FTK 4: Large Animal Anesthesia Flashcards
premedication options for horses? (3)
alpha-2 agonists, acepromazine, opioids
acepromazine in horses
goal?
administration?
method of action?
reversal agent?
risks?
PREMEDICATION
goal = to produce CALMING effect & NOT ANALGESIC, but can enhance other analgesic drugs’ activity
administration = PO, IV, IM
method of action = BLOCKS dopamine centrally & peripherally, causes adrenergic blockade that causes HYPOTENSION
reversal agent = none
risks = can cause PARAPHIMOSIS in stallions
alpha-2 agonists in horses
what types of drugs are these?
examples of drugs?
goals?
clinical signs it causes?
risks?
PREMEDICATION, THE MOST COMMON
phenothiazine tranquilizers
examples of drugs?
1. xylazine (LEAST alpha 2 to alpha 1 specific)
2. romifidine
3. detomidine
4. dexmedetomidine (MOST alpha 2 to alpha 1 specific)
goals?
RELIABLE sedation, sometimes can cause spontaneous reactions
clinical signs it causes?
hypotension
bradycardia
decreased GI motility
risks?
2nd degree AV block
SEIZURES if injected into carotid accidentally
opioids in horses
examples of common drugs?
risks?
examples?
1. butorphanol
2. morphine
risks?
dramatic excitatory reactions
GI stasis
what kind of pain does morphine treat MOST potently?
SUPERFICIAL pain, not as good with visceral pain
3 sites for IV administration in horse? what’s the most common?
- jugular vein (most common)
- cephalic vein
- lateral thoracic vein (over thorax)
4 goals of premedication in horses?
- analgesia
- muscle relaxation
- reduced amount of induction & maintenance anesthetic drugs
- improved quality of induction & recovery
what 3 things must be done prior to induction in horses?
- put on a SOFT halter
- rinse out mouth
- give adequate sedation (alpha-2 agonists, likely dexmedetomidine)
what 2 kinds of drugs are given PRIOR to induction in horses?
for SEDATION…
alpha-2 agonists like dexmedetomidine to help PREVENT excitatory reactions while inducing
for MUSCLE RELAXATION…
benzodiazepines (midazolam/diazepam) & guaifenesin
4 kinds of drugs used FOR induction in horses? (often given alone or not?)
- benzodiazepines (midazolam & diazepam)
- propofol
- ketamine
- guaifenesin
Often given IN CONJUNCTION
benzodiazepines in horses
2 examples?
pros?
cons?
examples = midazolam & diazepam
used as co-induction agents
pros?
1. reduces anesthetic drug requirements
2. minimal cardiovascular compromise
3. muscle relaxant
cons?
1. ataxia
2. long duration of action
3. can cause profound excitatory reactions
guaifenesin in horses
can be used as ____
= definition
something special about the product
INDUCTION agent
= centrally acting skeletal muscle relaxant
COMPOUNDED product
ketamine in horses
can be used as ____
= definition
effects when used alone?
often given with ___ & ___
reversal available?
INDUCTION agent
= dissociative NMDA receptor antagonist that acts as an indirect sympathomimetic
effects when used alone?
–> swallowing, nystagmus, laryngeal/eye reflexes, muscle rigidity, tearing
often given with MUSCLE RELAXANTS (benzodiazepines & guaifenesin) to prevent effects alone
NO REVERSAL AVAILABLE
what should we check for after induction but prior to tubing in horses?
PULSE QUALITY AND PRESENCE
what 3 things are needed for intubation in horses?
- ET tube
- cuffed syringe
- Bite block
3 steps for blind orotracheal intubation in horses? what might be needed?
- make sure HEAD AND NECK are extended, and pull tongue out to the side through the DIASTEMA
- Place bite block between incisors
- Advance ET tube through the oropharynx, larynx, then trachea
Might need an ENDOSCOPE for guidance
3 types of drugs & examples for MAINTENANCE of anesthesia in horses?
- INJECTABLES
used for SHORT procedures like FIELD CASTRATIONS (30-45 minutes)
- triple drip (guaifenesin/midazolam, acepromazine, xylazine)
- multiple ketamine boluses CRI
- propofol - INHALANTS
used for LONG procedures (45+ minutes)
- isoflurane
- desflurane
- sevoflurane - ADJUNCTIVE agents
used in CONJUNCTION with inhalants or injectables to help LOWER anesthetic requirements; done via LOCOREGIONAL technique
- alpha-2 agonists –> help reduce MAC for inhalant anesthetics
- lidocaine CRI
what type of anesthesia machine is often used in LA medicine? what’s the average size in kg and tidal volume for a horse?
PISTOL-driven to ensure MORE ACCURATE TIDAL VOLUME DELIVERY
avg horse size = 450 kg
avg tidal volume = 7-8 L
what 5 clinical signs do we use as parameters during MONITORING for equine anesthesia?
- palpebral reflex
- corneal reflex
- eye position
- nystagmus
- lacrimation
TOO LIGHT vs. APPROPRIATE vs. TOO DEEP for 5 clinical signs during MONITORING for equine anesthesia
TOO LIGHT
palpebral reflex = brisk
corneal reflex = brisk
eye position = central
nystagmus = rapid
lacrimation = present
APPROPRIATE
palpebral reflex = slow
corneal reflex = present
eye position = VENTROMEDIAL
nystagmus = absent or slow
lacrimation = absent
TOO DEEP
palpebral reflex = absent
corneal reflex = absent
eye position = central
nystagmus = absent
lacrimation = absent
7 medical tools for EQUINE MONITORING
- ECG = HR & rhythm
- INVASIVE blood pressure via arterial catheter; **Non-invasive less accurate for adults but OK for minis/foals
- SpO2 (pulse ox for pulse)
- EXPIRED CO2 & inhalant concentration
- INSPIRED O2, CO2 & inhalant concentration
- Arterial blood gas for OXYGENATION
- Body temperature
what type of lead placement is used for HORSES? name 3 locations
BASE-APEX lead placement
R arm = JUGULAR GROOVE or WITHERS
L arm = BEHIND ELBOW
L leg = INGUINAL AREA or PECTORAL MUSCLE
4 arteries that can be used for INVASIVE BP in HORSES?
- transverse facial artery
- facial artery
- auricular artery
- lateral metatarsal artery
equine RECOVERY from anesthesia
time at which there’s the HIGHEST CHANCE OF MORBIDITY & MORTALITY
need to give SEDATION via alpha-2 agonists + acepromazine to allow animal to REGAIN COORDINATION before trying to stand
can EXTUBATE once horse SWALLOWS
animal should go from LATERAL to STERNAL position
make sure REDUCED STIMULI –> put BLINDFOLD on eyes/ears
5 different approaches to equine anesthesia recovery?
- UNASSISTED but SUPERVISED
- Head-and-tail rope
- Mat recovery
- Sling recovery
- Pool recovery
5 different COMPLICATIONS that can arise in HORSES from anesthesia RECOVERY?
- MUSCULOSKELETAL
- fractures
- myopathy - RESPIRATORY
- obstruction
- pulmonary edema - OPHTHALMIC
- corneal ulceration - CARDIOVASCULAR
- NEUROPATHY
4 main concerns for RUMINANTS while under anesthesia?
- SALIVATION –> high during anesthesia
- REGURGITATION –> can cause ASPIRATION, from RUMEN SHIFTING
- BLOAT –> esophageal opening CLOSED in recumbency, STOPS ERUCTATION
**If rumen gets enlarged, can DECREASE CO - HYPOVENTILATION –> worsens with bloat
preanesthetic PREPARATION (3) in ADULT BOVIDS & CALVES/SMALL ruminants
(1) FOOD RESTRICTION = **IF ANIMAL IS EATING SOLID FOOD, THEN NEED TO RESTRICT!! WANT TO PREVENT REGURGITATION/ASPIRATION
ADULT bovids
- Feed = 24-28 hours
- Water = 6-12 hours
**Can auto-hydrate & auto-feed off of rumen, so need to decrease water and food components
CALVES/SMALL ruminants
- Feed = 12 hours
- Water = 6-8 hours
(2) PHYSICAL EXAM
(3) IV CATHETERIZATION
- USUALLY JUGULAR
- cephalic & auricular also options
PREMEDICATIONS for RUMINANTS (adult bovids vs. calves/small ruminants)
adult bovids
1. ALPHA-2 AGONISTS –> CAUTION, ruminants are much more sensitive to them (1/10 of a horse dose, 1/20-1/30 of a swine dose)
2. ACEPROMAZINE
calves/small ruminants
1. BENZODIAZEPINES –> can usually use MIDAZOLAM alone
2. +/- OPIOIDS –> butorphanol or morphine
why should we NOT give alpha-2 agonists to calves/small ruminants?
causes changes in their alveolar MACROPHAGES, leading to pulmonary edema, hypoxemia & death
INDUCTION agents in RUMINANTS (all)
usually use both MUSCLE RELAXANTS & INJECTABLES
Muscle relaxants
1. BENZODIAZEPINES
2. GUAIFENESIN
INJECTABLES
1. KETAMINE
2. PROPOFOL
CONCERNS for SMALL RUMINANTS during INDUCTION? (4)
- CANNOT OPEN MOUTH MUCH –> HARD TO INTUBATE
- narrow intermandibular space
- thick tongue base - REGURGITATION/ASPIRATION –> need suction tool readily available
- SALIVATION
- HEAD/NECK MUST BE EXTENDED
SMALL RUMINANT POSITIONING & INTUBATION
Positioning can be STERNAL OR LATERAL
Intubation = using DIRECT LARYNGOSCOPY, INSERT STYLE & pass ET TUBE OVER IT
CONCERNS for RUMINANTS/CALVES during INDUCTION? (3)
- REGURGITATION/ASPIRATION
- SALIVATION
- POSITIONING
ADULT BOVID INTUBATION & note about nasogastric tubes
often via DIGITAL PALPATION
- stick finger into oral cavity & over trachea/stylet, put ET tube over it and remove stylet
**nasogastric tubes may require stylets as well!
CALF INTUBATION (position & method)
position = STERNAL recumbency
method = DIRECT LARYNGOSCOPY +/- stylet
MAINTENANCE of anesthesia in ruminants? (2 types & examples)
- INJECTABLES
- usually given CRI
- KETAMINE
- PROPOFOL
- BENZODIAZEPINES - INHALANTS
- often given WITH INJECTABLE CRI to help REDUCE MAXIMUM DOSE OF INHALANT NEEDED because RUMINANTS ARE SENSITIVE
- iso, sevo, des
how do we know when RUMINANTS are at appropriate anesthetic depth?
eye will roll STRAIGHT VENTRALLY, so can ONLY SEE SCLERA
if CENTRAL, then TOO LIGHT or TOO DEEP
tidal volume and RR in RUMINANTS vs. HORSES
Ruminants have LOWER tidal volume and HIGHER RR than horses
parameters/equipment for ruminant anesthesia (8)
- ECG (HR & rhythm)
- BP –> USUALLY invasive, sometimes non-invasive
- Tidal volume
- RR
- Mucous membrane color
- CRT
- Body temperature
- SpO2
POSITIONING for ruminants DURING anesthesia?
should be on PADDED MAT with HEAD DOWN so that SALIVA & REGURGITANT MATERIAL CAN DRAIN
RECOVERY for ruminants (how they recover, in what position/why, extubation)
- usually recover QUIETLY & don’t try to MOVE PREMATURELY LIKE HORSES
- usually in STERNAL RECUMBENCY WITH HEAD DOWN so that ERUCTATION & LIQUID CAN LEAVE MOUTH (prevent aspiration)
- ET tube can be left in for O2 supplementation, EXTUBATION when CHEWING & SWALLOWING
CAMELID ANESTHESIA (not much for this)
1. premedication
2. induction
3. intubation
4. maintenance/monitoring
5. recovery
- premedication = ALPHA-2 AGONISTS
- induction = depends HIGHLY ON BEHAVIOR
- intubation = DIFFICULT, has LONG SOFT PALATE & HIGH RISK OF REGURGITATION
- maintenance & monitoring = neck can be EASILY DAMAGED if in wrong position
- recovery = relatively smooth
BEFORE surgery protocols for pigs (2)
- WITHHOLD FOOD/WATER because risk of VOMITING during perianesthetic period
- stop feeding night before procedure, can still have water - CAN try and give ANTI-EMESIS drugs prophylactically via AURICULAR catheter, but HARD because pigs are behavioral nightmares
PREMEDICATIONS in pigs & how they’re all administered (3)
**note about BIG pigs
GIVEN IM!
- butorphanol (opioid)
- midazolam (benzodiazepine)
- dexmedetomidine (alpha-2 agonist)
*BIG pigs can use DETOMIDINE
INDUCTION agents in pigs
INJECTABLES ARE MOST COMMON!
- ketamine or propofol
Can ALSO use inhalants via MASK
SPECIFIC considerations in PIGS for anesthesia (7)
- EPIGLOTTIS sits on TOP of the soft palate, so we must DISPLACE SOFT PALATE to INTUBATE ORALLY
- prone to LARYNGOSPASMS
- larynx has VENTRAL FLOOR FORNIX/twist; must TWIST ET tube once past larynx
- tube can get stuck in PHARYNGEAL DIVERTICULUM
- NARROW mouth opening/oropharyngeal space
- THICK tongue also has DORSAL PROTRUSION, difficult for tubing
- ENDOBRONCHIAL INTUBATION POSSIBLE into RIGHT cranial lung lobe because it MOVES CRANIALLY
MAINTENANCE & MONITORING of anesthesia for pigs
MAINTENANCE is based on INHALANT-BASED protocol + lidocaine CRI
MONITORING = ECG, SpO2, invasive or non-invasive BP, gas monitoring
RECOVERY of anesthesia for pigs (3)
in STERNAL recumbency in a RECOVERY STALL
can EXTUBATE ONCE THEY FIRST SWALLOW –> **DO THIS RAPIDLY TO AVOID LARYNGOSPASMS
can REVERSE BENZODIAZEPINES/ALPHA-2 AGONISTS
if a horse is TOO LIGHT, what would be the best combination to deepen? good alternative? what medication WOULDN’T be as effective?
KETAMINE will RELIABLY & QUICKLY DEEPEN!!
- provides ANALGESIA, PREVENTION OF PURPOSEFUL MOVEMENT while giving enough time to ALSO INCREASE INAHALANT/VOLATILE anesthetic
- **Alpha-2 agonists could be an alternative
Acepromazine can also deepen, but usually takes a long time to work
at what point during anesthesia can we correct any FLUID disturbances, such as hyperkalemia or hyponatremia?
during PERIANESTHETIC period (during surgery)
5 important factors for RECOVERY from MOST TO LEAST IMPORTANT
- ET tube placed properly w/ cuff INFLATED
- STERNAL recumbency
- Provision of OXYGEN supplementation
- Administration of flumazenil (premed)
- Heat support
