Neuraxial anesthesia I Flashcards
(81 cards)
1
Q
what are the indications for neuraxial anesthesia?
A
- Surgical procedures involving the lower abdomen, perineum, and lower extremities
- Orthopaedic surgery
- Vascular surgery on the legs
- Thoracic surgery (adjunct to GETA)
2
Q
what are the benefits of neuraxial anesthesia?
A
less of everything:
* post-op ileus
* thromboembolic events
* PONV
* respiratory complications
* bleeding
* narcotic usage
3
Q
what are other benefits?
A
- Great mental alertness
- Less urinary retention
- Quicker to eat, void, and ambulate
- Avoid unexpected overnight admission from complications of general anesthesia
- Quicker PACU discharge times* (*except when there is urinary retention)
- Preemptive anesthesia
- Blunts stress response from surgery
4
Q
what are the relative contraindications to neuraxial anesthesia?
A
- deformities of spinal column (spinal stenosis, kyphoscoliosis, ankylosing spondylitis)
- pre-existing spinal disease (MS, polio)
- chronic headache/backache
- > 3 failed attempts
5
Q
what are the absolute contraindications to neuraxial anesthesia?
A
- INR > 1.5
- plt < 100,000 (consider trends)
- PT 24-28
- aPTT 50-64
- BT 6-14 mins
- known coagulation disorder or taking anticoagulants
- patient refusal
- dermal site infection
- severe or critical valvular disease
- increased ICP
- severe CHF EF <30-40%
6
Q
what is the normal INR, Plt, PT, aPTT, and BT?
A
- Prothrombin time (PT) = 12 to 14 seconds
- International normalized ratio (INR) = 0.8 to 1.1
- Activated Partial Thromboplastin Time (aPTT) = 25 to 32 seconds
- Bleeding time = 3-7 minutes
- Platelet = 150,000 - 300,000 mm3
7
Q
what factors make up the intrinsic pathway?
A
Factors 12, 11, 9, 8
8
Q
what factors make up the extrinsic pathway?
A
Factors III and VII
9
Q
what makes up the common pathway?
A
Factors X, V, II, I
10
Q
what is the valvular area for AS and MS?
A
< 1.0 cm sq
11
Q
what is the valve area of mild, moderate, severe, and critical AS?
A
mild = >1.5 cm sq
moderate = 1.0-1.5 cm sq
severe = 0.7-1.0 cm sq
critical = <0.7 cm sq
12
Q
what is the death spiral?
A
- Hypotension = myocardial ischemia
- ischemic contractile dysfunction
- decreased CO
- worsening hypotension = increased ischemia
13
Q
what is spinal anesthesia?
A
- Local anesthetics injected into the subarachnoid space, blocking nerve transmission in the spinal cord
- resulting in loss of sensation and motor function in the lower body
- anesthetic injected into CSF
14
Q
what is the onset and spread of spinal anesthesia?
A
- very rapid onset (5 mins)
- may spread higher than expected
15
Q
does spinal anesthesia provide a dense or minimal sensory and motor block?
A
- provides a dense sensory and motor block
- complete loss of sensation and mobility
16
Q
which neuraxial anesthesia is most likely to cause hypotension?
A
spinal anesthesia
17
Q
what is epidural anesthesia?
A
- anesthetic into the epidural space
- bathes the spinal nerves
18
Q
what is the onset and spread of epidural anesthesia?
A
- very slow onset (10-15 mins)
- spread can be controlled with volume of LA
- spread determines the dermatomes and myotomes affected
19
Q
What is the nature of sensory and motor block for epidurals?
A
- sensory and motor block depend on site of injection
- block is segmental (based on level and volume)
- motor block is minimal (walking epidurals)
20
Q
Do epidurals cause hypotension?
A
Yes but less than spinal anesthesia
21
Q
What is found in the epidural space? Where is it located?
A
- the epidural space is a potential space outside of the dura mater
- contains fat, blood vessels, and spinal nerve roots
22
Q
Which neuraxial anesthesia involves injecting LA into CSF?
A
Spinal anesthesia
23
Q
What is the duration of action for spinals vs epidurals?
A
- spinals have limited and fixed duration of action as they are usually one time injections
- epidurals have unlimited duration of action as they are usually infusions
24
Q
At which level can spinals be injected?
A
- L3-L4
- L4-L5
- L5-S1
25
At which level can epidurals be administered?
* can be administered at any level
* lumbar epidural L1-L5 (for lower body parts)
* thoracic epidural T10-L2 (for upper body parts)
* caudal epidural S1-S5, sacral hiatus (pedi)
26
Which neuraxial anesthesia requires more skill? Why?
* Epidurals are more difficult due to loss-of-resistance technique + epidural space can vary across spinal levels
* Spinals have a definitive CSF endpoint (easier to identify)
27
Which neuraxial anesthesia is dose based? Which is volume based?
Spinal anesthesia is DOSE-BASED
Epidural anesthesia is VOLUME-BASED
28
What is the concentration of LA in spinals vs epidurals?
Spinal LA are more concentrated and fixed
Epidural LA can vary
29
What is LAST?
Local Anesthetic Systemic Toxicity
* life threatening complication that occurs when excess LA enters the bloodstream
* leads to systemic effects
30
What are the causes of LAST?
* accidental IV injection
* overdose
* tumescent liposuction due to rapid absorption
31
What are the CNS effects of LAST based on serum concentration?
1-5 mcg/ml = analgesia
5-10 mcg/ml = circumoral numbness, tinnitus, twitching, hypotension, myocardial depression
10-15 mcg/ml = seizures, unconsciousness
15-25 mcg/ml = apnea, coma
>25 mcg/ml = cardiovascular depression
32
How can LAST be avoided in epidurals?
* test dose and monitor for early signs of toxicity
* aspiration before injection (to rule out vascular entry)
* inject slowly and in small increments
33
Which neuraxial anesthesia has a higher risk of LAST?
Epidural anesthesia since there is more vasculature and higher volume administered
*spinals can still cause LAST
34
How does gravity affect spinal vs epidural anesthesia?
Spinal anesthesia relies on baricity since it is injected into CSF
Epidural anesthesia relies on positioning
35
What is a hyperbaric LA? Hyperbaric LA? Isobaric LA?
Baricity refers to the density of LA (for spinals only)
Hyperbaric = more dense than CSF, will sink to the bottom
Hypobaric = less dense than CSF, will float
Isobaric = same density as CSF, minimal spread via gravity (spread dependent on injection site)
36
What is the volume of LA per segment needed to spread LA in epidurals?
1-2 ml per segment
37
how many cervical, thoracic, lumbar, sacral, coccyx vertebrae are there?
**"Breakfast at 7, lunch at 12, dinner at 5"**
**"S5/C4"**
* cervical = 7
* thoracic = 12
* lumbar = 5
* sacral = 5-fused
* coccyx = 4-fused
38
what are the 2 segments of the vertebrae? what is excluded from this?
* anterior segment = body
* posterior segment = vertebral arch
* excluding C1
39
what structure(s) link the anterior and posterior segments together?
* pedicle
* lamina
40
what houses the spinal cord, nerve roots, and epidural space?
vertebral foramen
41
what process sticks out laterally? which sticks out posteriorly?
* transverse process = bilaterally
* spinous process = posteriorly (midline landmark)
42
what is the major difference between thoracic and lumbar spinous processes?
* Cervical and thoracic spinous processes tilt downward
* Lumbar spinous processes stick out directly backwards (easier for needle access)
43
what are the soft pads between each vertebra that act as shock absorbers?
intervertebral discs
anulus fibrosus + nucleus pulposus
44
what is the opening between the vertbera where spinal nerves exit the spine?
intervertebral foramina
45
what joints connect each vertebra to one another?
inferior articular process to superior articular process
46
what are the functions of facet joints?
* guide and limit the spine's movement
* If a facet joint gets injured, it can press on nearby spinal nerves
* pain and muscle spasms in the area of skin served by that nerve (dermatome)
47
what is the landmark for L4?
superior aspect of iliac crest
48
what is the landmark for S2?
posterior superior iliac spine
49
what is Tuffier's line? what is its other name?
* horizontal line runs across the top edges of the hip bones (iliac crests) and matches the L4 vertebra
* space above this line aligns with the L3 - L4
* space below this line aligns with the L4 - L5
* AKA **intercristal line**
50
how does tuffier's line/intercristal line differ from adults vs Pedi?
infants up to one year, the Intercristal line corresponds with the L5 - S1
>1 yr = L4
51
what vertebra is the vertebral prominens?
C7
52
at what vertebra is the rib margin?
L1
rib margin 10cm from midline
53
what is located at the base of the sacrum and aligns with S5?
sacral hiatus
54
what ligament covers the sacral hiatus?
sacrococcygeal ligament
55
where is caudal anesthesia administered? what type of anesthesia is it?
caudal anesthesia is administered in the sacral hiatus
epidural anesthesia (since there is no CSF)
56
what is the landmark for caudal anesthesia? what does it do?
sacral cornua
guards the area of the sacral hiatus
57
where does the spinal cord originate?
medulla oblongata
58
what is the area of the spinal cord that tapers off in the end? which level does it end?
* conus medullaris
* adults = L1-L2
* infants = L3
59
what is the bundle of spinal nerves extending past the conus medullaris called?
cauda equina
extends from conus medullaris to dural sac
60
what nerve roots are in the cauda equina?
* L2 - S5
* coccygeal nerve
61
where does the dural sac end for adults? infants?
adults = S2
infants = S3
62
what anchors the spinal cord to the coccyx? what is it made of?
filum terminale
extension of the pia mater
conus medullaris to coccyx
63
what are the different parts of the filum terminale? what do they attach?
internal = conus medullaris to dural sac
external = dural sac to sacrum
64
where are the spinal arteries located and how many?
**1 anterior** spinal artery = midline x1 (supply motor function)
**2 posterior** spinal artery = laterally x2 (supply sensory function)
65
which is more vulnerable to ischemia: sensory or motor function? why?
**motor function (anterior spinal artery)** is more vulnerable
sensory function (posterior spinal artery) is supplied by 2 posterior arteries and have more collateral vessels
66
what is anterior spinal artery syndrome?
ischemia of the anterior spinal artery (1)
loss of motor function, pain, and temperature sensation
67
which arteries do the posterior spinal arteries connect to?
* subclavian arteries
* intercostal arteries
68
what are the causes of anterior spinal artery syndrome? (4)
* Low blood pressure (profound hypotension)
* Mechanical blockage
* Blood vessel disease (vasculopathy)
* Bleeding (hemorrhage)
69
does the anterior spinal artery have any collateral vessels?
not much
may receive from **intercostal artery** or **iliac arteries** but is **variable**
70
what are the spinal ligaments from posterior to anterior?
supraspinous ligament
interspinous ligament
ligamentum flavum
posterior longitudinal ligament
anterior longitudinal ligament
71
what ligaments are spared when doing the paramedian approach vs midline?
paramedian does not puncture **supraspinous** and **interspinous ligaments**
approach is to the side which bypasses these ligaments
72
how is a paramedian approach performed? what angles?
from midline, move the needle **1cm to the side** and **1cm down**
angle the needle **15 degrees** from midline laterally
angle the needle **15 degrees** cephalad (pointing up)
73
how is a midline apporach performed? what angles?
locate landmarks and position needle **midline**
angle the needle **10 degrees** cephalad (pointing up)
74
when is a paramedian apporach indicated? how is patient positioned?
* When the interspinous ligament is calcified or the patient cannot flex their spine
* sitting, lying on their side, or face down
75
what is the order of meningeal laters (outer to inner)?
Dura mater
arachnoid mater
pia mater
76
what are the key spaces in the spinal cord?
**epidural space** = outside of the dura (contains fat and blood vessels)
**subdural space** = between the dura and arachnoid mater (potenital space)
**subarachnoid space** = between the arachnoid mater and pia mater (contains CSF)
77
what structures surround the epidural space?
* foramen magnum (top)
* sacrococcygeal ligament (bottom)
* posterior longitudinal ligament (anterior)
* ligamentum flavum (posterior)
* vertebral pedicles (lateral)
78
what does the epidural space contain?
* fat
* blood vessels
* lymphatics
* nerves
79
what is Batson's plexus?
epiural veins
Valveless and form a plexus draining blood from the cord and its linings
80
how can vessels be avoided when doing an epidural?
ensure a midline approach
posterior spinal veins are located laterally (2) - if punctured that means you are off midline
81
what increases the risk of accidental venous puncture when doing an epidural? why?
obesity and pregnancy
veins become engorged making it more likely to get punctured
