Conditioned pain modulation and situational pain catastrophizing as preoperative predictors of pain following chest wall surgery: a prospective observational cohort study

Pain trajectories and neuropathic pain symptoms following lung cancer surgery: A prospective cohort study

BACKGROUND

Persistent postsurgical pain (PPSP) after lung cancer surgery is common and current definitions are based on evaluations at a single time point after surgery. Pain intensity and symptoms may however fluctuate and change over time, and be impacted by multiple and shifting factors. Studies of postoperative recovery patterns and transition from acute to chronic pain are needed for further investigation of preventive measures and treatments to modify unfavourable recovery paths.

METHODS

In this explorative study, 85 patients undergoing surgery due to either presumptive or confirmed lung cancer reported pain intensities bi-monthly for 12 months. Pain trajectories during recovery were investigated, using group-based trajectory modelling. Associations with possible risk factors for PPSP, including clinical variables and anxiety and depression score (HADS), were also explored.

RESULTS

A trajectory model containing three 12-month pain recovery groups was computed. One group without PPSP fully recovered (50%) within two to three months. Another group with mild-intensity PPSP followed a protracted recovery trajectory (37%), while incomplete recovery was observed in the last group (13%). Acute postoperative pain and younger age were associated with a less favourable recovery trajectory. More neuropathic pain symptoms were observed in patients with incomplete recovery.

CONCLUSIONS

Three clinically relevant recovery trajectories were identified, based on comprehensive pain tracking. Higher acute postoperative pain intensity was associated with an unfavourable pain recovery trajectory.

SIGNIFICANCE STATEMENT

Understanding the transition from acute to chronic postoperative pain and identifying preoperative risk factors is essential for the development of targeted treatments and the implementation of preventive measures. This study (1) identified distinct recovery trajectories based on frequent pain assessment follow-ups for 12 months after surgery and (2) evaluated risk factors for unfavourable postoperative pain recovery paths. Findings suggest that early higher postoperative pain intensity is associated with an unfavourable long-term recovery path.

Comparison of Conventional Anesthesia Nurse Education and an Artificial Intelligence Chatbot (ChatGPT) Intervention on Preoperative Anxiety: A Randomized Controlled Trial

PURPOSE

This study aimed to evaluate the effects of an artificial intelligence (AI) chatbot (ChatGPT-3.5, OpenAI) on preoperative anxiety reduction and patient satisfaction in adult patients undergoing surgery under general anesthesia.

DESIGN

The study used a single-blind, randomized controlled trial design.

METHODS

In this study, 100 adult patients were enrolled and divided into two groups: 50 in the control group, in which patients received standard preoperative information from anesthesia nurses, and 50 in the intervention group, in which patients interacted with ChatGPT. The primary outcome, preoperative anxiety reduction, was measured using the Japanese State-Trait Anxiety Inventory (STAI) self-report questionnaire. The secondary endpoints included participant satisfaction (Q1), comprehension of the treatment process (Q2), and the perception of the AI chatbot's responses as more relevant than those of the nurses (Q3).

FINDINGS

Of the 85 participants who completed the study, the STAI scores in the control group remained stable, whereas those in the intervention group decreased. The mixed-effects model showed significant effects of time and group-time interaction on the STAI scores; however, no main group effect was observed. The secondary endpoints revealed mixed results; some patients found that the chatbot's responses were more relevant, whereas others were dissatisfied or experienced difficulties.

CONCLUSIONS

The ChatGPT intervention significantly reduced preoperative anxiety compared with the control group; however, no overall difference in the STAI scores was observed. The mixed secondary endpoint results highlight the need for refining chatbot algorithms and knowledge bases to improve performance and satisfaction. AI chatbots should complement, rather than replace, human health care providers. Seamless integration and effective communication among AI chatbots, patients, and health care providers are essential for optimizing patient outcomes.

Is conditioned pain modulation (CPM) affected by negative emotional state?

BACKGROUND

Conditioned pain modulation (CPM) is an experimental paradigm, which describes the inhibition of responses to a noxious or strong-innocuous stimulus, the test stimulus (TS), by the additional application of a second noxious or strong-innocuous stimulus, the conditioning stimulus (CS). As inadequate CPM efficiency has been assumed to be predisposing for clinical pain, the search for moderating factors explaining inter-individual variations in CPM is ongoing. Psychological factors have received credits in this context. However, research concerning associations between CPM and trait factors relating to negative emotions has yielded disappointing results. Yet, the influence of anxious or fearful states on CPM has not attracted much interest despite ample evidence that negative affective states enhance pain. Our study aimed at investigating the effect of fear induction by symbolic threat on CPM.

METHODS

Thirty-seven healthy participants completed two experimental blocks: one presenting aversive pictures showing burn wounds (high-threat block) and one presenting neutral pictures (low-threat block). Both blocks contained a CPM paradigm with contact heat as TS and hot water as CS; subjective numerical ratings as well as contact-heat evoked potentials (CHEPs) were assessed.

RESULTS

We detected an overall inhibitory CPM effect for CHEPs amplitudes but not for pain ratings. However, we found no evidence for a modulation of CPM by threat despite threat ratings indicating that our manipulation was successful.

DISCUSSION

These results suggest that heat/thermal CPM is resistant to this specific type of symbolic threat induction and further research is necessary to examine whether it is resistant to fearful states in general.

SIGNIFICANCE

The attempt of modulating heat conditioned pain modulation (CPM) by emotional threat (fear/anxiety state) failed. Thus, heat CPM inhibition again appeared resistant to emotional influences. Pain-related brain potentials proved to be more sensitive for CPM effects than subjective ratings.

Chronic post-thoracotomy pain after lung cancer surgery: a prospective study of preoperative risk factors

OBJECTIVES

The objective of this longitudinal cohort study was to investigate if preoperative pain mechanisms, anxiety, and depression increase risk of developing chronic post-thoracotomy pain (CPTP) after lung cancer surgery.

METHODS

Patients with suspected or confirmed lung cancer undergoing surgery by either video-assisted thoracoscopic surgery or anterior thoracotomy were recruited consecutively. Preoperative assessments were conducted by: quantitative sensory testing (QST) (brush, pinprick, cuff pressure pain detection threshold, cuff pressure tolerance pain threshold, temporal summation and conditioned pain modulation), neuropathic pain symptom inventory (NPSI), and the Hospital Anxiety and Depression Scale (HADS). Clinical parameters in relation to surgery were also collected. Presence of CPTP was determined after six months and defined as pain of any intensity in relation to the operation area on a numeric rating scale form 0 (no pain) to 10 (worst pain imaginable).

RESULTS

A total of 121 patients (60.2 %) completed follow-up and 56 patients (46.3 %) reported CPTP. Development of CPTP was associated with higher preoperative HADS score (p=0.025), higher preoperative NPSI score (p=0.009) and acute postoperative pain (p=0.042). No differences were observed in relation to preoperative QST assessment by cuff algometry and HADS anxiety and depression sub-scores.

CONCLUSIONS

High preoperative HADS score preoperative pain, acute postoperative pain intensity, and preoperative neuropathic symptoms were was associated with CPTP after lung cancer surgery. No differences in values of preoperative QST assessments were found. Preoperative assessment and identification of patients at higher risk of postoperative pain will offer opportunity for further exploration and development of preventive measures and individualised pain management depending on patient risk profile.

Neural mechanisms underlying the conditioned pain modulation response: a narrative review of neuroimaging studies

ABSTRACT

Processing spatially distributed nociceptive information is critical for survival. The conditioned pain modulation (CPM) response has become a common psychophysical test to examine pain modulation capabilities related to spatial filtering of nociceptive information. Neuroimaging studies have been conducted to elucidate the neural mechanisms underlying the CPM response in health and chronic pain states, yet their findings have not been critically reviewed and synthesized before. This narrative review presents a simplified overview of MRI methodology in relation to CPM assessments and summarizes the findings of neuroimaging studies on the CPM response. The summary includes functional MRI studies assessing CPM responses during scanning as well as functional and structural MRI studies correlating indices with CPM responses assessed outside of the scanner. The findings are discussed in relation to the suggested mechanisms for the CPM response. A better understanding of neural mechanisms underlying spatial processing of nociceptive information could advance both pain research and clinical use of the CPM response as a marker or a treatment target.

Conditioned pain modulation and offset analgesia: Influence of sex, sex hormone levels and menstrual cycle on the magnitude and retest reliability in healthy participants

BACKGROUND

Conditioned Pain Modulation (CPM) and offset analgesia quantify impairment of endogenous pain modulation, but magnitude and reliability vary broadly between studies, indicating influencing factors that are not currently controlled for. The aim of this study was to quantify magnitude and retest reliability of CPM and offset analgesia in healthy participants, whilst investigating the influence of sex and sex hormone levels.

METHODS

62 participants (30 female) completed the study. We tested CPM (heat-cold paradigm) and offset analgesia on six days within two menstrual cycles (tests were performed in each phase of two subsequent menstrual cycles, with similar time-points for men).

RESULTS

Median offset effect was -29.4% in female and -22.5% in male participants (as change from initial stimulus). Median early CPM effects were -16.7% for women versus -13.3% for men. Reliability (intra-class correlation coefficient (ICC)) was similar between the main measures, offset effect (female: 0.48, male: 0.47) and early CPM effect (female: 0.49, male: 0.43). There was significant variance between individual experimental parameters within protocols but not between sexes or menstrual phases. While oestradiol and progesterone did not correlate with the magnitude of effect within sexes, we found that testosterone levels explained an estimated 5-10% of variance within individual responses in all sexes.

CONCLUSIONS

Our results show that the reliability of both CPM effect and offset analgesia were independent of sex and menstrual cycle phase. The magnitude of CPM and offset effects were weakly influenced by sex and testosterone levels, indicating an area for future research, rather than clinical significance.

SIGNIFICANCE STATEMENT

This study investigated CPM and offset analgesia in parallel, across sexes and during two menstrual cycles while assessing the impact of sex hormones. Reliability seems to depend on experimental parameters rather than participant characteristics, while the magnitude of effect could be weakly linked to sex hormones and sex.

No relevant differences in conditioned pain modulation effects between parallel and sequential test design. A cross-sectional observational study

Background

Conditioned pain modulation (CPM) is measured by comparing pain induced by a test stimulus with pain induced by the same test stimulus, either during (parallel design) or after (sequential design) the conditioning stimulus. Whether design, conditioning stimulus intensity and test stimulus selection affect CPM remains unclear.

Methods

CPM effects were evaluated in healthy participants (N = 89) at the neck, forearm and lower leg using the cold pressor test as the conditioning stimulus. In three separate experiments, we compared the impact of (1) design (sequential versus parallel), (2) conditioning stimulus intensity (VAS 40/100 versus VAS 60/100), and (3) test stimulus selection (single versus dual, i.e., mechanical and thermal). Statistical analyses of the main effect of design (adjusted for order) and experiment were conducted using linear mixed models with random intercepts.

Results

No significant differences were identified in absolute CPM data. In relative CPM data, a sequential design resulted in a slightly lower CPM effect compared to a parallel design, and only with a mechanical test stimulus at the neck (−6.1%; 95% CI [−10.1 to −2.1]) and lower leg (−5.9%; 95% CI [−11.7 to −0.1]) but not forearm (−4.5%; 95% CI [−9.0 to 0.1]). Conditioning stimulus intensity and test stimulus selection did not influence the CPM effect nor the difference in CPM effects derived from parallel versus sequential designs.

Conclusions

Differences in CPM effects between protocols were minimal or absent. A parallel design may lead to a minimally higher relative CPM effect when using a mechanical test stimulus. The conditioning stimulus intensities assessed in this study and performing two test stimuli did not substantially influence the differences between designs nor the magnitude of the CPM effect.

Association of preoperative pain catastrophizing with postoperative pain after lower limb trauma surgery

OBJECTIVES

To evaluate an association between preoperative Nepali pain catastrophizing scale (N-PCS) scores and postoperative pain intensity and total opioid consumption.

METHODS

In this prospective cohort study we enrolled 135 patients with an American Society of Anaesthesiologists physical status I or II, aged between 18 and 65 years, and scheduled for surgery for lower-extremity fracture under spinal anaesthesia. Maximum postoperative pain reported during the 24 h was classified into two groups, no-mild pain group (Numeric rating scale [NRS] scores 1-3) and a moderate-severe pain group (NRS 4-10). The Pearson's correlation coefficient was used to compare the association between the baseline N-PCS scores and outcome variables, i.e., the maximum NRS pain score and the total tramadol consumption within the first 24 h after surgery. Logistic regression models were used to identify the predictors for the intensity of postoperative pain.

RESULTS

As four patients violated the protocol, the data of 131 patients were analyzed. Mean N-PCS scores reported by the moderate-severe pain group was 27.39 ± 9.50 compared to 18.64 ± 10 mean N-PCS scores by the no-mild pain group (p < 0.001). Preoperative PCS scores correlated positively with postoperative pain intensity (r = 0.43, [95% CI 0.28-0.56], p < 0.001) and total tramadol consumption (r = 0.36, [95% CI 0.20-0.50], p < 0.001). Preoperative pain catastrophizing was associated with postoperative moderate-severe pain (odds ratio, 1.08 [95% confidence interval, 1.02-1.15], p = 0.006) after adjusting for gender, ethnicity and preoperative anxiety.

CONCLUSION

Patients who reported higher pain catastrophizing preoperatively were at increased risk of experiencing moderate-severe postoperative pain.

CLINICAL TRIAL REGISTRATION

www.clinicaltrials.gov Identifier: NCT03758560.

The predictive value of quantitative sensory testing: a systematic review on chronic postoperative pain and the analgesic effect of pharmacological therapies in patients with chronic pain

Studies have suggested that quantitative sensory testing (QST) might hold a predictive value for the development of chronic postoperative pain and the response to pharmacological interventions. This review systematically summarizes the current evidence on the predictive value of QST for chronic postoperative pain and the effect of pharmacological interventions. The main outcome measures were posttreatment pain intensity, pain relief, presence of moderate-to-severe postoperative pain, responders of 30% and 50% pain relief, or validated questionnaires on pain and disability. A systematic search of MEDLINE and EMBASE yielded 25 studies on surgical interventions and 11 on pharmacological interventions. Seventeen surgical and 11 pharmacological studies reported an association between preoperative or pretreatment QST and chronic postoperative pain or analgesic effect. The most commonly assessed QST modalities were pressure stimuli (17 studies), temporal summation of pain (TSP, 14 studies), and conditioned pain modulation (CPM, 16 studies). Of those, the dynamic QST parameters TSP (50%) and CPM (44%) were most frequently associated with chronic postoperative pain and analgesic effects. A large heterogeneity in methods for assessing TSP (n = 4) and CPM (n = 7) was found. Overall, most studies demonstrated low-to-moderate levels of risk of bias in study design, attrition, prognostic factors, outcome, and statistical analyses. This systematic review demonstrates that TSP and CPM show the most consistent predictive values for chronic postoperative pain and analgesic effect, but the heterogeneous methodologies reduce the generalizability and hence call for methodological guidelines.

Development and Validation of a Predictive Model of Pain Modulation Profile to Guide Chronic Pain Treatment: A Study Protocol

Introduction: Quantitative sensory testing is frequently used in research to assess endogenous pain modulation mechanisms, such as Temporal Summation (TS) and Conditioned Pain Modulation (CPM), reflecting excitatory and inhibitory mechanisms, respectively. Numerous studies found that a dysregulation of these mechanisms is associated with chronic pain conditions. In turn, such a patient's “profile” (increased TS and/or weakened CPM) could be used to recommend different pharmacological treatments. However, the procedure to evaluate these mechanisms is time-consuming and requires expensive equipment that is not available in the clinical setting. In this study, we aim to identify psychological, physiological and socio-demographic markers that could serve as proxies to allow healthcare professionals to identify these pain phenotypes in clinic, and consequently optimize pharmacological treatments.

Method: We aim to recruit a healthy participant cohort (n = 360) and a chronic pain patient cohort (n = 108). Independent variables will include psychological questionnaires, pain measurements, physiological measures and sociodemographic characteristics. Dependent variables will include TS and CPM, which will be measured using quantitative sensory testing in a single session. We will evaluate one prediction model and two validation models (for healthy and chronic pain participants) using multiple regression analysis between TS/CPM and our independent variables. The significance thresholds will be set at p = 0.05, respectively.

Perspectives: This study will allow us to develop a predictive model to compute the pain modulation profile of individual patients based on their biopsychosocial characteristics. The development of the predictive model is the first step toward the overarching goal of providing clinicians with a set of quick and cheap tests, easily applicable in clinical practice to orient pharmacological treatments.

Identification of neural and psychophysical predictors of headache reduction after cognitive behavioral therapy in adolescents with migraine

ABSTRACT

Cognitive behavioral therapy (CBT) is a psychological intervention that involves development of coping strategies to reduce the experience of pain. Although CBT is a promising intervention to reduce headache days in patients with migraine, it may not be effective for all patients. Thus, there is a need to identify markers that could predict which patients will respond to CBT. We aimed to determine whether baseline brain function and amygdalar connectivity, assessed by functional magnetic resonance imaging, or pain modulation capacities, assessed by the conditioned pain modulation (CPM) response, can predict a reduction in headache days after CBT in adolescents with migraine. Patients with migraine (n = 20; age range 10-17 years) completed 8 weekly CBT sessions. The CPM response was examined in the trapezius and the leg. Headache days significantly decreased after CBT (P < 0.001). Greater functional connectivity before CBT between the right amygdala and frontal gyrus, anterior cingulate cortex, and precentral gyrus was related to greater headache reduction after CBT. Greater reduction in headache days after CBT was related with less efficient CPM response before CBT at the trapezius (r = -0.492, P = 0.028) but not at the leg. This study found that headache reduction after CBT was related to right amygdala connectivity with frontal and sensorimotor regions at baseline as well as baseline pain modulation capacities. These findings suggest that individual differences in brain function and pain modulation can be associated with clinical improvements and help with determination of CBT responsiveness.

Distraction by a cognitive task has a higher impact on electrophysiological measures compared with conditioned pain modulation

Background

Conditioned pain modulation (CPM) evaluates the effect of a painful conditioning stimulus (CS) on a painful test stimulus (TS). Using painful cutaneous electrical stimulation (PCES) as TS and painful cold water as CS, the pain relief was paralleled by a decrease in evoked potentials (PCES-EPs). We now aimed to compare the effect of CPM with cognitive distraction on PCES-induced pain and PCES-EP amplitudes.

Methods

PCES was performed using surface electrodes inducing a painful sensation of 60 (NRS 0–100) on one hand. In a crossover design healthy subjects (included: n = 38, analyzed: n = 23) immersed the contralateral hand into 10 °C cold water (CS) for CPM evaluation and performed the 1-back task for cognitive distraction. Before and during the CS and 1-back task, respectively, subjects rated the pain intensity of PCES and simultaneously cortical evoked potentials were recorded.

Results

Both CPM and cognitive distraction significantly reduced PCES-EP amplitudes (CPM: 27.6 ± 12.0 μV to 20.2 ± 9.5 μV, cognitive distraction: 30.3 ± 14.2 µV to 13.6 ± 5.2 μV, p < 0.001) and PCES-induced pain (on a 0–100 numerical rating scale: CPM: 58 ± 4 to 41.1 ± 12.3, cognitive distraction: 58.3 ± 4.4 to 38.0 ± 13.0, p < 0.001), though the changes in pain intensity and PCES-amplitude did not correlate. The changes of the PCES-EP amplitudes during cognitive distraction were more pronounced than during CPM (p = 0.001).

Conclusions

CPM and cognitive distraction reduced the PCES-induced pain to a similar extent. The more pronounced decrease of PCES-EP amplitudes after distraction by a cognitive task implies that both conditions might not represent the general pain modulatory capacity of individuals, but may underlie different neuronal mechanisms with the final common pathway of perceived pain reduction.

Spatial aspects of pain modulation are not disrupted in adolescents with migraine

OBJECTIVE

To compare spatial pain modulation capabilities between adolescents with and without migraine.

BACKGROUND

Conditioned pain modulation (CPM) responses at the leg are similar in adolescents with versus without migraine. However, the anatomical region of testing may affect spatial pain modulation capabilities as differences in nociceptive processing between patients with migraine and healthy controls are found in local areas that are near the site of clinical pain but not in nonlocal areas. This study aimed to examine spatial pain modulation capabilities tested by the CPM paradigm using test stimulus applied to a local body area.

METHODS

Nineteen adolescents with migraine (age 14.9 ± 2.3, mean ± SD; 16 female) and 20 healthy adolescents (age 13.8 ± 2.5, mean ± SD; 16 female) completed this case-control study at Cincinnati Children's Hospital Medical Center. Pressure pain thresholds (PPT) were assessed at the trapezius before and during immersion of the foot in a cold water bath (8°C).

RESULTS

In the migraine group (146.0 ± 79.1, mean ± SD), compared to healthy controls (248.0 ± 145.5, mean ± SD), significantly lower PPT (kilopascal) values were found (estimate = 124.28, 95% CI: 58.98, 189.59, p < 0.001; effect size: d = 1.40). No differences between the groups were found for pain intensity and unpleasantness ratings of cold-water immersion nor the CPM response.

CONCLUSIONS

This study found altered ascending nociceptive processing of mechanical stimuli at the neck in adolescents with migraine. However, endogenous pain modulatory mechanisms were functional and not altered. In light of other studies, impairments in inhibitory control may not be involved in migraine pathophysiology in pediatric patients regardless of stimulus location.

A Conceptual Model of Biopsychosocial Mechanisms of Transition from Acute to Chronic Postsurgical Pain in Children and Adolescents

Acute and chronic pain are highly prevalent and impactful consequences of surgery across the lifespan, yet a comprehensive conceptual model encompassing biopsychosocial factors underlying acute to chronic pain transition is lacking, particularly in youth. Building on prior chronic postsurgical pain models, we propose a new conceptual model of biopsychosocial mechanisms of transition from acute to chronic postsurgical pain. This review aims to summarize existing research examining key factors underlying acute to chronic postsurgical pain transition in order to guide prevention and intervention efforts aimed at addressing this health issue in children. As pain transitions from acute nociceptive pain to chronic pain, changes in the peripheral and central nervous system contribute to the chronification of pain after surgery. These changes include alterations in sensory pain processing and psychosocial processes (psychological, behavioral, and social components), which promote the development of chronic pain. Patient-related premorbid factors (eg, demographic factors, genetic profile, and medical factors such as premorbid pain) may further modulate these changes. Factors related to acute injury and recovery (eg, surgical and treatment factors), as well as biological response to surgery (eg, epigenetic, inflammatory, and endocrine factors), may also influence this process. Overall, longitudinal studies examining temporal pathways of biopsychosocial processes including both risk and resiliency factors will be essential to identify the mechanisms involved in the transition from acute to chronic pain. Research is also needed to unravel connections between the acute pain experience, opioid exposure, and sensory pain processing during acute to chronic pain transition. Furthermore, future studies should include larger and more diverse samples to more fully explore risk factors in a broader range of pediatric surgeries. The use of conceptual models to guide intervention approaches targeting mechanisms of transition from acute to chronic pain will significantly advance this field and improve outcomes for children and adolescents undergoing surgery.

Is Preoperative Quantitative Sensory Testing Related to Persistent Postsurgical Pain? A Systematic Literature Review

Persistent postsurgical pain (PPSP) is a common complication of surgery that significantly affects quality of life. A better understanding of which patients are likely to develop PPSP would help to identify when perioperative and postoperative pain management may require specific attention. Quantitative sensory testing (QST) of a patient's preoperative pain perception is associated with acute postoperative pain, and acute postoperative pain is a risk factor for PPSP. The direct association between preoperative QST and PPSP has not been reviewed to date. In this systematic review, we assessed the relationship of preoperative QST to PPSP. We searched databases with components related to (1) preoperative QST; (2) association testing; and (3) PPSP. Two authors reviewed all titles and abstracts for inclusion. Inclusion criteria were as follows: (1) QST performed before surgery; (2) PPSP assessed ≥3 months postoperatively; and (3) the association between QST measures and PPSP is investigated. The search retrieved 905 articles; 24 studies with 2732 subjects met inclusion criteria. Most studies (22/24) had moderate to high risk of bias in multiple quality domains. Fourteen (58%) studies reported a significant association between preoperative QST and PPSP. Preoperative temporal summation of pain (4 studies), conditioned pain modulation (3 studies), and pressure pain threshold (3 studies) showed the most frequent association with PPSP. The strength of the association between preoperative QST and PPSP varied from weak to strong. Preoperative QST is variably associated with PPSP. Measurements related to central processing of pain may be most consistently associated with PPSP.

The Effect of Pain Catastrophizing on Endogenous Inhibition of Pain and Spinal Nociception in Native Americans: Results From the Oklahoma Study of Native American Pain Risk

BACKGROUND

Conditioned pain modulation (CPM) is a task that involves measuring pain in response to a test stimulus before and during a painful conditioning stimulus (CS). The CS pain typically inhibits pain elicited by the test stimulus; thus, this task is used to assess endogenous pain inhibition. Moreover, less efficient CPM-related inhibition is associated with chronic pain risk. Pain catastrophizing is a cognitive-emotional process associated with negative pain sequelae, and some studies have found that catastrophizing reduces CPM efficiency.

PURPOSE

The current study examined the relationship between catastrophizing (dispositional and situation specific) and CPM-related inhibition of pain and the nociceptive flexion reflex (NFR; a marker of spinal nociception) to determine whether the catastrophizing-CPM relationship might contribute to the higher risk of chronic pain in Native Americans (NAs).

METHODS

CPM of pain and NFR was assessed in 124 NAs and 129 non-Hispanic Whites. Dispositional catastrophizing was assessed at the beginning of the test day, whereas situation-specific catastrophizing was assessed in response to the CS, as well as painful electric stimuli.

RESULTS

Situation-specific, but not dispositional, catastrophizing led to less NFR inhibition but more pain inhibition. These effects were not moderated by race, but mediation analyses found that: (a) the NA race was associated with greater situation-specific catastrophizing, which led to less NFR inhibition and more pain inhibition, and (b) situation-specific catastrophizing was associated with greater CS pain, which led to more pain inhibition.

CONCLUSIONS

Catastrophizing may contribute to NA pain risk by disrupting descending inhibition.

Acute alcohol effects on conditioned pain modulation, but not temporal summation of pain

Although pain reduction after alcohol administration has repeatedly been demonstrated, alcohol effects on advanced and clinically relevant dynamic pain paradigms are still unknown. As such, temporal summation of pain (TSP) and conditioned pain modulation (CPM) indicate mechanisms of endogenous pain modulation and involve certain neurotransmitter systems crucially influenced by alcohol. Our study is the first to investigate acute alcohol effects on TSP and CPM. We investigated 39 healthy subjects in a placebo-controlled within-subject design and targeted alcohol levels of 0.06% (dose 1) and 0.08% (dose 2). Pain threshold, TSP, and CPM were evaluated before and after an alcoholic or placebo drink. Temporal summation of pain was assessed as enhanced pain response to 5 repetitive contact heat stimuli (threshold +3°C). Conditioned pain modulation was tested as pain inhibition when a conditioning stimulus (46°C hot water) was applied concurrently to a test stimulus (contact heat; threshold + 3°C). Both alcohol doses boosted CPM, with a greater effect size for the higher dose. Conditioning stimulus ratings increased after alcohol intake but were not correlated with CPM, suggesting independence of these effects. Temporal summation of pain was not affected by alcohol, and alcohol effects on pain threshold were small and limited to the higher dose. Our findings suggest that analgesic alcohol effects might be mainly driven by an enhancement of endogenous pain inhibition. The frequent use of alcohol as self-medication in chronic pain might be motivated by alcohol temporarily restoring deficient CPM, thus leading to pain relief in the short run and alcohol-related problems in the long run.

Evidence for Continuing Buprenorphine in the Perioperative Period

OBJECTIVE

Given there are conflicting recommendations for the perioperative management of buprenorphine, we conducted a retrospective cohort study of our surgery patients on buprenorphine whose baseline dose had been preoperatively continued, tapered, or discontinued.

MATERIALS AND METHODS

We reviewed charts of patients on buprenorphine who had received elective surgery at Stanford Healthcare from January 1, 2013 to June 30, 2016. Our primary outcome of interest was the change in pain score, defined as mean postoperative pain score-preoperative pain score. We also collected data on patients' tapering procedure and any postoperative nonbuprenorphine opioid requirements.

RESULTS

Out of ∼1200 patients on buprenorphine, 121 had surgery of which 50 were admitted and included in the study. Perioperative continuation of transdermal buprenorphine resulted in a significantly lower change in pain score postoperatively (0.606±0.878) than discontinuation (4.83±1.23, P=0.012). Among sublingual patients, there was no statistically significant difference in the change in pain score between those who were tapered to a nonzero dose versus discontinued (P=0.55). Continuation of sublingual buprenorphine resulted in fewer nonbuprenorphine scheduled opioid prescriptions than its taper or discontinuation (P=0.028). Finally, tapers were performed with great variability in the tapering team and rate of taper.

DISCUSSION

On the basis of our findings, we implemented a policy at our institution for the continuation of perioperative buprenorphine whenever possible. Our work reveals crucial targets for the education of perioperative healthcare providers and the importance of coordination among all perioperative services and providers.

Correlation of Preoperative State Anxiety and Pain Six Weeks After Surgical Correction of Pectus Excavatum

Background

Pain is a major concern in the early postoperative phase after correction of pectus excavatum. Most studies only focus on pain management in the first days after surgery and describe methods to alleviate the pain immediately postoperatively. The severity of postoperative pain may be influenced by anxiety. So far, few studies have looked into the relationship between anxiety and postoperative pain after pectus excavatum correction.

Objectives

This study aimed to investigate the correlation between preoperative anxiety and late postoperative pain scores.

Methods

This was a prospective cohort study. Anxiety was assessed with the State and Trait Anxiety Inventory questionnaire. Visual analogue scale (VAS) for pain scores assessed the pain at rest and activity. Anxiety was measured before surgery and pain scores six weeks after surgery. A hierarchical linear regression analysis was performed to investigate the correlation between baseline anxiety and pain measurements six weeks after surgery.

Results

In this study, 136 patients were included. State anxiety was not associated with postoperative pain (mean of pain on activity and in rest), only with pain on activity after six weeks. Age and sex were not effect modifiers in any of the models. Relevant confounding factors, although not significant, consisted of trait, sex, minor complications, epidural duration, major complications, and the number of stabilizer plates. The explained variance of state anxiety on VAS for pain scores was minimum after 6 weeks.

Conclusions

Preoperative anxiety does not appear to influence postoperative pain after PE correction.

The Brief Measure of Emotional Preoperative Stress (B-MEPS) as a new predictive tool for postoperative pain: A prospective observational cohort study

Background

Preoperative patients’ vulnerabilities such as physical, social, and psychological are implicated in postoperative pain variability. Nevertheless, it is a challenge to analyze a patient's psychological profile in the preoperative period in a practical and consistent way. Thus, we sought to identify if high preoperative emotional stress, evaluated by the Brief Measure of Emotional Preoperative Stress (B-MEPS) scale is associated with higher postoperative pain levels and poor rehabilitation in patients submitted to intermediate or major surgery. Moreover, the possible neurobiological or neurophysiological mechanisms implicated in high preoperative emotional stress, evaluated through preoperative quantitative sensory pain tests and serum biomarkers BDNF and S100B were investigated.

Methods

We conducted a prospective, observational, cohort study of ASA 2 and 3 adult patients undergoing major urologic, gynecologic, proctologic and orthopedic surgeries from March 2017 to March 2018. B-MEPS and Central Sensitivity Inventory were evaluated preoperatively, followed by a sequence of experimental pain tests and serum biomarkers collection. Postoperative evaluation carried out within the first 48 hours after surgery comprehended pain at rest and movement-evoked pain, and the consumption of morphine. Quality-of-Recovery was also evaluated in the 3rd postoperative day.

Results

23 (15%) out of 150 patients included in the study presented high emotional preoperative stress. Variables significantly related to preoperative stress were: previous psychiatric diagnosis and Central Sensitization Inventory result. Mean movement-evoked pain in the first 12 to 48 hours was 95–105% higher than pain at rest. A mixed model for repeated measures showed a sustainable effect of B-MEPS as a movement-evoked pain predictor. Previous pain, cancer surgery, and preoperative pressure pain tolerance were also independent predictors of postoperative pain. Moderate to severe postoperative movement-evoked pain was predictive of poor rehabilitation in 48 hours after surgery.

Conclusion

We confirmed that a brief screening method of preoperative emotional states could detect individuals prone to experience severe postoperative pain. Specific interventions considering the stress level may be planned in the future to improve perioperative outcomes.

Age does not affect sex effect of conditioned pain modulation of pressure and thermal pain across 2 conditioning stimuli

Introduction:

Conditioned pain modulation (CPM) is a laboratory test resulting in pain inhibition through activation of descending inhibitory mechanisms. Older adults consistently demonstrate reduced CPM compared with younger samples; however, studies of sex differences in younger cohorts have shown mixed results.

Objectives:

This study tested for sex differences in CPM within samples of younger and older adults.

Methods:

Participants were 67 younger adults (mean age = 25.4 years) and 50 older adults (66.4 years). Study conditioning paradigms were the cold-pressor test and contact heat pain administered in separate sessions. Pressure pain threshold and ramping suprathreshold heat were the test stimuli across three time points after presentation of the conditioning stimuli (CS).

Results:

Significant inhibition was observed during both testing sessions. The hypothesis for sex differences across both age cohorts was supported only for ∆PPTh. However, sex differences did not reach significance for either paradigm using ascending suprathreshold heat as the test stimuli. The overall trend was that younger males experienced the strongest CPM and older females the weakest. From a methodological perspective, duration differences were seen in CPM, with inhibition decaying more quickly for PPTh than for suprathreshold heat pain. Furthermore, there were no differences in inhibition induced by cold-pressor test and contact heat pain as CS.

Conclusion:

Sex differences were similar across both age cohorts with males experiencing greater inhibition than females. Cross-sectional associations were also demonstrated between CPM inhibition and measures of recent pain, further supporting CPM as an experimental model with clinical utility.

Identifying At-Risk Subgroups for Acute Postsurgical Pain: A Classification Tree Analysis

Objective

Acute postsurgical pain is common and has potentially negative long-term consequences for patients. In this study, we evaluated effects of presurgery sociodemographics, pain experiences, psychological influences, and surgery-related variables on acute postsurgical pain using logistic regression vs classification tree analysis (CTA).

Design

The study design was prospective.

Setting

This study was carried out at Chongqing No. 9 hospital, Chongqing, China.

Subjects

Patients (175 women, 84 men) completed a self-report battery 24 hours before surgery (T1) and pain intensity ratings 48-72 hours after surgery (T2).

Results

An initial logistic regression analysis identified pain self-efficacy as the only presurgery predictor of postoperative pain intensity. Subsequently, a classification tree analysis (CTA) indicated that lower vs higher acute postoperative pain intensity levels were predicted not only by pain self-efficacy but also by its interaction with disease onset, pain catastrophizing, and body mass index. CTA results were replicated within a revised logistic regression model.

Conclusions

Together, these findings underscored the potential utility of CTA as a means of identifying patient subgroups with higher and lower risk for severe acute postoperative pain based on interacting characteristics.

Association Between Spinal Cord Stimulation and Top-Down Nociceptive Inhibition in People With Failed Back Surgery Syndrome: A Cohort Study

BACKGROUND

Descending nociceptive inhibitory pathways often malfunction in people with chronic pain. Conditioned pain modulation (CPM) is an experimental evaluation tool for assessing the functioning of these pathways. Spinal cord stimulation (SCS), a well-known treatment option for people with failed back surgery syndrome (FBSS), probably exerts its pain-relieving effect through a complex interplay of segmental and higher-order structures.

OBJECTIVE

To the best of our knowledge, no clinical studies have thoroughly investigated the associations between SCS and CPM.

DESIGN

This was a prospective cohort study in people with FBSS.

METHODS

Seventeen people who had FBSS and were scheduled for SCS were enrolled in this study. The CPM model was evaluated at both sural nerves and was induced by electrical stimulation as the test stimulus and the cold pressor test as the conditioning stimulus.

RESULTS

Before SCS, less than 30% of the participants with FBSS showed a CPM effect. Significant increases in the electrical detection threshold on the symptomatic side and the nonsymptomatic side were found. On the symptomatic side, no differences in the numbers of CPM responders before and after SCS could be found. On the nonsymptomatic side, more participants showed a CPM effect during SCS. Additionally, there were significant differences for CPM activation and SCS treatment.

LIMITATIONS

Limitations were the small sample size and the subjective outcome parameters in the CPM model.

CONCLUSIONS

This study revealed a bilateral effect of SCS that suggests the involvement of higher-order structures, such as the periaqueductal gray matter and rostroventromedial medulla (key regions in the descending pathways), as previously suggested by animal research.

Ultrasound-guided bilateral quadratus lumborum block vs. intrathecal morphine for postoperative analgesia after cesarean section: a randomized controlled trial

Background

Adequate pain control after cesarean section (CS) is crucial for mothers caring for newborns, and early ambulation to avoid thromboembolism and chronic abdominal and pelvic pain. This randomized controlled trial compared the efficacy of quadratus lumborum block (QLB) and intrathecal morphine (ITM) for analgesia after CS.

Methods

Ninety women at ≥ 37 weeks pregnancy scheduled for elective CS were enrolled. All patients received spinal anesthesia and post-operative QLB. They were randomly allocated to Control (anesthesia: 0.1 ml saline, QLB: 24 ml saline), ITM (anesthesia: 0.1 mg morphine, QLB: 24 ml saline), or QLB groups (anesthesia: 0.1 ml saline, QLB: 24 ml 0.375% ropivacaine). Integrated analgesia score (IAS) and numerical rating scale (NRS) scores at rest and during movement, morphine requirements in the first 48 h, time to first morphine dose and morphine-related side effects were recorded.

Results

IASs and NRS scores at rest and during movement were significantly lower in QLB and ITM group than in Control group. Moreover, IASs and NRS scores at rest and during movement were lower in QLB group than in ITM group. Time to first morphine dose was significantly longer in QLB group than in ITM and Control group. Furthermore, morphine requirements in the first 48 h were significantly lower in QLB group than ITM and Control group. Incidence of morphine-related side effects was significantly higher in ITM group than in QLB and Control group.

Conclusions

QLB and ITM are effective analgesic regimens after CS. However, QLB provides better long-lasting analgesia and reduced total postoperative morphine consumption.

Designing and conducting proof-of-concept chronic pain analgesic clinical trials

Introduction:

The evolution of pain treatment is dependent on successful development and testing of interventions. Proof-of-concept (POC) studies bridge the gap between identification of a novel target and evaluation of the candidate intervention's efficacy within a pain model or the intended clinical pain population.

Methods:

This narrative review describes and evaluates clinical trial phases, specific POC pain trials, and approaches to patient profiling.

Results:

We describe common POC trial designs and their value and challenges, a mechanism-based approach, and statistical issues for consideration.

Conclusion:

Proof-of-concept trials provide initial evidence for target use in a specific population, the most appropriate dosing strategy, and duration of treatment. A significant goal in designing an informative and efficient POC study is to ensure that the study is safe and sufficiently sensitive to detect a preliminary efficacy signal (ie, a potentially valuable therapy). Proof-of-concept studies help avoid resources wasted on targets/molecules that are not likely to succeed. As such, the design of a successful POC trial requires careful consideration of the research objective, patient population, the particular intervention, and outcome(s) of interest. These trials provide the basis for future, larger-scale studies confirming efficacy, tolerability, side effects, and other associated risks.

Electrophysiological characterisation of central sensitisation in canine spontaneous osteoarthritis

In man, central sensitisation (CS) contributes to the pain of osteoarthritis (OA). Dogs with spontaneous OA may also exhibit CS. Electrophysiological reflex measurements are more objective than behavioural assessments and can be used to evaluate CS in preclinical and clinical studies. It was hypothesised that dogs suffering from OA would exhibit electrophysiological characteristics indicative of CS, associated with reduced diffuse noxious inhibitory controls (DNICs). One hundred and seventeen client-owned dogs were recruited to the study. Hind limb nociceptive withdrawal reflex thresholds, stimulus response, and temporal summation characteristics were recorded, during alfaxalone anaesthesia, from 46 OA dogs, 29 OA dogs receiving nonsteroidal anti-inflammatory drugs (OANSAIDs), and 27 breed- and weight-matched control dogs. Efficacy of DNIC was evaluated in 12 control and 11 of the OA dogs, by application of a mechanical conditioning stimulus to the contralateral forelimb. Nociceptive withdrawal reflex thresholds were higher in OA compared with control dogs (P = 0.02). Stimulus response characteristics demonstrated an augmented response in OANSAID dogs compared with OA (P < 0.001) and control (P < 0.001) dogs. Temporal summation demonstrated exaggerated C-fibre-mediated responses in both OA (P < 0.001) and OANSAID (P = 0.005) groups, compared with control animals. Conditioning stimulus application resulted in inhibition of test reflex responses in both OA and control animals (P < 0.001); control animals demonstrated greater inhibition compared with OA (P = 0.0499). These data provide evidence of neurophysiological changes consistent with CS in dogs with spontaneous OA and demonstrate that canine OA is associated with reduced DNIC.

Time perspective as a moderator of a relationship between preoperative pain and acute postoperative pain

The aim of this article was to test time perspective as a moderator of the relationship between pain before surgery and acute postoperative pain. Time perspective (ZTPI) and pain before surgery (SF-MPQ) were assessed pre-operatively in 112 patients. The results suggest that past-negative time perspective and fatalistic perspective are significant moderators of the link between preoperative pain and acute postoperative pain. In a case of weak past-negative perspective and weak present-fatalistic perspective, the relationship between preoperative pain and acute postoperative pain is not significant.

Risk factors for severe acute pain and persistent pain after surgery for breast cancer: a prospective observational study

Background and objectives

There are few prospective studies providing comprehensive assessment of risk factors for acute and persistent pain after breast surgery. This prospective observational study assessed patient-related, perioperative, and genetic risk factors for severe acute pain and persistent pain following breast cancer surgery.

Methods

Women presenting for elective breast cancer surgery completed State Trait Anxiety Inventory, Beck Depression Inventory, and Pain Catastrophizing Scale questionnaires preoperatively. Diffuse noxious inhibitory control and mechanical temporal summation were assessed. A blood sample was obtained for genetic analysis. Analgesic consumption and pain scores were collected in the post-anesthesia care unit, and at 24 and 72 hours. Patients were contacted at 1, 3, 6, and 12 months to assess persistent pain. Primary outcome was maximum acute pain score in first 72 hours and secondary outcome was persistent pain.

Results

One hundred twenty-four patients were included in analysis. Increased duration of surgery, surgeon, and higher pain catastrophizing scores were associated with increased severity of acute pain, while preoperative radiotherapy was associated with reduced severity. Persistent pain was reported by 57.3% of patients. Postdischarge chemotherapy (OR 2.52, 95% CI 1.13 to 5.82), postdischarge radiation (OR 3.39, 95% CI 1.24 to 10.41), severe acute pain (OR 5.39, 95% CI 2.03 to 15.54), and moderate acute pain (OR 5.31, 95% CI 1.99 to 15.30) were associated with increased likelihood of persistent pain.

Conclusions

Increased duration of surgery, higher pain catastrophizing score, and surgeon were associated with increased severity of acute pain. Preoperative radiation was associated with lower acute pain scores. Postsurgery radiation, chemotherapy, and severity of acute pain were associated with increased likelihood of persistent pain.

Trial registration

NCT03307525.

Persistent Postsurgical Pain

The development of chronic pain is considered a major complication after surgery. Basic science research in animal models helps us understand the transition from acute to chronic pain by identifying the numerous molecular and cellular changes that occur in the peripheral and central nervous systems. It is now well recognized that inflammation and nerve injury lead to long-term synaptic plasticity that amplifies and also maintains pain signaling, a phenomenon referred to as pain sensitization. In the context of surgery in humans, pain sensitization is both responsible for an increase in postoperative pain via the expression of wound hyperalgesia and considered a critical factor for the development of persistent postsurgical pain. Using specific drugs that block the processes of pain sensitization reduces postoperative pain and prevents the development of persistent postoperative pain. This narrative review of the literature describes clinical investigations evaluating different preventative pharmacologic strategies that are routinely used by anesthesiologists in their daily clinical practices for preventing persistent postoperative pain. Nevertheless, further efforts are needed in both basic and clinical science research to identify preclinical models and novel therapeutics targets. There remains a need for more patient numbers in clinical research, for more reliable data, and for the development of the safest and the most effective strategies to limit the incidence of persistent postoperative pain.

Pain Modulation: From Conditioned Pain Modulation to Placebo and Nocebo Effects in Experimental and Clinical Pain

Accumulating evidence reveal important applications of endogenous pain modulation assessment in healthy controls and in patients in clinical settings, as dysregulations in the balance of pain modulatory circuits may facilitate pain and promote chronification of pain. This article reviews data on pain modulation, focusing on the mechanisms and translational aspects of pain modulation from conditioned pain modulation (CPM) to placebo and nocebo effects in experimental and clinical pain. The specific roles of expectations, learning, neural and neurophysiological mechanisms of the central nervous system are briefly reviewed herein. The interaction between CPM and placebo systems in pain inhibitory pathways is highly relevant in the clinic and in randomized controlled trials yet remains to be clarified. Examples of clinical implications of CPM and its relationship to placebo and nocebo effects are provided. A greater understanding of the role of pain modulation in various pain states can help characterize the manifestation and development of chronic pain and assist in predicting the response to pain-relieving treatments. Placebo and nocebo effects, intrinsic to every treatment, can be used to develop personalized therapeutic approaches that improve clinical outcomes while limiting unwanted effects.

Pain Catastrophizing is Not Associated With Spinal Nociceptive Processing in People With Chronic Widespread Pain

Objectives:

Pain catastrophizing has been associated with higher pain intensity, increased risk of developing chronic pain and poorer outcomes after treatment. Despite this, the mechanisms by which pain catastrophizing influences pain remain poorly understood. It has been hypothesized that pain catastrophizing may impair descending inhibition of spinal level nociception. The aims of this study were to compare spinal nociceptive processing in people with chronic widespread pain and pain-free controls and examine potential relationships between measures of pain catastrophizing and spinal nociception.

Materials and Methods:

Twenty-six patients with chronic widespread pain and 22 pain-free individuals participated in this study. Spinal nociception was measured using the nociceptive flexion reflex (NFR) threshold and NFR inhibition, measured as the change in NFR area during exposure to a second, painful conditioning stimulus (cold water immersion). Pain catastrophizing was assessed using the Pain Catastrophizing Scale and a situational pain catastrophizing scale.

Results:

Compared with pain-free controls, patients with chronic widespread pain had higher pain catastrophizing scores and lower NFR thresholds. Although NFR area was reduced by a painful conditioning stimulus in controls, this was not apparent in individuals with chronic widespread pain. No significant correlations were observed between measures of pain catastrophizing and spinal nociception.

Discussion:

Despite increased excitability and decreased inhibition of spinal nociception in patients with chronic widespread pain, we could find no evidence of a significant relationship between pain catastrophizing and measures of spinal nociceptive processing.

Current methods and challenges for acute pain clinical trials

This article reviews current methods and challenges and provides recommendations for future design and conduct of clinical trials of interventions to treat acute pain.

Introduction:

The clinical setting of acute pain has provided some of the first approaches for the development of analgesic clinical trial methods.

Objectives:

This article reviews current methods and challenges and provides recommendations for future design and conduct of clinical trials of interventions to treat acute pain.

Conclusion:

Growing knowledge about important diverse patient factors as well as varying pain responses to different acute pain conditions and surgical procedures has highlighted several emerging needs for acute pain trials. These include development of early-phase trial designs that minimize variability and thereby enhance assay sensitivity, minimization of bias through blinding and randomization to treatment allocation, and measurement of clinically relevant outcomes such as movement-evoked pain. However, further improvements are needed, in particular for the development of trial methods that focus on treating complex patients at high risk of severe acute pain.

Pain and sensory disturbances following surgical repair of pectus carinatum

BACKGROUND/PURPOSE

The purpose of this study was to assess the characteristics of persistent postoperative pain and sensory disturbances following surgical repair of pectus carinatum.

METHODS

Using a prospective observational design, 28 patients were assessed before, 6 weeks and 6 months after a modified Ravitch operation for pectus carinatum. Postoperative pain was assessed using the Short Form McGill Pain Questionnaire. Sensory testing was conducted to detect brush-evoked allodynia and pinprick hyperalgesia. Additionally, generic and disease-specific quality of life was assessed using the Short Form-36 Health Survey and the Nuss Questionnaire Modified for Adults before and after surgery.

RESULTS

Six weeks after surgery, ten patients reported mild pain or discomfort. Six months after surgery, four patients reported only mild pain. Allodynia was detected in two patients 6 weeks and 6 months after surgery. Hyperalgesia was detected in eight patients 6 weeks after surgery, and in six patients 6 months after surgery. Generic quality of life was significantly improved over time.

CONCLUSIONS

The study showed no significant pain problems, a tendency to reduced sensory disturbances and significant improvements in quality of life 6 months after surgical repair of pectus carinatum. Future studies should include a longer follow-up period to determine if these positive results are persistent.

LEVELS OF EVIDENCE

1 (Prognosis Study).

Psychophysical and psychological predictors of acute pain after breast surgery differ in patients with and without pre-existing chronic pain

The prediction of acute postoperative pain would be of great clinical advantage, but results of studies investigating possible predictors are inconsistent. Here, we studied the role of a wide variety of previously suggested predictors in 74 patients undergoing breast surgery. Preoperatively, patients filled out the Pain Sensitivity Questionnaire (PSQ) and a set of psychological questionnaires (the Beck Depression Inventory [BDI], State-Trait Anxiety Inventory [STAI], and Pain Catastrophizing Scale [PCS]) and participated in an experimental pain testing session, including assessment of conditioned pain modulation (CPM), temporal summation, and responses to heat, pinprick, and pressure pain. Postoperatively, patients reported pain intensity. Stepwise linear regression analysis was used to test for prediction of maximal pain on postoperative day 1 in the whole cohort and in the subgroups of patients with and without pre-existing chronic pain. In the total group, linear regression identified only the expectation of postoperative pain intensity as significant predictor (F[1,65] = 6.5, P < 0.05), explaining 9% of the variance. In patients without pre-existing chronic pain, a smaller CPM effect predicted more postoperative pain, explaining 17% of the variance (F[1,48] = 9.9, P < 0.01). In patients with pre-existing chronic pain, higher PSQ and PCS scores predicted more postoperative pain, together explaining 54% of the variance (F[2,19] = 11.1, P < 0.001). In conclusion, prediction of acute postoperative pain in the whole group was limited. This might be due to differing predictors in specific subgroups of patients. Although CPM predicted pain in patients without pre-existing chronic pain, PSQ and PCS predicted pain in patients with pre-existing chronic pain.

Safety of Patient-Controlled Analgesia After Surgery in Children And Adolescents: Concerns And Potential Solutions

Patient-controlled analgesia (PCA) is common practice for acute postoperative pain management. Postoperative PCA use decreases pain intensity and improves patient satisfaction when compared to non-PCA routes of medication administration. Although PCA has several advantages regarding efficacy and safety, adverse events remain a concern. Programming errors and protocols, patient monitoring, and PCA by proxy or with continuous infusion are recurring silent dangers of PCA use in children and adolescents. Innovative considerations need to be emphasized for future improvement of PCA devices for elective surgical patients. With technology within the healthcare setting advancing at a fast pace, smart pump technology is something to look forward to.

Preoperative Norepinephrine Levels in Cerebrospinal Fluid and Plasma Correlate With Pain Intensity After Pediatric Spine Surgery

PURPOSE

Catecholamines were found to be involved in descending pain modulation and associated with perioperative pain. The purpose of the present study was to investigate the relationship between preoperative concentrations of catecholamines and postoperative pain intensity of pediatric patients.

METHODS

Fifty adolescents with idiopathic scoliosis scheduled for elective spinal fusion surgery were enrolled in this prospective cohort study. Preoperative plasma and cerebrospinal fluid (CSF) samples were collected and analyzed by mass spectrometry. Pain intensity was assessed during the acute postoperative period and in the intermediate period.

RESULTS

Preoperative plasma concentrations of norepinephrine (NE) and normetanephrine (NME), as well as the CSF concentration of NE, were significantly correlated with the presence of pain six weeks after surgery (r = 0.48, 0.50, and 0.50, respectively; p < .002). We also found that preoperative NE levels in CSF were significantly higher in patients reporting moderate to severe pain intensity than in patients with mild pain during the first day following surgery (0.268 ± 0.29 ng/mL vs. 0.121 ± 0.074 ng/mL, p = .01), as well as between patients reporting pain and painless patients at 6 weeks postsurgery (0.274 ± 0.282 ng/mL vs. 0.103 ± 0.046 ng/mL respectively, U = 69.5, p = .002).

CONCLUSIONS

These results support the potential role of catecholamine levels in predicting postoperative pain intensity.

Evoked potentials after painful cutaneous electrical stimulation depict pain relief during a conditioned pain modulation

BACKGROUND

Conditioned pain modulation (CPM) evaluates the pain modulating effect of a noxious conditioning stimulus (CS) on another noxious test stimulus (TS), mostly based solely on subjective pain ratings. We used painful cutaneous electrical stimulation (PCES) to induce TS in a novel CPM-model. Additionally, to evaluate a more objective parameter, we recorded the corresponding changes of cortical evoked potentials (PCES-EP).

METHODS

We examined the CPM-effect in 17 healthy subjects in a randomized controlled cross-over design during immersion of the non-dominant hand into 10 °C or 24 °C cold water (CS). Using three custom-built concentric surface electrodes, electrical stimuli were applied on the dominant hand, inducing pain of 40-60 on NRS 0-100 (TS). At baseline, during and after CS we assessed the electrically induced pain intensity and electrically evoked potentials recorded over the central electrode (Cz).

RESULTS

Only in the 10 °C-condition, both pain (52.6 ± 4.4 (baseline) vs. 30.3 ± 12.5 (during CS)) and amplitudes of PCES-EP (42.1 ± 13.4 μV (baseline) vs. 28.7 ± 10.5 μV (during CS)) attenuated during CS and recovered there after (all p < 0.001). In the 10 °C-condition changes of subjective pain ratings during electrical stimulation and amplitudes of PCES-EP correlated significantly with each other (r = 0.5) and with CS pain intensity (r = 0.5).

CONCLUSIONS

PCES-EPs are a quantitative measure of pain relief, as changes in the electrophysiological response are paralleled by a consistent decrease in subjective pain ratings. This novel CPM paradigm is a feasible method, which could help to evaluate the function of the endogenous pain modulation processes.

TRIAL REGISTRATION

German Clinical Trials Register DRKS-ID: DRKS00012779 , retrospectively registered on 24 July 2017.

Experimental manipulations of pain catastrophizing influence pain levels in patients with chronic pain and healthy volunteers

Pain catastrophizing (PC) has been related to pain levels in both patients experiencing acute or chronic pain and in healthy volunteers exposed to experimental pain. Still, it is unclear whether high levels of pain catastrophizing lead to high levels of pain or vice versa. We therefore tested whether levels of pain catastrophizing could be increased and decreased in the same participant through hypnotic suggestions and whether the altered level of situation-specific pain catastrophizing was related to increased and decreased pain levels, respectively. Using the spontaneous pain of 22 patients with chronic tension-type headache and experimentally induced pain in 22 healthy volunteers, participants were tested in 3 randomized sessions where they received 3 types of hypnotic suggestions: Negative (based on the 13 items in the Pain Catastrophizing Scale), Positive (coping-oriented reversion of the Pain Catastrophizing Scale), and Neutral (neutral sentence) hypnotic suggestions. The hypnotic suggestions significantly increased and decreased situation-specific PC in both patients and healthy volunteers (P < 0.001). Also, the levels of pain intensity and pain unpleasantness were significantly altered in both patients and healthy volunteers (P < 0.001). Furthermore, regression analyses showed that changes in pain catastrophizing predicted changes in pain in patients (R = 0.204-0.304; P < 0.045) and in healthy volunteers (R = 0.328-0.252; P < 0.018). This is the first study to successfully manipulate PC in positive and negative directions in both patients with chronic pain and healthy volunteers and to show that these manipulations significantly influence pain levels. These findings may have important theoretical and clinical implications.

Endogenous Opiates and Behavior: 2015

This paper is the thirty-eighth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2015 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia, stress and social status, tolerance and dependence, learning and memory, eating and drinking, drug abuse and alcohol, sexual activity and hormones, pregnancy, development and endocrinology, mental illness and mood, seizures and neurologic disorders, electrical-related activity and neurophysiology, general activity and locomotion, gastrointestinal, renal and hepatic functions, cardiovascular responses, respiration and thermoregulation, and immunological responses.

Are preoperative experimental pain assessments correlated with clinical pain outcomes after surgery? A systematic review

BACKGROUND

Pain after surgery is not uncommon with 30% of patients reporting moderate to severe postoperative pain. Early identification of patients prone to postoperative pain may be a step forward towards individualized pain medicine providing a basis for improved clinical management through treatment strategies targeting relevant pain mechanisms in each patient. Assessment of pain processing by quantitative sensory testing (QST) prior to surgery has been proposed as a method to identify patients at risk for postoperative pain, although results have been conflicting. Since the last systematic review, several studies investigating the association between postoperative pain and more dynamic measures of pain processing like temporal summation of pain and conditioned pain modulation have been conducted.

OBJECTIVES

According to the PRISMA guidelines, the aim of this systematic review was to evaluate whether assessment of experimental pain processing including measures of central pain mechanisms prior to surgery was associated with pain intensity after surgery.

METHODS

Systematic database searches in PubMed and EMBASE with the following search components: QST, association, and postoperative pain, for studies that assessed the association between QST and pain after surgery were performed. Two authors independently reviewed all titles and abstracts to assess their relevance for inclusion. Studies were included if (1) QST was performed prior to surgery, (2) pain was assessed after surgery, and (3) the association between QST and pain after surgery was investigated. Forty-four unique studies were identified, with 30 studies on 2738 subjects meeting inclusion criteria. The methodological quality of the include studies was assessed and data extraction included study population, type of surgery, QST variables, clinical pain outcome measure and main result.

RESULTS

Most studies showed moderate to high risk of bias. Type of surgery investigated include 7 studies on total knee replacement, 5 studies on caesarean section, 4 studies on thoracic surgery, 2 studies on herniotomy, 2 studies on hysterectomy/myomectomy, 1 study on tubal ligation, 1 study on gynecologic laparoscopy, 1 study on arthroscopic knee surgery, 1 study on shoulder surgery, 1 study on disc herniation surgery, 1 study on cholecystectomy, 1 study on percutaneous nephrolithotomy, 1 study on molar surgery, 1 study on abdominal surgery, and 1 study on total knee replacement and total hip replacement. The majority of the preoperative QST variables showed no consistent association with pain intensity after surgery. Thermal heat pain above the pain threshold and temporal summation of pressure pain were the QST variables, which showed the most consistent association with acute or chronic pain after surgery.

CONCLUSIONS

QST before surgery does not consistently predict pain after surgery. High quality studies investigating the presence of different QST variables in combination or along with other pain-related psychosocial factors are warranted to confirm the clinical relevance of QST prior to surgery.

IMPLICATIONS

Although preoperative QST does not show consistent results, future studies in this area should include assessment of central pain mechanisms like temporal summation of pressure pain, conditioned pain modulation, and responses to pain above the pain threshold since these variables show promising associations to pain after surgery.

A review of anesthetic techniques and outcomes following minimally invasive repair of pectus excavatum (Nuss procedure)

BACKGROUND

Pectus excavatum (PE) is the most common congenital chest wall deformity, occurring in 1 : 1000 children with a male to female ratio of 4 : 1. Several procedures have been described to manage this deformity, including cartilage resection with sternal osteotomy (the Ravitch procedure) and a minimally invasive repair technique (the Nuss procedure). While initially described as a nonthoracoscopic technique, the current surgical approach of the Royal Childrens Hospital involves thoracoscopic assistance. Postoperative pain is significant in patients undergoing the pectus repair and multiple analgesic regimens have been advocated with continuous thoracic epidural infusions and opioid infusions the most common. Some authors have advocated patient-controlled analgesia (PCA), paravertebral nerve blocks (PVNB), and wound infusion catheters as alternatives.

AIMS

The primary aim of this study was to assess our experience with postoperative pain and analgesia requirements associated with the minimally invasive repair of pectus excavatum in children.

METHODS

This is a retrospective cohort study with a contemporaneous comparison group examining patients treated between January 2005 and December 2015 for minimally invasive repair of pectus excavatum by the Nuss procedure.

RESULTS

Two hundred and seventeen patients [mean age 14.9 (sd 1.9) years] with pectus excavatum treated at the Royal Childrens Hospital between 2005 and 2015 were identified. All patients were managed with thoracic epidural analgesia and intravenous morphine infusions. The epidural was effective in the postanesthesia care unit in 97.3% (failure to place an epidural rate was 4 (1.9%); no block on awakening 0.9%). A further 4 (1.8%) were removed within 24 h. The mean morphine equivalent dose in the first 24 h was 0.8 mg·kg^-1 ·day^-1 . PCA was continued for a mean of 3.8 days and the total mean morphine equivalent dose was 2.2 mg·kg^-1 ·day^-1 . Minor complications occurred in 67 (30.9%) with postoperative nausea and vomiting in 36 patients (16.6%) and urinary retention requiring an indwelling catheter in 40 patients (18.4%).

CONCLUSION

An epidural-based analgesic regime is associated with low pain scores and few acute complications. The continuation of morphine analgesia after the first postoperative day is common but associated with an increased incidence of urinary retention and nausea and vomiting.

Time perspective as a predictor of acute postsurgical pain and coping with pain following abdominal surgery

BACKGROUND

The aim of this study was to predict acute postsurgical pain and coping with pain following surgery based on preoperative time perspectives. Time perspective is a basic dimension of psychological time. It is a tendency to focus on a particular time area: the past, the present and the future.

METHOD

Seventy-six patients completed measures of time perspective and pain 24 h before abdominal surgery. During the 3 days after surgery, measures of pain and coping with pain were completed.

RESULTS

We performed hierarchical regression analyses to identify predictors of acute postsurgical pain and how patients cope with it. These analyses suggested that a preoperative past-negative time perspective can be a predictor of postoperative pain level and catastrophizing after surgery.

CONCLUSION

The findings of our study indicate the importance of time perspective, especially the past perspective, in dealing with postoperative pain.

SIGNIFICANCE

Our research indicates that a preoperative past-negative time perspective is a significant predictor of acute postsurgical pain intensity and the strongest predictor of pain catastrophizing.