9. Anaesthesia in birds and reptiles

Question 1

What are the basic anaesthetic principles?

Answer 1

• restraint and handling
• health check/weight/BCS
• food
• analgesia
• fluids
• premedication
• induction
• maintenance
• recovery

Question 2

What considerations are there for reptiles ?

Answer 2

• handling- docile, no diaphragm (pressure on the lungs)
• Vasovagal reflex- trance-like state (applying gentle pressure to eyelids), to stimulate parasympathetic nervous system
• Stimulus for respiration driven by lowered pO2
• weight (g)
• blood testing- ventral tail vein
• fasting 24hrs prior
• fluid therapy

Question 3

Which pre-medicants can we use for reptiles?

Answer 3

Acepromazine (IM) 1hr prior to induction to reduce amount of anaesthetic.

Diazepam and midazolam (IM)

Butorphanol (IM) 20 mins prior- combined with midazolam

Question 4

What is the process for induction in reptiles?

Answer 4

• never to be immobilised by chilling them down
• Ketamine (IM) usually combined with medetomidine- careful dosing, excess of 110mg/kg = bradycardia and death
• Alfaxalone (IM) - permits intubation
• Propofol (IV) - rapid induction and recovery- risk of apnoea and cardiac depression
• Gaseous induction- consider breath holding, environmental pollution

Question 5

What can we use to maintain anaesthesia in reptiles?

Answer 5

• ketamine (IM) combined with midazolam, xylazine or medetomidine
• Isoflurane- maintenance anaesthetic
• Sevoflurane- cannot be used alone, would require an injectable anaesthetic as well

Question 6

How can we monitor anaesthetic in reptiles?

Answer 6

• HR and rhythm
• Pule ox- not useful
• capnography- use is debatable due to cardiac shunting of blood
• Body temperature- cloacal probe monitoring

Question 7

How can we manage pain in reptiles?

Answer 7

• General signs- immobility, anorexia, abnormal locomotion/posture, aggressiveness
• Morphine- prolonged onset (2-8hrs)
• Carpofen (IM), Meloxicam (PO)
• Tramadol - weak opioid activity on mu receptors
• ketamine can be used as a prat of multimodal anaesthesia
• local anaesthetics lignocaine and bupivacaine

Question 8

What can aid recovery in reptiles?

Answer 8

• rapid recovery after isoflurane
• Alfaxalone or ketamine= prolonged recovery
• minimise stress
• keep patient intubated on IPPV with oxygen until reptile is breathing by itself
• Doxopram (IV/IM) - stimulate breathing
• fluid therapy

Question 9

What circulatory physiology features are important to note in birds?

Answer 9

• Birds have separate ventilatory and gas exchange compartments
• they have complete tracheal rings - less susceptible to collapse
• significant variation in tracheal length - implications for anatomical dead space
• two complete cycles of inspiration and expiration are needed to exchange the inhaled gas completely

Question 10

What circulatory considerations are there for birds?

Answer 10

• high metabolic demands necessary for flight
• proportionally larger heart
• obtaining a HR can be difficult due to high frequency
• BP to be monitored

Question 11

Why is important we monitor thermoregulation in birds?

Answer 11

• 29-43 C normal temp
• high body surface= rapid heat radiation
• once anaesthetised, birds are immobilised so less heat generated
• Anaesthesia redistributes blood flow and depresses thermoregulatory response, further promoting heat loss

Question 12

What should we look at during a pre-anaesthetic evaluation?

Answer 12

• medical history
• examination of cage (droppings)
• acclimation to new surroundings
• physical examination
• body weight
• hydration status (mucous membranes/ elasticity of the eyelid skin

Question 13

What pre-anaesthetic supportive care can we put in place for birds?

Answer 13

• fluid support (40-60ml/kg/day
• estimation of fluid replacement based on BW and dehydration %
• PO only used for mild dehydration
• SC commonly used for moderate dehydration
• Fasting- goal is to reduce regurgitation and minimise hypoglycaemia- dependant on the species

Question 14

What do need to consider prior to anaesthesia in birds?

Answer 14

• restraint (stress can kill)
• weight
• preoxygenation
• IV access (basilic, medial metatarsal or jugular vein)
• Intraosseous catheter

Question 15

What advantages or disadvantages are there to intubating a bird?

Answer 15

advantages- reduces dead space, opens airways for IPPV

disadvantages- trauma to the airway, airway resistance risk, occulated tube

Question 16

what are air sac catheters?

Answer 16

• inserted into the air sac for induction and maintenance

- adverse effects including apnoea, SC emphysema, plugging of the tube and bacterial contamination

Question 17

Which pre-medicants can we use for birds?

Answer 17

• Sedatives and tranquilisers- decreases anxiety and fear
• Alpha-2 agonists- xylazine and medetomidine (most common), dexmedetomidine can be reversed and provide analgesia
• Often used alongside benzodiazepines

Question 18

How do we induct and maintain anaesthesia in birds?

Answer 18

• ketamine with diazepam (IM/IV)
• Propofol is effective and safe if CV function is monitored
• injectable agents are preferred in comparison to inhalants
• highly variable in effects between species

Question 19

What do we monitor in birds?

Answer 19

• one person must be consistently monitoring the bird the whole way through
• blood glucose to be monitored, particularly for long procedures

Question 20

What can we do to aid recovery?

Answer 20

• connected to O2 as long as possible
• recovery signs include muscle fasciculations, wing and leg movements
• extubating once beak tone returns
• quiet, dark recovery room

Question 21

How can we monitor analgesia in birds?

Answer 21

• must be knowledgeable with normal/abnormal behaviours
• prey species can be difficult to use pain scoring- even staff can be viewed as a threat
• Opioids
• NSAIDS- ketoprofen, carprofen, meloxicam