Analgesia relates to elimination or management of pain. Analgesia, like anaesthesia, may be local, or general.
Pain, a cognitive experience common to all mammals, is usually classified as either inflammatory or neuropathic. The underlying causes of pain in cats may be complex and may be multifactorial (e.g. long-term pain associated with lymphoma causes inflammatory as well as neuropathic pain).
Pain may also be judged longitudinally, for example in degenerative joint disease, where bouts of acute pain are preceded with periods of relative pain-free states.
A fuller description of pain types include:
- Visceral Pain - is a dull, deep, constantly aching pain. It is also poorly defined and often responds best to narcotic analgesics when pain is significant.
- Inflammatory and somatic pain - frequently described in humans as well localized, constant, and aching. Common sources of this type of pain include bone metastases, tissue damage, and musculoskeletal, dental, and integument pain. In humans, this type of discomfort responds well to analgesics such as aspirin, acetaminophen, or the non-steroidal anti-inflammatory drugs (NSAIDs).
- Neuritic Pain - involves inflammation of nerves or nerve roots, which can be a paraneoplastic syndrome or a direct effect of cancer compression, causes neuritic pain. Humans describe this as a constant dull aching pain that may have periods of burning "shock-like" sensations.
- Neuropathic Pain - is the result of a damaged segment of the nervous system that normally transmits pain stimuli. This is due to metabolic, immunologic, or direct physical effects on the nervous system. It is difficult to control with standard analgesics.
Control of pain in lame or operative animals involves broad classes of compounds such as NSAID and opioids. Delivery of analgesia can be via oral, parenteral, epidural, local, or transdermal routes. Non-pharmacologic pain management strategies include acupuncture therapy, massage, and diet.
Commonly used analgesics in cats include:
- NSAIDs - include meloxicam and aspirin
- Opioids - including buprenorphine, morphine and butorphanol
- Corticosteroids - including dexamethasone, prednisolone and methylprednisolone acetate
- Adrenergic agonists - alpha2 agonists such as xylazine and medetomidine
- Ketamine - provides excellent superficial analgesia but rather poor visceral analgesia. Recently, interest in ketamine has increased because of its potential role in preventing wind-up (sensitization) of central nociceptive pathways. Ketamine is an antagonist of the excitatory neurotransmitter glutamate at the N-methyl-D-aspartate (NMDA) receptors in the spinal cord and brain. Inhibition of the NMDA receptors prevents or decreases exaggerated pain states in laboratory animals and people. Thus, ketamine may be incorporated into the anaesthetic protocol to prevent the development of exaggerated or chronic pain states.
- Woolf, CJ (2004) Pain: moving from symptom control toward mechanism-specific pharmacological management. Ann Intern Med 140:441-451
- Costigan, M Scholz, J & Woolf, CJ (2009) Neuropathic pain: a maladaptive response of the nervous system to damage. Annu Rev Neurosci 32:1-32