It is important to understand how the proper prevention and treatment of acute surgical pain can decrease morbidity and mortality, speed surgical healing, and prevent long-term issues, such as persistent post-operative pain. Equally important is how we measure pain; if we cannot see pain scores increasing, we cannot anticipate the next level of pain. If we do not anticipate—and get ahead of increasing levels of pain—we will have to “chase” the pain and use much higher levels of pharmaceuticals to treat it. This means we have an increased risk of drug side effects and risks. Finally, it is important to use medications that have proven beneficial for treating acute pain. Pain scales This article concentrates on canine and feline patients. Below are my two favorite pain scales, but you may have others you find and prefer, which is okay. Whatever you choose, make sure it is validated. Grimace scales Cats currently have a grimace pain scale that is very useful in the clinical setting.1 I like grimace scales, as any interaction with the patient alters how they will act: cats are small carnivores but prey for larger carnivores. When they know they are being closely observed or manipulated, many patients will put on a “game face” to appear as healthy as possible and less desirable to be hunted and eaten. What if the cat is facing away from the front of the enclosure? Be immediately suspicious this cat is in pain and is trying to shut out the outside world (Figure 1). Figure 1. This cat is recovering from a surgical procedure and has her back to the front of the cage. Although you cannot fully appreciate the grimace, you can also tell by her hunched position she is in pain. Photos courtesy Sheilah Robertson Glasgow Composite Measure Pain Scale Short Form (CMPS-SF) Dogs can react to our interaction with them, just like cats do. Unfortunately, as of this writing, there is not a validated dog grimace scale. My favorite tool is the CMPS-SF. Although part of this scale is to observe the dog from a distance, it also involves palpating around the incision site.2 This requires two people to avoid injury to themselves should the dog react aggressively/protectively to the palpation. What not to use Distressingly, I am seeing patients on referral that are only being treated with drugs that have either no known pain prevention properties for that species or have been shown to be ineffective. The list is long, but I will mention the four I often see. Tramadol is an effective pain medication in our feline patients, but no studies are showing it has the same opioid activity in our canine patients. It is also a strong serotonin and norepinephrine reuptake inhibitor and can result in serotonin syndrome,3 a dangerous and hard-to-treat reaction. Gabapentin is an anti-convulsant drug that can help suppress neuropathic pain. This can be a useful adjunct drug where neuropathic pain is present. However, it has no place in the treatment of acute post-surgical pain. Sending a patient home on gabapentin may make them appear comfortable from the sedative effect, but these animals can be suffering in silence. Oral opioids, such as codeine and hydrocodone, have poor absorption and undependable pain-relieving effects. The same is true for fentanyl patches. Inhalant anesthetics, such as isoflurane or sevoflurane. These drugs produce amnesia, profound sedation and restraint. They have no inherent pain-relieving properties of their own. Pharmaceuticals Sodium channel blockers, such as lidocaine, bupivacaine, and the delayed-release bupivacaine liposome injectable suspension, are the only drugs we have that are complete analgesics. Everything else we use is hypoalgesics. Used properly, these drugs can effectively block pain and greatly reduce the dosages and frequency of other pain medications. For example, they can be used locally or spinally with infusion pumps for several days postoperatively. It is beyond the scope of this article to describe uses and doses for locals, and I strongly recommend the book Small Animal Regional Anesthesia and Analgesia by Luis Campoy. Opioids fall into three categories: agonists (morphine, hydromorphone, methadone, and fentanyl are widely used in the U.S.), agonist-antagonists (butorphanol and nalbuphine), and partial agonists (buprenorphine). There is also an antagonist category that includes naloxone. Opioids should be considered for every surgical procedure, and the most effective opioids are those in the agonist category. They can be used along with other classes of drugs, such as sodium channel blockers. It is not unusual for some animals to become dysphoric on opioids: this often includes pacing and vocalizing, which should not be mistaken for a pain response. When you try to interact with a dysphoric animal, they are often not responsive to attempts to interact with them. Rather than reverse the opioid with an antagonist and having the animal become acutely painful, you can either increase other pain medications, especially alpha-2 drugs and local infusions, or if need be, you can replace the agonist with butorphanol. Butorphanol is a less effective opioid but will displace the agonist and rarely produces dysphoria itself. For a complete list of doses, uses, and contraindications, check out the 2022 WSAVA guidelines for the recognition, assessment and treatment of pain.5 A pre-operative cat that has received an opioid injection. Anti-inflammatory drugs. Non-steroidal anti-inflammatory drugs are useful both during and after the operative period. They have both analgesic and anti-inflammatory effects and, depending on the specific drug, can be used as an injectable. If used during surgery, close attention to blood pressure must be maintained. NSAIDs can lower blood pressure in the anesthetized patient, which can cause underperfusion of some organs, especially the kidneys. Acetaminophen is another drug with minimal anti-inflammatory properties but analgesic properties. It can be safely used in dogs (not cats) for the immediate operative and postoperative periods to help control pain. Alpha-2 adrenoreceptor drugs are used for both their sedative and analgesic properties. This class of drugs can greatly reduce the stress response in dogs and cats. When combined with opioids, much lower doses can be used for similar effects. They can also be used during recovery when delirium and dysphoria occur. This drug must be avoided in animals with certain heart conditions. Various characteristics of drugs in this class is described in the WSAVA guidelines.5 Ketamine is an N-methyl-D-aspartate (NMDA) receptor antagonist. The NMDA pathway is a centrally acting pain pathway, and ketamine exerts its analgesic effects here. It should never be used by itself but as part of a multi-modal pain therapy with either opioids, alpha-2 adrenergics, or both. Maropitant, is indicated for treating vomiting. Although one study4 suggests it might have mild pain-relieving properties, I like it to prevent vomiting in patients receiving opioids. When human surgical patients are surveyed, they often list vomiting as worse than pain. We cannot survey our own patients, but my experience tells me they would probably say the same if they could. This preoperative dog that has received an opioid injection. In addition to the nausea, there is evidence of distress with the wrinkle at the commissure of his lips and the furrowed brow. Conclusion Operative and post-operative pain control can seem overwhelming. This article barely touches on the different pharmaceuticals that can be utilized in the pursuit of pain control. The reader does not have to dive into the deep end and use every single drug modality mentioned here. However, once you have developed some protocols, your patients and their caregivers will be happier with your outcomes. Section 3 of the 2022 WSAVA guidelines for the recognition, assessment, and treatment of pain provides an excellent resource of example protocols for various procedures,5 such as ovariohysterectomy (OHE), castration, and orthopedic surgery. This dog was recovering from anesthesia after a cranial cruciate ligament (CCL) repair and was displaying signs of dysphoria. The patient was on a morphine, lidocaine, ketamine drip and had an infusion catheter at the surgery site. Author could have treated it with an alpha 2 and gotten the same results, but felt they had good enough pain control to go with the local infusion. Michael C. Petty, DVM, is a veterinary school graduate at Michigan State University. Dr. Petty has devoted his professional life to the care and well-being of animals, especially in pain management. Petty is the past president of the International Veterinary Academy of Pain Management. A frequent speaker and consultant, he has published articles in veterinary journals and serves in an advisory capacity to several pharmaceutical companies on pain management topics. Petty has been the investigator/veterinarian in 12 FDA pilot and pivotal studies for pain management products. He has lectured both nationally and internationally on pain management topics. References https://www.felinegrimacescale.com/ https://wsava.org/wp-content/uploads/2020/01/Canine-CMPS-SF.pdf Indrawirawan Y, McAlees T. Tramadol toxicity in a cat: case report and literature review of serotonin syndrome. J Feline Med Surg. 2014 Jul;16(7):572-8. https://www.vet.cornell.edu/research/awards/201601/efficacy-maropitant-cerenia-adjunct-analgesic-dogs https://wsava.org/global-guidelines/pain-guidelines/
