2. Rabbit Anesthesia Flashcards
Why should we NOT compare rabbits to dogs and cats?
higher metabolic rate, smler reserves of glycogen predisposes to hypoglycemia
higher O2 consumption so reduced tolerance to hypoemia
hypothermia: high body surface area to V ratio, radiant heat loss - cover patient, evaporative heat loss (clip as minimal as necessary, minimize use of scrub and alcohol solution
What is unique about the respiratory system of rabbits?
visualization of larynx is difficult
prone to laryngospasm
obligate nasal breathers
thoracic cavity: very small, small tidal volume (4-6ml/kg)
clinical and subclinical resp dz (P. multocida)
be careful with positioning bc lg abdominal organs can push against diaphragm
What is unique about the digestive system of the rabbit
Allow water up to premed
can NOT vomit
fast rabbits 1-2hrs to reduce presence of food in oral cavity
check for food in oral cavity - clean w/ cotton swabs (guinea pigs)
post-op ileus is common, predisposing factors: pain, starvation, stress, diet change, drugs
encourage to eat in post-anes period
What do we need to consider with small mammal anesthesia?
Accurate dosing of drugs: accurate BW, dilute drugs if necessary, use appropriate syringe size (insulin syringe)
Anesthesia protocols: don’t extrapolate from other species
Compression of thoracic cavity: hands, instruments, drapes
What is the average blood volume of a rabbit?
50-78ml/kg
they have less tolerance for hemorrhage
A cotton tip applicator can hold 0.17ml of bleed
A 4x4 gauze sponge can hold 7ml of blood
What is the anesthetic mortality of rabbits?
overall: 1.39-4.8%
sick: 7.37%
Post anesthesia: 64%
Perianasthesia GI: 38%
What increases the anesthetic risk in rabbits?
Stress (prey species): provide a rabbit friendly environment, use premed to reduce stress during induction, minimize handling, pain management
Underlying dz - malnourished (dental tx) and dehydration, sub-clinical resp dz (pasteurellosis), uterine carcinoma
Failure to address perioperative issues
Lack of familiarity and expertise bc of size, ETT technically demanding, fewer veins for catheter, pain
inc risk of hypothermia (slow metabolism and delayed recovery)
Prolonged procedures > anesthesia time > ileus
Supportive care will reduce anesthetic morbidity and mortality
What is your normal pre-op blood tests
- PCV: 34%–43%
- TP: 5.0–7.5 g/dL
- BG: 4.1–8.2 mmol/L
- Blood glucose can be used as a prognostic indicator (stress, clinical disease)
- BUN 15-30 mg/dL
How can we avoid disaster with rabbit anesthesia?
Be prepared, know normals, full clinical exam and hx, consider pre-op blood work
stabilize condition b4 anesthesia, don’t starve, accurate rate
always calculate doses for anesthetic agents, reversals and emergency drugs
What is the normal HR, temp and RR of a rabbit?
Heart Rate 200-300
Respiratory Rate 32-60
Temperature 38.5-39.5
What are some anesthesia and procedure related complications?
hypothermia/tension/ventilation
hypoxemia
Bradycardia
procedure: pain, hemorrhage
What drugs might we use in rabbits for premed?
Acepromazine, midazolam, dexmedetomidine, opioids, anticholinergic drugs
How is acepromazine used for rabbit anesthesia?
- 0.1-0.25 mg/kg (IM, SC, IV)
- Long duration, not reversible – prolonged recovery
- Peak effect after 30-45 min
- Hypotension: peripheral α1 receptor blockade – vasodilation
- Only use in healthy animals
Very long lasting (6-8hrs), not reversable
How is midazolam used in rabbit premed
- 0.5 - 2mg/kg (IM, SC, IV)
- Water soluble can be administered IM
- Minimal cardiopulmonary effects
- Produces moderate sedation and muscle relaxation
- Reversal: Flumazenil (0.05-0.1mg/kg IV, IM)
- Combine with an opioid
How is dexmedetomidine used in rabbit premed?
- 0.02-0.05mg/kg (IM, SC)
- Mild to profound sedation
- Respiratory and cardiovascular depression
- Peripheral vasoconstriction
- Reversible with Atipamezole
- Combine with an opioid
How is opioids used in rabbit premed?
- Provide analgesia and will increase sedation
- Reversible with Naloxone (0.01-0.1mg/kg, IM, IV)
Buprenorphine - 0.05 - 0.1mg/kg (IM, SC, IV), 6-8 hours
Butorphanol - 0.5 - 2 mg/kg (IM, SC, IV) 2 hours
Hydromorphone - 0.1- 0.3mg/kg (IM, SC, IV)
Methadone - 0.3-0.7 mg/kg (IM, SC, IV)
How are anticholinergic drugs used in rabbit premed?
- Not routinely administered as premedication
- Used to treat bradycardia
- Negative effects on gastrointestinal motility!
Atropine - 0.1-0.2 mg/kg (IM, SC, IV)
- 61% of rabbits possess atropine esterase
Glycopyrrolate - 0.01-0.1mg/kg (IM, SC, IV)
What do we need to do when inducing rabbits?
always preoxygenate
always monitor during induction/intubation
have monitoring attached to patient
IV cath, have enough induction agent
masking down should not be first option for rabbits - humane exposure, stressful, not enough time to intubate
What are the injectable induction agents for rabbits?
KETAMINE (1- 5 mg/kg, IV, IM)
* Combine with benzodiazepine (midazolam 0.5mg/kg)
* High doses (up to 25mg/kg) can provide surgical anesthesia
PROPOFOL (2-8 mg/kg, IV)
* Requires IV access prior to induction
ALFAXALONE (1-4 mg/kg IV)
* Could be given IM – large volume
TITRATE TO EFFECT TO AVOID INDUCTION APNEA
KETAMINE (1- 5 mg/kg, IV, IM)
* Combine with benzodiazepine (midazolam 0.5mg/kg)
* High doses (up to 25mg/kg) can provide surgical anesthesia
PROPOFOL (2-8 mg/kg, IV)
* Requires IV access prior to induction
ALFAXALONE (1-4 mg/kg IV)
* Could be given IM – large volume
What do we need to keep aware of when using volatile induction agents?
should only be 2nd choice to IV induction
always use w/ premed to reduce stress and struggling
beware of breath holding
apnea induced bradycardia
introduce volatile gradually
pre-oxygenate if possible
oxygen flow rates greater than 100ml/kg/min with well fitted mask
What volatile agents are used for induction?
ISOFLURANE
* MAC: 2.5%
* Pungent smell – breath holding more likely
* Induction apnea
SEVOFLURANE
* MAC 3.5-4.1%
* Less pungent – better tolerated
* Faster induction ? - Depth of anesthesia may alter more rapidly
* Induction apnea
What is a facemask?
Mask for volatile agents
close fitting: reduces envirocontam, avoid inhaling of room air
Diaphragm can be adapted using an exam glove
clear: visual assessment
low V: minimize dead space
What is lidocaine constant rate infusions?
prokinetic effects
improved food intake and fecal output in rabbits following OHE
anesthetic sparing (reduces iso MAC)
analgesia
anti-inflam/anti-endotoxin
How do we intubate a rabbit?
can use a mask, or v-gel (supraglottic airway device)
or blind intubation, can do direct visualization (videoendoscope, laryngoscope, otoscope
Why do we intubate rabbits?
protects airway, allows efficient oxygen supplementation, allows positive-pressure ventilation, reduces human exposure
What do we need to keep in mind with rabbit intubation?
- 2.0 -3.5mm (un)cuffed ET tube
- Ensure rabbit is adequately anesthetized
- Pre-oxygenate
- Prone to laryngospasm: Use lidocaine (careful toxic dose)
- Sternal recumbency with hyper-extended neck
- to align the larynx and the trachea with the oropharynx
- Continuously monitor heart rate during induction/intubation
What are some intubation techniques?
blind method (no visualization of the glottis
technically difficult initially
easy and quick to perform once experienced
no extra cost, possible damage to glottis and risk of laryngospasm, possible unsuccessful due to entrapment of epiglottis
risk of aspiration if unnoticed presence of food in pharynx
How do we blind intubate rabbits?
- Premeasure ETT/atomizer to level of larynx
- Sternal recumbency and hyper-extend neck
- Insert ET-tube to pre-measured point
- Condensation appearing in tube during expiration
- Instill lidocaine 2% (neat) via small catheter/atomizer through ET tube
- Gently advance ET-tube during inspiration while:
- Listening at the connector end of the tube
- Watching capnograph
How do we confirm tracheal tube placement?
ventilate and listen for resp sounds on both sides of thorax
use capnograph
coughing
Watch for condensation ( fogging of tube during expiration)
repeated attempts of intubation are not recommended. Risk of laryngeal trauma and spasm > resp obstruction
How do we intubate using the laryngoscope/otoscope?
direct visualization
* Can move soft palate and expose the glottis if necessary
* Technically challenging compared to dog/cat
* Unexperienced user can cause tissue damage
* Minimal equipment necessary: laryngoscope/otoscope + stylet
What is the procedure for intubating with direct visualization?
- Sternal recumbency and hyper-extend neck
- Requires an assistant to open the mouth
- Hold rabbit’s mouth wide open
– Use bandage material as retractor - Gently pull tongue out of mouth
- Use small laryngoscope
- Insert ET tube
What is the endoscopic intubation method?
- Direct visualization allows rapid and accurate intubation
- Technical challenging – learning curve
- No risk of aspiration or soft tissue damage
- Expensive equipment needed
- Side-by-side or endoscope can act as stylet
What complications might we run into with rabbit intubation?
- Difficult placement
- Laryngospasm
- Trauma to the oropharyngeal soft tissue
- Tube dislodgement, occlusion, and kinking
- Postintubation oropharyngeal swelling
What is the supraglottic airway device?
Always use with capnograph
Can be easily dislodged when animal is moved
faster placement than ETtubeation
Less trauma than blind intubation
Why might we need IV access?
Cephalic, lat saphenous, marginal auricular vein (complications: sloughing, chemical phlebitis, mechanical irritation from catheter or bandage”Dont use central auricular artery
Fluids: 10ml/kg/hr (+/- 2.5%-5% dextrose)
How do we monitor anesthetic depth?
Palpebral reflex, eye position: unreliable
nicitans membrane will move over cornea
corneal reflex should be maintained
CV system: auscultation, doppler, pulse oximetry: ear, tongue, digit
ECG
Temp (avoid hypo and hyperthermia)
What is the post-op care like for rabbits?
Analgesia: NSAID (meloxicam 0.5-1mg/kg SQ), Opioids (buprenorphine, hydromorphone, butorphanol
Stress free enviro, continue to monitor
Prolonged recover > check for hypothermia and hypoglycemia
residual drug effects (reversals)
Feed as soon as possible
