Feline Analgesia in 2003
Margie Scherk, DVM, DABVP (Feline)
Vancouver, BC, Canada

Perspective: feline pain management

Over the centuries of providing care for animals, we have generally neglected the most humane and basic aspect of care, namely freedom from pain. As we have become more sophisticated in our diagnostic capabilities, and have more therapeutic options available, we have drifted away from compassion and empathy.

Why is this? 1) Belief that non-human animals don't experience pain the way we do 2) Inability to assess pain in non-verbal individuals 3) Fear that illness may make our patients susceptible to adverse reactions to analgesics 4) Lack of understanding about analgesic agents 5) Few choices for analgesics in the past

Interestingly, many of our clients are aware that their cats are painful and are grateful when we offer their friends analgesia. Clients relate to pain more than any other thing we discuss with them.

Let's look at each one of these false myths. While there are species as well as individual differences in the magnitude of pain experienced, some of which is based on expectations or anticipation, pain is a real phenomenon that occurs as a result of a tissue injury induced neurologic response. This nociceptive response sends signals to the brain, via the A fibers (quick pain) and C fibers (delayed sensation) of the spinal cord, resulting in the interpretation and experience of PAIN!!!!! Worse still: pain interferes with healing and can; in fact, make the disease process more harmful. Hypotension, gastrointestinal injury, hypothermia and immunosuppression may all occur as negative physiologic results of pain. The body in response to the trauma releases all sorts of leukotrienes: some of these are helpful, but many aggravate the problem.

As a result, if a patient has, or is going to have tissue trauma, analgesic therapy is required. Assess the pain potential of the procedure. If it is something that would hurt you, give your patient the benefit of the doubt and offer analgesia. Start analgesia BEFORE the pain occurs. Once it starts, it is harder to control. This is the concept of "pre-emptive analgesia". Tissue and nerve trauma causes release of leukotrienes and prostaglandins, which stimulate the C fibers (dull aching pain) and A fibers (sharp pain). These stimuli are related to the spinal cord, which transmits the messages to the brain. Once the nociceptive response has been recognized by the cerebral cortex, "wind up" occurs and the pain is more difficult to alleviate.

What if you aren't sure if the patient is hurting, as he/she is anorectic and lethargic, but there is no history of trauma? Because it can be difficult, especially in cats, to determine of they are in pain, it is humane to apply a "test dose" of a short acting, reversible narcotic agent to see if their demeanour improves. If this is the case, analgesia must be considered in planning the longer-term care.

What are signs of pain in the feline patient?

 Inability to rest/sleep

 Inappropriate activity level

 Sitting in the back of the kennel

 Mental attitude/demeanour (stupor or anxiety)

 Changes in attitude/personality

 Poor haircoat

 Facial expression, staring, fixed gaze, dilated pupils

 Lack of appetite and thirst

 Self-mutilation

 Vocalizations

 Posture

 Tachycardia

 Tachypnea

 Hypo- or hyperthermia

 Hypo- or hypertension

Can we harm a painful patient with judicious use of analgesics? It is unlikely if we use doses that are appropriate for that species. "Morphine mania" was the name given to the dysphoric manic state that cats given morphine at doses appropriate for dogs achieve. Because of this, the myth arose that cats can't tolerate narcotics. Nothing could be further from the truth. Cats tolerate narcotics very well. Doses for commonly used narcotics are listed in Table 1. Interestingly, patients who are ill tolerate opioid narcotics better than healthy, non-painful patients do. This is important to note, as the dose selected should be lower for preemptive analgesia prior to an elective procedure in the well patient. This concept of "pre-emptive" analgesia is crucial. As already mentioned, provision of analgesia before stimulation of trauma, prevents central sensitization, thereby reducing the amount as well as the duration of analgesia required. Another concept is that of "balanced analgesia" which, similar to the concept of balanced anaesthesia, refers to using a combination of analgesic agents to provide synergism while reducing the amount of each agent and thus, the risk of adverse effects from any of them.

Narcotics are not a substitute for attentive and compassionate nursing care. Good and frequent observation, a safe, clean, comfortable quiet environment all enhance healing and a sense of wellbeing. Kind, gently spoken words and gentle handling are irreplaceable. TLC!

OPIOIDS

Knowing that opioids are safe in cats has opened up a wide range of therapeutic options. We have numerous mu agonists to choose from as well as agonist-antagonist agents. In addition to this, we have a variety of routes that can be used effectively to prevent or free a patient from pain. While in IV route is the best way for systemic analgesia, because we can titrate the dose well ("dose to effect") as well as having optimal circulatory benefits of drug distribution, there is also great benefit to be had from epidural administration of morphine, oxymorphone, fentanyl or buprenorphine. The epidural route has the benefit of analgesia without sedation, minimal cardiopulmonary depression as well as prolonged effect with opioids. Local anaesthetic agents, bupivicaine and lidocaine provide a more rapid onset of epidural anaesthesia but don't last as long as opioids. Unless an epidural catheter has been placed, repeat dosing is difficult.

Other local blocks are beneficial and safe in cats. Ring blocks are recommended for declaws by some anaesthetists.

The transdermal fentanyl patch has opened new doors for providing pain relief and comfort for patients postoperatively as well as for patients with chronic cancer pain.

Alpha 2-agonists such as medetomidine may be considered for cats (off label use).

While ketamine HCl does not provide adequate analgesia alone or in conjunction with diazepam, there is recent evidence suggesting that ketamine may prevent sensitization and thus reduce the amounts of other analgesics used in balanced analgesia.

Table 1. Opioids

 Oxymorphone: systemic: 0.025-0.1 mg/kg IV (IM, SC) q2-6h (Dogs: 0.05-0.2 mg/kg IV (IM, SC) q2-4h

 Morphine: preservative free 0.1-0.4 mg/kg IV (IM, SC) q4h pre-treat with diphenhydramine (Dogs: 0.2-2.0 mg/kg IV (IM, SC)

 Meperidine: not recommended for cats

 Fentanyl injectable: 20-40 ug/kg IV (IM, SC) q1h or 2-4 mcg/kg/h by constant rate infusion

 Fentanyl transdermal patches: Cats 25 ucg/h patches: ramp 6-12 hours, last ~100 hours

 Dogs:

 < 10kg 25 ucg/h: ramp 12-24 hours, last 72 hours

 10-29kg: 50 ucg/h: ramp 12-24 hours, last 72 hours

 >30kg: 75-100 ucg/h: ramp 12-24 hours, last 72 hours

 Codeine: 0.5-2.0 mg/kg PO q 6-8h

 Butorphanol: 0.1-1.0 mg/kg IV (IM, SC) q2-6h (dogs: q12h)

 Buprenorphine: 5-10 ug/kg IV (IM, SC) q 6-8h (Dogs: 5-20 ug/kg IV (IM, SC) q 6-8h)

 Pentazocine citrate: not recommended for cats

 Nalbuphine: not recommended for cat

Nonsteroidal Antiinflammatory Drugs: are less useful in cats than they are in dogs. These drugs, as in dogs, must only be used in patients who are well hydrated and have been shown to be free from pre-existing renal, hepatic or gastrointestinal disease. Acetaminophen is highly toxic for cats. Flunixin meglumine, etodolac, meclofenamic acid, naproxen and piroxicam are not recommended for use in cats. Some people are using low doses of carprofen in cats; others recommend not using it because of gastrointestinal toxicity. Aspirin, ketoprofen and ketorolac can be used but at much reduced dose and/or frequency than in dogs. (Table 2)

Table 2. NSAIDs

 Aspirin:10-25 mg/kg PO q 48-72h (Dogs:10-25 mg/kg PO q 12h)

 Ketoprofen:1 mg/kg PO q24h for 5 days or 1-2 mg/kg IV, SC, IM q 24h for 5 days

 Ketorolac tromethamine:0.25 mg/kg IM q 8-12h, 1-2 times (Dogs:0.3-0.5mg/kg IV, IM q 8-12h, 1-2 times)

 Carprofen:1-4 mg/kg PO q24h?

 Meloxicam 0.1 mg PO eod

Transdermal fentanyl patch

 For moderate to severe pain

 Cancer pain

 Pancreatitis, abdominal pain

 Terminal pain/palliative care

 Chronic pain

 Post operative

 Pre-emptive

Speaker Information
(click the speaker's name to view other papers and abstracts submitted by this speaker)

Margie Scherk, DVM, DABVP (Feline)
Vancouver, BC, Canada


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