Postsurgical pain management: Take a pre-emptive approach

While this review will focus on postoperative pain management, it is important that we acknowledge the critical perioperative elements that lay the foundation for ideal patient pain management. Pain control needs to be in place before the surgeon's blade contacts skin in order to minimize central and peripheral sensitization. Without adequate pre-emptive analgesia, the nociceptive process ramps up unabated by general anesthesia. Receptor sensitivity increases and structural rewiring can occur.

It behooves us to minimize overall perioperative pain as the intensity of perioperative pain correlates with the risk for chronic postoperative pain.

Preanesthetic medications need to include opioid analgesics as well as sedative/tranquilizers to moderate patient stress and early pain. Non-sterodial anti-inflammatory drugs (NSAIDs) may be considered in the preanesthetic phase for NSAID-tolerant patients if the surgical team appropriately monitors, and effectively manages, patient blood pressures during anesthesia. Recommended presurgical pain management techniques include local/regional anesthetic blocks, analgesic constant-rate infusions and epidural injections. Intraoperative strategies include ongoing constant-rate infusions or intermittent bolus opioids. Immediate postoperative options include ongoing constant-rate infusions, NSAIDs for tolerant patients not given NSAIDs preoperatively, cold therapy and intermittent bolus opioids.

It should be noted that surgical technique appears to have a major impact on chronic postoperative pain risk. Meticulous attention to surgical technique helps minimize patient risk for chronic pain.

Postoperative medication options for use at home offer a broad range of choices. As with perioperative analgesia, multimodal outpatient strategies offer superior patient benefit while minimizing the likelihood of adverse events. The practice should provide the owner with pain-assessment guidelines to engage them in the pain-management process as part of the team. Research suggests that animals are much more hesitant to show signs of pain when away from the familiar surroundings and away from their friends. The patient is more likely to show its true comfort level when it returns home. The owner needs to have guidelines for higher doses or additional medications if signs of pain are evident.

Postoperative oral (PO) analgesic choices include tramadol, amantadine, NSAIDs and gabapentin. Tramadol is a dual-mode analgesic. It is metabolized into two isomers, each with different analgesic benefit; one provides a mu agonist effect while the other provides a monoamine reuptake inhibition analgesic effect. Tramadol is available in relatively inexpensive 50-mg tablets. Tramadol is generally dosed at 3 to 5 mg/kg PO TID to QID. It is a bitter medication, making it less suited to cat use unless the cat can be pilled with the tramadol placed in a gelatin capsule. Tramadol is compatible with most other analgesic medications but should be used cautiously, if at all, for patients on SSRIs, TCAs and MAOIs. Tramadol may reduce seizure threshold. Use with caution in patients with a seizure history.

Amantadine targets the glutamate/NMDA that plays such a critical role in central sensitization. It is available in 100-mg capsules and a 10-mg/ml liquid. Dosing ranges from 3 to 5 mg/kg PO SID. Because amantadine is primarily excreted unchanged through the kidneys, its dose should be reduced for patients in renal failure. Although unlikely, signs of intolerance or excess dosing include general agitation and diarrhea. Like tramadol, amantadine's bitter taste often limits its use in cats.

While NSAIDs usually are well tolerated drugs as a class, they are not without potential for GI upset as well as liver and renal concerns. Healthy patients usually tolerate five to seven days of an NSAID without adverse effects. NSAID can be coordinated with tramadol, amantadine, and gabapentin if needed for more complex pain. Remember that patients may respond and tolerate certain NSAIDs better than others. Only trial and error can predict the best choice for a given patient.

Postoperative NSAID use in cats is a limited option. There are no oral NSAIDs currently approved in the United States for the cat. That being said, many veterinarians are using the meloxicam liquid for ongoing analgesia in cats. After an initial dose of 0.1 mg/kg, the dose is reduced to 0.05 mg/kg every 24 hours for up to four days. For accurate dosing it is recommended that a TB syringe or insulin syringe be used to draw up the exact drug volume. The injectable Metacam® product is currently labeled for a one-time dose of 0.3 mg/kg (0.14 mg/lb) SC. Oral dosing following this injectable is not recommended.

Gabapentin has a broad dose range; 1 to 10 mg/kg PO BID to TID. The least expensive options include the generic 100-mg and 300-mg capsules. It also is available in 400-mg, 600-mg and 800-mg sizes. The 50-mg/ml liquid should not be used due to its xylitol content. Cats generally accept gabapentin compounded in a cat-friendly, flavored base. Gabapentin can be used for three to five days after less painful procedures, longer for major procedures like amputations. Gabapentin is a very useful post-declaw medication for cats, preferably teamed with buprenorphine and, possibly, meloxicam if the patient is NSAID-tolerant. Gabapentin primarily is excreted unchanged through the kidneys. Its dose should be reduced for patients in renal failure.

Butorphanol and buprenorphine are not logical oral (per os) analgesics. Mixing either with an antibiotic or flavored liquid is not recommended. The enterohepatic first-pass effect renders 80 percent to 90 percent of these opioids ineffective. Even when properly dosed, butorphanol provides only mild analgesia of short duration. For example, a 20-kilogram dog would require 20 mg of butorphanol every hour to sustain a mild but very costly analgesic effect. There are much better choices outlined above.

Transmucosal (TM) drug delivery is a very attractive route because it bypasses the enterohepatic first-pass effect and it often is easier to administer a small volume of liquid inside the cheek pouch of a cat, compared to pilling a cat multiple times a day. Buprenorphine is absorbed efficiently through the oral mucosa of the cat. Bioavailability is the same for TM as IV in the cat. Early feedback from a recent study suggests that the TM route may be an efficient delivery route for dogs. The author doses buprenorphine at 0.020 to 0.030 mg/kg TID. At these doses, buprenorphine represents a fairly pricey ongoing analgesic for dogs of moderate to larger size.

Transdermal choices include the fentanyl and lidocaine patches. These are attractive when managing a patient poorly tolerant or very resistant to oral medications. The patches can be used in combination with the above oral medications, including tramadol. In general, it is unwise to depend on fentanyl patch-based analgesia as the only patient analgesic tool because of significant interpatient variability in the plasma level achieved. Lidocaine patches are useful adjacent to the incisional area but not over the incision. They are particularly attractive for postoperative amputation cases. When used, the lidocaine patch must be carefully protected by a bandage or other device to prevent patient ingestion and the associated toxicity risk.

Physical rehabilitation therapy (PRT) plays an important role in postoperative pain management. Pet owners can be coached to do some simple modalities at home to keep their companions comfortable.

Cold compresses can be used 15 minutes at a time every hour on the surgical site. Passive range of motion (PROM) can be used after orthopedic surgery to help maintain flexibility and decrease contractures. PROM is generally performed three to five times daily for 10 to 15 repetitions each. With guidance from a PRT practitioner, pet owners can learn joint compressions to alleviate discomfort.

Massage techniques can be used for pain and edema control on the affected area, as well as on other muscle groups that may be affected by an altered gait.

Another consideration is for pet owners to purchase or rent an electrical stimulation unit for home use. Electrical stimulation can help relieve muscle tension, stimulate the release of endogenous endorphins, stimulate blood flow, control edema and help with fracture healing. The staff involved in instructing owners in all these techniques must be trained in and comfortable with their use.

Dr. Stein, a diplomate of the American Academy of Pain Management, is developing the Animal Pain Management Center in Buffalo, N.Y., a practice devoted to improving the quality and extending the length of pets' lives. He is president of the International Veterinary Academy of Pain Management (IVAPM), and serves as an anesthesia and pain-management consultant for the Veterinary Information Network.