11 – Alpha2-Agonists Clinical Application Flashcards
What are the many applications of alpha2 agonists in vet med?
- Pre-medication
- Sedation for minor procedures
- Infusion intra- and post- operatively
- Sedation in recovery period
- Adjunct for local blocks
- Epidural administration
Premedication: small animals example
- Dexmedetomidine
Dexmedetomidine: premedication for small animals
- Highly selective for alpha 2 receptor
- Excellent sedative for healthy exotics
- Always combine with an opioid for more reliable results
- Quality of sedation is profound, but can overrride
if IV administration of dexmedetomidine (premed for small animals)
- Decrease dose by half
Dexmedetomidine dose dependent CV and respiratory depression: choose dose based on number of factors:
- Patient temperament
- Hydration status
- Anticipated pain levels of procedures
Dexmedetomidine onset of action (IM)
- 15mins
Dexmedetomidine duration of action
- 45mins to 1hr
Dexmedetomidine reversable available
- Atipamezole
Premedication: large animals example
- Xylazine
Xylazine (premedication large animals)
- Horses, ruminants, camelids
- Excellent sedative for healthy patients
- Quality of sedation=excellent
- Reflex bradycardia profound but transient
- *can be reversed if necessary (RARE)
- **does for ruminants is lower=more sensitive
Xylazine (premedication large animals): onset of action
- Minutes
Xylazine (premedication large animals): duration of action (IV)
- 30-45 mins
Premedication: horses example
- Detomidine
Detomidine (premedication in horse)
- Good quality sedation: may be slight more ataxic/depressed then with xylazine
- Onset and duration similar to xylazine
Sedation for minor procedures; small animals example
- Dexmedetomidine
Dexmedetomidine (minor procedures in small animals)
- Profound sedation for minor procedures (quill removal, laceration repair)
o Even more with IV (place catheter for ‘top ups’ to be easier) - Combine with opioid to improve quality of sedation
- Combined with local block if possible
Dexmedetomidine (minor procedures in small animals): reversible
- Get rid of drugs once procedure is complete
Sedation for standing procedures: large animals example
- Xylazine
- Detomidine
Xylazine (sedation for standing procedures): horses
- Teeth floats, minor lacerations
- Feet firmly planted, but can still kick!
- Often combined with BUTORPHANOL
Xylazine (sedation for standing procedures): cows
- Foot trims
- Combine with BUTORPHANOL
- Will result in recumbency in 15mins
- Duration of action: 60mins
- *reversible with Tolazoline IM (avoid excitement)
Detomidine (sedation for standing procedures)
- Often combined with opioid (BUTORPHONAL)
- Longer standing procedures=make up infusion and administer to effect
o Laparoscopic ovariectomy
o Rectovaginal fistula
Dexmedetomidine: infusion during surgery
- *anesthetic sparing and analgesia
- Be aware of bradycardia with bolus
- More effective when combined with an opioid infusion (Fentanyl/Remifentanil)
- Not commonly administered to cats as an infusion
- *very beneficial in horses (less used in dogs and cats)
Dexmedetomidine: infusion during post-operative period
- *analgesia and sedation
- Indications
o Anxious dogs
o Fractious dogs
o Painful dogs (need something more than an opioid)
Dexmedetomidine: addition to local anesthetic
- *prolongs duration of block
- Mix with local anesthetic and administer in same syringe
o Amount is small - Some systemic uptake=may see increased levels of sedation
Mechanism of action with dexmedetomidine + local anesthetic
- Vasoconstriction associated with alpha2 agonist DELAYS clearance of local anesthetic from the site
Dexmedetomidine in epidurals: small animals
- Not routinely used
- Direct neurotoxic effects have not been fully tested
Dexmedetomidine in epidurals: large animals
- Prolongs duration of blockade
- Easily accessible for practitioners
- Does NOT produce motor blockage
- Often combined with local anesthetics or opioids
- Produce analgesia
- Adverse effects (ataxia, recumbency): can be reversed
- Systemic absorption occurs: CAUTION
Xylazine in epidurals: horses
- Provide 2.5 hours of perineal analgesia
- No hind limb ataxia 1/5th the dose typically given systemically
- *if combined with lidocaine=do NOT exceed 10mL
o More volume you put in=further it will spread
Detomidine in epidurals: horses
- Potent analgesic AND sedative effects
- Sedation, ataxia, recumbency, and CV effects can occur
- Use low doses
- Analgesia will spread cranially
- Duration is shorter than xylazine: 2 hours
- Diuresis occurs
Romifidine in epidurals: horses
- Analgesia inconsistent: if works=4hrs of analgesia
- Spreads cranially similar to detomidine
- Sedation, bradycardia and decreased RR has been reported
Xylazine alone in epidurals: cattle
- Onset of action: 10mins
- Duration of action: 3-4hours
Xylazine combined with lidocaine in epidurals: cattle
- Onset of action: 5mins
- Duration of action: 6hrs
Side effects of xylazine +/- lidocaine in epidurals: cattle
- Mild to moderate sedation
- Mild ataxia
- Decreased ruminal motility
- Bradycardia
Romifidine in epidurals: cattle
- Analgesia and sedative effect=dose dependent in intensity and duration of action
Specific breed/species considerations
- Bradycephalics and animals with laryngeal paralysis
- Blocked cats
- Diabetic implications
- *UNEXPECTED AROUSAL: do NOT trust it!
Bradycephalics and animals with laryngeal paralysis considerations
- Beware of use
- Pharyngeal and laryngeal MUSCLE RELAXATION may further impair compromised airway
- *DECREASED ESOPHAGEAL SPINCTER TONE=increased risk of regurgitation
Blocked cats considerations
- MUSCLE RELAXATION may aid in passage of urethral catheter
Diabetic implications: considerations
- Reduced insulin leads to increased hepatic glycogenolysis and gluconeogenesis causing HYPERGLYCEMIA
- Clinical relevance: minimal (can manage hyperglycemia and they will be hyperglycemic due to stress)
