Equine ASA III Cases Flashcards
9 y/o Thoroughbred “Niko” presents with acute, severe colic of 3-4 hours. Borborygmi is absent in all quadrants. MM are pink-purple and has a CRT of 3-5 sec and a slow jugular fill. Distal limbs and ears are cold to the touch. There is no gastric reflux and rectal palpation shows marked large colon distension.
What are 5 anticipated complications?
- hypotension due to hypovolemia, vasodilation (endotoxemia, anesthetics given by rDVM), impaired cardiac contractility (hypocalcemia, anesthetics), increased intrathoracic pressure due to mechanical ventilation
- hypoventilation
- hypoxemia due to abdominal distension causing atelectasis
- pain
- recovery
What are 4 ways to manage expected hypotension in ASA III horses?
- use invasive bP monitoring
- use MAC-sparing drugs
- IV fluids through a second IVC
- cardio-supportive infusions - Dobutamine, Phenylephrine, Norepinephrine
What are 2 ways to manage expected hypoventilation in ASA III horses?
- monitor with capnography and arterial blood gas
- prepare to use a mechanical ventilator (can cause hypotension!)
What are 2 ways to manage hypoxemia in ASA III horses?
- monitor with pulse oximetry and arterial blood gas
- use a mechanical ventilator and PEEP
What are the 2 most common ways of managing pain in ASA III horses?
- NSAIDs - Flunixin meglumine
- systemic analgesics - butorphanol, lidocaine infusion
How can recovery be optimized for ASA III horses?
- short-acting sedation, like Xylazine or Romifidine
- reversals - Flumazenil, Tolazoline
- uncuffed NT with O2 insufflation
- padded mattress, head/tail rope
What premedication, induction, and maintenance are recommended in ASA III horses?
Xylazine + Butorphanol
Ketamine + Guaifenesine
ISO in O2 + Lidocaine CRI
What are the likely causes of hypoxemia, hypoventilation, and poor pulse quality seen in ASA III horses?
V/Q mismatch caused by compression atelectasis
poor pulmonary perfusion due to large alveolar dead space = elevated PaCO2 and strong respiratory drive
hypotension caused by hypovolemia, vasodilation with endotoxemia, or hypertension caused by rDVM giving Xylazine
V/Q mismatch:
Why is intermittent positive pressure ventilation commonly recommended in ASA III horses? What does it do?
high abdominal pressure causes smaller tidal volume and faster RR
opens the abdomen to reduce pressure and improve pulmonary compliance and tidal volume
What should PEEP be set to? What does it do? What precaution should be noted?
5-20 cmH2O
combats compressive forces on the lungs
compromises the CV system and inhibits return of blood to the heart
How is anesthetic depth typically maintained in ASA III horses?
increase oxygen flow rate to increase FiO2 faster while lowering ISO vaporizer settings to avoid excessive depth
What are signs/causes of altered preload, afterload (SVR), and contractility?
dorsal recumbency, IPPV +/- PEEP, hypovolemia
pink/purple MM, CRT < 1 sec
pulse pressure
What is recommended for hypotension management of ASA III horses? What are other more controversial options?
dobutamine infusion - improves chances of placeing arterial lines
phenylephrine or norepinephrine infusions - vasoconstriction may further decrease CO
What are the 5 steps to managing hypotensive ASA III horses?
- evaluate patient
- reduce anesthetic depth
- correct bradyarrhythmia (rare in equines)
- IV fluid bolus
- cardiovascular support drugs
