J.P.A.M. van Loon

Intra-articular opioid analgesia is effective in reducing pain and inflammation in an equine LPS induced synovitis model.

REASONS FOR PERFORMING STUDY Intra-articular administration of morphine as a local analgesic and anti-inflammatory drug is widely used in human medicine. In equids, little is known about its clinical analgesic and anti-inflammatory efficacy. OBJECTIVES To use an inflammatory orthopaedic pain model to investigate the analgesic and anti-inflammatory effects of intra-articularly administered morphine as a new treatment modality in horses with acute arthritis. METHODS In a crossover study design, synovitis was induced in the left or right talocrural joint by means of intra-articular injection of 0.5 ng lipopolyssacharide (LPS). The effect of 120 mg morphine, intra-articularly administered at 1 h after induction of synovitis, was evaluated using both physiological and behavioural pain variables. Synovial fluid was sampled at 0, 4, 8, 28 and 52 h after induction of synovitis and analysed for total protein concentration, leucocyte count and for prostaglandin E(2), bradykinin and substance P concentrations by ELISA. Ranges of motion of metatarsophalangeal and talocrural joints were measured as kinematic variables with the horses walking and trotting on a treadmill under sound and lame conditions. Clinical lameness scores and several behavioural variables related to the perception of pain were obtained. RESULTS LPS injection caused marked transient synovitis, resulting in increased concentrations of inflammatory synovial fluid markers, clinical lameness, joint effusion and several behavioural changes, such as increased time spent recumbent, decreased limb loading at rest and decreased time spent eating silage. Intra-articular morphine resulted in a significant decrease in synovial white blood cell count, prostaglandin E(2) and bradykinin levels and improvement in clinical lameness, kinematic and behavioural parameters, compared to placebo treatment. CONCLUSIONS Intra-articular morphine offers potent analgesic and anti-inflammatory effects in horses suffering from acute synovitis. POTENTIAL RELEVANCE Local administration of opioids may be useful for horses with acute inflammatory joint pain and offers possibilities for multimodal analgesic therapies without opioid-related systemic side effects.

Umbilical cord clamping in term piglets: A useful model to study perinatal asphyxia?

Perinatal asphyxia results in tissue and cellular changes during the reperfusion period and clinical signs like perinatal mortality and decreased vitality at birth in newborn piglets. This study aimed to develop and validate a model of birth asphyxia, mimicking the evolvement of birth asphyxia in natural farrowings by conducting umbilical cord clamping (UCC) in term piglets during caesarean sections under general anaesthesia. In total 23 piglets were subjected to 5-8min of UCC and 24 piglets served as controls. Acid-base balance values and heart rates measured before UCC remained fairly constant throughout the surgical procedure, indicating nearly identical starting conditions of piglets within and between litters. UCC resulted in a significant, mild, mixed respiratory-metabolic acidosis (pH 7.22, pCO(2) 9.8kPa, BE(ecf) 2mmol/L, lactate 6.5mmol/L; controls: pH 7.31, pCO(2) 8.5kPa, BE(ecf) 5mmol/L, lactate 4mmol/L) at 10min after birth (defined as simultaneous cutting of the umbilical cord and removal of a plastic bag that had been placed over the head to avoid air intake). Heart rates were significantly decreased during UCC (range: 83-107beats/min versus 128-134beats/min in controls). Rectal temperatures and changes in body weight until 72h of life were not affected by UCC. Interestingly, four control and seven clamped piglets did not survive as no independent respiration could be attained. Birth weights and duration of UCC of these piglets did not differ significantly from those in surviving control and clamped piglets. In conclusion the mixed respiratory-metabolic acidosis arising in the surviving clamped piglets is not as severe as can be expected in highly asphyxiated, vaginally delivered newborn piglets. Repeatability of the model is compromised by considerable variation in the individual response to UCC.

Systematic pain assessment in horses.

Accurate recognition and quantification of pain in horses is imperative for adequate pain management. The past decade has seen a much needed surge in formal development of systematic pain assessment tools for the objective monitoring of pain in equine patients. This narrative review describes parameters that can be used to detect pain in horses, provides an overview of the various pain scales developed (visual analogue scales, simple descriptive scales, numerical rating scales, time budget analysis, composite pain scales and grimace scales), and highlights their strengths and weaknesses for potential clinical implementation. The available literature on the use of each pain assessment tool in specific equine pain states (laminitis, lameness, acute synovitis, post-castration, acute colic and post-abdominal surgery) is discussed, including any problems with sensitivity, reliability or scale validation as well as translation of results to other clinical pain states. The review considers future development and further refinement of currently available equine pain scoring systems.

Upregulation of articular synovial membrane μ-opioid-like receptors in an acute equine synovitis model.

Intra-articular injection of opioids provides analgesia in painful equine joints and μ-opioid receptors (MORs) have been demonstrated in equine synovial membranes. The aim of this study was to determine whether acute inflammatory conditions will lead to up-regulation of MOR in equine synovial membranes and whether anti-inflammatory treatment can prevent any such upregulation. In a two-period, blinded, placebo-controlled randomised cross-over design, lipopolysaccharide (LPS, 1.0 ng) was injected into the left or right middle carpal joint of seven healthy ponies. Arthroscopy and synovial membrane biopsy was performed under general anaesthesia at baseline, 48 h (T48) and 672 h (T672) after LPS injection, with ponies assigned to receive either phenylbutazone (PBZ 2.2mg/kg PO BID) or placebo from 2h post-LPS. Ponies were scored for pain and lameness. Repeated synovial fluid samples were obtained and the degree of synovitis scored both macroscopically and microscopically. The density and staining pattern of MOR-like protein in synovial membrane biopsies over the course of the synovitis with or without PBZ treatment was evaluated using immunohistochemical techniques. LPS injection consistently induced a severe transient synovitis. Pain and lameness were significantly attenuated by treatment with PBZ. Up-regulation of MOR-like protein in the inflamed equine synovial membrane could be demonstrated in the placebo treated animals, but not in the PBZ-treated animals overall, although there were no significant differences at any individual time-point between the two groups. It was concluded that acute inflammation will up-regulate MOR, while anti-inflammatory treatment will attenuate this response.

In vivo effects of phenylbutazone on inflammation and cartilage-derived biomarkers in equine joints with acute synovitis

Although phenylbutazone (PBZ) is commonly used in equine orthopaedic practice, little is known about its in vivo effects on joint inflammation and cartilage turnover. This study investigates the effects of PBZ on inflammatory parameters, matrix metalloproteinase (MMP) activity and cartilage biomarkers in equine joints with acute synovitis. In a two-period cross-over study, transient synovitis was induced at T = 0 h in the middle carpal joint of seven ponies by lipopolysaccharide (LPS) injection. Ponies received PBZ (2 mg/kg PO twice daily) or placebo for 1 week, starting at T = 2 h. Arthroscopic assessment of the middle carpal joint was performed at T = -504, 48 and 672 h. Synovial fluid (SF) was sampled at T = -504, 0, 8, 24, 48, 168, 336 and 672 h and analysed for leukocytes and total protein, substance P, general MMP activity, glycosaminoglycans (GAG), collagen II cleavage marker C2C and synthesis marker CPII. Markers in PBZ- vs. placebo-treated joints were compared over time using a linear mixed model. LPS injection caused marked transient synovitis without visible cartilage changes. Substance P and general MMP activity were not significantly reduced by PBZ treatment, nor were SF GAG or C2C concentrations at any time point. Concentration of CPII was significantly lower at T = 24 and 168 h in PBZ treated joints compared to placebo. Although PBZ is clinically effective in treating acute synovitis, it does not limit inflammation-induced cartilage catabolism and may transiently reduce collagen anabolism as evidenced by SF markers.

Lumbosacral spinal cord somatosensory evoked potentials for quantification of nociception in horses.

REASONS FOR PERFORMING STUDY There is a need for objective evaluation and quantification of the efficacy of analgesic drugs and analgesic techniques in horses. OBJECTIVES To determine whether lumbosacral spinal cord somatosensory evoked potentials (SSEP) can be a useful and reliable tool to assess nociception in equines. METHODS SSEPs and electromyograms (EMG) from the epaxial muscles were recorded simultaneously, following electrical stimulation applied to the distal hindlimb in lightly anaesthetised Shetland ponies (n=7). In order to validate the model, the effect of increasing stimulus intensity was documented and the conduction velocities (CV) of the stimulated nerves were calculated. The effect of epidurally applied methadone (0.4 mg/kg bwt) in a randomised, crossover design was investigated. RESULTS Two distinct complexes (N1P1 and N2P2) were identified in the SSEP waveform. Based on their latency and conduction velocity and the depressant effect of epidurally applied methadone, the SSEP N2P2 was ascribed to nociceptive Adelta-afferent stimulation. The SSEP N1P1 originated from non-nociceptive Abeta-afferent stimulation and was not influenced by epidurally applied methadone. CONCLUSIONS AND POTENTIAL RELEVANCE The nociceptive Adelta component of the SSEP, the N2P2 complex, is presented as a valid and quantitative parameter of spinal nociceptive processing in the horse. Validation of the equine SSEP model enables the analgesic effects of new analgesics/analgesic techniques to be quantified and analgesia protocols for caudal epidural analgesia in equidae improved.

Use of epidurally derived evoked potentials for quantification of caudal nociception in ponies.

OBJECTIVE To determine whether epidurally derived evoked potentials (EPs) can be used to reliably assess nociception and antinociception in ponies. ANIMALS 7 ponies. PROCEDURES EPs and electromyograms (EMGs) from the quadriceps femoris muscles were recorded simultaneously, following electrical stimulation applied to the distal portion of the hind limb. The effect of increasing stimulus intensity, conduction velocities of the stimulated nerves, effect of epidurally applied methadone, and effect of systemically administered propofol were evaluated. RESULTS In the EP and EMG waveforms, 2 distinct complexes, the EP N25 and P50 and the EMG P27 and N62, respectively, were identified. On the basis of their latency and calculated conduction velocities, the EP P50 and EMG N62 were considered to be related to nociception (AD-mediated). All complexes increased significantly in amplitude with increasing stimulus intensity and decreased significantly following epidural administration of methadone or systemic administration of propofol. CONCLUSIONS AND CLINICAL RELEVANCE Although the experimental setup allowed successful discrimination between tactile- and nociceptive-associated responses, the identified EPs, considered to reflect activity in the spinal cord, could not be definitively differentiated from activity in the lumbosacral epaxial musculature. Further research is required to refine measurement techniques to allow for discrimination between these 2 signals. Similar to other species, neurophysiologic variables such as EPs could potentially become a useful additional tool in quantifying nociception in equidae.

Oxygen supplementation before induction of general anaesthesia in horses.

Reasons for performing study: Hypoventilation or apnoea, caused by the induction of general anaesthesia, may cause hypoxaemia. Preoxygenation may lengthen the period before this happens. No scientific studies are published on preoxygenation in equine anaesthesia. Objectives: To determine whether supplementation of oxygen at a flow rate of 15 l/min for 3 min via a nasal cannula before induction of general anaesthesia is effective in elevating the arterial partial pressure of oxygen (PaO2) directly after induction. Study design: Randomised, prospective clinical trial. Methods: A total of 18 American Society of Anesthesiologists physical status 1 or 2 adult horses undergoing elective anaesthesia were randomly allocated to one of 2 groups. The first group (control) received no oxygen supplementation before induction of general anaesthesia, whereas the second group (oxygen) did. All horses were anaesthetised with intravenous detomidine, butorphanol, ketamine, midazolam and isoflurane. Directly after induction (T = 0) and 30 min later (T = 30) an arterial blood sample was taken for blood gas analysis. At T = 30 an estimate of intrapulmonary shunt fraction (Qs/Qt) was calculated. Results: At T = 0 arterial partial pressure of oxygen (PaO2) was significantly higher in the oxygen group compared with the control group (11.0 ± 2.6 kPa vs. 7.4 ± 1.6 kPa; mean ± s.d., P = 0.005) and at T = 30 differences were not statistically significant. Partial pressure of carbon dioxide (PaCO2) and Qs/Qt did not differ between groups. Conclusions: Supplementing oxygen by a nasal cannula before induction of general anaesthesia in horses is feasible and does effectively elevate the PaO2 immediately after induction. Future research is needed to determine whether supplementation of oxygen before induction of general anaesthesia in horses will affect outcomes.

Objective pain assessment in horses (2014–2018)

In recent decades, much effort has been invested in scientific studies of objective and reliable assessment of pain in horses. Various types of pain assessment tools have been described and (partly) validated for different types of pain in horses. Currently, composite pain scales and facial expression-based pain scales seem to be the most promising tools for pain assessment in horses and numerous studies have recently been published on the use of these pain scales in horses. Therefore, this narrative review mainly focusses on these two types of pain scales and on the studies that have appeared describing these type of pain scales in horses. The extent to which these pain scales have been validated (sensitivity, specificity, inter-observer reliability etc.) and their potential use for clinical pain states is discussed. Possible future directions for new studies and their possible aid in assessing pain in hospitalised and ridden horses are presented. In this way, improved pain scoring could improve criteria used to evaluate the clinical efficacy of new analgesic drugs and techniques, potentially benefiting equine welfare.