Management of Regional, Spinal, & Epidural Anesthesia - Quiz 5 Flashcards
Which Local Anesthetics are Esters?
Procaine
Cocaine
Chloroprocaine
Tetracaine
Which Local Anesthetics are Amides?
Lidocaine
Mepivacaine
Bupivicaine
Etidocaine
Ropivacaine
What is the general structure of Local Anesthetics?
Aromatic Lipophlic Ring
+
Intermidiate Chain (Ester/Amide)
+
Amine
Local anesthetics with a ______ pKa will have a faster onset b/c a larger portion of the molecule is uncharged/non-ionized
Local anesthetics with a lower pKa value will have a faster onset b/c a larger portion of the molecule is uncharged/non-ionized
What is the Mechanism of Action of Local Anesthetics?
Directly stops influx of Na+ to block nerve conduction by inhibiting the propogation of action potentials
How does a lot of Protein binding affect Local Anesthetics?
Prolong Duration of Effect
What kind of nerve fibers are more easily blocked?
Thin, Myelinated nerve fibers are more easily blocked
A-Alpha Fibers
Biggest Diameter
Most Myelination
Fastest Conduction
Motor Function & Propioception
A-Beta Fibers
4-15µm Diameter
Second Fastest Conduction
Motor, Touch & Pressure Sensation
A-Gamma Fibers
4-15µm Diameter
Muscle Spindles & Reflex
A-Delta Fibers
3-4µm Diameter
Slowest Conducting A Fiber
Pain & Temperature Sensation
B Fibers
4µm Diameter
Slower Conduction & Less Myelination than A FIbers
Preganglionic Autonomic Nerves
C Fibers
1-2µm Diameter
Slowest Conduction
Pain & Temperature Impulses
Unmyelinated
What is the Order of Anesthesia with Local Anesthetics?
- Sympathetic Block, Vasodilation, ↑Skin Temp
- Loss of Pain & Temp Sensation
- Loss of Proprioception
- Loss of Touch & Pressure Sensation
- Motor Paralysis
How are Local Anesthetic Metabolised?
Esters: Cholinesterase (1 min half life)
Amides: Liver (2-3 hr half life)
What is Baricity in regards to Local Anesthetics?
LA Classification based on their density relative to Density of CSF
EX: Hypobaric, Isobaric, Hyperbaric
What is Epinephrine’s affect on Local Anesthetics?
↓Systemic Toxicity
↓Rate of Absorption
↓Bleed
↑Block Intensisty
Helps evaluate test dose
When should Epinephrine not be added to Local Anesthetics?
Blocks in places w/ poor circulation
Bier Block
Pt hx of uncontrolled HTN, CAD, Arrhythmia, Hyperthryoid, utero-Placental Insufficiency
How does Sodium Bicarb affect Local Anesthetics?
↑pH –> ↑non-ionized concentration
↑Rate of Diffusion & Speeds Onset
How much Bicarb should be added to Lidocaine, Mepivacaine, and Bupivacaine?
Lidocaine & Mepivacaine
1 mEq per 10mL
- *Bupivacaine**
0. 1 mEq per 10 mL
What is the result of adding an Opioid to Local Anesthetics?
Adding 50-100mcg of Fentanyl would be synergistic
Shorten Onset
↑Intensity
↑Duration of Block
How can Systemic Toxicity d/t accidently IV injection of Local Anesthetics be avoided?
Aspirate before Injecting
Epi Test Dose
Proper Technique
What are the early signs of CNS toxicity from Local Anesthetics?
Lightheadedness
Tinnitus
Metallic Taste
Blurry Vision
Toung & Lip Numbness
What are the later signs of CNS toxicity from Local Anesthetics?
Muscle Twitching
Loss of Consciousness
Grand Mal Seizure
Coma
What is the treatment for CNS Toxicity from Local Anesthetics?
Give O2
Versed 1-2mg
Thiopental 50-200mg
Propofol
What are the symptoms of CV Toxicity from Local Anesthetics?
↓Contractility
↓Conduction
Loss of Vasomotor Tone
CV Collapse (Especially from Bupivacaine/Etidocain)
What is the treatment for CV Toxicity from Local Anesthetics?
Give O2
Volume
Pressors
Inotropes
Cardioversion
Takes a while to treat
What are the Categories of Regional Anesthesia?
Central/Neuraxial
Spinal, Epidural, Caudal
Peripheral
Pain Management
The use of Neuraxial blockade is found to ________ post-op mortality & morbidity
The use of Neuraxial blockade is found to reduce post-op mortality & morbidity
(Overall its better… less complications, earlier return of GI fxn)
How is a Neuraxial block achieved and what are the advantages?
Inject LA into CSF in the Subarachnoid/Intrathecal Space
Easy to Perform
Uses less LA
Less Discomfort on Placement
More Intense Block
What are some indications for a Spinal?
Surgery of Lower Abdomen, Lower Extremities, & Perineum
Wat are Absolute Contraindications to Spinal?
Pt. Refused or Lack of Cooperation
↑ICP
Pre-existing Coagulopathy
Skin Infection @ Site
Hypovolemia
Spinal Cord Disease
What are some Relative Contraindications to Spinal?
Fixed Cardiac Output
Sepsis
Difficult Airway
Indeterminate Neuro Disease
When should NSAIDs be stopped before Neuraxial Interventions?
No Contraindication
When should Plavix & Abciximab be stopped befor Neuraxial Interventions?
7 Days Before
When should Ticlopidine & Tirofiban be stopped before Neuraxial Interventions?
14 Days
When shoudl Eptifibatide be stopped before Neuraxial Interventions?
4-8 hours before
What are symptoms of a Spinal/Epidural Hematoma?
New Lower Limb Numbness & Weakness
New Back Pain
New Bowel/Bladder problems
Why is timing important for treating Spinal/Epidural Hematoma?
Must be surgically decopressed in < 8 hours for best outcomes
What is the minimal segmental level of Spinal Anesthesia for Lower Extremities?
T12
What is the minimal segmental level of Spinal Anesthesia for Hip, Bladder, Vaginal, & Prostate surgeries?
T10
What is the minimal segmental level of Spinal Anesthesia for Testes, Ovaries, & Lower Extremities?
T8
What is the minimal segmental level of Spinal Anesthesia for Lower Intraabdominal?
T6
What are the Vertebral Column Regions?
7 Cervical
12 Thoracic
5 Lumbar
5 Sacral
4 Coccygeal
What are the three Intralaminar Ligaments that Binds vertebrae together?
Supraspinous - Apices of Spinous Processes
Interspinous - Spinous Processes
Ligamentum Flavum - Caudal Edge to Cephalad Edge
How far does the Spinal Cord extend during Fetal Life?
Extends length of Vertebral Canal & ends at L3 at birth.
Which direction does the Spinal Cord form as it reaching Adult Position?
Forms Cephalad until reaches Adult Position of L1 by 2 y.o.
What structures form the Cauda Equina?
Conus Medularis
Lumbar, Sacral, & Coccygeal Nerve Roots
Why are Spinal Needles placed below L2?
Mobility of Spinal Nerves reduce needle trauma
What are the 3 Meninges that cover the Spinal Cord?
Pia Mater
Arachnoid - b/t dura & pia
Dura Mater - tough fibrous sheath
What is found in the Subarachnoid and is clear & colorless?
Cerebrospinal Fluid
What is the Total Volume of CSF and how much of it is in the Spinal Canal?
Total CSF: ~ 140 mL
Spinal Canal CSF: 30-80 mL
How much CSF does the body produced per day?
500 mL/day made by the choroid plexuses of cerebral ventricles.
What is the Specific Gravity of CSF?
1.004 - 1.009
What Factors affect Level of Spinal Block?
- Drug Dose
- Site of Injection
- Baricity of LA
- Pt. Position during and after injection
- Drug Volume
- Turbulence of CSF
- increases spread (rapid injection, coughing, movement)
- Intra-Abdominal Pressure
- Preggos, Obese, Ascities, Abd. Tumors
- Spinal Curve
How does Intra-Abdominal Pressure affect Level of Spinal Block?
Pressure on Inferior Vena Cava = Epidural Venous Engorgement and reduces CSF volume
LA spreads farther
What is the most common Local Anesthetic solution for Spinal Anesthesia and how does it work?
Hyperbaric Solution - contain Glucose
Flow to most Dependent part of CSF Column
How do Hypobaric Solutions work?
Contain Sterile Water
Flows to Highest part of CSF Column
(Perineal procedures in Prone)
What are the advantages of using Isobaric Solutions?
Predictable spread regardless of position
Increase dose = Increase Duration more than Spread
What is the Paramedian approach to placing a Spinal?
For patients who can flex all the way or have Ossified spine ligaments
Place needle next to midline and aim upwards & towards the middle
Which Spinous Process is aligned along the upper borders of the Iliac Crests?
L4 or L3-L4 Space
Spinals are usually between L2-L3, L3-L4, L4-L5 spaces
What are the steps to Spinal Needle Placement?
- Place needle w/ bevel parallel to longitudinal fibers to reduce headache
- Advance until increased resistance then POP w/ loss of resistance
- Remove stylet - you should see free flow of CSF
- Withdraw & Reposition if there is paresthesia
- Rotate needle 90 degrees until good CSF flow
How is the LA given once the Spinal Needle is placed?
- Aspirate CSF to confirm
- Slowly Inject LA
- Reaspirate to confirm placement in subarachnoid
- Gently remove needle
How long does it take for fixation of Local Anesthetic?
20 minutes
What is the sequence of Local Anesthetic Blockade?
Autonomic > Sensory > Motor
(each by 2 segments)
What are possible CV complications to Spinal Local Anesthesia?
Hypotension & Bradycardia
What are treatments for CV complications to Spinal Anesthesia?
500-1000cc before Spinal
Oxygen
Vasopressors
Atropine
Epinephrine
CPR
What are the Pulmonary Effects of Spinal Anesthesia?
Minimal change to Tidal Volume
Dyspnea for pts w/ lung disease relying on accessory muscles
What are the complications of Spinal Anesthesia?
- Failure of Block
- Post-Dural Puncture Headache
- High Spinal
- Nausea
- Urinary Retention
- Hypoventilation
- Backache
How wide is the Epidural space at Midline Lumbar and at the Mid-Thoracic Region?
Lumbar: 5-6 mm wide
Mid-Thoracic: 3-5 mm wide
How does an Epidural Block work?
Acts directly on Spinal Nerve Roots
Gets access to CSF via uptake through dura
Slow Onset & Less Intense
Segmental Anesthesia
Selective Blockade
How is Epidural Anesthesia different from Spinal Anesthesia?
Titratable for Pain or Anesthesia
Greater Control of Sensory & Motor Block than Spinal
How does Epidural Anesthesia Spread?
- Anatomically along Spinal Canal
- Horizontally: Dural Cuffs & into CSF
- Longitudinally:
- Cephalad along Paravertebral trunks
- Intradural Spinal Roots
- Dorsal & Ventral Spinal Roots
- Dorsal Root Ganglia
- Spinal Cord
- Brain
Why must large amounts of Local Anesthetics be used for Epidurals?
Diffusion Dependent
This is why onset is so long
Why should the needle always enter the Epidural midline regardless of approach?
Widest area to reduce risk of puncturing epidural vein, spinal artery & spinal nerve root.
What is the Technique for Lumbar Epidural?
Loss of Resistance or Hanging Drop Technique
Use Long 25g Needle inserting upward to get into ligaments
What is the Technique for Thoracic Epidurals?
Same as Lumbar, but insert Needle more upward
Needs smaller dose of local Anesthestic
What is the Epidural Test dose and Why is it Given?
3mL of LA w/ 1:200,000 Epinephrine
No effect if placement is correct
If in CSF: Rapidly Behaves like Spinal
If in Epidrual Vein: 20-30% HR Increase
What are Factors that affect Epidural Block?
- Volume of LA
- Age
- Pregnancy
- Speed of Injection
- Position
- Spread of Block
What are the Adjuncts to Local Solution for Epidural?
Epinephrine
Opioid (Fentany/Duramorph)
Bicarb
How does SNS block with Regional compare is Inhaled Anesthetics?
SNS block is Slower w/ less risk of abrupt hypotension
What are ways to use Epidural Anesthesia?
Single Shot Epidural
Continous Epidural
Combined Spinal - Epidural
Combined Epidural - General
Caudal Anesthesia