Test 1 Flashcards
What are the classifications and characteristics of A fibers?
alpha, beta, gamma, delta; fast, sharp, well-localized sensation
Name whether or not A, B, C fibers are myelinated or non-myelinated.
A and B are myelinated and C is non-myelinated.
What are the characteristics of C fibers?
slow, prolonged, poorly-localized; non-myelinated
What is the innervation, function, conduction velocity, and diameter of A-alpha fibers?
muscle spindle motor to skeletal; proprioception, motor; 15um; 100 m/s
What is the innervation, function, conduction velocity, and diameter of A-beta fibers?
touch and pressure afferents; touch, pressure; 10um; 50 m/s
What is the innervation; function, conduction velocity, and diameter of A-gamma fibers?
motor to muscle spindles; muscle spindles; 5um; 25 m/s
What is the innervation, function, conduction velocity, and diameter of A-delta fibers?
mechanoreceptors, nociceptors; pain (sharp), temperature; <5um; 25 m/s
What is the innervation/function, conduction velocity, and diameter of Type B fibers?
sympathetic pre-ganglionic, autonomic; <3um; 10 m/s
What is the function, conduction velocity, and diameter of Type C-dorsal root fibers?
pain (dull), temperature; 1um; 1 m/s
What is the function, conduction velocity, and diameter of Type C-sympathetic fibers?
post-ganglionic; 1um; >1 m/s
Review the image for interscalene block.
The targets of anesthesia for this block are the roots and proximal trunks of the brachial plexus where they are sandwiched between the anterior and middle scalene muscles at the level of the sixth cervical vertebra (C6).
The trunks are contained within the interscalene fascial sheath at this level. This block is indicated mostly for surgical anesthesia to the shoulder, upper arm, and forearm, but is often insufficient for the hand. A continuous block via interscalene catheter provides excellent analgesia after shoulder arthroplasty.
Identify the landmarks for the interscalene block.
The main surface landmark (sternocleidomastoid muscle) used for this block can be accentuated by asking the patient to reach for the ipsilateral knee and by rotating the head approximately 45º to the non-operative side. The head should also be slightly elevated, and the patient should be instructed to take a deep breath (contraction of the scalenus muscles accentuates the interscalene groove).
The interscalene groove lies immediately behind the lateral border of the clavicular head of the sternocleidomastoid muscle at the level of the cricoid cartilage (C6) and is located approximately 1 cm above the separation of the sternal and clavicular heads of the sternocleidomastoid muscle.
Define Transduction:
Noxious stimuli translated into electrical activity at the sensory nerve endings
Define Transmission:
Propagation of impulses throughout the sensory nervous system.
Define Modulation:
Efferent control of pain.; Modulation is telling the body “its not going to be so bad”.
Label the following structures of the Myelinated Nerve Fiber:
Ultrastructural features of myelinated (A) and unmyelinated (B) nerve fibers. (1) Nucleus and cytoplasm of a Schwann cell; (2) axon; (3) microtubule; (4) neurofilament; (5) myelin sheath; (6) mesaxon; (7) node of Ranvier; (8) interdigitating processes of Schwann cells at the node of Ranvier; (9) side view of an unmyelinated axon; (10) basal lamina.
Picture of anatomy of peripheral nerve:
Picture of the Unmyelinated Nerve Fiber:
________ or _______ pathways transmit pain, temperature, pressure, touch, vibratory sense, and proprioceptive information to the CNS.
Sensory or Afferent
Receptors for pain and temperature are located in the ________ and _______; those for pressure, touch, vibratory sense, and proprioception are located in the ________.
epidermis; dermis; dermis
Receptors can be classified as _______, which are located near the surface of the skin and oral mucosa, and _________, which are located in deeper skin layers, joint capsules, ligaments, tendons, muscles, and periosteum.
exteroceptors; proprioceptors
______ order neurons in the ganglia reach the spinal cord and synapse with the ______ order neuron.
first; second
What is a the primary site of opioid spinal analgesia?
substantia gelatinosa; apex of the posterior horn of the gray matter of spinal cord is capped by a V-shaped mass of translucent, gelatinous neuroglia called S.G.; Many mu and k opioid receptors, presynaptic and postsynaptic are found on these nerve cells; it is gelatinous due to low concentration of myelinated fibers.
How many cervical vetebrae exist in the human spinal cord?
7
How many cervical nerves exist in the human spinal cord?
8
How many thoracic vertebrae exist in the human spinal cord?
12
How many lumbar vertebrae exist in the human spinal cord?
5
Where does the spinal cord begin and end in the adult human vertebrae?
begins at the occipital bone and extends down between the first and second lumbar vertebrae; specifically, from the foramen magnum through to the conus medullaris near the second lumbar vertebrae; terminates in a fibrous extension known as the filum terminale (cauda equina)
How many sacral segments exist in the human spinal column?
S1-S5
How many pairs of spinal nerves exist in the human spinal vertebrae?
31 pairs; 1 pair for each segment; except 8 total for the 7 cervical, and 1 total for the 3 coccygeal segments
Of the Type A fibers, which is the slowest to be blocked? fastest?
Type A alpha is slowest, Type A delta is fastest (based on sensitivty to block on powerpoint chart)
How do local anesthetics work?
they reversibly decrease the rate of depolarization and repolarization; mainly act by inhibiting sodium influx through sodium-specific ion voltage gated channels in the neuornal cell membrane; action potential normally increases with the rush in of Na+
Tell whether dorsal and ventral are efferent or afferent.
Remember “DAVE”; Dorsal afferent, Ventral Efferent
What nerve fiber comes first in the order of a block?
Light myelinated Type B fibers; they are preganglionic/autonomic fibers with high sensitivity (based on graph in slides)
Describe visceral pain.
results from activation of nociceptors of the thoracic, pelvic, or abdominal viscera (organs); often diffuse, difficiult to localize and referred to as distant; can be a sharp pain and may increase in discomfort with deep breathing
Which fiber can be associated with a patient in acute sharp pain? Also associated with temperature.
A delta fiber
What is the sensory pathway originating in the spinal cord that transmits information to the thalmus about pain, temperature, itch, and crude touch?
The spinothalamic tract
Which part of the spinothalamic tract transmits pain and temperature?
lateral
Which part of the spinothalamic tract transmits crude touch and pressure?
anterior (ventral)
According to the Gokin article, what fibers were the most susceptible to minimal lidocaine concentrations?
Faster conducting C-fibers were more susceptible than slower ones. At 1% lidocaine, all fibers were tonically blocked.
Put the following in the correct order of “block”: A-Beta, B, A-delta, A-gamma, A-Alpha, C
B, C & A-delta, A-gamma, A-Beta, A-Alpha
Are C-fibers efferent or afferent?
They are both.
Review the following image.
Name the fiber that is a primary afferent fiber, large in diameter, fast-conducting (travel rate of 20 m/s), and myelinated.
A-delta fibers; they respond only to mechanical stimuli over a specfic intensity and are associated with a sharp, localized, and pricking quality of pain.
What is the neurotransmitter in the dorsal hor and the receptor that it acts on for an A-delta fiber?
Glutamate acting on AMPA receptors
What is the neurotransmitter in the dorsal horn for C-fibers, and the receptors they act on?
Glutamate along with certain peptides such as substance P and the receptors for glutamate are AMPA and N-methyl-D-asparate (NMDA)
The mode of transmission of an action potential through each node of Ranvier in myelinated nerve cells is called?
Saltatory conduction
Name the layers of a neuron from the outermost layer inwards:
epineurium, perineurium, fasicle, endoneurium
When are muscle tissues most sensitive?
during contraction and ischemia
What actions cause pain to visceral tissue?
sensitive to twisting and distention; insensitive to cutting, heating, and pinching (think of what they do during lap procedures)
How many milligrams of lidocaine are present in 15ml of 1% solution?
150mg
If you have a T-6 sensory block, what level is the sympathetic and motor block?
T-8 for motor and T-4 for sympathetic
When injection local anesthetic for an epidural, you inject into the _______ space; for a spinal you inject into the __________ space.
epidural; sub-arachnoid
At every level of the spine, nerve roots exit the central nervous system and enter the peripheral nervous system through openings called the _______.
foramina
The position of the white matter and gray matter in the spinal column is opposite to the brain. The white matter is in the _______ and the gray matter is _______ and has a _______ shape.
periphery; central; butterfly
Between what two vertebrae does the C8 nerve exit through?
T1 and C7; each nerve exits between the upper set of vertebrae (ex: C7 exits b/w C6 and C7)
There is a strong correlation between volume and the cranial migration of local administration in the epidural space. Do larger volumes increase or decrease the cephalad distribution of local anesthetics?
increases; epidural administration naturally has a cephalad migration
When performing a spinal you draw a horizontal line from the top of the iliac crest. What is this line called and what spinous process does it intersect?
Tuffier’s line; passes through L4 spinous process
How many vertebrae are in the lumbar spine?
How many vertebrae are in the cervical spine?
7
How many vertebrae are in the thoracic spine?
12
What 3 ligaments do you penetrate when performing an epidural or spinal?
supraspinous, interspinous, and ligamentum flavum
SAB pathway from skin level is…..
skin, subq, supraspinous, interspinous, ligamentum flavum, epi-space, dura, arachnoid, sub-arachnoid (target), pia mater
What is the normal total volume of cranial and spinal CSF?
150ml
How many ml of CSF are produced and reabsorbed each day?
500ml
What is the typical needle size used for a SAB? epidural?
24-25 gauge; epidural is tuohy needle 16-18 gauge
What are some signs/symptoms of intravascular injection of local anesthetic?
circumoral numbness/tingling, metallic taste, tennitus, possible seizure or CV collapse
What is a major sign of a total spinal?
hypotension caused by decreased CO (CV collapse) and decreased preload
What is the duration of Lidocaine/Mepivacaine? (Long, Short, Intermediate)
Intermediate
What are the 3 most important factors in determining distribution of local anesthetics?
baricity of solution, position of patient during and just after injection, and dose injected
What factors increase the duration of a local anesthetic?
vasoconstrictors, alkalinization (increases the speed of onset by increasing the un-ionized portion which will penetrate the lipid membrane), clonidine (alpha-2 agonist—unclear on action of prolongation), site of injection (most rapid onset and the densest block occurs at site of injection)
What is the key factor in the height of a block?
Volume
Dosing guidelines for epidurals in adults is ___ to ____ ml per segment to be blocked.
1-2 ml per segment; example: T10 block from L3-4 injection…. 9-18ml of local anesthetic
What are absolute contraindications to epidural blockade?
patient refusal, hypovolemia (sympathectomy with severe hypovolemia can cause profound circulatory collapse), increased ICP (may predispose pt to brainstem herniation if accidental dural puncture occurs or if large volume is rapidly injected into epidural space), and infection at site
Where does the spinal cord end in the adult?
between L1 and L2
What is the primary site of action for local anesthetics with spinals and epidurals?
nerve root
What is the initial dose of an epidural when given above the lumbar spine?
0.7 to 1 ml per segment
type of injection that anesthetizes a small area - one or two teeth and associated structures/tissues
local infiltration
Local infiltration injection is deposited near
apices or terminal nerve endings
Type of injection that anesthetizes a larger area than the local infiltration
nerve block
the nerve block injection is deposited near
large nerve trunks
Abnormal sensation from an area such as burning or prikcling
parathesia
What is a post-op risk of an improperly placed epidural that punctures past the eidural space?
Anytime you perform a spinal you are at risk of a post-dural puncture headache; an epidural catheter is larger and can cause a greater leak in this space.
What fibers are myelinated, autonomic, and pre-ganglionic?
Type B fibers
Which of the following has the greatest effect on the blockade level of spinal anesthesia: local anesthetic choice, dosage, volume, density?
dosage
Which of the following has the greatest effect on the level of epidural anesthesia: dosage, density, local anesthetic, volume?
volume injected
Would spinal anesthesia be indicated for a patient in a fixed volume cardiac state? (stenosis)
NO!!!!!!!!
Fibers that are associated with temperature, touch, and post-ganglionic autonomic are _________.
C-fibers
What is the most effective block for all portions of the upper extremity that is carried out at the division of the brachial plexus?
supraclavicular block
Why are very obese patients not good candidates for supraclavicular blocks?
because it relies principally on bony and muscular landmarks
All local anesthetics share a basic structure of _______ end, __________ chain, and _________ end.
aromatic; intermediate; amine
Local anesthetics are divided into two groups: amino _____ and amino ______.
esters and amides
cocaine, procaine, 2-chloroprocaine, and tetracaine are all examples of amino ______.
esters
lidocaine, prilocaine, etidocaine, mepivacaine, bupivacaine, and ropivacaine are examples of amino ______.
amides
Chloroprocaine has a ______ onset and a _______ duration of action. It’s principal use is in producing _______ anesthesia for _______ (length?) procedures.
rapid; short; epidural; short
Why is epinephrine typically added to LA’s including lidocaine?
d\t vasodilation (prilocaine is structurally similar to lidocaine, but causes much less vasodilation and can be used without epi)
Lower concentrations provide _______ blockade (type) principally, and as the concentration is increased, the effectiveness of _______ blockade increases with it.
sensory, motor
Ropivacaine appears to be _____ cardiotoxic than Bupivacaine.
less
Overall, the most effective concentration of epinephrine as a vasocontrictor is a ___ : _______ concentration.
1:200,000
Why should epinephrine be added to the LA at the time of initial block instead of using commercially prepared LA/Epi solutions?
When epi is added in the commercial production process, it is necessary to add stabilizing agents b/c epi rapidly loses its potency on exposure to air and light. The added agents lower the pH of the LA to 3-4 range and because of higher pKa’s of LA, this slows rate of onset of effective regional block. Commercial prepared solutions are appropriate after initial bolus onset.
Phenylephrine is principally used in spinal anesthesia to prolong the block. This can be achieved by adding ___ - ____ mg of phenylephrine to the drug.
2-5
When using a nerve stimulator, the needle should be positioned to a point where muscle contraction can be elicited with _____ to _____ mA. Then you can inject ___ ml of LA to see if the muscle contraction is abolished.
0.5-0.1 mA; 1ml
How does the ultrasound work?
U.S. waves reflect off tissues and return to the transducer–> after emitting the wave it switches to a receive mode–> when the waves return to the transducer, the piezoelectric crystals vibrate again, this time transforming the sound energy into electrical energy–> whiter objects (hyperechoic) represent a larger degree of reflection and higher signal intensities–> darker (hypoechoic) images represent less reflection and weaker signal intensities.
Name the mHz setting for the ultrasound to achieve the following depths: 1-4cm: _____; 4-6cm:_____; deep tissues: _____
12-13 mHz; 8-10 mHz; 3-8 mHz
What are the “clinical pearls” to assessing a brachial plexus block prior to surgery? (the 4 P’s)
“push” assesses radial; “pull” assesses musculocutaneous nerve; “pinch” the fingers of the ulnar or median nerve (base of 5th digit)
_________ block is effective for surgery of the shoulder or upper arm b/c the roots of the ________ _______ are most easily blocked with this technique.
interscalene; brachial plexus
True or False: Interscalene blocks are not useful in obese patients.
False: even obese patients typically have identifiable scalene and vertebral body
What type of patients should an interscalen block be avoided in?
with impaired lung function d\t proximity to phrenic nerve….. but this doesn’t matter if you’ll be doing regional with general because enough innervation of phrenic nerve will return by end of the surgery.
With interscalene blocks, lidocaine and mepivacaine without epinephrine lasts approx ___ to ___ hours and with epi lasts approx ____ to ____ hours.
2-3; 3-5
With interscalene blocks, bupivacaine and ropivacaine without epi last approx ___ to ___ hours; with epi lasts approx ___ to ___ hours.
4-6 hours; 8-12 hours
Interscalene block is often performed at level of the ____ vertebral body, which is at the level of cricoid cartilage.
C6; have patient lift head off bed to intensify the borders of the sternocleidomastoid muscle; roll fingers onto anterior scalene and into interscalene groove at level of C6.
(pick the correct choice) Once in the interscalene groove, the needle should be inserted in a slightly CAUDAL OR CEPHALAD and slightly ANTERIOR OR POSTERIOR direction.
caudal and posterior
Name some problems/complications that can arise from an interscalene block.
Subarachnoid injection, epidural block, intravascular injection, pneumothorax, and phrenic block
_______ artery runs anterior to the anterior scaene muscle.
vertebral
When appropriate pressure is applied, no more than ___ to ___ cm of th needle should be necessary to reach the brachial plexus.
1 to 1.5 cm
The first two structures that should be identified with ultrasound when performing an interscalene block is _____ _____ and the ______ ______ ______.
carotid artery (pulsatile, hypoechoic, resistant to compression) and internal jugular vein (non-pulsatile, compressible, and hypoechoic)
What type of sensation is encountered by the practitioner when the needle is advanced into the brachial plexus sheath b\w the C5 and C6 ventral nerve roots?
“popping” sensation
What is the preferred MhZ for the ultrasound when performing an interscalene block?
12 mhz since it is a superficial block
What are some complications of a peripheral nerve block?
Neurologic complications following peripheral nerve block can be caused by one or more of the following factors:
Mechanical trauma to the nerve
Needle trauma
Intraneuronal (intrafascicular) injection
Neuronal ischemia
Inadvertent needle placement into unwanted locations
Neurotoxicity of local anesthetics
Drug error (injection of wrong drug)
Infection
In many instances, the insult may be caused by a combination of these factors.
What nerve is likely to be missed when doing an interscalene brachial plexus block?
ulnar nerve….. because of using the more cephalad approach
Who performed the first brachial plexus block (1889)
Halstead
Along which vertebrae does the brachial plexus correspond?
C5-T1 (+ or - C4, T2)
Where in the brachial plexus does the interscalene approach block?
roots/trunks
Where in the brachial plexus does the supraclavicular approach block?
trunks/divisions
Where in the brachial plexus does the infraclavicular approach block?
Cords
Where in the brachial plexus does the axillary approach block?
terminal branches
How many divisions are located in the brachial plexus?
6; 3 ventral and 3 dorsal
Review the brachial plexus:
review the brachial plexus:
review the following nerve innerventions for the brachial plexus:
What dermatome represents half of the 4th digit and all of the 5th? (hand)
C8
What dermatome represents your index finger, 2nd digit, and half of 3rd digit?
C7
What dermatome represents the thumb?
C6
What fingers does the ulnar nerve innervate?
The median aspect of the ring finger and the 5th finger.
What fingers does the median nerve innervate?
medial aspect of thumb, the index finger, middle finger, and lateral aspect of ring finger
For argument’s sake…. (or for the book purposes) should you use lidocaine with epinephrine with digital blocks? Why or Why Not?
The rationale is simple: Epinephrine activates alpha receptors in vascular endothelium, causing constriction of peripheral blood vessels.1 In end arteries, vasoconstriction will lead to ischemic necrosis of the involved tissue. The logic is compelling, but is the conclusion valid?
When performing an interscalene block you should inject a FAST or SLOW injection of ___ to ____ ml of solution.
slow; 30-40ml; no deeper than 1.5cm
What is Horner’s Syndrome?
Ptosis , Miosis, and Anhidrosis
Name the complications of an interscalene approach?
epidural spread, intravascular injection, phrenic block, Horner’s Syndrome
Put the following in order of absorption rates of local anesthetics (Fastest to Slowest): SubQ infiltration, epidural block, brachial plexus, femoral nerve, sciatic, caudal, intercostal
intercostal> caudal> epidural> brachial plexus> sciatic> femoral> SubQ
Name some early signs of lidocaine toxicity?
dizziness, tinnitus, lightheaded
Local anesthetic potency is primarily determined by _______ ______.
lipid solubility
Motor innervation of the biceps is provided by the ________ nerve.
musculocutaneous
The triceps muscle is provided motor innervation by the _________ nerve.
radial
If a patient is on blood thinners or has increased bleeding time, which brachial plexus block should be avoided?
Infraclavicular (OF COURSE….. b\c how are you going to hold pressure on the clavicle)
The musculocutaneous nerve branches off after the cords, and thus will not be properly blocked by which plexus approach?
Axillary
A Bier block can be performed by injecting _____ ml of ____ % Lidocaine. Must allow at least 20-35 minutes before removing tourniquet to decrease risk of toxicity.
35-50ml; 0.5% lidocaine
Review the nerve innervations in the arm:
Name the cord that the radial nerve comes from?
Posterior cord
Name the cord the musculocutaneous nerve comes from?
lateral
What cord does the axillary nerve come from?
Posterior
What cord does the median nerve come from?
Lateral and Medial
What cord does the ulnar nerve come from?
Medial
What cord does the Medial antebrachial cutaneous nerve come from?
Medial
