Comparative evaluation of effect and efficacy of three different premedication protocols in dwarf rabbits (Oryctolagus cuniculus) undergoing orchiectomy

Rabbits have a higher anaesthesiological risk than other small animals, with a percentage of mortality of about 1.39% compared to dogs (0.17%) and cats (0.24%) [1]. The aim of this study is to identify a suitable and effective premedication protocol for elective surgery, reducing anaesthetic complications and perioperative stress in this species. Fifteen male dwarf rabbits, classified as ASA I, were selected for this prospective, clinical study. All patients were randomized into three groups (5 rabbits per group), which were administered three different premedication protocols: MDM (midazolam = 0.2 mg/kg, dexmedetomidine = 25 mcg/kg and methadone = 0.2 mg/kg), DKM (dexmedetomidine = 25 mcg/kg, ketamina = 20 mg/kg and methadone = 0.2 mg/kg) and MKM (midazolam = 0.2 mg/kg, ketamine = 20mg/kg and methadone = 0.2mg/kg). During the preoperative period, heart rate (HR), respiratory rate (RR) and sedation score (0 = normal; 11 = deep sedation) were monitored 5, 10, 15 and 20 minutes after premedication (T5, T10, T15, T20, respectively). Subsequently, the auricular vein was cannulated and the V- GEL mask was positioned in order to administer oxygen and isoflurane. In this preoperative phase, ataxia, incoordination and reactions to manual stimulation were registered. During the intraoperative period, the main cardiovascular and respiratory parameters were monitored 10 minutes before the start of surgery (BASE), during skin incision (SKIN), traction of the funiculus (TESTIS) and suture (SUTURE). Intraoperative nociception was assumed if HR or MAP increased by > 20% from baseline, in which case a bolus of fentanyl (5 μg/kg) was administered. At the end of the surgery, HR, RR and temperature (T°) were monitored 10, 20, 30, 40, 50 and 60 minutes after extubation (Post10, Post20, Post30, Post40, Post50, Post60, respectively). The quality of recovery (QR) was assessed at each postoperative time using a specific score (1 = excellent; 6 = very bad). Cardinal data were compared between the groups and at each time of the study with the ANOVA and the Tukey-Kramer tests; scores data were analysed with the Dunn test (P<0.05). In the preoperative period, at T5 (MKM = 72±35.09; DKM = 104.8±60.3; MDM = 115.2±43.9 breath/min), T10 (MKM = 39.2±16.8; DKM = 69.6±52.8; MDM = 96.4±49.6 breath/min), T15 (MKM = 35.2±16.09; DKM = 50±30.1; MDM = 65.6±26.6 breath/min), and T20 (MKM = 35.2±18.4a; DKM = 43.2±21.4; MDM = 64.8±30.2 breath/min), RR was significantly lower in all groups compared to T0 (MKM = 135.2±58.6; DKM = 129.6±14.8; MDM = 151.6±12.3 breath/min). Moreover, in DKM group [9 (8-9)], sedation score (SS) was higher than the other two groups at T10 [MDM=7 (6-8), MKM=6 (6-6)]. However, in DKM group, 4/5 patients showed signs of ataxia and incoordination. During the post-operative phase of the study, the QR, in MDM group [2.5 (1-3)], was already better at Post10 compared to the other two groups [DKM=4 (3-5); MKM=4 (4-4)]. Results of our study showed that the three protocols are valid and safe for routine surgery in rabbits; however, the premedication protocols that include ketamine cause severe ataxia and incoordination, that persist also in the postoperative period [2]. We assume that in short-term surgeries such as orchiectomy (about 20 minutes), ketamine is not the drug of choice as its duration of action is longer than surgical times. In conclusion, considering the sensitivity of the rabbit to the stress and the need to quickly feed and resume large organ functions, protocols including ketamine do not appear to be suitable for rabbit orchiectomy, and, in general, for short-term procedures, compared to protocols that include dugs as benzodiazepines and alpha2-agonists.