Nerve Blocks Flashcards
Technique for brachial plexus nerve block
Axillary approach - Puncture site is located cranial to the acromion and medial to the subscapularis
Blocks distal humerus
What nerves are blocked (7) and which spinal nerves (4) form the brachial plexus
Formed from ventral branches of C6, C7, C8, and T1
Blocks suprascapular, subscapular, axillary, musculocutaneous, radial, median, and ulnar nerves
Tuohy needle
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
Epidural complications
Urine retention
Hypotension/bradycardia
Horner’s syndrome
Respiratory depression - phrenic nerve paralysis
Total spinal anesthesia
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
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
Which local anesthetic is the least chondrotoxic
Mepivacaine - negligible effects in vitro - therefore drug of choice for intra-articular administration
Local anesthetic MOA (4) when injected intrathecally (epidural)
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
Name two amino-amides
Lidocaine and bupivacaine
Lidocaine class of drug and duration of action
Class 1b antiarrhythmic drug
Duration 1-3 hours (with epinephrine)
Why does bupivacaine cause more toxicity than other local anesthetics
Highly lipophilic
Bupivacaine potency, duration, and onset
4x as potent as lidocaine
Duration of action is 3-10 hours
20-30 minute onset of action
Cardiotoxicity of local anesthetics MOA and what can worsen toxicity?
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)
Cardiac effects seen on ECG from local anesthetics
Prolonged PR and QRS intervals and prolonged refractory period
