Efficacy of an epidural combination of morphine and detomidine in alleviating experimentally induced hindlimb lameness in horses

Comparing the anti-nociceptive, sedative and clinicophysiological effects of epidural detomidine, detomidine-lidocaine and lidocaine in donkeys

BACKGROUND

Epidural analgesia using the alpha-2 agonist detomidine (DE), alone or in combination with lidocaine (LD), is frequently employed for standing surgical procedures in horses, but its use has not been evaluated in donkeys.

METHODS

In a randomised controlled prospective trial, 24 healthy adult donkeys were assigned to four groups (n = 6), each receiving 40 μg/kg of DE, 0.22 mg/kg of LD, combined DE and LD (DELD) or 0.9% sterile normal saline epidurally. After epidural injection of each treatment, the onset, degree and duration of sedation and anatomical extension of anti-nociception were observed.

RESULTS

DE and DELD treatments resulted in complete bilateral analgesia with loss of sensation in the tail, perineum, inguinal area, chest and the caudal aspect of the upper pelvic limb, and extended distally to the dorsal metatarsal area. DE and DELD resulted in a significantly (p < 0.05) longer duration of anti-nociception (110 ± 15.4 min and 141.6 ± 14.7 min, respectively) than LD (75.8 ± 4.9 min). The DELD duration of sedation was significantly (p < 0.05) longer than the DE duration (118.3 ± 19.4 min and 108.3 ± 7.5 min, respectively).

LIMITATION

The current study's main limitation is using only one dose of DE.

CONCLUSION

DE and DELD produced a very effective, safe and acceptable sedative and analgesic effect in the perineal and inguinal regions of donkeys.

Comparative evaluation of sedative and anti-nociceptive effects of epidural romifidine, romifidine-lidocaine, and lidocaine in donkeys (Equus asinus)

Background

Local and regional anesthetic procedures are valuable tools in veterinary practice. Caudal epidural administration of local anesthetic agents is widely reported for surgical interventions of the tail, anus, rectum, vulva, vagina, urethra, and bladder in the standing horse. Epidural analgesia is also obtained using various drugs such as alpha-2 adrenoceptor agonists, dissociative anesthetics, and opioids. The present study evaluates the anti-nociceptive and sedative effects of epidural administration of romifidine, a romifidine-lidocaine combination, and lidocaine alone in donkeys.

Materials and methods

In a randomized prospective study, twenty-four healthy adult donkeys were assigned to four groups (three experimental and one control; n = 6) received either 50 μg/kg of romifidine, 0.30 mg/kg of lidocaine, combined romifidine (50 μg/kg) and lidocaine (0.30 mg/kg) diluted in 0.9% sterile normal saline solution to a total injection volume of 12 ml, or an equivalent volume of sterile saline epidurally. After epidural injection of each treatment, the onset, degree, and duration of sedation and anatomical extension of anti-nociception were documented. Observations began immediately (time 0) pre-administration and at 5, 15, 30, 45, 60, and 30-min intervals subsequently until 210 min after drug injection. Time to onset of perineal analgesia was documented every minute after the epidural injection by evaluating the animal's response to pinpricks.

Results

Only romifidine and romifidine-lidocaine induced mild to moderate sedation. Romifidine, romifidine-lidocaine, and lidocaine induced complete bilateral caudal epidural analgesia with loss of sensation in the perineum, tail, inguinal region, caudal aspect of the upper hind limb, chest areas, and extended distally to the dorsal metatarsal area. Sedation lasted longer (p < 0.05) with romifidine (160 ± 15.4 min) than with romifidine-lidocaine (141.6 ± 13.2 min). Longer-lasting analgesia (p < 0.05) was obtained with romifidine (158.3 ± 9.8 min) and romifidine-lidocaine (165 ± 9.4 min) than with lidocaine (75.8 ± 8 min).

Conclusions

Epidural administration of a single dose of romifidine or a combination of romifidine-lidocaine produced mild to moderate sedation and complete anti-nociception in the perineal and inguinal regions of donkeys. The clinical usefulness of epidural romifidine or romifidine-lidocaine combinations to perform obstetric procedures in donkeys needs to be assessed.

Caudal epidural catheterization for pain management in 48 hospitalized horses: A descriptive study of demographics, complications, and outcomes

The placement of caudal epidural catheters in horses has become more frequent as a multi-modal analgesic strategy. Despite its integration into clinical practice, there are limited reports describing the use of caudal epidural catheterization for prolonged use in horses. The purpose of this study was to characterize the hospitalized caseload undergoing epidural catheterization for long-term epidural analgesic administration, to report the response to epidural therapy and observed complications, and to describe patient outcomes. Medical records of hospitalized equine patients that underwent placement of a caudal epidural catheter for analgesic management between 2017 and 2021 were analyzed retrospectively. For the 62 catheters placed in the 48 cases, the most frequent diagnosis category prompting epidural analgesia was orthopedic (43/48, 89.6%). Synovial sepsis was the most frequent specific diagnosis prompting epidural catheter placement (11/48, 22.9%). The initial response to epidural therapy was characterized as positive for 37/62 (59.7%) catheters. Complications were documented for 46/62 (74.2%) catheters. However, most of these complications were classified as mild (51.6%) or moderate (14.5%), and exaggerated physiologic responses were observed most frequently. Of the horses studied, 52.1% survived to be discharged from the hospital. With awareness of potential complications and vigilant monitoring, caudal epidural catheters should be considered for equine patients as an analgesic strategy.

Cervical Epidural Spinal Analgesia for Acute Management of Severe Unilateral Forelimb Lameness: Case Report

A 20-year-old Quarter Horse gelding was presented with severe right forelimb lameness (5/5 AAEP Lameness Scale) due to a tear of the superficial digital flexor muscle which was diagnosed via palpation of swelling and ultrasonography revealing major muscle fiber disruption and hematoma formation. When traditional systemic therapy (non-Steroidal anti-inflammatories) did not restore clinically acceptable comfort and the risk of supporting limb laminitis became a reasonable concern, a cervical epidural catheter was placed between the first and second cervical vertebrae in the standing, sedated patient using ultrasound guidance. The gelding was treated with epidural morphine (0.1 mg/kg every 24 h then decreased to 0.05 mg/kg every 12 h) and was pain-scored serially following treatment. Spinal analgesia was provided for 3 days. Pain scores significantly decreased following each treatment with morphine, and the gelding was successfully managed through the acutely painful period without any adverse effects associated with the C1-C2 epidural catheter placement technique, the epidural morphine, or contralateral limb laminitis. At the 2-month follow-up, the gelding was walking sound with no complications seen at the catheter insertion site. In this case, spinal analgesia using epidural morphine administered via a cervical epidural catheter was an effective and technically achievable option for pain management associated with severe forelimb muscle injury in a horse.

Analgesic and Cardiopulmonary Effects of Epidural Romifidine and Morphine Combination in Horses

The study aim is to compare the effects of epidural administration of two different doses of romifidine combined with morphine in horses. A prospective crossover blinded experimental design was used. Five adult healthy horses two males and three females with a mean body weight of 380 ± 45 Kg (335-425 kg), were studied. Treatments consisted of romifidine 30 μg/kg (R30) or 60 μg/kg (R60) combined with morphine 0.1 mg/kg with a washout interval of 72 hours, administered through an epidural catheter placed at the first intercoccygeal space. Heart rate (HR) and respiratory rate (f_R), pH, blood gases, arterial blood pressures (mmHg), and threshold for electrical noxious stimulation was evaluated for 120 minutes and after 240 minutes of epidural injection. Data were collected before injections and every 15 minutes for 120 minutes, and at 240 minutes of epidural administration. Significant sedation occurred in both treatments with no statistically significant difference between them. There were significant changes in f_R and HR from baseline but no difference between treatments. Arterial blood pressures were significantly lower in R60 treatment from 75 up to 120 minutes post epidural injection. Analgesia was considered moderate for both treatments lasting longer with romifidine at 60 μg/kg. Epidurally administered romifidine and morphine combination in horses produces dose-dependent sedation, arterial hypotension, and antinociceptive effects.

Epidural administration of opioid analgesics improves quality of recovery in horses anaesthetised for treatment of hindlimb synovial sepsis

BACKGROUND

Opioid epidural analgesia has been shown to provide effective analgesia in horses. There is a lack of evidence regarding the effect of opioid epidural analgesia on quality of recovery in horses.

OBJECTIVES

Identify whether opioid epidural analgesia influences quality of recovery in horses undergoing general anaesthesia required for management of hindlimb synovial sepsis.

STUDY DESIGN

Single-centre retrospective cross-sectional study.

METHODS

Data were obtained from the clinical records of horses which had undergone arthroscopic or tenoscopic surgery for management of hindlimb synovial sepsis over a 9-year period in a referral hospital population. Multivariable logistic regression analysis was used to identify the perioperative factors that impact on quality of recovery.

RESULTS

Records from 149 horses, undergoing 170 general anaesthetics were included. Multivariable logistic regression analysis showed that opioid epidural analgesia (OR 3.0, 95% CI 1.2 to 7.2, P = .02) was associated with good quality of recovery, whereas Cob breeds (OR 0.16, 95% CI 0.06 to 0.46, P = .001), age (in years) (OR 0.90, 95% CI 0.83 to 0.97, P = .004) increasing intraoperative dosages (in mg/kg) of thiopental (OR 0.64, 95% CI 0.46 to 0.90, P = .01) or ketamine (OR 0.42, 95% CI 0.18 to 0.98, P = .04) were associated with poor quality of recovery.

MAIN LIMITATIONS

Certain variables that may influence quality of recovery, such as patient temperament and hindlimb orthopaedic co-morbidities were not recorded. The clinical prediction model obtained is only applicable to the specific facilities, population and perianaesthetic management practiced at our institution.

CONCLUSIONS

Opioid epidural analgesia is significantly associated with good quality of recovery in horses undergoing general anaesthesia required for management of hindlimb synovial sepsis. Other risk factors, such as increasing age, cob breed, use of higher intraoperative dosages (in mg/kg) of ketamine and/or thiopental, were associated with poor quality of recovery.

Comparison of analgesic and systemic effects of bupivacaine, methadone, or bupivacaine/methadone administered epidurally in conscious sheep

OBJECTIVE

The aim of this study was to evaluate the combination of bupivacaine and methadone administered epidurally in sheep.

METHODS

Six healthy female mixed-breed sheep weighing 35-46 kg and aged 12-18 months were included. Each sheep was assigned to receive three treatments: 0.5 mg/kg 0.25% bupivacaine (BP), 0.3 mg/kg 1% methadone (MT) or 0.25 mg/kg bupivacaine and 0.15 mg/kg methadone (BPMT). All drugs were injected into the lumbosacral space through an epidural catheter. Each animal received each treatment at random. Heart rate, arterial blood pressure (systolic, diastolic and mean), respiratory rate, rectal temperature, analgesia, sedation and motor block were determined before treatment and at predetermined intervals.

RESULTS

The duration of analgesia was 240, 220, and 180 min for BP, MT and BPMT, respectively (P < 0.05). Motor block for all agents was mild to moderate. None or the treatments significantly altered the heart rate, blood pressure or respiratory rate.

CONCLUSION

Our findings suggest that lumbosacral epidural administration of bupivacaine, methadone or a combination of the two drugs can provide perioperative analgesia in sheep as part of their management for surgical procedures in the flank and hindlimbs.

Attitude of Brazilian veterinarians in the recognition and treatment of pain in horses and cattle

OBJECTIVE

The objective of this study was to assess the use of analgesics, describe the attitudes of Brazilian veterinarians towards pain relief in horses and cattle and evaluate the differences due to gender, year of graduation and type of practice.

STUDY DESIGN

Prospective survey.

METHODS

Questionnaires were sent to 1000 large animal veterinarians by mail, internet and delivered in person during national meetings. The survey investigated the attitudes of Brazilian veterinarians to the recognition and treatment of pain in large animals and consisted of sections asking about demographic data, use of analgesic drugs, attitudes to pain relief and to the assessment of pain. Descriptive statistics were used to analyze frequencies. Simple post hoc comparisons were performed using the chi-square test.

RESULTS

Eight hundred questionnaires were collected, but 87 were discarded because they were incomplete or blank. The opioid of choice for use in large animals was butorphanol (43.4%) followed by tramadol (39%). Flunixin (83.2%) and ketoprofen (67.6%) were the most frequently used NSAIDs by Brazilian veterinarians. Respondents indicated that horses received preoperative analgesics for laparotomy more frequently (72.9%) than cattle (58.5%). The most frequently administered preoperative drugs for laparotomy in horses were flunixin (38.4%) and xylazine (23.6%), whereas the preoperative drugs for the same surgical procedure in cattle were xylazine (31.8%) and the local administration of lidocaine (48%). Fracture repair was considered the most painful surgical procedure for both species. Most veterinarians (84.1%) believed that their knowledge in this area was not adequate.

CONCLUSIONS AND CLINICAL RELEVANCE

Although these Brazilian veterinarians thought that their knowledge on recognition and treatment of pain was not adequate, the use of analgesic in large animals was similar in Brazil to that reported in other countries.

Effect of flunixin meglumine on the amelioration of lameness in dairy steers with amphotericin B-induced transient synovitis-arthritis

OBJECTIVE

To characterize amphotericin B-induced lameness in cattle and to ascertain the analgesic effects of flunixin meglumine by use of multimodal assessment.

ANIMALS

10 healthy Holstein steers free from musculoskeletal disease.

PROCEDURES

Steers were randomly allocated to a treatment or negative control group. Amphotericin B was injected into the distal interphalangeal joint of the lateral claw of the left hind limb of all steers. Treatment steers received flunixin meglumine at the time of synovitis-arthritis induction and at 12 hours after induction. Control steers received no medication. Multimodal analysis included vital parameters, visual lameness score, behavioral monitoring with accelerometers, pressure mat analysis, and plasma cortisol determination before and after induction. Data were analyzed by use of linear mixed models with treatment and time designated as fixed effects, accounting for repeated measures on individual calves.

RESULTS

Amphotericin B injection induced moderate, transient lameness. Control steers were more than twice as likely to be lame as treatment steers (mean ± SD lameness score, 92.2 ± 8.1 % vs 40.7 ± 2.5%). Treatment steers placed significantly greater force and contact area on the affected foot and greater force, impulse, and contact area on the paired claw, compared with control steers. Furthermore, treatment steers spent considerably less time in recumbency than controls.

CONCLUSIONS AND CLINICAL RELEVANCE

Amphotericin B successfully induced synovitis-arthritis in dairy steers that was transient in nature. Flunixin meglumine was efficacious in providing analgesia for these steers.

Continuous peripheral neural blockade to alleviate signs of experimentally induced severe forelimb pain in horses

OBJECTIVE

To investigate the efficacy and safety of a low-volume, single-catheter, continuous peripheral neural blockade (CPNB) technique to locally deliver bupivacaine to alleviate signs of severe forelimb pain resulting from experimentally induced tendonitis in horses.

DESIGN

Randomized controlled experimental trial.

SAMPLE

14 horses and 5 forelimbs from equine cadavers.

PROCEDURES

Horses underwent collagenase-induced superficial digital flexor tendonitis in the midmetacarpal region of 1 forelimb. To deliver analgesia, a closed-tip catheter was placed from lateral to medial, approximately 12 cm distal to the accessory carpal bone, between the suspensory ligament and accessory ligament of the deep digital flexor tendon. Success of catheter placement and anesthetic delivery was documented ex vivo in 5 forelimbs from equine cadavers. Effective analgesia in affected forelimbs of horses from continuous (n = 7) versus intermittent (7) local anesthetic delivery (intermittent peripheral neural blockade; IPNB) was compared over a 3-day period.

RESULTS

Horses that received CPNB in the affected forelimb were less lame than horses that received IPNB. A lower proportion of CPNB-treated horses had behavioral and physiologic signs of pain, compared with IPNB-treated horses. Neither technique completely blocked the sensation of pain or resulted in swelling in the distal portion of the forelimb, vasodilation, or an increase in lameness. After removal, Staphylococcus aureus was cultured from 1 catheter tip.

CONCLUSIONS AND CLINICAL RELEVANCE

For short-term treatment, CPNB was more effective than IPNB for reduction in signs of severe pain in the distal aspect of the forelimb of horses.

In vitro evaluation of the effect of the opioid antagonist N-methylnaltrexone on motility of the equine jejunum and pelvic flexure

REASONS FOR PERFORMING STUDY

Although potent analgesics, opioids decrease intestinal activity, leading to ileus in many species. N-methylnaltrexone (MNTX), an opioid antagonist which does not cross the blood-brain barrier and antagonises the morphine effect on the intestine, directly stimulates motility and restores function without affecting analgesic properties. While its use has been reported in human subjects, there is no information with regard to its usage in the horse.

OBJECTIVES

To determine whether MNTX has an effect on contractile activity of the equine jejunum and pelvic flexure.

METHODS

Using circular smooth muscle strips obtained from 8 mature horses, increasing concentrations of MNTX were added to tissue baths in the range of 1 x 10(-9) to 1 x 10(-5) mol/l, and contractile responses were recorded for 3 mins. Data were analysed using a repeated measures ANOVA to determine whether there was a significant drug effect compared to baseline activity. Data were analysed between the jejunum and pelvic flexure using a Mann-Whitney U test. Statistical significance was established as P < 0.05.

RESULTS

The administration of MNTX significantly increased the contractile frequency and amplitude at all concentrations relative to baseline (P < 0.0001) for the jejunum. The response was greatest at 1 x 10(-7) mol/l (P = 0.0005), with a mean difference from baseline of 115.12 g/cm2. The highest concentration evaluated (1 x 10(-5) mol/l) had a mean contractile strength of 69.76 g/cm2, which was significantly greater than baseline activity (P = 0.04). A significant increase in contractile activity for the colon was detected at 3 x 10(-7) mol/l and all subsequent concentrations (P < 0.04). Unlike the jejunum, the contractile activity of the pelvic flexure increased progressively with the addition of each subsequent concentration.

CONCLUSIONS

N-methylnaltrexone has a direct effect on circular smooth muscle of the equine jejunum and pelvic flexure resulting in an increase in contractile activity.

POTENTIAL RELEVANCE

N-methylnaltrexone could potentially be used in conjunction with morphine to provide potent and effective analgesia without compromising intestinal function. Further in vivo investigations are required to determine whether this agent antagonises morphine's effect on motility.

A comparison of epidural buprenorphine plus detomidine with morphine plus detomidine in horses undergoing bilateral stifle arthroscopy

OBJECTIVE

To compare the analgesic efficacy of buprenorphine plus detomidine with that of morphine plus detomidine when administered epidurally in horses undergoing bilateral stifle arthroscopy.

STUDY DESIGN

Prospective, randomized, blinded clinical trial.

ANIMALS

Twelve healthy adult horses participating in an orthopedic research study. Group M (n = 6) received morphine (0.2 mg kg(-1)) and detomidine (0.15 mg kg(-1)) epidurally; group B (n = 6) received buprenorphine (0.005 mg kg(-1)) and detomidine (0.15 mg kg(-1)) epidurally.

METHODS

Horses received one of two epidural treatments following induction of general anesthesia for bilateral stifle arthroscopy. Heart rate (HR), mean arterial blood pressure (MAP), end-tidal CO(2) (Pe'CO(2)), and end-tidal isoflurane concentrations (E'Iso%) were recorded every 15 minutes following epidural administration. Post-operative assessment was performed at 1, 2, 3, 6, 9, 12, and 24 hours after standing; variables recorded included HR, respiratory rate (f(R)), abdominal borborygmi, defecation, and the presence of undesirable side effects. At the same times post-operatively, each horse was videotaped at a walk and subsequently assigned a lameness score (0-4) by three ACVS diplomates blinded to treatment and who followed previously published guidelines. Nonparametric data were analyzed using Wilcoxon's rank-sum test. Inter- and intra-rater agreement were determined using weighted kappa coefficients. Statistical significance was set at p <or= 0.05.

RESULTS

No statistically significant differences were found between groups with respect to intra-operative HR, MAP, E'Iso%, or post-operative HR, gastrointestinal function and cumulative median lameness scores. Post-operative f(R) in group B [24 (12-30), median (range)] breaths per minute was significantly higher than in group M [18 (15-20)] breaths per minute, p = 0.04.

CONCLUSIONS AND CLINICAL RELEVANCE

In horses undergoing bilateral stifle arthroscopy, these doses of buprenorphine plus detomidine injected epidurally produced analgesia similar in intensity and duration to that of morphine plus detomidine injected epidurally.

Morphine-associated pruritus after single extradural administration in a horse

Pruritus following a single administration of 100 microg kg(-1) of preservative-free morphine sulphate given via an extradural catheter was seen in a 580 kg horse. The catheter was placed in the first intercoccygeal space. Focal irritation, represented by both local alopecia over the left gluteal muscles and serum exudation, occurred 4-8 hours after injection. This was attributed to the extradural morphine administration.

Analgesic effects of epidural administration of hydromorphone in horses

OBJECTIVE

To evaluate the effects of epidural administration of hydromorphone on avoidance threshold to noxious electrical stimulation of the perineal, sacral, lumbar, and thoracic regions in horses.

ANIMALS

6 healthy adult horses.

PROCEDURE

Horses were assigned to receive hydromorphone (0.04 mg/kg) or a control solution (20 mL of sterile water) administered epidurally into in the first intercoccygeal space. Treatments were administered at time intervals of > or = 7 days. Electrical stimulation was applied for 6 hours after epidural injection over the dermatomes of the perineal, sacral, lumbar, and thoracic regions, and the avoidance threshold voltage was recorded.

RESULTS

Administration of sterile water did not change the avoidance threshold. Hydromorphone significantly increased the avoidance threshold by 20 minutes after injection, which lasted until 250 minutes after epidural administration in the perineal, sacral, lumbar, and thoracic regions. Profound analgesia (avoidance threshold > 40 V) was achieved only in the perineal region at 60 minutes after epidural administration of hydromorphone. Analgesia for all dermatomes was considered moderate for 250 minutes after epidural injection.

CONCLUSIONS AND CLINICAL RELEVANCE

Epidural administration of hydromorphone increases the avoidance threshold to noxious electrical stimulation in the perineal, lumbar, sacral, and thoracic regions in horses for 250 minutes after injection. Hydromorphone epidural administration may prove useful in the management of horses with pain of moderate to mild intensity.

Anesthesia of the critically ill equine patient

There is a plethora of information regarding anesthetic management of horses; however, controlled studies of the critically ill equine patient are few. These patients should be managed like any equine anesthetic candidate but much more stringently:I. Preoperative evaluation and appropriate therapy may represent the difference between life and death during the intraoperative and recovery periods. 2. The anesthetic induction and maintenance protocol should be based on the individual situation of the veterinary facility and personnel("comfort zone"). 3. Appropriate monitoring and intraoperative supportive measures are essential. 4. The anesthetic period is a significant perturbation to homeostasis. Even if the horse seems to have done well (ie, as indicated by the cardiopulmonary values), a problem-free anesthetic period does not guarantee a successful recovery, and close monitoring should continue until the horse is ambulatory. 5. Critically ill patients are often in a negative energy balance. Supportive measures to ensure an adequate caloric intake, such as enteral or parenteral nutrition, facilitate healing and return of homeostasis.

A comparison of the analgesic effects of caudal epidural methadone and lidocaine in the horse

OBJECTIVE

To evaluate and compare the effects of caudal epidural administration of methadone (METH) and lidocaine (LIDO) on tolerance to thermal stimulation over the dermatomes of the perineal, sacral, lumbar and thoracic regions in the horse.

STUDY DESIGN

A blinded, randomized, prospective, experimental cross-over study.

ANIMALS

Seven healthy horses, 15.7 +/- 4.9 years (mean +/- SD) of age, weighing 536 +/- 37 kg.

METHODS

The horses were randomly assigned to receive two treatments (group M: METH, 0.1 mg kg-1 or group L: LIDO, 0.35 mg kg-1) at intervals of at least 28 days. An 18-gauge 80-mm Tuohy epidural needle was placed in the first intercoccygeal space (Co1-Co2) in awake standing horses restrained in stocks. Analgesia was assessed by use of a probe maintained at a constant 62 degrees C by circulating hot water. The maximum stimulation time was 30 seconds. Bilateral stimulation was performed at five defined points. Before drug administration, baseline values of response time to thermal stimuli were obtained. Time to response was then measured 15 and 60 minutes after METH or LIDO administration and then hourly until the response returned to baseline at all stimulation points on two further assessments. Development of any ataxia and/or sedation was recorded. Positive pain responses were defined as purposeful avoidance movements of the head, neck, trunk, limbs and tail. Absence of attempts to kick, bite and turning of the head toward the stimulation site were used to indicate analgesia.

RESULTS

Caudal epidural administration of METH and LIDO significantly increased reaction time to thermal stimulation (one-sample t-test; p = 0.05). Analgesia in the perineal region was present 15 minutes after both METH and LIDO administration and progressed from caudal to cranial dermatones with time. The duration of a significant increase in reaction time was 5 hours after METH injection compared to 3 hours following LIDO. All horses defaecated and urinated normally, and no excitement, sedation or ataxia were observed after METH administration. The horses were unable to defaecate normally and were moderately to severely ataxic with hindlimb weakness after LIDO.

CONCLUSIONS

Caudal epidural administration of methadone has considerable potential in the management of perineal, lumbo-sacral and thoracic pain in horses. Regional differences exist in the onset, duration and intensity of the pain relief.

CLINICAL RELEVANCE

Epidural methadone administration provides analgesia with no measured side effects in these healthy adult horses.

Outcome of epidural catheterization for delivery of analgesics in horses: 43 cases (1998-2001)

OBJECTIVE

To determine reasons for epidural catheter placement among horses examined at a veterinary teaching hospital, efficacy of epidural administration of analgesics, duration of catheter placement, reasons for catheter removal, and complications encountered.

DESIGN

Retrospective study.

ANIMALS

43 horses.

PROCEDURE

Medical records were reviewed.

RESULTS

A total of 50 epidural catheters were placed in the 43 horses. Underlying conditions included fractures, lacerations, septic arthritis, myositis, perineal injuries, and cellulitis. Horses ranged from 2 to 21 years old and weighed between 365 and 795 kg (803 and 1,749 lb). Median duration of catheter placement was 96 hours (range, 1.5 to 480 hours). The response to epidural drug administration was reported as positive in 34 horses and negative in 4. There was no apparent response in 2 horses, and response could not be determined in 3. Three temporary patient-related complications associated with epidural catheter administration were observed. Technical problems associated with the epidural catheters included dislodgement of the catheter itself (7 catheters) or of the adapter or filter (5), obstruction (5), and leakage (5). Twenty-two catheters were removed because of resolution of the underlying condition, and 10 were removed because of complications. For 6 catheters, the reason for catheter removal was not recorded. The remaining 12 catheters were in place when the horses were euthanatized.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that epidural catheterization can be used successfully for repeated epidural delivery of analgesics and anesthetics in horses with various clinical conditions. Complications associated with epidural catheters or epidural drug administration were infrequent and transient.

Epidural morphine and detomidine decreases postoperative hindlimb lameness in horses after bilateral stifle arthroscopy

OBJECTIVE

To determine whether preoperative epidural administration of morphine and detomidine would decrease postoperative lameness after bilateral stifle arthroscopy in horses.

STUDY DESIGN

Prospective clinical controlled study.

ANIMALS

Eight adult horses that had bilateral arthroscopic procedures, including drilling of cartilage and subchondral bone within the femoropatellar joints.

METHODS

Horses were randomly separated into 2 groups. Preoperatively, 4 horses were administered a combination of epidural morphine (0.2 mg/kg) and detomidine (30 microg/kg), and 4 horses were administered an equivalent volume of epidural saline (0.9% NaCl) solution. Postoperative pain was assessed using 6 video recordings made at hourly intervals of each horse at a walk. Assessments began 1 hour after recovery from anesthesia. The recordings were scrambled out of sequence and evaluated by 3 observers, unaware of treatment groups, who scored lameness from 0 to 4. Lameness scores of the 2 groups of horses were compared using a Wilcoxon's rank sum test. Heart and respiratory rates were also measured at each hourly interval and compared between groups using a repeated-measures ANOVA; statistical significance was set at P <.05.

RESULTS

Preoperative administration of epidural morphine and detomidine significantly decreased lameness and heart rates after bilateral stifle arthroscopy. The greatest decrease was detected at hours 1 and 2 after recovery from anesthesia.

CONCLUSION

We conclude that horses undergoing a painful arthroscopic procedure of the stifle joint benefit from the administration of preoperative epidural morphine and detomidine.

CLINICAL RELEVANCE

Preoperative epidural administration of detomidine and morphine may be useful in decreasing postoperative pain after stifle arthroscopy as well as pain associated with other painful disorders involving the stifle joint, such as septic arthritis and trauma.

Diagnosing and treating pain in the horse. Where are we today?

This chapter begins by providing an overview of current philosophies relevant to equine pain management. Objective and subjective techniques for assessing pain and the limitations of these are then described in depth. The conclusion emphasizes the need for an evidence based approach to managing pain in the horse and sets the stage for subsequent chapters in this edition.

Management of gastrointestinal pain

Choice of an analgesic for gastrointestinal pain requires consideration of the cause of the pain, desired duration of pain relief, need for sedation, and potential side effects and toxicity, particularly in light of other drugs being used and effects on the gastrointestinal tract. It is imperative that close monitoring be continued to ensure that surgical lesions or worsening conditions are detected. Recent research in the field may lead to new drugs, drug combinations, and avenues of treatment that minimize the side effects of these drugs while maximizing their efficacy.

Management of equine orthopedic pain

Pain management is an extremely vital part of equine orthopedic surgery. Providing optimum analgesia for the patient will decrease recovery time, decrease physiologic stress on the animal, and provide maximum comfort during the post-operative period. The major analgesic drug categories and routes covered are nonsteroidal anti-inflammatory drugs, local anesthetics, intra-articular drugs, and epidurals.

Use of opioids for pain and anesthetic management in horses

REGIONAL ADMINISTRATION: There is limited, but convincing, evidence that epidural administration of morphine and some other mu-agonist opioids consistently relieves regional pain in horses. In addition, this effect is not accompanied by notable undesirable effects. On the other hand, a clinically important analgesic action has not been demonstrated for similarly administered kappa-agonist opioids. There has been little objective data presented to support the analgesic effectiveness of intra-articularly administered opioids in horses. However, the evidence of local opioid receptors legitimately encourages work to substantiate the value of intra-articular opioid administration to relieve joint-associated pain in horses. SYSTEMIC ADMINISTRATION: So far, study results do not provide convincing, objective evidence to support the opinion that systemically administered opioids consistently and effectively relieve pain in horses. Given this lack of evidence, and considering that opioids stimulate locomotor and other forms of unwanted excitant behavior, reduce propulsive gastrointestinal motility, decrease alveolar ventilation (especially in association with general anesthesia), and require regulatory and practical considerations for abuse potential in both humans and horses, we conclude that routine, indiscriminate administration of opioids for pain relief in horses is not justified. Identification and focused, objective study of selective beneficial opioid actions to provide guidance for appropriate clinical use is long overdue.

Epidural anesthesia and analgesia in horses

Intercoccygeal, or caudal, epidural injection of local anesthetics is a convenient method of producing analgesia and local anesthesia of the tail and perineal structures in conscious standing horses. This technique has been further developed to provide long duration analgesia and anesthesia by placement of catheters into the epidural space of horses. More recently, opioid, alpha-2 adrenergic agonists, ketamine and other analgesic agents have been administered by caudal epidural injection, providing pain relief in both conscious, standing and anesthetized, recumbent horses. This chapter describes the development of different anesthetic and analgesic epidural techniques in horses, methods for epidural injection and catheterization, and reviews the current literature related to epidural analgesia and pain control in horses.

Analgesic, hemodynamic, and respiratory effects induced by caudal epidural administration of meperidine hydrochloride in mares

OBJECTIVE

To determine the analgesic, hemodynamic, and respiratory effects induced by caudal epidural administration of meperidine hydrochloride in mares.

ANIMALS

7 healthy mares.

PROCEDURE

Each mare received meperidine (5%; 0.8 mg/kg of body weight) or saline (0.9% NaCl) solution via caudal epidural injection on 2 occasions. At least 2 weeks elapsed between treatments. Degree of analgesia in response to noxious electrical, thermal, and skin and muscle prick stimuli was determined before and for 5 hours after treatment. In addition, cardiovascular and respiratory variables were measured and degree of sedation (head position) and ataxia (pelvic limb position) evaluated.

RESULTS

Caudal epidural administration of meperidine induced bilateral analgesia extending from the. coccygeal to S1 dermatomes in standing mares; degree of sedation and ataxia was minimal. Mean (+/- SD) onset of analgesia was 12 +/- 4 minutes after meperidine administration, and duration of analgesia ranged from 240 minutes to the entire 300-minute testing period. Heart and respiratory rates, rectal temperature, arterial blood pressures, Hct, PaO2, PaCO2, pHa, total solids and bicarbonate concentrations, and base excess were not significantly different from baseline values after caudal epidural administration of either meperidine or saline solution.

CONCLUSIONS AND CLINICAL RELEVANCE

Caudal epidural administration of meperidine induced prolonged perineal analgesia in healthy mares. Degree of sedation and ataxia was minimal, and adverse cardiorespiratory effects were not detected. Meperidine may be a useful agent for induction of caudal epidural analgesia in mares undergoing prolonged diagnostic, obstetric, or surgical procedures in the anal and perineal regions.

Evaluation of the analgesic effects of epidurally administered morphine, alfentanil, butorphanol, tramadol, and U50488H in horses

OBJECTIVE

To evaluate and compare effects of epidurally administered morphine, alfentanil, butorphanol, tramadol, and U50488H on avoidance threshold to noxious electrical stimulation over the dermatomes of the perineal, sacral, lumbar, and thoracic regions in horses.

ANIMALS

5 healthy adult horses.

PROCEDURE

Using a Latin square complete repeated-measures design, horses were randomly assigned to receive 1 of 6 treatments (morphine, alfentanil, butorphanol, tramadol, U50488H, or sterile water) at intervals of at least 7 days. Agents were injected epidurally at the first intercoccygeal epidural space, and electrical stimulation was applied at repeated intervals for 24 hours to the dermatomes of the perineal, sacral, lumbar, and thoracic regions. Avoidance threshold to electrical stimulation was recorded.

RESULTS

Administration of butorphanol, U50488H, and sterile water did not induce change in avoidance threshold. Alfentanil increased avoidance threshold during the first 4 hours, but not significantly. Tramadol and morphine significantly increased threshold and analgesic effects. Complete analgesia (avoidance threshold, >40 V) in the perineal and sacral areas was achieved 30 minutes after tramadol injection, compared with 6 hours after morphine injection. Duration of complete analgesia was 4 hours and 5 hours after tramadol and morphine injections, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Epidural administration of tramadol and morphine induces long-lasting analgesia in healthy adult horses. Epidural administration of opioids may provide long-lasting analgesia in horses without excitation of the CNS.

Systemic and local effects associated with long-term epidural catheterization and morphine-detomidine administration in horses

OBJECTIVE

The purpose of this study was to determine the systemic and local effects associated with long-term epidural catheterization and epidural morphine-detomidine administration in horses.

STUDY DESIGN

Development of systemic or local effects was assessed by placing caudal epidural catheters in study horses and administering injections through the catheters every 12 hours for 14 days.

ANIMALS

Ten horses with epidural catheters that received daily injections; six uncatheterized horses presented for euthanasia.

METHODS

Horses received either 0.2 mg/kg morphine sulfate and 30 micrograms/kg detomidine hydrochloride or an equivalent volume of physiologic saline solution through epidural catheters. Systemic effects were compared between control and treatment horses by measuring physical parameters and hay and water consumption, as well as by evaluating major organs after euthanasia. Local effects were studied by examining cerebrospinal fluid and by grading representative samples of the spinal cord and surrounding tissues histologically for inflammation and fibrosis. Local effects were compared between control and treatment horses, as well as between catheterized (control plus treatment) horses and uncatheterized horses.

RESULTS

No significant difference was identified in daily variables or hay and water consumption between control and treatment horses. No growth was obtained from cerebrospinal fluid cultures. No significant difference in cerebrospinal fluid values or spinal tissue inflammation or fibrosis grades was shown between control and treatment horses. However, when compared with uncatheterized horses, cerebrospinal fluid red blood cell values were marginally higher and protein concentrations were significantly higher in the catheterized group. Lumbosacral and sacral spinal tissue segment inflammation grades, and sacral segment fibrosis grades were significantly higher in catheterized horses.

CONCLUSIONS

Long-term epidural administration of a morphine-detomidine combination is not associated with apparent adverse systemic effects in horses. Localized inflammation and fibrosis seem to be catheter-related.

CLINICAL RELEVANCE

Potential systemic and local effects are important considerations with long-term administration of a morphine-detomidine combination through indwelling epidural catheters for alleviation of chronic musculoskeletal pain in horses.