Chapter 122-125: Neuroaxial Anesthesia Flashcards
What are some advantages of using spinal anesthesia?
Decreased incidence of DVT, cardiac morbidity and mortality from decreased stress response, decreased bleeding and therefore need for transfusion; decreased incidence of LE graft occlusion and ? postoperative pneumonia.
In terms of how a spinal block sets up- how are the following temporally related?
Parasympathetic and sympathetic fibers, B fibers, C fibers and A fiers
Parasympathetic/Sympathetic lose conductivity before anything else and then C, followed by B and then A (which is why motor is last to go)
In terms of dermatome patterns and spinal anesthesia, how are motor fibers, skin anesthesia and autonomic nerve fibers related?
Because of increased sensitivity of the autonomic nerve fibers, blockade of the these nerves extends 2 dermatomes ABOVE the skin anesthesia and the motor is 2 dermatomes BELOW the skin anesthesia
What are important factors related the height of spinal anesthesia?
Baricity of solution, patient positioning both during injection and immeidately after injection; drug dose; injection site
Other less important factors include: age, height of patient, intraabdominal pressure (pregnancy, spinal stenosis), spinal curvature, volume of CSF, injectate volume, needle direction
What are CV effects of spinal anesthesia
vasodilation below block causes decreased SVR, decreased preload, and decreased CO. If get T1-T4 block you will block the cardiac accelerator fibers and get bradycardia and profound hypotension
What are pulmonary effects of spinal anesthesia?
if block up to mid thoracic level get decreased VC, but usually normal TV. For COPD patients that rely on their accessory muscles they may have respiratory compromise.
High spinal apnea is usually from hypoprofusion of brain stem, NOT block of C3-C6 (phrenic nerve)
Spinal cord ends at what level in adults?
L1-L2
Dural sac ends at what level in adults?
S2
What is the site of action for epidurally located local anesthesic?
Spinal nerve roots is the main target where the dura is relatively thin, only a small amount will diffuse across the dura into the subdural space
What is a good starting target to calculate the amount of local anesthetic to use in epidural?
1-1.5 mL of local anesthetic per segment to be blocked; once it starts to receed 1-2 dermatomes you will need approximately 50% of the original dose.
Be care in obese patients and pregnant patients as theirs may spread more cephalad than expected
What does adding epinepherine do to A) lidocaine and B) bupivicane in the epidural space?
A) lidocaine- prolongs the block by 50% by reducing systemic absorption and because the local anesthetic stays by the nerve roots the onset is quicker and duration is longer. It also acts on the alpha receptors located in the CNS modulating central pain processing centers.
B) No significant changes occur with addition of epi to bup
For labor CSE when can you get by with intrathecal opioids only?
During first stage of labor
What are some advantages of CSE technique for labor pain?
1) onset of anesthesia/analgesia is faster than epidural
2) less likely to fail with epidural because of verification of spinal portion
3) subsequent epidural dosing may provide greater sacral coverage because of translocation from dural hole
4) If use for c/s you have ability to redose as needed (i.e. protracted surgery course)
What are some disadvantages to CSE technique?
1) delayed ability to know if epidural catheter will work
2) intrathecal opioids cause itching
3) IT opioids may increase incidence of fetal heart rate declerations
What is the incidence of neurologic dysfunction from hemorrhagic complications from neuroaxial techniques?
Exact incidence is unknown, but incidence cited in literature is less than 1:150,000 epidurals and 1:220,000 spinals
