Anesthesia

Antimicrobial prophylaxis

— might be indicated prophylactically for certain surgical procedures or when known breaks in sterility occur, but should not be used as a substitute for proper aseptic techniques. Please consult the veterinarian about using antimicrobials for each individual animal.

Principles of Anesthetic Management

Prevention of perceived pain during surgery is the primary function of anesthesia. Anesthesia also enables humane restraint, improves safety, and increases technical efficiency. Although many factors affect choice of a particular anesthetic drug or technique, the greatest concern must be the well-being of the animal. A general rule of thumb is “aim only for the degree of restraint and anesthesia required” - more may not be better and often is associated with a greater potential for adverse effects.

Criteria for choosing anesthetic agents knowledge of the procedure and duration compatibility of the anesthetic with experimental design actions and properties of the anesthetic agent(s) biological characteristics of the selected species prior experience with the anesthetic in the species available equipment, personnel and facilities.

Anesthetic & Analgesia Definitions

anesthetic - a drug which causes a reversible loss of conscious awareness and sensation, including pain.
analgesic - a drug which causes an absence of pain in response to stimulation which would normally be painful; often, what is actually achieved following administration of an analgesic is hypoalgesia, or diminished pain in response to a stimulus.
sedative - a drug which produces a state of decreased motor activity, mental calmness, and drowsiness; does not imply analgesia, although most sedatives will increase the pain tolerance threshold by reducing anxiety and fear.
neuromuscular blocking agent (paralytic agent) - a drug which blocks transmission at the neuromuscular junction; these drugs lack anesthetic and analgesic properties. It is illegal to use a neuromuscular blocking agent for painful procedures, unless anesthetics or analgesic drugs are used in conjunction.

General Anesthesia provides overall insensitivity and unconsciousness.
Basic elements of general anesthesia include:


Two main delivery systems are used in veterinary medicine, inhalation and injection; a brief review of common drugs follows:

Hypnotic/sedative drugs are widely used for inducing or managing general anesthesia. They induce a dose-dependent spectrum of CNS depression, from sleep to deep general anesthesia. Higher doses may cause medullary paralysis, respiratory arrest and death. Examples include: pentobarbital, sodium thiamylal, sodium thiopental and chloral hydrate. alpha 2-Adrenergic receptor agonists have tranquilizing, sedative, and potent analgesic properties. Examples include: xylazine (trade name Rompum).
Dissociative drugs induce anesthesia, have short duration of action, a wide safety margin, and cause minimal cardiopulmonary depression. To decrease undesirable actions such as muscle hypertonus and emergence delirium, they may be used in combination with hypnotics, tranquilizers, or alpha 2-adrenergic agonists. Examples include: ketamine and tiletamine which is often in combination with the tranquilizer, zolazepam.
Muscle relaxants are predominantly central or peripheral acting. The peripheral acting muscle relaxants are devoid of sedative and analgesic properties. These drugs, when used during surgery, must be administered only in conjunction with general anesthetics. The investigator must remain aware that the animal is unable to respond with purposeful movement to noxious stimulation and the animal must be closely monitored (e.g. heart rate, arterial blood pressure) to ensure adequate general anesthesia. Examples include: succinylcholine and dimethyl tubocurarine.


Local and Regional Anesthesia — is used most often in large animals, such as horses, cattle or sheep. Localized insensitivity in awake or mildly sedated animals can result from topical application or injection of appropriate anesthetics in the region of the surgical incision (local anesthesia); injection in proximity to nerve trunks (nerve block); or injection into the subarachnoid or epidural spaces (regional anesthesia).

Local and regional anesthesia advantages include:

Local and regional anesthesia disadvantages Include:

Analgesic drugs — used to reduce pain are initiated pre-emptively during the surgical period and continued well into the postoperative recovery period. It is often erroneously presumed that an animal is not in pain, when there is no obvious change in behavior. Pain can be difficult to detect because of individual and species variation. "Typical" signs of pain include guarding the painful area, vocalization, licking, biting, self mutilation, signs of depression, grinding of teeth, restlessness, lack of mobility, failure to groom, abnormal posture, changes in sleep patterns, and failure to eat or drink. Pain can be assumed to have been present if administration of analgesics causes these signs to disappear.
Consultation with the attending veterinarian is recommended since there is tremendous variation between species as to their response to analgesic drugs. Limited animal studies have been conducted and for many species there will be widely different published dosage schedules. Never extrapolate from human data, please consult with the veterinarian.

Guidelines for the administration of analgesics

Medical and veterinary reports suggest analgesics are most effective when administered prior to the painful stimulus, before the surgical incision and tissue manipulation.
Analgesic drugs must be given at the proper initial dose and subsequent doses must be given according to schedule.
Federal law requires pain relief according to the same guidelines for a human patient undergoing a similar procedure.

In addition to the care which must be taken when choosing the proper dosage and schedule for a particular species, different analgesics are indicated for different types of pain:

All drugs, whether or not they are DEA regulated, must be properly labeled and included on the label must be the expiration date. Expiration dates should be checked periodically, at least once every three months, and expired drugs immediately discarded. It is a violation to use expired drugs on animals involved in research procedures (there are a few limited occasions wherein expired drugs may be used for terminal, non-survival procedures). Animal Care staff will discard any drug they observe to be improperly labeled, or in use after the expiration date has passed. At the minimum the label on a drug shall include: