Exam 2: Equine Anesthesia and Sedation

what general considerations need to be made with horses

• performance vs pet

• temperament

• minimum database

• location

• time of day (elective vs emergency)

• anatomic characteristics such as nasal breathhing and large GI

• sensitive GI tract

• neuropathy/myopathy with inadequate padding

• flight animals

what should be included in the pre anesthesia physical

• age, gender, breed, weight

• auscultation

• HR, RR

• any lameness or pain

• MM color

• CRT

what needs to be known about the procedure

• soft tissue vs orthopedic

• standing vs GA

• location

• duration

what procedures should be done before anesthesia

• fasting 8 hrs

• IV cath

• clean feet

• rinse mouth

what are important notes about premedication

• quiet environment

• decrease anxiety

• increase safety for horse and personnel

• decrease induction and maintinence drugs

• provide pre emptive analgesia

how are a2 agonists used in horses

• basis of sedation

• reliable and predictavle sedative

• can be combined with opioid to improve sedation

• possible arousal- keep environment quiet

• will cause head dropping and ataxia

how is acepromazine used in horses

• reliable sedative

• improved hemodynamics and arterial oxygenation in anesthetized horses

• often given 30min prior to walk up to pt

• concerns abt penile prolapse 1:10,000

how are opioids described in horses

• when given alone may cause excitement

• in combination with sedatives

• provide analgesia

• Butorphanol

• morphine, hydromorphone, methadone

what are your drug combos for induction

• ketamine and benzo

• ketamine and propofol

• ketamine and guaifensesin

• Telazol

what are the two major forms of induction in horses in terms of positioning and safety

• with and without swing door

• swing door is safer, as it does not require direct leading of the horse to lay down

how is intubation of horses described

blind intubation

what is the most common method of moving horses into the OR

ropes around the feet

whata re the goals of lateral positioning of horses

• protect the radial and facial nerve

• fully support gluteal muscles, dependent limb to C/T, upper limbs

what nerves can be impacted by incorrect positioning

• radial nerve

• sciatic nerve

• facial nerve

• laryngeal recurrent nerve

what muscles can be affected by incorrect positioning

• gluteal muscles

• all larger muscle groups

• neck muscles

how is PIVA described in horses

• inhalation in combination with
  -sedatives (xylazine, dexmedetomidine)
  -muscle relaxants (Guaifenesin)
  -opioids (butorphanol, morphine)
  -dissociative (ketamine)
  -local (lidocaine)

how is TIVA described in horses

• no inhalation, IV only

• triple drip of ketamine, guaifenesin, xylazine
  -max 60 min
  -maintins CV, less respiratory depression, good recovery

how should oxygen flow be maintained for horses

• first 15 minutes = 10L/min

• after reduce to 5L/min for 5-10min

• maintain at 3L/min

how should vaporizer settings be maintained in horses

• higher at first 5-10 min

• after reduce and titrate concentration as needed using Et(inhalant) as your guide

what are anticipated complications during anesthesia

• hypotension

• hypoventilation

• hypothermia

• pain

• ± hemorrhage

• hypoxemia

how should cardiovascular monitoring be performed in horses

• EKG using apex lead (looks upside down), HR 28-40bpm

• BP using invasive, hypotension = MAP <70 for maintinence of tissue perfusion

how is hypotension corrected in horses

dobutamine 0.5-5mch/kg/min

what are your choices for invasive blood pressure monitoring placement

• metataral artery

• facial artery

• transverse facial artery

how should ventilation be monitored in horses

• inhalant depresses ventilation, so hypoventilation is common

• capnography ETCO2

• normal paCO2 = 35-45

• hypercarbia >50

• paCO2 >ETCO2 (10-15)

• treat with mechanical ventilation

how should oxygenation monitoring be performed in horses

• 21% O2 = paO2 80-100

• 100% O2 = paO2 >500

• hypoxemia <60 on 21%

• spO2 (100% = >100)

• arterial blood gas

what are causes of hypoxemia in horses

• decreased FiO2 (deliver 100% O2)

• hypoventilation (mechanical ventilation)

• V/Q mismatch

• diffusion impairment is rare

• R to L anatomical shunt

how is a shunt defined and treatment

• atelectasis (absorption and or compression)

• bronchial obstruction

• alveolar recruitment maneuver

• positive end expiratory pressure

• bronchodilators

what are the consequences of pulmonary deadspace and treatmment

• severe hypotension with closure of vessels with positive pressure ventilation

• pulomary thromboembolism

• improve perfusion / CO

how is depth of anesthesia monitored in horses

• muscle tone

• eye position

• nystagmus yes or no

• soft blink/palpebral maintained if not too deep

• eye position can change during procedure

what are the risks associated with recovery in horses

• upper airway obstrution due to nasal edema

• self injury

• weak due to residual inhalant

what conditions provide the most risk during recovery

• anesthesia time >3 hrs

• orthopedic procedures

• very young or very old horses

• heavy breeds

• mares post partum

how can possible upper airway obstructions be managed in recovery

• ET tube may be left in place if concern of patent airway

• nasotracheal tube

• demand valve to support breathing till spontaneous breathing

• flow by oxygen during recovery as long as possible

how is unassisted recovery defined

• horse placed in recovery stall with no ropes and no personelle in the stall

what are forms of assisted recovery

• hand recovery

• rope recovery

• sling recovery

when do you choose field anesthesia

• if the horse cannot be transported to facility

• minor procedures that do not require OR such as castration, lac repairs, or enucleation

• short procedures that do not require inhalant

what are the benefits of field anethesia

• less equipment

• less expensive

• less CV and resp depression

• ideal for short procedures

• better recovery quality

what are the ideal locations for field anesthesia

• hospital = recovery stall

• outside= grass area that is dry, even, shaded, fenced in with no creeks or open water

what equipment is required for field anethesia

• ancillary (watch, record, pen, consent form, needles and syringes, heparinized flush, flush administration set, mouth wash syrnge, clean bucket)

• catheter (clippers, sterile scrub, local anesthetic, sterile gloves, suture, needle free injection port, heparin flush

• induction (padded halter, lead ropes, lunge lines)

• maintenance (towel + lubricant for eyes, ETT, oxygen supply)

• drugs (a2 agonists, ace, etamine, guaifenesine, benzos, opioids, locals, fluids)

• monitoring (SpO2 monitor, thermometer)

what is the use of TIVA in field anesthesia

• injectables only

• procedures not longer than 1 hr

• depending on type, duration following can be done with top ups or CRI

what is the limit for TIVA top ups and why is it limited

no more than 2, or recoveries are rough

how is monitoring described in field anesthesia

• less respiratory depression

• maintaining of swallow reflex depending on duration and type of procedure, intubation may not be mandatory

• less cardiovascular depressant effects

• hypotension less likely

how should vitals be monitored in field anesthesia

• palpate pulse at facial, transverse facial, or metatarsal artery, auscultate HR

• observe chest excursion, count resp rate

• subjectively evaluate airflow during inspiration and expiration out of both nostris

• body temp

• SpO2 to evaluate oxygenation