedetomidine (DEX) were evaluated for their suitability as ideal sedatives. RMZ and DEX, both of which are currently available in pediatric medicine, have shown great promise in initial publications. To date, only very limited data concerning RMZ in small children are available. RMZ is a novel, ultrashort-acting benzodiazepine that is metabolized by tissue esterase, largely independent of organ function. It has a context-sensitive half-life of approximately 10 min, with minimal accumulation even with prolonged use. Its effects can be completely reversed with flumazenil. DEX, an isomer of medetomidine, is a potent α2-receptor-agonist with multiple indications in anesthesia and intensive care medicine. It has coanalgesic potential, allows for 'arousal sedations' and has a low profile for cardiorespiratory side effects. DEX is metabolized in the liver and is predominantly excreted renally. Both drugs show potential in the prevention and treatment of delirium, with DEX having additional neuroprotective effects. DEX and RMZ possess several properties of an optimal sedative, including clinically insignificant main metabolites and a broad dosage range, indicating their potential to reduce the incidence of sedation-related life-threatening events in children. However, further clinical research is necessary to better evaluate their potential risks.

Postoperative pain at Landspitali: A prospective study

BACKGROUND

Moderate or severe postoperative pain is common despite advances in surgical technique and perioperative analgesia. This study aimed to assess the prevalence and severity of postoperative pain following procedures requiring anaesthesia and identify factors associated with increased risk of postoperative pain.

METHODS

Surgical patients ≥18 years of age were prospectively questioned on level of current pain on a numerical rating scale (NRS) from 0 to 10 in the post-anaesthesia care unit (PACU) and on resting, active and worst pain experienced in the first 24 h postoperatively. Clinical data was obtained from medical records. Descriptive statistics were applied, and predictors of worst pain assessed as moderate/severe (NRS ≥ 5) on postoperative day one were assessed using multivariable logistic regression.

RESULTS

Of 438 included participants, moderate/severe pain occurred in 29% on the day of surgery and 70% described their worst pain as moderate/severe on postoperative day one. Procedures with the highest incidence of moderate/severe pain on the day of surgery were gynaecology-, plastic-, abdominal-, breast-, and orthopaedic procedures. On postoperative day one, patients undergoing vascular-, orthopaedic-, and abdominal operations most commonly rated their worst pain as moderate/severe. Female sex (OR = 2.15, 95% Cl 1.21-3.88, p = .010), chronic preoperative pain (OR = 4.20, 95% Cl 2.41-7.51, p < .001), undergoing a major procedure (OR = 2.07, 95% Cl 1.15-3.80, p = .017), and any intraoperative remifentanil administration (OR = 2.16, 95% Cl 1.20-3.94, p = .01) had increased odds of rating the worst pain as moderate/severe. Increased age (OR = 0.66 per 10 years (95% Cl 0.55-0.78, p < .001)) and undergoing breast-, gynaecology-, otolaryngology-, and neurosurgery (OR = 0.15-0.34, p < .038) was associated with lower odds of moderate/severe pain on postoperative day one.

DISCUSSION

In our cohort, patients rated their current pain in the PACU similarly to other studies. However, the ratio of patients rating the worst pain experienced as moderate/severe on postoperative day one was relatively high. The identified patient- and procedural-related factors associated with higher odds of postoperative pain highlight a subgroup of patients who may benefit from enhanced perioperative monitoring and pain management strategies.

Effect of Remimazolam on Pain Perception and Opioid-Induced Hyperalgesia in Patients Undergoing Laparoscopic Urologic Surgery-A Prospective, Randomized, Controlled Study

Background and Objectives: The effects of midazolam, a benzodiazepine, on pain perception are complex on both spinal and supraspinal levels. It is not yet known whether remimazolam clinically attenuates or worsens pain. The present study investigated the effect of intraoperative remimazolam on opioid-induced hyperalgesia (OIH) in patients undergoing general anesthesia. Materials and Methods: The patients were randomized into three groups: group RHR (6 mg/kg/h initial dose followed by 1 mg/kg/h remimazolam and 0.3 μg /kg/min remifentanil), group DHR (desflurane and 0.3 μg /kg/min remifentanil) or group DLR (desflurane and 0.05 µg/kg /min remifentanil). The primary outcome was a mechanical hyperalgesia threshold, while secondary outcomes included an area of hyperalgesia and clinically relevant pain outcomes. Results: Group RHR had a higher mechanical hyperalgesia threshold, a smaller hyperalgesia postoperative area at 24 h, a longer time to first rescue analgesia (p = 0.04), lower cumulative PCA volume containing morphine postoperatively consumed for 24 h (p < 0.01), and lower pain intensity for 12 h than group DHR (p < 0.001). However, there was no significant difference in OIH between groups RHR and DLR. Conclusions: Group RHR, which received remimazolam, attenuated OIH, including mechanically evoked pain and some clinically relevant pain outcomes caused by a high dose of remifentanil. Further research is essential to determine how clinically meaningful and important the small differences observed between the two groups are.

Variation in Intraoperative Opioid Administration by Patient, Clinician, and Hospital Contribution

Importance

The opioid crisis has led to scrutiny of opioid exposures before and after surgical procedures. However, the extent of intraoperative opioid variation and the sources and contributing factors associated with it are unclear.

Objective

To analyze attributable variance of intraoperative opioid administration for patient-, clinician-, and hospital-level factors across surgical and analgesic categories.

Design, Setting, and Participants

This cohort study was conducted using electronic health record data collected from a national quality collaborative database. The cohort consisted of 1 011 268 surgical procedures at 46 hospitals across the US involving 2911 anesthesiologists, 2291 surgeons, and 8 surgical and 4 analgesic categories. Patients without ambulatory opioid prescriptions or use history undergoing an elective surgical procedure between January 1, 2014, and September 11, 2020, were included. Data were analyzed from January 2022 to July 2023.

Main Outcomes and Measures

The rate of intraoperative opioid administration as a continuous measure of oral morphine equivalents (OMEs) normalized to patient weight and case duration was assessed. Attributable variance was estimated in a hierarchical structure using patient, clinician, and hospital levels and adjusted intraclass correlations (ICCs).

Results

Among 1 011 268 surgical procedures (mean [SD] age of patients, 55.9 [16.2] years; 604 057 surgical procedures among females [59.7%]), the mean (SD) rate of intraoperative opioid administration was 0.3 [0.2] OME/kg/h. Together, clinician and hospital levels contributed to 20% or more of variability in intraoperative opioid administration across all analgesic and surgical categories (adjusting for surgical or analgesic category, ICCs ranged from 0.57-0.79 for the patient, 0.04-0.22 for the anesthesiologist, and 0.09-0.26 for the hospital, with the lowest ICC combination 0.21 for anesthesiologist and hosptial [0.12 for the anesthesiologist and 0.09 for the hospital for opioid only]). Comparing the 95th and fifth percentiles of opioid administration, variation was 3.3-fold among anesthesiologists (surgical category range, 2.7-fold to 7.7-fold), 4.3-fold among surgeons (surgical category range, 3.4-fold to 8.0-fold), and 2.2-fold among hospitals (surgical category range, 2.2-fold to 4.3-fold). When adjusted for patient and surgical characteristics, mean (square error mean) administration was highest for cardiac surgical procedures (0.54 [0.56-0.52 OME/kg/h]) and lowest for orthopedic knee surgical procedures (0.19 [0.17-0.21 OME/kg/h]). Peripheral and neuraxial analgesic techniques were associated with reduced administration in orthopedic hip (51.6% [95% CI, 51.4%-51.8%] and 60.7% [95% CI, 60.5%-60.9%] reductions, respectively) and knee (48.3% [95% CI, 48.0%-48.5%] and 60.9% [95% CI, 60.7%-61.1%] reductions, respectively) surgical procedures, but reduction was less substantial in other surgical categories (mean [SD] reduction, 13.3% [8.8%] for peripheral and 17.6% [9.9%] for neuraxial techniques).

Conclusions and Relevance

In this cohort study, clinician-, hospital-, and patient-level factors had important contributions to substantial variation of opioid administrations during surgical procedures. These findings suggest the need for a broadened focus across multiple factors when developing and implementing opioid-reducing strategies in collaborative quality-improvement programs.

Opioid infusions at different times of the day produce varying degrees of opioid-induced hyperalgesia

BACKGROUND

Opioids are metabolised by enzymes the activities of which vary with the circadian rhythm. We examined whether opioid infusions administered at different times of the day produce varying degrees of opioid-induced hyperalgesia (OIH) in animal experiments and clinical studies.

METHODS

Male Sprague-Dawley rats received remifentanil infusions (1 μg kg-1·min-1 for 1 h) at Zeitgeber times (ZT) 0, 4, 8, 12, 16, or 20 h. Rhythmicity of mechanical hypersensitivity was assayed after the infusion. Mechanical hypersensitivity, drug concentration, and metabolic enzyme activity of Wistar rats that received sufentanil (10 μg kg-1; four consecutive i.p. injections at 15-min intervals) or remifentanil infusion at ZT0 or ZT8 were assayed. Sixty patients who underwent abdominal laparoscopic surgery under general anaesthesia received remifentanil infusion (0.15 μg kg-1 min-1) and sufentanil injection (0.2 μg kg-1) at induction and skin incision, respectively. Postoperative pressure pain sensitivity, pain Numeric Rating Scale (NRS), drug concentrations, and nonspecific esterase activity were assessed.

RESULTS

Sprague-Dawley rats that received remifentanil infusion exhibited a robust rhythmic paw withdrawal threshold (JTK_CYCLE: P=0.001, Q=0.001, Phase=26). Wistar rats infused with remifentanil or sufentanil at ZT8 exhibited greater OIH (P<0.001) than those infused at ZT0, with higher blood concentrations (P<0.001) and lower metabolic enzyme activities (P=0.026 and P=0.028, respectively). Patients in the afternoon group exhibited higher pressure pain sensitivity at forearm (P=0.002), higher NRS (P<0.05), higher drug concentrations (sufentanil: P=0.037, remifentanil: P=0.005), and lower nonspecific esterase activity (P=0.024) than the morning group.

CONCLUSIONS

Opioid infusions administered at different times of day produced varying degrees of OIH, possibly related to circadian rhythms of metabolic enzyme activities.

CLINICAL TRIAL REGISTRATION

NCT05234697.

Pupillary monitoring decreases remifentanil consumption during laparoscopic uterine surgery and improves postoperative recovery

BACKGROUND

The aim of this paper was to explore pupillary monitoring for determining remifentanil consumption during general anesthesia and evaluating postoperative recovery quality.

METHODS

Eighty patients undergoing elective laparoscopic uterine surgery were randomly divided into pupillary monitoring group (Group P) and control group (Group C). In Group P, remifentanil dosage during general anesthesia was determined according to pupil dilation reflex; in Group C, it was adjusted according to hemodynamic changes. Intraoperative remifentanil consumption and endotracheal tube extraction time were recorded. The Numerical Rating Scale (NRS) Score, hemodynamic changes, and opioid-related adverse reactions in the post-anesthesia care unit were also recorded. The parameters of pupil light reflex from extubation to 30 min after extubation were analyzed in Group P, and the responsiveness of these parameters and hemodynamic changes to NRS was determined by ROC curve analyses.

RESULTS

Compared with Group C, in Group P, intraoperative remifentanil consumption, the NRS Score at 20 minutes after extubation, extubation time, and the incidence of nausea, vomiting, and respiratory amnesia were all significantly decreased (all, P<0.05). In Group P, ∆HR and ∆MAP had no value in judging the change of NRS. The ROC values and diagnostic cutoff values of ΔInit, ΔACV, and ΔMCV responding to NRS variation were 0.775 (95% CI: 0.582-0.968), 0.734(95% CI: 0.537-0.930), and 0.822 (95% CI: 0.648-0.997) and 0.21 (sensitivity, 92.3%; specificity, 23.1%), -1.3 (sensitivity, 92.3%; specificity, 18.3%), and -1.0 (sensitivity, 84.6%; specificity, 17.7%), respectively.

CONCLUSIONS

Intraoperative pupil dilation reflex monitoring can reduce remifentanil consumption and improve postoperative recovery quality. Furthermore, postoperative pupil light reflex monitoring can help evaluate pain degree with high sensitivity.

Pharmacological Treatments and Therapeutic Drug Monitoring in Patients with Chronic Pain

Pain is an unpleasant sensory and emotional experience that affects every aspect of a patient's life and which may be treated through different pharmacological and non-pharmacological approaches. Analgesics are the drugs most commonly used to treat pain, and in specific situations, the use of opioids may be considered with caution. These drugs, in fact, do not always induce optimal analgesia in patients, and several problems are associated with their use. The purpose of this narrative review is to describe the pharmacological approaches currently used for the management of chronic pain. We review several aspects, from the pain-scale-based methods currently available to assess the type and intensity of pain, to the most frequently administered drugs (non-narcotic analgesics and narcotic analgesics), whose pharmacological characteristics are briefly reported. Overall, we attempt to provide an overview of different pharmacological treatments while also illustrating the relevant guidelines and indications. We then report the strategies that may be used to reduce problems related to opioid use. Specifically, we focus our attention on therapeutic drug monitoring (TDM), a tool that could help clinicians select the most suitable drug and dose to be used for each patient. The actual potential of using TDM to optimize and personalize opioid-based pain treatments is finally discussed based on recent scientific reports.

Long-Term Exposure to Morphine Induces Cross-Tolerance to Acute Antinociceptive Effect of Remifentanil on Somatic and Visceral Stimuli in Rats

Purpose

Remifentanil is one of the most commonly used opioids intraoperatively. Previous reports indicate that long-term use of opioids may lead to cross-tolerance to remifentanil, which poses a challenge in the control of acute pain intraoperatively. However, there is limited information regarding cross-tolerance to remifentanil, especially in visceral pain. Therefore, this study aimed to examine cross-tolerance to remifentanil in somatic and visceral tolerance using morphine-tolerant rats.

Methods

Six male Sprague-Dawley rats were allocated to the morphine and saline groups each. Tolerance to the antinociceptive effect of morphine was induced in rats in the morphine group. Remifentanil was continuously infused intravenously at 10 mcg/kg/min for 120 min to assess cross-tolerance from morphine to remifentanil. The antinociceptive effects on somatic and visceral nociceptive stimuli were measured using the tail-flick (TF) and colorectal distension (CD) tests, respectively. The antinociceptive efficacy was evaluated by converting the response threshold to the percentage maximal possible effect (%MPE).

Results

Remifentanil increased the %MPE in the morphine and saline groups in both the tests; however, the increase in %MPE was attenuated significantly in the morphine group compared with that in the saline group at 60, 90, and 120 min (all P < 0.01) in the TF test and at 90 and 120 min in the CD test (all P <0.05).

Conclusion

Our results indicate that morphine-tolerant rats exhibit cross-tolerance to remifentanil's acute antinociceptive effects on somatic and visceral stimuli. Cross-tolerance to remifentanil should be considered in the perioperative management of patients using morphine.

Thalamocortical circuits drive remifentanil-induced postoperative hyperalgesia

Remifentanil-induced hyperalgesia (RIH) is a severe but common postoperative clinical problem with elusive underlying neural mechanisms. Here, we discovered that glutamatergic neurons in the thalamic ventral posterolateral nucleus (VPLGlu) exhibited significantly elevated burst firing accompanied by upregulation of Cav3.1 T-type calcium channel expression and function in RIH model mice. In addition, we identified a glutamatergic neuronal thalamocortical circuit in the VPL projecting to hindlimb primary somatosensory cortex glutamatergic neurons (S1HLGlu) that mediated RIH. In vivo calcium imaging and multi-tetrode recordings revealed heightened S1HLGlu neuronal activity during RIH. Moreover, preoperative suppression of Cav3.1-dependent burst firing in VPLGlu neurons or chemogenetic inhibition of VPLGlu neuronal terminals in the S1HL abolished the increased S1HLGlu neuronal excitability while alleviating RIH. Our findings suggest that remifentanil induces postoperative hyperalgesia by upregulating T-type calcium channel-dependent burst firing in VPLGlu neurons to activate S1HLGlu neurons, thus revealing an ion channel-mediated neural circuit basis for RIH that can guide analgesic development.

Effectiveness of two extended-release buprenorphine formulations during postoperative period in neonatal rats

Information on the effectiveness of a new long-lasting buprenorphine formulation, extended-release buprenorphine, in the neonatal rat is very limited. This study compares whether a high dose of extended-release buprenorphine (XR-Hi) attenuates thermal hypersensitivity for a longer period than a low dose of extended-release buprenorphine (XR-Lo) in a neonatal rat incisional pain model. Two experiments were performed. Experiment one: Male and female postnatal day-5 rat pups (n = 38) were randomly assigned to 1 of 4 treatment groups and received a subcutaneous administration of one of the following: 1) 0.9%NaCl (Saline), 0.1 mL; 2) sustained release buprenorphine (Bup-SR), 1 mg/kg; 3) XR-Lo, 0.65 mg/kg; and 4) XR-Hi, 1.3 mg/kg. Pups were anesthetized with sevoflurane in 100% O₂ and a 5 mm long skin incision was made over the left lateral thigh and underlying muscle dissected. The skin was closed with surgical tissue glue. Thermal hypersensitivity testing (using a laser diode) and clinical observations were conducted 1 hour (h) prior to surgery and subsequently after 1, 4, 8, 24, 48, 72 h of treatment. Experiment two: The plasma buprenorphine concentration level was evaluated at 1, 4, 8, 24, 48, 72 h on five-day-old rat pups. Plasma buprenorphine concentration for all treatment groups remained above the clinically effective concentration of 1 ng/mL for at least 4 h in the Bup-SR group, 8 h in XR-Lo and 24 h in XR-Hi group with no abnormal clinical observations. This study demonstrates that XR-Hi did not attenuate postoperative thermal hypersensitivity for a longer period than XR-Lo in 5-day-old rats; XR-Hi attenuated postoperative thermal hypersensitivity for up to 4 h while Bup-SR and XR-Lo for at least 8 h in this model.

The Effects of Remifentanil and Fentanyl on Emergence Agitation in Pediatric Strabismus Surgery

Emergence agitation (EA) is one of the main concerns in the field of pediatric anesthesia using sevoflurane. We investigated the effects of remifentanil and fentanyl on the incidence of EA in pediatric patients undergoing strabismus surgery. Ninety children were randomly allocated into two groups and received either remifentanil (group R: intraoperatively remifentanil 0.2 μg/kg/min) or fentanyl (group F: fentanyl 2 μg/kg at anesthetic induction) intraoperatively. After surgery, EA incidence was assessed using a four-point agitation scale and Pediatric Anesthesia Emergence Delirium (PAED) scale in the post-anesthesia care unit. Face, leg, activity, cry, and consolability (FLACC) scores for postoperative pain were also assessed. The incidence of EA using the four-point agitation scale (scores ≥ 3) was similar in both groups (remifentanil group, 28.89% vs. fentanyl group, 24.44%). Similar results were obtained using the PAED scale (scores > 12), with an incidence of 33.33% in the remifentanil group and 26.67% in the fentanyl group. Differences in FLACC scores were not found to be statistically significant. A single bolus administration of fentanyl during anesthetic induction and continuous infusion of remifentanil during surgery had similar effects on the EA incidence in these pediatric patients.

Comparison of Intraoperative Infusion of Remifentanil Versus Fentanyl on Pain Management in Patients Undergoing Spine Surgery: A Double Blinded Randomized Clinical Trial

Background

Remifentanil is an ultra-short-acting opioid which facilitates hemodynamic management. However, there are concerns about postoperative Remifentanil hyperalgesia because of its potent fast onset and offset.

Objectives

The aim of this study was to determine visual analog scale (VAS), postoperative pain, and morphine used in two groups after spine surgery.

Methods

In this randomized clinical trial study, 60 patients aged 18 - 60 years old, according to the American Society of Anesthesiology (ASA) I - II, who underwent spinal canal stenosis or scoliosis surgery, were divided into two groups. In the control group, patients received 0.07 - 0.1 µg/kg/h intraoperative Fentanyl infusion, and in the intervention group 0.1 - 0.2 µg/kg/min remifentanil was infused during the surgery. Both groups received 15 mg/kg intravenous Acetaminophen 20 minutes before the end of the surgery. Postoperative pain score and morphine consumption were measured 6, 12, 24, and 48 hours after discharge from the post-anesthesia care unit (PACU).

Results

During the first 12 hours, VAS and morphine consumption were significantly higher in remifentanil group (P < 0.001). However, no significant difference was found between the two groups in morphine consumption 12 - 48 hours after surgery.

Conclusions

These findings suggest that Remifentanil infusion during surgery may increase postoperative pain. Also, VAS and morphine consumption were higher during the first 12 hours.

Postoperative Drip-Infusion of Remifentanil Reduces Postoperative Pain-A Retrospective Observative Study

Development of remifentanil-induced hyperalgesia (RIH) postoperatively is an unpleasant experience that requires further treatment. This study assessed the effects of gradual withdrawal combined with drip infusion of remifentanil on postoperative pain and the requirement for rescue analgesics. A total of 559 patients receiving total intravenous anesthesia with propofol and remifentanil were enrolled. All patients either underwent gradual withdrawal of remifentanil (GWR) or gradual withdrawal combined with drip infusion (GWDR) with a dose of 1 mcg·kg⁻¹ for 30 min after extubation. The numeric rating scale (NRS) and the requirement of rescue analgesics were assessed. The requirement for rescue analgesics was significantly lower in the GWDR group than in the GWR group (13.2% vs. 35.7%; p < 0.001). At the post-anesthetic care unit (PACU), patients in the GWDR group had a lower NRS pain score (p < 0.001). In addition, in the postoperative 2nd hour, patients in the GWDR group had a significantly lower NRS than the GWR group (beta, −0.31; p = 0.003). No remifentanil-related adverse effects were observed. We found that gradual withdrawal combined with drip infusion of remifentanil required less rescue analgesics and reduced pain scores. The new way of remifentanil administration may be effective to prevent RIH.

Mechanisms, diagnosis, prevention and management of perioperative opioid-induced hyperalgesia

Opioid-induced hyperalgesia (OIH) occurs when opioids paradoxically enhance the pain they are prescribed to ameliorate. To address a lack of perioperative awareness, we present an educational review of clinically relevant aspects of the disorder. Although the mechanisms of OIH are thought to primarily involve medullary descending pathways, it is likely multifactorial with several relevant therapeutic targets. We provide a suggested clinical definition and directions for clinical differentiation of OIH from other diagnoses, as this may be confusing but is germane to appropriate management. Finally, we discuss prevention including patient education and analgesic management choices. As prevention may serve as the best treatment, patient risk factors, opioid mitigation, and both pharmacologic and non-pharmacologic strategies are discussed.

Comparison of Pupillometry With Surgical Pleth Index Monitoring on Perioperative Opioid Consumption and Nociception During Propofol-Remifentanil Anesthesia: A Prospective Randomized Controlled Trial

BACKGROUND

Intraoperative monitoring with pupillometry has shown promising results for nociception/antinociception balance monitoring. However, its benefits in clinical practice remain unproven. The aim of this study was to evaluate the efficacy of intraoperative pupillometry monitoring on intraoperative opioid consumption and postoperative pain compared to surgical pleth index (SPI), another widely investigated monitoring.

METHODS

American Society of Anesthesiologists (ASA) I-II patients scheduled for elective laparoscopic cholecystectomy were included. This prospective, parallel-arm, single-center study was conducted in 2 steps. First, we evaluated the feasibility of using pupillometry and SPI monitoring compared with conventional hemodynamic monitoring. Next, a parallel-arm, double-blind randomized study compared the peak postoperative pain measured with numerical rating scale (NRS) from 0 (no pain) to 10 (extreme pain) as a primary outcome between pupillometry (pupillometry group, n = 43) and SPI monitoring (SPI group, n = 43) using Mann-Whitney U test. Secondary outcomes included intraoperative remifentanil consumption, postoperative opioid responsiveness (a decrease in NRS by ≥1 after fentanyl administrations), number of analgesic administrations, and opioid-related complications.

RESULTS

In the preliminary study (n = 50), remifentanil consumption was less under pupillometry monitoring compared to SPI monitoring, and peak postoperative pain was lower under pupillometry compared to conventional monitoring. In the main study (n = 86), peak postoperative pain and intraoperative remifentanil consumption were lower in the pupillometry group (median [first to third quartile], 5 [4-6]; mean ± standard deviation [SD], 0.078 ± 0.019 μg·kg·minute) compared to the SPI group (7 [5-8] and 0.0130 ± 0.051 μg·kg·minute; P < .001), with the median difference in peak postoperative pain of -1 and its 95% confidence interval between -2 and -0.5. The pupillometry group had better responsiveness to fentanyl (84.6% vs 61.0%; P = .005) and lower number of analgesic administrations (2 [1-2] vs 2 [1-3]; P = .048) compared to the SPI group.

CONCLUSIONS

Intraoperative pupillometry monitoring reduced intraoperative remifentanil consumption and postoperative pain. It may be an alternative option for intraoperative opioid control under general anesthesia in adult patients.

Paralytics, Sedation, and Steroids in Acute Respiratory Distress Syndrome

In this article, we discuss the literature behind the use of paralytics, sedation, and steroids in acute respiratory distress syndrome. We explore the controversies and discuss the recommendations for the use of these agents.

Opioid-Induced Hyperalgesia Is Associated with Dysregulation of Circadian Rhythm and Adaptive Immune Pathways in the Mouse Trigeminal Ganglia and Nucleus Accumbens

The benefits of opioid-based treatments to mitigate chronic pain can be hindered by the side effects of opioid-induced hyperalgesia (OIH) that can lead to higher consumption and risk of addiction. The present study advances the understanding of the molecular mechanisms associated with OIH by comparing mice presenting OIH symptoms in response to chronic morphine exposure (OIH treatment) relative to control mice (CON treatment). Using RNA-Seq profiles, gene networks were inferred in the trigeminal ganglia (TG), a central nervous system region associated with pain signaling, and in the nucleus accumbens (NAc), a region associated with reward dependency. The biological process of nucleic acid processing was over-represented among the 122 genes that exhibited a region-dependent treatment effect. Within the 187 genes that exhibited a region-independent treatment effect, circadian rhythm processes were enriched among the genes over-expressed in OIH relative to CON mice. This enrichment was supported by the differential expression of the period circadian clock 2 and 3 genes (Per2 and Per3). Transcriptional regulators in the PAR bZip family that are influenced by the circadian clock and that modulate neurotransmission associated with pain and drug addiction were also over-expressed in OIH relative to CON mice. Also notable was the under-expression in OIH relative to CON mice of the Toll-like receptor, nuclear factor-kappa beta, and interferon gamma genes and enrichment of the adaptive immune processes. The results from the present study offer insights to advance the effective use of opioids for pain management while minimizing hyperalgesia.

Perioperative opioid analgesia-when is enough too much? A review of opioid-induced tolerance and hyperalgesia

Opioids are a mainstay of acute pain management but can have many adverse effects, contributing to problematic long-term use. Opioid tolerance (increased dose needed for analgesia) and opioid-induced hyperalgesia (paradoxical increase in pain with opioid administration) can contribute to both poorly controlled pain and dose escalation. Hyperalgesia is particularly problematic as further opioid prescribing is largely futile. The mechanisms of opioid tolerance and hyperalgesia are complex, involving μ opioid receptor signalling pathways that offer opportunities for novel analgesic alternatives. The intracellular scaffold protein β-arrestin-2 is implicated in tolerance, hyperalgesia, and other opioid side-effects. Development of agonists biased against recruitment of β-arrestin-2 could provide analgesic efficacy with fewer side-effects. Alternative approaches include inhibition of peripheral μ opioid receptors and blockade of downstream signalling mechanisms, such as the non-receptor tyrosine kinase Src or N-methyl-D-aspartate receptors. Furthermore, it is prudent to use multimodal analgesic regimens to reduce reliance on opioids during the perioperative period. In the third paper in this Series we focus on clinical and mechanism-based understanding of tolerance and opioid-induced hyperalgesia, and discuss current and future strategies for pain management.

Opioid-free anesthesia within an enhanced recovery after surgery pathway for minimally invasive lumbar spine surgery: a retrospective matched cohort study

OBJECTIVE

Enhanced recovery after surgery (ERAS) and multimodal analgesia are established care models that minimize perioperative opioid consumption and promote positive outcomes after spine surgery. Opioid-free anesthesia (OFA) is an emerging technique that may achieve similar goals. The purpose of this study was to evaluate an OFA regimen within an ERAS pathway for lumbar decompressive surgery and to compare perioperative opioid requirements in a matched cohort of patients managed with traditional opioid-containing anesthesia (OCA).

METHODS

The authors performed a retrospective analysis of prospectively collected data. They included 36 patients who underwent lumbar decompression under their ERAS pathway for spinal decompression between February and August 2018. Eighteen patients who received OFA were matched in a 1:1 ratio to a cohort managed with a traditional OCA regimen. The primary outcome was total perioperative opioid consumption. Postoperative pain scores (measured using the numerical rating scale [NRS]), opioid consumption (total morphine equivalents), and length of stay (time to readiness for discharge) were compared in the postanesthesia care unit (PACU). The authors also assessed compliance with ERAS process measures and compared compliance during 3 phases of care: pre-, intra-, and postoperative.

RESULTS

There was a significant reduction in total perioperative opioid consumption in patients who received OFA (2.43 ± 0.86 oral morphine equivalents [OMEs]; mean ± SEM), compared to patients who received OCA (38.125 ± 6.11 OMEs). There were no significant differences in worst postoperative pain scores (NRS scores 2.55 ± 0.70 vs 2.58 ± 0.73) or opioid consumption (5.28 ± 1.7 vs 4.86 ± 1.5 OMEs) in the PACU between OFA and OCA groups, respectively. There was a clinically significant decrease in time to readiness for discharge from the PACU associated with OFA (37 minutes), although this was not statistically significantly different. The authors found high overall compliance with ERAS process measures (91.4%) but variation in compliance according to phase of care. The highest compliance occurred during the preoperative phase (94.71% ± 2.88%), and the lowest compliance occurred during the postoperative phase of care (85.4% ± 5.7%).

CONCLUSIONS

OFA within an ERAS pathway for lumbar spinal decompression represents an opportunity to minimize perioperative opioid exposure without adversely affecting pain control or recovery. This study reveals opportunities for patient and provider education to reinforce ERAS and highlights the postoperative phase of care as a time when resources should be focused to increase ERAS adherence.

Role of spinal cyclooxygenase-2 and prostaglandin E2 in fentanyl-induced hyperalgesia in rats

BACKGROUND

Accumulated evidence suggests that spinal cyclooxygenase-2 (COX-2) and prostaglandin E2 (PGE2) may be implicated in the development of opioid-induced hyperalgesia.

METHODS

Rats received subcutaneous fentanyl injections at different doses (20-80 μg kg^-1), four separate times at 15-min intervals. Some rats only received fentanyl (60 μg kg^-1 × 4 doses) with or without surgical incision. Fentanyl-induced hyperalgesia was evaluated via a tail-pressure or paw-withdrawal test. The concentrations of spinal COX-2, EP-1 receptor (EP-1R) mRNA, and PGE2 were measured. The effects of the COX-2 inhibitor, parecoxib (intraperitoneal 10 mg kg^-1), or the EP-1R antagonist, SC51089 (intraperitoneal 100 μg kg^-1), on hyperalgesia and spinal PGE2 were examined.

RESULTS

Acute repeated injections of fentanyl dose-dependently induced mechanical hyperalgesia, which reached a peak at the 1^st day and persisted for 1-4 days postinjection. This hyperalgesia could be partly or totally prevented by the pretreatment of either parecoxib or SC51089. Consistently, the levels of spinal COX-2 mRNA and PGE2 were also dose-dependently increased, reaching a peak at the first day and persisting for 2 days postinjection. Pretreatment with parecoxib could block the increase in spinal PGE2 and had no effects on spinal COX-2 and EP-1R mRNA. Fentanyl injection enhanced incision-induced mechanical and thermal hyperalgesia.

CONCLUSIONS

Acute repeated fentanyl administration dose-dependently produced mechanical hyperalgesia and augmented surgery induced postoperative hyperalgesia. This behavioural change was paralleled with an increase in spinal COX-2 mRNA and PGE2 after fentanyl administration. Inhibition of COX-2 or blockade of EP-1R can partly or totally prevent hyperalgesia.

Excessive remifentanil during total intravenous anesthesia is associated with increased risk of pain after robotic thyroid surgery

The widespread use of remifentanil during total intravenous anesthesia (TIVA) has raised concerns about the risk of postoperative remifentanil-associated pain. Although a recent meta-analysis suggests that remifentanil-associated pain is unlikely to occur in patients with TIVA because of the protective effect of co-administered propofol, the evidence is not conclusive. We retrospectively assessed 635 patients who received robotic thyroid surgery under TIVA to evaluate the risk of remifentanil-associated pain. Postoperative pain was evaluated using 11-point numeric rating scale (NRS). Time dependent Cox proportional hazards regression analysis was used to determine the risk factors of treatment-requiring pain (NRS > 4) during the first 48 postoperative hours. Postoperative pain rapidly decreased, and treatment-requiring pain remained in 12.8% (81 out of 635) of patients at 48 hours postoperatively. After adjusting for the time-dependent analgesic consumption, intraoperative use of remifentanil > 0.2 mcg/kg/min was a positive predictor of postoperative pain with a hazard ratio of 1.296 (95% C.I., 1.014–1.656, P = 0.039) during 48 hours after surgery. In conclusion, excessive use of remifentanil during TIVA was associated with increased risk of pain after robotic thyroid surgery. Prospective trials are required to confirm these results and determine whether decreasing remifentanil consumption below the threshold can reduce postoperative pain.

The influence of dexmedetomidine on remifentanil-induced hyperalgesia and the sex differences

In the clinical settings, patients often develop opioid-induced hyperalgesia (OIH) after utilization of high dose intra-operative remifentanil. Systemic α2 agonists, including dexmedetomidine, are believed to reduce pain and opioid requirements after surgery, thus decreasing the incidence of hyperalgesia. The present study aimed to investigate the effect of dexmedetomidine on remifentanil-induced hyperalgesia and explored the sex differences. A total of 48 patients (24 male, 24 female) with an American Society of Anesthesiologists physical status of I-II that were undergoing thyroidectomy were randomly assigned to one of the following six groups: Male controlled group (MC) and female controlled group (FC) (group MC, n=8 and group FC, n=8), which received a preoperative placebo of 0.2 µg.kg^-1 normal saline and intraoperative remifentanil 0.2 µg.kg^-1.min^-1; male and female group with low-dose dexmedetomidine (group MD1, n=8 and group FD1, n=8), which received preoperative dexmedetomidine 0.2 µg.kg^-1 and intraoperative remifentanil 0.2 µg.kg^-1.min^-1; and male and female groups with high-dose dexmedetomidine (group MD2, n=8 and group FD2, n=8), which received dexmedetomidine 0.6 µg.kg^-1 and intraoperative remifentanil 0.2 µg.kg^-1.min^-1. Result indicated that the visual analog scale (VAS) scores and morphine dosing frequency were significantly higher in MC and FC groups compared with the other same sex groups. Furthermore, the mechanical hyperalgesia threshold and patients' analgesia satisfaction score after surgery were significantly lower in MC and FC groups. Notably, the frequency of post-operative chills, nausea and vomiting were significantly lower in groups MD1, MD2, FD1 and FD2. The present findings indicated that low- and high-dose dexmedetomidine injection significantly decreased the patient's risk of enhanced pain intensity and increased postoperative morphine dosing caused by remifentanil-induced hyperalgesia. These findings suggest that the influence of dexmedetomidine displayed minimal significant differences between sex. Trial registration no., IRB2018-YX-001 (Name of registry: Institutional Medical Ethics Committee of Tianjin Medical University General Hospital; date of registration: February 1, 2016).

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.

Withdrawal from spinal application of remifentanil induces long-term potentiation of c-fiber-evoked field potentials by activation of Src family kinases in spinal microglia

It is well known that remifentanil, a widely used intravenous anesthesia drug, can paradoxically induce hyperalgesia. The underlying mechanisms are still not clear despite the wide investigations. The present study demonstrated that withdrawal from spinal application of remifentanil could dose-dependently induce long term potentiation (LTP) of C-fiber evoked field potentials. Remifentanil withdrawal could activate Src family kinases (SFKs) in microglia, and upregulate the expression of tumor necrosis factor alpha (TNFα) in spinal dorsal horn. Furthermore, pretreatment with either microglia inhibitor Minocycline, SFKs inhibitor PP2 or TNF αneutralization antibody could block remifentanil withdrawal induced spinal LTP, whereas supplement of recombinant rat TNFα to the spinal cord could reverse the inhibitory effect of Minocycline or PP2 on remifentanil withdrawal induced LTP. Our results suggested that TNFαrelease following SFKs activation in microglia is involved in the induction of LTP induced by remifentanil withdrawal.

Intraoperative electroacupuncture relieves remifentanil-induced postoperative hyperalgesia via inhibiting spinal glial activation in rats

Background

Accumulating studies have suggested that remifentanil, the widely-used opioid analgesic in clinical anesthesia, can activate the pronociceptive systems and enhance postoperative pain. Glial cells are thought to be implicated in remifentanil-induced hyperalgesia. Electroacupuncture is a complementary therapy to relieve various pain conditions with few side effects, and glial cells may be involved in its antinociceptive effect. In this study, we investigated whether intraoperative electroacupuncture could relieve remifentanil-induced postoperative hyperalgesia by inhibiting the activation of spinal glial cells, the production of spinal proinflammatory cytokines, and the activation of spinal mitogen-activated protein kinases.

Methods

A rat model of remifentanil-induced postoperative hyperalgesia was used in this study. Electroacupuncture during surgery was conducted at bilateral Zusanli (ST36) acupoints. Behavior tests, including mechanical allodynia and thermal hyperalgesia, were performed at different time points. Astrocytic marker glial fibrillary acidic protein, microglial marker Iba1, proinflammatory cytokines, and phosphorylated mitogen-activated protein kinases in the spinal cord were detected by Western blot and/or immunofluorescence.

Results

Mechanical allodynia and thermal hyperalgesia were induced by both surgical incision and remifentanil infusion, and remifentanil infusion significantly exaggerated and prolonged incision-induced pronociceptive effects. Glial fibrillary acidic protein, Iba1, proinflammatory cytokines (interleukin-1β and tumor necrosis factor-α), and phosphorylated mitogen-activated protein kinases (p-p38, p-JNK, and p-ERK1/2) were upregulated after surgical incision, remifentanil infusion, and especially after their combination. Intraoperative electroacupuncture significantly attenuated incision- and/or remifentanil-induced pronociceptive effects, spinal glial activation, proinflammatory cytokine upregulation, and phosphorylated mitogen-activated protein kinase upregulation.

Conclusions

Our study suggests that remifentanil-induced postoperative hyperalgesia can be relieved by intraoperative electroacupuncture via inhibiting the activation of spinal glial cells, the upregulation of spinal proinflammatory cytokines, and the activation of spinal mitogen-activated protein kinases.

The Price We Pay for Radical Curative Pelvic Exenterations: Prevalence and Management of Pain

BACKGROUND

Pelvic exenterations are extensive surgical procedures for locally advanced or recurrent malignancies of the pelvis. However, this is often at the cost of significant morbidity due to perioperative pain, which has been poorly studied.

OBJECTIVE

This study aims to review perioperative pain management in patients undergoing pelvic exenteration.

DESIGN

This is a retrospective review of patients undergoing pelvic exenteration between January 2013 and December 2014. Data were gathered from medical records and a prospectively maintained database.

SETTING

This study was conducted at a single quaternary referral center for pelvic exenteration.

PATIENTS

Consecutive patients underwent pelvic exenteration at a single center.

INTERVENTIONS

Pelvic exenteration was performed in consecutive patients.

MAIN OUTCOMES MEASURES

Primary outcomes were the prevalence of preoperative pain, preoperative opiate use (type, dosage), and postoperative pain (verbal numerical rating scale). Secondary outcomes included the number of pain consultations and correlations between preoperative opiate use, length of stay, and extent of resection (en bloc sacrectomy and nerve excision).

RESULTS

Ninety-nine patients underwent pelvic exenteration. Sixty-one patients (61.6%) underwent major nerve resection and/or sacrectomy. Thirty patients (30%) required opiates preoperatively, with a mean daily morphine equivalent of 72.9 mg (SD 65.0 mg). Patients on preoperative opiates were more likely to have worse pain postoperatively and to require higher opiate doses and more pain consultations (9.3 vs 4.8; p < 0.001). Major nerve excision and sacrectomy were not associated with worse postoperative pain. By discharge, 60% still required opiate analgesia.

LIMITATIONS

Retrospective study design, the subjective nature of pain assessment because of a lack of valid methods to objectively quantify pain, and the lack of long-term follow-up were limitations of this study.

CONCLUSIONS

Perioperative pain is a significant issue among patients undergoing pelvic exenteration. One in three patients require high-dose opiates preoperatively that is associated with worse pain outcomes. Potential areas to improve pain outcomes in these complex patients could include increased use of regional anesthesia, antineuropathic agents, and opiate-sparing techniques. See Video Abstract at http://links.lww.com/DCR/A572.

Pupillometry-guided Intraoperative Remifentanil Administration versus Standard Practice Influences Opioid Use

Background

Pupillometry has shown promising results for assessing nociception in anesthetized patients. However, its benefits in clinical practice are not demonstrated. The aim of this prospective randomized study was to evaluate the impact of intraoperative pupillometry monitoring on perioperative opioid consumption in major gynecologic surgery.

Methods

After receiving ethics committee approval and written consent of patients, American Society of Anesthesiologists status I to II women undergoing gynecologic surgery were included in this single-blinded, prospective, parallel-arm randomized study. General anesthesia was standardized with propofol–remifentanil target-controlled infusion. Patients were randomly assigned into two groups. In the pupillometry group, remifentanil administration was guided by pupillary diameter changes. In the standard group, remifentanil administration was left to the discretion of the anesthesiologist. The primary outcome was intraoperative remifentanil consumption.

Results

Fifty-five patients were analyzed. Remifentanil consumption was markedly decreased in the pupillometry group (3.8 [3.4 to 4.8 µg · kg–1 · h–1] vs. 7.9 µg · kg–1 · h–1 [6.5 to 9.0 µg · kg–1 · h–1] in the standard group; difference = 4.2 µg · kg–1 · h–1 [95% CI, 3.0 to 5.3 µg · kg–1 · h–1]; P &lt; 0.001). Cumulative 0- to 12-h morphine consumption was reduced in the pupillometry group (two-way repeated measures ANOVA 0.3 ± 0.1 vs. 0.4 ± 0.2 mg/kg; P = 0.048). A telephone survey 3 months after surgery revealed that 15 of 29 patients in the standard group still experienced procedure-related pain versus 3 of 23 in the pupillometry group (chi-square P = 0.037). No adverse events associated with pupillometry were observed during the study.

Conclusions

The use of pupillometry to guide intraoperative analgesia reduced intraoperative remifentanil consumption and postoperative morphine requirements. The possible consequences of decreasing intraoperative remifentanil in terms of chronic pain require further investigation.

Monitoring of nociception, reality or fiction?

There are currently various projects underway that attempt to monitor the nociceptive responses caused by surgical stress and ensure patients the best analgesic conditions. The systemic response to surgical stress has repercussions in the postoperative period, such as worse pain control, delayed recovery, greater complications, longer stay in resuscitation and hospital units, and increased healthcare costs. However, treatment with higher doses of opioids than necessary may lead to slower awakening, increased drowsiness and adverse effects, as well as situations of postoperative opioid-induced hyperalgesia. There are 2 large groups of nociceptive monitoring according to the origin of the theoretical objective of monitoring response to the stimulus, that may derive from changes in the electroencephalogram or the response of the autonomic nervous system.

Analgesia after liver transplantation

This article addresses postoperative analgesia in patients with end-stage liver disease who have undergone liver transplantation (LT). Postoperative analgesia determines how patients perceive LT. Although important, this topic is underrepresented in the current literature. With an increased frequency of fast tracking in LT, efficient intra- and postoperative analgesia are undergoing changes. We herein review the current literature, compare the benefits and disadvantages of the therapeutic options, and make recommendations based on the current literature and clinical experience.