Clinicophysiological Effects of Spinally Administered Ketamine and Its Combination with Xylazine and Medetomidine in Healthy Goats

Intrathecal adenosine enhances the antinociception of Xylazine in goats

Background

The role of adenosine (AD) in neuromodulation of nociceptive signaling at the level of the spinal cord has been established in both preclinical and clinical models. Recently, the signaling pathway that involves adenosine 5-monophosphate activated protein kinase has been reported to mediate the antinociceptive effects of xylazine (XYL). The objective of this study was to investigate the antinociceptive, cardiorespiratory and hematological effects of intrathecal administration of combined XYL-AD in goats as compared to XYL alone. Six clinically healthy adult goats weighing 25 ± 2 kg were randomly assigned to one of three groups in a cross-over design. Goats were sedated with XYL (0.05 mg/kg, IM) in all groups. Ten min later, 0.9% saline solution [SAL group], XYL (0.05 mg/kg) [XYL group] or a combination of XYL (0.05 mg/kg) and AD (2000 µg) [XYL-AD group] was injected intrathecally. Antinociception scores and both cardiorespiratory and hematological parameters were measured before XYL sedation and intrathecal injection (baseline), and at 5, 10, 15, 30, 60, 90, 120 and 150 min thereafter.

Results

The XYL-AD group showed significantly earlier onset of antinociception [5 (5–7) min] than XYL [13 (12–14.25] min (P = 0.031). The duration of complete antinociception in goats that received XYL-AD was significantly longer (P = 0.031) than that received XYL alone [65 (58.75–66.25) and 47.5 (43.75–51.25) min, respectively]. In both XYL and XYL-AD groups, heart rate (HR), arterial blood pressure (SAP, MAP and DAP) were significantly decreased (P < 0.05) compared to the baseline. Compared to the SAL group, a statistically significant reduction in HR from 10 to 150 min (P < 0.05) was detected in the XYL group contrary to the XYL-AD group. Differences in the hematological parameters among different groups were insignificant.

Conclusions

AD injected intrathecally interacts synergistically with XYL to promote antinociception in goats. This discovery supports the use of AD in combination with XYL in clinical trials.

Telemetry monitoring for non-invasive assessment of changes in core temperature after spinal drug administration in freely moving rats

INTRODUCTION

There are no data available about the effects of spinally administered drugs on thermoregulation in freely moving animals. The first goal of the present study was to throw light on the consequences of intrathecally administered saline as a vehicle on core temperature and motor activity in unrestrained conditions. The second goal was to characterize the effects of morphine on these parameters as a widely used antinociceptive drug in spinal anesthesia, and reveal the potential role of the N-methyl-d-aspartate (NMDA) receptors in these processes.

METHODS

For these purposes, male Wistar rats were catheterized intrathecally, and E-Mitter battery-free transponders were implanted intraabdominally to continuously monitor core temperature and locomotor activity.

RESULTS

Saline induced a short-lasting hyperactivity accompanied by significant and prolonged hyperthermia that was blunted by systemic paracetamol administration. Morphine had no impact on motor activity; however, it caused high but equivalent degree hyperthermia in a wide dose range (1-15 μg), suggesting that it reached its peak effect. In the highest applied dose (25 μg), the NMDA receptor antagonist kynurenic acid blunted the saline-induced hyperthermia, and all doses caused higher hyperactivity compared to vehicle or morphine injections. In combination, kynurenic acid significantly inhibited the morphine-induced hyperthermia.

DISCUSSION

These data suggest that this method might be a valuable tool for investigating the thermoregulatory and locomotor effects of different drugs at spinal level; however, the prolonged effects of intrathecal vehicle injections should also be considered. The results point out that morphine is a very potent hyperthermic drug that may act primarily on the efferent limb of thermoregulation, at least partially, via an indirect NMDA-receptor mediated action mechanism.

Evaluation of the clinical and analgesic effects of subarachnoid ketamine-lidocaine administration in goats undergoing mastectomy

Twenty adult female goats affected with chronic mastitis were subjected to mastectomy or hemimastectomy under subarachnoid regional analgesia using a ketamine-lidocaine combination. Ketamine at 1.5 mg/kg and lidocaine hydrochloride at 1.25 mg/kg were administered intrathecally at the lumbosacral intervertebral space. Goats were then subjected to a 120-minute observation period for systemic or neurotoxic symptoms such as agitation, restlessness, hind limb paralysis, or seizures. In addition, analgesia of the caudal abdominal region and signs of systemic sedation were scored on a scale of 0–3. Heart rate, respiratory rate, and rectal temperature were also recorded prior to (baseline values) and at 5, 15, 30, 60, 90, and 120 minutes after administration. Mastectomy or hemimastectomy operation was carried out after full assurance of the analgesic effect on the udder and caudal abdominal region. Time of onset of surgical analgesia (score 3) was achieved at 15 minutes and lasted for 60 minutes. Maximal sedation score was recorded at 15 minutes and lasted for 60 minutes, then decreased thereafter, with the lowest sedation score recorded at 120 minutes. There was a significant (P<0.05) rise in heart rate at some point between 5–90 minutes, while the respiratory rate and rectal temperature did not change significantly from baseline values. Postoperatively, animals did not show any signs of pain or discomfort. Follow-up on the operated goats showed that all wounds were fully healed without any significant complications. In goats, intrathecal administration of ketamine-lidocaine combination resulted in a safe and effective analgesia of the caudal abdominal and udder region sufficient to perform mastectomy or hemimastectomy.

Caudal epidural analgesia using lidocaine alone or in combination with ketamine in dromedary camels Camelus dromedarius

This study was performed to investigate the analgesic effect of lidocaine and a combination of lidocaine and ketamine following epidural administration in dromedary camels. Ten 12-18-month-old camels were randomly divided into two equal groups. In group L, the animals received 2% lidocaine (0.22 mg/kg) and in group LK the animals received a mixture of 10% ketamine (1 mg/kg) and 2% lidocaine (0.22 mg/kg) administered into the first intercoccygeal (Co1-Co2) epidural space while standing. Onset time and duration of caudal analgesia, sedation level and ataxia were recorded after drug administration. Data were analysed by U Mann-Whitney tests and significance was taken as p &lt; 0.05. The results showed that epidural lidocaine and co-administration of lidocaine and ketamine produced complete analgesia in the tail, anus and perineum. Epidural administration of the lidocaine-ketamine mixture resulted in mild to moderate sedation, whilst the animals that received epidural lidocaine alone were alert and nervous during the study. Ataxia was observed in all test subjects and was slightly more severe in camels that received the lidocaine-ketamine mixture. It was concluded that epidural administration of lidocaine plus ketamine resulted in longer caudal analgesia in standing conscious dromedary camels compared with the effect of administering lidocaine alone.