Regional Anesthesia Flashcards
Nocieption has what 2 systemic effects?
- Sympathetic stimulation - catecholamines —> incr HR and BP
- Stress response - ACTH incr —> cortisol and BG
What are reasons to provide regional anesthesia?
- Pre-emotive analgesia: reduction of anesthetic drugs
- Reduction of intraoperative complications
- better intra/postoperative pain control
- Faster return to normal activities
- prevents stress response
- Better immune system activity
What are the target structures for topical/surface anesthesia and what are some instances you might use it?
Target structures = free nerve endings, nociceptors
- Uses:
- larynx: avoid laryngospasm
- splash block: reduce postoperative pain
- corneal: proparacaine drops for eye exam
- skin desensitization: EMLA cream - venipuncture/small mass removal (1 cm deep)
Describe local infiltration method and list some of its uses
injection of local anesthetic solution into and around the planned surgical field; does NOT target a specific nerve
Uses:
- resection of cutaneous/superficial mass
- surgical closure of lacerations
- procedures involving an appendage
Name some specific examples of local infiltration
- Line block; infiltrate the SQ and underlying tissues
- Intratesticular block; only for castration
- Ring block; extremity, distal limbs, tail, horn (dehorning)
Where should you make sure to NEVER use lidocaine with epinephrine?
Where there is no collateral circulation; I.e. tail, horn
Where are epidurals most commonly performed in small animals?
The lumbosacral space
The epidural space is between what two anatomical structures?
The interarcuate (flavum) ligament and the dura mater
What are your landmarks for performing an LS epidural on a small animal?
- Iliac crest
- medial sacral crest
- spinous process of L7
When performing an epidural, what is the order of the structures pierced by the needle?
- Skin
- Supraspinous ligament
- Interspinous ligament
- Interacuate ligament (roof of epidural space)
What things are included in an epidural kit?
A Tuohy needle, a loss of resistance syringe, and an epidural catheter
Describe the hanging drop technique
- Advance the Tuohy needle until the interarcuate ligament is perceived
- Removed the stylet and fill the hub of the needle with saline
- When the needle enters the epidural space, the drop should be aspirated
False negatives can occur
Describe the loss of resistance technique
- Advance the Tuohy needle until the interarcuate ligament is perceived
- Remove the stylet and attach the syringe to the hub
- Apply small pressure to the plunger and advance the needle thru the interarcuate ligament
- The resistance to the injection of air suddenly drops when needle enters the epidural space
How do epidurals using local anesthetics vs. opioids differ?
- LA epidurals cause motor AND sensory blockade
- autonomic block causes vasodilation
- Opioid epidurals cause analgesia WITHOUT motor blockade
What are the 2 most common local anesthetics used to perform epidurals?
- Lidocaine: fast onset, short duration (<90 min)
- Bupivicaine: slow onset, long duration (up to 6-8h)
- Low concentration bupivicaine: shorter motor block but preserves sensory block
What are the 2 most common opioids used to perform epidurals?
- Fentanyl: high lipid solubility—>absorbed to systemic circulation = duration < 2 hr
- Morphine: low lipid solubility—>slow onset over 1 hr, duration = 12 hr
- SE: severe pruritus and urinary retention
Studies show that epidural anesthesia can provide dose/volume-dependent analgesia to areas of the body outside of just the LS space. What is the term for this?
Segmentary analgesia
Why might you perform a sacro-coccygeal epidural?
- Perineal surgery
- Pelvic limb surgeries
- Urethral obstructions - cats
What is a true and tested method of determining adequate sacrococcygeal epidural needle placement in cats?
A nerve stimulation test
Describe peripheral nerve blocks
- Injection of a LA around a periph nerve to temporarily block sensory and/or motor functions for perioperative pain control
- Injection of small volume of LA produces a great area of desensitization
- precision on injection plays essential role in success rate
T or F: intraneural injections can produce nerve damage
True
What are some disadvantages to using blind techniques for locating a peripheral nerve?
Use anatomical landmarks
- Relies on experience of operator
- Subjective
- variable success rate
- higher volume of LA needed
- higher nerve puncture/damage risk
- individual anatomical variation
Describe some advantages and disadvantages of using nerve stimulation to locate a peripheral nerve
Electrical current used to depolarize the motor component of a mixed nerve; current required to depolarize the nerve related to nerve-to-needle distance
- Adv: high success rate, lower volume of LA needed
- Disadvantages:
- Pure sensory nerves cannot be located by this method
- Needles are insulated so only conduct current at the tip
Why is ultrasound guided peripheral nerve location the gold standard for peripheral nerve blocks?
- Allows real time visualization of nerves and vascular structures, as well as visualization of the LA spread around the nerve
- However, equipment is expensive and there’s a learning curve
What type of ultrasound transducer do you want for US guided peripheral nerve blocks?
- High frequency (10-15 MHz), low penetration (2-5 cm), high definition
What nerves might be blocked using a blind ring block for a declawing procedure?
The radial, ulnar and median nerves
What are some indications to perform an infraorbital nerve block?
- Nose surgeries
- Rhinoscopy
- Extractions (incisors, canines)
What should you be careful of when performing an infraorbital block in cats and brachycephalic dogs?
Ocular puncture
What are the indications for a maxillary nerve block?
- Same as infraorbital (extractions, nose surgeries, rhinoscopy)
- molar extractions
- maxillary surgeries
What is a good rule of thumb for any block?
Always aspirate before injection to check extravascular position
What are the indications for an inferior alveolar (mandibular) nerve block?
- Mandibular fractures
- mandibular teeth extractions
What is a potential complication with inferior alveolar nerve blocks?
Spread and block of lingual nerve
Intercostal nerve blocks should be performed on what side of the rib?
Caudal
What are the indications for intercostal blocks?
- Lateral thoracotomies
- Rib fractures
- Mass removals
