Regional Anesthesia Flashcards
How long does it take for the spinal cord to go from L3 in the newborn to L1?
20-24mos
Which ligament binds the epidural space posteriorly?
ligamentum flavum
Where is the epidural space the widest?
L2
Where is the epidural space the narrowest?
C5
What are the two high points of the vertebral column when the patient is lying supine?
L3 and C3
What are the two low points of the vertebral column when the patient is lying supine?
S2 and T6
What is ALWAYS going to be the principle site of action for spinals or epidurals?
the nerve root
Name the 3 main structures you pass through to get to the epidural space.
1) supraspinous ligament
2) interspinous ligament
3) ligamentum flavum
What are the 3 primary layers of the spinal meninges before reaching the cord?
1) dura mater (outermost–> toughest–> extends from foramen magnum to S2-3)
2) arachnoid mater (middle layer–> delicate, nonvascular–> ends at S2–> almost like spiderweb)
3) pia mater (closely adheres to spinal cord–> delicate, highly vascular)
Where is the subarachnoid space and CSF found?
between the arachnoid and pia mater
What is the easy way to remember the 3 outer layers and location of the subarachnoid space before the spinal cord?
DASP Dura Arachnoid Subarachnoid space Pia
Where is the epidural space located?
it is a potential space bound by the dura mater and the ligamentum flavum
Describe the blood supply to the spinal cord and nerve roots.
blood supply to the spinal cord and nerve roots is derived from a single anterior spinal artery and paired posterior spinal arteries
The principal site of action for neuraxial blockade is the ______.
nerve root
How much CSF do we have at any time? in the subarachnoid space?
100-150ml; 25-35ml
How much CSF do we produce per day?
500mL
How do vasoconstrictors prolong a spinal block?
decrease absorption
When administering a spinal, where is the concentration the greatest?
at the site of injection
What is the normal specific gravity of CSF?
1.004-1.009
James Bond 1.007 is in the middle
Label in relation to CSF: SAME, GREATER, LESS
Isobaric
same
Label in relation to CSF: SAME, GREATER, LESS
hyperbaric
greater
Label in relation to CSF: SAME, GREATER, LESS
hypobaric
less
Is sterile water hypo, hyper, or iso baric?
hypobaric
Is dextrose 5-8% hypo, hyper, or iso baric?
hyperbaric
What direction will a hyperbaric spinal given at L2 while the patient was sitting go if the patient is immediately laid supine?
cephalad. Think of the high and low points
What determines the duration of spinal anesthesia?
rate of elimination
What is the predominant action of a sympathetic blockade d\t local anesthetics?
venodilation
venodilation–> reduces venous return, SV, CO, and BP
What are the two causes for bradycardia following local anesthetic administration?
1) blockade of cardiac accelerator fibers
2) decreased venous return (from venodilation)
* Bainbridge reflex (unopposed vagal stimulation)
What is the BEST means for treating hypotension during spinal anesthesia?
physiologic not pharmacologic
*give fluids if not normovolemic, if normovolemic give ephedrine
Why do you not want to give fluids that are rich in glucose, but instead give balanced salt solutions for hypotension?
b\c glucose can act as a diuretic
What is the difference between a high spinal and a total spinal?
high spinal is >T4
total spinal goes all the way
What is an advantage of a spinal over epidural?
ability to control the spread of anesthetic by controlling the specific gravity of the solution and the position of the patient
Are there any time restraints to receiving neuraxial anesthesia for patients taking NSAIDs or aspirin?
No
When can a catheter be removed from a patient on IV heparin therapy?
2-4 hours after the last heparin dose; heparinization can occur one hour after catheter removal
What are the special considerations for patients on warfarin therapy?
controversial
- should d\c at least 4 days before surgery
- should check INR (neuraxial block may be given if perioperative INR is <1.5)
What is an acceptable INR in order to administer a neuraxial block to a patient on warfarin?
<1.5
The catheter should not be removed until INR is _____.
<1.5
Do not place or remove a neuraxial catheter if INR is ______.
> 1.5
What considerations for neuraxial anesthesia should be made for a patient who has received, is receiving, or will be receiving fibrinolytic or thrombolytic drug therapy?
should NOT receive neuraxial for 10 DAYS
First dose of LMWH can be given _____ hours after removal of the catheter.
2 hours
What are two other names for L4?
1) Tuttier’s line
2) intercristal line
Spinal, epidural, and caudal blocks are all considered ________.
neuraxial anesthesia
Describe the distribution of local anesthetic when injected into the subarachnoid space.
spreads to nerves of the cauda equina and laterally to the nerve rootlets and nerve roots–> may also diffuse into the spinal cord
Which two structures will you not pass through during a lateral approach to a spinal?
1) supraspinous ligament
2) interspinous ligament
Infection as a result of spinal anesthesia:
predisposing factors?? (5)
1) advanced age
2) diabetes mellitus
3) alcoholism
4) cancer
5) AIDS
Infection as a result of spinal anesthesia:
classic symptoms?? (3)
1) high fever (only seen with meningitis, not PDPH)
2) nuchal rigidity
3) severe headache
Nausea and vomiting should be viewed as signs of ______ until proven otherwise.
central hypoxia
What is the most common complication of spinal anesthesia? second?
backache; headache (PDPH)
When does the patient start to feel a PDPH?
within 12-72 hours; the earlier the onset, the more severe
- self limiting
- can last 10 days
Name s\s of PDPH (caused by traction on cranial nerves).
1) nausea and loss of appetite
2) photophobia
3) changes in auditory acuity
4) tinnitus
5) depression
6) feel miserable
7) tearful
8) bed-ridden
9) dependent
10) diplopia and cranial nerve palsies
What cause a PDPH?
loss of CSF in the subarachnoid space–> medulla and brainstem drop into the foramen magnum, stretching the meninges, vessels, and nerves–> headache
Blood patch should be _____ to _____mL.
10-30ml aseptically drawn blood
- injected into epidural space until the patient can feel pressure in back
- after the blood patch, bed rest for 1-2 hours before ambulating
- 1st= 89-95% resolution
What are the conservative treatments for PDPH?
1) lie flat
2) hydration
3) caffeine (IV/oral)–> cerebral vasoconstriction
In regards to nerve types, what is the order in which they are blocked with local anesthesia?
B fibers–> C fibers and A-delta–> A-gamma–> A-beta–> A-alpha
In regards to nerve types, what is the order of most to least sensitive?
“LSU”
Large myelinated
Small myelinated
Unmyelinated
Label whether the following is a characteristic of a spinal (S) or epidural (E):
takes less time to perform
S
Label whether the following is a characteristic of a spinal (S) or epidural (E):
catheter used for post op pain management
E
Label whether the following is a characteristic of a spinal (S) or epidural (E):
pain during surgery is less
S
Label whether the following is a characteristic of a spinal (S) or epidural (E):
rapid onset
S
Label whether the following is a characteristic of a spinal (S) or epidural (E):
less hypotension
E
Label whether the following is a characteristic of a spinal (S) or epidural (E):
sensory and motor block quality is better
S
Label whether the following is a characteristic of a spinal (S) or epidural (E):
can prolong block with catheter
E
Distance from skin to epidural space:
Average adult?
4-6cm
Distance from skin to epidural space:
Fat, I mean obese person?
up to 8cm
Distance from skin to epidural space:
thin person?
approximately 3cm
Is a lumbar epidural injection associated with a more cranial or caudal spread?
cranial
Why may there be a delay in onset to an epidural at L5 or S1?
b\c of the larger size of the nerve roots
What is the prevalence of a epidural hematoma?
1:150,000
What are the s\s of a epidural hematoma?
sharp back and leg pain–> numbness and weakness, sphyncter dysfunction
What is the best test for epidural hematoma?
MRI or CT scan
What ensures a good outcome for a patient with a epidural hematoma?
surgical decompression within 8-12 hours
Name some complications of epidural blockade:
- penetrate a blood vessel
- epidural hematoma
- dural puncture
- back ache
- neural trauma
- air embolism (children)
- subdural catheterization
- intravascular catheterization (small alloquots)
- infection
- headache
- hypotension
- resp depression/resp failure
- bradycardia
- total spinal secondary to subarachnoid injection (intubate and sedate)
- Horner’s syndrome
- trigeminal nerve palsy
Why do you perform a test dose after satisfactory placement of a epidural catheter?
to detect both subarachnoid and intravascular injection
What is the most common regional anesthetic in children?
caudal block
Where do you insert the needle when doing a caudal block?
through the sacrococcygeal membrane
- the injection should feel like an injection into the epidural space
- should be NO local pain on injection
When doing a caudal block should you be able to aspirate CSF, air, or blood?
No
What is the “whoosh” test?
for caudal blocks–> whoosh test with air while listening with stethoscope over midline lumbar spine
When performing a caudal block, the patient reports a feeling of fullness or paresthesia from the sacrum to the soles of the feet. What should you do?
nothing, this is normal during injection and will cease upon completion
A volume of _____ml is required to get a sensory level block at T10 to T12.
25-35mL
Is caudal or epidural anesthesia associated with higher plasma levels?
caudal
Is distribution time longer for epidural or for caudals?
caudal; d\t nerve size
What is the most frequent problem with caudal blocks?
ineffective blockade
What is the most common post-op complaint after a caudal block?
pain at insertion site
What are the two greatest advantages of US guided regional anesthesia?
1) ability to see where the tip of needle is in relation to anatomical structures
2) see the spread of local anesthesia
What are high frequency sound waves generated in specific frequency ranges and sent through tissues?
ultrasound waves
_____ frequencies penetrate deeper than _____ frequencies.
lower; higher
What is best to visualize shallow structures less than 4cm from the skin?
high frequency (10-13mHz)
What is best for visualizing deeper structures?
low frequency (2-5mHz)
As sound passes through tissue it is ______, _______, or allowed to _________, depending on the echodensity of the tissue.
absorbed, reflected, pass through
Substances that absorb sound well are termed ______.
anechoic (echolucent)
Anechoic substances like blood and CSF (high water content) appear _____ on a US.
dark
Substances low in water content or high in materials that are poor sound conductors are called _______. Give examples.
hyperechoic (they bounce the sound back)
-air and bone
How do hyperechoic substances appear on the US?
very bright
The middle “shades of gray” on a US are due to substances that fall in the middle of anechoic and hyperechoic. These are called _____.
hypoechoic (vessels, etc)
If you are doing a caudal block for a child, what is the initial dose?
0.5-1.0mg/kg of 0.125% to 0.25% bupivacaine
Where in the plexus is the phrenic nerve located?
C3-C5, but C4 is 70% contribution
What is the cervical plexus?
C1-C5
What is the brachial plexus?
C5-C8, T1
Name the dermatome and nerve involved.
pain in small finger
ulnar nerve, C8
What two nerves innervate the thumb?
radial and median
What is the only nerve that gives extension in the hand?
radial nerve
Name the nerve:
supination of forearm
radial
Name the nerve:
pronation of forearm
median
What nerve provides flexion at the wrist?
median and ulnar
________ nerve provides extension at the elbow, while ________ nerve provides flexion at the elbow.
radial; musculocutaneous
What surgery is a good indication for use of a cervical block?
CEA
Ipsilateral means _______.
same side
Contralateral means ______.
opposite side
A cervical plexus block is performed for C____ to C_____ by injecting ____mL of local anesthetic at each level.
C1-C4; 4mL
What are 4 complications that can result from a cervical plexus block?
1) block phrenic nerve (hiccups)
2) Horner’s syndrome (ipsilateral ptosis, miosis, facial and arm flushing, anhydrosis, and nasal congestion)
3) hoarseness (RLN block)
4) accidental subarachnoid or epidural injection
Which plexus block provides adequate analgesia for shoulder and proximal humerus?
interscalene
Intense C5-C7, Least C8-T1
______ is the level of the cricoid cartilage.
C6
What nerve may not be blocked with a interscalene block?
ulnar nerve
Puncture of the _______ artery is a complication of an interscalene block.
vertebral artery
What block: Where is the brachial plexus MOST compact (3 trunks)?
supraclavicular block
What is the most homogenous block of the brachial plexus that even includes the ulnar nerve?
supraclavicular
What is the biggest risk associated with supraclavicular blocks?
pneumothorax
What is “X” marks the spot for a supraclavicular block?
1) most inferior part of the interscalene groove
2) 2 cm’s from midpoint of the clavicle
What is the major concern when performing a infraclavicular block?
1) pneumothorax
2) hemothorax
Which plexus block ensures blockade of the musculocutaneous nerve?
infraclavicular
Brachial Plexus Anatomy at the Axilla:
What nerves are in the bundle at this level?
1) musculocutaneous (but lies outside the sheath–> requires a separate block to cover)
2) median
3) radial
4) ulnar
Can you do both a ulnar and radial block at the hand?
not at the same time–> compromise circulation
EPI should not be added to blocks __________.
below the elbow
What is the BEST block for knee surgery?
femoral and sciatic
What is the largest nerve trunk in the body?
sciatic (lumbosacral trunk)
What nerves compose the lumbosacral trunk?
L4-5, S1-3
The sciatic provides sensory to where?
sensory fibers to the posterior hip capsule as well as the knee; ALL sensory distal to the knee except the anteromedial aspect which is covered by the saphenous; motor to the hamstrings and to all the lower extremity muscles distal to the knee
What are the complications associated with a retrobulbar block?
1) retrobulbar injection
2) retrobulbar hemorrhage: bleeding in eye, temp loss of vision, lens occluded by blood, IOP may decrease
3) Intra-arterial injection (MOST COMMON; 1-3%)
4) injection into optic nerve sheath
5) oculocardiac refex
How long must you leave the tourniquet up for following a Bier block?
20 min or you can get LA toxicity
The most common causative organism in epidural abscesses is: ________.
staphylococcus aureus
When doing a CSE, how far should the spinal needle extend beyond the tip of the epidural needle?
7-10mm
How much clonidine should you add to your spinal anesthetic?
15-45mcg
What is the recommended dose (mg) for epinephrine when added to tetracaine?
0.2 to 0.3
What level of spinal anesthesia will be necessary to eliminate thigh tourniquet discomfort?
T12
What is the easiest, most frequently used, and lowest complication risk of the brachial plexus blocks?
axillary
The axillary approach to the brachial plexus block is best suited for procedures where?
elbow, hand, forearm
How much pressure should you apply on the proximal tourniquet when administering an IV regional anesthetic in the upper extremity?
SBP + 100
What nerve is immediately lateral to the achilles tendon in the patients ankle?
sural
