On this page: Definition | Signs of Pain and Distress | What is Pain? | Types of Pain | Why Treat Pain? | Timing of Analgesia | Mechanisms of Analgesia | Drug Classes | Routes of Administration | Regulations
Definition:
The absence of pain in the presence of stimuli that would normally be painful.
Signs of Pain and Distress:
Spectrum of clinical signs:
- Vocalization
- Hunched posture
- Ruffled coat
- Aggression or fear
- Self injurious behavior
- Weight loss
- Immobility or attempts to escape
- Isolation from the group
- Disinterest in surroundings
- Protection of affected body part
- Ocular discharge
- Soiled coat
- Salivation
- Panting
- Sweating
- Skeletal muscle contractions (shivering, tremors, spasms)
- Urination, defecation, evacuation of anal sacs
What is Pain?
“An unpleasant sensory and emotional experience associated with actual or potential tissue damage.” - International Association for the Study of Pain
Types of Pain
Somatic
- Superficial (skin)
- Deep (tendons, joints, muscles, bones, fascia)
Visceral
- Organ related
- Diffuse, often referred to other locations
Acute
- Associated with a diagnosable underlying physical pathology
- Usually responds to classic analgesics
Chronic
- Pain that persists for more than 6 months
- Not merely an extension of acute pain
- Includes neuropathic pain
- Pain may continue even after peripheral nociceptive input ceases
- Often unresponsive to treatment
Why Treat Pain?
- Moral and legal issues
- Pain has detrimental effects on metabolic, immune, pulmonary, gastrointestinal and cardiac functions
- Pain also has negative impact on higher central nervous system centers with all its implications
Timing of Analgesia
3 time points:
1. Preoperative Analgesia (Preemptive)
- Refers to the reduction or prevention of pain prior to the noxious stimulus
- To prevent the “priming” effect of nociceptive stimulation on the CNS, thereby reducing the pain experienced in the post trauma period
- Preemptive analgesics can reduce induction and intraoperative anesthetic requirements
- Opioids may be incorporated into the preanesthetic regime to provide preemptive analgesia
2. Intraoperative Analgesia
- Administration of analgesics to patient while undergoing a painful procedure
- The timing should be prior to the anticipated pain inducing stimulus
3. Postoperative Analgesia
- In order to assist the animal during the recovery and rehabilitative periods
- To decrease the duration of pain associated physiological alterations
Mechanisms of Analgesia:
- Interfere with nociceptive processing within spinal cord – Opioids (narcotics)
- Diminish nociceptor activation by blocking synthesis of pain receptor stimulators (prostaglandins) – Non steroidal anti inflammatory drugs (NSAIDS)
- Block peripheral nerve transmission – Local anesthetics
- Acts at level of spinal cord, causing pre and post synaptic inhibition –Adrenergic agonists
Drug Classes:
The severity of the pain of each individual should determine the analgesic regimen. It should be noted that the an animal's response to an analgesic may depend on species, weight, age and medical condition.
- Opioids e.g. Buprenorphine, morphine, butorphanol, fentanyl
- NSAIDS –e.g. Acetylsalicyclic acid, phenylbutazone, acetaminophen
- Local anesthetics – e.g. Lidocaine, bupivicaine, EMLA cream
- Adrenergic agonists – e.g. Xylazine
Routes of Administration:
- Parenteral – Intravenous, intramuscular, subcutaneous
- Topical or intradermal
- Oral (i.e. gavage, drinking water, jello)
- Transdermal patch (i.e. fentanyl)
- Vascular access port
- Osmotic pump
Regulations:
- Due to the potential for abuse, permits and/or valid practice licenses are required for the purchase, distribution and administration of opioids
- Up to date record keeping logs are mandatory
- Storage in a double locked cabinet or preferably a wall safe. Access limited to a select few individuals
- Research licenses: o Applications sent to Bureau of Drug Surveillance in Ottawa