Equine Anesthesia Flashcards
Physiologic Consequences of General Anesthesia and Recumbency in the Horse: Maintenance Phase (5)
- dec Oxygenation ( 30% if breathing room air)
- dec Alveolar Ventilation
- dec Cardiac Output (HR * SV)( 40-50%)
- dec Blood Pressure (if patient is receiving inhalant anesthetics)
- dec GI motility
Physiologic Consequences of General Anesthesia and Recumbency in the Horse: Recovery Phase (3)
- dec Coordination
- dec Muscle strength
- Altered mentation
requirements for pre anesthetic prep for environment in horses
-Quiet
-Safe: Fences, Rocks, Hooks
-Clean
-Minimal Dust/Particles (Eyes)
-Assistance
requirements for pre anesthetic prep for equipment in horses
-Halter and lead rope
-Additional ropes
-Monitoring equipment
-Pads (in hospital)
requirements for pre anesthetic prep for the patient in horses
-History
-PHYSICAL EXAMINATION-including weight estimation or measurement
-Pre-operative Blood Tests if necessary
-Fasting; mature horses no food for 12 hours, do not take away water
-mouth flush (if you plan to intubate)
-shoes (ideally not shod or consider putting on bandages)
-keep mae and foal together until one is anesthetized
-concurrent meds
-dewormers; avoid close to the anesthetic period
-IV access
-optimize hemodynamic status-fluids
what can you do if you want 10-15 minutes of anesthesia
give premed and then induce with IV anesthetics
what can you do if you want <1hour of anesthesia
give premed and then induce with IV anesthetics, and then give IV bolus or infusion or inhalant
what can you do if you want >1 hour of anesthesia
give premed and then induce with IV anesthetics, and then give inhalant
goals of premedication (6)
Profound sedation
Reliable
Predictable
Consistent level of sedation
Good Muscle Relaxation
‘Manageable’ Effects on the Cardiopulmonary System
premed options for horses
- Alpha-2 Adrenergic Agonists
– Xylazine
– Romifidine
– Detomidine
– Medetomidine - Phenothiazines
– Acepromazine (rarely used alone) - Benzodiazepines
– Diazepam, Midazolam - Opioids
- COMBINATIONS
– ALPHA-2 AGONISTS AND OPIOIDS
goals of induction (5)
Rapid
Controlled
Predictable
Good Muscle Relaxation
‘Manageable’ Effects on the Cardiopulmonary System
induction options for horses (3)
– Ketamine and Diazepam
– Ketamine
– Guaifenesin (GG) and Ketamine
benefit of combo benzos/ketamine
improved relaxation of skeletal muscle
effects of guaifenesin
- Centrally acting muscle relaxant
- Minimal cardiovascular effects
- Relaxation of skeletal muscle
goals of anesthesia maintenance (3)
Predictable
Good Muscle Relaxation
Minimal Effects on the Cardiopulmonary System
maintenance options for horses; IV vs inhalant
A. Intravenous
* Alpha-2/ketamine bolus injections as needed
* Triple Drip – Xylazine/Guaifenesin/Ketamine
* Other infusions
B. Inhalant
* Halothane, Isoflurane ………..Sevoflurane, Desflurane
* ± MAC reducing agents-lidocaine, alpha-2 agonists
how to assess efficacy of IV anesthesia maintenance
- Muscle relaxation
– Not as profound as with inhalant anesthetics - Depth of Anesthesia
– Difficult to judge depth of anesthesia based on eye reflexes, eye position, tearing or muscle relaxation - Cardiopulmonary
– Blood pressure maintained
– Hypoxemia…as always a concern!
3 recommendations to do for IV GA
– Administration via IV catheter
– Administer supplemental oxygen
– Limit duration of anesthesia to 1 hr
GA of foals <2 weeks of age
diazepam -> ketamine -> inhalant iso
GA of foals >2 weeks of age
unhealthy foal
diazepam -> ketamine -> inhalant iso
healthy foal
xylazine -> ketamine+diazepam -> inhalant iso
things to consider for equine airways
-Obligate nasal breathers
-Nasotracheal intubation; Reduced size (radius) of airway
-Orotracheal intubation
-Anatomy:
* Jaw mobility-limited
airway management; field vs in hospital, technique
- Field Anesthesia:
– Most commonly, no artificial airway
– Minimal risk of regurgitation or airway obstruction if appropriate positioning - In-hospital
– Orotracheal commonly performed for oxygen and/or inhalant anesthetic delivery - Technique
– Blind Intubation
supportive measures for equine anesthesia (4)
- Padding
– To prevent: myopathies, neuropathies - Oxygen ± Ventilatory Support
- Fluids
- Inotropes
indications and examples of inotropes to use in equine anesthesia
indications
-Treat low cardiac output
-Treat low blood pressure
examples
-dobutamine
-dopamine
-ephedrine
-calcium
fluids that can be given as support during equine anesthesia
-Lactated Ringers (or other balanced electrolyte solution)
-Hypertonic Saline (7.5%)
is anesthetic mortality high or low in horses
unfortunately high…
risk factors for anesthesia death in horses (5)
- Preoperative Patient Status (>ASA 1)
- Breed (DRAFT BREED)
- Surgical Time (Longer…)
- Incidence of hypotension
- Incidence of hypoxemia
what can decreased oxygen delivery to tissues lead to
-myopathy
-cardiopulmonary arrest
-post op ileus and colic
what leads to injury during recovery
-dec coordination
-dec muscle strength
-altered mentation
how to reduce morb/mort associated with GA (4)
Optimize Patient Pre-operatively
* Hydration Status
– Hypertonic Saline
– Isotonic Crystalloids
Maintenance of Mean Blood Pressure
* Maintain > 70 mmHg
Optimize Oxygenation
Minimize Surgery Time
