Perioperative pain

Changes of the nociceptive flexion reflex threshold in patients undergoing cardiac surgery-a prospective clinical pilot study

Opioid dosage for general anaesthesia and sedation relies on surrogate parameters such as heartrate and blood pressure. This implies the risk of both under- and overdosing. A promising tool to provide target-oriented opioid dosing is measuring the nociceptive flexion reflex threshold (NFRT). The aim of this study was to investigate the individual trajectories and to determine this methods' clinical practicability in the perioperative setting of cardiac surgery. NFRT was measured preoperatively (twice as baseline), immediately after surgery and later in the general ward (primary outcomes). No intraoperative measurements were performed since neuromuscular blockade hinders NFRT assessment. Administered analgesics and pain scores were also recorded (secondary outcomes). Data were collected from August 2019 to March 2020. 264 patients scheduled for cardiac surgery were screened for eligibility. 55 patients were included, 30 rendered datasets for analysis. Thresholds after conclusion of surgery [T_ICU: median (IQR), 31.1 mA (21.5-50.0 mA)] were significantly higher than preoperatively [T_pre: 9.2 mA (5.4-13.4 mA); P < 0.001]. In 11 patients (36.7%), no immediate postoperative reflex response was elicited. Later, all reflexes returned, but thresholds remained significantly higher than preoperatively [T_post: 11.9 mA (9.2-16.6 mA); P = 0.043]. NFRT values after surgery were higher compared to baseline measurements. Subsequently they decreased but did not reach their baseline levels. There was no corresponding dose-dependency, suggesting multimodal effects on the nociceptive system. Unless measurements are not prevented by technical issues NFRT-assessment appears to be a future tool to target analgesics in patients not able to self-report pain. Trial registration Study registration: DRKS00021617. https://www.drks.de/drks_web/navigate.do?navigationId=trial.HTML&TRIAL_ID=DRKS00021617 (registered retrospectively).

Piezoelectric versus conventional techniques for orthognathic surgery: Systematic review and meta-analysis

PURPOSE

A systematic review and meta-analysis of the advantages and disadvantages of the piezo surgery comparing with conventional osteotomy in orthognathic surgery.

METHODS

We conducted this systemic review in accordance with the preferred reporting items for systematic reviews and meta-analysis (PRISMA) statement. We searched for relevant studies in the PubMed/MEDLINE, Embase databases, Lilacs, Scopus and Science Direct to identify prospective and retrospective studies, compare patient outcomes (intraoperative blood loss, operative time, neurosensory disturbance) after performing orthognathic surgery by conventional saw or piezo-electric device. According to pool individual results we used the mean difference (MD) with the 95% confidence interval (95% CI).

RESULTS

Among three studies that used conventional saw and three studies used piezo-electric device and nine studies used both techniques, the operative time required to perform orthognathic standard procedures was longer using piezo-electric device compared to conventional saw. The results showed that during using the conventional saw to perform orthognathic surgery the amount of the blood loss was higher than the amount while using piezo-electric device (MD -140.4 mL; P = 0.29). based on the studies that evaluated neurosensory disturbance, after 3 months and 6 months respectively, neurosensory disturbance was seen in 23.8% and 23.4% of patient who underwent conventional osteotomy versus 4.3% and 2.4% of the patients who underwent surgery in which piezo surgery was used. Our meta-analysis showed difference in neurosensory disturbance between piezo-surgery and conventional surgery at 3 months (MD -19.5; P = 0.11) and 6 months (MD -21; P = 0.5) postoperatively.

CONCLUSION

Piezo-electric device enabled lower blood loss and higher nerve integrity rates in outcomes according to the complications that associated with orthognathic surgery.

TLR4/NF-κB signaling activation in plantar tissue and dorsal root ganglion involves in the development of postoperative pain

Background

Severe postoperative pain remains a clinical problem that impacts patient’s rehabilitation. The present work aims to investigate the role of Toll-like receptor-4 (TLR4) activation in wounded plantar tissue and dorsal root ganglion (DRG) in the genesis of postoperative pain and its underlying mechanisms.

Results

Postoperative pain was induced by plantar incision in rat hind paw. Plantar incision led to increased expression of TLR4 in ipsilateral lumbar 4–5 (L4/L5) DRGs, which occurred at 2 h and was persistent to the third day after surgery. Similar to the change in TLR4 expression, there was also significant increase in phosphorylated nuclear factor-kappa B p65 (p-p65) in DRGs after surgery. Immunofluorescence staining revealed that the increased expressions of TLR4 and p-p65 not only in neuronal cells but also in satellite glial cells in DRG. Furthermore, the enhanced expressions of TLR4 and p-p65 were also detected in plantar tissues around the incision, which was observed starting at 2 h and lasting until the third day after surgery. Prior intrathecal (i.t.) injections of TAK-242 (a TLR4-specific antagonist) or 4',6-diamidino-2-phenylindole-dihydrochloride (PDTC, a nuclear factor-kappa B activation inhibitor) dose dependently alleviated plantar incision-induced mechanical allodynia and thermal hyperalgesia and inhibited the increased expressions of p-p65, tumor necrosis factor-alpha, and interleukin-1 beta in DRG. Prior subcutaneous (s.c.) plantar injection of TAK-242 or PDTC also ameliorated pain-related hypersensitivity following plantar incision. Moreover, the plantar s.c. injection of TAK-242 or PDTC inhibited the increased expressions of p-p65, tumor necrosis factor-alpha, and interleukin-1 beta not only in local wounded plantar tissue but also dramatically in ipsilateral lumbar 4–5 DRGs.

Conclusion

TLR4/ nuclear factor-kappa B signaling activation in local injured tissue and DRG contribute to the development of postoperative pain via regulating pro-inflammatory cytokines release. Targeting TLR4/ nuclear factor-kappa B signaling in local tissue at early stage of surgery may be an effective strategy for the treatment of postoperative pain.

Comparison of intrathecal morphine and surgical-site infusion of ropivacaine as adjuncts to intravenous patient-controlled analgesia in living-donor kidney transplant recipients

INTRODUCTION

This prospective observational study compared the postoperative analgesic effectiveness of intrathecal morphine (ITM) and surgical-site infusion (SSI) of ropivacaine as adjuncts to intravenous (IV) patient-controlled analgesia (PCA) (fentanyl) in living-donor kidney transplant recipients.

METHODS

Patients undergoing living-donor kidney transplantation who received ITM or SSI in addition to IV PCA were included. Rescue analgesia was achieved with IV meperidine as required. The primary outcome, measured using the Numeric Pain Rating Scale (NRS), was pain at rest and when coughing. Patients were assessed for 48 hours after surgery.

RESULTS

A total of 53 patients (32 ITM, 21 SSI) were included in the study. The ITM group showed significantly lower NRS scores, at rest and when coughing, for up to 12 and eight hours. NRS scores were comparable between the groups at other times. The ITM group had significantly less postoperative systemic opioid requirement in the first 24 hours, but there was no significant difference between the systemic opioid consumption of the groups on postoperative Day 2. In the ITM group, 3 (9.4%) patients presented with bradypnoea and 1 (3.1%) with excessive sedation in the first 12 postoperative hours. More patients in the ITM group developed pruritus requiring treatment during the first 24 hours. There were no differences between the groups in other outcomes (e.g. nausea/vomiting, change in pulmonary or kidney functions).

CONCLUSION

Compared with SSI, ITM reduced immediate postoperative pain and IV opioid consumption on postoperative Day 1 after living-donor kidney transplantation, but at the cost of increased pruritus and respiratory depression.

The uptake of transdermal fentanyl in a pregnant sheep model

OBJECTIVE

To evaluate the maternal and foetal uptake of transdermal fentanyl patch applied to the groin of pregnant sheep following surgery.

STUDY DESIGN

Prospective series.

ANIMALS

A group of 16 singleton pregnant sheep underwent anaesthesia for laparotomy, hysterotomy and instrumentation of the foetus. Of these ewes 10 (101 ± 12 days of gestation) were used to evaluate the maternal uptake of transdermal fentanyl, and the efficacy of the drug in the postoperative period (n = 10). To determine the extent of transplacental transfer of fentanyl, six ewes from the group of 10, and six other ewes (92 ± 1 days' gestation) were studied.

METHODS

A 75 μg hour^-1 fentanyl patch was placed onto the woolless skin of the medial thigh close to the groin at the end of surgery. Maternal blood samples were collected from the cephalic or jugular vein, and pain and sedation scores were determined, prior to application of the patch (time 0) and at 3, 6, 12, 24, 36 and 48 hours after. A commercial Fentanyl ELISA kit was used to determine the concentration of fentanyl. Paired maternal and foetal blood samples were collected 48 hours after surgery. Animals were euthanized at the end of the study. Data were tested for normality and compared with Student t test or one-way anova and are expressed as mean ± standard deviation or median (range).

RESULTS

Recovery from anaesthesia and surgery was uneventful in all ewes. The dose of fentanyl was 1.4 ± 0.2 μg kg^-1 hour^-1. The maximum maternal plasma concentration of fentanyl was 0.547 ng mL^-1 (range, 0.349-0.738 ng mL^-1) at 12 hours. After 48 hours, the concentration of fentanyl was 0.381 ng mL^-1 (range, 0.211-0.487 ng mL^-1; maternal) and 0.295 ng mL^-1 (range, 0.185-0.377 ng mL^-1; foetal; p = 0.175). The placental transfer rate of fentanyl was 77%.

CONCLUSIONS AND CLINICAL RELEVANCE

The uptake of fentanyl varied between animals. The placental transfer rate of fentanyl was 77%.

Postoperative pain-from mechanisms to treatment

INTRODUCTION

Pain management after surgery continues to be suboptimal; there are several reasons including lack of translation of results from basic science studies and scientific clinical evidence into clinical praxis.

OBJECTIVES

This review presents and discusses basic science findings and scientific evidence generated within the last 2 decades in the field of acute postoperative pain.

METHODS

In the first part of the review, we give an overview about studies that have investigated the pathophysiology of postoperative pain by using rodent models of incisional pain up to July 2016. The second focus of the review lies on treatment recommendations based on guidelines and clinical evidence, eg, by using the fourth edition of the "Acute Pain Management: Scientific Evidence" of the Australian and New Zealand College of Anaesthetists and Faculty of Pain Medicine.

RESULTS

Preclinical studies in rodent models characterized responses of primary afferent nociceptors and dorsal horn neurons as one neural basis for pain behavior including resting pain, hyperalgesia, movement-evoked pain or anxiety- and depression-like behaviors after surgery. Furthermore, the role of certain receptors, mediators, and neurotransmitters involved in peripheral and central sensitization after incision were identified; many of these are very specific, relate to some modalities only, and are unique for incisional pain. Future treatment should focus on these targets to develop therapeutic agents that are effective for the treatment of postoperative pain as well as have few side effects. Furthermore, basic science findings translate well into results from clinical studies. Scientific evidence is able to point towards useful (and less useful) elements of multimodal analgesia able to reduce opioid consumption, improve pain management, and enhance recovery.

CONCLUSION

Understanding basic mechanisms of postoperative pain to identify effective treatment strategies may improve patients' outcome after surgery.

Prolonged Perioperative Low-Dose Ketamine Does Not Improve Short and Long-term Outcomes After Pediatric Idiopathic Scoliosis Surgery

STUDY DESIGN

A randomized, double-blind, placebo-controlled study, with a six-month follow-up period.

OBJECTIVES

The aim of this study was to test the hypothesis that a 72-hour dose of subanesthetic ketamine in this surgical procedure reduces postoperative morphine use and to assess whether there are fewer adverse effects, if postoperative recovery is faster, if there is less peri-incisional hyperalgesia, or if there is lower incidence of persistent postsurgical pain.

SUMMARY OF BACKGROUND DATA

Tissue injury and high opioid requirements following posterior spinal fusion surgery produce central sensitization, which can in turn be associated with hyperalgesia and chronic pain. Clinical trials involving this type of procedure using subanesthetic ketamine doses have assessed pain and morphine requirements with contradictory results. The effects of prolonged subanesthetic ketamine doses on postoperative recovery, mechanical hyperalgesia, and the incidence of chronic pain are unknown.

METHODS

A total of 48 pediatric patients between 10 and 18 years diagnosed with idiopathic scoliosis were randomized to receive perioperative low-dose ketamine or placebo for 72 hours. They received general anesthesia, intraoperative remifentanil, and morphine postoperatively (patient-controlled analgesia). We measured morphine consumption, pain at rest and during movement (coughing), undesirable effects, and sedation during morphine treatment. The onset of oral intake, ambulation, and hospital stay were recorded. The extent of the peri-incisional hyperalgesia was measured at 72 hours and pain controls were conducted postsurgery.

RESULTS

Primary endpoint results (total cumulative morphine consumption while admitted) were obtained in 44 patients. Results were 2.72 (SD 1.13) in the placebo group and 3.13 (SD 1.13) in the study group (P = 0.2903), with no significant differences. Moreover, differences were not found between the experimental group and the placebo group in the secondary endpoints analyzed.

CONCLUSION

Our findings do not support the routine combining of prolonged subanesthetic ketamine doses with opioids in posterior fusion surgery in children with idiopathic scoliosis.

LEVEL OF EVIDENCE

2.

Regional analgesia in postsurgical critically ill patients

Regional analgesia intrinsically, based on its physiological effects, is routinely used for the perioperative treatment of pain associated with surgical procedures. However, in other areas such as the non-surgical treatment of acute pain for patients in a critical condition, it has not been subjected to specific prospective studies. If we confine ourselves to the physiological effects of the nerve block, in a situation of stress, the indications for regional anaesthesia in this group of patients extend to the management of a wide variety of medical as well as postsurgical conditions, of trauma patients and of other painful procedures performed in the patient's bed. The critical patient certainly must be analyzed individually as their own primary conditions is of vital importance, as well as any associated conditions they have developed that can potentially increase the risk of systemic toxicity or morbidity, such as, coagulopathies, infection, immunosuppressive states, sedation and problems associated with mechanical ventilation. This review aims to assess the role of regional analgesia in critically ill patients, placing it within the algorithm decision tree of the professional responsible for patients in critical care units, all based on the evidence of potential benefits according to the published literature.

Opioid-Sparing Effect of Ketamine in Children: A Meta-Analysis and Trial Sequential Analysis of Published Studies

INTRODUCTION

Reducing postoperative opioid consumption is a priority given its impact upon recovery, and the efficacy of ketamine as an opioid-sparing agent in children is debated. The goal of this study was to update a previous meta-analysis on the postoperative opioid-sparing effect of ketamine, adding trial sequential analysis (TSA) and four new studies.

MATERIALS AND METHODS

A comprehensive literature search was conducted to identify clinical trials that examined ketamine as a perioperative opioid-sparing agent in children and infants. Outcomes measured were postoperative opioid consumption to 48 h (primary outcome: postoperative opioid consumption to 24 h), postoperative pain intensity, postoperative nausea and vomiting and psychotomimetic symptoms. The data were combined to calculate the pooled mean difference, odds ratios or standard mean differences. In addition to this classical meta-analysis approach, a TSA was performed.

RESULTS

Eleven articles were identified, with four added to seven from the previous meta-analysis. Ketamine did not exhibit a global postoperative opioid-sparing effect to 48 postoperative hours, nor did it decrease postoperative pain intensity. This result was confirmed using TSA, which found a lack of power to draw any conclusion regarding the primary outcome of this meta-analysis (postoperative opioid consumption to 24 h). Ketamine did not increase the prevalence of either postoperative nausea and vomiting or psychotomimetic complications.

CONCLUSIONS

This meta-analysis did not find a postoperative opioid-sparing effect of ketamine. According to the TSA, this negative result might involve a lack of power of this meta-analysis. Further studies are needed in order to assess the postoperative opioid-sparing effects of ketamine in children.

Long-term weight gain and economic impact in pigs castrated under local anaesthesia

Castration is a controversial practice in swine production because in some countries is still performed without anaesthesia, and therefore causes intense suffering and stress to animals. This study investigated the effect of pre-surgical administration of local anaesthesia (LA) on the growth performance of piglets until the end of the growth phase (102 days). Piglets aged 3 to 5 days were selected in pairs of similar weights and same age. They were originated from 22 litters. The groups were randomly assigned to one of two treatments. Castration was performed with (LA; n = 45) or without (NLA; n = 45) intra-testicular administration of 0.5 mL of 2% lidocaine plus adrenaline per testicle, administered by an automatic repeating vaccinator. Castration was performed 10 min later. Average daily weight gain and economic impact were evaluated between the intervals before castration until 21 (weaning phase), before castration until 60 (end of the initial nursery phase) and before castration until 102 (growth phase) days of age. Average daily weight gain data were analyzed by comparing the average daily weight gain between the weaning phase, 60 and 102 days of age versus the initial weight (pre-castration). At the end of the growing phase, animals treated with LA showed greater weight gain than animals castrated without anaesthesia. LA also showed improved cost:benefit ratio and theore might provide greater economic benefit under the conditions used in this study. Our findings have proved that castration with LA improves long-term weight gain of piglets.

Effect of preoperative flupirtine on postoperative morphine sparing in patients undergoing total abdominal hysterectomy

Background:

Flupirtine is a unique non-opioid, centrally acting analgesic with muscle relaxant properties. So far no study has evaluated, use of preoperative flupirtine on postoperative morphine sparing effect in patients undergoing total abdominal hysterectomy (TAH).

Materials and Methods:

We performed a prospective, controlled, and randomized study in 50 female patients of American Society of Anesthesiologists physical status I–II, aged between 30 and 60 years scheduled for TAH under general anesthesia (GA). Patients were randomized to receive either single dose flupirtine 100 mg or placebo 1 h prior to surgery. A standard anesthetic and analgesic protocol was followed in both the groups. Postoperatively, a titrated loading dose of intravenous morphine 0.1 mg/kg was followed with patient-controlled analgesia with morphine (bolus of 0.01 mg/kg with a lockout time of 7 min). The primary outcome was cumulative morphine consumption at 48 h postoperatively. Secondary outcomes included hemodynamics, visual analog scale (VAS) at rest, VAS on cough, and any adverse effects.

Results:

All enrolled 50 patients completed the follow-up. The cumulative mean morphine consumption (standard deviation [SD]) at 48 h (40.4 [6.0] vs. 47 [6.6] mg, P = 0.001) was reduced in-group flupirtine as compared with placebo. The cumulative mean VAS at rest (SD) (3 [0.7] vs. 3.7 [0.7], P = 0.001) and on cough (3 [0.9] vs. 3.8 [0.5], P = 0.002) were reduced in-group flupirtine as compared with placebo at 48 h postoperatively.

Conclusion:

Preoperative use of flupirtine exhibited morphine sparing effect in patients following TAH under GA at 48 h.

Reduced somatosensory impairment by piezosurgery during orthognathic surgery of the mandible

PURPOSE

This clinical trial aimed to test the hypothesis that piezosurgery causes reduced nerval irritations and, thus, reduced somatosensory impairment when used in orthognathic surgery of the mandible.

METHODS

To this end, 37 consecutive patients with Angle Class II and III malocclusion were treated using bilateral sagittal split osteotomies (BSSO) of the mandible. In a split mouth design, randomized one side of the mandible was operated using a conventional saw, while a piezosurgery device was used on the contralateral side. In order to test the individual qualities of somatosensory function, quantitative sensory testings (QSTs) were performed 1 month, 6 months and 1 year after surgery.

RESULTS

A comparison of the data using a two-way analysis of variance (ANOVA) revealed a significant reduction in postoperative impairment in warm detection threshold (WDT) (P = 0.046), a decreased dynamic mechanical allodynia (ALL) (P = 0.002) and a decreased vibration detection threshold (VDT) (P = 0.030) on the piezosurgery side of the mandible as opposed to the conventionally operated control side. In the remaining QSTs, minor deviations from the preoperative baseline conditions and a more rapid regression could be observed.

CONCLUSIONS

Piezosurgery caused reduced somatosensory impairment and a faster recovery of somatosensory functions in the present investigation.

Analgesic effect of intrathecal bumetanide is accompanied by changes in spinal sodium-potassium-chloride co-transporter 1 and potassium-chloride co-transporter 2 expression in a rat model of incisional pain

Accumulating evidence has demonstrated that the sodium-potassium-chloride co-transporter 1 and potassium-chloride co-transporter 2 have a role in the modulation of pain transmission at the spinal level through chloride regulation in the pain pathway and by effecting neuronal excitability and pain sensitization. The present study aimed to investigate the analgesic effect of the specific sodium-potassium-chloride co-transporter 1 inhibitor bumetanide, and the change in spinal sodium-potassium-chloride co-transporter 1 and potassium-chloride co-transporter 2 expression in a rat model of incisional pain. Results showed that intrathecal bumetanide could decrease cumulative pain scores, and could increase thermal and mechanical pain thresholds in a rat model of incisional pain. Sodium-potassium-chloride co-transporter 1 expression increased in neurons from dorsal root ganglion and the deep laminae of the ipsilateral dorsal horn following incision. By contrast, potassium-chloride co-transporter 2 expression decreased in neurons of the deep laminae from the ipsilateral dorsal horn. These findings suggest that spinal sodium-potassium-chloride co-transporter 1 expression was up-regulated and spinal potassium-chloride co-transporter 2 expression was down-regulated following incision. Intrathecal bumetanide has analgesic effects on incisional pain through inhibition of sodium-potassium-chloride co-transporter 1.

Preventive analgesia for postoperative pain control: a broader concept

Pain from surgical procedures occurs as a consequence of tissue trauma and may result in physical, cognitive, and emotional discomfort. Almost a century ago, researchers first described a possible relationship between intraoperative tissue damage and an intensification of acute pain and long-term postoperative pain, now referred to as central sensitization. Nociceptor activation is mediated by chemicals that are released in response to cellular or tissue damage. Pre-emptive analgesia is an important concept in understanding treatment strategies for postoperative analgesia. Pre-emptive analgesia focuses on postoperative pain control and the prevention of central sensitization and chronic neuropathic pain by providing analgesia administered preoperatively but not after surgical incision. Additional research in pre-emptive analgesia is warranted to better determine good outcome measurements and a better appreciation with regard to treatment optimization. Preventive analgesia reduces postoperative pain and consumption of analgesics, and this appears to be the most effective means of decreasing postoperative pain. Preventive analgesia, which includes multimodal preoperative and postoperative analgesic therapies, results in decreased postoperative pain and less postoperative consumption of analgesics.

A prospective, randomized controlled trial of circumcision in adult males using the CO2 laser: modified technique compared with the conventional dorsal-slit technique

OBJECTIVE

The purpose of this study was to investigate the safety and efficacy of a modified CO2 laser technique for circumcision in adult males as compared with the conventional dorsal-slit method.

BACKGROUND DATA

Circumcision is one of the most commonly performed surgeries in the world. Although present techniques produce a good long-term result, there is a continuing need to improve the safety and efficacy of the circumcision procedure.

MATERIALS AND METHODS

Data were analyzed from a prospective randomized controlled clinical study comparing two different operative techniques for adult circumcision: the modified CO2 laser circumcision technique, and the conventional dorsal-slit technique. A total of 300 patients >18 years of age were recruited in this study. Several perioperative data, including age, indications, operation time, intraoperative blood loss, complications, and postoperative pain were analyzed. Differences between the CO2 laser technique and the conventional technique were compared.

RESULTS

There was no statistically significant difference in age distribution and indications between the two groups. Compared with the conventional group, there were shorter operative time, less blood loss and lower postoperative complication rate in the laser group. The CO2 laser technique was associated with much less pain, as quantitated by a 10 point visual analogue scale (VAS) pain score at both 1 day and 7 days postoperatively.

CONCLUSIONS

The modified CO2 laser technique that we introduced offers a simple, safe, faster, and effective alternative method to the conventional technique in adult male circumcision, with decreased blood loss, pain, and complications.

Pain behaviour after castration of piglets; effect of pain relief with lidocaine and/or meloxicam

Behavioural responses and the effect of lidocaine and meloxicam on behaviour of piglets after castration were studied. A total of 144 piglets of 2 to 5 days of age were allocated to one of six treatments: castration (CAST), castration with lidocaine (LIDO), castration with meloxicam (MELO), castration with lidocaine and meloxicam (L + M), handling (SHAM) and no handling (NONE). Behaviour was observed for 5 days after the procedure, growth until weaning was recorded and characteristics of the castration wound noted. MELO piglets showed significantly (P < 0.05) more no pain-related behaviour than CAST and LIDO at the afternoon after castration, and were not significantly different from SHAM and NONE. LIDO piglets showed an increase (P < 0.001) in tail wagging, lasting for 3 days. This increase was not seen in L + M piglets. The occurrence of several behaviours changed with age, independent of treatment. A treatment effect on growth was not found. Wound healing was rapid in all treatments, but thickening of the heal was observed in several piglets, suggesting perturbation in the cicatrization process. Our study showed a pain-relieving effect of meloxicam after castration. Local anaesthesia resulted in piglets performing more tail wagging during the first few days after castration, which was prevented by administering meloxicam in combination with local anaesthesia.

The effect of post-surgical neuroplasticity on the stability of systemic pain perception: a psychophysical study

BACKGROUND

Surgery-induced neuroplasticity at spinal and supra-spinal levels is assumed to evoke a clinical acute post-operative pain (cAPOP) experience, which is expressed by allodynia and/or hyperalgesia. It remains unclear whether the systemic pain perception measured outside the incision area remains unchanged and whether it is affected by the presence of cAPOP.

AIMS

This study explored whether the systemic perception of experimental pain would be altered towards hypersensitivity following elective gynecological surgery unmasked by opioids.

METHODS

A perioperative psychophysical evaluation of heat pain thresholds (HPT) and pain estimations were obtained in a remote bodily area before and after surgery among 35 women.

RESULTS

The ratings for both pain dimensions of intensity and unpleasantness remained stable following surgery. However, there was a reduction found in HPT the day after surgery (43.6 ± 2.2 °C to 42.2 ± 3.1 °C, p = 0.002). This reduction was associated with lower HPT measured before surgery (r = .56, p < 0.000) and with higher cAPOP intensity obtained at rest (r = -.44, p = 0.008).

CONCLUSIONS

This post-surgical allodynia, as reflected by the systemic enhancement of pain perception, may represent plasticity in the central pain pathways at the supra-spinal level. Pre-surgical assessment of a patient's pain perception profile may predict certain pain dimensions of post-surgical pain plasticity. The evaluation of individual pain profiles may contribute to a mechanism-based approach aimed to attenuate the cAPOP.

Effects of nefopam on early postoperative hyperalgesia after cardiac surgery

OBJECTIVE

The purpose of this randomized, double-blind placebo-controlled study was to evaluate the effect of nefopam, a centrally acting antinociceptive compound, on the development of hyperalgesia after sternotomy. Preventive strategy giving nefopam from the early stage of anesthesia was compared with a postoperative strategy only and placebo.

DESIGN

This study was double-blinded and randomized.

SETTING

It was conducted in a single university hospital.

PARTICIPANTS

Ninety American Society of Anesthesiologists II to III patients scheduled for elective cardiac surgery.

INTERVENTIONS

Patients were assigned randomly to receive a 0.3-mg/kg bolus of nefopam at the induction of anesthesia followed by a continuous infusion of 0.065 mg/kg/h for 48 hours (G1), a 0.3-mg/kg bolus of nefopam at the end of surgery followed by a continuous infusion of 0.065 mg/kg/h for 48 hours (G2), or a placebo (G3). Postoperative analgesia was based on morphine patient-controlled analgesia and rescue analgesia when necessary. Postoperative hyperalgesia, pain scores, morphine consumption, and postoperative cognitive dysfunction were assessed for the first 48 hours and thereafter on postoperative days 4 and 7.

MEASUREMENTS AND MAIN RESULTS

The postoperative extent of dynamic hyperalgesia and the decrease of the nociceptive threshold evaluated by von Frey filaments at the sternal midline were smaller in group 1 and group 2 compared with the placebo group at the 24th hour. The primary objective was the extent of hyperalgesia at the midline given as the mean (standard deviation [SD]) (4.4 [2.5] cm for G1, 4.1 [2.7] for G2, and 6.1 [2.7] cm for G3. The punctuate is given as mean (SD) (64 [43] g for G1, 68 [40.8] g for G2, and 32 [27] g for G3; with p < 0.05 for the comparisons of extent and punctuate hyperalgesia between G1 and G3 and G2 and G3). The extent of hyperalgesia was not significantly different among the 3 groups on days 2, 4, and 7 after surgery. There were no significant differences in pain scores, morphine consumption, or postoperative cognitive dysfunctions.

CONCLUSIONS

Nefopam administered during the perioperative period slightly reduced acute hyperalgesia after cardiac surgery, but this was not associated with improved analgesic efficacy.

Preoperative scar hyperalgesia is associated with post-operative pain in women undergoing a repeat Caesarean delivery

BACKGROUND

Over 1.4 million Caesarean deliveries are performed annually in the United States, out of which 30% are elective repeat procedures. Post-operative hyperalgesia is associated with an increased risk for persistent post-surgical pain; however, there are no data on whether residual scar hyperalgesia (SHA) from a previous Caesarean delivery (CD) persists until the next delivery. We hypothesized that residual SHA may be present in a substantial proportion of women and is associated with increased post-operative pain.

METHODS

One hundred and sixty-three women scheduled for a repeat CD under spinal anaesthesia were enrolled into the study. Mechanical temporal summation (mTS) and SHA index were measured preoperatively. SHA was considered present when the index was >0. Post-operative pain scores at 12, 24 and 48 h and wound hyperalgesia (WHA) at 48 h were recorded.

RESULTS

SHA was present in 67 women 41% with a median SHA index of 0.42 (Q (25)  = 0.25; Q (75)  = 1.1, range 0.03-4.25). Women with SHA had overall higher post-operative pain scores and SHA was correlated with preoperative mTS (r = 0.164, p < 0.05), post-operative pain severity (r = 0.25, p < 0.002) and WHA at 48 h (r = 0.608, p < 0.001). Severe pain (visual analogue pain scale-S48 ≥ 7, n = 20) was predicted with a sensitivity and specificity of 60% and 62%, respectively. Positive predictive value was 18% and negative predictive value was 92%.

CONCLUSIONS

Preoperative SHA is present in 41% of women scheduled for repeat CD and is associated with increased mTS and post-operative pain. Screening for preoperative SHA may predict women at risk for increased post-operative pain, and guide post-operative analgesia to include anti-hyperalgesic drugs.

Use of lidocaine patch for percutaneous endoscopic lumbar discectomy

BACKGROUND

Lidocaine patch (L5P) has demonstrated short-term efficacy in treating both acute surgical pain and chronic neuropathic pain with tolerable side effects. Percutaneous endoscopic lumbar discectomy (PELD) is the mainstay of minimally invasive spine surgery (MISS). Sufficient analgesia during PELD surgery makes the patient consider it real MISS. This study was performed to evaluate the efficacy and adverse effects of lidocaine patch in patients who underwent PELD under local anesthesia.

METHODS

L5P (L group) or placebo (P group) was randomly applied on the skin of the back covering the anticipated path of the working channel before 1 hour of surgery in 100 patients who underwent a single level PELD at L4-L5. Efficacy of the lidocaine patch was assessed by patient's numeric rating scale (NRS) of pain at each stage during the surgery and by a 5-scale grading of the satisfaction with the anesthesia of the operator and patients after surgery.

RESULTS

Mean NRS scores at the stages of needle insertion, skin incision, serial dilation and insertion of working channel, and subcutaneous suture were significantly lower in the L group than the P group. Postoperative operator's and patients' satisfaction scores were also significantly higher in L group than in the P group. There were subtle adverse effects in both groups.

CONCLUSIONS

L5P provided better pain relief during PELD, especially at the stage of needle insertion, skin incision, serial dilation and insertion of working channel, and subcutaneous suture. It also provided higher patient and operator postoperative satisfaction, with only subtle adverse effects.

Ketamine for perioperative pain management in children: a meta-analysis of published studies

INTRODUCTION

Balanced analgesia, using both opioid and nonopioids agents, has become the standard care for postoperative pain management. Ketamine, a compound with analgesic and antihyperalgesic properties, has been shown to decrease postoperative pain and opioid requirements in adults. The goal of the present meta-analysis was to investigate postoperative analgesic properties of ketamine in pediatric patients.

MATERIAL AND METHODS

A comprehensive literature search was conducted to identify clinical trials that used ketamine as a perioperative analgesic compound in children and infants. Outcomes measured were postoperative analgesic consumption, pain intensity and duration of sensory block (when ketamine was used by caudal route) during the postoperative care unit (PACU) stay and the early postoperative period (6-24 h after leaving the operative room). The data from each trial were combined to calculate the pooled odds ratios or standard mean differences and their 95% confidence intervals.

RESULTS

Thirty-five randomized, blinded controlled studies were retrieved from the literature. Systemic ketamine was effective in decreasing PACU pain intensity and analgesic requirement but failed to influence early (6-24 h) pain intensity and analgesic requirement. Ketamine administered locally during tonsillectomy, decreased PACU and early (6-24 h) pain intensity and PACU analgesic requirements. Used as an adjuvant for caudal analgesia, ketamine increased the duration of sensory block and PACU analgesic requirement without impacting PACU pain intensity. Ketamine failed to exhibit a postoperative opioid-sparing effect.

CONCLUSIONS

This meta-analysis found that administration of ketamine was associated with decreased PACU postoperative pain intensity and nonopioid analgesic requirement. However, ketamine failed to exhibit a postoperative opioid-sparing effect.

[Predictors of chronic pain following surgery. What do we know?]

Chronic postoperative pain is known to be a significant clinical and economic problem. The estimated mean incidence is high and varies between 10 and 50%, with variations mostly related to procedure-specific conditions. High-risk types of surgeries are e.g. thoracotomy, breast or inguinal hernia surgery and amputations. Although there is increasing knowledge about the incidence of chronic postoperative pain after certain types of surgical procedures, there are only limited data related to the mechanisms and pathophysiology leading to chronic pain after surgery. Neuropathic pain components have been discussed, especially following operations with a high incidence of nerve damage (for example axillary lymphadenectomy). Besides surgical factors it seems that there are a number of other factors which likely increase the risk of chronic postoperative pain. These predictors for the development of chronic postoperative pain are multiple and include individual genetic factors, age and sex of the individual patient, preoperative chronic pain, psychosocial factors, neurophysiological factors, intraoperative nerve and muscle damage, postoperative complications and acute pain in the early postoperative period. Quantitative sensory testing including tests of inhibitory circuits like DNIC might help to predict the risk of individual patients even before surgery has started. The perioperative identification of patients who are at high risk for developing chronic pain after surgery is therefore a major goal for the future. This may help to develop preventive treatment strategies and avoid treatments with side effects for patients who are not at risk for developing chronic pain after surgery. Due to a lack of appropriate data for sufficient preventive approaches an effective postoperative acute pain management and a nerve-conserving surgical technique are the major keys in the prophylaxis of chronic postoperative pain.

Skin incision induces expression of axonal regeneration-related genes in adult rat spinal sensory neurons

Skin incision and nerve injury both induce painful conditions. Incisional and postsurgical pain is believed to arise primarily from inflammation of tissue and the subsequent sensitization of peripheral and central neurons. The role of axonal regeneration-related processes in development of pain has only been considered when there has been injury to the peripheral nerve itself, even though tissue damage likely induces injury of resident axons. We sought to determine if skin incision would affect expression of regeneration-related genes such as activating transcription factor 3 (ATF3) in dorsal root ganglion (DRG) neurons. ATF3 is absent from DRG neurons of the normal adult rodent, but is induced by injury of peripheral nerves and modulates the regenerative capacity of axons. Image analysis of immunolabeled DRG sections revealed that skin incision led to an increase in the number of DRG neurons expressing ATF3. RT-PCR indicated that other regeneration-associated genes (galanin, GAP-43, Gadd45a) were also increased, further suggesting an injury-like response in DRG neurons. Our finding that injury of skin can induce expression of neuronal injury/regeneration-associated genes may impact how clinical postsurgical pain is investigated and treated.

PERSPECTIVE

Tissue injury, even without direct nerve injury, may induce a state of enhanced growth capacity in sensory neurons. Axonal regeneration-associated processes should be considered alongside nerve signal conduction and inflammatory/sensitization processes as possible mechanisms contributing to pain, particularly the transition from acute to chronic pain.

Incidence and risk factors for chronic pain after caesarean section under spinal anaesthesia

This study investigated the incidence and risk factors associated with chronic pain after elective caesarean section under spinal anaesthesia in an Asian population. A prospective cohort study was conducted among subjects who underwent elective caesarean section under spinal anaesthesia, with morphine patient-controlled analgesia administered for 24 hours postoperatively. Perioperative, surgical and obstetric factors were investigated prospectively. Phone surveys were conducted to identify risk factors associated with chronic pain. A total of 857 subjects completed both the perioperative study and phone survey. The incidence of wound scar pain for three months after surgery was 9.2% (79). Of the 51 subjects with persistent pain at the time of subsequent survey, 9.8% (n = 5) had constant pain, 9.8% (n = 5) had daily pain and 23.5% (n = 12) had pain intermittently, at an interval of days. The independent risk factors for development of chronic pain were higher pain scores recalled in the immediate postoperative period (odds ratio [OR, 95% confidence interval] 1.348 [1.219 to 1.490], P = 0.0001), pain present elsewhere (OR 2.471 [1.485 to 4.112], P = 0.001) and non-private insurance status (OR 1.679 [1.034 to 2.727], P = 0.036). The two most common sites of pain other than wound pain were back pain (n = 316) and migraine (n = 87).

Animal models of acute surgical pain

Animal models of tissue injury have been used to investigate the mechanisms of pain. Here, we describe a variety of animal models that have been used to mimic acute surgical pain in human subjects, which include the plantar, tail, and gastrocnemius incision models. We also provide discussion on animal models of laparotomy, thoracotomy, visceral pain, and bone injury. Preclinical studies using these models have provided insights into the mechanisms and causes of acute surgical pain as well as the treatment options to control postsurgical pain.

Clinical and radiological evaluation of Trabecular Metal and the Smith-Robinson technique in anterior cervical fusion for degenerative disease: a prospective, randomized, controlled study with 2-year follow-up

A prospective, randomized, controlled study was carried out to compare the radiological and clinical outcomes after anterior cervical decompression and fusion (ACDF) with Trabecular Metal (TM) to the traditional Smith-Robinson (SR) procedure with autograft. The clinical results of cervical fusion with autograft from the iliac crest are typically satisfactory, but implications from the donor site are frequently reported. Alternative materials for cervical body interfusion have shown lower fusion rates. Trabecular Metal is a porous tantalum biomaterial with structure and mechanical properties similar to that of trabecular bone and with proven osteoconductivity. As much as 80 consecutive patients planned for ACDF were randomized for fusion with either TM or tricortical autograft from the iliac crest (SR) after discectomy and decompression. Digitized plain radiographic images of 78 (98%) patients were obtained preoperatively and at 2-year follow-up and were subsequently evaluated by two senior radiologists. Fusion/non-fusion was classified by visual evaluation of the A-P and lateral views in forced flexion/extension of the cervical spine and by measuring the mobility between the fused vertebrae. MRI of 20 TM cases at 2 years was successfully used to assess the decompression of the neural structures, but was not helpful in determining fusion/non-fusion. Pain intensity in the neck, arms and pelvis/hip were rated by patients on a visual analog scale (VAS) and neck function was rated using the Neck Disability Index (NDI) the day before surgery and 4, 12 and 24 months postoperatively. Follow-ups at 12 and 24 months were performed by an unbiased observer, when patients also assessed their global outcome. Fusion rate in the SR group was 92%, and in the TM group 69% (P < 0.05). The accuracy of the measurements was calculated to be 2.4 degrees . Operating time was shorter for fusion with TM compared with autograft; mean times were 100 min (SD 18) and 123 min (SD 23), respectively (P = 0.001). The patients' global assessments of their neck and arm symptoms 2 years postoperatively for the TM group were rated as 79% much better or better after fusion with TM and 75% using autograft. Pain scores and NDI scores were significantly improved in both groups when compared with baseline at all follow-ups, except for neck pain at 1 year for the TM group. There was no statistically significant difference in clinical outcomes between fusion techniques or between patients who appeared radiologically fused or non-fused. There was no difference in pelvic/hip pain between patients operated on with or without autograft. In our study, Trabecular Metal showed a lower fusion rate than the Smith-Robinson technique with autograft after single-level anterior cervical fusion without plating. There was no difference in clinical outcomes between the groups. The operative time was shorter with Trabecular Metal implants.

Can we predict persistent postoperative pain by testing preoperative experimental pain?

PURPOSE OF REVIEW

Although it is recognized that medical and surgical procedures may lead to persistent postoperative pain, predicting which patients are at risk for developing chronic pain presents an ongoing challenge. Clinical observations indicate that similar invasive procedures associated with consequent peripheral tissue damage can cause a wide range of pain experience. This broad variability is likely a consequence of the diversity in the central pain processing of the peripherally generated noxious stimulation. Therefore, advanced psychophysical measures that dynamically represent central pain modulation mechanisms may be used to determine an individual's susceptibility to developing persistent postoperative pain. This review highlights how, and to what extent, preoperative experimental pain testing can be utilized in predicting persistent postoperative pain.

RECENT FINDINGS

Conflicting findings emerged regarding the role of traditional experimental pain tests, including pain threshold, supra-threshold magnitude estimation, and tolerance in the prediction of acute postoperative pain. Less efficient endogenous modulation and greater sensitization, as preoperatively assessed by advanced experimental pain tests, were associated with higher persistent postoperative pain scores.

SUMMARY

The preoperative identification of individuals who have enhanced pain sensitivity and are at risk for developing persistent postoperative pain is important to providing them with better treatment that is specifically tailored to their altered pain modulation, as represented psychophysically.

Disrupted sleep the night before breast surgery is associated with increased postoperative pain

Despite the best available clinical care, pain after surgery is a virtually universal patient experience that can have pervasive negative consequences. Given the large variability among patients in postoperative pain levels, research on novel modifiable risk factors is needed. One such factor suggested by recent experimental studies indicates that disruption of even a single night's sleep can increase subsequent pain in healthy volunteers. In this preliminary clinical study, we tested the hypothesis that poor sleep the night before surgery would predict heightened postoperative pain. Patients (n=24) scheduled for routine breast-conserving surgical procedures for the diagnosis or treatment of cancer were recruited and wore an actigraphy device providing objective, validated measures of sleep duration and disruption (low sleep efficiency). Pain severity and interference with daily activities for the week after surgery was assessed with the Brief Pain Inventory. As hypothesized, multiple regression analyses revealed that lower sleep efficiency was a significant predictor of greater pain severity and interference, controlling for age, race, and perioperative analgesics as appropriate. Sleep efficiency was not significantly related to measures of depressed mood, emotional upset, or relaxation assessed on the morning of surgery. Patients with sleep efficiency in the lowest tertile had clinically higher levels of pain (>2 points) compared with patients in the highest sleep efficiency tertile. Sleep duration had no significant effects. This preliminary clinical study supports the possibility that sleep disruption on the night before surgery may increase patients' experience of pain after surgery. Research to investigate the mechanisms underlying these effects and to explore the possible clinical benefits of interventions to improve patients' sleep before surgery is now warranted.

[New substances and applications for postoperative pain therapy]

The onset of postoperative pain is the result of various pathophysiological mechanisms and depends on the type of surgery performed. Therefore, any adequate postoperative pain treatment requires multimodal and procedure-specific analgesia. In addition to reducing perioperative complications and improving patient comfort, optimal postoperative pain management also represents an important quality characteristic which can influence the patient in their choice of hospital. In the past 1-2 years, known groups of substances have been rediscovered for postoperative pain therapy (e.g., Gabapentin and Pregabalin, i.v. Lidocaine, Ketamine or glucocorticoids), while new substances (coxibe, oral oxycodone+naloxone) and applications have been developed. The present overview article discusses the advantages and disadvantages of these substances and analgesic methods, as well as their specific areas of application.

Postoperative pain--clinical implications of basic research

Postoperative incisional pain is a unique and common form of acute pain. Although ample evidence indicates that an efficeous postoperative pain treatment reduces patient morbidity and patient outcome, recent studies demonstrate that about 50-70% of patients experience moderate to severe pain after surgery indicating that postoperative pain remains poorly treated. Perhaps important reasons for this quandary are distinct mechanisms of incisional nociception compared to other pain conditions limiting our regimen to drugs designed for other clinical pain problems. Another reason might be the lack of an in depth knowledge about the pathophysiology and neuropharmacology of postoperative pain. Basic research offers important insights in the mechanisms of postsurgical incisional pain and the translation of experimental results into clinical practice will have important implications on the improvement of new multimodal treatment regimens based postoperative pain mechanisms. In the present review, recent developments in experimental postsurgical incisional pain research will be described and their possible relevance for clinical practice discussed.