Analgesics & Sedatives Part 1: Pain Pathways, Pt.2 Local anesthetics

Question 1

What are the 5 distinct processes involved in the pain pathway?

Answer 1

1. Transduction
2. Transmission
3. Modulation
4. Projection
5. Perception

Question 2

What is the definition of chronic pain?

Answer 2

Pain that persists longer than is providing protection

Question 3

What are the hallmarks of chronic pain?

Answer 3

1. Hyperalgesia
2. Allodynia

Question 4

What is allodynia?

Answer 4

• Non painful stimuli elicits pain
• Abnormal or confused response to a non-painful stimuli

Ex: petting or brushing hair elicits pain when it shouldn’t normally cause pain

Question 5

What is hyperalgesia?

Answer 5

exaggerated perception of pain

Primary: occurs at the site of injury
Secondary: occurs beyond the region of injury

Question 6

Neuron alteration occurs through 2 main changes:

Answer 6

1. Peripheral sensitization -Nociceptors
2. Central sensitization - Modulation

Question 7

What happens with secondary hyperalgesia?

Answer 7

• Vasodilation
• Inflamm mediators activate more nociceptors adjacent to injury

Question 8

___________ occurs in the dorsal horn of the spinal cord and involves _______ receptors

Answer 8

Central sensitization/Modulation, NMDA receptors

Question 9

What parts of the pain pathway do local anesthetics work on?

Answer 9

Transduction, Transmission, and Modulation

NOT PERCEPTION

Question 10

What local anesthetics are metabolized in plasma and eliminated in urine?

Answer 10

Esters

Ex: proparacaine

Question 11

What local anesthetics are metabolized by the liver and eliminated in urine?

Answer 11

Amides like..

1. Lidocaine
2. Bupivacaine
3. Mepivacaine
4. Ropivacaine

Question 12

Which of the following have a longer half life?
A. Amides
B. Esters

Answer 12

A. Amides

Question 13

Local use of lidocaine can be used concurrently with ___________

Answer 13

Epinephrine

** vasoconstriction allows for prolonged effects at local site of injury

Question 14

What underlying disease may increase the duration of action of amides?

Answer 14

Hepatic insufficiency

** bc metabolized by liver, causes drug accumulation

Question 15

What is the main effect of local anesthetics?

Answer 15

Reversible blockade of transmission in peripheral nerves or spinal cord to STOP PAIN signal from progressing

Question 16

What is an IMPT species difference when administering local anesthetics?

Answer 16

CATS are sensitive and require lower doses

SHEEP more sensitive than other livestock

Question 17

Why would you local anesthetics via a coccygeal epidural?

Answer 17

Feline urinary obstruction

Blocks pudendal and pelvic nerves

Question 18

Which of the following amides has the fastest onset of action?

Answer 18

Lidocaine

Question 19

What is the most commonly used local anesthetic in vet med?

Answer 19

Lidocaine

Question 20

Mixing lidocaine with ________ can reduce pain/stinging at the site of injection

Answer 20

Sodium bicarb

Question 21

Clinical uses of systemic lidocaine?

Answer 21

1. Class 1B antiarrhythmic - used to control ventricular tachycardia
2. Preanesthetic
3. Analgesic and some anti-inflamm properties (Ex: pancreatitis, post op visceral pain)
4. Antioxidant properties (helps prevent ischemia-reperfusion injury)
5. GI prokinetic to stimulate GI motility in horses (treat/prevent post op ileus)

Question 22

_________ can be used systemically to control ventricular tachycardia

Answer 22

Lidocaine

Question 23

Clinical uses for bupivacaine?

Answer 23

1. Regional analgesia
2. Onychectomy (declaw)
3. Wound soaker catheter

Question 24

Bupivacaine Liposome injectable suspension (Nocita) is FDA approved and labeled for…

Answer 24

1. Cranial cruciate repair
2. Onychectomy (declaw)

Question 25

__________ can be used for diagnostic nerve blocks in horses

Answer 25

Mepivacaine and Ropivacaine

Question 26

___________ are similar to lidocaine but less irritating

Answer 26

Mepivacaine and Ropivacaine

Question 27

List the amides from shortest to longest duration of action

Answer 27

1. Lidocaine (shortest)
2. Mepivacaine
3. Ropivacaine
4. Bupivacaine (longest)

Question 28

________ can be used topically as an ophthalmic formulation to numb the eye for a corneal and conjunctival eye exam

Answer 28

Proparacaine

Question 29

Contraindications of proparacaine?

Answer 29

Long term corneal use can cause toxic effects over time!!

Question 30

___________ is a ester local anesthetic that is very toxic to cats, resulting in heinz body anemia

Answer 30

Benzocaine

Question 31

What is the MOA for local anesthetics?

Answer 31

Binds to Na+ channel receptors, resulting in a Na+ channel blockade

** prevents nerve impulse from transmitting pain to next step in pain pathway

Question 32

Regarding PK of local anesthetics, ___________ and __________ are blocked before _____________

Answer 32

Pain sensation and autonomic transmission blocked before motor transmission

Question 33

When placing a wound soaker catheter, which analgesic is recommended for use?

Answer 33

Bupivacaine

Question 34

When doing an intercostal nerve block, injections should be administered ___________

Answer 34

Caudal to the rib head at the level of the transverse spinal processes

Question 35

Although uncommon, what complications can occur when doing an intercostal nerve block?

Answer 35

1. Pneumothorax
2. Accidnetal IV admin
3. Pumonary damage
4. Phrenic nerve paresis

Question 36

Intercostal nerve blocks using analgesics is indicated for _____________

Answer 36

Thoracotomy patients, chest tubes, rib fractures

Question 37

Risks associated with local analgesics?

Answer 37

1. Nerve injury
2. Local irritation
3. Risk of toxicity if systemically absorbed
   - CNS stimulation OR depression
   -cardiovasc depression

Question 38

Systemic toxicity of analgesics can be treated with __________

Answer 38

IV lipid emulsion (ILE)