Anesthesia and Pain Case Challenge
An 8-year-old, 30 kg, mixed-breed dog presents with recent onset of left hind leg lameness. Radiographs and subsequent biopsy revealed the presence of an osteosarcoma of the distal femur. The decision to amputate the limb is made. How would you manage this dog’s acute perioperative pain using a wound soaker catheter? Calculate doses and volumes of local anesthetic needed to maintain pain control and duration of treatment.
Limb amputation causes significant pain that is best managed by a multimodal analgesic strategy in the perioperative period and for several weeks after surgery. An excellent protocol would be to premedicate this dog with acepromazine, 0.025 mg/kg, and hydromorphone 0.1 mg/kg. Anesthesia is induced with ketamine-midazolam (0.5 ml of each drug per 9 kg IV, given to effect) and maintained with isoflurane. A lumbosacral epidural with 0.1 mg/kg sterile preservative-free morphine is placed preoperatively. Prior to closure, a wound soaker catheter with a diffusion area of 4 – 5 inches is placed in the deepest fascial layer of the wound, exiting towards the dorsal lumbar region. After wound closure, a dose of 6 mls of 0.5% bupivacaine ([30 kg X 1.0 mg/kg]/5 mg/ml) is injected through the catheter, which is secured to the skin. Postoperatively, the dog is given a 2.2 mg/kg dose of carprofen SQ and a continuous infusion of lidocaine through the wound soaker is started. His now lower bodyweight is taken into account (27 kg). The volume for this size wound is approximately 3 mls/hour, which at 2 mg/kg/hour is 2.7 mls per hour of 2% (20 mg/ml) lidocaine. Using a syringe pump, lidocaine is delivered to the wound for a total of 36 hours. During this time, intermittent IV buprenorphine (0.01 – 0.02 mg/kg q 6 hours) or hydromorphone (0.05 – 0.1 mg/kg, q 6 hours) are given, if needed according to pain assessment. The dog may be discharged on oral carprofen plus tramadol +/- gabapentin, continuing for as much as 2 weeks.