Neuraxial Anesthesia & Local Anesthetic Dosing Flashcards
Lance Carter, CAA
Descent of the Spinal Cord & Dural Sac
Neuraxial Anatomy
(Layers From Skin to CSF)
Spinal Vertebrae
Spinal Nerve Roots
Nerve Roots
Spinal/Epidural Landmarks
Finding The L3-4 Landmark
T10 (Umbilicus) Dermatome
T4 (Nipple) Dermatome
T5-L1 (Vasomotor Tone) Dermatome
T5-L1 (Vasomotor Tone) Dermatome (Cont’d)
T1-T4 (Cardiac Accelerator Fibers) Dermatome
C3-C5 (Phrenic Nerve) Dermatome
C6-C8 (Hands/Fingers) Dermatome
C6-C8 (Hands/Fingers) Dermatome (Cont’d)
Other Neuraxial Dermatomes
Sympathetic vs. Sensory vs. Motor Blockade
Sympathetic Blockade
Nerves are more easily blocked if they are:
Differential Blockade
Epidural
EpiduralAdvantages
(Compared To Spinals) (4)
EpiduralDisadvantages
(Compared To Spinals) (2)
EpiduralDisadvantages
(Compared To Spinals) (3-4)
“Walking Epidural”
Spinal Anesthesia
Spinal Needle Options
18ga “Introducer Needle”
Purpose Of The 18ga Introducer Needle
22ga Spinal Needle
Common Uses For The 22ga Spinal Needle
25ga Spinal Needle
27ga Spinal Needle
27ga Spinal Needle
Continuous Spinal Anesthesia
The Problem With Continuous Spinal Anesthesia
Practical Use Of Continuous Spinal Anesthesia
Management Of Continuous Spinal Anesthesia
Continuous Spinal Anesthesia After Accidental Wet Tap
Baricity Of Spinals
Hyperbaric Spinal
Hyperbaric Spinal For The Supine Position
Effect of Glucose on Hyperbaric Spinal for the Supine Position
Hyperbaric “Saddle” Block
Hypobaric Spinal
Isobaric Spinal
Combined Spinal Epidural (CSE) Technique
“Espocan” CSE Needle
Combined Spinal Epidural (CSE) Advantages (3)
Combined Spinal Epidural (CSE) Disadvantage (1)
Dural Puncture Epidural Technique
(A New Form of Continuous Spinal Anesthesia?)
Dural Puncture Combined Spinal Epidural Technique
- An epidural needle is placed
- A spinal needle is inserted through the Tuohy needle and punctures the dura
- The spinal needle is removed without dosing intrathecal medication
–This leaves a small hole in the dura - The epidural catheter is placed and hooked up to an infusion pump
- The local anesthetic primarily goes into the epidural space, but a small portion is allowed to “leak into” the intrathecal space through the hole that was created by the spinal needle
–This technique allows faster sacral onset and greater sacral spread of the local anesthetic, and it results in a lower incidence of unilateral block
Dural Puncture Epidural Technique Advantages (3)
Dural Puncture Epidural Technique Disadvantage (1)
Epidural vs. Spinal Dosing Summary
Caudal Anesthesia Landmarks
Caudal Anesthesia
Caudal Technique Video
Caudal Technique
- Palpate the sacral hiatus
- This is covered by the sacrococcygeal ligament
- It is above the coccyx and between the sacral cornu (bony prominences lateral to the sacral hiatus) - Insert the needle through the sacral hiatus at a 45° angle
- Advance cephalad until a “pop” is felt
- Advance the cannula over the needle and remove the needle
- Aspirate before injecting
Lumbar Epidurals
When epidurals are performed in the lumbar or thoracic region, it is possible for the needle to cause spinal cord or nerve root damage, due to the proximity of the spinal cord and nerve roots
-Therefore, when epidurals are performed in the lumbar or thoracic region, it is vital that the patient be awake (so that they can alert the anesthetist of any parasthesias) to reduce the chance of nerve injury
Caudal Epidurals
Epidural Blocks In Children
Advantages of Caudal Anesthesia (3)
Disadvantages of Caudal Anesthesia (5)
Caudal Anesthesia in Adults?
Factors Affecting The Neuraxial Spread Of Local Anesthetics (7)
- *1. Total mg dose**
- Higher doses spread more than lower doses
- *2. Total volume injected**
- 10mL 1% lidocaine (100mg) will spread more than 1mL 10% lidocaine (100mg)
- *3. Addition of epi**
- Prolongs the block, but doesn’t raise the block level
- *4. Addition of narcotic**
- Increases the density (“strength”) of the block
- Height of the patient (more so than weight)
- The shorter you are, the more likely the block will travel “too high”
- *6. Positioning**
- Trendelenburg = more cephalad spread of local anesthetic
- Reverse Trendelenburg = less cephalad spread of local anesthetic
- Lateral: the block will be more one sided
- *7. Weight of the patient**
- The more obese (heavy) the patient:
- The further (higher) the local anesthetic will spread
- The lower the local anesthetic dose requirement
Why would obese patients/or twin pregnancies have an increased chance of a high block?
Duration of Neuraxial Blocks in the Elderly
Summary Of Onset, Duration, & Dosing For Neuraxial Blocks In Elderly Patients
Absolute Contraindications to Neuraxial Anesthesia (8)
1. Patient refusal
2. Infection at the injection site (because a block could lead to possible meningitis or an epidural abscess)
3. Severe hypovolemia (because there’s a good chance that the patient wouldn’t be able to tolerate the sympathectomy)
4. Coagulopathy (could lead to a possible epidural hematoma)
4a. Thrombocytopenia
In OB, platelet counts >80,000-100,000 are generally considered safe prior to neuraxial blockade (Protocols for High-Risk Pregnancies, 5th edition, page 169)
4b. Elevated PT/PTT/INR
- *5. Severe aortic stenosis**
- Sympathectomy drops preload & afterload, and preload/afterload should be maintained with aortic stenosis
- *6. Severe mitral stenosis**
- For the same reason as aortic stenosis
- *7. Sepsis**
- Could lead to meningitis
8. Elevated intracranial pressure (ICP)
-These patients can’t tolerate the sympathectomy because a high MAP is required to perfuse the head in patients with intracranial hypertension
(Cerebral perfusion pressure = MAP – ICP)
Complications from Neuraxial Blocks (11)
Relative Contraindications To Neuraxial Anesthesia (4)
Diagnosing Back Pain
Epidural Abscess
Epidural Hematoma
Transient Neurologic Symptoms (TNS)
Cauda Equina Syndrome (CES)
Post Dural Puncture Headache (PDPH)
If an anesthetist accidentally wet taps a patient, they have two options:
The symptoms of post dural puncture headache
The incidence of post dural puncture headache
Treatment For Post Dural Puncture Headache (PDPH) (3)
- *1. Autologous blood patch**
- “Epidural blood patch (EBP) is currently the gold standard for PDPH treatment, with a success rate ranging from 90% to 99%”
- This should not be attempted until all signs show that the local anesthetic has worn off. Blood patch attempts prior to local anesthetic wearing off have been associated with total spinal anesthesia (https://www.youtube.com/watch?v=F-MOX3fELGU)
2. Analgesics, caffeine, and generous fluid administration have also been used to treat PDPH
3. Neostigmine and Atropine combination?
“While neostigmine cannot cross the blood–brain barrier, it passes the choroid plexus, and together with atropine, both affect the CSF secretion and the cerebral vascular tone, contributing in improving PDPH”
Regional Anesthesia Advantages (compared to GA) (4)
Esters vs. Amides
Local Anesthetics with Epinephrine
Tetracaine (Pontocaine)
Most Common Local Anesthetics For
Labor Epidural Dosing (4)
Marcaine (Usually Diluted to 0.1-0.25%) Advantages
Marcaine (Usually Diluted to 0.1-0.25%) Disadvantages (3)
Marcaine Toxic Dose & Reversal Of Toxicity
Ropivacaine (Naropin) 0.2%
Lidocaine (2% or 1.5% with Epi) Advantages (2)
Lidocaine (2% or 1.5% with Epi) Disadvantages (2)
Lidocaine (2% or 1.5% with Epi) Disadvantageous Neurological Effect
Chloroprocaine (Usually 3%) Advantages (2)
Chloroprocaine (Usually 3%) Disadvantages (3)
Epidural Bolusing
Prior to bolusing through an epidural catheter, the CAA should:
Initial Epidural Test Dose
Epidural Loading Dose
Dose To Increase The Density Of The Epidural Block
Raising The Epidural Block Level Gradually
Raising The Epidural Block Level Immediately
Best choice for emergency C-sections?
Preservatives in Local Anesthetics
Parabens (i.e. Methylparaben)
Parabens (i.e. Methylparaben) contraindications?
Sulfites (Bisulfite or Metabisulfite)
Are sulfites safe for epidurals and spinals?
EDTA
Conclusion for spinals and epidurals
Preservatives In Bier Block Local Anesthetics
Bicarbonate
Alpha Agonists
Duramorph
Advantages of Neuraxial Opioids
Disadvantages of Neuraxial Opioids
Epidural vs. Spinal Opioids
Drug Ionization
Placing An Acidic Drug In A More Basic Environment
Placing A Basic Drug In A More Acidic Environment
Placing A Drug In An Ideal pH Environment
pKa of a Drug
How would you speed up the onset time of a local anesthetic in the following example?
Acidic Drugs (pH < 7.4) in Basic Environment
Acidic Drugs (pH < 7.4) in Acidic Environment
Basic Drugs (pH > 7.4) in Acidic Environment
Basic Drugs (pH > 7.4) in Basic Environments
pKa of Acidic & Basic Drugs
Summary Of How pH Relates to pKa
Adding bicarb to the local anesthetic will?
Local Anesthetics Containing Epinephrine
Question
Question
Factors That Determine Local Anesthetic Onset (4)
- *1. How ionized the local anesthetic is**
- The higher the ionization, the slower the onset
- *2. How close the local anesthetic’s pH is to the local anesthetic’s pKa**
- The closer the local anesthetic’s pH is to pKa, the less ionization, and the faster the onset
- *3. How close the local anesthetic’s pKa is to physiologic pH**
- The closer the local anesthetic’s pKa is physiologic pH, the less ionization, and the faster the onset
4. How lipid soluble the local anesthetic is
Factors That Determine Local Anesthetic Potency (3)
Table Summary Of The Effects Of Lipid Solubility
