Flashcards in Regional and Neuraxial Anesthesia Deck (92)
Anterior or posterior nerve roots carry sympathetic outflow? Motor outflow?
Where do you expect the C8 dermatome to include?
The 5th finger and medial aspect of the arm
A-alpha nerve fibers are responsible for what? Are they large or small and myelinated or unmyelinated?
Motor (thick myelinated)
A-delta nerve fibers are responsible for what? Are they large or small and myelinated or unmyelinated?
Pain & temperature (thin myelinated)
C nerve fibers are responsible for what? Are they large or small and myelinated or unmyelinated?
Pain & temp (small, unmyelinated)
Why do you have differential blockade with spinal anesthesia when using a hyperbaric spinal anesthetic?
Local anesthetic concentration in the intrathecal space at more cephalad levels are lower than in the caudal levels
Where does the sympathetic chain run?
Where does the parasympathetic chain run?
CN III, VII, IX, X, S2-S4
Why would a patient develop cardiac arrest after neuraxial block?
Unopposed vagal influence on the heart
Why would a patient with severe aortic stenosis die after spinal anesthesia?
In patients with AS, LVEDP is high -> spinal anesthesia decreases preload and afterload -> decreased aortic diastolic pressure results in decreased LV perfusion -> MI
How does spinal anesthesia affect inspiratory and expiratory mechanics?
Decreased both (intercostal and abdominal muscles) -> decreases pulmonary reserve
What do local anesthetics bind to?
Intracellular side of the alpha subunit of voltage gated sodium channels during the inactivated or activated states (not resting state)
What does pKa determine for local anesthetics?
Onset of action (although concentration and environmental pH also plays a role)
What determines potency of a local anesthetic?
What determines duration of action of anesthetics?
Protein binding, larger doses (longer duration), vasodilatory activity (more vasodilatory = shorter duration i.e. lidocaine)
Rate the following in highest rate of absorption to lowest: IV, caudal, brachial plexus, sciatic, subQ, tracheal, intercostal, paracervical, epidural
IV > tracheal > intercostal > caudal > paracervical > epidural > brachial plexus > sciatic (peripheral nerve) > subQ
What kind of local anesthetic was probably used if a patient has an allergic reaction and what compound is it mostly due to?
Esters because of PABA formation after metabolism; although some amides contain preservatives (methylparaben) which can also cause an allergic reaction
How are ester local anesthetics metabolized?
Metabolized by pseudocholinesterases
What local anesthetic can cause methemoglobinemia?
Benzocaine (independent of metabolism?) and prilocaine (metabolized to O-toluidine derivatives which oxidizes iron to the ferric state)
How are amide local anesthetics metabolized?
What is transient neurologic symptoms and what local anesthetic is classic for it?
Radicular irritation after spinal anesthesia (i.e. burning and aching in buttocks and lower extremities with NO loss of sensation or motor function); Lidocaine
Intravascular bupivacaine or ropivacaine injections require what treatment?
Intralipids; other local anesthetics are less protein bound and are less responsive to intralipids
How long do you need to wait to give a single shot spinal/epidural in patients with once daily lovenox? Twice daily lovenox? When can you restart the lovenox?
Once: 12 hours after last dose and restart 6 hours after block
Twice: 24 hours after last dose, and restart 24 hours after block
When can you place an epidural catheter with a patient on lovenox for DVT ppx? When can you remove an epidural catheter? When can you restart lovenox after catheter is in? After catheter is removed?
Placement: 12 hours after last dose
Restart: 6-8 hours after catheter placed
Remove: 12 hours after last dose
Restart: 2 hours after catheter removed
How long should clopidogrel be stopped before an epidural is placed?
What INR and aPTT is the cutoff for epidural placement?
INR should be less than 1.5
aPTT less than 40
How long do you need to wait for epidural placement in a patient with heparin ppx? When can you restart the heparin?
Placement: Anytime; if more than ppx dosing, check aPTT and it should be less than 40
Can restart after 1 hour after catheter placement
The inferior tip of the scapula correlates to what vertebral level? Prominent cervical thoracic process? Superior iliac crest? Posterior superior iliac spine?
If a patient is given a hyperbaric lidocaine spinal injection and laid supine, what spinal level would the block travel caudally?
T6 (normal kyphosis of the back in the supine patients limit the movement to this level)