Isoflurane sparing action of epidurally administered xylazine hydrochloride in anesthetized dogs

Epidural administration of combinations of ropivacaine, morphine and xylazine in bitches undergoing total unilateral mastectomy: a randomized clinical trial

OBJECTIVE

To investigate the epidural administration of combinations of ropivacaine, morphine and xylazine in bitches undergoing unilateral mastectomy.

STUDY DESIGN

Prospective, randomized, blinded, clinical study.

ANIMALS

A total of 22 bitches scheduled to undergo unilateral mastectomy for mammary tumor excision.

METHODS

Dogs were anesthetized with acepromazine (0.02 mg kg^-1) and morphine (0.3 mg kg^-1) intramuscularly, propofol intravenously (IV) and isoflurane. Prior to the beginning of surgery, dogs were randomly administered one of three epidural treatments: ropivacaine (0.75 mg kg^-1) with morphine (0.1 mg kg^-1) (group RM, n = 7); ropivacaine with xylazine (0.1 mg kg^-1) (group RX, n = 8); or ropivacaine with morphine and xylazine (group RMX, n = 7). Cardiopulmonary variables and the expired concentration of isoflurane (Fe'Iso) were recorded intraoperatively. Meloxicam (0.1 mg kg^-1) was administered IV during skin closure. Postoperative pain scores were evaluated with the Glasgow composite measure pain scale short form for 24 hours, and rescue analgesia with morphine (0.5 mg kg^-1) was administered intramuscularly when pain scores were ≥ 6/24.

RESULTS

Fe'Iso was significantly higher in group RM than in groups RX and RMX. Heart rate decreased significantly in groups RX and RMX, but blood pressure remained within acceptable values. The number of dogs administered rescue analgesia within 24 hours was significantly higher in group RX (seven dogs, 87.5%) than in groups RM (one dog, 14.3%; p = 0.01) and RMX (two dogs, 28.6%; p = 0.04). Time to standing was significantly longer in group RX than in group RM.

CONCLUSIONS AND CLINICAL RELEVANCE

All epidural treatments provided adequate antinociception with minimal cardiovascular adverse effects during mastectomy. The inclusion of morphine (groups RM and RMX) provided the best postoperative analgesia. Owing to the undesirable effect of xylazine on ambulation, the combination ropivacaine-morphine appeared to provide greater benefits in bitches undergoing unilateral mastectomy.

Alternatives to Opioid Analgesia in Small Animal Anesthesia: Alpha-2 Agonists

Alpha-2 agonists have potent analgesic effects, in addition to their sedative actions. Alpha-2 agonists provide analgesia through any of several routes of administration, including parenteral, oral, epidural or intrathecal and intraarticular, because of spinal and supraspinal actions. Systemic doses are short acting, whereas local administration at the site of action result in longer analgesic effects. The potent cardiovascular and respiratory effects of alpha-2 agonists should be considered when used as analgesics.

Minimum alveolar concentration: Key concepts and a review of its pharmacological reduction in dogs. Part 1

OBJECTIVE

To outline the major components of the minimum alveolar concentration (MAC) and review the literature in regard to pharmacological manipulation of the MAC of halothane, isoflurane, sevoflurane, enflurane, and desflurane in dogs. The pharmacologic agents included are alpha-2 agonists, benzodiazepines, propofol, maropitant, opioids, lidocaine, acepromazine, non-steroidal anti-inflammatory agents, and NMDA antagonists. Part 1 will focus on summarizing the relevance, measurement, and mechanisms of MAC and review the effects of alpha-2 agonists, benzodiazepines, and propofol on MAC.

DATABASES USED

PubMed, Google Scholar, CAB Abstracts. Search terms used: minimum alveolar concentration, MAC, dog, canine, inhaled anesthetic potency, isoflurane, sevoflurane, desflurane, enflurane, and halothane.

CONCLUSIONS

Many drugs reduce the MAC of inhaled anesthetics in dogs, and allow for a clinically important decrease in inhalant anesthetic use. A decrease in MAC may decrease the adverse cardiovascular and pulmonary effects associated with the use of high concentrations of inhaled anesthetics.

An Update on Drugs Used for Lumbosacral Epidural Anesthesia and Analgesia in Dogs

This review aims to report an update on drugs administered into the epidural space for anesthesia and analgesia in dogs, describing their potential advantages and disadvantages in the clinical setting. Databases searched include Pubmed, Google scholar, and CAB abstracts. Benefits of administering local anesthetics, opioids, and alpha₂ agonists into the epidural space include the use of lower doses of general anesthetics (anesthetic “sparing” effect), perioperative analgesia, and reduced side effects associated with systemic administration of drugs. However, the potential for cardiorespiratory compromise, neurotoxicity, and other adverse effects should be considered when using the epidural route of administration. When these variables are considered, the epidural technique is useful as a complementary method of anesthesia for preventive and postoperative analgesia and/or as part of a balanced anesthesia technique.

Isoflurane MAC determination in dogs using three intensities of constant-current electrical stimulation

OBJECTIVES

To compare isoflurane minimum alveolar concentrations (MACs) in dogs determined using three intensities of constant-current electrical stimulation applied at the tail, and thoracic and pelvic limbs, and to compare isoflurane MACs obtained with all combinations of electrical stimulation and anatomic site with those obtained using the tail clamp as the noxious stimulus.

STUDY DESIGN

Randomized trial.

ANIMALS

Six mixed-breed, adult female dogs aged 1-2 years and weighing 11.1 ± 4.4 kg.

METHODS

In each dog, MAC was determined by the bracketing method with the tail clamp (MACTAILCLAMP ), and three electrical currents (10 mA, 30 mA, 50 mA) at three anatomic sites (thoracic limb, pelvic limb, tail). Each MAC achieved with electrical stimulation was compared with MACTAILCLAMP using a mixed-model anova and Dunnett's procedure for multiple comparisons. The effects of current intensity and anatomic site on isoflurane MAC were tested using a mixed-model anova followed by Tukey's test for multiple comparisons (p < 0.05).

RESULTS

Mean MACTAILCLAMP was 1.69%. MACs achieved with currents of 30 mA and 50 mA did not differ independently of anatomic site. When currents of 10 mA were applied to the tail and thoracic limb, resulting MACs were lower than those obtained using currents of 30 mA and 50 mA. Currents of 30 mA and 50 mA provided MACs that did not differ from those of MACTAILCLAMP , whereas a current of 10 mA achieved the same result only for the pelvic limb.

CONCLUSIONS AND CLINICAL RELEVANCE

Isoflurane MAC is affected by current intensity and anatomic site. Current intensities of 30 mA and 50 mA provided consistent results when applied to the tail, and thoracic and pelvic limbs that did not differ from those obtained using the tail clamp. Consequently, they can be used in place of the tail clamp in MAC studies in dogs.

Anesthesia differentially modulates spontaneous network dynamics by cortical area and layer

Anesthesia is widely used in medicine and research to achieve altered states of consciousness and cognition. Whereas changes to macroscopic cortical activity patterns by anesthesia measured at the spatial resolution of electroencephalography have been widely studied, modulation of mesoscopic and microscopic network dynamics by anesthesia remain poorly understood. To address this gap in knowledge, we recorded spontaneous mesoscopic (local field potential) and microscopic (multiunit activity) network dynamics in primary visual cortex (V1) and prefrontal cortex (PFC) of awake and isoflurane anesthetized ferrets (Mustela putoris furo). This approach allowed for examination of activity as a function of cortical area, cortical layer, and anesthetic depth with much higher spatial and temporal resolution than in previous studies. We hypothesized that a primary sensory area and an association cortical area would exhibit different patterns of network modulation by anesthesia due to their different functional roles. Indeed, we found effects specific to cortical area and cortical layer. V1 exhibited minimal changes in rhythmic structure with anesthesia but differential modulation of input layer IV. In contrast, anesthesia profoundly altered spectral power in PFC, with more uniform modulation across cortical layers. Our results demonstrate that anesthesia modulates spontaneous cortical activity in an area- and layer-specific manner. These finding provide the basis for 1) refining anesthesia monitoring algorithms, 2) reevaluating the large number of systems neuroscience studies performed in anesthetized animals, and 3) increasing our understanding of differential dynamics across cortical layers and areas.