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Neuraxial Anesthesia Flashcards

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1
Q

Neuraxial Anesthesia

A
  • can be used in combo with GA or alone or after for post-op analgesia
  • single dose or catheter for intermittent boluses or continuous infusion
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2
Q

Benefits of Neuraxial Anesthesia

A
  • In high risk pts may decrease risk of venous thrombosis, PE, cardiac comps, bleeding, resp depression, transfusion requirements, PNE, vascular graft occlusion
  • Post-op epidural analgesia may reduce mech vent need & time to extubation in abd or thoracic surgery pts
  • Epidural/spinals (regional anesthesia) for C-section has decreased mortality & morbidity compared to GA
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3
Q

Spinal Column General Anatomy

A

from foramen magnum to L1 in adults, L3 in children

Dura Mater + Arachnoid Mater usually stuck together
Subarachnoid space = CSF
Pia mater adherent to spinal cord

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4
Q

Filum Terminale

A

an extension of the Pia mater which attaches the end of the spinal cord (conus medullaris) to the coccyx

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5
Q

Spinal Vs. Epidural

A

spinal requires less medication = a dense sensory and motor blockade

epidural requires more = a differential blockade

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6
Q

Differential Blockade

A

sympathetic is most cephalad: 1-2 segments above sensory

motor is most caudal

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7
Q

Primary Site of Action for Neuraxial Anesthesia & Physiologic Response

A

the nerve root

results from inhibited sympathetic and unopposed parasympathetic

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8
Q

Posterior V Anterior Nerve Roots

A

Posterior: somatic & visceral sensation
Anterior: efferent motor & autonomic outflow

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9
Q

Nervous System Breakdown

A

CNS: brain & spinal cord

PNS –> autonomic –> SNS & PNS
PNS –> somatic –> sensory & motor

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10
Q

Sympathetic Nervous System

A

thoracolumbar - T1-L2
most preganglionic synapse with postganglionic in the paravertebral ganglia

stellate ganglion: inferior cervical + first thoracic

T1-T4 are cardiac accelerator fibers

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11
Q

massive sympathetic response

A

tachycardia, bronchodilation, dry mouth, diaphoresis

anatomically & functionally more systemic

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12
Q

parasympathetic

A

craniosacral outflow
CN 3: midbrain
CN 7: pons
CN 9 & 10: medulla

Sacral segments S2, S3, S4

more selective & localized

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13
Q

massive parasympathetic response

A

bronchoconstriction (wheezing), bradycardia, miosis, vomitting, defecating, seizing

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14
Q

BP Effects of Neuraxial Anesthesia

A

varying level of decreased HR/BP

Hypotension: vasomotor tone is mostly determined by T5-L1 sympathetic fibers which innervating arterial & venous smooth muscle

  • vasodilation of veins = reduced preload & CO
  • vasodilation of arteries = impaired compensatory vasoconstriction
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15
Q

HR effects of neuraxial anesthesia

A

bradycardia.
a high blockade may inhibit the cardiac accelerator fibers at T1-T4

there is unopposed vagal tone which can = sudden cardiac arrest

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16
Q

Treatment of hypotension/bradycardia r/t neuraxial anesthesia

A

first line: ephedrine
glycopyrolate or atropine can be used for sympathetic bradycardia

IVF bolus 5-10ml/kg IF appropriate renal & cardiac function

head down = autotransfusion

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17
Q

Cephalad block effect on hemodynamic instability

A

more cephalad block = more hemodynamic instability

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18
Q

Pulmonary Effects of Neuraxial Anesthesia

A

usually minimal (phrenic nerve - innervating diaphragm - at C3-5)

severe CLD may require accessory muscles to breathe - these can be inhibited

post-op thoracic epidural analgesia in high risk patients is BENEFICIAL - decreased risk of PNE & respiratory failure - improves Oxygenation - decreases duration of mech vent

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19
Q

GI effects

A

unopposed vagal stim = small contracted gut & increased peristalsis- helpful for intestinal surgery

post-op epidural analgesia = decreased opioid need = quicker return of gut function

hepatic blood flow reduced with any type of anesthesia

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20
Q

GU effects

A

renal blood flow maintained

urinary retention - impairment of PNS & SNS - intraop catheter OR careful IVF admin & monitor for bladder distention

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21
Q

Major Indication for Neuraxial Blocks

A

Breast/thoracic/major abd - epidural + GA

Hip/knee replacement - can do spinal/epidrual alone

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22
Q

Absolute Contraindications to Neuraxial anesthesia

A 
coagulation abnormalities
severe hypovolemia 
increased ICP 
infection at injection site
thrombolytic/fibrinolytic therapy
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23
Q

Relative Contraindications to Neuraxial anesthesia

A 
aortic/mitral stenosis 
severe LF outflow obstruction
sepsis
severe spinal deformity
pre-existing neurological defects
uncooperative pt
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24
Q

Anticoagulants + Neuraxial Blockade

A

bleeding in the closed space of spinal canal = hematoma = pressure on spinal cord or caudal equina = infarction or ischemia = paraplegia or severe neurologic injury

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25
Warfarin
interval from last dose to placement/removal: 4-5 days
26
Heparin
interval from last dose to placement/removal: | IV OR SubQ: 4-6 hrs & verify aPTT
27
Clopidogrel
interval from last dose to placement/removal: 5-7 days interval from placement/removal to next dose: - with loading dose: 6 hrs - without: immediate
28
Argatroban
thrombin inhibitor | AVOID neuraxial anesthesia
29
Aspirin & NSAIDS
okay to continue
30
Prominent Landmarks
T7 - level with inferior tip of scapula L4 - tip of iliac crests - Tuffiers Line L4-L5: largest intervertebral space S2: bw posterior superior iliac spine
31
thoracic vs cervical/lumbar vertebrae
thoracic spinous processes point much more caudal & therefore require a greater cephalad angle
32
Passing of Needle layers
skin - subQ tissue - muscle - SSL - ISL - ligament flavum - epidural space - dura mater - subdural space - arachnoid mater - subarachnoid space
33
Midline Approach Steps
1. palpate & identify space 2. clean - set up sterile 3. skin wheel with LA with 25g needle 4. introducer slightly above caudal spinous process with 10 degree cephalad angle 5. remove stylet: CSF should drip 6. attach syringe - gently aspirate - slowly inject 0.5ml/s 7. complete, aspirate again to check placement 8. remove all together 9. assess level of blockade by testing temp or pin prick sensation
34
Paramedian approach
can bypass calcified ligaments 1 cm lateral and directed toward middle of the interspace ligamentum flavum will be first resistance met
35
Dermatomes
``` C5: clavicles C6: thumb C8: ring & little fingers T4: nipples T10: umbilicus S2, 3, 4: perineum L1,2,3,4: anterior & inner surfaces of lower limbs ```
36
Spinal Needles & Catheters
sharp cutting tip: Quincke blunt tip: Whitacre 25g smaller gauge + blunt tip = reduced risk of PDPH
37
Factors influencing the level of a spinal block
baricity positioning drug dosage - larger dose = more cephalad site of injection - more cephalad = more cephalad block
38
Baricity
migration depends on its density relative to CSF (1.003) hyperbaric = denser/heavier hypobaric = lighter/less dense
39
Positioning + baricity
Head up: hyperbaric settles caudal & hypobaric migrates cephalad lateral: hyperbaric will have greater effect on the dependent side & hyperbaric will have a greater effect on the non-dependent side isobaric tends to remain AT the level of injection
40
Baricity Supine position
anatomy will limit migration T4-T7 is the most dependent area T4 is the apex of the thoracolumbar curve - limiting spread
41
other factors affecting height of block
pt height, age, intraabd pressure, direction of bevel on injection, anatomy
42
spinal additives
all are preservative free | vasoconstrictors (A agonists & epi) & opioids prolong duration and/or improve quality
43
Epidural Anesthesia General
wider range of applications can be cervial, thoracic, lumbar surgical anesthesia, OB, post-op pain, chronic pain single shot, boluses, or continuous motor block can range from none to complete slower onset (10-20 min) less dense - segmental block can provide analgesia without motor blockade
44
segmental block
a band of blockade at certain nerve roots, leaves those above/below unblocked
45
Epidural Needles
``` 16-18g blunt bevel 15-30 degree gentle curve at tip - helps to push away dura after passing through the ligament flavum Tuohy Needle avg adult passes 4-6 cm obese pt may pass 8 cm ```
46
checking epidural placement
aspirate - confirm absence of blood test dose - 3ml of LA with 5mcg/ml epidural a 30 BPM increase in HR in 30s lasting 30s may mean you are intravascular immediate profound motor block may mean you are intrathecal
47
Factors Affecting Level of Epidural Block
Drug Vol: 1-2ml per segment to be blocked - to get T4 from L4-L5 would need 12-24ml Pt height: shorter may require less per segment, closer to.1 interspace decreases with age - require less additives usually help quality more than prolonging duration
48
Spinal Analgesia patho
diffuses into substantia gelatinous (Rexed lamina II) unites with opioid receptors of primary pain afferent Mu-1, Mu-2, kappa, delta spinal opioid analgesia primarily Mu-2 increased frequency of pruritus & urinary retention
49
Intrathecal Opioid
diffuses out of intrathecal space slowly onset of analgesia is slow, duration is prolonged early ventilatory depression does not occur - systemic uptake is minimal rostral speed = late resp depression (6-12hrs after)
50
Epidural Opioid
onset slow, duration prolonged systemic uptake is greater here = early ventilatory depression late depression also - rostral spread
51
epidural placement
sudden loss of resistance as you pass the ligamentum flavum
52
Hitting bone
superficially - needle hitting a lower spinous process deeper - midline - may be hitting an upper spinous proccess deeper - medial - may be hitting a lamina
53
pain or persistent paresthesias on injection of drugs
withdraw needle and re-direct
54
Caudal epidural anesthesia
usually for pends in combo with GA for procedures beneath umbillicus penetration of sacrococcygeal ligament covering the sacral hiatus (the unfused S4/S5) - groove above coccyx bw sacral Cornu (bony prominences)
55
three areas of neuraxial complications
adverse/exaggerated physiological responses catheter placement/injury drug toxicity - SLAT or caudal equina syndrome
56
Adverse/Exaggerated physiologic responses
``` urinary retention high block total spinal cardiac arrest horner syndrome ```
57
catheter placement complications/injury
``` PDPH backache neural injury bleeding- epidural hematoma incorrect placement - inadequate anesthesia, infection, inadvertent intravascular or intrathecal block ```
58
PDPH
occurs w/I 72 hrs intracranial hypotension from leak of CSF = sagging of brain & supporting structures S/S: HA, N/V, stiff neck, visual changes Risk Factors: pregnancy, female, young age, low BMI, cutting needle, large gauge Tx: rest, blood patch, caffeine, lie flat
59
High/Total Spinal
``` rapid ascending sympathetic/sensory/motor block bradycardia hypotension dyspnea difficulty swallowing ``` can progress to unconsciousness & respiratory depression
60
Spinal-Epidural Hematoma
progressive motor & sensory block with bladder/bowel dysfunction
61
Lidocaine
``` amide - 4.5mg/kg -- with epi: max 7mg/kg OR 500mg fast onset DOA: 1-2 hr intermediate potency ```
62
Bupivicaine
amide 2mg/kg -- with epi: max 3 mg/kg OR 200mg SLOW onset DOW: 3-10 hr - LONG acting has a high affinity for cardiac proteins - can produce cardiac toxicity
63
Mepivacaine
amide 4.5mg/kg -- with epi: 7mg/kg OR 500 mg intermediate onset DOA: 2-4hrs
64
Procaine
Ester 7mg/kg spinal primarily SLOW onset DOA: 1-2hrs
65
Chloroprocaine
ester 11mg/kg -- with epi: 14mg/kg OR 1g FAST onset DOA: 30min-1hr
66
MOA of LAs
produce a reversible blockade of conduction of electrical impulses at the alpha subunit of sodium channels ONSET: pain - temp - touch - pressure - motor
67
Metabolism of LAs
esters - hydrolysis via tissue & plasma cholinesterase amide - liver via CYP system
68
LA Properties
all are weak bases pKa: the pH at which there is an equal fraction of ionized & non-ionized lower pKa = greater non-ionized fraction = faster onset once in the nerve the charged IONIZED fraction binds the Na++ channels
69
DOA of LA
more lipid soluble = longer higher potency = longer more protein bound = longer

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