Motor effects of fentanyl in isoflurane-anaesthetized pigs and the subsequent effect of ketanserin or naloxone.

OBJECTIVE: To examine the effect of ketanserin and naloxone on fentanyl-induced motor activity in isoflurane-anaesthetized pigs. STUDY DESIGN: Randomized, blinded, prospective two-group study. ANIMALS: A group of 12 crossbred pigs weighing 22-31 kg. METHODS: Fentanyl was administered to isoflurane-anaesthetized pigs at 7.5 µg kg-1 hour-1 for 40 minutes intravenously, followed by an intravenous injection of naloxone 0.1 mg kg-1 or ketanserin 1 mg kg-1. Electromyography (EMG) and accelerometry were used to record motor unit activity and tremors, respectively. To test the effect of drug administration on motor activity, data from a 5 minute period at baseline, immediately before and after antagonist injection were compared in a mixed model; p < 0.05. RESULTS: Results are reported with the median difference, 95% confidence intervals and corresponding p-values in brackets. Fentanyl significantly increased EMG activity [30.51 (1.84-81.02) µV, p = 0.004] and induced tremors [0.09 (0.02-0.18) m s-2, p < 0.001] in 10 of 12 pigs. Ketanserin significantly reduced EMG [32.22 (6.29-136.80) µV, p = 0.001] and tremor [0.10 (0.03-0.15) m s-2, p = 0.007] activity. No significant effect was found for naloxone on EMG [26.76 (-13.28-91.17) µV, p = 0.4] or tremors [0.08 (-0.01-0.19) m s-2, p = 0.08]. CONCLUSIONS AND CLINICAL RELEVANCE: Fentanyl can induce motor activity in anaesthetized pigs, with a suggested link to the serotonergic system. This study shows that ketanserin can antagonize this activity, which supports the role of serotonin. This knowledge contributes to the general understanding of the motor effects of fentanyl and especially the problem of tremors in anaesthetized pigs.

From wires to waves, a novel sensor system for in vivo pressure monitoring.

Pressure monitoring in various organs of the body is essential for appropriate diagnostic and therapeutic purposes. In almost all situations, monitoring is performed in a hospital setting. Technological advances not only promise to improve clinical pressure monitoring systems, but also engage toward the development of fully implantable systems in ambulatory patients. Such systems would not only provide longitudinal time monitoring to healthcare personnel, but also to the patient who could adjust their way-of-life in response to the measurements. In the past years, we have developed a new type of piezoresistive pressure sensor system. Different bench tests have demonstrated that it delivers precise and reliable pressure measurements in real-time. The potential of this system was confirmed by a continuous recording in a patient that lasted for almost a day. In the present study, we further characterized the functionality of this sensor system by conducting in vivo implantation experiments in nine female farm pigs. To get a step closer to a fully implantable system, we also adapted two different wireless communication solutions to the sensor system. The communication protocols are based on MICS (Medical Implant Communication System) and BLE (Bluetooth Low Energy) communication. As a proof-of-concept, implantation experiments in nine female pigs demonstrated the functionality of both systems, with a notable technical superiority of the BLE.

Cardiovascular effects of intravenous morphine in anesthetized horse.

Objectives: To investigate whether morphine causes a change in mean arterial blood pressure (MAP) heart rate (HR) and oxygen extraction (OE) rate in healthy horses anesthetized with isoflurane and a dexmedetomidine infusion. Material and methods: The study design was prospective clinical, randomized, blinded two groups including 33 horses. All horses were sedated with romifidine IV, and anesthesia was induced with midazolam IV and ketamine IV and maintained with isoflurane in oxygen and medical air and a dexmedetomidine infusion. As a baseline venous and arterial blood, HR and MAP were sampled. Thereafter either morphine 0.1 mg kg-1 IV or an equivalent volume of NaCl 0.9% IV was administered. HR and MAP were then further sampled for 5 min before venous and arterial blood was again sampled. OE was calculated based upon arterial and venous blood gas analysis. To evaluate the change in minimum MAP, mean HR, and OE, the differences between baseline and observation period values were further termed delta MAP, delta HR, and delta OE. Individual delta MAPs were normalized to the minimum baseline value and are reported as a percentage. Alpha was set to 0.05. Confidence intervals 95% (CI) were calculated for delta MAP, delta HR, and delta OE within groups, and for the difference between groups. Results: The 95% CIs for delta MAP (%), delta HR (min-1), and delta OE (mL/dL) in the morphine group were -20.5 to -9.0, 0.6 to 3.1, and -0.1 to 0.6 and in the placebo group were -17.4 to -10.1, 0.2 to 2.0, and -0.2 to 0.3, respectively. The 95% CI for the differences in delta MAP (%), delta HR (min-1), and delta OE (mL/dL) were -5.5 to 7.6, -2.3 to 0.7, and -0.7 to 0.2, respectively. The minimum MAP of one horse in the morphine group decreased around 50% between baseline and observation period with almost unchanged OE and HR. Conclusion and clinical relevance: The effects of morphine 0.1 mg kg-1 IV on HR, MAP, and OE in healthy horses anesthetized with isoflurane and a CRI of dexmedetomidine are minimal.

Lidocaine spray 10% prior to intravenous catheterisation in dogs.

A common and to some degree painful procedure in veterinary practice is to insert an intra-venous catheter. In both human and veterinary medicine, a topical mixture of lidocaine and prilocaine (EMLA cream) has shown to reduce the pain, however a period of 60 min between application and initiation of the procedure is recommended. This time lapse is not always suitable for clinical practise and a shorter time before anaesthetic effect is therefore desirable. Lidocaine has a shorter time lapse (1-3 min) when used on mucus membrane; however, the effect of lidocaine for desensitization of skin has shown variable results in humans. The aim of the study was to evaluate the effect of topical lidocaine spray 10% on the response to placement of venous catheters in dogs. Topical lidocaine spray 10% or NaCl 0.9% was administered prior to placing an intravenous catheter in the cephalic vein. A cross-over of treatment with 2 h wash out period was used before placing a catheter in the opposite cephalic vein. The procedure was video recorded and the dogs' responses were later scored by three persons blinded to treatment using a visual analogue scale. The VAS scores were normalised and the mean difference between treatments were compared using Wilcox signed-rank test. This study could not find a statistical difference between the treatments (P = 0.1763) and could conclude that no significant difference in response to intravenous catheterisation was found between application of NaCl 0.9% or lidocaine 10% prior to the procedure.

Macrocirculatory Parameters and Oxygen Debt Indices in Pigs During Propofol Or Alfaxalone Anesthesia When Subjected to Experimental Stepwise Hemorrhage.

Background: Pigs are anesthetized when used for emergency procedures live tissue training (LTT) of civilian and military medical personnel or for experimental purposes, but there is a paucity in the literature regarding anesthesia of pigs for this purpose. Objective(s): The main goals of the study were to compare oxygen debt, macrocirculatory parameters, and time to cardiac arrest between pigs in hemorrhagic shock and anesthetized with propofol-ketamine-dexmedetomidine or alfaxalone-ketamine-dexmedetomidine. Design: A prospective, non-blinded randomized study design was used. Sixteen pigs were randomized in blocks of four to be anesthetized with either propofol-ketamine-dexmedetomidine (n = 8) or alfaxalone-ketamine-dexmedetomidine (n = 8) as a continuous infusion. Interventions: Premedication with ketamine 15 mg kg-1 and midazolam 1 mg kg-1 was given i.m. Anesthesia was maintained with propofol 8 mg kg-1 h-1 or alfaxalone 5 mg kg-1 h-1 combined with ketamine 5 mg kg-1 h-1 and dexmedetomidine 4 µg kg-1 h-1 i.v. A stepwise, volume-controlled model for hemorrhage was created by exsanguination. Main Outcome Measures: Indices of oxygen debt (lactate, base excess, and oxygen extraction), macrocirculatory (PR, SAP, DAP, MAP, and CI, SVI, and TPR) variables, and time to death was compared between groups. Results: Pigs in the alfaxalone group had significantly higher SAP than pigs given propofol. No difference in other macrocirculatory variables or indices of oxygen debt could be found. A blood loss of 50% of the total blood volume or more was possible in most pigs with both anesthetic regimes. Conclusions: Pigs anesthetized with propofol or alfaxalone combined with ketamine and dexmedetomidine tolerated substantial blood loss.

Inhibition and facilitation of nociceptively evoked muscular activity by fentanyl or dexmedetomidine in isoflurane-anaesthetized pigs.

OBJECTIVE: To investigate motor and cardiovascular responses to dexmedetomidine or fentanyl in isoflurane-anaesthetized pigs. STUDY DESIGN: Experimental, balanced, block randomized, two-group design. ANIMALS: A group of 16 crossbred pigs, 55 ± 8 days (mean ± standard deviation) old. METHODS: Deltoid electromyography (EMG) was recorded during isoflurane anaesthesia. Electrical stimulation using 5, 10, 20 and 40 mA of the distal right thoracic limb elicited a nociceptive withdrawal reflex (NWR), quantified by the area under the curve (AUC) for the simulation intensity versus EMG amplitude response curve. Latency to movement evoked by clamping a claw for maximum 60 seconds was noted. Arterial blood pressure and pulse rate were recorded. Data were sampled at baseline and during dexmedetomidine 0.25, 0.5, 1.0, 2.0, 4.0 and 8.0 µg kg-1 hour-1 or fentanyl 5, 10, 20, 40, 80 and 160 µg kg-1 hour-1 infusions. The influence of infusion rate on NWR AUC and spontaneous EMG was analysed using a mixed model, with p < 5%. RESULTS: NWR AUC increased at fentanyl 5 µg kg-1 hour-1 but decreased at fentanyl 40, 80 and 160 µg kg-1 hour-1 and dexmedetomidine 4.0 and 8.0 µg kg-1 hour-1. All pigs at fentanyl 80 µg kg-1 hour-1, and three pigs at dexmedetomidine 8.0 µg kg-1 hour-1 had mechanical latencies greater than 60 seconds. Spontaneous EMG activity increased accompanied by visually evident 'shivering' at fentanyl 5, 10 and 20 µg kg-1 hour-1 but decreased at dexmedetomidine 2, 4 and 8 µg kg-1 hour-1. Clinically relevant effects of increasing infusion rates on blood pressure or pulse rate were not observed. CONCLUSION AND CLINICAL RELEVANCE: If anaesthetic plane or antinociception is evaluated in pigs, response to claw clamping and NWR will not necessarily give uniform results when comparing drugs. If only one method is used, results should be interpreted cautiously.

A comparison of respiratory function in pigs anaesthetised by propofol or alfaxalone in combination with dexmedetomidine and ketamine.

BACKGROUND: General anaesthesia in pigs maintained with intravenous drugs such as propofol may cause respiratory depression. Alfaxalone gives less respiratory depression than propofol in some species. The aim of the investigation was to compare respiratory effects of propofol-ketamine-dexmedetomidine and alfaxalone-ketamine-dexmedetomidine in pigs. Sixteen pigs premedicated with ketamine 15 mg/kg and midazolam 1 mg/kg intramuscularly were anaesthetised with propofol or alfaxalone to allow endotracheal intubation, followed by propofol 8 mg/kg/h or alfaxalone 5 mg/kg/h in combination with ketamine 5 mg/kg/h and dexmedetomidine 4 µg/kg/h given as a continuous infusion for 60 min. The pigs breathed spontaneously with an FIO2 of 0.21. Oxygen saturation (SpO2), end-tidal CO2 concentration (PE'CO2), respiratory rate (fR) and inspired tidal volume (VT) were measured, and statistically compared between treatments. If the SpO2 dropped below 80% or if PE'CO2 increased above 10.0 kPa, the pigs were recorded as failing to complete the study, and time to failure was statistically compared between treatments. RESULTS: Alfaxalone treated pigs had significantly higher respiratory rates and lower PE'CO2 than propofol treated pigs, with a fR being 7.3 /min higher (P = 0.01) and PE'CO2 0.8 kPa lower (P = 0.05). SpO2 decreased by 0.6% and fR by 1.0 /min per kg increase in body weight in both treatment groups. Three of eight propofol treated and two of eight alfaxalone treated pigs failed to complete the study, and times to failure were not significantly different between treatments (P = 0.75). CONCLUSIONS: No major differences in respiratory variables were found when comparing treatments. Respiratory supportive measures must be available when using both protocols.

Development of a Multimodal Apparatus to Generate Biomechanically Reproducible Spinal Cord Injuries in Large Animals.

Rodents are widespread animal models in spinal cord injury (SCI) research. They have contributed to obtaining important information. However, some treatments only tested in rodents did not prove efficient in clinical trials. This is probably a result of significant differences in the physiology, anatomy, and complexity between humans and rodents. To bridge this gap in a better way, a few research groups use pig models for SCI. Here we report the development of an apparatus to perform biomechanically reproducible SCI in large animals, including pigs. We present the iterative process of engineering, starting with a weight-drop system to ultimately produce a spring-load impactor. This device allows a graded combination of a contusion and a compression injury. We further engineered a device to entrap the spinal cord and prevent it from escaping at the moment of the impact. In addition, it provides identical resistance around the cord, thereby, optimizing the inter-animal reproducibility. We also present other tools to straighten the vertebral column and to ease the surgery. Sensors mounted on the impactor provide information to assess the inter-animal reproducibility of the impacts. Further evaluation of the injury strength using neurophysiological recordings, MRI scans, and histology shows consistency between impacts. We conclude that this apparatus provides biomechanically reproducible spinal cord injuries in pigs.

Rocuronium infusion: A higher rate is needed in diabetic than nondiabetic dogs.

OBJECTIVE: To determine the infusion rates that maintain the train-of-four (TOF) ratio within 20-70% in dogs and compare the infusion rates between diabetic and nondiabetic dogs. STUDY DESIGN: Prospective clinical study. ANIMALS: In total, 47 dogs scheduled for phacoemulsification were included with a median (80% central range) bodyweight of 10.6 (5.7-35.5) kg and age of 7 (1-11) years. Diabetes mellitus was previously diagnosed in nine dogs. METHODS: After premedication using acepromazine and methadone, anaesthesia was induced by intravenous (IV) propofol and maintained by isoflurane and fentanyl or remifentanil. The TOF ratio was monitored by stimulating the peroneal nerve and the response quantified by accelerometry. Rocuronium 0.5 mg kg-1 was administered IV, and further infused to maintain the TOF ratio between 20% and 70%. The infusion rates of rocuronium were compared by the Mann-Whitney test between diabetic and nondiabetic dogs, and the influence of age, sex, bodyweight, body temperature, end-tidal carbon dioxide, end-tidal isoflurane concentration, mean arterial blood pressure, pulse rate and time from induction and time from rocuronium bolus to stable rocuronium infusion rate were investigated in a stepwise, forward regression model. RESULTS: A stable infusion rate was found in 42 dogs. A higher median (80% central range) infusion rate was found in diabetic [0.43 (0.35-0.50) mg kg-1 hour-1] compared with nondiabetic dogs [0.30 (0.20-0.50) mg kg-1 hour-1] (p = 0.013). None of the other variables investigated were found to significantly influence the infusion rate. CONCLUSIONS AND CLINICAL RELEVANCE: There is a quite large individual variation in the infusion rates of rocuronium needed to maintain a stable neuromuscular block in a varied population of dogs. Of the variables investigated, diabetes mellitus was the only one found to significantly influence the infusion rate of rocuronium.

The effect of lipopolysaccharide (LPS) on inflammatory markers in blood and brain and on behavior in individually-housed pigs.

Most of us have experienced deterioration of mood while ill. In humans, immune activation is associated with lethargy and social withdrawal, irritability and aggression; changes in social motivation could, in theory, lead to less functional interactions. This might also be the case for animals housed in close confinement. Tail biting in pigs is an example of damaging social behavior, and sickness is thought to be a risk factor for tail biting outbreaks. One possible mechanism whereby sickness may influence behavior is through cytokines. To identify possible mediators between immune activation and behavioral change, we injected 16 gilts with lipopolysaccharide (LPS; O111:B4; 1.5 µg kg-1 IV through a permanent catheter). In LPS-treated pigs, a significant increase in cortisol, TNF-α, IL-1 receptor antagonist, IL-6, and IL-8 was observed alongside decreased activity within the first 6 h after the injection. CRP was elevated at 12 and 24 h after injection, and food intake was reduced for the first 24 h after injection. Three days post-injection, LPS pigs had lower levels of noradrenaline in their hypothalamus, hippocampus and frontal cortex compared to saline-injected pigs. Pigs injected with LPS also had higher levels of the pro-inflammatory cytokine IFN-γ in their frontal cortex compared to saline-injected pigs. Thus, a low dose of LPS can induce changes in brain cytokine levels and neurotransmitter levels that persist after inflammatory and stress markers in the periphery have returned to baseline levels.

Dexmedetomidine or fentanyl? Cardiovascular stability and analgesia during propofol-ketamine total intravenous anaesthesia in experimental pigs.

OBJECTIVE: To compare cardiovascular function and response to nociception during total intravenous anaesthesia in pigs with propofol, ketamine and either dexmedetomidine or fentanyl administered as a continuous infusion. STUDY DESIGN: Blinded, randomized, balanced, crossover study ANIMALS: Eight immunocastrated male, mixed breed pigs with a mean ± standard deviation body weight of 26.4 ± 1.9 kg for dexmedetomidine and 27.5 ± 3.8 kg for fentanyl treatment. METHODS: The animals were anaesthetized twice with either propofol-ketamine-dexmedetomidine (DEX) or fentanyl (FENT). DEX was infused at 2, 4 and 8 µg kg-1 hour-1 and FENT at 25, 50 and 100 µg kg-1 hour-1. Each infusion rate was administered for 80 minutes prior to commencing the next. Heart rate (HR), 3-lead electrocardiogram, systolic, mean and diastolic arterial blood pressure (SAP, MAP, DAP) in addition to cardiac output measured by transpulmonary thermodilution was used to monitor cardiovascular function. Mechanical and electrical stimulation (nociceptive withdrawal reflex, NWR) was used to elicit nociceptive responses. Similar anaesthetic depth was determined based on the NWR response. Cardiovascular parameters were compared statistically at this time. Additionally, response to nociceptive stimulation and cardiovascular response over time were compared. RESULTS: DEX-treated pigs had significantly higher HR, SAP, DAP, MAP, systemic vascular resistance, haemoglobin concentration, content of oxygen in arterial and venous blood and oxygen delivery index than FENT-treated pigs at similar anaesthetic depth, whereas stroke volume index was significantly higher in FENT. Motoric response to mechanical nociceptive stimulation was abolished prior to any decrease in NWR response in FENT, whereas the two responses decreased more in unison in DEX. The cardiovascular response to nociception was less pronounced in DEX than in FENT. CONCLUSIONS AND CLINICAL RELEVANCE: Propofol combined with ketamine and either fentanyl or dexmedetomidine provides stable cardiovascular conditions in normovolaemic, healthy pigs. Based on cardiovascular response and depression of NWR, dexmedetomidine apparently provides superior analgesia to fentanyl.

Temporary hindlimb paresis following dystocia due to foetal macrosomia in a Celebes crested macaque (Macaca nigra).

A multiparous Celebes crested macaque presented with dystocia due to foetal macrosomia, causing foetal mortality and hindlimb paresis. After emergency caesarean section, recovery of motor function took 1 month before hindlimbs were weight bearing and 2 months before re-integration with the troop.

CT imaging of the eustachian tube using focal contrast medium administration: a feasibility study.

OBJECTIVES: We aim to develop an imaging technique for visualization of the Eustachian tube (ET) lumen. STUDY DESIGN: A prospective, experimental study in an animal model and in human cadaver specimens. METHODS: Applying iodixanol to the middle ear in two human temporal bone specimens, followed by computed tomography (CT) examinations, we optimized contrast dilution, CT algorithm, and head positioning for visualization of contrast passage through the ET. Myringotomy was performed on eight rabbits. Based on the cadaver study, a 20% iodixanol solution was applied to the middle ear, and subsequent CT scans were performed to observe iodixanol in the epipharynx. For some animals, the procedure was repeated on the contralateral ear. We performed the procedure twice on four subjects. Twenty examinations were included. Iodixanol appearance in the ET and the epipharyngeal orifice was assessed qualitatively on CT scans. The tympanic membrane was inspected after 1 or 2 weeks, and histopathological examination of six contrast-exposed temporal bones was performed. RESULTS: The cadaver study provided information on imaging technique and contrast dosage. In rabbits, iodixanol passed through the ET in 19 of the 20 ears. Qualitatively, optimal visualization was seen after 9 to 12 minutes. Clinical inspection after 1 or 2 weeks revealed normal middle ear status. Histopathological samples showed no sign of inflammatory reaction in the tympanic membrane, middle ear, or ET. CONCLUSION: Iodixanol application to the middle ear is feasible, safe, and demonstrates patency of the ET. LEVEL OF EVIDENCE: N/A.

The cardiovascular status of isoflurane-anaesthetized horses with and without dexmedetomidine constant rate infusion evaluated at equivalent depths of anaesthesia.

OBJECTIVE: To compare cardiac index and oxygen extraction at equivalent depths of anaesthesia between isoflurane-anaesthetized horses and horses anesthetized with isoflurane and dexmedetomidine CRI. STUDY DESIGN: Sequential, blinded, randomized, balanced, crossover study. ANIMALS: Eight horses weighing a mean ± standard deviation of 478 ± 58 kg. METHODS: Horses were premedicated with 0.03 mg kg(-1) acepromazine intramuscularly (IM) and 8 µg kg(-1) dexmedetomidine intravenously (IV). Anaesthesia was induced with 2.5 mg kg(-1) ketamine and 0.1 mg kg(-1) midazolam IV and maintained with isoflurane in oxygen and air. Horses were mechanically ventilated. Fractional concentration of end-tidal isoflurane (Fe'Iso) was stabilized at 1.7% with a CRI of 0.9% NaCl (IsoNaCl), or at 1.1% with 1.75 µg kg(-1)  hour(-1) dexmedetomidine (IsoDex). Mean arterial blood pressure was maintained above 60 mmHg by dobutamine infusion. Following nociceptive electrical stimulation, Fe'Iso was stabilized at a 0.1% lower concentration and nociceptive stimulation was repeated. This procedure was continued until the horse moved. Fe'Iso values prior to the concentration at which movement occurred were considered to indicate equivalent depths of anaesthesia between treatments. Cardiac index and oxygen extraction were compared at equivalent depths of anaesthesia using a paired Student's t-test. RESULTS: Cardiac index differed between IsoNaCl at 61 ± 12 mL kg(-1)  minute(-1) and IsoDex at 48 ± 10 mL kg(-1)  minute(-1) (p = 0.047). In addition, oxygen extraction differed between IsoNaCl at 3.4 ± 0.8 mL kg(-1)  minute(-1) and IsoDex at 4.5 ± 0.5 mL kg(-1)  minute(-1) (p = 0.0042). Two horses receiving IsoNaCl were administered dobutamine at equivalent depths of anaesthesia (7.0 and 28.8 µg kg(-1)  hour(-1) , respectively). CONCLUSIONS AND CLINICAL RELEVANCE: Cardiovascular function in horses receiving isoflurane and 1.75 µg kg(-1)  minute(-1) dexmedetomidine is more compromised than in horses receiving a higher concentration of isoflurane and 0.9% NaCl CRI.

Antinociceptive effect of buprenorphine and evaluation of the nociceptive withdrawal reflex in foals.

OBJECTIVE: To elicit and evaluate the NWR (nociceptive withdrawal reflex) in 2 and 11 day old foals, to investigate if buprenorphine causes antinociception and determine if the NWR response changes with increasing age. The effect of buprenorphine on behaviour was also evaluated. STUDY DESIGN: Prospective, experimental cross-over trial. ANIMALS: Nine Norwegian Fjord research foals. METHODS: Buprenorphine, 10 µg kg(-1) was administered intramuscularly (IM) to the same foal at 2 days and at 11 days of age. The NWR and the effect of buprenorphine were evaluated by electromyograms recorded from the left deltoid muscle following electrical stimulation of the left lateral palmar nerve at the level of the pastern. Mentation, locomotor activity and respiratory rate were recorded before and after buprenorphine administration. RESULTS: We were able to evoke the NWR and temporal summation in foals using this model. Buprenorphine decreased the root mean square amplitude following single electrical stimulation (p < 0.001) in both age groups, and increased the NWR threshold following single electrical stimulation in 2 day old foals (p = 0.0012). Repeated electrical stimulation at 2 Hz was more effective to elicit temporal summation compared to 5 Hz (p < 0.001). No effect of age upon the NWR threshold was found (p = 0.34). Sedation when left undisturbed (11 occasions), increased locomotor activity when handled (9 occasions) and tachypnea (13 occasions) were common side-effects of buprenorphine. CONCLUSION AND CLINICAL RELEVANCE: These findings indicate that buprenorphine has antinociceptive effect in foals. Opioid side effects often recognized in adult horses also occur in foals.

The influence of a continuous rate infusion of dexmedetomidine on the nociceptive withdrawal reflex and temporal summation during isoflurane anaesthesia in dogs.

OBJECTIVE: To examine the influence of a low dose dexmedetomidine infusion on the nociceptive withdrawal reflex and temporal summation in dogs during isoflurane anaesthesia. STUDY DESIGN: Prospective experimental blinded cross-over study. ANIMALS: Eight healthy mixed breed dogs, body weight Mean ± SD 26.5 ± 8.4 kg and age 25 ± 16 months. METHODS: Anaesthesia was induced with propofol and maintained with isoflurane (Fe'ISO 1.3%) delivered in oxygen and air. After stabilization, baseline recordings (time 0) were obtained, then a dexmedetomidine bolus (1 µg kg(-1) IV) followed by a continuous rate infusion (1 µg kg(-1) hour(-1)) or saline placebo were administered. At times 10, 30 and 60 minutes after the initial bolus, electrical stimulations of increasing intensity were applied over the lateral plantar digital nerve, and administered both as single and as repeated stimuli. The resulting reflex responses were recorded using electromyography. Data were analysed using a multivariable linear regression model and a Kruskal Wallis test for single stimulation data, and repeated measures anova and paired t-test for repeated stimulation data. RESULTS: The AUC for the stimulus-response curves after single stimulation were similar for both treatments at time 0. At times 10, 30 and 60 the AUCs for the stimulus-response curves were significantly lower with dexmedetomidine treatment than with placebo. Temporal summation was evident in both treatments at times 0, 10, 30 and 60 starting from a stimulation intensity of 10 mA. The magnitude of temporal summation was smaller in dexmedetomidine than in placebo treated dogs at time 10, 30 and 60, but not at time 0. CONCLUSIONS: During isoflurane anaesthesia, low dose dexmedetomidine suppresses the nociceptive reflex responses after single and repeated electrical stimulation. CLINICAL RELEVANCE: This experimental study confirms previous reports on its peri-operative efficacy under clinical conditions, and further indicates that dexmedetomidine might reduce the risk of post-operative chronic pain development.

Abnormal motor activity during anaesthesia in a dog: a case report.

Seizures or convulsions that occur during anaesthesia in veterinary patients are infrequently reported in the literature. Consequently, the incidence of such events is unknown. Several drugs commonly used in clinical veterinary anaesthesia have been shown to induce epileptiform activity in both human clinical patients and experimental candidates. The present case report describes convulsions in a four-year old male Bernese mountain dog during maintenance of anaesthesia with isoflurane after premedication with acepromazine and methadone followed by co-induction with propofol and ketamine. The dog had no history of previous convulsions. The use of several sedative and anaesthetic drugs makes it difficult to find one single causative pharmaceutical.