Chapter 23 - Chemical restraint for standing procedures Flashcards
What factors should be considered when deciding between standing sedation and general anesthesia for a surgical procedure in a horse? (6)
1.Type of procedure
2.Temperament of the horse
3.Anesthetic and surgical facilities
4.Personal experience
5.Preexisting medical conditions
6.Owner compliance
What is the primary goal of chemical restraint for standing surgery in horses?
To keep the horse calm, sedated, and indifferent to environmental or noxious stimulation, while ensuring the horse remains standing with minimal ataxia.
Why is it important for sedatives to be administered in a quiet environment?
Sedatives work best when given to a quiet horse, and suboptimal drug effects may result if the horse is excited before or during drug administration.
What is the difference in drug onset and dosage when sedatives are administered intramuscularly (IM) compared to intravenously (IV)?
IM administration requires longer onset times and higher doses compared to IV administration, and the sedation is less predictable due to variable absorption.
What is an advantage of using constant-rate infusion (CRI) of sedatives over repeated bolus administration?
CRI is less cumbersome for the veterinarian, may cause fewer adverse effects, and provides a more constant level of sedation.
What should be considered when initiating CRI sedation to achieve the desired effects more quickly?
loading dose should be administered, as it takes four to five half-lives to reach steady-state plasma concentrations and sedation if no loading dose is given.
What factors should be considered when choosing a sedation protocol for standing procedures?
- Health status and temperament of the horse
- Type and duration of the planned procedure
- Drug availability
- Personal experience
What is the benefit of administering multiple drugs simultaneously for chemical restraint in horses?
Administering multiple drugs may allow the use of reduced dosages, making the procedure safer and more effective than using larger doses of a single drug.
What class of drugs is most commonly used for standing sedation in adult horses?
α2-adrenoreceptor agonists
Which α2-adrenoreceptor agonists are most frequently used for standing sedation in equine practice?
- Xylazine
- Detomidine
- Romifidine
What other α2-adrenoreceptor agonists, although not registered for horses, have been used successfully in this species?
Medetomidine
Dexmedetomidine
What are reasonable starting doses for medetomidine and dexmedetomidine in horses for standing sedation?
Medetomidine: 5 to 7 μg/kg IV
Dexmedetomidine: 3 to 5 μg/kg IV
What is a key disadvantage of using intramuscular (IM) administration of sedatives in horses?
Sedation by the IM route is less predictable because absorption from IM sites is variable.
What complications may arise if sedatives are administered to an excited horse?
The effects of the sedatives may be suboptimal, resulting in inadequate sedation or safety risks during the procedure.
What are the risks of performing painful procedures on standing horses without adequate local or regional anesthesia?
The horse may experience insufficient analgesia, leading to movement or ataxia, which increases the risk to personnel and may affect the success of the procedure.
What is the main effect of α2-adrenoreceptor agonists on the cardiovascular system?
Decreases cardiac output
Which α2-adrenoreceptor agonist provides the longest sedation?
Detomidine
What fibers are involved in the increased sensitivity to touch?
Aβ fibers
For how long do xylazine or medetomidine provide sedation in short procedures?
15–20 minutes
What side effect is reduced when α2-adrenoreceptor agonists are administered IM compared to IV?
Hypertensive response
What cardiovascular side effect is dose-dependent in α2-adrenoreceptor agonist administration?
Bradycardia
What respiratory effect is commonly associated with α2-adrenoreceptor agonists?
Respiratory depression
What happens when α2-adrenoreceptor agonists are injected intracarotidly?
Excitement and seizures
Why might α2-adrenoreceptor agonists fail to sedate stressed horses?
Increased catecholamines
Which horses need higher doses of α2-adrenoreceptor agonists?
Mules (approximately 50%)
What class of drugs should never be administered IV following α2-adrenoreceptor agonists?
Potentiated sulfonamides = fatal arrythmias
At what age are α2-adrenoreceptor agonists not recommended for foals?
<14 days
What cardiovascular effect is prevented by combining acepromazine with α2-adrenoreceptor agonists?
Initial hypertension
What happens when opioids are added to α2-adrenoreceptor agonists in terms of sedation?
Synergistic effect
Which condition can result from prolonged head lowering during sedation?
Facial and nasal edema
What drug is sometimes added to a romifidine CRI for dentistry procedures?
Butorphanol
What can be administered to treat mucosal edema in sedated horses?
Phenylephrine nasal drops
What effect is often seen in very young foals (<14d) sedated with α2-adrenoreceptor agonists?
Recumbency, use benzodiazepines + opioids instead
Base-apex electrocardiogram (paper speed 25 mm/sec) showing a second-degree atrioventricular (AV) block in a horse. Note the progressive prolongation of the PQ interval before one beat drops that is characteristic of a Wenckebach or Mobitz type I second-degree AV block (in contrast, the PQ interval remains constant prior to the P-wave, which suddenly fails to conduct to the ventricles in a Hay or Mobitz type II second-degree AV block). This is a typical arrhythmia observed in horses sedated with α2-adrenoreceptor agonists. AUER book
Which horses need lower doses of α2-adrenoreceptor agonists?
Draft horses
Which α2-adrenoreceptor antagonist is most selective?
Atipamezole
When should α2-adrenoreceptor antagonists be used?
Emergency situations
What is abolished by using α2-adrenoreceptor antagonists?
Analgesic effect
What side effects may occur after α2-antagonist administration?
Agitation, stress
Which antagonists are associated with anecdotal fatalities?
Yohimbine, tolazoline
Name the 3 α2-antagonist
- Yohimbine
- Tolazoline
- Atipamezole
What should be avoided during treatment of hypotension?
Epinephrine
Which drug is preferred for treating vasodilation-induced hypotension?
Phenylephrine
Name the 5 phenothiazine and dosage of the most known
Acepromazine 0.02-0.05 mg/kg IV
IM 0.02-0.05 mg/kg
PO 0.1 mg/kg
2. Chlorpromazine
3. Propiopromazine
4. Propionylpromazine
5. Promethazine
How does acepromazine affect packed cell volume (PCV)?
Decreases PCV by 20% due to RBç sequestration
What is the mechanism behind PCV decrease with acepromazine?
Splenic sequestration
What side effect is observed in stallions after acepromazine administration?
Priapism
In which horses should phenothiazines be avoided?
Epileptic patients
How long can acepromazine effects last in some horses?
6–10 hours
What effect does acepromazine have on thermoregulatory control?
Loss of control be careful in foals and ponies
What dosage of acepromazine can cause penile prolapse?
0.01 mg/kg
What is a controversial effect of phenothiazines?
Platelet function
Which side effect is more severe with IV administration of acepromazine compared to IM or oral?
Hypotension
Does the ACP diminish GI motility?
yes acepromazine diminishes GI motility
It is important to remember before sedating a horse with acepromazine that the negative effects on blood pressure and PCV can persist for more than _____ hours
acepromazine that the negative effects on blood pressure and PCV can persist for more than 10 hours
Is there an antagonist available for ACP?
No
Why are butyrophenones not recommended in horses?
Unpredictability, side effects
Which benzodiazepines are commonly used in horses?
Diazepam, midazolam, zolazepam
What neurotransmitter do benzodiazepines facilitate?
GABA
What are the effects of benzodiazepines on muscle relaxation?
Excellent relaxation
Why should benzodiazepines not be used for standing sedation in adult horses?
Unreliable sedation
Which type of horse are benzodiazepines reliable sedatives for?
Neonatal foals
What effects can opioids produce when used alone in horses?
Restlessness, agitation
What can block the dosage-dependent increase in spontaneous locomotor activity caused by opioids?
Naloxone, acepromazine
What severe side effects can occur at higher doses of propofol in horses?
Ataxia, muscle weakness
Which drugs are considered for long-term tranquilization in horses?
eserpine, fluphenazine, chlorpromazine
What can benzodiazepines cause in adult horses at higher doses?
Severe ataxia
Which route should midazolam be administered if IM is the only option?
IM route
What side effect can benzodiazepines stimulate that is beneficial in managing chronic grass sickness?
Food intake
What concerns arise with prolonged benzodiazepine sedation in foals?
Hypoglycemia, hypothermia
Which antagonist is used to reverse benzodiazepines?
Flumazenil 0.01-0.04 mg/kg IV slowly
What is the mechanism of action of benzodiazepines?
Benzodiazepines produce their pharmacologic effects by facilitating the actions of γ-aminobutyric acid (read gamma aminobutyric acid GABA), the principal inhibitory neurotransmitter in the CNS
Advantages of benzodiazepines (2)
- excelent muscle relaxation
- minimal cardiovascular respi depression
Can you give midazolam IV and IM
Yes, midazolam can be given both ways but dizepam is only IV
What are the side effects of benzodiazepines
Anxiolytic
hypnotic
anti-convulsive
no analgesia
unreliable sedation
severe ataxia
Benzodiapines provide analgesia?
No ANALGESIA ! It provides sedations and recumbency but not analgesia, that is why it has to be combined with opioid or local anesth in foals
In what situation should antagonists be used with benzodiazepines?
Respiratory depression
What side effect can opioids cause in healthy, pain-free horses?
Excitement, dysphoria
What type of sedation is produced when opioids are combined with benzodiazepines in foals?
Good-quality sedation
What do opioids act via to produce their effects?
Opioid receptors
