Special Species Dr. Bennett Flashcards
What are considered special species?
Considerations
Small mammals
incr pub awareness they are capable of experiencing pain & distress
specific challenges due to:
unfamiliar species
unfamiliar drugs
research requirements & legislation
ethical aspects of research projects
What may be some causes for anesthetic deaths in rabbits compared to dogs & cats
maybe relate to CV & resp problems
? due to large surface area:volume ration
high metabolic rate & high rish of hypoglycemia
difficult to intubate due to small size & problems of maintaining patent airway
Pre anesthetic assesment of small mammals
rats, mice & hamsters are nocturnal
rabbita are activea at dawn & dust (crepuscular)
pre anesthetic management of small mammals
No fasting due to:
Rats & mice do not vomit, prone to hypoglycemia & dehydration
Rabbits & GP experience GI disturbances leading to changes in gut flora, ileus & enterotoxemia
All spp exhibit neophobia (fear of new things) - feed usual diet
plus high-energy & high water content
all are coprophagic- avoi use of E collar
Complications seen in anesthesia of sm mammals
high risk of hypothermia
How to administer drugs to small mammals
SQ preferred into scruff or flank
IP may be unreliable
IM (avoid if volume large)
use drugs w/ wide safety margin
ideally are reversible
e.g. Alfaxalone
IV access in sm mammal spp
Rats: lateral tail v., make sure they are warm
Rabbits: auricular, cephalic & saphenous v.
GP & ferrets: cephalic v. (potentially saphenous v. also)
Use EMLA cream prior
What is most commonly used injectable in lab rodents
Ketamine
used in combo with Alpha2 agonist
Inhalant anesthetics in sm mammals
Isoflurane & sevoflurane
adverse effects well documented
can be used in all common lab rodents
isoflurane undergoes virtually no biotransformation
Considerations of inhalant anes drugs w/ sm mammals
Mask induction may be associated w/ breath holding esp in Rabbits
some aversion to inhalants due to smell in rats & mice
less with Sevo & halothane than Iso
Iso particularly irritating to GP
Airway management & intubation of sm mammals
placing ET tube narrows the airway & increases resistance to exhalation & potentiall the work of breathing
Rabbit intubation
specific laryngoscope available for rabbits
Types of breathing systems used in sm mammals
T-piece & Bain:
non-rebreathing
low resistance
need ot minimize dead space in order to prevent rebreathing
TV: 5-10 mL/kg small rodents
Maintenance of body temp in sm mammals
electric & warm water blankets available
forced hot air blankets not practical in rats & mice
recover in an incubator
Postoperative care & pain assessment in sm mammals
Can have changes in facial expression!
Opioids in small mammals
Buprenophine used most commonly
35 x as potent as morphine in rats IM
long duration of action: 3-5 h mice, 6-8 h rats
less incidence of respiratory depression
May cause pica esp in rats
analogous to vomiting in other spp
if occurs switch to non opioid analgesic
NSAIDs in sm. mammals
all drugs licensed fro use in animals can be administered in lab animals
oral meloxicam is highly palatable
duration of action not clear
8-24 hours
Local anes in sm mammals
may be suitable for some procedures in combo with GA
dont exceed:
Lidocaine 10 mg/kg
bupivicaine 2 mg/kg
Gabapentin & pregabalin in sm mammals
MAC sparing effects of gabapentin in rats using both iso & sevo
Specifice Ferret anesthesia
sedation: medetomidine & butorphanol, reversal with atipamezole
What are most commonly encountered reptiles for anesthesia
Crocodilians (alligators & crocs)
Chelonians (tortoises & turtles)
Squamates (snakes & lizards)
Species specific considerations for reptiles
Metabolism & thermoregulation
CV system
Pulmonary system
Renal system
Hepatic system
some spp terrestrial & others aquatic!
Reptile metabolism & thermoregulation
Poikilothermic/ectothermic
lower rates of metabolism compared to mammals
oxygen consumption varies from almost zero to that of a restin mammal (spp dependent)
Perferred optimal temperature zone (POTZ)
ensures optimal metabolic function
approx 20-25° C for aquatic & temperate spp
25-35° C for tropical spp
reptile CV physiology
Squamates & chelonians
3 chambered heart - 2 atria 1 ventricle
Crocodilians
4 chambered heart somewhat similar to mammals
blood can be shunted from R-L & L-R
can lead to awakening during anesthesia
may affect patient monitorin e.g. blood gas analysis & SpO2
BP varies by spp & environment
values vary between 15-30 mmHg in chelonians, 60-80 mmHg in lizards
reptile pulmonary system
Chelonians & lizards:
paired lungs
chelonians obligate nasal breathers
Snakes
single functional R lung
many also possess a R tracheal lung
functional units are ediculi & faveoli analogus to alveoli
anesthetic drugs may have more respiratory depressant effects compared w/ mammals (lack of diaphragm)
Chelonians: dorsal survace of lung is attached to carapace, ventra surface to abdominal viscera, no ribcage, mm used in locomotion are also involved in ventilation
high FiO2 may depress ventilation
recovery may be faster breathing room air (green iguana)
renal system of reptiles
blood from hind limbs & tail may pass via the kidney before returning to heart
little apparent effect on drug PK in healthy animals
preferable to avoid nephrotoxic drugs inj into hindlimbs
hepatic system of reptiles
similar in structure & function to mammals
metabolic capacity lower than mammals
thought to be responsible for prolonged recoveries seen after anesthesia
Pt assessment of reptiles
obtain bodyweight & assess gen. appearance
Maintain POTZ
Drug admin in reptiles
Snakes: IM epaxial muscles
lizards: IM triceps, biceps, quadriceps, semi-mem & semi-tend & tail
Don’t use tail in gecko!
Snakes and lizards
ventral coccygeal vein
palatine vein
Tortoise and turtles
dorsal coccygeal vein
IV catheterization
coccygeal and abdominal veins
jugular vein in tortoises
Venous sinuses
using stylet of an IV catheter
Sedatives used in reptiles
Benzodiazepines and alpha2-adrenoceptor agonists in combination injectable anesthetic drugs usually IM.
E.g. Medetomidine
◦E.g. Midazolam
both can be reversed
injectable anesthetics
Propofol
drug of choice if IV access is available
give slowly to avoid respiratory depression
CRIs have been used in Green iguanas
Alfaxalone
minimal effect on HR & ventilation
Ketamine
effects (spp/dose) dependent
recovery may be prolonged
intubation in reptile
In chelonians and crocodilians
tracheal rings are complete –avoid cuffed ET tubes
In chelonians
trachea bifurcates quite rostrallyso it is easy to intubate a bronchus
Maintenance of anesthesia in reptiles
Iso or sevo
Options
IM sedation –large and aggressive animals
ketamine +/-medetomidine or midazolam
tiletamine+zolazepam
IV induction of anesthesia
propofol
alfaxalone
Mask or chamber induction
Fluid therapy of reptiles
some debate since blood is hypotonic compared to birds and mammals
use isotonic saline diluted (9:1 with sterile water)
“reptile ringers” -> 2 parts 2.5% dextrose/0.45% saline and 1 part LRS
may use lactated of acetated fluids
some query about ability to metabolize lactate
hypertonic crystalloids and colloids may be used in hypovolaemic animals
start at 1-2 mL/kg and re-assess
anes monitoring in reptiles
ECG
differences from mammals in configuration
ETCO2
not reliable due to intra-pulmonary shunting of blood
pulse oximetry
not validated for reptilian species
◦protect the eyes
pain assessment & mgmt in reptiles
Opioids
species differences in response
some information about morphine, tramadol, buprenorphine, butorphanol and hydromorphone
NSAIDs
evidence supports the efficacy of these drugs
Meloxicam
high bioavailability PO
dose 0.2 mg/kg IV or PO
Local anesthetics
lidocaine
