Spinal & Epidural Lecture 2 Flashcards
(79 cards)
1
Q
What is another term for the epidural veins? What makes them different from other veins?
A
Batson’s plexus→ valveless, engorged with obesity and pregnancy
2
Q
What is the Plica Mediana Dorsalis?
A
Thin connective tissue located between ligamentum flavum and dura mater→ divides epidural space from right and left
3
Q
What is a differential dx for unilateral epidural block?
A
Pronounced plica mediana dorsalis
4
Q
What is located in the subarachnoid space?
A
- CSF
- Nerve roots (blocked with spinals)
- Spinal cord
5
Q
What is characteristic feeling when performing intrathecal anesthesia?
A
“Pop” from needling passing through dura mater
6
Q
Where is the subdural layer of the spinal cord located?
A
Potential space located between dura mater and arachnoid mater
7
Q
What happens if anesthetic is accidentally injected into the subdural space when trying to perform and epidural or spinal block?
A
Could cause high spinal effect and results in failed spinal block
8
Q
A
A) Epidural space
B) Dura mater
C) Subdural space
D) Arachnoid mater
E) Subarachnoid space
F) Pia mater
9
Q
Where does the dura mater start and end?
A
Starts: opening on foramen magnum
Ends: extends down to dural sac
10
Q
Which meningeal layer is highly vascular?
A
Pia mater (covers spinal cord)
11
Q
What is the function of the pia mater in regards to local anesthestic?
A
Reabsorption of LA with spinal blocks (when LA is in subarachnoid space)
12
Q
How many PAIRS of cervical spinal nerves are there?
A
8 pairs
13
Q
Where do the C1-C7 spinal nerves exit?
A
Above the corresponding vertebrae
14
Q
Where does C8 spinal nerve exit?
A
Below C7 vertebra
15
Q
How many thoracic, lumbar, and sacral spinal nerve pairs?
A
12 pairs of thoracic
5 pairs of lumbar
5 pairs of sacral
16
Q
How many coccygeal spinal nerves are there?
A
1 pair
17
Q
What forms each spinal nerve?
A
- Anterior (ventral) nerve root→ motor and autonomic info from SC to body
- Posterior (dorsal) nerve root→ sensory info from body to SC
18
Q
What is a dermatome?
A
Area of skin that receives sensory nerves from a single spinal nerve root
19
Q
What level dermatome has to be blocked for a C-section?
A
Up to T4
20
Q
What are the cardiac accelerators?
A
T1-T4
21
Q
What nerve transmits sensations in the face?
A
Trigeminal nerve (CN V)
22
Q
What nerve is blocked for an airway block?
A
Areas of trigeminal nerve (CN V)
23
Q
What is the target/site of action for LA during spinal anesthetic?
A
- Myelinated preganglionic fibers of spinal nerve roots
- Inhibits neural transmission in superficial layers of SC
24
Q
What is the process for epidural anesthesia reaching the site of action?
A
- Diffusion→ LA diffuses through dural cuff to reach nerve root
- Leakage→ LA can leak through intervertebral foramen into paravertebral area (green area)
25
What are the 7 factors that affect spinal LA spread?
1) Baricity
2) Patient position
3) Dose
4) Site of injection
5) Volume of CSF (non controllable factor)
6) Increased intra-abdominal pressure (non controllable)
7) Older age (non controllable)
26
What is the most reliable factor affecting how far and wide the LA spreads when using hypo or isobaric solution?
Dose
27
How does CSF volume impact the spread of local anesthetics in the intrathecal space?
Low CSF volume creates extensive spread of LA in intrathecal space
28
How does advanced age impact LA distribution for spinal anesthesia?
CSF volume decreases with age and neural nerves are vulnerable to LA and CSF volume decreases
29
How does pregnancy impact spinal LA distribution/block height?
Decreased CSF volume from increased intraabdominal pressure→ creates pressure on dural sac and directs CSF up
30
If you give an LA that is hyperbaric and want to it travel up what can you do?
Position patient supine and angle head down (hyperbaric= sinks)
31
What do you need to consider when planning the dose of a spinal LA?
- Length of duration
- Baricity
32
What is the best access spot for spinal anesthesia?
L3-L4 has a bigger gap in spinous process than L4-L5
33
What factors have NO effect on the spread of spinal LA?
- Barbotage (aspirating CSF into syringe)
- Speed of injection
- Orientation of bevel
- Adding vasoconstrictor
- Gender
34
What does the spread of the LA in a spinal or epidural space determine?
Block height
35
What things significantly affect the spread of epidural LA?
- LA volume (MOST IMPORTANT DRUG RELATED FACTOR)
- Level of injection
- LA Dose
- Pregnancy (non controllable factors)
- Old age (non controllable)
36
What factors have a small effect on spread of epidural LA?
- LA concentration
- Pt position
- Height (taller/shorter stature)
37
Which factors do not affect the spread of epidural LA?
- Anesthetic additives (may change onset time or duration but not spread)
- Direction of bevel
- Speed of injection
38
Local anesthetics are all _________ bases
Weak
39
Why does chloroprocaine have a faster onset than lidocaine?
Difference in concentration
40
How does pregnancy/ old age impact spread of epidural anesthetic?
No effect→ no csf in epidural space
41
A laboring pt is complaining of pain in coccyx and already received her epidural. We tried position changes that did not help. What should you do next to help with her pain?
Add pain med to epidural (opioid)
*would not add more LA in epidural if patient is already numb because wouldnt want to block motor while pt is trying to push*
42
Where is the most spread when accessing lumbar site for epidural?
Cephalad
43
Where would you anticipate the LA to spread for mid thoracic epidural placement?
Balanced spread both cephalad and caudad
44
Where would you anticipate spread for cervical epidural placement?
Caudad
45
How much LA would you give via epidural if you are access L1 and wanting to block up to T4?
9 segments = 9mL
46
Which nerve fibers block first?
Preganglionic B fibers
47
Which nerve fibers block second?
C fibers (post ganglionic fibers and dorsal root pain/temp/touch)
48
Which nerve fibers block 3rd?
A gamma (skeletal muscle tone)
A delta (Fast pain/temp/touch)
49
Which nerve fibers block last?
A alpha (Motor)
A beta (touch/pressure)
50
How does LA concentration of motor blockage compare to sensory and autonomic blockage LA concentration?
Autonomic blockade requires lower concentration of LA than sensory and motor (highest level of blockade)→ sensory blockade requires higher concentration of LA than autonomic and lower concentration that motor (Higher block level than motor)
Sensory block level→ 2-6 above is sympathetic → 2 levels below sensory is motor block
51
What order do the nerves block after LA is injected into nerve bundle?
B fibers → C fibers → A delta fibers → A gamma→ A beta→ A alpha
52
If spinal anesthetic sensory block is at T8, what is the SNS level block and motor level block
SNS: T2-T6
Motor: T10
53
Which nerve fibers are responsible for venodilation and hypotension?
Preganglionic (autonomic) B fibers
54
What order do the nerve fibers for spinal blockade reverse/recover?
Opposite from order they blocked
*Motor comes back first*
55
What are the levels of the Modified Bromage Scale?
0: No motor block
1: Slight motor block→ pt cant raise extended leg but can still move knees/feet
2: Moderate motor block→ pt cant raise extended leg or move knee CAN move feet
3: Complete motor block→ cant move legs, knees, or feet
56
What is the purpose of the Modified Bromage Scale?
Specifically looks at function of lumbosacral nerves (does not assess movement above these regions)
57
What are the 1st, 2nd, and 3rd sensory senses to be blocked with neuraxial?
1) Temperature (check sensory with something cold ie alcohol pad)
2) Pain
3) Touch/pressure
58
How does neuraxial anesthesia affect CV system?
- Decreases preload (venodilation from sympathectomy)
- Decreases afterload (partial arterial dilation from sympathectomy)
- Decreases Cardiac output (may have initial increase then decrease over time d/t change in bv dilation speed)
- Decrease in HR (cardiac accelerator blockade
- Activation of reflexes from bradycardia: (benzold jarisch reflex, reverse bain bridge reflex)
59
How does neuraxial anesthesia impact SVR in healthy pts vs elderly or cardiac pts?
Healthy: decrease SVR by 15%
Elderly/cardiac issues: decreases SVR up to 25%
60
What is the Benzold-Jarisch Reflex?
- Response to ventricular underfilling causing bradycardia/asystole
- Mediated by 5-HT3 receptors in Vagus nerve and ventricular myocardium
61
What is the reverse bain bridge reflex triggered by?
Reduced stretching of right atrium→ causes bradycardia
62
What is a fatal complication of unopposed parasympathetic tone to cardioaccelerator fibers?
- Sudden cardiac arrest (from profound bradycardia and hypotension)
- Can be seen with young adults with high parasympathetic tone *20-60 min after onset of spinal
63
What are some PREVENT options to decrease spinal-anesthesia induced hypotension? Give before spinal*
- Vasopressors
- 5HT3 antagonists (8mg zofran): decrease reflexes that cause bradycardia (Bezolds-Jarisch from vagus nerve)
- Fluid management (coloading/preloading)
- Positioning (left tilt for pregnant women to relieve pressure on IVC)
64
What is the difference between coloading and preloading?
- Co-loading: IV fluids 15mL/kg after spinal block
- Preloading: Isotonic solution 30 min before procedure
65
What are treatment options for spinal-anesthesia induced hypotension?
- Vasopressors (ephedrine/neo)
- Anticholinergics (atropine)
- Fluids (crystalloids or colloids)
- Position caution (tburg can reduce cerebral perfusion and could increase block height d/t gravity)
66
How does neuraxial anesthesia affect pulmonary system?
- Minimal impact→ ERV decreases
- Common for COPD/obese pts to have dyspnea from loss of sensory feedback from chest area (semifowlers and talk to calm pt, only use O2 is desatting)
- Rare to have apnea/nerve paralysis that stops breathing
67
What is Pickwickian syndrome?
Morbid obesity
68
Where does sympathetic innervation of GI tract stem from? What effects does neuraxial anesthesia have on GI system?
- T5-L2
- Reduction of sympathetic tone increases in PNS activity
69
What is the function of the parasympathetic NS afferent and efferent branches? (increases with neuraxial anesthesia)
*PNS innervation from vagus nerve*
- Afferent: sensation of satiety, distension, and nausea
- Efferent: tonic contractions, sphincter relaxation, peristalsis, secretion
70
What is the function of sympathetic NS in the GI tract through afferent and efferent branches?
*T5-L2*
- Afferent: Visceral pain
- Efferent: Inhibit peristalsis and gastric secretion, sphincter contraction and vasoconstriction
71
What happens in the GI system as a result of unopposed vagal tone from neuraxial anesthesia?
- Relaxes sphincters
- Increases peristalsis
- Small contracted gut with active peristalsis (20% incidence N/V)
- Increase GI blood flow
- Nausea/ vomiting (20% of pts)
- Reduce post op ileus in abd surgery
72
Sympathetic blockade above ______ affects bladder control (relaxes urinary sphincter tone)
T10
73
How does addition of neuraxial opioids affect GU system?
- Decrease detrusor contraction (sensation to void)
- Increase in bladder capacitance (bladder scan before DC)
*These changes can lead to urinary retention/incontinence and need for foley catheter with neuraxial anesthesia*
74
How does neuraxial anesthesia impact metabolic/endocrine system?
- Somatic and visceral afferent fiber activation from pain, tissue trauma, and inflammaton= elevated cortisol, epi, NE, vasopressin, activation of RAAS
- Can partially or totally block neuroendocrine response
- Max benefit if neuraxial blockade occurs before surgical stimulus
75
What is the structure of local anesthetics?
76
What determines the onset of action, potency, and duration of action of local anesthetics?
77
What part of the VG Na+ channel does the LA block?
Inside the channel→ acidity inside cell ionizes LA and blocks from the inside
78
Local anesthetics with pKa close to physiologic pH will have ________ onset of blockade as more molecules remain in the non ionized state
Faster
79
What factors influence the uptake and plasma concentration of local anesthetics?
- Site of injection
- Tissue blood flow
- Physiochemical properties
- Metabolism
- Addition of vasoconstrictor
