The effects of failing to control pain: an experimental investigation

Acceptance and commitment therapy reduces psychological distress in patients with cancer: a systematic review and meta-analysis of randomized controlled trials

Objective

This study aimed to systematically review and meta-analyze the clinical efficacy of acceptance and commitment therapy (ACT) in patients with cancer and psychological distress.

Methods

Randomized controlled trials (RCTs) from seven English electronic databases were systematically investigated from inception to 3 October 2023. A total of 16 RCTs from 6 countries with 711 participants were included in this study. Estimated pooled effect sizes (ESs) were calculated via inverse-variance random-effects or fixed-effects (I2 ≤ 50%) model and presented by standardized mean difference (SMD). Subgroup analyses were performed to reduce confounding factors and heterogeneity, and the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) system was used to evaluate the quality of the pooled ESs.

Results

The pooled ESs revealed that statistically significant improvements in anxiety [postintervention SMD = -0.41 (95% confidence interval (CI), -0.71, -0.11); p = 0.008; I2 = 65%; follow-up SMD = -0.37 (95% CI, -0.66, -0.08); p = 0.01; I2 = 29%], depression [postintervention SMD = -0.45 (95% CI, -0.63, -0.27); p < 0.001; I2 = 49%; follow-up SMD = -0.52 (95% CI, -0.77, -0.28); p < 0.001; I2 = 0%], and psychological flexibility [postintervention SMD = -0.81 (95% CI, -1.50, -0.11); p = 0.02; I2 = 84%; follow-up SMD = -0.71 (95% CI, -1.12, -0.31); p = 0.0006; I2 = 38%] in ACT-treated participants were observed compared to patients treated with control conditions. However, other outcomes, such as physical symptom alleviation, were not significantly associated.

Conclusion

The findings of this systematic review and meta-analysis suggest that ACT is associated with improvements in anxiety, depression, and psychological flexibility in patients with cancer.

Systematic review registration

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42022320515.

Acceptance and Commitment Therapy for chronic pain on functioning: A systematic review of randomized controlled trials

Chronic pain is a worldwide health problem, Acceptance and Commitment Therapy (ACT) is regarded as one of the promising interventions. ACT aims to help chronic pain patients to create space for pursuing valued life activities in spite of pain. This systematic review of randomized controlled trials (RCTs) examined the efficacy of ACT on functioning for chronic pain. Literature search was performed among seven databases, and 12 RCTs were retrieved. The revised Cochrane risk of bias tool (RoB 2.0) was employed to assess the quality of the 12 RCTs, of which 10 were rated as "low risks", and 2 as "some concerns". Effect sizes of single RCTs and the pooled effect sizes of meta analyses were all rated by Grading of Recommendations Assessment, Development, and Evaluation (GRADE) system. Low to moderate evidence showed that ACT played a positive immediate role in functioning for patients with chronic pain; however, it is inconsistent whether the effect can be sustained. More RCTs are warranted within specific chronic pain conditions.

Does the performance of lower limb peripheral nerve blocks differ among orthopedic sub-specialties? A single institution experience in 246 patients

OBJECTIVES

Continuous peripheral nerve blocks (cPNBs) have shown promising results in pain management after orthopaedic surgeries. However, they can be associated with some risks and limitations. The purpose of this study is to describe our experience with the cPNBs regarding efficacy and adverse events in patients undergoing orthopedic surgeries on the lower extremity in different subspecialties.

METHODS

This is a prospective cohort study on collected data from perineural catheters for pain management after orthopedic surgeries in lower limbs. Catheters were placed by experienced anesthesiologists using sterile technique. After an initial bolus dose of 10-20 mL ropivacaine 0.5% (weight adjusted), the catheters were secured and connected to disposable mechanical infusion pumps with ropivacaine 0.2% (basal infusion rate = 6 mL/h; weight adjusted (0.2 mL/kg/h)). After catheterization, the patients were examined daily, by specially educated acute pain service nurses. Pro re nata (PRN) or fixed boluses (10 mL bupivacaine 0.25%; weight adjusted) with an upper limit of 4 times/day, were administered if indicated. Patients' demographic data, physiological status, and pre-op intake of opioids and other analgesics were registered. The severity of post-operative pain was assessed with 'Numeric Rating Scale' (NRS) and 'Face, legs, Activity, Cry, Consolability' (FLACC) scale for adults and children, respectively. The need for additional opioids and possible complications were registered.

RESULTS

We included 547 catheters of 246 patients (Range 1-10 catheters per patient). Overall, 115 (21%) femoral, 162 (30%) saphenous, 66 (12%) sciatic, and 204 (37%) popliteal sciatic nerve catheter were used. 452 (83%) catheters were inserted by a primary procedure, 61(11%) catheters employed as a replacement, and 34 catheters (6.2%) used as a supplement. For guiding the catheterization, ultrasound was applied in 451 catheters (82%), nerve stimulator in 90 catheters (16%), and both methods in 6 catheters (1.1%). The median duration a catheter remained in place was 3 days (IQR = 2-5). The proportion of catheters with a duration of two days was 81, 79, 73, and 71% for femoral, sciatic, saphenous, and popliteal nerve, respectively. In different subspecialties, 91% of catheters in wound and amputations, 89% in pediatric surgery, 76% in trauma, 64% in foot and ankle surgery, and 59% in limb reconstructive surgery remained more than two days. During first 10 days after catheterization, the proportion of pain-free patients were 77-95% at rest and 63-88% during mobilization, 79-92% of the patients did not require increased opioid doses, and 50-67% did not require opioid PRN doses. In addition to 416 catheters (76%), which were removed as planned, the reason for catheter removal was leaving the hospital in 27 (4.9%), loss of efficacy in 69 (13%), dislodgement in 23 (4.2%), leakage in 8 (1.5%), and erythema in 4 catheters (0.73%). No major complication occurred.

CONCLUSIONS

After orthopaedic procedures, cPNBs can be considered as an efficient method for improving pain control and minimizing the use of additional opioids. However, the catheters sometimes might need to be replaced to achieve the desired efficacy.

The Stressful Characteristics of Pain That Drive You NUTS: A Qualitative Exploration of a Stress Model to Understand the Chronic Pain Experience

OBJECTIVE

Despite decades of research on the identification of specific characteristics of situations that trigger a physiological stress response (novelty, unpredictability, threat to the ego, and sense of low control [NUTS]), no integrative research has examined the validity of this framework applied to pain experiences. This study aimed to 1) explore the stressful characteristics of pain among individuals living with chronic pain and 2) examine whether the NUTS framework comprehensively captures the stressful nature of pain.

SUBJECTS

Participants were 41 adult participants living with chronic pain.

METHODS

Interviews in six focus groups were conducted in French using a semistructured interview guide. Participants first discussed how pain is stressful. Then, they were introduced to the NUTS framework and commented on the extent to which it captured their experience. The verbatim transcriptions of interviews were reviewed using reflexive thematic analysis. Analyses were conducted in French; quotes and themes were translated into English by a professional translator.

RESULTS

The pain-NUTS framework adequately captured participants' experiences. Multiple aspects of pain (pain intensity fluctuations, pain flare-up duration, pain quality and location, functional limitations, diagnosis and treatment) were associated with one or more stress-inducing characteristics. In addition, a second layer of meaning emerged in the context of chronic pain that provided contextual information regarding when, how, and why pain became more or less stressful.

CONCLUSIONS

The NUTS characteristics seem to offer a comprehensive framework to understand how pain and its context of chronicity can be a source of stress. This study provides preliminary support for the pain-NUTS framework to allow the formal integration of pain and stress research.

Efficacy of non-opioid analgesics to control postoperative pain: a network meta-analysis

Background

The aim of this network meta-analysis (NMA) was to evaluate the safety and efficacy of intravenous (IV) Meloxicam 30 mg (MIV), an investigational non-steroidal anti-inflammatory drug (NSAID), and certain other IV non-opioid analgesics for moderate-severe acute postoperative pain.

Methods

We searched PubMed and CENTRAL for Randomized Controlled Trials (RCT) (years 2000–2019, adult human subjects) of IV non-opioid analgesics (IV NSAIDs or IV Acetaminophen) used to treat acute pain after abdominal, hysterectomy, bunionectomy or orthopedic procedures. A Bayesian NMA was conducted in R to rank treatments based on the standardized mean differences in sum of pain intensity difference from baseline up to 24 h postoperatively (sum of pain intensity difference: SPID 24). The probability and the cumulative probability of rank for each treatment were calculated, and the surface under the cumulative ranking curve (SUCRA) was applied to distinguish treatments on the basis of their outcomes such that higher SUCRA values indicate better outcomes. The study protocol was prospectively registered with by PROSPERO (CRD42019117360).

Results

Out of 2313 screened studies, 27 studies with 36 comparative observations were included, producing a treatment network that included the four non-opioid IV pain medications of interest (MIV, ketorolac, acetaminophen, and ibuprofen). MIV was associated with the largest SPID 24 for all procedure categories and comparators. The SUCRA ranking table indicated that MIV had the highest probability for the most effective treatment for abdominal (89.5%), bunionectomy (100%), and hysterectomy (99.8%). MIV was associated with significantly less MME utilization versus all comparators for abdominal procedures, hysterectomy, and versus acetaminophen in orthopedic procedures. Elsewhere MME utilization outcomes for MIV were largely equivalent or nominally better than other comparators. Odds of ORADEs were significantly higher for all comparators vs MIV for orthopedic (gastrointestinal) and hysterectomy (respiratory).

Conclusions

MIV 30 mg may provide better pain reduction with similar or better safety compared to other approved IV non-opioid analgesics. Caution is warranted in interpreting these results as all comparisons involving MIV were indirect.

Impact of controllability on pain and suffering

Supplemental Digital Content is Available in the Text.

Introduction:

Chronic pain and pain-related suffering are major health problems. The lack of controllability of experienced pain seems to greatly contribute to the extent of suffering. This study examined how controllability affects the perception of pain and pain-related suffering, and the modulation of this effect by beliefs and emotions such as locus of control of reinforcement, pain catastrophizing, and fear of pain.

Methods:

Twenty-six healthy subjects received painful electric stimulation in both controllable and uncontrollable conditions. Visual analogue scales and the “Pictorial Representation of Illness and Self Measure” were used to assess pain intensity, unpleasantness, pain-related suffering, and the level of perceived control. We also investigated nonverbal indicators of pain and suffering such as heart rate, skin conductance, and corrugator electromyogram.

Results:

Controllability selectively reduced the experience of pain-related suffering, but did not affect pain intensity or pain unpleasantness. This effect was modulated by chance locus of control but was unrelated to fear of pain or catastrophizing. Physiological responses were not affected by controllability. In a second sample of 25 participants, we varied the instruction. The effect of controllability on pain-related suffering was only present when instructions focused on the person being able to stop the pain.

Discussion:

Our data suggest that the additional measure of pain-related suffering may be important in the assessment of pain and may be more susceptible to the effects of perceived control than pain intensity and unpleasantness. We also show that this effect depends on personal involvement.

Psychiatric and physical comorbidities and pain in patients with multiple sclerosis

Background

It has been observed that patients with multiple sclerosis (MS), who have psychiatric and physical comorbidities such as depression and COPD, have an increased risk of experiencing more pain. In this study, we have distinguished between pain intensity and pain affect, as the latter, particularly, requires treatment. Furthermore, while pain and comorbidities have been assessed using questionnaires, this is possibly a less reliable method for those who are cognitively vulnerable.

Objective

The aim of this study was to determine whether psychiatric and physical comorbidities can predict pain intensity and pain affect in MS patients, susceptible to cognitive impairment.

Methods

Ninety-four patients with MS and 80 control participants participated in this cross-sectional study. Besides depression and anxiety, 47 additional comorbidities were extracted from patients’ medical records. Depression and anxiety were assessed using the Beck Depression Inventory and the Symptom Check List-90. Pain was assessed using the Number of Words Chosen Affective, Coloured Analog Scale, and the Faces Pain Scale. Cognitive functions, for example, memory and executive functions, were assessed using several neuropsychological tests.

Results

The main findings indicate that psychiatric comorbidities (depression and anxiety) predict both pain intensity and pain affect and that total physical comorbidity predicts only pain affect in MS patients, susceptible to cognitive impairment.

Conclusion

Both psychiatric and physical comorbidities predict pain affect. All three clinical outcomes enhance MS patients’ suffering.

Controllability and hippocampal activation during pain expectation in fibromyalgia syndrome

To examine the role of perceived control in pain perception, fibromyalgia patients and healthy controls participated in a reaction time experiment under different conditions of pain controllability. No significant differences between groups were found in pain intensity and unpleasantness ratings. However, during the expectation of uncontrollable pain, patients compared to controls showed higher hippocampal activation. In addition, hippocampal activity during the pain expectation period predicted activation of the posterior cingulate cortex (PCC), precuneus and hippocampus during pain stimulation in fibromyalgia patients. The increased activation of the hippocampus during pain expectation and subsequent activation of the PCC/precuneus during the lack of control phase points towards an influence of pain perception through heightening of alertness and anxiety responses to pain in fibromyalgia patients.

Perceived control alters the effect of acute stress on persistence

We often encounter setbacks while pursuing our goals. Success requires that we cope with these negative outcomes and choose to persist in spite of them. For example, learners may be more likely to continue a course after failing an assessment if they control their emotional reactions to the setback and study harder. However, the ability to effectively cope with the negative emotion inherent in such setbacks can be compromised by acute stress present in daily life (e.g., struggles in the household), which can subsequently lead to problems with persisting with a goal. The present study examined whether increasing the perception of control over setbacks (e.g., belief that a setback was caused by a correctable mistake rather than uncontrollable factors) can guard against the influence of a prior acute stressor on reactions to setbacks. Participants underwent a socially evaluated cold water stress or a nonstress control procedure. Afterward, they performed a behavioral task designed to measure persistence through controllable and uncontrollable setbacks. We observed that exposure to an acute stressor led to a detrimental effect on decision making by decreasing persistence behavior. Importantly, we also observed that the perception of control protected against the effect of preexisting stress and helped promote persistence. That is, stress impaired persistence through uncontrollable setbacks, but the impairment was alleviated by presenting setbacks as controllable. The findings demonstrate a potential avenue for improving the maintenance of goals aimed at behavior change, which can be susceptible to effects of stress.

Attitudes and Beliefs of Working and Work-Disabled People with Chronic Pain Prescribed Long-Term Opioids

OBJECTIVE

This study was designed to gain insight into the apparent contradiction between the perspectives of researchers and policy makers, who have questioned the efficacy and safety of chronic opioid therapy for non-cancer pain patients, and the patients themselves, who often indicate that the therapy has value.

SUBJECTS

A convenience sample of 54 patients on chronic opioid therapy was studied.

METHODS

Participants completed a questionnaire specifically designed for the study, and also several standard instruments that addressed functional interference, emotional functioning, and possible misuse of opioids. Their treating physicians rated the participants on the severity of their disability and the success of their opioid therapy.

RESULTS

Although participants reported significant ongoing pain, they gave positive global ratings to their opioid therapy, and reported little concern about addiction or side effects of opioids. They strongly endorsed the beliefs that opioids helped them control their pain and allowed them to participate in important activities such as work. They expressed the belief that their pain would be severe if they did not have access to opioids, and reported negative experiences with tapering or discontinuing opioids in the past. Work-disabled participants reported higher levels of affective distress, catastrophizing, and functional interference than working participants, and were judged by their physicians to be relatively less successful in managing their pain.

CONCLUSION

The results of this study suggest several tentative hypotheses about why patients on chronic opioid therapy value opioids, and identified several areas for systematic investigation in the future.

Acute painful stress and inflammatory mediator production

BACKGROUND

Proinflammatory pathways may be activated under conditions of painful stress, which is hypothesized to worsen the experience of pain and place medically vulnerable populations at risk for increased morbidity.

OBJECTIVES

To evaluate the effects of pain and subjective pain-related stress on proinflammatory activity.

METHODS

A total of 19 healthy control subjects underwent a single standard cold-pressor pain test (CPT) and a no-pain control condition. Indicators of pain and stress were measured and related to inflammatory immune responses [CD8+ cells expressing the integrin molecule CD11a (CD811a), interleukin (IL)-1 receptor agonist (IL-1RA), and IL-6] immediately following the painful stimulus and compared to responses under no-pain conditions. Heart rate and mean arterial pressure were measured as indicators of sympathetic stimulation.

RESULTS

CPT was clearly painful and generated an activation of the sympathetic nervous system. CD811a increased in both conditions, but with no statistically significantly greater increase following CPT (p<0.06). IL-1RA demonstrated a non-statistically significant increase following CPT (p<0.07). The change in IL-6 following CPT differed significantly from the response seen in the control condition (p<0.02).

CONCLUSIONS

These findings suggest that CP acute pain may affect proinflammatory pathways, possibly through mechanisms related to adrenergic activation.

The effect of pain-related fear on sexual arousal in women with superficial dyspareunia

The role of pain-related fear in the etiology and/or maintenance of superficial dyspareunia is still unclear. The objective of this experiment was to investigate the effects of pain-related fear on sexual arousal in women with superficial dyspareunia (n=48) and women without sexual complaints (n=48). To induce pain-related fear, participants were told that they had a 60% chance of receiving painful stimuli while being exposed to one of two erotic film clips. Genital arousal was assessed using vaginal photoplethysmography. Self-reported ratings of genital sensations and affect were collected after both erotic stimulus presentations. Elevated levels of skin conductance and higher ratings of experienced threat during the pain threat condition indicated that fear was successfully elicited. Pain-related fear impeded genital arousal in all women. Women of both groups reported significantly less positive affect and more negative affect when threatened. Although women with dyspareunia did not differ in their genital responsiveness from women without sexual complaints, they experienced overall significantly more negative affect than the control group. The present results indicate that pain-related fear reduces genital and subjective sexual responding in women with and without sexual problems. We conclude that emotional appraisal of the sexual situation determines genital responsiveness in both sexually dysfunctional and functional women.

The influence of perceived control and self-efficacy on the sensory evaluation of experimentally induced pain

BACKGROUND AND AIMS

Prior research has demonstrated the role of perceived control and self-efficacy beliefs over pain in reducing pain and pain-related disability. The present study aimed to examine the independent influence of perceived control and self-efficacy beliefs on the subjective evaluation of pain.

METHODS

Healthy participants (N = 79) were randomly assigned to one of four conditions that were formed by manipulations of perceived control and self-efficacy. At two occasions in the experimental procedure pain was induced by means of electrical stimulation (16 s) to the lower forearm. Prior to and following upon each pain stimulus, participants completed ratings of pain intensity and pain unpleasantness.

RESULTS

High self-efficacy regarding the ability to exert control over pain resulted in a significant reduction in anticipated pain intensity, anticipated pain unpleasantness, and experienced pain intensity ratings. Furthermore, anticipated pain intensity was found to mediate the relation between self-efficacy and experienced pain intensity.

CONCLUSIONS

It is concluded that in order to observe beneficial effects of offering control over pain, it is important that individuals are convinced (i.e. have high self-efficacy) that they are able to exert this control successfully.

Effects of pain acceptance and pain control strategies on physical impairment in individuals with chronic low back pain

Psychosocial treatments for chronic pain are effective. There is a need, however, to understand the processes involved in determining how these treatments contribute to behavior change. Control and acceptance strategies represent two potentially important processes involved in treatment, although they differ significantly in approach. Results from laboratory-based studies suggest that acceptance-oriented strategies significantly enhance pain tolerance and behavioral persistence, compared with control-oriented strategies. There is a need, however, to investigate processes of acceptance and control directly in clinical settings. The present study investigated the effects of three brief instructional sets (pain control, pain acceptance, continued practice) on demonstrated physical impairment in 74 individuals with chronic low back pain using an analogue experimental design. After controlling for baseline performance, the pain acceptance group demonstrated greater overall functioning on a set of 7 standardized physical tasks relative to the other two groups, which did not differ from one another. Further, the acceptance group exhibited a 16.3% improvement in impairment, whereas the pain control group worsened by 8.3% and the continued practice group improved by 2.5%. These results suggest that acceptance may be a key process involved in behavior change in individuals with chronic pain.

Noise within the social context: annoyance reduction through fair procedures

The social context of noise exposure is a codeterminant of noise annoyance. The present study shows that fairness of the exposure procedure (sound management) can be used as an instrument to reduce noise annoyance. In a laboratory experiment (N = 117) participants are exposed to aircraft sound of different sound pressure level (SPL: 50 vs 70 dB A)--which is experienced as noise--while they work on a reading task. The exposure procedure (fair versus neutral) is modeled in line with findings from social justice theory. In the fair condition, participants can voice their preference for a certain sound sample, although they cannot deduce whether their preference is granted. In the neutral condition, participants are not asked to voice their preference. Results show the predicted interaction effect of sound pressure level and procedure on annoyance: Annoyance ratings are significantly lower in the fair condition than in the neutral condition, but this effect is found only in the 70 dB condition. When the SPL is considerably disturbing, fair procedures reduce noise annoyance. Consequences of the reported findings for both theory and practice are discussed.

Anterolateral prefrontal cortex mediates the analgesic effect of expected and perceived control over pain

Perceived control attenuates pain and pain-directed anxiety, possibly because it changes the emotional appraisal of pain. We examined whether brain areas associated with voluntary reappraisal of emotional experiences also mediate the analgesic effect of perceived control over pain. Using functional magnetic resonance imaging, we compared self-controlled noxious stimuli with physically identical stimuli that were externally controlled. Self-controlled stimulation was accompanied by less pain and anxiety and higher activation in dorsal anterior cingulate (dACC), right dorsolateral, and bilateral anterolateral prefrontal (alPFC) cortices. Activation in dACC and right alPFC was negatively correlated with pain intensity ratings. For externally controlled pain, activation in right alPFC was inversely correlated with the participants' general belief to have control over their lives. Our results are consistent with a reappraisal view of control and suggest that the analgesic effect of perceived control relies on activation of right alPFC. Failure to activate right alPFC may explain the maladaptive effects of strong general control beliefs during uncontrollable pain.

An evaluation of the measurement of pain catastrophizing by the coping strategies questionnaire

Measurement and conceptual issues of pain catastrophizing have been raised in the literature. The issues of construct redundancy and measurement overlap have received particular attention, with suggestions that measures of pain catastrophizing are confounded with measures of negative mood, namely depression. The current study sought to investigate these issues in the coping strategies questionnaire-catastrophizing subscale (CSQ-CAT), a widely used measure of pain catastrophizing. Chronic pain patients (n=152) were recruited from the University of Florida pain clinics and completed a battery of psychological measures. Regression analyses indicated that measures of depression, anxiety, and anger accounted for 69% and 19% of the variance in measures of pain catastrophizing and pain, respectively. Trait anger and the cognitive and fearful dimensions of depression and anxiety were uniquely associated with pain catastrophizing. After controlling for measures of negative mood, pain catastrophizing contributed minimally to the prediction of pain. This study suggests that the CSQ-CAT is highly related to measures of negative mood and raises doubts about its measurement of the construct of pain catastrophizing. Results also provide support for theoretical accounts of the relationships between pain catastrophizing, negative mood, and pain. Clinical implications, future research directions, and alternative measures of pain catastrophizing are discussed.

The Fear of Pain Questionnaire (FPQ): Further psychometric examination in a non-clinical sample

The present study sought to examine psychometric properties of the Fear of Pain Questionnaire (FPQ), a measure of pain-related fear, in a sample of undergraduates. Confirmatory factor analysis confirmed the previously reported three-factor model of the FPQ (e.g. severe pain, minor pain, medical pain), but some items may be redundant. With respect to the reliability of the FPQ, both the FPQ and the subscales showed good internal consistency and test-retest stability was moderate to good. Convergent and predictive validity of the FPQ (and the subscales) were partly supported by moderate correlations with related constructs and with self-reported fear associated with three experimental pain tests. Discriminant validity of the FPQ (and the subscales) was partly supported by low correlations with unrelated self-report measures. Moreover, modest correlation coefficients were found between the FPQ and other pain-related measures. Finally, the minor pain subscale of the FPQ accounted for pain intensity scores on the ischemic pain test and the remaining subscales and the FPQ total scores accounted for pain tolerance on the electrical stimulation test and the thermal pain test. Results are discussed and directions for future research are provided.

Consequences of Inadequate Postoperative Pain Relief and Chronic Persistent Postoperative Pain

Inadequately controlled pain has undesirable physiologic and psychologic consequences such as increased postoperative morbidity, delayed recovery, a delayed return to normal daily living, and reduced patient satisfaction. Importantly, the lack of adequate postoperative pain treatment may lead to persistent pain after surgery, which is often overlooked. Overall, inadequate pain management increases the use of health care resources and health care costs. This article reviews the physiologic and psychologic consequences of inadequately treated pain, with an emphasis on chronic persistent postoperative pain.