Pain Management Case of the Month: Remy

Multimodal Perioperative Pain Control in a Cocker Spaniel

by Rodrigo Rosa, MV

Signalment and History A 9-year-old neutered male American cocker spaniel, “Remy,” presented with a 2-month history of left pelvic limb lameness. He was treated symptomatically by another veterinarian with carprofen (2 mg/ kg, PO BID), which provided partial improvement of his clinical signs.

Physical Examination and Diagnostics

Upon presentation, the patient was alert and nonoverweight (10.9 kg with a body condition score of 5/9).

General physical exam findings were unremarkable. Leash-controlled gait evaluation revealed a grade 3/5 left pelvic limb lameness with slight internal rotation of the left pes. The patient received maropitant citrate (1 mg/kg SQ) and was sedated with dexmedetomidine (10 􀀫g/kg IM) and butorphanol (0.4 mg/kg IM). Evaluation of the left stifle revealed a positive tibial compression test and palpable synovial effusion. The right stifle was considered normal. Radiographic findings included a steep tibial plateau angle (32.7􀀤), cranial displacement of the infrapatellar fat pad, and mild muscle atrophy. Taken together, these findings led to a presumptive diagnosis of left cranial cruciate ligament rupture (CCLR). Preoperative blood work was performed and the results were unremarkable.

The pathogenesis of canine CCLR was discussed, including the benefits and drawbacks of static versus dynamic surgical techniques. The TPLO technique was chosen because of its versatility, high rate of success, and capacity to neutralize dynamic forces within the stifle. The client declined the option of pursuing a referral to a board-certified surgeon. The implications of both acute and chronic pain caused by CCLR were thoroughly discussed. Gabapentin (15 mg/kg TID) was started for its potential to prevent hyperalgesia. Carprofen (2 mg/kg BID) was continued for anti-inflammatory support.

Treatment and Outcome

On the day of surgery, the dog was premedicated with maropitant citrate (1 mg/kg SQ) and dexmedetomidine (5 􀀫g/kg IM). He had received omeprazole (1 mg/kg PO BID) for 48 hours, gabapentin (15 mg/kg), and trazodone (10 mg/kg) the same day and had fasted for 6 hours before the procedure. An IV catheter was applied and monitoring by ECG and pulse oximetry was initiated.

General anesthesia was induced with midazolam (0.1 mg/kg IV), propofol (2 mg/kg IV), and fentanyl (1 􀀫g/kg IV) after face-mask preoxygenation for 5 minutes. A sterile, lubricated endotracheal tube was applied and general anesthesia was maintained with isoflurane at 0.5 to 1%. Standard monitoring was maintained, including ECG, capnography, pulse oximetry, and Doppler-BP. IV LRS solution was administered at 2.5 mL/kg/hour; this infusion was added to the CRI of anesthetics to reach a total volume of 5 mL/kg/hour. Loading doses of lidocaine (0.5 mg/kg IV) and ketamine (0.25 mg/kg IV) were administered. Fentanyl, lidocaine, and ketamine CRI (FLK-CRI) were administered at 2.4 􀀫g/ kg/hour, 1.5 mg/kg/hour, and 0.6 mg/ kg/hour, respectively.

Cefazolin sodium was administered (22 mg/kg IV) and repeated every 90 minutes. A hot-air blanket system was used to minimize the potential for hypothermia. The TPLO procedure was performed according to a published technique. All incised tissues (except the synovium) were infiltrated with bupivacaine liposome injectable solution (5.3 mg/kg single local infiltration). Carprofen (2.2 mg/kg SQ) was administered and the wound was dressed in a sterile adhesive bandage. Postoperative radiographs were obtained and cold compression therapy was started immediately after surgery. The FLK-CRI rate was reduced by 50% and discontinued 2 hours later. Pain level (Colorado State Acute Pain Score, CAPS) and vital parameters were monitored every 30 minutes.

The patient was slightly restless after extubation but CAPS Score remained 0 to 1. The behavior was considered compatible with mild postanesthetic dysphoria. One dose of dexmedetomidine (2 􀀫g/kg IV) was administered. After 20 minutes of unconsciousness, during which vital signs were continuously monitored, the patient awoke peacefully with a CAPS score of 0/4. He was able to stand and ambulate without assistance within 4 hours.

Twenty-four hours after surgery, the patient had a good appetite and continued to walk using the repaired limb. CAPS score remained 0/4. He was discharged with recommendations to continue carprofen and gabapentin. A postoperative rehabilitation plan was prescribed; the individual therapeutic modalities were demonstrated to the client.

Postoperative radiograph. Clinical Outcome The preemptive use of trazodone and gabapentin minimized patient stress, and the microdose of dexmedetomidine allowed easy IV catheterization. Omeprazole and maropitant were used to prevent esophageal irritation and nausea, respectively. Administration of midazolam, fentanyl, and propofol facilitated smooth induction of anesthesia without any associated apnea. The FLK-CRI had a significant MAC-sparing effect on isoflurane, which was maintained at 1% or less during the procedure.

The patient exhibited mild dysphoria upon extubation without signs of pain (CAPS score 0/4); this was most likely due to infiltration with bupivacaine liposome during wound closure. He was able to ambulate with partial use of the repaired limb within 4 hours after surgery. CAPS score remained 0/4 twenty-four hours later. Swelling at the surgical site remained minimal, most likely due to aggressive use of cold-compression therapy. Lameness was mild at 2 weeks (grade 2/5) and had resolved entirely by 8 weeks after the procedure; this may be due to the preemptive use of carprofen and gabapentin, and guided physical rehabilitation techniques during the recovery period.

Conclusion

Chronic postsurgical pain (CPSP) has been reported in 41% of dogs undergoing TPLO. This highlights the need for a multimodal analgesic protocol. The preemptive use of trazodone and gabapentin offered a desirable calming effect in this anxious patient and may have contributed to the prevention of hyperalgesia. Maropitant controlled narcotic-induced nausea and allowed the patient to resume feeding within 4 hours. Dexmedetomidine facilitated the placement of an IV catheter and acted synergistically with fentanyl to enhance analgesia. Midazolam decreased the dose of propofol required to allow endotracheal intubation. The FLK-CRI provided excellent intraoperative analgesia and decreased isoflurane MAC.

Fentanyl was chosen for its robust analgesic properties, rapid onset, and short duration activity. These properties provided the anesthetist with great analgesic flexibility while maintaining the capacity to make necessary adjustments to correct for potential respiratory and/or cardiovascular depression (neither observed in this case). IV lidocaine was chosen for its analgesic- and anesthetic-sparing properties. Ketamine was added to prevent hyperalgesia through its NMDA-receptor blocking effect.

Bupivacaine liposome local infusion and cold-compression therapy provided dependable analgesia for 72 hours after surgery.

One potential deficiency associated with this case is the lack of preoperative locoregional anesthesia. Epidural blocks or femoral and sciatic ultrasound/nerve-locator-guided blocks with bupivacaine are now used for all pelvic limb orthopedic procedures performed by this author. The postsurgical rehabilitation protocol utilized in this case offered the owner a set of clear guidelines for basic at-home physiotherapy. The exercises prescribed were designed as a means to restore muscular strength and function as well as to maintain joint range of motion and proprioception.

The author recognizes that postoperative physiotherapy should ideally be substantially more comprehensive and regularly guided by a veterinary physiotherapist.

Despite this limitation, the patient made an uneventful recovery,

returning to the preinjury activity level 12 weeks after surgery. The client was very pleased with the outcome of the procedure and with the analgesic protocol prescribed.

Rodrigo Rosa, MV, attended veterinary school at the Federal University of Parana (Brazil), followed by a rotating internship at the Ventura Medical and Surgical Group (Ventura, California). His primary interests include orthopedic, oncological, and minimally invasive surgery as well as pain management. He lives in New Hampshire with his wife and daughter.

 

 

Photo credits: Photos courtesy of Rodrigo Rosa