Anesthesia & Analgesia
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Anesthesia & Analgesia. Anesthesia?. The loss of feeling or sensation…. General Anesthesia A state of unconsciousness in which there is loss of sensation throughout the body. Local Anesthesia. Loss of sensation only in part of the body, the animal remains conscious. Anesthetic Agents.

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The loss of feeling or sensation…

  • General Anesthesia

  • A state of unconsciousness in which there is loss of sensation throughout the body.

Local Anesthesia

  • Loss of sensation only in part of the body, the animal remains conscious.

Anesthetic agents
Anesthetic Agents

Drugs that produce anesthesia

  • General Anesthetics

  • Most frequently given by inhalation or injection.

  • Injectable forms may be given intravenously (IV), intramuscularly (IM), or intraperitoneally (IP).

    • General anesthetics most often given by injection include the barbiturates (pentobarbital) and Ketamine.

    • Gas anesthetics are usually administered via an anesthetic machine. (Isoflurane)

Anesthetic agents1
Anesthetic Agents

Drugs that produce anesthesia

  • Local Anesthetics

  • Most frequently given by injection or applied topically.

    • The injection numbs the area around the injection site, the animal remains fully awake. Lidocaine and Marcaine are examples of local injectable anesthetics.

    • Topical anesthetics may be liquids, sprays ointments, or creams. Ophthaine, a brand of anesthetic eye drops, is an example of a topical anesthetic preparation.

Stages of anesthesia
Stages of Anesthesia

During induction of general anesthesia, animals pass through various stages indicative of the level of anesthesia.

Stage 1: excitatory, disorientation, vocalization, urination, defecation.

Stage 2: loss of consciousness with or without struggling and whining, many reflexes are intact but righting reflex is lost, rapid irregular breathing and rigidity.

Stage 3: surgical stage of anesthesia, with loss of reflexes, muscle relaxation, deep and rhythmic breathing, planes 1-4 (light to deep).

Stage 4: medullary paralysis with respiratory arrest, hypotenstion and imminent death. Cardio- pulmonary resuscitation and drugs to reverse anesthesia must be given or anima will die.

Anesthesia analgesia

Monitoring the Anesthetized Patient

  • Any anesthetized animal must be watched very closely!

  • Vital signs, including:

    • Color of mucous membranes

    • Capillary refill time

    • Heart rate

    • Pulse

    • Respiratory rate and depth

  • Must be observed and evaluated throughout the procedure.

Anesthesia analgesia

Monitoring the Anesthetized Patient

Other parameters that can be monitored with special equipment are blood pressure, electrocardiogram and blood gases.

Frequent measurement of body temperature is very important, because general anesthetics can cause hypothermia.

Anesthetized animals should be placed on a warm surface, both during surgery and the post-operative recovery period, to prevent hypothermia.

Anesthesia analgesia

Down Enough?

In addition to monitoring vital signs, the animal must also be monitored to determine that it is adequately anesthetized.

A patient that is too deeply anesthetized can be close to death, whereas a patient that is insufficiently anesthetized may be feeling pain.

Anesthesia analgesia

Signs of Adequate Anesthesia

Adequate general anesthesia is accompanied by loss of muscle tone reflected in loss of purposeful movements, however, hamsters and gerbils may retain “swimming” or purposeless movements even in deep surgical anesthesia.

There is a loss of reflexes for example corneal, pinnae and pedal. There should be no response to aversive stimuli e.g. tail pinch, pinching abdominal skin with forceps and a lack of vocalization. Twitching of whiskers is lost with progression from light to medium anesthesia. There are changes in the depth and frequncy of respiration and cardiovascular parameters.

Anesthesia analgesia

Monitoring the Depth of Anesthesia

  • Assess movement, stimulus perception and reflexes – (cornea, toe, tail or ear).

  • Observe chest wall movement.

  • Pulse, heart rate, direct or indirect blood pressure (cuff or doppler).

  • Mucus membrane color at muzzle, feet, ears and tongue.

  • Temperature

Anesthesia analgesia


The post-operative period starts when surgery has been completed, and ends when the animal is returned to the routine husbandry program SOP 7.3.

During the immediate post-operative period, the animal is observed closely, usually in a warm, quiet environment.

When animals wake up from anesthesia, they normally go through a period of involuntary and uncontrolled motions.

During this time, the animal must be prevented from injuring itself or a technician.

Anesthesia analgesia

When recovering an animal…

  • The animal should be placed by itself in a recovery cage. Not with other animals.

  • Food and water bowls should be removed.

  • Provide a heat source.

  • The animal is never left unattended.

  • Follow any post operative instructions from the veterinarian.

Anesthesia analgesia


Pain Relief

  • Because the anatomic structures and neurophysiologic mechanisms leading to the perception of pain are similar in humans and non-human animals, it is reasonable to assume that if a stimulus:

    • is painful to humans,

    • is damaging or potentially damaging to tissues, or

    • induces escape and emotional responses in an animal,

    • Then it must be considered painful to that animal.

Anesthesia analgesia

How do I know if it’s in pain?

Pain is a perception of potential or actual tissue damage resulting from the stimulation of specialized nerve endings in the tissues.

Under local anesthesia, nerve pathways are blocked, thus no pain is perceived, even though the brain is functioning.

General anesthesia causes a loss of consciousness, even though the nerve pathways are open, the animal feels no pain because the pain perception areas in the brain are not functioning.

Anesthesia analgesia

Pain – Acute or Chronic?

  • Pain may be acute or chronic, depending on the length of time they are experienced.

    • Acute pain has a short and often a relatively severe course.

    • Chronic pain is that which persists over a longer period of time.

Humans can describe pain by its characteristics (dull, sharp, stinging), its location, and changes in its intensity.

In animals, however, pain assessment and evaluation can only be made from signs exhibited by the animal.

Anesthesia analgesia

Assessing Pain - Acute

Acute pain is usually more intense than chronic pain. Behavioral changes that relate to acute pain must be compared to known environmental factors and the activity cycle of the animal. Behavioral signs of acute pain include…


The animal protects the painful area by moving away or biting the handler.


Vocalization on movement or palpation of the painful area.


The animal repeatedly licks, bites, or scratches the painful area. If the pain is centered in anb ear or limb, the animal may exhibit repeated head or limb shaking.

Anesthesia analgesia


The animal paces, constantly shifts its weight, or repeatedly stands up and lies down. The sexual cycle of the animal must also be considered in deciding weather it is experiencing pain; females in “heat” and males exposed to females in heat usually show increased restlessness.


This is most readily seen in horses. Several mammalian species, including dogs, cats, rats, mice, and rabbits have so few sweat glands that sweating is not a useful sign of pain.


Panting is the equivalent to sweating in some species that lack sweat glands in the skin. Environmental temperatures must be noted, as this behavior is also a heat stress reaction.

Tooth grinding:

This is common in large or non-rodent species, especially horses, sheep and rabbits.


The animal lies down for prolonged periods. The position the animal assumes when lying down must be compared to its normal sleeping or resting time and posture.

Anesthesia analgesia


The animal exhibits reluctance or difficulty moving or rising from a lying to a sitting or standing position.

Abnormal postures:

This includes behaviors and postures such as head pressing standing with a tucked abdomen, hanging the head down, head tilting, and stiff-leggedness.

Anesthesia analgesia

Assessing Pain - Chronic

Chronic pain is usually less intense than acute pain. It tends to be intermittent and thus more difficult to detect than acute pain. Behavioral changes relating to chronic pain include:

  • Limping or carrying a limb.

  • Licking or rubbing an area of the body.

  • Reluctance to rise and move.

  • Loss of appetite.

  • Change in temperament or behavior toward handlers.

  • Change in bowel and/or urinary activity.

  • A lack of self-grooming, as indicated by a ruffled and soiled hair coat.

Anesthesia analgesia

Whatever the type or cause of pain, every effort should be made to reduce it. Pain relief, or analgesia, is often accomplished with drugs.

Commonly used analgesic drugs are acetaminophen (Tylenol) buprenorphine and the non-steroidal anti-inflammatory drugs (NSAID) like aspirin and ibuprofen.