General considerations

While the importance of acute perioperative pain management for dogs and cats has been embraced by veterinarians in recent years, chronic pain management has lagged behind. Barriers to effective chronic pain control in animals include the following:

• lack of appreciation that many chronic disease processes and cancers are associated with significant pain (Table 4.1);
  
• inability to assess chronic pain in dogs and cats;
  
• lack of knowledge of drugs, drug therapy, and other pain-relieving techniques;
  
• lack of communication with clients and lack of involvement of clients in the assessment and treatment phases;
  
• underuse of nursing staff for assessment and re-evaluation of pain in hospitalized patients.

There are four main steps in overcoming these barriers and assuring that chronic pain management is optimized in veterinary patients:

(1) Assure that veterinarians have the appropriate education and training about the importance of alleviating pain, assessment of pain, available drugs and potential complications, and interventional techniques.

(2) Educate the client about realistic expectations surrounding pain control and quality of life and convey the idea that most patients’ pain can be managed. This involves letting the client know that owner involvement in evaluating the pet and providing feedback on therapy is crucial to success. The veterinarian and owner should both participate in developing effective strategies to alleviate pain. The clients’ involvement also helps decrease their feelings of helplessness.

(3) Thoroughly assess the pet’s pain at the start and throughout the course of therapy, not just when it becomes severe.

(4) Have good support from the veterinary practice or institution for the use of opioids and other controlled substances.

Table 4.1. Common conditions that may be associated with chronic pain in dogs and cats

Although pharmacological treatment is a mainstay of chronic pain treatment, adjunctive nondrug therapies such as acupuncture may play an important role in patient management. It must also be remembered that surgery is an important treatment modality for many types of chronic pain and radiation therapy may be useful for treatment or palliation of neoplastic disease.

A basic approach to chronic pain management can be summarized as follows:

(1) Assess the pain. Ask for the owner‘s perceptions of the pet‘s pain or of any compromise in its quality of life.

(2) Believe the owner. The owner sees the pet every day in its own environment and knows when alterations in behavior occur. Owners can rarely suggest diagnoses but do know when something is wrong. The veterinarian should become familiar with the owner’s terminology when explaining the pet’s abnormal behaviors to establish a baseline of communication for further assessment in the home environment once therapy has been initiated.

(3) Choose appropriate therapy depending on the stage of the disease. Anything other than mild pain should be treated with more than one class of analgesic or with an analgesic drug combined with nondrug adjunctive therapy. Also consider concurrent problems and drug therapy; be aware of potential drug interactions and toxicity.

(4) Deliver the therapy in a logical, coordinated manner and explain carefully to the owner about any possible side effects.

(5) Empower the clients to participate actively in their pet‘s treatment; ask for feedback and updates on how the therapy is working.

The importance of alleviating pain

Veterinarians have an ethical obligation to treat animal pain. Most undertreatment of chronic pain is probably a result of lack of adequate knowledge and resources rather than a lack of concern. Outward show of concern for the pet and family is important for demonstrating a bond-centered approach to chronic therapy and pain management. It is important for the veterinarian to foster good communication surrounding primary therapy and pain treatment and at the same time demonstrate empathy for the owner. In cancer patients especially, pain prevention and treatment are not the only aspects that impact animal welfare, and veterinarians must evaluate all aspects of welfare when making treatment decisions. The five freedoms have been suggested as a rubric for the evaluation of an animal’s welfare (Table 4.2).

The approach to the treatment of chronic pain in dogs and cats should be one that considers all aspects of welfare. For each freedom, the severity, incidence, and duration of perturbation should be considered. In the case of pain, the longer the pain lasts, such as in long-standing painful cancers, the more welfare is compromised.

It is of significant interest that the provision of analgesics significantly reduces the tumor-promoting effects of undergoing and recovering from surgery. Surgery is well known to suppress several immune functions, including natural killer (NK) cell activity in animals and people, probably as a result of substances released such as catecholamines and prostaglandins. This suppression of NK cell activity can enhance metastasis. The reduction of the tumor-promoting effects of surgery by analgesics seems to be due to the alleviation of pain-induced reductions in NK cell function, but unrecognized factors other than immune cells probably also play a role. Thus, the provision of adequate perioperative pain management in oncological surgery may protect clinical patients against metastatic sequelae. Pain therapy itself may protect against metastasis and possibly the local extension of cancer.

Table 4.2. Five freedoms for evaluation of animal welfare

Assessment of chronic pain

Assessment of pain in animals can be difficult and frustrating. The tolerance of pain in a veterinary patient probably varies greatly from individual to individual as it does in humans. Coupled with the innate ability of dogs and particularly cats to mask significant disease and pain, the task becomes even more challenging. Often veterinarians need to rely on pet owner experience to help define pain in animals. The mainstay of chronic pain assessment in cats and dogs involves recognizing changes in behavior. Table 4.3 outlines behaviors that are indicative of pain. The main point to remember is that any change in behavior can be associated with pain. Veterinarians should also allow technicians and other staff members to be involved in the assessment. Technicians and other staff members are usually better able to evaluate pain and quality of life in animals because they spend more time with the patients in the hospital. Thus, they are more likely to be able to converse in a relaxed and informal way with pet owners.

Table 4.3. Behaviors that may be associated with chronic pain in dogs and cats

The best and most important people to assess their animal’s behavior are the owners. Often owners need education as to what signs to look for or be informed that certain behaviors may be indicative of pain. Once very specific changes in behavior can be identified and recorded, these can be used to monitor the effectiveness of analgesic therapy. This approach has proved very sensitive in the evaluation of chronic pain caused by osteoarthritis. In cases where pain does not cause a specific behavioral change and only vague signs are observed, the owner is still the best person to assess the pet’s pain or quality of life. Owner feedback can also be used as an indicator of the effectiveness and appropriateness of therapy. Physiological variables such as heart rate, respiratory rate, temperature, and pupil size have been shown to be unreliable measures of acute perioperative pain in dogs and are therefore unlikely to be useful in chronic pain patients.

Principles of alleviation of chronic pain

The general approach of the WHO ladder is a three-step hierarchy (see Figure 4.1). Within the same category of drugs there can be different side effects for individuals. Therefore, if possible, it may be best to substitute drugs within a category before switching therapies. It is always best to try to keep dosage scheduling as simple as possible. The more complicated the regimen, the more likely owner noncompliance. Drugs should be dosed on a regular basis, not just as needed as pain becomes moderate to severe. Continuous analgesia will facilitate maintaining patient comfort. Additional doses of analgesics can then be administered as pain is intermittently more severe. Adjuvant drugs can be administered to help with specific pathophysiologies of pain and anxiety.

Figure 4.1. WHO “analgesic ladder” for treatment of cancer pain in humans.

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