Recent advances in our understanding of pain: how should they affect management?

Evaluation of the use of thermal thresholds to investigate NSAID analgesia in a model of inflammatory pain in cats

This study evaluated thermal threshold (TT) testing for investigation into NSAID analgesia in cats. Seven cats participated in two crossover studies. TTs were measured on thoracic skin using a device developed specifically for cats. Skin temperature was recorded, then the heater activated. At the behavioural end point heating was stopped and temperature (=TT) recorded. In part 1, TTs were measured following subcutaneous (SC) ketoprofen or saline. In part 2, the process was repeated after intradermal kaolin induced mild inflammation at the test site. TTs were measured before treatment and two hourly for 24 h. In part 1, skin temperature did not change but in part 2 it increased more after saline than ketoprofen. TT did not change significantly after any treatment. However, after ketoprofen TT fell below the 95% confidence interval (CI) in part 1 and increased above it in part 2. The method detected some NSAID effects but is unlikely to be sufficiently sensitive for study of NSAID analgesia.

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.

Effect of caudal epidural xylazine on intraoperative distress and post-operative pain in Holstein heifers

OBJECTIVE

To compare the effects of caudal epidural xylazine versus saline on tolerance of paravertebral nerve block and flank surgery and on post-operative pain in heifers used for a veterinary student training laboratory.

STUDY DESIGN

Randomized controlled prospective study.

ANIMALS

Fourteen one-year-old, nongravid, healthy Holstein heifers, weighing 360 +/- 5 kg.

METHODS

Xylazine (0.05 mg kg(-1)) or 0.9% saline (5 mL) was injected using a caudal epidural technique to seven heifers undergoing a flank surgery. Nerve block of the right paravertebral fossa was performed using equal parts of lidocaine 2% and bupivacaine 0.5%. Heart and respiratory rates, rectal temperature, rumination frequency, and appetite were recorded before and at 4, 8, and 24 hours after surgery. Scores were recorded for: tolerance of local anesthesia injections (pre-operatively), sedation, ataxia and distress (intraoperatively, every 30 minutes), and pain (4, 8, and 24 hours post-operatively).

RESULTS

The animals reaction to local anesthetic injection was judged to be less in the xylazine group by both an experienced observer (p<0.001) and student surgeons (p<0.01). The xylazine group required less local anesthetic (82.9 +/- 13.8 mL) versus the saline group (108.4 +/- 19.6 mL, p=0.035). Intraoperatively, xylazine heifers were more sedated at all times (p-values from <0.001 to 0.017), were more ataxic for the first 1.5 hours (p-values from <0.001 to 0.026), and lower in distress at all times (p-values from <0.001 to 0.007). No difference in post-operative pain or physiologic variables was found, except immediately post-operatively, rectal temperature was higher in the xylazine group (39.5 +/- 0.3 degrees C) than in the saline group (38.6 +/- 0.2 degrees C, p<0.001).

CONCLUSION AND CLINICAL RELEVANCE

Compared with epidural saline, caudal epidural xylazine reduced distress of anesthetic injection and surgical manipulation in heifers and an improvement in animal well-being was apparent. This effect may have been as a result of sedation. Pre-operative epidural xylazine did not appear to improve post-surgical analgesia in our study.

A comparison of preoperative tramadol and morphine for the control of early postoperative pain in canine ovariohysterectomy

OBJECTIVE

To compare morphine with tramadol for the management of early postoperative pain following ovariohysterectomy after pyometra in dogs.

STUDY DESIGN

Prospective randomized blinded clinical trial.

ANIMALS

Thirty female dogs, 2-14 years old.

METHODS

Animals were randomly divided into two equal groups. Group 1 received 0.2 mg kg-1 of morphine IV and group 2 received 2 mg kg-1 of tramadol IV after the induction of anesthesia. The dogs were premedicated with acepromazine, and anesthesia was induced with intravenous midazolam and ketamine. Isoflurane was used for the maintenance of anesthesia. The variables measured were: analgesia; sedation; cardiac and respiratory rates; arterial blood pressure; end-tidal isoflurane and carbon dioxide (Pe'CO2); oxyhemoglobin saturation (SpO2); plasma catecholamines; serum cortisol and glucose concentrations; pH and blood gases. The animals were monitored for 6 hours after the administration of the analgesic agent.

RESULTS

There were no differences between the two groups with regard to analgesia, sedation, SpO2, pH and blood gases, cardiovascular variables, glucose, catecholamine and cortisol concentrations. Forty minutes postopioid administration, the end-tidal isoflurane concentration was significantly lower in the morphine-treated group as compared to the tramadol group. At 30 minutes following opioid injection, Pe'CO2 was significantly higher in the morphine group than in the tramadol group. Two dogs in the tramadol group and one in the morphine group were given morphine postoperatively because of increasing pain scores.

CONCLUSION AND CLINICAL RELEVANCE

Morphine and tramadol, administered preemptively can be used safely in dogs to control early pain after ovariohysterectomy without significant adverse effects.

Potential sources of neck and back pain in clinical conditions of dogs and cats: a review

Pathological neck and back pain occurs in many medical conditions of dogs and cats. Pain may arise from a variety of structures including the intervertebral discs, facet joint capsules, dorsal root ganglia, vertebral ligaments, the vertebral periosteum, and the meninges. The source of this pain is dependent upon the type of disease process and its location within or surrounding the spinal column. Diseases can directly or indirectly stimulate pain sensors (nociceptors). Inflammatory diseases may hypersensitize these receptors or nociceptive pathways with inflammatory mediating substances such as serotonin, histamine and potassium. Diseases resulting in mechanical compression of nociceptors or nociceptive pathways may also result in neck or back pain. A thorough understanding of spinal pain occurring in dogs and cats will lead to more accurate diagnoses and treatments and may provide information regarding prognoses for various diseases. Evidence pointing to sources of spinal pain taken from scientific and clinical studies of a variety of species including humans is provided. Suspected or known sources of neck and back pain occurring in several clinical conditions of dogs and cats are discussed.

Feline perioperative pain management

Veterinary surgeons today are performing increasingly complex and invasive feline surgical procedures. In light of this, it is crucial that perioperative pain management in these patients be a top priority. This article outlines pain physiology and pathophysiology, pain recognition and management strategies, relevant pharmacology, and techniques for local and regional analgesia in cats.

Avian analgesia

Understanding behavioral indicators of pain and other assessment techniques can help one to recognize pain in birds and prompt us to treat birds with analgesics. An analgesic plan needs to include several modalities to help reduce pain in the avian patient. Analgesic therapy should be directed at treating the disease/injury in the periphery, and the changes that occur in the central nervous system (CNS). Both opioid and nonsteroidal anti-inflammatory drug (NSAID) therapeutics can be selected to provide analgesia for the avian patient.

Physiology of pain

The substantial increase in our collective knowledge of pain physiology and pharmacology over the past decade has had a significant effect on the practice of clinical veterinary medicine. An overview of the basic anatomical and physiologic components of nociceptive processing is presented, as well as a discussion of the sensitizing events that occur within the nervous system in acute and chronic pathologic pain states. The unique features of visceral and neuropathic pain are also outlined. With the goal of improving the success of our therapeutic interventions, the final section is devoted to the various classes of analgesic drugs and techniques, and how they are best incorporated into pain management strategies.