Equine Anesthesia Flashcards
What are stallions prone to when on acepromazine
Penile prolapse / priapism
What does Xylazine cause in the third trimester of pregnancy when administered
Abortion
What is the normal HR, RR, and temperature of horses
HR - 28-40bpm
RR - 8-16bpm
Temp - 99.5-101.3 F
What are normal HR, RR, and Temp of donkeys
HR - 35-50bpm
RR - 12-28bpm
Temp - 97.2-100F
Where do you typically place a venous catherization and what do you use
-Jugular vein
-Aseptic technique with a 12gauge catheter and suture to skin with nylon
What do you do to prep a horse for anesthesia
-Fast for 4-6 hours
-withhold water for 2 hours
-rinse mouth with pressurized water (removes any foreign material that would attach to endotracheal tube and become a contaminate)
-remove horseshoes if they have it
What are some premedications
-Alpha-2 agonist -> potential sedatives with some analgesic effect
*Xylaxine, detomidine, romifidine
-Acepromazine -> mild sedative (anxiolytic), can cause penile prolapse
-Opioids
*Butorphanol -> most common analgesic
*mu agonist (Hydromorphone, methadone, morphine) -> severe pain
-Flunixine meglumine -> analgesic
-Meloxicam -> analgesic
-muscle relaxants
*centrally acting - Benzodiazepines, GGE, Gabapentin
*peripherally acting - dantrolene (on skeletal muscle), non-depolarizing blockers and depolarizing blockers
What is the best option of premedications to cause sedation/analgesia in the horse but may cause reduced GI motility -> colic
Mu agonist opioids and alpha-2
What is a common muscle relaxant used primarily in horses
-Guaifenesin (GGE/GG)
*muscle relaxant before induction - given at high volumes so you admin with a flutter valve to be able to give it all
-causes skeletal muscle to relax with minimal cardiovascular and respiratory effects
**Component of TIVE or PIVA for maintenance anesthetic
Why has GGE been replaced largely by benzodiazepines
-it’s a powder which is inconvenient because you have to dilute it and that adds a potential for it to get contaminated
-might cause thrombophlebitis at high concentrations
What do you consider when giving premeds to horses
Horses should be in an induction/recovery box, have padded stall, quiet environment,
Horse is restrained properly and there is communication within the team
Give premed drugs - produced enough sedation and relaxation before inducing anesthesia
What is the inducing agent of choice in horses
Ketamine
**make sure you give muscle relaxant first
What is needed to intubate a horse and what is the technique used
-26mm diameter ET tube, mouth gag/ bite block to keep jaws apart
-ensure the neck is extended and tube is lubricated
-Intubate BLINDLY
-then inflate cuff
What do you have to keep in mind when positioning a horse on the theatre table
-keep them only one lateral recumbency throughout
-move slowly when you changing body position
-cushion the head, neck, shoulders, and pelvis
-stretch and spread limbs apart
-protect eyes from trauma, pressure
What is the oxygen flow rate for induction and maintenance
-After induction and at end of six- 20ml/kg/min
-Maintenance- 10ml/kg/min
What is required for maintenance of anesthesia
-Large animal circle anesthetic circuit
-Mechanical ventilation (IPPV)
-Dobutamine CRI to maintain of arterial blood pressure
-use of local anesthetic drugs as much as possible
-sevoflurane or isoflurane
-PIVA
*causes MAC reduction, provides analgesia, adverse effect reduction
*use Ketamine, medetomidine, lidocaine
-TIVA
*superior analgesia, less cardiovascular depression, decreases sx stress, lowers morbidity/mortality
*alpha 2, muscle relaxant, ketamine (xylazine, GGE, ketamine)
How do you measure anesthetic depth in a horse
-look at CNS reflex
*surgical plane - weak palpebral reflex and anal tone, no response to noxious stimulus
*too light - lacrimation, nystagmus, movement, blinking, cornealcreflex present, tachycardia, tachypnea
*too deep - absent palpebral reflex, absent corneal reflex, dry cornea, bradypnea, apnea, bradycardia, hypotension
What are some common complications of anesthesia in horses
-Hypoventilation
*maintain ETCO2 around 35-45mmHg
*give mechanical ventilation if procedure is longer than 45 minutes
-Hypotension
*give crystaloids or colloids as needed
*dobutamine CRI - standard of care (POs inotrope)
-others ephedrine (pos inotrop) or phenylephrine (peripheral vasoconstriction)
What is risky about horses recovering from anesthesia and what should you do to minimize it
-excitable flight and myopathy risk
-provide soft padding, no slip recovery boxes
Sedate with alpha 2 agonist to delay standing attempts
-give butorphanol if additional analgesia/sedation is needed
-extubation after swallowing reflex or if they had an invasive upper airway sx then exubate after standing to prevent blood obstruction
-give supplemental oxygen to minimize hypoxemia risk
-temp control
What are the two general categories of recovery technique
-unassisted
*generally in healthy horses and for short anesthetic events
-Assisted recovery
*for old, weak, ill patients; long procedures or othropedic procedures
What are the different assisted recovery techniques
-Manual assistance = hand recovery inside box
*foals and small equine where one person is at the head with the halter and another at the tail
-Head and tail ropes
*inside or out of box with ropes attached to rings on the wall
-inflatable air cushion
*stops horse from standing on the air filled bed and you can deflate when they are totally awake. This also minimizes nerve compression but takes a while to clean up afterward
-Sling recovery
*used for extremely debilitated patients and those with fractures
-pool raft system
*not commonly available and expensive but it’s used for orthopedic repairs
When are horses considered hypotensive
MAP <70mmHg
SAP < 90mmHg
How would you treat hypotension in horses
-treat underlying cause
-reduce anesthetic drug rate
-fluids -
*crystalloids 10ml/kg, colloids 5ml/kg, blood if hemorrhagic
-cardio active drugs - dobutamine and ephedrine
What is one of the most common causes of morbidity/mortality of horse anesthesia and what are the different types
-myopathies!
*w/ rhabdomyolysis
-compartmentalism myopathy
- malignant hyperthermia
*w/o rhabdomyolysis
-hyperkaelemic periodic paresis
