Sheep anaesthesia protocol evaluation for traumatology surgeries

In recent years, approximately 20 000 sheep have been used every year in biomedical research across Europe. Especially orthopaedic studies frequently rely on sheep because of the weight and size of the animal, as well as the regeneration time of healing like in humans. Here, surgical interventions are commonly used, and researchers are obliged to minimize any kind of suffering according to the 3R principle (reduce, refine, replace) and animal’s welfare legislation. There is responsibility to ensure appropriate anaesthesia and/or analgesia for all ruminants undergoing painful procedures. The aim of this study is to evaluate how the heart rate and noninvasive arterial pressure of sheep change during traumatological operations. Twenty female Lithuania black-headed sheep at the age of 13–14 months and 30–35 kg of body weight were obtained and handled at the Biological Research Centre of the Lithuanian University of Health Sciences. Permission for the study was obtained from national regulatory bodies. After arrival, the animals were given 2 weeks of habituation to the staff members and regular handfeeding. Prior to surgery, the sheep were not fasted. The sheep underwent general anaesthesia. The sheep were pre-treated with xylazine (0.05 mL/kg, i.m.) and, after 5 min, with fentanyl (1 mL i.m.) before general anaesthesia was induced using propofol CRI (20 mg/kg/h, i.v.). Following orotracheal intubation, anaesthesia was maintained with propofol (20 mg/kg/h), fentanyl (3 mL/h), 21% of oxygen, and 1 L/min of ambient air by inhalation. Oxygen saturation, temperature, heart rate (HR), respiratory rate (RR) and non-invasive blood pressure were monitored continuously. For local anaesthesia, 2% lidocaine (max. 4 mg/kg,) was administered along the incision sites. As soon as the animals breathed spontaneously, they were ex-tubated and the rumen tube was removed. Regarding pain management, ketoprofen (2 mg/kg, i.v.) was administered following 3 days post-surgery. In this study, it was observed that only after premedication the heart rate was lower than after starting the procedure after 15 min, 95.8 ± 27.63 and 104.4 ± 31.1 beats per minute, respectively. This can be influenced by the intubation of the animal, because approximately after 10–15 min from laying the animal on the table, the animal was intubated. The heart rate remained within normal range for young sheep throughout the operation. The average duration of surgery was 52 ± 22.5 min. Vital parameters were monitored every 15 min during surgery. During data processing, the dynamics of mean non-invasive arterial pressure were observed, MAP was highest at the beginning, 127 mmHg ± 27.3 mmHg, and slowly decreased during the entire surgery. This is possibly the influence of anaesthetics, as all drugs used for anaesthesia dilate blood vessels and thus reduce arterial pressure. Blood pressure remained higher than normal range during the entire procedure. The study found that the blood pressure of the sheep remained high even though signs of pain such as the pinch test, reflexes and pupillary movement were negative, ensuring adequate analgesia. An anaesthesia protocol, ensuring analgesia and adequate anaesthesia were used, but closer monitoring is needed in future studies.