Further studies on the antinociceptive activity and respiratory effects of buprenorphine in sheep

Effect of three opioid-based analgesic protocols on the perioperative autonomic-mediated cardiovascular response in sheep

Few reports evaluate the clinical effects of opioids in sheep during experimental surgical procedures. Catecholamine-mediated haemodynamic changes resulting from surgical noxious stimulation are blunted by opioids. The aim of this study was to evaluate the efficacy of three opioid-based analgesic protocols in avoiding a 20% increase in heart rate (HR) and/or mean arterial blood pressure (MAP) during experimental intervertebral disk nucleotomy in sheep. Eighteen female Brogna sheep were anaesthetized with propofol and maintained with a fixed end-tidal isoflurane concentration of 1.5 ± 0.1%. Sheep were assigned to one of three groups that intravenously received methadone 0.3 mg/kg (group M), fentanyl 2 µg/kg followed by 10 µg/kg/h (group F), or buprenorphine 10 µg/kg and 30 minutes later ketamine 1 mg/kg followed by 5 mg/kg/h (group BK). Intravenous fentanyl at 2 µg/kg would have been used for rescue analgesia in case HR and/or MAP had increased. During surgery, HR and MAP values did not increase over 20% in all groups. All animals maintained the percentage change between -4 and 7% for both variables; only one sheep in group BK had an increase in MAP superior to 20% after ketamine administration before surgical stimulation. In group M, HR decreased over time and in group BK, MAP tended to increase during surgery. All the opioid-based protocols tested were able to control the cardiovascular response to noxious stimulation in sheep undergoing spinal surgery, although ketamine may have represented a confounding factor.

A large animal neuropathic pain model in sheep: a strategy for improving the predictability of preclinical models for therapeutic development

Background

Evaluation of analgesics in large animals is a necessary step in the development of better pain medications or gene therapy prior to clinical trials. However, chronic neuropathic pain models in large animals are limited. To address this deficiency, we developed a neuropathic pain model in sheep, which shares many anatomical similarities in spine dimensions and cerebrospinal fluid volume as humans.

Methods

A neuropathic pain state was induced in sheep by tight ligation and axotomy of the common peroneal nerve. The analgesic effect of intrathecal (IT) morphine was investigated. Interspecies comparison was conducted by analyzing the ceiling doses of IT morphine for humans, sheep, and rats.

Results

Peroneal nerve injury (PNI) produced an 86% decrease in von-Frey filament-evoked withdrawal threshold on postsurgery day 3 and the decrease lasted for the 8-week test period. Compared to the pre-injury, sham, and contralateral hindlimb, the IT morphine dose that produces 50% of maximum analgesia (ED₅₀) for injured PNI hindlimb was 1.8-fold larger and E_max, the dose that produces maximal analgesia, was 6.1-fold lower. The sheep model closely predicts human IT morphine ceiling dose by allometric scaling. This is in contrast to the approximately 10-fold lower morphine ceiling dose predicted by the rat spinal nerve ligated or spared nerve injury models.

Conclusion

PNI sheep model has a fast onset and shows stable and long-lasting pain behavioral characteristics. Since the antinociceptive properties of IT morphine are similar to those observed in humans, the PNI sheep model will be a useful tool for the development of analgesics. Its large size and consistent chronic pain behavior will facilitate the development and evaluation of surgical intervention and gene therapy. The PNI sheep pain model provides us with the opportunity for multi-species testing, which will improve the success of clinical trials.

Animal model development for the Penn State pediatric ventricular assist device

In March 2004, the National Heart, Lung, and Blood Institute awarded five contracts to develop devices providing circulatory support for infants and small children with congenital and acquired cardiac disease. Since 2004, the team at Penn State College of Medicine has developed a pneumatically actuated ventricular assist device (VAD) with mechanical tilting disk valves. To date, hemodynamic performance, thrombogenesis, and hemolysis have been chronically evaluated in 16 animals, including 4 pygmy goats and 12 sheep. Major complications, mainly respiratory failure, have been encountered and resolved by a multi-disciplinary team. Multi-modal analgesia, appropriate antibiotic therapy, and attentive animal care have contributed to successful outcomes. Time after implant has ranged from 0 to 40 days. Most recently, a sheep implanted with Version 3 Infant VAD was electively terminated at 35 days postimplant, with no major adverse events. This report describes a successful in vivo model for evaluating a pediatric VAD.

Effectiveness of non-steroidal anti-inflammatory drugs and epidural anaesthesia in reducing the pain and stress responses to a surgical husbandry procedure (mulesing) in sheep

In this study, we examined the potential of several widely used non-steroidal anti-inflammatory drugs (NSAIDs) and other analgesics to reduce pain and stress in sheep after surgery. Because mulesing involves a greater degree of tissue trauma than other surgical husbandry procedures such as castration or tail-docking, it provides a more rigorous and conservative test to identify potentially useful analgesic strategies in sheep. Merino lambs (5 weeks of age) were randomised into eight treatment groups: (1) carprofen; (2) flunixin; (3) ketoprofen; (4) buprenorphine; (5) xylazine; (6) lignocaine epidural; (7) saline control; (8) sham control. The NSAIDs were administered 1.5 h before mulesing, buprenorphine 0.75 h and xylazine and lignocaine 0.25 h before mulesing. Pain- and discomfort-related behaviours were recorded for 12 h after mulesing, and plasma cortisol concentrations were measured before mulesing and 0.5, 6, 12, 24 and 48 h after mulesing. The results indicated that no single analgesic treatment provided satisfactory analgesia during both the surgical mulesing procedure and the ensuing period of pain associated with the inflammatory phase. However, there were indications that two NSAIDs (carprofen and flunixin) showed good potential as analgesics during the inflammatory phase. A combination of short- and long-acting analgesics may be needed to provide more complete pain relief. In conclusion, the administration of some NSAIDs offers the potential for good analgesia in sheep for the inflammatory phase following the tissue trauma of surgical husbandry procedures. Other analgesic options need to be considered if the acute stress response to the procedure is to be reduced.

Comparison of perioperative analgesic protocols for dogs undergoing tibial plateau leveling osteotomy

OBJECTIVE

To compare effects of 3 commonly used perioperative analgesic protocols (epidural injection, intra-articular injection, and intravenous [IV] injection) for management of postoperative pain in dogs after tibial plateau leveling osteotomy (TPLO).

STUDY DESIGN

Prospective, randomized clinical trial.

ANIMALS

Fifty-six healthy dogs with naturally occurring cranial cruciate ligament rupture.

METHODS

Dogs were premedicated with IV hydromorphone and acepromazine and were randomly assigned to receive either E (preoperative epidural injection with morphine and bupivacaine), IA (pre- and postoperative intra-articular injections of bupivacaine), or C (neither epidural morphine and bupivacaine, nor intra-articular bupivacaine). All dogs were administered hydromorphone (0.05 mg/kg IV) at extubation and as needed to maintain comfort postoperatively. Patients were observed and monitored continuously for 24 hours and discomfort was assessed using visual analog pain scores (VASs), multifactorial pain scores (MPSs), and response to a pressure nociceptive threshold (PNT) measuring device. Time to 1st dose and the total doses of hydromorphone required to achieve adequate comfort for each dog were recorded.

RESULTS

No differences in measured indices of postoperative pain were observed between dogs of each treatment group; VAS (P=.190), MPS (P=.371), and PNT (P=.160). Time to 1st analgesic intervention was longer for Group E compared with Group C (P=.005) and longer for Group IA compared with Group C (P=.032). Although time to 1st intervention between Groups E and IA were longer for Group E, differences were not significant. To provide an adequate level of comfort, more analgesic interventions were administered to dogs in Group C compared with dogs in group E (P=.015). On average, more hydromorphone was administered to Group C compared with Group IA (P=.072) and to Group IA compared with Group E (P=.168), but statistical significance was not reached for these data.

CONCLUSIONS

In this study population, significant differences were seen in time to 1st hydromorphone dose between Groups E and IA compared with Group C. As well, more supplemental analgesia was administered to Group C compared with Group E to maintain the same level of postoperative comfort. Although differences between Groups E and IA tended to favor the epidural group, differences were minimal and not statistically significant.

CLINICAL RELEVANCE

Our results suggest that regardless of analgesic protocol, measured indices of pain in dogs after TPLO can be minimized if dogs are continuously observed and appropriately supplemented with parenteral opioids. However, the frequency of postoperative opioid dosing can be minimized and may be a factor when contemplating supplementary use of epidural or intra-articular injections as part of a balanced analgesic approach.

An analgesic evaluation of isoxsuprine in horses

Isoxsuprine is used clinically to treat navicular disease and laminitis in horses. Although it is thought to increase digital and laminar blood flow, isoxsuprine's mechanism of action remains controversial, and analgesia has been suggested recently as such possible mechanism. This research investigated the analgesic potential of isoxsuprine in healthy horses submitted to a mechanical nociceptive test. Isoxsuprine (1.2 mg/kg), xylazine (1.1 mg/kg), distilled water : ethanol 95% (2 : 1, v/v, 20 ml) and saline (0.9%, 20 ml) were injected intravenously, and nociceptive thresholds were measured over 90 min. Only xylazine significantly increased nociceptive thresholds, confirming that alpha(2)-adrenoceptor agonists produce analgesia in horses. Our results do not support an analgesic mechanism of action for isoxsuprine in horses, suggesting that other mechanisms might account for the clinical efficacy of this drug or that mechanical nociceptive testing may not be sufficiently sensitive to demonstrate an analgesic effect for this drug.

Cardiovascular and endocrine responses to cutaneous electrical stimulation after fentanyl in the ovine fetus

OBJECTIVE

The purpose of this study was to determine whether physical stimulation is stressful to the ovine fetus, as judged from physiologic changes that are similar to those reported for other stressors (such as hypoxia); whether any stress response could be blocked by clinically used doses of fentanyl; and whether fentanyl alone had any potentially deleterious physiologic effects in the fetus.

STUDY DESIGN

We investigated the effect of fentanyl analgesia on the cardiovascular and endocrine response to cutaneous electrical stimulation in the late gestation (>125 days) ovine fetus (n=7 fetuses). Chronically implanted catheters and blood flow probes were used to measure fetal arterial blood pressure, heart rate, carotid and femoral blood flow, pH, Po(2), Pco(2), lactate, cortisol, and beta-endorphin levels before, during, and for 1 hour after 5 minutes of cutaneous electrical stimulation to the lip, forelimb, and abdomen, in a crossover design. Clinically used 30 or 150 microg doses of fentanyl (which approximated 10 or 50 microg/kg estimated fetal weight) or saline solution were given intravenously to the fetus 2 minutes before stimulation.

RESULTS

When compared with the control, stimulation caused a significant rise in fetal heart rate (P=.003; mean maximal rise, 48.6+/-14.0 beats/min, 0-10 minutes after the start of stimulation) but caused no change in any other parameters studied. Neither dose of fentanyl attenuated the changes in heart rate that were observed in response to stimulation alone. Fentanyl alone significantly increased fetal heart rate, carotid blood flow, and lactate and cortisol levels and significantly decreased pH and Po(2).

CONCLUSION

Cutaneous electrical stimulation in the fetal sheep causes an increase in heart rate, which fentanyl does not block. Fentanyl itself has significant effects on the cardiovascular and endocrine system, which might adversely affect the fetus.

Comparison of pethidine, buprenorphine and ketoprofen for postoperative analgesia after ovariohysterectomy in the cat

Sixty cats which underwent an ovariohysterectomy were randomly allocated into four treatment groups. One group (controls) received no analgesics postoperatively, and the others received either a single dose of buprenorphine (0.006 mg/kg) intramuscularly, or pethidine (5 mg/kg) intramuscularly, or ketoprofen (2 mg/kg) subcutaneously. The analgesia obtained after each treatment was assessed by three measures. There were significant differences between the groups both for the requirement for intervention analgesia (P = 0.0008) and for the overall clinical assessment (P = 0.0003) with ketoprofen requiring least intervention analgesia and having the best overall clinical assessment, followed by buprenorphine then pethidine. The control group required the most intervention analgesia and had the worst overall clinical assessment. Visual analogue scale scoring for pain produced significant differences between the groups from one hour after the operation, with the cats which were given ketoprofen tending to have lower pain scores than the other groups.

General anesthetic techniques in ruminants

Sedation, anesthesia, protection of the airway during general anesthesia, and control of pain in the perioperative period are important considerations in the management of sheep, goats, and cattle. Though ruminants are classically considered farm animals and are often intended for the production of food and fiber, these species are used extensively in research and teaching and they are increasingly important as companion animals. Whatever their use may be, anesthetic and analgesic drugs and techniques should be used to ensure minimal stress and discomfort during the perioperative period.

Analgesia in dogs after intercostal thoracotomy: a clinical trial comparing intravenous buprenorphine and interpleural bupivacaine

We prospectively studied 26 dogs that presented for intercostal thoracotomy. Dogs were premedicated with oxymorphone, induced with diazepam and etomidate, and anesthesia was maintained with isoflurane in oxygen. Preoperatively, animal patients were randomly assigned to one of two groups. Group 1 (n = 13) received buprenorphine (10 microgram/kg intravenously [IV]) every 6 hours for 24 hours starting 10 minutes before tracheal extubation. Group 2 (n = 13) received 0.5% bupivacaine (1.5 mg/kg) administered interpleural (IP) by slow injection through a pediatric feeding tube fixed to the most dorsal aspect of the thoracotomy incision. Interpleural injections were administered with each dog placed in lateral recumbency with the incision positioned ventrally; IP injections were administered every 4 hours for 24 hours starting 10 minutes before tracheal extubation. All cases were monitored in the intensive care unit for 24 hours postoperatively. The analgesic efficacy of each regimen was evaluated using a pain scoring system that included a subjective pain score, heart rate, and respiratory rate. Arterial blood pressure, arterial blood gases, oxygen saturation, body temperature, and changes in the electrocardiogram or neurological status were also noted. Significant increases in mean heart rate, respiratory rate, and total pain score occurred after surgery in dogs in the buprenorphine group. In contrast, dogs in the bupivacaine group had no significant changes when compared with their preoperative values. Dogs in the bupivacaine group had significantly decreased total pain scores and better PaO2 and oxygen saturation values when compared with the dogs receiving buprenorphine. Hypoventilation did not occur in either group.

Analgesic activity and respiratory effects of butorphanol in sheep

The analgesic drug butorphanol tartrate has proved useful clinically in horses and dogs but its analgesic profile had not yet been investigated in sheep. This study was initiated to determine the thermal and mechanical antinociceptive activity of butorphanol (at the dose rates 0.05, 0.1 and 0.2 mg kg-1) in sheep. The drug produced significant analgesia in the thermal test system, the duration of which was dose related but no significant elevation in mechanical pressure thresholds could be detected. In a further set of experiments the dose rate was increased to 0.4 mg kg-1 and mechanical testing was repeated. There was still no clinically significant elevation in pressure thresholds. At a dose rate of 0.2 mg kg-1 the drug had no detectable effect on respiratory blood gas tensions. Behavioural changes were severe if a dose rate of 0.2 mg kg-1 was exceeded.