Central sensitization as a result of surgical pain: investigation of the pre-emptive value of pethidine for ovariohysterectomy in the rat

Pharmacokinetics of Sustained-release and Extended-release Buprenorphine in Mice after Surgical Catheterization

The Guide for the Care and Use of Laboratory Animals strongly encourages the use of pharmaceutical-grade chemicals and analgesics. Sustained-release buprenorphine (SRB) is administered extralabel to rodents to mitigate moderate to severe pain. An FDA-indexed buprenorphine formulation-extended-release buprenorphine (XRB)-has recently become available and is currently the only pharmaceutical-grade slow-release buprenorphine formulation approved for use in mice and rats. However, no studies have directly compared the pharmacokinetic parameters of SRB and XRB in surgically catheterized mice. To this end, we compared the plasma buprenorphine concentrations and pharmacokinetic parameters of SRB and XRB in mice after surgical catheterization. We hypothesized that mice treated before surgery with SRB or XRB would have circulating buprenorphine concentrations that exceeded the therapeutic threshold for as long as 72 h after surgery. Male and female C57Bl/6J mice were anesthetized, treated with a single dose of either SRB (1 mg/kg SC) or XRB (3.25 mg/kg SC), and underwent surgical catheterization. Arterial blood samples were collected at 6, 24, 48, and 72 h after administration. Weight loss after surgery (mean ± SEM) was similar between groups (SRB: males, 12% ± 2%; females, 8% ± 2%; XRB: males, 12% ± 1%; females, 8% ± 1%). Both SRB and XRB maintained circulating buprenorphine concentrations above the therapeutic level of 1.0 ng/mL for 72 h after administration. Plasma buprenorphine concentrations at 6, 24, and 48 h were significantly greater (3- to 4-fold) with XRB than SRB, commensurate with XRB's higher dose. These results support the use of either SRB or XRB for the alleviation of postoperative pain in mice. The availability of FDA-indexed XRB increases options for safe and effective pharmaceutical-grade analgesia in rodents.

Postoperative Acupuncture is as Effective as Preoperative Acupuncture or Meloxicam in Dogs Undergoing Ovariohysterectomy: a Blind Randomized Study

Background

Acupuncture has the same analgesic effect as non-steroidal antiinflammatory drugs and opioids. It is challenging to perform preoperative acupuncture in unmanageable animals, while the residual postoperative anesthetic effect facilitates the performance of acupuncture postoperatively.

Objectives

To compare preoperative acupuncture or meloxicam versus postoperative acupuncture for postoperative analgesia after ovariohysterectomy.

Methods

This is a horizontal prospective positive control blind randomized experimental study. Thirty-six dogs were randomly divided into three groups: GA (preemptive acupuncture), GPA (postoperative acupuncture), and GM (meloxicam 0.2 mg/kg IV preoperatively). After sedation with acepromazine (0.05 mg/kg IM), anesthesia was induced with propofol (5.3 ± 0.3 mg/kg) and maintained with isoflurane/O2. Fentanyl (2 μg/kg, IV) was administered immediately before surgery. Bilateral acupuncture was performed at acupoints Large intestine 4, Spleen 6, and Stomach 36 for 20 minutes, before (GA) or immediately after surgery (GPA). Pain was evaluated by an observer blind to the treatment using the Glasgow scale before and for 24 hours after ovariohysterectomy. Dogs with a score ≥ 6 received rescue analgesia with morphine (0.5 mg/kg IM). Nonparametric data were analyzed by the Kruskal-Wallis test, followed by Dunn's test and parametric data by ANOVA followed by Tukey's test.

Results

Two GA and one GPA dogs received rescue analgesia once. Two GM dogs received rescue analgesia and one of those was treated again twice. There were no differences in the number of dogs receiving rescue analgesia between groups (p = 0.80).

Conclusion

Postoperative acupuncture was as effective as preoperative acupuncture or meloxicam in female dogs undergoing ovariohysterectomy.

Preventing Pediatric Chronic Postsurgical Pain: Time for Increased Rigor

Chronic postsurgical pain (CPSP) results from a cascade of events in the peripheral and central nervous systems following surgery. Several clinical predictors, including the prior pain state, premorbid psychological state (e.g., anxiety, catastrophizing), intraoperative surgical load (establishment of peripheral and central sensitization), and acute postoperative pain management, may contribute to the patient’s risk of developing CPSP. However, research on the neurobiological and biobehavioral mechanisms contributing to pediatric CPSP and effective preemptive/treatment strategies are still lacking. Here we evaluate the perisurgical process by identifying key problems and propose potential solutions for the pre-, intra-, and postoperative pain states to both prevent and manage the transition of acute to chronic pain. We propose an eight-step process involving preemptive and preventative analgesia, behavioral interventions, and the use of biomarkers (brain-based, inflammatory, or genetic) to facilitate timely evaluation and treatment of premorbid psychological factors, ongoing surgical pain, and postoperative pain to provide an overall improved outcome. By achieving this, we can begin to establish personalized precision medicine for children and adolescents presenting to surgery and subsequent treatment selection.

Intravenous Acetaminophen Does Not Provide Adequate Postoperative Analgesia in Dogs Following Ovariohysterectomy

Simple Summary

Acetaminophen is the most commonly used pain relief (analgesic) agent in humans worldwide and its use is becoming more frequent in dogs. However, limited evidence supports this use. This study aimed to investigate the analgesic effect of acetaminophen when administered as an intravenous injection post-operatively in female dogs. A total of 34 dogs were randomly divided into two groups and either administered acetaminophen or saline intravenously immediately after desexing. The dogs had their pain levels evaluated at 10, 20, 40, 60, 120, and 180 min after awakening from general anesthesia and the pain levels between groups were compared. Concurrently, the dogs had blood collected at 2, 5, 10, 40, and 80 min following injection of the acetaminophen. The blood was analyzed to quantify the levels of acetaminophen in the body. This study found that acetaminophen was no better than saline in providing analgesia in dogs following surgery. This study suggests that acetaminophen used alone may not be an appropriate post-operative analgesic agent for desexing procedures.

Abstract

(1) Objective: To investigate the analgesic effects of intravenous acetaminophen after intravenous administration in dogs presenting for ovariohysterectomy. (2) Methods: 14 ASA I client-owned female entire dogs. In this randomized, blinded, clinical study, dogs were given meperidine and acepromazine intramuscularly before induction of anesthesia with intravenous propofol. Anesthesia was maintained with isoflurane in oxygen. Intravenous acetaminophen 20 mg/kg or 0.9% NaCl was administered postoperatively. Pain assessments were conducted using the Glasgow Pain Scale short form before premedication and at 10, 20, 60, 120, and 180 min post-extubation or until rescue analgesia was given. The pain scores, times, and incidences of rescue analgesia between the groups was compared. Blood was collected before and 2, 5, 10, 20, 40, and 80 min after acetaminophen administration. Acetaminophen plasma concentration was quantified by liquid chromatography-mass spectrometry. The acetaminophen plasma concentration at the time of each pain score evaluation was subsequently calculated. (3) Results: There was no significant difference in pain scores at 10 min, highest pain scores, or time of rescue analgesia between groups. In each group, 3 dogs (43%) received rescue analgesia within 20 min. (4) Conclusions: Following ovariohysterectomy in dogs, there was no detectable analgesic effect of a 20 mg/kg dosage of intravenous acetaminophen administered at the end of surgery.

Rhythmic Change of Cortical Hemodynamic Signals Associated with Ongoing Nociception in Awake and Anesthetized Individuals: An Exploratory Functional Near Infrared Spectroscopy Study

BACKGROUND

Patients undergoing surgical procedures are vulnerable to repetitive evoked or ongoing nociceptive barrage. Using functional near infrared spectroscopy, the authors aimed to evaluate the cortical hemodynamic signal power changes during ongoing nociception in healthy awake volunteers and in surgical patients under general anesthesia. The authors hypothesized that ongoing nociception to heat or surgical trauma would induce reductions in the power of cortical low-frequency hemodynamic oscillations in a similar manner as previously reported using functional magnetic resonance imaging for ongoing pain.

METHODS

Cortical hemodynamic signals during noxious stimuli from the fontopolar cortex were evaluated in two groups: group 1, a healthy/conscious group (n = 15, all males) where ongoing noxious and innocuous heat stimulus was induced by a contact thermode to the dorsum of left hand; and group 2, a patient/unconscious group (n = 13, 3 males) receiving general anesthesia undergoing knee surgery. The fractional power of low-frequency hemodynamic signals was compared across stimulation conditions in the healthy awake group, and between patients who received standard anesthesia and those who received standard anesthesia with additional regional nerve block.

RESULTS

A reduction of the total fractional power in both groups-specifically, a decrease in the slow-5 frequency band (0.01 to 0.027 Hz) of oxygenated hemoglobin concentration changes over the frontopolar cortex-was observed during ongoing noxious stimuli in the healthy awake group (paired t test, P = 0.017; effect size, 0.70), and during invasive procedures in the surgery group (paired t test, P = 0.003; effect size, 2.16). The reduction was partially reversed in patients who received a regional nerve block that likely diminished afferent nociceptive activity (two-sample t test, P = 0.002; effect size, 2.34).

CONCLUSIONS

These results suggest common power changes in slow-wave cortical hemodynamic oscillations during ongoing nociceptive processing in conscious and unconscious states. The observed signal may potentially promote future development of a surrogate signal to assess ongoing nociception under general anesthesia.

EDITOR’S PERSPECTIVE

Clinical Management of Pain in Rodents

The use of effective regimens for mitigating pain remain underutilized in research rodents despite the general acceptance of both the ethical imperative and regulatory requirements intended to maximize animal welfare. Factors contributing to this gap between the need for and the actual use of analgesia include lack of sufficient evidence-based data on effective regimens, under-dosing due to labor required to dose analgesics at appropriate intervals, concerns that the use of analgesics may impact study outcomes, and beliefs that rodents recover quickly from invasive procedures and as such do not need analgesics. Fundamentally, any discussion of clinical management of pain in rodents must recognize that nociceptive pathways and pain signaling mechanisms are highly conserved across mammalian species, and that central processing of pain is largely equivalent in rodents and other larger research species such as dogs, cats, or primates. Other obstacles to effective pain management in rodents have been the lack of objective, science-driven data on pain assessment, and the availability of appropriate pharmacological tools for pain mitigation. To address this deficit, we have reviewed and summarized the available publications on pain management in rats, mice and guinea pigs. Different drug classes and specific pharmacokinetic profiles, recommended dosages, and routes of administration are discussed, and updated recommendations are provided. Nonpharmacologic tools for increasing the comfort and wellbeing of research animals are also discussed. The potential adverse effects of analgesics are also reviewed. While gaps still exist in our understanding of clinical pain management in rodents, effective pharmacologic and nonpharmacologic strategies are available that can and should be used to provide analgesia while minimizing adverse effects. The key to effective clinical management of pain is thoughtful planning that incorporates study needs and veterinary guidance, knowledge of the pharmacokinetics and mechanisms of action of drugs being considered, careful attention to individual differences, and establishing an institutional culture that commits to pain management for all species as a central component of animal welfare.

Preoperative Oral Pregabalin Reduces Acute Pain after Thoracotomy

BACKGROUND:

Nowadays pain control is one of the most important challenges for physicians, surgeons and anesthesiologists. New drugs and procedures to control pain have always been a major topic for researches.

AIM:

In this study, we evaluated the effects of preoperative pregabalin administration on relieving postoperative pain after thoracotomy surgery.

MATERIALS AND METHODS:

This study is a randomised, double-blind clinical trial, performed on 60 patients who underwent thoracotomy at Afzalipour hospital in Kerman, Iran. They were divided into case and control groups. Two hours before surgery an oral capsule of 300 mg pregabalin or placebo was given to patients. All patients similarly underwent general anaesthesia. Pain, nausea and vomiting were evaluated based on the visual analogue scale (VAS) and frequency. This study was verified and obtained the ethics committee code of K/92/489 from Kerman University of Medical Sciences.

RESULTS:

The average age of the pregabalin group was 39.7 ± 5.8 years and the control group 41.3 ± 6.1 years. The average pain score after regaining consciousness was 6.1 ± 0.2 in the case group and 7.9 ± 0.1 in the control group, and there was a significant difference between the 2 groups (p-value = 0.002). In the control group, 2 patients and the intervention group 3 patients, experienced nausea and vomiting. There was a significant difference between the overall average pethidine consumption and the average visual analogue scale in both groups.

CONCLUSION:

Pregabalin administration before thoracotomy is effective to reduce postoperative pain in patients. More research is needed to determine the optimal dose of pregabalin for preoperative administration.

Evaluation of a novel biodegradable thermosensitive keto-hydrogel for improving postoperative pain in a rat model

This study evaluates the sustained analgesic effect of ketorolac-eluting thermosensitive biodegradable hydrogel in the plantar incisional pain model of the rat hind-paw. A ketorolac-embedded 2, 2'-Bis (2-oxazolin) (BOX) linking methoxy-poly(ethylene glycol) and poly(lactide-co-glycolide) (mPEG-PLGA) diblock copolymer (BOX copolymer) was synthesized as keto-hydrogel based on optimal sol-gel phase transition and in vitro drug release profile. The effect of keto-hydrogel on postoperative pain (POP) was assessed using the established plantar incisional pain model in hind-paw of rats and compared to that of ketorolac solution. Pain and sensory threshold, as well as pain scoring, were evaluated with behavioral tests by means of anesthesiometer and incapacitance apparatus, respectively. Pro-inflammatory cytokine levels (TNF-α, IL-6, VEGF, and IL-1β) around incisional wounds were measured by ELISA. Tissue histology was assessed using hematoxylin and eosin and Masson’s trichrome staining. Ten mg/mL (25 wt%) keto-hydrogel showed a sol-gel transition at 26.4°C with a 10-day sustained drug release profile in vitro. Compared to ketorolac solution group, the concentration of ketorolac in tissue fluid was higher in the keto-hydrogel group during the first 18 h of application. Keto-hydrogel elevated pain and sensory threshold, increased weight-bearing capacity, and significantly reduced the levels of TNF-α, IL-6, and IL-1β while enhanced VEGF in tissue fluid. Histologic analysis reveals greater epithelialization and collagen deposition around wound treated with keto-hydrogel. In conclusion, our study suggests that keto-hydrogel is an ideal compound to treat POP with a secondary gain of improved incisional wound healing.

Behavioral pharmacology of pain

Behavioral methods are extensively used in pain research. Rodent modeling tends to rely on evoked responses but there is a growing interest in behavioral readouts that may capture elements of ongoing pain and disability, reflecting the major clinical signs and symptoms. Clinically, analgesics show greater efficacy in acute pain after standard surgery than in chronic conditions but are never completely effective on a population basis. In contrast, experimental pharmacological studies in rodents often demonstrate full efficacy, but there is variability in sensitivity between models and readouts. Full efficacy is rarely seen when more complex or multiple readouts are used to quantify behavior, especially after acute surgery or in studies of clinical pain in animals. Models with excellent sensitivity for a particular drug class exist and are suitable for screening mechanistically similar drugs. However, if used to compare drugs with different modes of action or to predict magnitude of clinical efficacy, these models will be misleading. Effective use of behavioral pharmacology in pain research is thus dependent on selection and validation of the best models for the purpose.

Evaluation of contact heat thermal threshold testing for standardized assessment of cutaneous nociception in horses - comparison of different locations and environmental conditions

Background

The aim of the study was to evaluate the performance of contact heat thermal stimulation in horses at different body sites and under different environmental conditions and different test situations. Five warm-blood horses were equipped with the thermal probe located on the skin of nostril (N), withers (W) or coronary band (C). Skin temperature and reaction temperature (thermal threshold) at each location were measured and percent thermal excursion (% TE = 100 * (threshold temperature - skin temperature)/(cut-out temperature - skin temperature) was calculated. Environmental conditions were changed in partial random order for all locations, so each horse was tested in its familiar box stall and stocks, in the morning and evening and at warm and cold ambient temperatures. Type of reaction to the stimulus and horse’s general behaviour during stimulation were recorded. The stimulation sites were examined for the occurrence of possible skin lesions.

Results

Skin temperatures were significantly different during warm and cold ambient temperatures at all three locations, but remained constant over repeated stimulation. An obvious response to stimulation before reaching cut-out temperature could be detected most frequently at N and W in boxes during warm ambient temperatures. The most frequent type of reaction to thermal stimulation at the nostril was headshaking (64.6%), skin twitching at the withers (82.9%) and hoof withdrawal at the coronary band (79.2%).

Conclusion

The outcome of thermal threshold testing depended on ambient temperature, stimulation site and environment. Best results with the WTT2 in horses were obtained at the nostrils or withers in a familiar environment at warm ambient temperatures.

Involvement of spinal orexin A in the electroacupuncture analgesia in a rat model of post-laparotomy pain

BACKGROUND

Orexin A (OXA, hypocretin/hcrt 1) is a newly discovered potential analgesic substance. However, whether OXA is involved in acupuncture analgesia remains unknown. The present study was designed to investigate the involvement of spinal OXA in electroacupuncture (EA) analgesia.

METHODS

A modified rat model of post-laparotomy pain was adopted and evaluated. Von Frey filaments were used to measure mechanical allodynia of the hind paw and abdomen. EA at 2/15 Hz or 2/100 Hz was performed once on the bilateral ST36 and SP6 for 30 min perioperatively. SB-334867, a selective orexin 1 receptor (OX1R) antagonist with a higher affinity for OXA than OXB, was intrathecally injected to observe its effect on EA analgesia.

RESULTS

OXA at 0.3 nmol and EA at 2/15 Hz produced respective analgesic effects on the model (P<0.05). Pre-surgical intrathecal administered of SB-334867 30 nmol antagonized OXA analgesia and attenuated the analgesic effect of EA (P<0.05). However, SB-334867 did not block fentanyl-induced analgesia (P>0.05). In addition, naloxone, a selective opioid receptor antagonist, failed to antagonize OXA-induced analgesia (P>0.05).

CONCLUSIONS

The results of the present study indicate the involvement of OXA in EA analgesia via OX1R in an opioid-independent way.

A rat model of postoperative pain

Research on pain resulting from an incision is crucial for developing therapies for postoperative pain, a condition for which effective and inexpensive treatments are not yet available. Because of the gap between preclinical models of persistent pain (e.g., inflammatory, neuropathic) and acute postsurgical pain, efforts have been undertaken to develop methods for studying pain caused by incisions. To this end, a rat model for postoperative pain has been developed. The model uses a plantar incision in the hindpaw and is characterized by persistent, reduced withdrawal thresholds to mechanical stimuli, as is the case in patients after surgery. The pain behaviors are greatest immediately after recovery from anesthesia. The enhanced responsiveness remains remarkable for several days and then gradually decreases. The model is useful for screening test compounds that may be effective in reducing postoperative pain and for understanding pain mechanisms associated with incisions.

The pathophysiology of acute pain: animal models

PURPOSE OF REVIEW

Trauma, surgery, and burns are three common clinical scenarios that are associated with significant acute pain. This review describes the pathophysiology of acute pain utilizing three preclinical models: surgery, burn, and fracture.

RECENT FINDINGS

In general, there is greater interest directed toward peripheral mediators of acute pain. Studies indicate that treatment against nerve growth factor, interleukins, and ischemic-like mediators may provide valuable avenues for treatment of acute pain. By targeting the periphery, analgesic therapies may have reduced side-effects.

SUMMARY

Peripheral mediators of acute pain can vary depending upon the type of injury. Treatment aimed toward those mediators specific to the injury may improve acute pain management in the future. It will be important to translate these findings into clinical trials in the future.

Pregabalin in acute and chronic pain

Pregabalin is a gamma-amino-butyric acid analog shown to be effective in several models of neuropathic pain, incisional injury, and inflammatory injury. In this review, the role of pregabalin in acute postoperative pain and in chronic pain syndromes has been discussed. Multimodal perioperative analgesia with the use of gabapentinoids has become common. Based on available evidence from randomized controlled trials and meta-analysis, the perioperative administration of pregabalin reduces opioid consumption and opioid-related adverse effects in the first 24 h following surgery. Postoperative pain intensity is however not consistently reduced by pregabalin. Adverse effects like visual disturbance, sedation, dizziness, and headache are associated with higher doses. The advantage of the perioperative use of pregabalin is so far limited to laparoscopic, gynecological, and daycare surgeries which are not very painful. The role of the perioperative administration of pregabalin in preventing chronic pain following surgery, its efficacy in more painful surgeries and surgeries done under regional anesthesia, and the optimal dosage and duration of perioperative pregabalin need to be studied. The efficacy of pregabalin in chronic pain conditions like painful diabetic neuropathy, postherpetic neuralgia, central neuropathic pain, and fibromyalgia has been demonstrated.

The Rat Grimace Scale: a partially automated method for quantifying pain in the laboratory rat via facial expressions

We recently demonstrated the utility of quantifying spontaneous pain in mice via the blinded coding of facial expressions. As the majority of preclinical pain research is in fact performed in the laboratory rat, we attempted to modify the scale for use in this species. We present herein the Rat Grimace Scale, and show its reliability, accuracy, and ability to quantify the time course of spontaneous pain in the intraplantar complete Freund's adjuvant, intraarticular kaolin-carrageenan, and laparotomy (post-operative pain) assays. The scale's ability to demonstrate the dose-dependent analgesic efficacy of morphine is also shown. In addition, we have developed software, Rodent Face Finder^®, which successfully automates the most labor-intensive step in the process. Given the known mechanistic dissociations between spontaneous and evoked pain, and the primacy of the former as a clinical problem, we believe that widespread adoption of spontaneous pain measures such as the Rat Grimace Scale might lead to more successful translation of basic science findings into clinical application.

Current attitudes to, and use of, peri-operative analgesia in dogs and cats by veterinarians in New Zealand

AIM

To investigate the attitudes of veterinary practitioners in New Zealand to pain and analgesia, and their use of analgesic drugs, in dogs and cats.

METHODS

A questionnaire posted to 1,200 practising veterinarians was used to gather information about the use of analgesia in dogs and cats, assessment of pain, attitudes to pain relief, analgesic drugs and procedures used, factors affecting choice of analgesic agent, and veterinary demographics, continuing education and staffing.

RESULTS

Three hundred and twenty questionnaires with useable data were returned, a response rate of 28%. Male and female veterinarians were evenly represented. The analgesic agents most commonly used were morphine (opioids) and carprofen (a non-steroidal anti-inflammatory drug; NSAID). Use of peri-operative pain relief ranged from 50% for castration of cats to 91% for fracture repair in dogs. For most procedures, female veterinarians scored pain at a significantly higher level than their male colleagues. Fifty-eight percent of respondents considered their knowledge in the area of assessment and treatment of pain was adequate.

CONCLUSIONS

This survey was considered representative of veterinarians working in companion animal practice in New Zealand. Results indicated a relatively high use of peri-operative analgesia, including both pre-emptive and multi-modal analgesia, in cats and dogs, although there was still some disparity between the perception of how painful a procedure was and the consequent use of pain relief.

CLINICAL RELEVANCE

The establishment of current attitudes and practices indicates to practising veterinarians how their own use of analgesics compares with that of their colleagues. It also provides information to educators on potential areas of focus, given that 42% of respondents felt their knowledge in the area of assessment and treatment of pain was inadequate.

Pain and nociception in reptiles

The ability of reptiles to "feel" pain and the significance of pain or nociception on physiologic homeostasis is an exceedingly complex question requiring integration of both physiologic and behavioral evidence. Until further information is available, it would seem most ethical for veterinarians to assume that reptiles are capable of feeling pain, and to treat or manage pain when there is reasonable evidence that pain is present. With increased information available regarding analgesic use in reptiles and with the heightened awareness of the importance of analgesia for zoologic companion animals, it is likely that more veterinarians will provide pain relief to their reptile patients.

Comparison of the effects of tramadol, codeine, and ketoprofen alone or in combination on postoperative pain and on concentrations of blood glucose, serum cortisol, and serum interleukin-6 in dogs undergoing maxillectomy or mandibulectomy

OBJECTIVE

To compare analgesic effects of tramadol, codeine, and ketoprofen administered alone and in combination and their effects on concentrations of blood glucose, serum cortisol, and serum interleukin (IL)-6 in dogs undergoing maxillectomy or mandibulectomy.

ANIMALS

42 dogs with oral neoplasms.

PROCEDURES

30 minutes before the end of surgery, dogs received SC injections of tramadol (2 mg/kg), codeine (2 mg/kg), ketoprofen (2 mg/kg), tramadol+ketoprofen, or codeine+ketoprofen (at the aforementioned dosages). Physiologic variables, analgesia, and sedation were measured before (baseline) and 1, 2, 3, 4, 5, and 24 hours after surgery. Blood glucose, serum cortisol, and serum IL-6 concentrations were measured 1, 3, 5, and 24 hours after administration of analgesics.

RESULTS

All treatments provided adequate postoperative analgesia. Significant increases in mean+/-SD blood glucose concentrations were detected in dogs receiving tramadol (96+/-14 mg/dL), codeine (120+/-66 mg/dL and 96+/-21 mg/dL), ketoprofen (105+/-22 mg/dL), and codeine+ketoprofen (104+/-16 mg/dL) at 5, 1 and 3, 5, and 3 hours after analgesic administration, respectively, compared with preoperative (baseline) values. There were no significant changes in physiologic variables, serum IL-6 concentrations, or serum cortisol concentrations. Dogs administered codeine+ketoprofen had light but significant sedation at 4, 5, and 24 hours.

CONCLUSIONS AND CLINICAL RELEVANCE

Opioids alone or in combination with an NSAID promoted analgesia without adverse effects during the 24-hour postoperative period in dogs undergoing maxillectomy or mandibulectomy for removal of oral neoplasms.

Long-lasting analgesic effects of intraoperative thoracic epidural with bupivacaine for liver resection

OBJECTIVES

Continuous epidural analgesia may be considered in liver resection but is often avoided because of possible coagulopathies and the risk of epidural hematoma in the postoperative period. On the other hand, there is no coagulation defect during the surgery. Effective prevention of postoperative pain may require continuous sensory ablation throughout the surgery event.

METHODS

A prospective, randomized, double-blind study was conducted to evaluate the efficacy of intraoperative epidural anesthesia on postoperative morphine consumption via patient-controlled analgesia after liver surgery in 2 groups of patients. One group (epidural) received, intraoperatively, thoracic epidural bupivacaine perfusion (0.5% at 3 mL/hr) added to preoperative intrathecal morphine (0.5 mg) and fentanyl (15 microg). The other group (placebo) was administered the same intrathecal narcotics but with a sham epidural. Forty-four patients scheduled for major liver resection (> or =2 segments) were recruited. Patient-controlled analgesia morphine consumption, pain at rest and with movement, sedation, nausea, pruritus, and respiratory frequency were evaluated at 6, 9, 12, 18, 24, 36, and 48 hrs after intrathecal morphine injection.

RESULTS

Patients in the placebo group consumed twice as much morphine during each time interval than patients in the epidural group (at 48 hrs: 123 [SD, 46] vs 59 [SD, 25] mg; P < 0.0001). Pain evaluation on visual analog scale at rest and on movement was lower in the epidural group (P = 0.017 and P = 0.037).

CONCLUSION

Intraoperative thoracic epidural infusion of bupivacaine, added to intrathecal morphine, decreased postoperative morphine consumption with better pain relief compared with the placebo.

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.

Models and mechanisms of hyperalgesia and allodynia

Hyperalgesia and allodynia are frequent symptoms of disease and may be useful adaptations to protect vulnerable tissues. Both may, however, also emerge as diseases in their own right. Considerable progress has been made in developing clinically relevant animal models for identifying the most significant underlying mechanisms. This review deals with experimental models that are currently used to measure (sect. II) or to induce (sect. III) hyperalgesia and allodynia in animals. Induction and expression of hyperalgesia and allodynia are context sensitive. This is discussed in section IV. Neuronal and nonneuronal cell populations have been identified that are indispensable for the induction and/or the expression of hyperalgesia and allodynia as summarized in section V. This review focuses on highly topical spinal mechanisms of hyperalgesia and allodynia including intrinsic and synaptic plasticity, the modulation of inhibitory control (sect. VI), and neuroimmune interactions (sect. VII). The scientific use of language improves also in the field of pain research. Refined definitions of some technical terms including the new definitions of hyperalgesia and allodynia by the International Association for the Study of Pain are illustrated and annotated in section I.

A comparison of tepoxalin-buprenorphine combination and buprenorphine for postoperative analgesia in dogs: a clinical study

The present study compares the analgesic effect of a tepoxalin-buprenorphine combination to that of buprenorphine alone in the 24 h peri-operative period in 20 dogs undergoing cranial cruciate ligament repair, which were randomly assigned to the two treatment protocols (n = 10). Additionally, possible side effects induced by tepoxalin were investigated. Analgesia was compared using a visual analogue scale (VAS) and a multifactorial pain scale (MFPS), by an anaesthetist blinded from treatment. Analysis of the overall VAS-scores showed a significant decrease over time in both treatment groups. The decrease in the two groups was not significantly different from each other. No significant differences were found between the MFPS-scores of both protocols. Potential side effects of tepoxalin were investigated by venous blood sampling before premedication and 24 h after extubation, a buccal mucosal bleeding time test and recording of vomiting, diarrhoea and adverse effects at the surgical site. Analysis of the blood parameters showed that fibrinogen levels were overall higher 24 h after surgery in both protocols, but were significantly more elevated in the tepoxalin group. No significant differences were found for the other blood parameters. Statistically, tepoxalin failed to improve analgesia induced by buprenorphine. There was no convincing evidence that the administration of tepoxalin was not associated with gastrointestinal side effects. There were no significant adverse effects on renal function and primary haemostasis.

Nonsteroidal anti-inflammatory drugs in cats: a review

OBJECTIVE

To review the evidence regarding the use of nonsteroidal anti-inflammatory drugs (NSAIDs) in cats.

DATABASES USED

PubMed, CAB abstracts.

CONCLUSIONS

Nonsteroidal anti-inflammatory drugs should be used with caution in cats because of their low capacity for hepatic glucuronidation, which is the major mechanism of metabolism and excretion for this category of drugs. However, the evidence presented supports the short-term use of carprofen, flunixin, ketoprofen, meloxicam and tolfenamic acid as analgesics in cats. There were no data to support the safe chronic use of NSAIDs in cats.

Carprofen and buprenorphine prevent hyperalgesia in a model of inflammatory pain in cats

A model of nociceptive threshold determination was developed for evaluation of NSAID analgesia in cats. In a crossover study, eight cats received carprofen (4 mg/kg), buprenorphine (0.01 mg/kg) or saline (0.3 ml) subcutaneously before intradermal kaolin injection on the antebrachium to induce mild inflammation. Pressure thresholds were measured at the injected site using blunt-ended pins advanced by manual inflation of a bladder within a bracelet. Bladder pressure was recorded as threshold (PT) at the behavioural end point. Baseline PT were recorded before kaolin injection (time 0). PT was measured at 2-10 h intervals for 52 h. PT below the lower 95% confidence interval (CI) of baseline values indicated hyperalgesia. After saline, hyperalgesia was detected from 2-6 h, 22-26 h, and at 30 and 36 h. After carprofen, PT remained within the 95% CI. After buprenorphine, PT remained within the 95% CI except at 2h. Carprofen and to some extent buprenorphine, prevented inflammatory hyperalgesia.

Evaluation of epidural administration of morphine or morphine and bupivacaine for postoperative analgesia after premedication with an opioid analgesic and orthopedic surgery in dogs

OBJECTIVE

To evaluate the analgesic efficacy of epidural administration of morphine or a morphine-bupivacaine combination administered before orthopedic surgery in dogs that received opioid premedication.

DESIGN

Prospective, randomized, blinded, clinical study.

ANIMALS

36 healthy adult dogs that underwent elective orthopedic surgery on a pelvic limb.

PROCEDURES

Each dog received 1 of 3 epidural treatments before surgery. Anesthetic and supportive care protocols were standardized. Dogs under going different surgical procedures were randomly allocated among the 3 treatment groups. Respiratory and cardiovascular variables, end-tidal isoflurane concentration, and requirements for rescue analgesia were monitored. Postsurgical analgesia was evaluated with a multiparametric pain scoring system and by determination of rescue analgesia requirements and cortisolemia.

RESULTS

The morphine-bupivacaine combination was associated with lower values than morphine or a saline solution for intraoperative arterial blood pressure; minimum and maximum isoflurane requirements; and postoperative pain scores, rescue analgesia requirements, and plasma cortisol concentrations. Values obtained after administration of morphine alone were not significantly different from those obtained after administration of saline solution for most variables.

CONCLUSIONS AND CLINICAL RELEVANCE

The preoperative epidurally administered morphine-bupivacaine combination induced better analgesia than morphine alone and should be considered for use in clinical patients. The degree of hemodynamic depression associated with the combination was considered acceptable for healthy patients undergoing elective surgery.

Cardiopulmonary effects of sufentanil long acting on sevoflurane anaesthesia in dogs

OBJECTIVE

To evaluate the cardiopulmonary effects of sufentanil long acting (SLA) in sevoflurane-anaesthetized dogs.

STUDY DESIGN

Randomized prospective study. Animals Forty female dogs (beagles) aged 1-2 years, weighing 11.97 +/- 1.40 kg.

MATERIALS AND METHODS

The dogs were divided into five groups of eight. Two control groups were used: group A received intramuscular (IM), SLA (50 microg kg(-1)) alone, while group B received the SLA vehicle followed by sevoflurane anaesthesia for 90 minutes. In the other groups, SLA (50 microg kg(-1) IM) was given immediately before (group C(0)), 15 minutes before (group D(15)) or 30 minutes (group E(30)) before induction [with intravenous (IV) thiopental] of sevoflurane anaesthesia lasting for 90 minutes. Heart rate, arterial blood pressure, respiratory rate (f(r)), arterial oxygen haemoglobin saturation and end-tidal sevoflurane concentration (Fe'SEVO) were measured every 10 minutes during anaesthesia and at 2, 4 and 24 hours after induction (not Fe'SEVO). Acid-base and blood gas analyses were performed.

RESULTS

Sufentanil LA reduced heart rate and increased arterial CO(2) tensions during anaesthesia. Respiratory depression was least in group E(30) compared with groups C(0) and D(15). Bradycardia was present for at least 24 hours. Respiratory rate was least in group B although arterial O(2) and CO(2) tension values were acceptable up to 24 hours after anaesthesia.

CONCLUSIONS

Pre-anaesthetic medication with SLA moderately aggravated the cardiopulmonary effects of sevoflurane.

CLINICAL RELEVANCE

In spite of a moderate depressant effect on cardiorespiratory parameters, SLA may be of use as pre-anaesthetic medication before sevoflurane anaesthesia in dogs. Intermittent positive pressure ventilation may occasionally be necessary.

Mechanisms of incisional pain

Postoperative, incisional pain is a unique but common form of acute pain. Because effective postoperative analgesia reduces morbidity following surgery, new treatments continue to be sought. It is through the development of investigational models and studies of the mechanisms that perioperative medicine can be advanced. This article reviews studies on a rat plantar hindpaw model for postoperative pain and proposes mechanisms for enhanced excitability of sensory neurons caused by incisions.

Pain management in cats--past, present and future. Part 1. The cat is unique

Cats are popular pets but until recently their perioperative and traumatic pain was seriously underestimated and under treated. There are several causes of this under treatment. First, it may be difficult to detect pain in cats, because they do not demonstrate overt pain-associated behaviour. Secondly, there are relatively few analgesic drugs with market authorization for cats. Thirdly, cats have an unfortunate reputation for toxicity from analgesic drugs, particularly opioid-induced mania and classical non steroidal anti inflammatory drug toxicity. Fourthly, cats are deficient in some metabolic pathways used to metabolise analgesic drugs in other species; this may lead to genuine toxicity or to lack of effect. Recently, understanding of feline behaviour and physiology has improved, leading to better clinical management of this enigmatic species. Behavioural methods are proving to be the best means of assessing pain, and knowledge of unique feline physiology has enabled rational treatment protocols to be developed specifically for cats.

Differential expression of central metabotropic glutamate receptor (mGluR) subtypes in a clinical model of post-surgical pain

Tissue damage during surgery can induce 'central sensitization' and the development of pain and hyperalgesia post-operatively. Metabotropic glutamate receptors (mGluRs) contribute to nociception, inflammatory pain and hyperalgesia. This study characterized the temporal expression of group I (mGluR(1), mGluR(5)) and II (mGluR(2), mGluR(3)) mGluRs in spinal cord following abdominal surgery. Lumbar spinal cord was recovered from adult sheep euthanased 5 h, 1, 2, 3 and 6 days after undergoing a midline laparotomy, and processed for mGluR mRNA (real-time PCR, in situ hybridization) and protein (Western blotting). mGluR(5) mRNA was up-regulated 5 h and 1 day post-surgery in laminae I-II of the spinal cord dorsal horn. mGluR(5) protein was increased 1 day post-surgery. A delayed induction of mGluR(2) and mGluR(3) mRNAs and mGluR(2/3) protein occurred in spinal cord 3 days after surgery. By 6 days, mGluR(2) mRNA levels had returned to normal, however, mGluR(3) mRNA and mGluR(2/3) protein remained elevated. No change was detected in mGluR(1). These results demonstrate that mGluRs are differentially regulated following surgery and support a link between mGluR-mediated activity and post-surgical pain.

Anti-nociceptive and Sedative Effects of Sufentanil Long Acting during and after Sevoflurane Anaesthesia in Dogs

The purpose of the present study was to determine the most effective time interval between the administration of sufentanil long acting (LA) and the induction of sevoflurane anaesthesia in dogs. The occurrence of sedation, analgesia and other marked side-effects were evaluated in addition to the possible dosage-reducing effect of sufentanil on sevoflurane in dogs. Forty clinically normal beagles aged 1-2 years and weighing between 8.4 and 13.6 kg were included. Two control groups were used: one group of dogs (A) received sufentanil LA (50 microg/kg i.m.) and a second group (B) the sufentanil vehicle followed by standard inhalation anaesthesia of 90 min. After premedication with sufentanil LA immediately before (C0), 15 min (D15) or 30 min (E30) prior to induction with thiopental (i.v.) the dogs were anaesthetized for 90 min with sevoflurane in oxygen. Pain and sedation scores were evaluated every 10 min during sevoflurane anaesthesia and at 2 (T120), 4 (T240) and 24 h (T1440) after initiation of anaesthesia. The occurrence of adverse reactions such as hypothermia, lateral recumbency, ataxia, noise sensitivity, vomiting, defaecation, salivation, nystagmus and excitation was observed at the same time-points. During the recovery period pain scores were lower and sedation scores higher in the sufentanil LA groups. In many dogs acceptable pain and sedation scores persisted during 24 h. Several dogs showed ataxia, lateral recumbency, arousal on auditory stimulation, defaecation, salivation and excitation at several time-points after sufentanil LA administration. Sufentanil LA in addition to sevoflurane anaesthesia offered beneficial dosage-reducing analgesic effects up to 69.8% for thiopental and 78.3% for sevoflurane; although several typical opioid side-effects occurred. To achieve this advantageous dosage-reducing effect 15 min should be respected between sufentanil LA administration and induction of sevoflurane anaesthesia.

Systemic lidocaine infusion as an analgesic for intraocular surgery in dogs: a pilot study

OBJECTIVE

To determine if systemic administration of lidocaine during intraocular surgery reduces post-operative ocular pain.

STUDY DESIGN

Randomized, masked, controlled experimental trial.

ANIMALS

Twelve dogs weighing 15.5 +/- 1.7 kg (mean +/- SD) and aged 2.5 +/- 0.6 years.

METHODS

All dogs underwent a baseline ophthalmic examination and subjective pain score. Anesthesia consisted of acepromazine (0.1 mg kg(-1), i.m.), propofol (4-6 mg kg(-1), i.v.), and isoflurane in oxygen. There were three groups each receiving a bolus followed by an infusion (n=4): saline (0.3 mL kg(-1) i.v. + 0.2 mL kg(-1) hour(-1) i.v.); morphine (0.15 mg kg(-1) i.v. + 0.1 mg kg(-1) hour(-1) i.v.); and lidocaine (1.0 mg kg(-1) i.v. + 0.025 mg kg(-1) minute(-1) i.v.). All treatments began 15 minutes prior to starting of phacoemulsification and lens removal from the right eye. Pain scores were recorded at 0.5, 1, 2, 3, 4, 6, 8, 16, and 24 hours after t=0 (extubation). Rescue morphine was administered (1.0 mg kg(-1) i.m.) if the subjective pain score > or =9 (maximum=24), and the dog was excluded from further data analysis. Differences in pain scores and time-to-treatment failure (TTF) were analyzed using the Wilcoxon's rank sum test. Differences in incidence of treatment failure were analyzed using Fisher's exact test. Physiologic data were analyzed using repeated measures ANOVA. Significance was defined as P<0.05.

RESULTS

Incidence of treatment failure was 100% in saline-treated dogs and 50% in morphine- or lidocaine-treated dogs. There was no difference in intraocular pressure, aqueous flare, cell count (or protein) between groups in the operated eye at any time following extubation.

CONCLUSION AND CLINICAL RELEVANCE

This pilot study suggests that intraoperative lidocaine may provide analgesic benefits similar to morphine for intraocular surgery in dogs, but more definitive research is needed. This model appears to be appropriate for pain assessment studies as the negative control group demonstrated 100% failure rate.

Ovariohysterectomy in the rat: a model of surgical pain for evaluation of pre-emptive analgesia?

Ovariohysterectomy in the rat led to the induction of abdominal postures and referred mechanical allodynia in the hind paws. The latter was differentiated into static and dynamic subtypes. The abdominal postures were present up to 4-5 h, whilst the two types of allodynia lasted for at least 2 days. A single administration of morphine 30 min before surgery dose-dependently (0.1-3 mg/kg, s.c.) blocked the development of abdominal postures and the two types of mechanical allodynia. The highest dose of morphine almost completely blocked these responses. The duration of action of 3 mg/kg morphine was short and similar (1.5-2 h) when administered either before or after surgery. However, multiple administrations of morphine (0.5 h before, and 0.5 and 2 h after surgery) blocked the development of abdominal postures and both allodynias for up to 2 days. In contrast, administration of three doses of morphine (3 mg/kg) in a similar dosing regime but starting 24 h after surgery, only blocked the two types of allodynia for 4 h. These data indicate the importance of blocking the induction phase of surgical pain and support the concept of pre-emptive analgesia. It is suggested that the ovariohysterectomy model should prove to be useful for studying mechanisms and designing novel therapeutic strategies for the treatment of post-operative pain.