Part 1: History / Introduction
Part 6: Pain in the Avian Species
Part 7: Anesthesia and Analgesia, Chronic Pain (Please scroll down)
Part 8: Quality-of-Life Issues
Part 7: Anesthesia and Analgesia, Chronic Pain
Regional Anesthesia and Analgesia
Local anesthetics such as lidocaine and bupivacaine block the sodium channels in the nerve axon. These channels carry the nerve impulses in the nerve fibers to the spinal cord and brain. They interfere with the conduction of the action potentials, or nerve sensations, along the nerve. The events from the first recognition of pain, the transmission to the spinal cord, the modulation and transmission to the brain, ending with the movement away from the painful stimulus happen almost instantaneously. The neuron path travels at about 700 mph.
Veterinarians and their physician and dental counterparts use a technique for local anesthesia called a “splash block.” Dentists inject a tiny amount (called a bleb) of Novocain in first, and when it has numbed the area a little, they inject another and another until the entire area is numb. Veterinarians make several subcutaneous injections; the space in the skin is very thin, so they follow the incision line with little blebs of anesthesia until the entire line is blocked.
Because birds are more sensitive to the effects of the drugs, the practitioner must be very careful about dosage, and will often use a lower dose of anesthesia than he would for mammals. Also, systemic uptake of the drug is more rapid with birds, and metabolism may be prolonged, increasing the possibility of toxic reactions. Side effects may include fine tremors, ataxia, sleepiness, recumbency (lying down), seizures, stupor (unresponsiveness), cardiovascular effects, and death.
When general anesthesia is needed, the two most commonly used gases are isoflurane and sevoflurane. These two gases are very safe; they are not volatile as previous gases had been, and patients awaken without the confusion that had occurred with previous gases. The bird is given an opioid once he is anesthetized to diminish the painful stimuli occurring during and after the surgery. Post-operative opioids are administered every 2-3 hours intramuscularly to maintain the analgesic effect.
Drugs may be given orally or parenterally (in a way other than by mouth or into the digestive tract.) Injections may be given:
Intraosseously (into the bone)
Subcutaneously (into the skin)
Intramuscularly (into the muscle)
Intrasternally (into the sternum) or
- ly (into the vein)
There are two different types of analgesic pain killers: opiods and Non-Steroidal Anti-Inflammatories (NSAIDS). Opiods reversibly bind to specific receptors in the central and peripheral nervous systems. Clinical effects depend on the preparation of the drug, the dose, the route of administration, and the species being given the drug. NSAIDS work to reduce the cyclooxygenase (COX) enzymes in the body. Cyclooxygenase is an enzyme produced by the body to respond to tissue injury. COX-2 inhibitors block prostaglandins which cause pain and inflammation. Since COX-1 enzymes also protect the stomach and promote blood clotting; it is advisable not to inhibit these enzymes.
COX-2 inhibitors also decrease the sensitivity of the nerve endings. NSAIDS are used mostly to relieve arthritis pain and visceral, muscular pain, and to decrease inflammation associated with surgery. When injury occurs, the COX enzymes initiate a cascade of reactions which release substances that cause inflammation and sensitization of the nerve endings. NSAIDS inhibit these COX-2 enzymes, thereby reducing inflammation at the site of the injury.
Chronic, painful conditions, such as joint disease and neoplasia, are progressive and degenerative. It’s often difficult to assess and treat these conditions in birds since the response to analgesia is based on the evaluation of behavior of each bird.
NSAIDS are the first course of therapy for chronic disorders. They have no sedative effects and last longer than opiods. Carprofen, meloxicam, and celecoxib are frequently administer as they have few side effects and may be administered orally in small birds. Dosages begin low and increase over time as necessary. Monitoring renal and hepatic function every few months and CBC’s are recommended. Stronger NSAIDS may be needed for degenerative joint disease and cancer; however, they come with the risk of renal toxicity and gastric ulceration when given in high dosages. If the pain is not controlled with NSAIDDS, opioid use may be indicated.
Many medications and modalities used in mammals, especially dogs and cats, have not been tested in birds. Cancer treatment, although now commonplace in mammals, is generally not used in birds because of the dangers of side effects and lack of sufficient evidence of their success. Birds are too fragile for such aggressive therapy.