Local anaesthetic blocks Flashcards
What are the 2 types of local anaesthetics and how are they metabolised?
Amides: Metabolized by liver (e.g. lidocaine, bupivacaine)
Esters: Metabolized by plasma cholinesterases (e.g. procaine)
How do local anaesthetics work?
Local anesthetics are weak bases that exist in equilibrium between:
- Non-ionized (neutral), lipid-soluble form (B): Penetrates lipid membrane
- Ionized (charged), water-soluble form (BH+): Binds to sodium channel receptor within channel pore, blocking nerve signal transmission
Why are local anesthetics formulated as acidic hydrochloride salts?
To increase water solubility & ionization (pH 4–7), ensuring effectiveness in their water-soluble, charged form
What is the purpose of adding vasoconstrictors (e.g., adrenaline) to local anesthetics?
To prolong duration of action by reducing systemic absorption
What is the purpose of a testicular block during castration?
Provides intraoperative nociception & postoperative pain relief by diffusing to spermatic cord & associated structures
Reduces pain from surgical crushing of tissue at castration site
How is a testicular block performed?
- Use sterile hypodermic needle (25- to 22-Ga, length depending on patient size)
- Insert needle into testicular body, directing tip toward spermatic cord
- Aspirate to ensure needle is not in blood vessel
- Inject recommended dose of local anesthetic (bupivacaine, ropivacaine, or lidocaine) until testicle becomes slightly turgid or volume limit is reached
How do we inject local anaesthetic for a testicular block for castration?
Cats: Inject local anesthetic as needle exits testicle to block skin & subcutaneous tissue over incision
Dogs: Inject anesthetic into skin & subcutaneous tissue at prescrotal incision site
How is local anaesthetic used during an ovariohysterectomy?
Direct infiltration of mesovarium ligament
Alternatively, splash block can be applied to the ovaries
Additional step:
- lavage of peritoneal cavity with local anaesthetic to provide additional analgesia (careful with dosage)
skin & subcutaneous tissues at incision site should also be infiltrated with local anaesthetic.
What is retrobulbar anaesthesia, and when is it used?
Retrobulbar anaesthesia involves injecting local anaesthetic behind eye to block nerves & provide pain relief during ophthalmic procedures, such as enucleation
What are the indications for lumbosacral and sacrococcygeal epidurals in veterinary medicine?
Tail amputations (canine and feline).
Perineal urethrostomies.
Anal sacculectomies.
Catheterisation for relief of urethral obstruction.
Perineal relaxation for the delivery of puppies/kittens.
Other surgeries involving the penis or perineal region.
What anatomical regions are targeted with lumbosacral and sacrococcygeal epidurals?
Lumbosacral epidural: Provides analgesia & anaesthesia for hindlimb and pelvic region surgeries
Sacrococcygeal epidural: Focused on the tail and perineal region
What is the purpose of a rostral maxillary (infraorbital) dental block?
It provides analgesia for rostral maxillary soft tissues only (not teeth or bone)
Where is the local anaesthetic injected for a rostral maxillary (infraorbital) block?
injection made near infraorbital foramen, targeting infraorbital nerve
What nerve block is this?
Rostral maxillary (infraorbital)
Label the nerves
What does the superior alveolar nerve (SAN) innervate?
teeth & bone adjacent to the teeth within the maxilla
Often classified along with infraorbital nerve (ION), but it actually branches from this nerve caudal to them entering maxillary foramen at caudal aspect of maxilla
It can be blocked intraorally or extra- orally
What are the 2 methods of blocking the caudal maxilla?
Describe extra oral technique of blocking the maxilla
- Needle inserted below cranioventral border of zygomatic arch, between caudal border of maxilla & cranial border of mandibular ramus
- Needle advanced parallel to plane of hard palate & 1cm caudal to lateral canthus of eye
- needle is advanced until bone is felt, aspirate! ++ risk of venepuncture
What are the 2 methods of blocking the mandible?
What kind of block is this?
Mandibular block (rostral)
What is Intravenous Regional Analgesia (IVRA), and when is it used?
IVRA, also called Bier block, provides short-term anaesthesia for distal limb procedures, such as toe amputation
How is IVRA performed for toe amputation?
- Insert IV cannula into distal vein (e.g., cephalic or saphenous)
- Desanguinate limb using Esmarch bandage
- Place & tighten a proximal tourniquet
- Remove Esmarch bandage & inject lidocaine via cannula
- Remove cannula, inflate BP cuff, & prep limb for surgery
How does the tourniquet aid IVRA?
prevents systemic distribution of anaesthetic, ensuring localised effect & safety
What anaesthetic is commonly used for IVRA?
Lidocaine is injected to provide regional analgesia
What block is this?
Bier block in cattle
What is a RUMM block, and what does it involve?
RUMM stands for Radial, Ulnar, Median & Musculocutaneous nerve block
It involves:
- Blocking the radial nerve from a lateral approach.
- Blocking ulnar, median & musculocutaneous nerves from medial approach
What are soak catheters?
large bore catheters with tiny holes for distributing local anaesthetic into surgical site
Used for analgesia in limb amputations, extensive reconstructive surgeries, mammary strips & total ear canal ablation (TECA)
Placed before closing incision & secured to skin at end of surgery
What is a nerve locator, and what is it used for?
delivers small electrical impulses to identify nerves during regional anaesthesia
helps precisely locate target nerve by eliciting muscle twitches, improving block accuracy & minimising complications
What are the benefits of femoral and sciatic nerve blocks (PNBs) compared to epidurals?
Reduced risk of urine retention
Decreased perioperative & postoperative opioid consumption
Less impact on mean arterial blood pressure (MAP) during anaesthesia.
How do PNBs contribute to multimodal anaesthesia?
Reduce inhalational anaesthetic requirements, sparing isoflurane
Minimise side effects of opioids (e.g., nausea, dysphoria, inappetence)
Lower risk of perioperative hypotension in high-risk patients
How is lidocaine used intravenously for pain management in veterinary practice?
Lidocaine is used as CRI (Continuous Rate Infusion) for soft tissue pain in dogs & equines, such as in colic cases.
What are the benefits of IV lidocaine as a CRI?
Reduces inhalational anaesthetic requirements (decreases MAC).
Lowers opioid doses required.
Contributes to balanced anaesthesia.
Can be useful postoperatively.
What precautions should be taken when using IV lidocaine?
Only use pure lidocaine (no adrenaline).
Avoid use in cats due to their sensitivity to lidocaine.
What are the signs of local anaesthetic toxicity?
Signs include airway compromise, seizures, and arrhythmias
How can local anaesthetic toxicity be managed?
Support patient (e.g., secure airway, treat seizures & arrhythmias).
Administer intralipid if needed.
How can local anaesthetic toxicity be prevented?
Carefully calculate the dose.
Always aspirate before injecting.
Use proper technique to minimise risks.
