• Cesar D Freire, Marcelo L A Torres, Denise T Fantoni, Ruben L Cavalcanti, and Jessica Noel-Morgan.
• Discipline of Anesthesiology, School of Medicine, Universidade de São Paulo, São Paulo, Brazil.
• Vet Anaesth Analg. 2010 Jan 1; 37 (1): 63-9.

ObjectiveTo evaluate the extent sensory and motor blocks produced by the epidural injection of different volumes of 0.25% bupivacaine (Bu) with methylene blue (MB), in dogs.Study DesignProspective experimental trial.AnimalsTwenty healthy adult mongrel dogs, weighing 9.9 +/- 1.9 kg.MethodsDogs were randomly allocated into one of four groups that received 0.2, 0.4, 0.6 or 0.8 mL kg(-1) of an epidural solution containing 0.25% Bu and MB. Sensory block was evaluated against time by pinching the tail, hind limb interdigital web, toenail bases and the skin over the vertebral dermatomes. Motor block was assessed by ataxia, hind limb weight-bearing ability and by loss of muscle tone of the tail and pelvic limbs. Data were collected at 2, 5, 10, 15 and 30 minutes after the end of epidural injection. After the final time point, dogs were euthanatized and laminectomies were conducted to expose the extent of the dural dye staining.ResultsThe volumes 0.2, 0.4, 0.6 and 0.8 mL kg(-1) of 0.25% Bu and MB blocked a mean of 5, 14.2, 20.2 and 21 dermatomes, respectively. The extent of the sensory block increased up to a volume of 0.6 mL kg(-1). Motor block was longer-lasting and more intense than sensory block. Complete dyeing of the spinal cord with MB was achieved in some dogs at 0.4 mL kg(-1) and all dogs at 0.6 mL kg(-1).ConclusionsThe volume of anesthetic injected into the epidural space plays an important role in the quality of the epidural anesthesia. At 0.25%, bupivacaine provided an efficient sensory block at 0.6 mL kg(-1).Clinical RelevanceRelatively high volumes (0.6 mL kg(-1)) of 0.25%, BU and MB were needed to produce an effective sensory and motor block caudal to the umbilicus, but all spinal cord segments were reached by MB at this dose.

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