32 – Peri-Operative Pain Management in Large Animals Flashcards
What are the arguments for use of analgesics in large animals?
- Pain results in poor recovery from anesthesia
- Animals are restless
- Animals do not eat well
- Decreased immune response due to STRESS
- Delayed wound healing
What are the arguments against use of analgesics in large animals?
- Over-use of injured area
- Side effects
o GI ulcers
o Constipation
o Ileus (but pain can also cause it, BALANCE)
o Behavioural alterations - Masks worsening of disease process
- Difficulty in recognizing pain
Head pain behaviour in horses
- Shake
- Snort
Jaw pain behaviour in horses
- Drooling
- Dropping food
- Losing weight
Limb pain behaviour in horses
- Stomp
- Limp
- Refusal to walk
- Lying down
- Abnormal stance (ex. leaning back when front limb sore)
Abdominal pain behaviour in horses
- Kick at belly
- Flank watch
- Roll
- Tail swish
- Violent behaviour
‘pain face’ of a horse
- Lowered ears
- Contraction of muscles above eye
- Tense stare
- Dilated nostril
- Tension of facial muscles
- Edged shaped muzzle with lips pressed together and flattened chin
Pain management in horses: analgesic drugs for
- Pre-medication/sedation
- Pre-emptive pain management
- Multi-modal analgesia
Pain management in horses: infusion techniques for
- Intra-operative
- Post-operative
Pain management in horses: epidural/spinal techniques for
- Standing procedures
- Post-operative long term pain management
What are the 5 ‘classes’ of analgesic drugs used in horses?
- NSAIDs
- Alpha-2 agonists
- Ketamine
- Opioids
- Local anesthetics
What are the benefits of NSAIDs in horses?
- Analgesic
- Anti-inflammatory
What are the potential harmful side effects of NSAIDs in horses?
- Gastric and colonic ulceration
- Renal tubular necrosis
- *more with chronic use
What are the usages of NSAIDs in horses?
- often administered PRE-OPERATIVELY anticipating inflammation that will occur during surgery
What are some examples of NSAIDs in horses (2)
- phenylbutazone
- flunixin meglumine
Phenylbutazone in horses for
- musculoskeletal inflammation and pain
Flunixin meglumine in horses for
- acute soft injury
- endotoxemia
- abdominal pain
What are the alpha-2 agonists used in horses?
- Xylazine
- Detomidine
- Medetomidine
- Dexmedetomidine
- Romifidine
What are the usages of alpha-2 agonists in horses?
- Pre-medication primarily for SEDATION
- Intra-operatively as a CRI for analgesia
- Post-operatively for sedation to ensure SMOOTH RECOVERIES from inhalation anesthesia
What are the benefits of alpha-2 agonists in horses?
- ANALGESIA
- Sedation
- Anesthetic sparing
What are the potential negative side effects of alpha-2 agonists?
- Bradycardia
- Vasoconstriction and hypertension
- Increased urine output (hyperglycemic diuresis)
- Decreased GI motility
- Ataxia
- *can get excited (need to be sedated: ’nose to knees’)
Xylazine in horses
- Used with KETAMINE and GGE (Guaifenesin) in ‘triple drip’
- Total intravenous anesthesia (TIVA)
Detomidine in horses
- Used for sedation and analgesia for standing procedures
- Often combined with an OPIOID
- Administered as an infusion (variable rate infusion (VRI))
Dexmedetomidine in horses
- Used for invasive procedures with INHALATION ANESTHESIA (PIVA)
o Once turn it off=it is gone (still need to SEDATE for recovery period) - *Ex. orthopedic surgery
Ketamine in horses
- Used as in induction agent
- Used in ‘triple drip’ mixture
- *provides analgesia
o Somatic
o NMDA antagonism: good for chronic (‘wind-up’) pain - *risk of excitement: but can be controlled with sedatives
What are some other beneficial effects of ketamine besides analgesia?
- Local anesthetic affects
- Potent anti-inflammatory effects
- Anesthetic sparing (decrease MAC by 37%)
What are the main opioids used in horses?
- Morphine (mu agonist)
- Butorphanol (kappa agonist)
What are opioids primarily used for in horses?
- Intra-operatively
o Not good sedative unless combined with an alpha-2 agonist - Appears to be effective in horses in pain OR undergoing invasive procedures=good analgesia
- DOES NOT REDUCE ISOFLURANE REQUIREMENTS (unlike dogs and cats)
What are some side effects of opioids?
- Excitement: control with sedatives (acepromazine, alpha-2 agonists)
o *give them first and them first and then do opioids - Decreased GI motility: decreased if administered IM or not given long term
Opioids dosage guidelines
- more severe than pain=greater dose required and lower risk of excitatory side effects
- give appropriate alpha-2 match for duration to eliminate risk of excitation
- sedation acepromazine reduces but does not ELIMINATE risk of excitement
- *SHOULD BE GIVEN TO EFFECT: NOT BY THE CLOK
- Clinical signs of underdose (ie. PAIN) may MIMIC signs of overdose (EXCITEMENT)
Morphine
- Used at LOW doses for horse in pain
- Duration: ~4hrs
- Side effects when use repeated dosing or high dosages
- Can enhance effects of other sedatives when used with standing sedation
- CV stimulation when used alone
- Can use for intra-articular analgesia (up to 24hours, less systemic side effects)
What are some side effects when morphine is given repeatedly or at high doses?
- Reduced GI motility
- Urinary retention
- Increased locomotor activity and ataxia
Morphine intraoperative uses (horses)
- CRI
- Higher dosages (0.25mg/kg)
- Clinical dosages
Morphine CRI (intraoperative use)
- Improved recovery characteristics
- No conclusive evidence that its use increases incidence of post-anesthetic colic
Morphine higher dosages (intraoperative use)
- Used for analgesia
- May increase isoflurane requirements
- May result in rough recoveries
Morphine clinical dosages (intraoperative use): recovery affect
- Does not affect recovery
Fentanyl
- Use is controversial: need large doses
o Maybe MAC reducing effect but increase in rough recoveries - Clinical benefit at this time: POST-OPERATIVE period via TRANSDERMAL PATCHES for pain control
Fentanyl patches
- Need 1-3 (‘for small animals’)
- Variable results
- May see excitement: may need acepromazine or alpha-2 sedation
- May need to supplement with another analgesic: NSAID
- Location may affect absorption
- *controlled drug (don’t want abuse)
Fentanyl patches absorption
- Better absorption from thorax or groin compared to a leg
Fentanyl patches: in foals
- One 100mcg/hr patch may be used
- Peak plasma levels after 14hrs
Remifentanil
- Used with success INTRA-OPERATIVELY
- Good recoveries
- Some reports of hyperthermia
- Can ONLY be used as CRI due to SHORT-HALF LIFE
- *Make sure analgesia is in place before turning off
Buprenorphine
- Long duration of action: up to 12hrs
- Behavioural side effects
- Sub-lingual administration might be useful
- New evidence: may provide better POST-OPERATIVE analgesia than butorphanol for minimally invasive procedures (ex. castration)
- Not really used at the school
What are some side effects of buprenorphine?
- Restlessness
- Head shaking
- Decreased GI motility for up to 4 hours
Butorphanol
- Can still produce excitement (delta receptors)
- Often used INTRA-OPERATIVELY
- Effective for VISCERAL ANALGESIA
- Duration: 45-1hr (IV)
o re-dosing is often necessary - does NOT change isoflurane requirements
- *does provide a more ‘stable’ anesthesia
- Post-operative usage
Butorphanol post-operative usage (horses)
- May need it IM every 3 hrs: analgesia is short last and not profound
- Can be injected
- Analgesia is NOT consistent as with an infusion but there is less risk of IMPACTION
Local anesthetics: Lidocaine
- As an infustion INTRA-OPERATIVELY w/o epinephrine!
- Loading dose and CRI
- *stop infusion at least 30 mins prior to recovery from general anesthesia: TO PREVETN ATAXIA
What are the pharmacological benefits of lidocaine?
- ANALGESIA
- Anti-inflammatory
- Anti-endotoxemic
- Pro-kinetic
- Anesthetic sparing
Partial IV anesthesia (PIVA)
- Combination of infusions (multimodal anesthesia)
- Useful technique to reduce isoflurane requirements
- Alpha-2 agonists, lidocaine, opioids, ketamine
Alpha-2 agonists indications and PIVA
- Invasive/painful procedures
- Orthopedic procedures: musculoskeletal pain and inflammation
Lidocaine indications and PIVA
- Colic surgeries
Opioids indications and PIVA
- Orthopedic surgeries
Ketamine indications and PIVA
- Somatic analgesia
o Supplement other drugs
What are other modes of providing analgesia (4)
- Epidurals
- Epidural catheters
- Wound/soaker catheters
- Local blocks
Epidurals
- Good for standing procedures
- Require sterile technique
- Relatively easy to place in standing horse (sacrococcygeal)
- Use preservative free drugs
- Usually once or twice daily treatment
- Administer drugs SLOWLY
Epidural catheters
- For LONG term pain management
- Sterile technique for placement and management!
Wound/soaker catheters
- Can provide postoperative analgesia for 2-3 days
- Preplace during surgery
- Commercial kits available
- Use LIDOCAINE infusions: 2-5ml/hr
- Use BUPIVICAINE infusions: 2-5ml every 6-10hours
- *maybe not used when remove a tumor?
Local blocks
- Intra-operative: anesthetic sparing:
- Post-operative: improve recovery and minimize need for other analgesic agents
Considerations for recovery
- Must STOP ALL INFUSIONS prior to moving into recovery box
- Give NSAIDs if warranted
- Consider local blocks if applicale
- Usually sedate with alpha-2 agonist
o Xylazine
o Romifidine
Pain behaviour in ruminants
- Abnormal stance and gait
- Unusual resting behaviours
- Vocalization
- Kicking and tail swishing
- Very subtle indicators (teeth grinding, reduced food, absence of rumination)
What are the analgesic drugs used for ruminants (5)?
- NSAID
- Opioids
- Ketamine
- Lidocaine
- Alpha-2 agoinsts
NSAIDs: ruminants
- Withdrawal times NOT well defined for meat or milk
- Primary risk=GI ulcer formation
What are some behavioural side effects that might be seen with opioids in ruminants and that may need to be adjusted?
- Sedation
- Dysphoria
- Excessive locomotor activity
- Excitement
- *can develop INTESTINAL STASIS with long term use
What are the 2 opioids used in ruminants?
- Morphine
- Butorphanol
Epidural opioids: ruminants
- Morphine: diluted in 10ml saline
- *sacrococcygeal administration (‘caudal epidural’)
In what animals can or are transdermal fentanyl patches used?
- Goats and sheep
- Llamas
- Pigs (placed behind ear or inner thigh)
What are the benefits of ketamine in ruminants
- Anesthetic sparing
- NMDA antagonist: good for chronic pain
- Good for somatic analgesia
Ketamine dosages in ruminants
- Higher dosages than in small animals
What is lidocaine used for in ruminants?
- **Infusion INTRA-OPERATIVELY w/o epinephrine
- Stop infustion at least 30 mins prior to recovery from general anesthesia to PREVENT prolonged recoveries
What are the pharmacological benefits of lidocaine? (ruminants)
- ANALGESIA
- Anti-inflammatory
- Anti-endotoxemic
- Pro-kinetic: improves GI motility
- Anesthetic sparing
What is the dosing of lidocaine in ruminants?
- Higher than HORSES and SMALL ANIMALS
Alpha-2 agonists: ruminants
- MORE SENSITIVE than horses
- *use 1/10th dose you would use in horse
Epidural use of alpha-2 agonists in ruminants
- Use 1/10th dose of xylazine you would use in a horse
