Laboratory Animals Flashcards
Three Regulatory Bodies Associated with Welfare of Lab Animals
- USDA Animal Welfare Act
- Office of Laboratory Animal Welfare
- Guide for Care and Use of Laboratory Animals
USDA Animal Welfare Act
o All warm-blooded species except laboratory bred mice, rats, birds
o Animal Welfare Regulations (AWRs) dictate housing requirements, care during transport, enrichment requirements
Office of Laboratory Animal Welfare
NIH funded research facilitates –> all animals involved in research, teaching
Guide for Care and Use of Labratory Animal
o Minimum welfare standard for laboratory animals for husbandry, housing, etc
o Reference document for all other regulations
Three Rs
o Reduction
o Replacement
o Refinement
Pathogens-Free Species
free of pathogens, environmental pathogens
o Biological safety cabinets, sterilized equipment
o GLOVES ALWAYS
Challenges Assoc with Small Patient Size
Difficult IV access: intraperitoneal (IP), IM, SC
IP: high failure rate – inadvertent drug delivery into fat, SQ, gut tissue
Need insulin/TB syringes, 25-30g
High metabolic rate – rapid drug metabolism
Prone to hypothermia
High surface area to body weight ratio –> increase heat loss
o Ventilation: need appropriately sized circuit, equipment
Rodents - General Features
Obligate nasal breathers
Nocturnally active – almost all feeding/drinking occurs during dark phase
Post sx pain, stress during light phase can suppress activity
Short fasting periods: hypoglycemia, dehydration
Rodents - central/head features
o Protruding eyeballs: lubricant (ointment less useful)
o Lack complete circle of Willis (anastomosis of arteries at base of brain): susceptible to cerebral ischemia upon ligation of common carotid
o Idiopathic epilepsy, hereditary diabetes reported
Rodents - Resp Changes
High chest wall compliance
Low residual capacity
Robust Bohr effect: small changes in pH have stronger effect on hemoglobin ‘s affinity for oxygen
Single left lobe, right separated into four or five lobes
Rats, hamster: cardiac striated muscle extends along pulmonary vessel walls, into lung tissue making them susceptible of spread of infection between agents
Blood Volume in Rodents
60-80mL/kg (6-8% BW)
Blood collection = 10% BW
Transfusion trigger: PCV <20%
Laboratory Mice
Large incisors with broad tongue difficult intubation
Fast, agile, do not acclimate well to handling – hand restraint requires knowledge, practice
Commercial restrainers, transfer boxes/containers
Laboratory Mice Drug Access
o IV access: lateral tail veins, submandibular venous plexus (blood draw only), orbital sinus
o SQ: flank, scruff
Rat Features
No gall bladder
Heart blood supply largely extra coronary from branches of mammary, subclavian arteries
Large incisors with broad tongue difficult intubation
Acclimate well to handling, intelligent
Hand restraint requires knowledge, practice
Commercial restrainers, transfer boxes/containers
“Tickling” acclimation
Rats IV Access
IV access: lateral tail veins, saphenous vein, jugular vein
Hamsters
o Cheek pouches with orifices near the angle of mouth: source of aspirated food material if not addressed prior to anesthesia
o Don’t usually vomit
o Hibernating: become mildly acidotic
o Anesthetic mortality = 3.7%
Drug Access Hamsters
o IV: jugular, cephalic, saphenous (medial or lateral)
o IO: tibial crest, intertrochanteric fossa of femur, ileal crest, proximal humerus
Induction in Rodents
Rapid induction, easy titration of ax
Can be challenge to maintain sterility, control ax if one person doing everything
Mask induction: technically easy to perform, not routinely intubated
Increased exposure to personnel
Decreases variations btw subjects –> minimize # of animals used in a study
o Rapid recovery vs injectables
Orden et al 2021 (VAA)
MACsevo in rats unchanged by CBD alone, MAC reduction by morph not enhanced by CBD (CBD + opioids = synergistic effect)
Propofol Use in Rodents
o Propofol if IV (rats)
IP admin: inconsistent depth, not recommended
Requires IVC Placement
Telazol in Rodents
High Mortality Rate
Tribomethanol (mice) (TBE)
Common in-vitro oocyte implantations
Peritonitis, high mortality of incorrectly stored or prepared
When successful, 15-20’ ax
Urethane
Ethyl carbamate, long-lasting, stable sx ax (6-10hr)
Few CV, resp AEs
Non-recovery procedures: CNS studies
* Depressed spinal reflexes, EEG comparable to sleep patterns, ANS reflexes preserved
Water soluble, metabolized by liver into ethanol+carbamic acid, renal excretion
Urethane MOA
- GABAA 23%
- a1 glycine R agonist 33%
- NMDA R antag 10%
- AMPA R antag 18%
- +/- AChR?
Adverse Effects of Urethane
IP: endocrine, metabolic effects = peritonitis, necrosis of abdo contents, massive leakage of plasma in pleural cavity
Carcinogen: PPE, proper disposal
alpha-chloralose
Numerous dose-dependent excitatory, inhibitory CNS effects
Long-lasting light ax with minimal CV effects
Prolonged induction, recovery – insufficient depth for sx
Analgesics in Rodents
Buprenorphine most commonly used: 35% of rodents that receive analgesia
Consider SR formulas – up to 72hr in mice, rats
* 40% rats skin irritation
Poor PO avail 5-10%, significant first pass hepatic metabolism –> PO DOA 1-2hr
SE: pica behavior
SE Opioids in Rodents
o Immunosuppression with very high doses of opioids for prolonged periods, potential effects on tumor growth
Ventilation in Rodents
rodents normally maintain themselves at 1:1IE
1:2, 1:3 to minimize effects of PPV (prolong expiratory time) on CV system
Depth in Rodents
o Depth: pedal withdrawal, auricular reflexes
o Minor changes in heart rate, respiratory rate equal indicators of changes in depth
CV Monitoring in Rodents
Pulse oximetry: pulsatile flow of RBCs past probe required
HR > 400bpm may cause difficulty in acquiring reading
ETCO2: requires intubation, limitations with both mainstream and side stream
BP:
Constraints with BP cuffs DT small patient size
High heart rate can decrease accuracy of oscillometric readings
Difficult to find artery for catheterization
Positioning of Rodents
little horses – weight of organs on diaphragm limits appropriate depth of breath
Ensure straight head slash neck for better air flow in non intubated patients
Pain Assessment in Rodents
Grimace scores validated for mice, rodents
Pain assessment: hunched posture, bruxism, grimace, tachycardia
Recovery of Rodents
–Ensure warming, avoid excessive fluid admin to minimize hypothermia = recover, eat quickly
–Home cage: no particulate bedding to avoid airway obstruction
–Often housed in corn cob bedding, replace with paper towel
–Keep separate from others while recovering: will attack, esp males
Clean off all detergents, chemicals from skin
–Grooming: may consume toxic small quantities from fur
Gel based hydration, electrolyte packs in cage
Common Peri-Anesthetic Complications with Rodents
o Hypothermia
o Insufficient depth of ax, movement – esp with mask maintenance if move nose from cone
o Excessive depth
o Labored respirations +/- resp arrest
o Inadvertent inj into spleen, GIT via IP
Delayed onset, slow recovery
o Difficulty monitoring: specialized equipment, patient visualization
Features of the Mouse Grimace Scale
Orbital tightening: closing of eye = pain
Nose bulge: bulging on nose bridge, squinting of face = pain
Check bulge: see nose bulge
Ear Position: rotate outward, backwards away from face - space btw ears increased
Whiskers: pulled back or stand on end, lose downward curve - pointed up
Features of the Rat Grimace Scale
Share same features of mouse grimace scale EXCEPT have flattening of nose, cheeks not bulging with pain
Gent et al 2019 (VAA)
Xe less aversive than CO2 when using 30% chamber vol/min fill rate, could improve welfare of mice
Did not show jumping, freezing behaviors, decreased locomotion
EEG: sedative effects from Xe, heightened arousal from CO2
Rabbit Mortality Rate under GA
1.39-4.8%, ill rabbits >7%
o Prey species, adept at hiding illness
Drug Access in Rabbits
IV access: marginal auricular, saphenous, cephalic
Auricular: risk necrosis
IO: trochanteric fossa of femur, greater tubercle of prox humerus, wing of ilium, tibial tuberosity
Chung et al 2022 (VAA)
ears that had EMLA cream applied for >60’ before catheter attempt = 10x more odds of successful catheter placement, EMLA or lido cream 10’ prior = 3x
Rabbits and Fasting
Fasting not required/recommended – inability to vomit, impt for normal GI motility
Alterations to gut flora, ileus, enterotoxemia
Functional ileus = fatal
Rabbits and Neophobia
(reluctant to eat, try new foods): offer palatable high energy, high water content supplements
Rabbits and Corprohagia
(eat stool): avoid inadvertent prevention by Elizabethan collar
Anticholinergics in Rabbits
Atropinease: present in 1/3-1/2 rabbits, faster metabolism of atropine
o Glyco recommended
Which opioid has been shown to have no effect on GI motility in rabbits?
Buprenorphine
Reabel et al 2022 (VAA
Blind vs endoscopic techniques
both techniques assoc with laryngeal damage, blind orotracheal intubation assoc with higher number of attempts, endoscopic groups required more dexmed/alfax
Anatomical Challenges with Rabbit Intubation n
Long, narrow oral cavity with fleshy tongues
Long incisors
Difficult visualization
Very sensitive to laryngeal stimulation – vasovagal reflex
Obligate nasal breathers
Epiglottis entrapped on dorsal surface of soft palate
(beneficial with nasotracheal intubation)
other techniques to intubate rabbits
Supraglottic airway device (VGEL), mask, nasotracheal intubation
Inhalants in Rabbits
More sensitive to vasodilatory effects of inhalant anesthetics than other species: hypotension occurs at levels of 1 MAC
Dopamine, phenylephrine tend to be ineffective – NE
Fentanyl, lidocaine, ketamine CRIs
Blood Pressure Measurement in Rabbits
Oscillometric moderately accurate FL normal-low pressures, less sensitive at detecting hypotension
Desprez et al 2022 (VAA)
vs cd aortic ABP in sevo ax rabbits, cuff with 41% ratio (2cm) on thoracic limb = best estimation of MAP vs cuff with 50% ratio (2.5cm), measurements on hind limb
Assessment of Depth in Rabbits
sx palpebral absent, corneal reflex present, deep/reg resp pattern, toe pinch absent (reliability: HL > FL)
Blood Glucose in Rabbits
prognostic indicator: stressed rabbits increased BG vs non stressed
High BG at presentation with obstructive ileus vs non
Edis et al 2022 (VAA)
rabbits undergoing OVH in theatre temp of 28C = significantly higher temp vs 23C, did not affect return to feeding/defecating
Location for IBP in Rabbits
central auricular artery
Features of the Rabbit Grimace Scale
Orbital Tightening
Cheek Flattening
Nostril Shape
Whisker Shape, Position
Ear Shape, Positionin
Features of the Bristol Rabbit Pain Scale
- Demeanor - looking around vs non responsive
- Locomotion - active vs not
- Posture - comfortable vs tense, stiff, hunched
- Ears - freely move toward sound vs no moment
- Eyes - open vs closed/tight
- Grooming - grooms vs no
Guinea Pigs and Chinchillas: Mortality Rate
3.8% for GPs, 3.3% for chinchillas
Respiratory Features of GPs, ChC
Lung fields: small due to combination of comparatively large hearts, profuse GI volume
High chest wall compliance
Low FRC
More alveoli with thinner diameters to maximize oxygen exchange
Vomiting in GPs, ChCs
Don’t usually vomit: lack coordinated brainstem response to complete emetic episode
Also reduced muscularity of diaphragm, long abdominal esophagus length, small abdominal esophageal circumference, medial position of esophagus in stomach
GP, ChC: fasting
Fasting not required/recommended – inability to vomit, impt for normal GI motility
Alterations to gut flora, ileus, enterotoxemia
Normally retain food in oropharynx
Can consider fasting zero to 8 hours for food, zero to two hours for water due to reduction of food material in oropharynx, reduce incidence of passive regurgitation, potentially reduced GI volume (probably negated by cecum)
Neophobic, coprophagic
Premedication in GP, ChC
o Prior to PMs: rinse oral cavity, clear mouth of food material using cotton tip applicators 30 to 60 minutes prior to anesthesia
Anatomic Challenges of GP, ChC Intubation
Long, narrow oral cavity
Difficult to visualize
Palatal ostium – central opening btw caudal tongue, soft palate (2-3mm)
Deviation of tube = damage to velopharyngeal folds
How to Intubate GP, ChC
Endoscopic assisted – rigid endoscope, otoscope, vaginal speculum
Guidewire advanced into airway
Airway mucosa = fragile
Potential for blood to obscure view, aspiration of blood, laryngeal trauma, tracheal tears, airway obstruction DT swelling
Alvarez et al 2022 (JAVMA)
SQ alfax 5mg/kg – reliable sedation for non-painful procedures in GPs, midaz 0.5mg/kg + alfax 5mgkg = longer, deeper sedation, more significant in adults
Mask Induction for GPs, ChCs
particularly irritating to GPs if used for mask induction
o Iso: ocular, nasal discharge > sevo: less lacrimation
o Least irritating = halothane
Monitoring for GPs, ChCs
Same as Rodents
NHP
New World (NW NHP) – trees – marmosets, tamarains, capuchins, tropical monkeys (owl, spider, howler, squirrel)
Old World (OW NHP) – scary – Baboons, macaques, Great Apes
Safety Considerations with NHPs
Sensitive nature for using NHPs
o Very intelligent, always thinking
Escape risks
Prehensile hands, fingers – may remove/reflect darts, pole syringes
Strength: ability to pull, scratch, bite
o Sharp teeth, long powerful limbs, +/- prehensile tail
o Handling to conscious NHP avoided DT stress to animal, risk of physical injuries to operator, risk of traumatic injury to patient
Disease Transmission Assoc with NHP
Cercopithecine Herpesvirus B endemic in macaques – fatal to humans, PPE
Tuberculosis – humans –> NHP, NHP–> humans
Measles – humans –> NHP
Other herpesviruses = reverse zoonotic danger to great apes, btw species
fasting guidelines in NHP
Monogastric: Fasting 6-8hr, 2-4hr in marmosets/tamarins
Allow access to water, electrolyte solution (Gatorade, clear Ensure)
Smaller sap-eating species prone to hypoglycemia
Other Considerations of NHP
Social animals: group housing
Segregate but should remain in sight/presence of conspecifics
Will usually be suspicious, know something up
PE, minimum database often performed under sedation, IV access via superficial veins
Gorillas: middle tibial vein (??)
NW NHP: caudal tail vein
Ketamine in NHP
Assoc with long-term cognitive impairment in NHPs if admin during sensitive period for brain development eg in utero, during first week of life
Tolerance: 3 consecutive days = increased time to recumbency by 35%
Airway Management with NHPs
Fasted: can regurgitate, vomit intubation recommended
Visualization = challenging
* Wide range of vocalization DT caudal descent of larynx (s resonance capacity), large part of tongue to be in hypopharynx – restricts visualization
Rich vascularization of larynx – prone to injury
Other Features that Make Intubation Difficult with NHPs
Positioning: consider dorsal recumbency on tilt table to maximize alignment of PO cavity with pharynx
Diameter of larynx, trachea smaller than species of equal weight
Copious secretions = thicker with anticholinergic administration
Damage to vocal chords VERY significant in these species!
Depth of ETT in NHPs
Proximal bifurcation of trachea, avoid passing tube past point of scapula (macaque)
Marmosets: length of trachea predicted = 0.42(craniosacrolength)
Analgesia in NHP
o LJ: no current scale that definitely assess pain in NHP
o Tend to hide behavioral signs of mild or moderate pain from unfamiliar observers, best monitored by familiar handler or remotely
o All commonly available analgesics can be used, long acting formulations preferred
Meloxicam – particularly palatable
Ferrets
Anesthetic mortality = 0.33%
Opioids: emetic effect, consider maropitant or ondansetron
Presumed to be MAC-sparing in ferrets
Best indicator of depth = jaw or masseter muscle tone
Prone to both hyper and hypothermia
BG monitoring: insulinomas common
Hedgehogs
Mantle (keratinaceous spines), roll into ball – difficult to examine
Narrow oral pharyngeal cavity
Caudally located pharynx
Prominent tongue base and large tonsils
Epiglottis = broad with a prominent apex, normally dorsal to soft palate and must be displaced to visualize the glottis
Which pocket pets are obligate nasal breathers?
Rodents
Rabbits
GPs, ChCs
NOT ferrets, SGs, HHs,
IV Access in HH, SG
HH: cephalic, saphenous veins
SG: virtually impossible
Premedication/Sedation in HH
HH: midaz + torb, +ket to deepen/lengthen
IN midaz effective
Alfaxalone also effective SC, IM
Telazol: no real effect of flumazenil
Premedication/Sedation in SGs
midaz can go IN, Telazol controversial – neurologic signs, death
Induction with SGs, Has
Chamber induction most common, monitor posture changes
SG: recumbent
* May vomit
HH: no longer assume defensive posture
* Rarely vomit
Intubation for HH, SGs
o Intubation is challenging
o Consider endoscopy using rigid tube or smaller, semi rigid fiber optic endoscopes and the use of stylets
o Helpful to have small Miller blades
o Usually need 1-2mm ETT for HH, 1-1.5mm ETT for SG
o Often maintain via face mask due to difficulties intubation
o Can use small rabbit V gel in larger HH (360-700g)
Recovery of His
brief period of tachypnea often occurs before arousal, attempted self removal of airway device
Recovery of SGs
self-mutilation following surgery very common, close monitoring during recovery essential
