Spinals part 2 Flashcards
in what order are nerve fibers sensitive to LA? (most sensitive to least sensitive)
in what order are they blocked? (first to last)
large myelinated > smaller myelinated > smaller unmyelinated
B fibers
C and A-Delta fibers
larger A-gamma, A beta, and A-alpha fiberes
what do B fibers do?
preganglionic sympathetic efferents
what do C and A-delta fibers do?
pain, temp, touch afferents
post ganglionic sympathetics
factors that affect differential blocks?
size/myelination of the fibers
nodes of ranvier
location depth
Na and K channels on each nerve
in waht order are the nervous systems blocked?
sympathetic, sensory, motor
sings of a sympathetic block? and how to sympathetic, sensory, and motor block levels compare?
BP changes may be the first sign, and is usually 2 segments higher than the sensory block, which is usually 2 levels higher than a motor block
most accurate way to check for sensory block?
sharp or broken tongue depressor
is loss of sensation to cold or sharp pain first?
sesation to cold is first and occurs at higher levels
what fibers are blocked first in motor blockade?
A beta and A gamma, A alpha is a profound block
2 most important factors that affect height of nerve block for SAB?
baricity and patient position
how do you get a saddle block? what is it good for?
sitting position for SAB, leave sitting for 3-5min with a hyperbaric solution. Great for lower perineal procedures
how does LA distribute in position is sitting to supine with hyperbaric solution?
it moves more cephalad to the dependent region of the lumbar curve
spine high points in cervical and lumbar lordosis?
C3 and L3
spine low points in thoracic and sacral kyphosis?
T6 and S2 low points
other factors affecting height of spinal block?
age - older ligamentum flavum gets tougher and intrathecal space gets compressed, so higher spread of LA
height, more distance to travel and can increase dose
weight, decrease in intrathecal and epidural space if obese or pregnant
spinal fluid rate of circulation (coughing and straining)
hypobaric LAs?
tetracaine 0.33% with water
lidocaine 0.5% with water
isobaric LAs?
tetracaine 0.5% with 50% CSF
lidocaine 2% with water
bupivicane 0.5% with water
hyperbaric LAs?
tetracaine 0.5% with 5% dextrose
lidocaine 5% with 7.5% dextrose
bupivicane 0.5% with 8% dextrose
bupivicaine 0.75% with 8% dextrose
primary goal of neuraxial anesthesia?
block afferent fibers located in dorsal roots
motor and sympathetic fibers are close and they get blocked as they pass through ventral root
why must you use preservative free LA in SAB?
parabns high allergy potential
sulfites neurotoxic
EDTA muscle pain and can cause tetany