Local anaesthesia for thoracic surgery in pigs: description of the techniques

Local anaesthesia for thoracic surgery in pigs: description of the techniques Carlotta Lambertini(1), Domenico Ventrella(1), Maria Laura Bacci(1), Alberto Elmi(2), Francesca Spaccini(1), Noemi Romagnoli(1) 1Dept. of Veterinary Medical Sciences, University of Bologna, Bologna-Italy 2Dept. of Veterinary Sciences, University of Pisa, Pisa - Italy Pigs are common translational models for testing biomedical devices requiring surgical procedures. The present study describes three different local-anesthetic (LA) techniques applied in experimental pigs undergoing thoracic surgery. Intercostal (IC) blocks and lumbar spinal (SA) or epidural anaesthesia (EA) were compared with the aim of investigating their feasibility, advantages and disadvantages. Twenty commercial hybrid pigs undergoing sternotomy as part of a study testing an extracorporeal circulation (ECC) device were considered. The animals were sedated with dexmedetomidine and tiletamine/zolazepam intramuscularly and, once the endotracheal intubation was achieved, general anaesthesia was maintained with either isoflurane and propofol infusion in combination with fentanyl infusion. After stabilization, the following LA techniques were applied: none, bilateral IC blocks and lumbar (L4-L5) SA or EA. With the pigs in lateral recumbency, the IC were performed blindly identifying the proximal third of each rib through digital palpation; lidocaine was then injected with a hypodermic needle at the caudal border of each rib. Neuraxial anaesthesias were performed with the pigs in lateral recumbency with the hind limb extended forward in order to widen the L3-L4 intervertebral space identified by digital palpation as previously described [1]. A spinal needle was used for spinal or epidural administration of tramadol or morphine. Intraoperative analgesia was considered inadequate if heart rate (HR) and mean arterial pressure (MAP) increased by 20% above the pre-operative values [2]. The IC blocks were the easiest to perform, however, drawbacks consist in the larger volume of drug administered and in the longer time interval necessary to complete the procedure if compared with the other two techniques. The correct needle placement for the blinded IC blocks relied only on the anatomical landmarks. Both the SA and the EA require more training, but they were faster once the skill was acquired. In these cases, the correct needle placement was confirmed by the appearance of the liquor or with the hanging drop technique respectively for the SA and the EA. The evaluation of the intraoperative analgesia was limited to the surgical procedure before commencing the ECC. The three LA techniques resulted in superior cardiovascular stability if compared with absence of LA techniques. No complications associated with these techniques were recorded. In conclusion, the three LA techniques were feasible and provided comparable intraoperative analgesia in pigs undergoing sternotomy, being a refinement for pigs undergoing thoracic surgeries. However, the identification of the anatomical landmarks cannot be overlooked, therefore their feasibility could be limited by the body condition of the animals. During ECC the effects of cardiovascular variables might limits their reliability for evaluation of nociception, therefore adjunctive monitoring devices, should be used to further compare the analgesic effects of these techniques during ECC [3]. References [1] Lambertini al. Transdermal spinal catheter placement in piglets: Description and validation of the technique, J Neurosci Methods, 255:17-21, 2015 [2] Haga et al. Electroencephalographic and cardiovascular indicators of nociception during isoflurane anaesthesia in pigs, Vet Anaesth Analg, 28:126-131, 2001 [3] Petrucci et al. The nociceptive withdrawal reflex during spinal analgesia in pigs undergoing veno-arterial extracorporeal membrane oxygenation: a prospective observational study, Front Vet Sci, 11:1449297, 2024