11. Rodent and Rabbit Anesthesia

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Rodent and Rabbit Anesthesia

Chapter 11

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Patient Evaluation

Difficult to obtain accurate information Shorter life spans Physical examination

Transport to clinic Observe normal behavior and respiratory pattern

before handling Safe and humane restraint

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Handling and Restraint

Mouse Pick up by base of the tail Rest on forearm for external examination Rest on rough surface for administration of

injectables Injection sites

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Handling and Restraint (Cont’d)

Rat Nocturnal animals; awaken before handling Pick up around shoulders or lift by base of tail Rest on forearm, restrain by tail or around

shoulders Injection sites

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Mouse Restraint

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Mouse Injections

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Rat Restraint

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Rat Injections

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Handling and Restraint

Hamster Temperament differences Nocturnal animal; awaken before handling Gentle and secure restraint

Gerbil Very active; can easily escape Be careful of skin on tail

Guinea Pig Immobile to agitated Swift and firm restraint

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Hamster Restraint

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Hamster Injection

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Guinea Pig Restraint

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Handling and Restraint

Rabbits Breed variations Support back; animals kick with hind legs Lift by skin over shoulders; support abdomen Injection sites

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Rabbit Restraint

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Small Mammal Physical Examination

Observe in transport box for undisturbed behavior

Respiratory rate and pattern probably elevated

Palpate or auscultate the heart rate

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Small Mammal Physical Examination (Cont’d)

Abnormalities Discharges from eyes and noses Labored/noisy respiration Soiled perineum Sunken eyes indicating dehydration Prominence of vertebrae and pelvis indicating

poor body condition Rabbit: prolonged capillary refill time

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Small Mammal Preanesthetic Diagnostic Tests

Blood tests Rabbits

Urinalysis Small rodents, rabbits, guinea pigs

Radiography Small rodents, rabbits, guinea pigs

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Preanesthetic Care

Don’t withhold food and water Except when stomach is involved in surgery Must reestablish feeding as soon as possible after

surgery Don't feed during the day

• Many animals are nocturnal Pain and discomfort can decrease appetite

Correct preexisting problems Supportive fluid therapy for dehydration

• IV, SC, IP, or intraosseous routes

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Preanesthesia

Sedation is rarely needed prior to general anesthesia Protocols include a combination of injectable

anesthetic agents or use of a chamber Rabbits may need prior sedation

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Preanesthesia (Cont’d)

Preanesthetics are used: Atropine

• Reduce salivation and bronchial secretions• Don’t use in rabbits

Opioid analgesics • 30-40 minutes prior to induction • Provides preemptive analgesia

Sedatives or tranquilizers• Given to rabbits prior to inhalation anesthesia

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Preanesthetic Agents

Anticholinergics Atropine and glycopyrrolate

Phenothiazines Acepromazine

• Sedates but does not immobilize rodents• Sedates rabbits and often provides enough

immobilization for minor procedures Benzodiazepines

Diazepam and midazolam• Marked sedation in rodents and rabbits

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Preanesthetic Agents (Cont’d)

Alpha2-agonists Xylazine, medetomidine, and dexmedetomidine

• Sedation with some analgesia Higher dose may provide immobilization Side effects

• Same as in dogs and cats except vomiting Reverse with yohimbine or atipamezole (preferred)

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Preanesthetic Agents (Cont’d)

Opioids Provide preemptive analgesia Commonly used in combination with sedative

agents • Acepromazine and butorphanol helpful to get blood

samples from rabbits

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General Anesthesia: Induction

Rabbits SC or IM routes most common IV may be possible

Small mammals IP route less painful than IM route

IP or IM vs. IV route of administration Cannot administer drug to effect One calculated dose is given High dose rates are required for proper depth Recovery times are prolonged

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General Anesthetic Agents: Cyclohexamine Agents

Ketamine Limited effect in small mammals when used alone Provides restraint in rabbits but not sufficient

analgesia Ketamine/acepromazine and ketamine/diazepam

or midazolam: produces surgical anesthesia in some rabbits and light anesthesia in small rodents

Ketamine/alpha2-agonist (medetomidine or xylazine): provides analgesia and surgical anesthesia

• Variable results in guinea pigs • Monitor anesthetic depth carefully

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General Anesthetic Agents: Cyclohexamine Agents (Cont’d)

Tiletamine Combined with zolazepam (Zoletil, Telazol)

• Light-to-medium anesthesia in small rodents Produces less analgesia than ketamine

combinations

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General Anesthetic Agents: Neuroleptanalgesics

Neuroleptic (droperidol, fluanisone) combined with analgesic (fentanyl) Provides restraint and analgesia in small

mammals Must combine with a benzodiazepine to produce

surgical anesthesia Recovery enhanced by reversing fentanyl

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General Anesthetic Agents

Barbiturates in small mammals Narrow safety margin Severe cardiovascular and respiratory depression Prolonged recovery May be administered IV to rabbits

Propofol Small rodents

• Not used because it must be administered IV Rabbits

• Short period of light anesthesia for ET intubation and gas anesthesia

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General Anesthetic Agents (Cont’d)

Alphaxalone Steroid anesthetic

• Induces anesthesia in rabbits Administered IV

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Inhalation Anesthetics: Small Mammals

Anesthetic chamber is the most convenient method to induce anesthesia Appropriate size Fill from bottom; excess gases removed from top

Isoflurane, desflurane, and sevoflurane used in small rodents Rapid induction; rapid recovery Deliver with precision vaporizer into chamber Maintain with face mask Scavenge waste gas

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Anesthetic Induction Chamber

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Inhalation Anesthetics: Rabbits

Rabbits often hold their breath when exposed to inhalation agents May lead to bradycardia Using face mask may lead to struggling Using chamber may result in violent attempts to

escape Preanesthetic agents are preferred prior to

induction Less struggling but may still hold breath Induce general anesthesia with face mask

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Intubation of Rabbits and Small Rodents

Rabbits Uncuffed ET tubes and laryngoscope with blade or

canine otoscope Larynx is visualized or blind technique

Small rodents Nasal catheter positioned in back of pharynx Does not allow for assisted ventilation Waste gases removed by extract tube close to

nose

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Nasal Catheter

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Monitoring Anesthesia

Out-of-circuit vaporizer Open, nonrebreathing system Fresh gas flow rates Depth of Anesthesia

Small rodents• Tail pinch and pedal withdrawal

Rabbits and guinea pigs• Ear pinch reflex

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Anesthetic Delivery in a Rabbit

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Monitoring Anesthesia

Heart rate and rhythm Rabbits and guinea pigs

• Auscultate chest wall, palpate chest wall, esophageal stethoscope (rabbit)

Small rodents• Palpate chest wall

Capillary refill time Rabbits only

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Monitoring Anesthesia (Cont’d)

Blood loss Small mammals have a small total blood volume Monitor blood loss carefully

Arterial blood pressure Rabbits only Catheter in central ear artery, oscillometric

technique, or Doppler probe

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Blood Pressure Monitoring and Pulse Oximeter Probe

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Monitoring Anesthesia

Respiratory rate and depth Observe chest movements; no reservoir bag Normal rates during anesthesia

• Small rodents 50-100 bpm; rabbits 30-60 bpm 50% drop in bpm requires attention

Pulse oximetry Need monitor with upper limit 350 bpm Place across hind foot in small rodents Place across a toe in large rabbits Tail, tongue, and ear can also be used

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Pulse Oximeter Probe

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Monitoring Anesthesia

Capnography Side-stream vs. mainstream capnographs

Thermoregulation Increased ratio of surface area to body weight Rapid cooling during anesthesia Monitor rectal temperature with electronic

thermometer Shave a minimal surgical site Place animal on a warming pad Warm fluids prior to administration Continue warming during the recovery period

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Postoperative Care

Recovery area 95º F (35º C) while animal is unconscious 79º F-81º F (26º C-28º C) after animal is

conscious Warm comfortable bedding (synthetic sheepskin) Encouraged to eat ASAP Provide water in familiar container SC or IP warmed fluids (98.6º F or 37º C) Postoperative analgesia

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Anesthetic Emergencies

Respiratory depression Determine cause Intubated

• Check ET tube placement; administer 100% oxygen Not intubated

• Extend head and neck and gently compress chest Small rodents

• Place soft rubber tubing or syringe barrel over nose and mouth and blow gently to inflate lungs

Administer doxapram

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Assisting Ventilation in a Rat

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Anesthetic Emergencies

Circulatory failure IV fluid therapy

• SC and IP routes provide minimum benefits Blood transfusion from donor animal Plasma volume expander

Cardiac arrest External cardiac massage Emergency drugs at appropriate dose rate and

volume

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Postoperative Analgesia

Pain assessment obstacles Nocturnal animals Fear or threat response to humans by going

immobile Procedure for undisturbed animals

Observe abnormal posture or hunched body Look for hair coat that is unkempt and ruffled with

piloerection Rats: black discharge from eyes and nose Animal positioned at back of cage or buried in

bedding

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Postoperative Analgesia (Cont’d)

Procedure for disturbed animals Encourage the animal to move and observe gait or

posture and the presence of aggression Apathy or aggression when handled Vocalization (or no vocalization) and biting Immobility

Monitor food and water intake by monitoring body weight

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Analgesic Agents

Opioids Shorter duration of action Buprenorphine preferred, 6-12 hours of action Other drugs may require repeated doses Combine with NSAID

Nonsteroidal antiinflammatory drugs Carprofen, ketoprofen, meloxicam Prolonged duration of action, 12-24 hours Monitor long-term use for side effects

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Analgesic Agents (Cont’d)

Local anesthetics Infiltrated around surgical wounds or specific

nerve blocks Narrow margin of safety; calculate dose carefully Shorter duration of action Topical agents used for venipuncture or IV

catheter placement Chronic pain

Arthritis, dental disease, neoplasia NSAIDs most successfully used; monitor long-

term use

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Administration of Analgesics

IV administration Difficult in small rodents; straightforward in rabbits

IM administration Rodents have small muscle masses

SC Preferred route for rodents

Oral May require firm physical restraint Can be added to highly palatable food if animal is

eating

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Analgesia and Postoperative Rules of Thumb

Don’t recover small mammals in the same room as their predators

Preemptive analgesia administration is usually more effective than postoperative administration

Opioids administered prior to inhalation anesthesia can reduce the amount of inhalant anesthetic needed

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Analgesia and Postoperative Rules of Thumb (Cont’d) Preemptive analgesia is more difficult when

injectable anesthetics are used If opioids are being used as the analgesic

with injectable anesthetics, the opioids should be administered at the end of the anesthetic period

Not all NSAIDs can be used safely preoperatively because of their effects on the kidney and bleeding times