Open access publications in the SLU publication database

Abstract

Pigs are commonly used in biomedical research, often subjected to complicated and invasive surgical procedures. The knowledge of appropriate analgesia and anaesthesia in pigs however is limited. Therefore, the general aim of the present thesis was to establish and evaluate opioid analgesia suitable for abdominal surgery in growing pigs. Isoflurane minimal alveolar concentration (MAC) was determined in growing pigs using claw pinching. Thereafter, each pig was randomly studied thrice to determine the MAC values in the following treatments: induction of anaesthesia with medetomidine and tiletamine/zolazepam given intramuscularly (MTZ); MTZ followed by epidural morphine (MTZ/M); and MTZ followed by intramuscular buprenorphine (MTZ/B). Pigs were subjected to abdominal surgery during isoflurane anaesthesia and physiological and behavioural effects of MTZ/M and MTZ/B compared to MTZ were evaluated. Transdermal fentanyl was applied and the effects were evaluated for 60 h in conscious pigs and in pigs treated with MTZ/M. Opioid serum concentrations were monitored up to 72 h after drug administration. Behaviour was analysed utilizing videotape recordings of pigs’ activity level before and after surgery. Induction of anaesthesia with MTZ reduced the isoflurane MAC in pigs by 68%. Additional epidural morphine and systemic buprenorphine decreased MTZ isoflurane MAC by 33% and 50%, respectively. Pigs treated with epidural morphine or systemic buprenorphine prior to abdominal surgery attained surgical anaesthetic depth with reduced isoflurane requirement. Induction of anaesthesia with MTZ improved arterial blood pressure and oxygenation compared to isoflurane induction. Epidural morphine did not influence the cardiorespiratory functions during anaesthesia but systemic buprenorphine affected the respiratory response in spontaneously breathing pigs. The postoperative activity level after epidural morphine was lower but the pigs gained weight and the feed intake was similar compared to before surgery. Combining epidural morphine and transdermal fentanyl resulted in initial return to regular activity levels and weight gain after surgery. Twelve hours after surgery these pigs showed decreased activity but still gained weight. Transdermal fentanyl alone in conscious pigs did not cause inactivity or sedation but resulted in inter-individual variations in fentanyl serum concentrations. Systemic buprenorphine caused unpredictable activity levels with postoperative decrease in weight and feed consumption. The analgesic properties of MTZ contributed to a substantial reduction in concentration of isoflurane required for maintenance of inhalation anaesthesia. Additional preoperative opioid analgesia further reduced the requirements of isoflurane needed to maintain an adequate anaesthetic depth. The opioids evaluated resulted in different behaviour postoperatively. Pigs treated with epidural morphine with or without transdermal fentanyl had good appetite and gained weight after abdominal surgery indicating improved postoperative recovery.