A Comparative Study of Intravenous Regional Anesthesia, and Brachial Plexus Block Using Hyperbaric Bupivacaine in Dogs
Department of Veterinary Medicine - Surgery and Anaesthesiology, Faculty of Veterinary Medicine, Federal University of Mato Grosso do Sul State, Brazil
The purpose of this study was to compare the use of hyperbaric bupivacaine in two types of blockades for distal forelimbs in dogs: brachial plexus block (BP) and intravenous regional anesthesia (IRA).
A prospective randomized study was conducted in 14 healthy dogs to compare the anesthetic and motor blocking, and hemodynamic and respiratory effects of the 2 anesthetic regional blockades. Animals were divided into two treatment groups of 7 animals each. Treatment 1.
BP - a 0.25% hyperbaric bupivacaine solution (3 mg/kg) was injected close proximity to the brachial artery and radial, median, ulnar, musculocutaneous, and axillary nerves. Brachial plexus was localized by using a nerve localizer (Xomed Vari-Stim®).
IRA - 0.5% hyperbaric bupivacaine solution (0.5 mg/kg) was injected into the radial vein after a tourniquet has been placed above the umero-radial joint (it remained for the first 20 minutes). All animals of both groups were sedated with 1% acepromazine. Anesthetic and motor-blocking, cardiovascular and respiratory effects were evaluated at predefined regular intervals of time before the sedation and infiltration of the blockades (baseline) and after administration. Cutaneous areas for the nerves of the distal forelimb were tested for nociceptive sensation by pinching the skin with hemostats.
Four of the 7 dogs in the IRA treatment presented painful reaction to the bupivacaine injection. Complete anesthesia was present before (mean +/- SD = 15 +/- 4 vs 25 +/- 6 minutes) and lasted longer (456 +/- 96 vs 175 +/- 80 minutes) for the BP versus IRA, respectively. None of the animals of IRA treatment presented complete blockade in the studied areas. In the BP group, all animals presented ptosis in the distal forelimb blockade. Motor blockade lasted longer and was more evident in the BP treatment. There was no significance difference (p<0.05) in the heart rate in both groups. There was no significant difference in the blood pressure measurements in the IRA treatment. In the BP treatment a significant decrease (p<0.05) of systolic blood pressure that lasted for 30 to 360 minutes was observed. There was a significant decrease of respiratory rate in the in the BP treatment (5 to 450 minutes) and in IRA treatment (30 to 170 minutes).
The brachial plexus block with 0.25% hyperbaric bupivacaine solution produces in the distal forelimb a safer and more efficient anesthesia, which duration lasts longer than an intravenous regional anesthesia with 0.5% hyperbaric bupivacaine in dogs. The brachial plexus block induces ptosis and respiratory depression and has little influence upon the cardiovascular system.