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APA > Spinal Blocks > Flashcards

Spinal Blocks Flashcards

1
Q

What is the term used to describe any type of anesthesia in the spinal canal or area?

A

Neuraxial

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2
Q

How can you differentiate amide from ester LAs?

A
  • amides have an “i” in their name

- Esters do not

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3
Q

All LAs are weak ________.

A

Bases

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4
Q

What does pKa tell you?

A

PKa= the pH where 50% of drug is ionized and 50% is non-ionized
- Lower pKa—> faster onset, greater fraction of molecules will exist in unionized form and will cross cell membrane easily (becomes ionized once inside the cell)

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5
Q

What is true if a LA is more ionized?

A

Will stay where you inject it- not enter cell- takes longer to work

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6
Q

A drug with a pKa of 9.0 will have a slower onset than one with a pKa of 8. Why is this?

A

The closer the pKa is to physiologic pH (7.4), the faster the onset
- pKa tells us how much is available and how fast it will cross the membrane

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7
Q

Describe the MOA for spinal anesthesia.

A
  • blocks nerve conduction
    • impaired propagation of action potential neurons
  • decreases rate of rise of action potential threshold so that threshold potential is not reached
  • interact directly with Na channel receptors - inhibits Na+ influx on channel (blocks Na channel open from the inside)
    • action potentials may start, but never reach threshold to continue sending msg down the axon
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8
Q

The intracellular environment is more acidic than the extracellular. Why is this important?

A
  • the acidic environment want to give up H+
  • it gives the H+ to the LA (weak base), making it ionized
  • LA is now active inside the cell and can go block the Na+ channel—> waits until channel opens and then block it from inside the cell
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9
Q

What are physiochemical factors of LAs that affect neural blockade?

A

LIPID SOLUBILITY:

  • increases potency
  • LAs more readily cross nerve membranes

PROTEIN BINDING:
- high protein binding = prolonged duration of effect

PKA:
- determines speed of onset of block

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10
Q

Wha this important regarding the size and function of nerve fibers?

A
  • thin fibers are more easily blocked than thick

- myelinated fibers are more readily block than unmyelinated —> LAs produce block at nodes of Ranvier

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11
Q

In which order are nerve fibers blocked?

A

B—> 3”m, light myelination
C—> 0.3-1.3 ”m, no myelination
A gamma and delta—> 2-6”m, moderate myelination
A alpha and ß—> 5-20 ”m, heavy myelination

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12
Q

What is the sequence of anesthesia?

A

ATPTP MVP

Autonomic (sympathectomy, peripheral vasodilation)
Temperature (loss of ...)
Pain 
*
Touch
Pressure
*
Motor
Vibration
Proprioception
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13
Q

How are esters metabolized?

A

Ester linkage readily cleaved by plasma cholinesterase
—> t 1/2≈ 1 min (in circulation)
- a product of its metabolism is p-aminobenzoic acid, which is what people may have an allergic reaction to

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14
Q

How are amides metabolized?

A

Via liver mechanisms

  • in liver disease may be prone to adverse reactions
  • elimination t 1/2= 2-3 hours (does not mean effect lasts this long)
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15
Q

What is baricity?

A

Density of medication relative to density/specific gravity of CSF

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16
Q

What does adding epi to a LA do?

A
  • prolongs duration
    • varies by type of LA—> if short acting, LA will benefit from adding epi. If LA is longer acting than epi then no use adding epi
  • decreases systemic toxicity
    • decreases rate of absorption
  • increases intensity of block
  • decreases surgical bleeding, if injected near incision
  • assists in evaluation of test dose
    • lets you know if you are in a blood vessel (don’t want LA to go systemic)
    • inject epi 1st (instead of LA)- watch VS to see if it goes systemic—> increase in HR
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17
Q

When would you not add epi to the LA?

A
  • block is in area of poor circulation
      • fingers, toes, penises
  • IV regional- Bier block
    • IV, stop blood flow (tourniquet), inject LA- LA seeps out into nerve
      - if epi present, will go systemic with tourniquet let down
  • hx of severe uncontrolled HTN, CAD, arrhythmia, hyperthyroidism, uterine-placental insufficiency
  • phenylephrine
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18
Q

What benefits does adding sodium bicarbonate to LA have?

A
  • increases pH—> increases concentration of non-ionized base
  • increases rate of diffusion across membrane- speeds onset of block
  • buffers pain- acids sting
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19
Q

What is the dose of sodium bicarbonate to add to LA?

A
  • 1 mEq/10mL lido or mepivicaine

- 0.1mEq/10mL bupivicaine (avoids ppt of drug)

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20
Q

What effect does adding an opioid to LA have?

A
  • adding 50-100”g fentanyl:
    • shortens onset
    • increases the level of block
    • prolongs duration
  • modulates pain transmission
    • action is synergistic with action of LA
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21
Q

Opioid use with LA has what side effect on respiration?

A
  • fentanyl: risk of early respiratory depression

- morphine: risk of early (local absorption) and late respiratory depression (systemic)

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22
Q

T/F True allergic reactions to LAs are common.

A

FALSE

  1. ) syncope, vaso-vagal, and tachycardia are NOT allergic reactions
  2. ) no reaction with amides—> pt may react to preservative if sensitive to PABA
  3. ) esters metabolite is similar to PABA —> may have allergic reaction to esters, but rare
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23
Q

How can systemic toxicity/OD of LA be minimized?

A
  • aspirate before injecting
  • test dose with epi containing solution
  • use small increment volumes (5mL at a time)
    • *** ALWAYS aspirate between injections **
  • proper technique during bier block —> wait at least 20-30 min before tourniquet release
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24
Q

What are symptoms of LA CNS toxicity?

A
  • light headed ness
  • tinnitus
  • metallic taste
  • visual disturbance
  • numbness of tongue and lip

May progress to: higher doses ≄ 14 ”g (on 0-28”g scale)

  • muscle twitching
  • loss of consciousness
  • grand mal seizures
  • coma
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25
Q

All toxicity tests were performed using which LA?

A

Lidocaine

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26
Q

Which respiratory gas has a major effect on toxicity?

A

CO2

- if you start to see signs of toxicity—> HYPERVENTILATE pt, don’t let CO2 climb!

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27
Q

What is the treatment of CNS toxicity?

A
  • administer O2
  • for seizure activity:
    - midazolam 1-2 mg, propofol, thiopentanol
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28
Q

What are signs of CV toxicity?

A
  • decreased contractility
  • decreased conduction
  • loss of peripheral vasomotor tone
  • CV collapse
  • IV injection of BUPIVICAINE or ETIDOCAINE may result in CV collapse, refractory to treatment because of high degree of tissue binding
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29
Q

How do you treat CV toxicity?

A
  • administer O2 (CO2 exacerbates it)
  • support circulatory volume, vasopressors and inotropes
  • ACLS if indicated (DONT GIVE ANY MORE LIDOCAINE- use amio instead)
  • TxV-tach with cardiversion
  • prolonged CPR needed until cardio toxic effects subside once drug is redistributed —> 40 min or longer
  • lipid emulsion
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30
Q

What is the dose for lipid emulsion?

A
  • bolus: 1.5mg/kg over 1 min

- 0.25 mL/kg infusion

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31
Q

How is post op morbidity and mortality effected when neuraxial block is used ?

A

Both may be decreased when neuraxial block is used, either alone or in combination with GA

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32
Q

When spinal analgesia is used, the risk if which complications is reduced?

A
  • venous thrombosis
  • PE
  • cardiac complications
  • vascular graft occlusion
  • respiratory depression and PNA
  • blood loss/transfusion (don’t really know why)
  • allows earlier return of GI function
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33
Q

What is a spinal?

A

Subarachnoid block

- intrathecal- same thing, used when using narcotics

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34
Q

What are typical doses for spinal, epidural an peripheral nerve block?

A
  • spinal: 1-2mL of LA
  • epidural: 10-30mL
  • peripheral nerve block: 20-30mL
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35
Q

What’s beneficial about using a spinal?

A
  • easy to perform
  • uses less LA
  • less discomfort (smaller volume)
  • more intense sensory and motor block
36
Q

Indications for a spinal:

A

Surgery of lower abdomen, lower extremities or perineum

- typically place in lumbar area and will spread up to ~ T6,7–> xyphoid

37
Q

What are key points for a pre-op exam?

A
  • Always document specific baseline neuro deficits
  • if s/s infection avoid spinal
  • current meds—> anticoags cause hematoma/paralysis
  • cardiac disease
  • AORTIC STENOSIS: fixed CO, dilation decreases Coronary Artery perfusion
38
Q

What are ABSOLUTE contraindications to a spinal?

A

1 is patient refusal!

  - doing so is battery, threatening to do it is assault - pt lack of cooperation - high ICP - coagulopathy - spina bifida - severe Aortic Stenosis
39
Q

What are relative contraindications for a spinal?

A
  • Coag that can be corrected
  • hypovolemia (correctable)
  • spinal cord disease
  • surgical time- spinal will only last so long
  • difficult airway-may be back up plan
  • musculoskeletal deformities-kyphosis, scoliosis, previous spine fusion
  • document all pre-existing neuropathies
40
Q

What are signs of a spinal/epidural hematoma?

A
  • new onset weakness or sensory deficit to Lower extremities
  • new onset back pain
  • new onset bowel/bladder dysfunction

*** must diagnose (MRI and NS c/s) and surgically decompress within 8 hours for best outcome

41
Q

What is the difference clinically, between a spinal hematoma and infection of the spine?

A
  • Infection will have similar s/s, but occurs 3-4 days later.
  • Hematoma s/s will show up within 1st 24 hours
42
Q

What are some landmarks you should know really well?

A
  • T4: Nipple line
  • T6, 7: Xyphoid Process
  • T 10: Umbilicus
  • C8: Pinky (watch for bradycardia- close to cardiac accelerators)
  • C6: Thumb
  • T1-T4: Cardiac Accelerators
43
Q

What are suggested minimum levels for spinal anesthesia?

A
  • lower extremity —-> T 12
  • hip, vagina, uterus, bladder, prostate—> T10
  • lowers ext. TQ, testes, ovaries—> T8
  • lower intra-abdominal—> T6
  • other intraabdominal—> T4
44
Q

How many vertebrae are in each section of the back?

A
  • 7 cervical—> 8 nerve roots (all other areas have 1 root/vertebrae)
  • 12 thoracic
  • 5 lumbar
  • 5 sacral
  • 4 coccygeal
45
Q

What is the part of the vertebra called where you feel for needle placement?

A

Spinous process- needle goes in indention between

46
Q

What are the three intralaminal ligaments?

A
  • supraspinous ligament: connects apices of spinous process.
    • most posterior
  • interspinous ligament: connects spinous processes, 1 for each level
  • ligamental flavum: connect caudal edge of vertebra above to cephalad edge of lamina below
    • most anterior
    • thickest/densest later- may feel a “pop” as needle passes through
47
Q

Where does the spinal cord end?

A

Adults: L1
Peds/infants: L3

Dural sac ends ~S2

48
Q

What makes up the caudal equina?

A
  • conus medullaris, lumbar sacral, and coccygeal nerve roots
49
Q

What 3 meninges cover the spinal cord?

A
  • dura mater:
    • tough fibrous sheath
    • runs the length of the rod
  • arachnoid: between dura and pia mater
  • pia mater: inner layer around cord
50
Q

What is the epidural space?

A

Potential space between ligament up flavum and dura mater

  • once the needle is here it creates a space to inject fluid- when fluid is gone, space goes away
  • 10-30mL injected - more layers to absorb through
51
Q

What is a spinal?

A

LA is injected into the subarachnoid space

  • 1-2 mL injected—>only has to go through pia mater to touch spinal cord
  • fast and all or nothing- blocks everything from that point down
52
Q

What are some facts about CSF?

A
  • clear, colorless fluid filling subarachnoid space
  • total CSF volume = 140mL
    - 30-80 in spinal canal, the rest in the brain
  • CSF SG= 1.004-1.009 @ 37˚C
  • CSF reabsorbed to maintain pressure 10-20 mH2o
53
Q

What are factors that affect the level of spinal blockade?

A
  • drug dose: directly proportional to level
  • drug volume: > volume = further spread
  • turbulence of CSF: turbulence increases spread
    • rapid injection, barbatoge (aspirate, inject, aspirate, inject), coughing, excessive pt movement
54
Q

How many mcg are the following concentrations:
0.5%
7.5%
2%

A

0.5%—> 5 mcg
7.5%—> 75mcg
2%—> 20mcg

55
Q

What else affects the level of spinal blockade?

A
  • increased intra-abdominal reassure
    • pregnancy- pressure dilates epidural vessels and vena cava- more pressure on spinal canal makes it smaller—> more spread
    • obesity, ascites, abdominal tumors
  • spinal curvature- lumbar lordosis, thoracic kyphosis
  • baricity of LA
56
Q

How would you make an LA hyper-hypo- or isobaric?

A
  • hyperbaric —> add dextrose to drug ( 5-8% dextrose)
    - SG > 1.0015
    - sinks in CSF
  • hypobaric—> mix with sterile water
    - SG <0.999
    - floats in CSF
  • isobaric—> mix with preservative free saline
    - theoretical advantage is predictable spread, independent of position
    * increasing dose will affect duration and more spread to higher dermatome
  • it is not possible to prepare a solution that is precisely isobaric
57
Q

Using which type of needle tip decreases incidence of post-dural puncture headache?

A

Non- cutting tip needle

58
Q

What is the land mark for L4, and where is the conus medullaris?

A

L4= iliac crest

Conus medullaris= T12 - L2 in 90% of people

59
Q

Describe the midline approach?

A
  • flat to 10˚
  • needle advanced through skin in same plane as spinal process with slight cephalad angle toward interlaminal space
  • if you hit bone, likely need to angle needle up a little
60
Q

Describe the paramedian approach?

A
  • helpful when pt cannot maximally flex back or when spinous ligament ossified
  • needle placed 1-1.5 cm lateral to midline of selected interspace
  • needle aimed medically and slightly cephalad- passes lateral to supraspinous ligament
  • if lamina contacted- redirect needle and walk of in medial and cephalad direction
61
Q

How do you find the destination for a spinal?

A
  • use the line across the iliac crest—> intersects spinous process of L4 or L3-L4 interspace
    • spinal anesthesia is usually done at L2-L3, L3-L4, and L4-L5 spaces
62
Q

What are key points for prep for a spinal?

A
  • prepare a larger area than you think you need
  • if kit contaminated—> get a new one—> contamination is NEUROTOXIC
  • check stylette and needle integrity
  • inject skin with 1% lidocaine
  • betadine only works if dry
  • chloroprep must dry for 3 minutes
63
Q

What are key points for needle placement in a spinal?

A
  • insert with bevel parallel to longitudinal fibers (decreases incidence of PDPH)
  • advance until resistance is felt going through ligamentum flavum
    - pop felt as it passes by ligamentum flavum
  • want slow drip of CSF free flowing - may rotate in 90˚ increments until good flow established
  • ** if parathesias with needle placement —> immediate withdrawal of needle and reposition
64
Q

How do you administer anesthetic during a spinal?

A
  • aspirate—> slowly inject —> re-aspirate to confirm needle tip still in subarachnoid space
  • gently remove needle as pt placed in desired position
  • in hyperbaric solution- when you aspirate you will se a little swirl of fluid (not seen in hypobaric solution)
65
Q

What do you do during the onset of the block?

A
  • ascending level assessed with pinprick or alcohol swab
  • closely monitor VS at least once/min until deemed stable —> HR, BP, RR
    • if hyovolemic BP will really drop
  • fixation of LA takes ~ 20 minutes
66
Q

Where are the autonomic, sensory and motor levels of the block?

A
  • level of autonomic block should be highest level of spinal (smaller C fibers affected fasest)
  • sensory level is 2 spinal levels below autonomic
  • motor level is 2 spinal levels below sensory level

A > S > M

67
Q

What is the CV response to a spinal?

A
  • hypotension: proportionate to the degree of sympathetic block achieved—> higher block = more hypotensive
  • vascular bed dilation- venous and arterial
  • decreased SVR with decreased venous return as a result
    • works in hypovolemic pt —> give IVF 500-1000mL bolus before you start
  • HR usually will not change-unless cardiac accelerators involved (T1-T4)
68
Q

What is the treatment of CV response?

A
  • if hx allows: pre-load with 15mL/kg IVF (500-100mL)
  • O2 mask
  • vasopressors
  • atropine: 0.4-0.8
  • epi—> drug of choice
  • CPR
69
Q

Why is epi the drug of choice for CV response?

A

Mixed alpha and beta agonist- treats bradycardia and hypotension
And increased peripheral SVR

70
Q

T/F You should just expect CV effects and be prepared for Bradycardia and hypotension.

A

True
Especially in elderly: HTN and dehydrated
Pregnant females: healthy vessels really dilate

71
Q

What are pulmonary effects of an autonomic block?

A
  • usually minimal- even with high level block
    —> chronic lung disease rely on accessory muscles more
    • accessory muscles impaired—> ineffective coughing/clearing secretions-may need to suction
  • use caution in pts with limited reserve *
72
Q

What are the 4 proven factors that affect level of anesthesia?

A
  1. ) Baricity of solution
  2. ) Position of pt—> during injection and immediately after
  3. ) Dose of drug
  4. ) Injection site
73
Q

What are complications of a spinal?

A
  • failed block
  • post-dural puncture headache (PDPH)
  • high spinal — >gets too high, can’t breath, heart doesn’t work right
  • nausea: OB pts almost always get nauseated d/t hypotension
  • urinary retention
  • hypoventilation
  • backache: can last a couple years- usually goes away sooner (ligament trauma)
74
Q

What is the depth to the dura and epidural space from the skin in an average person?

A

4-5cm
- needle has markings on it to measure depth
(Mid thoracic 3-5 mm wide, lumbar 5-mm wide)

75
Q

What is different with an epidural block?

A
  • onset of block is slower and less intense
  • anesthesia develops in a segmental manner—> selective blockade can be achieved
    • usually only trying to block sensory- not giving enough to block motor
    • can titration- give larger dose for motor block
  • LA spreads in both directions in epidural space (epidural space spreads all the way around spinal canal
  • epidural anesthesia is diffusion dependent- takes longer, must diffuse to Sa space
76
Q

What is the approach in an epidural?

A
  • needle should always enter midline regardless of approach (midline or paramedian)- where space is widest
    • decreases risk of puncturing epidural veins, spinal arteries, and nerve roots
  • inject local into supraspinous and interspinal ligaments
  • ligamentum flavum feels “rubbery”
  • use either loss of resistance or hanging drop techniques (drop of water at end of cath- when in epidural space low pressure- drop will suck in toward epidural space)
77
Q

Why is a thoracic epidural done?

A

To anesthetize the upper abdomen and thoracic regions

78
Q

What is different in a thoracic epidural?

A
  • requires smaller dose
  • thoracic vertebral spinous processes have more sharp downward angular ion
    • insert needle more cephalad
79
Q

If you know the concentration of LA is 1: 200,000, how do you find out how many mcg/mL that is?

A

1,000,000/200,000 = 5 mcg/mL

Divide 1 million by the ration to get the # of mcg per mL

80
Q

What happens with an epidural test dose?

A
  • 3mL of LA with 1:200,000 epi and 1.5% lidocaine (15mcg epi, 15 mg lido) injected prior to full dose
  • will have little effect if in epidural space
    • if in CSF will rapidly behave like a spinal
    • if injected into epidural vein—> pt will have a 20-30% increase in HR and metallic taste
81
Q

What are factors that affect level of epidural blockade?

A
  • volume of LA
  • age
  • pregnancy- vein engorgemnet, smaller space
  • speed of injection: alway inject in increments of 3-5 mL Q 3 min- aspirate every time before and after injection
  • position
  • spread
82
Q

After loading dose is given, what are ways we can control analgesia?

A

Maintain with intermittent dosing or continuous infusion.

  • intermittent used when high concentrations administered (2% lido or 0.5 % ropivicaine)
  • continuous infusion—> often dilute concentration of LA with low dose lipophillic opioid (fentanyl 1-5mcg/mL)
83
Q

Dense block = _______ motor involvement

A

More

84
Q

What are epidural adjuncts and why are they added?

A
  • epi: increases duration- stays in place
  • opioid:
    • fentanyl —>early respiratory depression
    • duramorph—> late respiratory depression
  • pH adjustment:
    - NaHCO3 1mL/10mL of LA
85
Q

Crossing from epidural to subarachnoid space is influenced by:

A
  • lipid solubility

- molecular weight

86
Q

What is seen with complications of an epidural?

A
  • back ache (30-40% in O.B)
  • PDPH: (1-2%), in wet tap increases incidence to 75%
  • trauma with catheter removal
    • cath can loop up and knot itself- gets stuck
    • make sure cath intact when you pull—> curved spine helps
87
Q

What needle tip is associated with a large dural perforation?

A

17g Touhy needle

APA (8 decks)

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