Objective: The objective of this study was to assess whether the volume or concentration of local anesthetic influences its spread and quality of lumbosacral epidural blockade when the total drug dose is fixed.Methods: A total of 30 healthy bitches, undergoing elective ovariohysterectomy received a lumbosacral epidural block with a fixed dose of 0.5 mg/kg b.w. bupivacaine after general anesthesia induction with propofol. Treatment 1 group (low volume, high concentration [LVHC], n=15) received 0.2 mL/kg b.w. of 0.25% bupivacaine, whereas treatment 2 group (high volume, low concentration [HVLC], n=15) received 0.3 ml/kg b.w. of 0.167% bupivacaine. Both solutions contained radio-opaque dye. Heart rate, blood pressure, respiratory rate, rectal temperature, cranial spread, first analgesic rescue, and motor blockade were determined at predetermined intervals.Results: At 5 min, the dorsal cranial spread levels of bupivacaine confirmed by radiographic examination were T8 (T1–T10) for HVLC treatment and T8 (T6–T10) for LVHC treatment (p=0.957). However, there was a significant difference (p=0.029) in the ventral spread levels between HVLC treatment (T2; C7-T6) and LVHC treatment (T6; T5–T11). The first analgesic rescue was needed after 249±58 min in the LVHC treatment group and after 179±32 min in the HVLC treatment group (p=0.0005).Conclusion: It was concluded, if the total dose is fixed, then administration of an HVLC bupivacaine local anesthetic solution in the lumbosacral epidural space seems to produce effective post-operative analgesia for ovariohysterectomy surgery in bitches
