Locoregional Anes SA & LA Flashcards
typical LA techniques
topical
SQ
Line block
wound soaker catheter
Topical anesthesia
EMLA cream (2.5% lidocaine + 2.5% prilocaine)
- 60 min before full onset, occlusive dressing
- IVC placement
Lidocaine patch (5% lidocaine)
- analgesic effect, not complete block
- placed on incision after closure
Ophthalmic
- Tetracaine or proparacine
Laryngeal
- 0.1 mL 2% lidocaine (feline intubation)
- topical to arytenoids
SQ
use for wounds, masses, skin biopsy
- Ventral midline line block*
- infliltrate SQ & muscle layers
- Wound soaker catheter*
- placed during sx, deep aspect close to visualized nerves
- delivers consisten 7 prolonged (1-2d) analgesia
- used for TECA, Amputation , oncologic sx, lg wound closure
IVRA aka “Bier block”
- used for distal extremity
- procedure 60-90 mL
- complications: tourniquet pain, ischemia/nerve inj, limb swelling, hematoma, LA toxicity
peripheral nerve blocks - head
Retrobulbar block
Maxillary n. block
Infraorbital n. block
Inferior alveolar n. block
Mental n. block
retrobulbar block
Indications:
- Enucleation
- Evisceration/prosthesis
- Intraocular surgery
Nerves affected:
- CN II, III, IV, V, VI, ciliary ganglion (parasympathetic)
Advantages:
- Post-op analgesia
- Globe immobility during surgery
- Decreased anesthetic and NMBD requirements
Complications:
- Retrobulbar hemorrhage
- Damage to optic nerve, extraocular mm.
- Globe penetration
- Intravascular injection
- Intrathecal injection (into optic nerve/subarachnoid space)
Preferred technique:
Inferior-temporal palpebral
- High resistance to injection indicates positioning within optic nerve sheath – injection may be fatal
Peripheral nerve blocks - thoracic limb
Cervical paravertebral block
Brachial plexus block
RUMM block
“declaw” block – distal radial, ulnar, median
cervical paravertbral block
- Less common block
- Technically difficult
- Anesthesia for entire thoracic limb incl. scapula and shoulder joint
- Ventral branches of C6, C7, C8, and T1 spinal nerves, proximal to brachial plexus
Brachial plexus
Anesthesia distal to and including the elbow
RUMM block
- Anesthesia for “distal thoracic limb”
(depends on accuracy of perineural injection)
- Radial, _u_lnar, median, and musculocutaneous nerves
- Requires 2 injection sites, one medial and one lateral
block for declaw
A pre-anesthetic block is indicated for intra- and post-op analgesia
Bupivacaine 1 mg/kg divided between sites, can dilute 1:1 with salin
Peripheral nerve blocks – pelvic limb
Femoral and sciatic nn.
Must be performed together for complete stifle block
Anesthetizes distal to mid-femur
As effective as epidural for stifle surgery
Intercostal n. block
- Anesthesia for thoracotomy, rib fractures, etc.
- Nerves run w/ artery and vein along CAUDAL aspect of rib
- Block at the incision space, and 2 spaces cranial and caudal (5 total)
- Aspirate before injection, avoid thoracic cavity
Intrapleural regional
- Local anesthetic injected into thoracic cavity
- Often delivered through indwelling chest tube post-thoracotomy
- Consider gravity!
- Affected side down for at least 20 mins after injection
- Generally safe and effective
Epidural
- Most commonly performed at the L-S space in small animals
- Requires heavy sedation or anesthesia
- Anesthesia caudal to umbilicus (generally)
Two options:
- Single injection (most common)
- Epidural catheter
Epidural – positioning
- Depends on anesthetist preference and patient condition
Sternal recumbency
- Easier to palpate landmarks
- Legs pulled forward (hips flexed) to maximize L-S space
- Allows hanging drop technique
Lateral recumbency
Epidural injection volume
- Higher volume → more cranial drug spread
- Concern for sympathetic blockade and hypotension with local anesthetic
- Volume 0.2 mL/kg will reach L1
- Sufficient for caudal abdomen, pelvic limbs, perineum
epidural drugs
Most commonly a local anesthetic + opioid
Bupivacaine + morphine
- This combo may provide analgesia for up to 24 hours
Morphine is less lipid soluble than other opioids
- More cranial spread
- Longer duration of action
- Morphine L-S epidural can provide analgesia to thoracic wall and thoracic limbs
epidural complications
Intrathecal (spinal) injection
Use ½ volume if CSF is obtained
Neural damage/toxicity
Use preservative-free, “for epidural use”
Infection
Sterile technique
Hypotension
Fluids and/or vasopressors
epidural opioids complications
Urinary retention
Express bladder post-operatively
Monitor closely for urination before discharge
Pruritis – uncommon
Equine eye
Auriculopalpebral n. block
- Prevents blinking – allows ophthalmic exam
- MOTOR BLOCK ONLY
Supraorbital n. block
- Sensory to middle 2/3 of upper eyelid and palpebral motor
- Used for placement of sub-palpebral lavage catheter (common use)
Retrobulbar block
- transpalpebral most common
- Most commonly used for standing enucleation
Equine epidural anesthesia
- Caudal (not lumbosacral) epidural
- Do not want to lose hind limb motor function
Uses:
- Control of rectal tenesmus
- Correction of uterine torsion, fetotomy, obstetric manipulations
- Tail amputation, rectovaginal fistula repairs, Caslick’s procedure
- Hindlimb procedures and pain (but do not use local anesthetics → motor blockade)
Location:
First coccygeal space
(Co1-Co2)
First movable articulation when tail is raised and lowered
Equine epidural anesthesia – drugs
Local anesthetics:
Remember – these cause motor blockade
Excessive cranial spread to spinal cord segments innervating the pelvic limbs ⇒ hindlimb ataxia or mm. weakness
EXTREMELY DANGEROUS IN A HORSE
Lidocaine 2% 6-8 mL in an adult horse is adequate for anus, perineum, rectum, vulva, vagina, urethra, bladder
Alpha-2 agonists:
Xylazine, detomidine (common)
Causes local analgesia and systemic alpha-2 effects (sedation, 2nd degree AV block, ataxia, etc)
Opioids:
Morphine
- Provides analgesia
- No risk of weakness or motor blockade
- Often administered through epidural catheter for longerterm (days) analgesia
- Hindlimb trauma, surgery, severe laminitis
Side effects: urticaria, ileus
Detomidine + morphine
Common combination
Can provide excellent analgesia for hindlimb pain
Local anesthesia for castration
Commonly used for adjunctive analgesia
Allows lower dose of general anesthetics
~20 mL lidocaine injected into each testicle
Should feel firm after injection
Quickly diffuses into spermatic cord to provide anesthesia
Line block
Lidocaine injected along proposed incision line
Inverted L block
Lidocaine injected into area dorsocaudal to last rib and ventrolateral to lumbar transverse processes
Proximal paravertebral thoracolumbar
Anesthetizes dorsal and ventral branches of T13, L1, L2 spinal nn.
Injection site 3-5 cm from dorsal midline, majority of drug deposited
at VENTRAL aspect
Disadvantages:
Technical difficulty (esp. fat cattle)
Scoliosis may cause difficulty closing incision
Risk of penetrating great vessels
Loss of motor control if LA migrates to femoral nn.
Distal paravertebral thoracolumbar
Dorsal and ventral branches of spinal nn. T13, L1, L2
Dorsal and ventral to transverse processes of L1, L2, and L4
Advantages over proximal paravertebral:
Lack of scoliosis
Less risk of penetrating major blood vessels
Caudal epidural
Obstetric manipulations and surgical procedures for tail, perineum, anus, rectum, vulva, vagina, prepuce, scrotum
Commonly and easily performed
S5-Co1 or Co1-Co2 space
Remember that total dose (volume x concentration) effects the cranial spread and extent of anesthesia
Local anesthetics, alpha-2 agonists, morphine
Lumbosacral epidural
Good for immature cattle, small ruminants, camelids, and pigs
(generally not for adult cattle)
L6-S1 space
Alpha-2 agonists commonly utilized
Similar technique as for dogs
Teat
Local anesthesia
- Ring block
- Inverted V block
- Teat cistern infusion
- IV regional anesthesia of the teat
Udder
Paravertebral block of L1, L2, L3
- Cranial aspect of udder and teats
High caudal epidural
- Caudal aspect of teats and udder
Foot
Common site of injury or disease
- Ring block
OR
- IVRA (similar technique as in small animal)
Testicular block for castration
Cattle, goats, sheep, swine
Lidocaine most common
Volume dependent on size of patient
Be cognizant of the maximum systemic dose, especially for smaller
animals
