Local Anesthetic Agents 2 Flashcards
What is part of “multi-modal pain therapy”?
Locoregional anesthesia
Dose reduction of anesthetics can lead to what?
Reduced side effects
Selective nociceptive blockade can provide what type of relief?
Short or long term pain relief
What are 3 formulations of local anesthetics?
- Injectable with preservatives
- Injectable without preservatives
- Topical
Where are topical anesthetics applied?
Skin or mucous membranes
Topical anesthetics are very effective on what 4 areas?
- Eyes
- Nose
- Mouth
- Arytenoids
Topical anesthesia has less effective penetration of what type of skin?
Intact skin
What is EMLA cream?
When is it applied?
How long does it last?
- Eutectic mixture of local anesthetics
- Apply for 1 hour prior to intended use
- Anesthesia for 2 hours
With a low dose of ELMA cream, a cat usually won’t develop what?
Methemoglobinemia
What is used to prevent laryngeal spams during intubation?
Approximately how much is used?
- Lidocaine spray
- 0.1 ml over arytenoids
A subcutaneous injection of small volumes of local anesthetic into tissues is what type of block?
Infiltrative local block
With an infiltrative local block, there is diffusion into where?
Surrounding tissue, anesthetizing nerve fibers and endings.
What are 3 examples of infiltration blocks?
- Incisional line block
- Inverted L block
- Soaker catheters
Which drug is usually used in an incisional line block?
Bupivacaine
Where is an incisional line block injected?
Laterally to incision.
What are the 2 landmarks of an inverted L block?
- Caudal border of Rib 13
- Ventral to lateral processes of lumbar vertebrae
What type of block gets deeper into tissues compared to topical?
Soaker catheter
A delivery tube and sterile multi-pore catheter is placed the the surgical site with what type of block?
Soaker catheter
How is local anesthetic delivered with a soaker catheter?
Intermittent injections or elastomeric reservoir pump
When is a soaker catheter placed?
After surgical procedure has been finished.
What are 2 measurements that need to be made for a soaker catheter?
- Length of catheter required for wound
- Length of catheter need to tunnel injection port under skin to a suitable site for administration
Do you need to suture in a soaker catheter?
No
What is a disadvantage of soaker catheters?
Now have FB in site of incision, may lead to infection.
Should you use a soaker catheter in an active dog?
No
What are 3 indications for use of a soaker catheter?
- Amputation
- Thoracotomy
- Total ear canal ablation
Which out of the following local anesthetic pKa’s would have the fastest onset of action when being delivered in human tissue?
a) pKa 7.5
b) pKa 7.8
c) pKa 8.1
d) pKa 8.4
e) all have similar onset of action
A) pKa 7.5
What is the first sign of toxicity you will witness in an awake animal administered Bupivacaine?
a) Seizures
b) Gastrointestinal ileus
c) Cardiovascular depression
d) Respiratory depression
e) Vomiting
C) Cardiovascular depression
Which nerve fibers are least susceptible to local anesthetics?
a) A delta fiber
b) C fibers
c) A alpha fibers
d) B fibers
e) A beta fibers
C) A alpha fibers (motor fibers)
Injection in the immediate vicinity of individual peripheral nerves or a nerve plexus describes what type of nerve block?
Peripheral nerve block
What are 5 examples of nerve groups that peripheral nerve blocks can be used on?
- Cranial
- Cervical
- Thoracic
- Lumbar
- Sacral
What are 4 examples of cranial nerve blocks commonly used in small animals?
- Infraorbital
- Maxillary
- Mandibular
- Mental
What are 4 locations desensitized by an infraorbital nerve block?
- Upper dental arcade adjacent to injection & rostral
- Upper lip & nose
- Dorsal aspect of nasal cavity
- Soft & hard palate
Where is the infraorbital foramen located?
Dorsal to the rostral edge of the upper fourth premolar.
Could an infraorbital nerve block work for molars?
No
What are 3 examples of indications for an infraorbital nerve block?
- Extraction of canine
- Extraction of incisor
- Extraction of premolar
What are 2 areas desensitized by a maxillary nerve block?
- Ipsilateral upper dental arcade
- Maxilla
Would both a maxillary and infraorbital nerve block be necessary?
No, maxillary will do everything infraorbital will do.
Where is the injection given for a maxillary nerve block?
Dorsal and caudal to the last molar and ventral to the junction of the zygomatic arch and maxilla.
Should injection site be shaved/cleaned for a maxillary nerve block?
Yes
What is an intraoral way to give a maxillary nerve block?
When would you not use this route?
- Just behind the last molar and straight up until reach bone.
- Severe gingivitis
What ipsilateral teeth are desensitized with a mandibular nerve block?
- Incisors
- Canine
- Premolars
- Molars
What is another area desensitized by a mandibular nerve block?
Skin and mucosa of chin and lower lip.
Where is an extraoral mandibular nerve block given?
Ventromedial aspect of ramus of mandible dorsal and rostral to the angular process.
Where is an intraoral mandibular nerve block given?
Just behind and a little bit medial to last molar. If teeth not present can still palpate for foramen.
What are 3 locations desensitized by a mental nerve block?
- Rostral mandible
- Ipsilateral canine
- Ipsilateral incisors
Where is a mental nerve block administered?
Middle mental foramen, ventral to lower first and second premolars.
What are 4 examples of cervical and thoracic nerve blocks?
- Brachial plexus
- Forelimb nerve
- Forefoot
- Intercostal nerve
Where does a brachial plexus block provide anesthesia?
Elbow and distal
What are 3 examples of uses for a brachial plexus block?
- Radius/ulna fracture
- Toe amputation
- Carpal arthrodesis
What is arthrodesis?
Permanent surgical immobilization of a joint.
Would a brachial plexus block be useful for a humerus fracture?
No
The brachial plexus includes which 4 cervical/thoracic nerves?
C6, C7, C8, T1
What might be caused if a brachial plexus block is penetrated into the thoracic cavity?
Cause a pneumothorax
Where is a brachial plexus nerve block administered?
Level of first rib, caudal border of where scapula ends.
What can a nerve stimulator help with?
Help locate a nerve for a block.
What 2 things need to be done with a nerve stimulator?
- Prime line with Bupivacaine
- Flush with saline
T/F: With a nerve stimulator, the closer the needle is to the nerve, the less current is needed to stimulate the nerve.
True
What are the 4 nerves affected in a forefoot nerve block?
- Dorsal branch of ulnar nerve
- Superficial branch of radial nerve
- Median nerve
- Palmar branch of ulnar nerve
What are 2 examples of procedures a forefoot block is used for?
- Declaw
- Toe amputation
Where must the needle be introduced with an intercostal block?
Caudal border of rib.
T/F: With an intercostal nerve block, you must desensitize at least one rib space cranial and caudal to the incision.
False - Must desensitize at least 2 rib spaces cranial and caudal to incision.
Why must multiple ribs be desensitized with an intercostal nerve block?
Nerve overlap
What are 2 examples of lumbar and sacral nerve blocks that provide anesthesia of the hind leg distal to the hip?
- Femoral nerve block
- Sciatic nerve block
Where is a femoral nerve block given?
What must be done before injecting?
- Femoral triangle on medial surface of thigh.
- Aspirate for blood since near femoral artery.
Is a sciatic nerve block given on the lateral or medial side?
Lateral
What are 2 areas hindlimb nerve blocks do not work for?
- Pelvis
- High femur fractures
Hindlimb nerve blocks are used for what portion of the leg?
Procedures from stifle distally (including stifle)
What is an example of a procedure hindlimb nerve blocks are good for?
Cruciate repair
Cranial epidurals are typically done where?
Between L7 and S1
1 mL/5 kg of lidocaine or bupivacaine will travel how far with an epidural?
Analgesia as far cranial L2
1 mL/3.5 kg of lidocaine or bupivacaine will travel how far with an epidural?
Analgesia as far cranial as T5
What is the epidural dose of bupivacaine 0.5%?
0.1 mL/kg
What is the epidural dose of preservative free morphine?
0.1 mg/kg
What is the minimum amount of solution needed to travel to the thorax?
What can be added for the last 0.1 mL?
- 0.3 mL/kg
- Saline
What are you more likely to penetrate when performing an epidural in a cat?
Why?
- Dural sac
- Dural sac ends closer to L7-S1
If CSF is obtained when performing an epidural in a cat then what should be done?
Decrease dose by 1/2
A less obvious “pop” is seen in what species?
Cat
How far does the spinal cord extend in sheep and goats?
Why is this significant?
- S2-S3
- More likely to get CSF
What drug is used for epidurals in sheep and goats?
What is the dose?
- Lidocaine
- 1 mL/4.5 kg
What can be used as a guide to the L/S space in pigs for an epidural?
Vertical line through patella
What drug is used for epidurals in pigs?
What is the dose?
- Lidocaine
- 1 mL/4.5 kg
What are 3 ways to tell if you are in the correct space for an epidural?
- Hanging drop technique
- Loss of resistance
- “Pops” when passing through ligamentum flavum
What should be used with an epidural needle to prevent all the tissue that has been passed through from coring up in the needle?
Stylette
What do you do if you puncture the dural sac?
Decrease volume by 50%
What do you do if you obtain blood through the needle in an epidural?
Remove needle and try again. Do not inject if you get blood.
What are 5 contraindications for an epidural?
- Sepsis
- Coagulopathy
- Local infection at site
- Lumbosacral fractures or dislocations
- Uncorrected hypovolemia
What are 3 potential complications seen with epidurals?
- Injection into vertebral vein
- Hypoventilation & apnea
- Hypotension
What is the preferred site for epidural anesthesia in horses?
Cattle?
Dogs?
Sheep, goats, pigs?
- Horses: 1st intercoccygeal joint (caudal)
- Cattle: 2nd intercoccygeal joint (caudal)
- Dogs: Lumbosacral junction (L7-S1) cranial
- Sheep, goats, pigs: Lumbosacral junction (L6-S1) cranial
What type of epidural can be used for surgical procedures involving the tail, perineum, anus, rectum, vulva, prepuce and skin of the scrotum?
Caudal epidural
Where is a caudal epidural given?
Either sacrococcygeal or first intercoccygeal space.
Does a caudal epidural affect the hind legs?
No
What is the dose for standing caudal epidural anesthesia in a 500 kg horse?
Small ruminant?
Cattle?
- Horses: 2% lidocaine 5-7 mL; 2% mepivacaine 5 mL
- Small ruminants: 1 mL of 2% lidocaine per 50 kg BW
- Cattle: 1 mL of 2% lidocaine per 100 kg BW
What is useful for long term post-operative pain control or painful ICU patients to reduce amount of parenteral analgesics necessary?
Epidural catheter
What type of needle is used for an epidural catheter?
For a regular epidural?
- Tuohy needle
- Spinal needle
A mixture of what 2 drugs is given in an epidural catheter?
- Morphine
- Bupivacaine
Most animals do not show what with an epidural catheter?
If you do see it, what can be done?
- Motor weakness
- Further dilute bupivacaine
Morphine and/or local anesthetics (mepivacaine is less irritating than lidocaine) can be used in what technique?
Intra-articular block
