Nerve Blocks

Question 1

Technique for brachial plexus nerve block

Answer 1

Axillary approach - Puncture site is located cranial to the acromion and medial to the subscapularis
Blocks distal humerus

Question 2

What nerves are blocked (7) and which spinal nerves (4) form the brachial plexus

Answer 2

Formed from ventral branches of C6, C7, C8, and T1
Blocks suprascapular, subscapular, axillary, musculocutaneous, radial, median, and ulnar nerves

Question 3

Tuohy needle

Answer 3

Comes insulated or non insulated
Curved at the distal tip
Facilitates placement of indwelling epidural or perineural catheters
Duller than hypodermic and spinal needles to feel all tissue planes

Question 4

Epidural complications

Answer 4

Urine retention
Hypotension/bradycardia
Horner’s syndrome
Respiratory depression - phrenic nerve paralysis
Total spinal anesthesia

Question 5

Urine retention
Hypotension/bradycardia
Horner’s syndrome
Respiratory depression
Total spinal anesthesia

these are all possible complications associated with epidurals. What is the MOA of each

Answer 5

Urine retention - due to detrusor muscle relaxation
Hypotension/bradycardia - sympathetic blockade
Horner’s syndrome - Blockade of sympathetic trunk at cervical dermatomes
Respiratory depression - extensive migration causing phrenic nerve paralysis
Total spinal anesthesia - depression of cervical spinal cord and brainstem

Question 6

Which local anesthetic is the least chondrotoxic

Answer 6

Mepivacaine - negligible effects in vitro - therefore drug of choice for intra-articular administration

Question 7

Local anesthetic MOA (4) when injected intrathecally (epidural)

Answer 7

Inhibit K and Ca channels at the level of the dorsal horn*
Inhibit substance P binding*
Increases intracellular Ca
Inhibit glutamatergic transmission in the spinal dorsal horn neurons reducing NMDA and neurokinin-mediated postsynaptic depolarizations

Question 8

Name two amino-amides

Answer 8

Lidocaine and bupivacaine

Question 9

Lidocaine class of drug and duration of action

Answer 9

Class 1b antiarrhythmic drug
Duration 1-3 hours (with epinephrine)

Question 10

Why does bupivacaine cause more toxicity than other local anesthetics

Answer 10

Highly lipophilic

Question 11

Bupivacaine potency, duration, and onset

Answer 11

4x as potent as lidocaine
Duration of action is 3-10 hours
20-30 minute onset of action

Question 12

Cardiotoxicity of local anesthetics MOA and what can worsen toxicity?

Answer 12

They block cardiac Na channels and decrease the max rise of Phase 0 of the action potential causing inhibition of cardiac conduction
Direct negative inotropic effects
Hyperkalemia can markedly increase CV toxicity (remember K gradient across cardiac myocyte membranes is important in establishing membrane potential)

Question 13

Cardiac effects seen on ECG from local anesthetics

Answer 13

Prolonged PR and QRS intervals and prolonged refractory period