Plasma concentrations at two dexmedetomidine constant rate infusions in isoflurane anaesthetized horses: a clinical study

OBJECTIVE

To determine dexmedetomidine plasma concentrations at two infusion rates in isoflurane anaesthetized horses and compare cardiovascular effects and anaesthetic recovery between treatments.

STUDY DESIGN

Prospective, randomized, masked clinical study.

ANIMALS

Healthy, adult, client-owned, non-food producing horses presented for castration.

METHODS

Premedication consisted of acepromazine, romifidine and morphine, and anaesthesia was induced with ketamine and midazolam. The horses were randomized to receive dexmedetomidine 0.5 μg kg^-1 hour^-1 (treatment DL, n = 7) or 1.75 μg kg^-1 hour^-1 (treatment DH, n = 7) for 90 minutes of isoflurane anaesthesia at an end-tidal concentration of 1.2%. Venous plasma concentrations were determined with liquid chromatography-electrospray-ionization-tandem mass spectrometry. Jugular venous and arterial blood was sampled for blood gas analysis at the start and end of the infusion. Changes in cardiovascular variables from the start to the end of the infusion, and recovery parameters were statistically compared between treatments.

RESULTS

Fourteen male horses, 2-6 years old, 325-536 kg were included. Mean ± standard deviation dexmedetomidine plasma concentrations at 30, 60 and 90 minutes with treatment DL were 0.22 ± 0.05, 0.29 ± 0.07 and 0.33 ± 0.08 ng mL^-1, and with treatment DH were 0.65 ± 0.11, 0.89 ± 0.10 and 1.01 ± 0.10 ng mL^-1. The 95% confidence interval for change minute^-1 in dexmedetomidine plasma concentrations between 75 and 90 minutes was 0-1% for both treatments. With treatment DH, the heart rate decreased significantly more from the beginning to the end of the infusion compared to DL (p = 0.043). No other significant differences were found between treatments in cardiovascular or recovery parameters.

CONCLUSIONS AND CLINICAL RELEVANCE

Infusion of dexmedetomidine in isoflurane anaesthetized horses resulted in plasma concentrations with low variation at both infusion rates, approaching stable levels after 75 minutes of infusion. No differences of clinical importance were found when comparing cardiovascular variables and quality of recovery between treatments.

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.