STRESS-RELATED BIOMARKERS, DYSPHORIA AND PAIN IN DOGS UNDERGOING GENERAL ANAESTHESIA AND SURGERY

Introduction General anaesthesia and surgery have been reported to cause stress in animals. Perioperative stress is associated with increased morbidity. Serum cortisol has been widely used as a stress marker. Dysphoria and pain can cause stress in animals. The present study evaluates stress response, dysphoria and pain associated with different premedication protocols (study 1), in dogs undergoing stifle surgery receiving different analgesic protocols (study 2), or in association with fentanyl administration in dogs under general anaesthesia (study 3). Methods All the studies of this project were performed after Ethical Committee approval. Study 1: Seventeen healthy dogs belonging to a guide dog for blind school were randomly divided into two groups on the basis of the premedication (acepromazine 10 µg/kg and methadone 0.1 mg/kg) administration route (intramuscular or intravenous) as part of a standard anaesthetic protocol for non invasive diagnostic procedures. Blood samples were collected on arrival in the hospital (TAR), induction of general anaesthesia (TINT), extubation (TEXT), and one hour after extubation (TPST). Serum cortisol was analysed in all samples. Dysphoria was evaluated postoperatively by a blind researcher. Study 2: Forty-five client-owned healthy dogs were divided into three groups which were randomly assigned to receive fentanyl VRI (dose adjusted to avoid nociceptive response), spinal anaesthesia (0,05 ml/kg 0,5% isobaric bupivacaine), or femoral and sciatic nerve block (0,3 ml/kg 0,5% bupivacaine) as part of a standard anaesthetic protocol during stifle surgery. Fifteen healthy dogs undergoing non invasive orthopaedic diagnostic procedures under general anaesthesia were included as control group. Blood samples were collected on arrival in the hospital (TAR), induction of general anaesthesia (TINT), extubation (TEXT), and one hour after extubation (TPST). Serum cortisol was analysed in all samples. Dysphoria and pain scores were evaluated postoperatively by a blind researcher. Study 3: Six healthy purpose dogs were enrolled in this double blinded cross over study and anaesthetised twice with a wash-out period of 15 days with a standard anaesthetic protocol, and fentanyl (5 µg/kg + 7.5 µg/kg/hr) or NaCl infusion. Blood samples were collected on arrival in the hospital (TAR), induction of general anaesthesia (TINT), extubation (TEXT), and one hour after extubation (TPST). Serum cortisol was analysed in all samples. Dysphoria was evaluated postoperatively by a blind researcher. Results Study 1: No differences were evinced among the two groups for age, weight, preoperative behaviour score, postoperative recovery score, glucose or cortisol levels at any time point. Study 2: In control, spinal and peripheral nerve block groups, serum cortisol and blood glucose were within normal levels at all time point and did not change after surgery. In the fentanyl group, cortisol and blood glucose levels were significantly higher after surgery (TEXT and TPST) compared to the other 3 groups and to the values registered before surgery (TAR and TINT). Dysphoria and postoperative pain scores were significantly higher in fentanyl group compared to the other groups. Fentanyl group required higher doses of opioids postoperatively. Study 3: No differences were evinced among the two groups for age, weight, preoperative behaviour score, postoperative recovery score, glucose or cortisol levels at any time point. Conclusions Premedication administration route does not modify the stress response in dogs. Spinal anaesthesia and peripheral nerve blocks improve the postoperative pain scores, reduce the occurrence of dysphoria and prevent the increase of cortisol levels compared to fentanyl administration in dogs undergoing orthopaedic surgery. These regional anaesthesia techniques can therefore reduce the stress response improving the postoperative outcome. When fentanyl is administered in absence of surgical stimulation it does not produce an increased stress response or higher incidence of dysphoria compared to the administration of NaCl.