Regional Anesthesia Flashcards
How do you tell the difference between esters and amindes?
ESTERS Procaine cocaine tetracaine chloroprocaine
AMIDES lidocaine mepIvacaine bupIvicaine etIdocaine ropIvacaine (have I’s in the beginning)
The amine portion makes LAs
hydrophilic
What is the ester chain
C-O-C
What is the amide chain
N-H
What is pKa
The pH at which 50% of the local anesthetic is ionized and 50% unionized
All LA have a pKa between
7.6-9.1
Is it the charged or uncharged molecule that is the most lipophilic and can access to the axon
unionized
pKa is only the _____ of onset. The ______ the pKa the faster the onset
speed
lower
LA needs to _______ to get into the cell. Inside the cell is _______ and the LA becomes _______. When ionized, it gets stuck in the cell and can attach to the receptor
unionized
acidic
ionized
MOA: Block nerve conduction by impairing propagation of the action potential in
axons
MOA: Decrease the rate of rise of the action potential such that the threshold potential is
not reached
MOA:
Interact directly with specific receptors on the Na+ channel, inhibiting
Na+ ion influx
How does lipid solubility effect the duration of action
increases potency
does account for some duration of action
How does protein binding effect the duration of action
a high degree of protein binding will prolong the duration of action
How does pKa effect the duration of action
speed of onset
Thick or thin fibers are more easily blocked
thin
Mylinated or unmylinated fibers are more easily blocked?
mylitated
produce block only at Node of Ranvier
Describe A alpha fibers
12-20mm
motor & proprioception
Describe A beta fibers
5-12mm
Touch (pressure) & proprioception
Describe A gamma fibers
3-6
Motor (muscle spindles)
Describe A delta fibers
2-5
Pain, touch, temp (cold)
Describe B fibers
<3mm
Preganglionic autonomic fibers
Describe C fibers
0.4mm
Pain (sharp), touch, temp (hot &cold)
Which fibers are NOT mylinated?
C fibers
Which fibers will be blocked first?
What will you see with this?
B fibers (with a little bit of C) periph vasodilation and elevated skin temp
What is the sequence of block
ATP/TP/MVP
Automatic touch pain
Temp pressure
Motor vibration proprioception
How are esters metabolized? How long is their half life in circulation?
plasma cholinesterase
about 1 minute (short!)
Degradation product of ester metabolism is a metabolite related to
p-aminobenzoic acid. (PABA)
How are amides metabolized? Where does this happen? How long is the elimination half life?
amide linkage is cleaved through N-dealkylation followed by hydrolysis.
This occurs primarily in the liver.
Elimination half-life is 2-3 hours.
What patients may be more susceptible to adverse reactions from amide local anesthetics.
severe hepatic disease
Does amount of local anesthetic in the liver matter to the length of the block?
No, because the site of action is the nerve
Local anesthetic solutions are classified as hypobaric, isobaric or hyperbaric based on their _____ relative to the density/specific gravity of cerebral spinal fluid (CSF).
density
What is the specific gravity of CSF?
1.003–1.009 at 37*C.
A hypobaric LA will
float
if you leave them sitting up = high spinal
An isobaric LA will
sit right where you put it (same baricity as CSF)
A hyperbaric LA will
sink
What happens if you don’t lay a patient down right away that got a hyperbaric LA block?
saddle block
Baricity changes level for about
5 minutes
What does adding epi to a LA do?
5 things
- Prolong duration of anesthesia
- Decrease systemic toxicity by decreasing rate of absorption
- Increase intensity
- Decrease surgical bleeding
- Assist in eval of test dose (HTN/tachy if accidental inject into vein/artery)
When would you NOT add epi to your LA?
4 reasons
- block in area with poor collateral circulation (NO fingers, toes, penile block with epi)
- Bier Block (IV regional)
- IV LA (when take tourniquet down - big flush of epi)
- History of severe uncontrolled HTN, CAD, arrhythmia, hyperthyroid, utero-placental insufficiency.
What could you add other than epi that would be better for HR
Phenylephrine
What does adding sodium bicarb to a local anesthetic do?
Raised the pH and increases the concentration of unionized (free) base
Increases rate of diffusion
SPEEDS UP ONSET
1mEq added to each 10ml of _____ or _______
lidocaine or mepivacaine
0.1mEq added to each 10ml of ________
bupivicaine
What does adding an opioid (50-100ug fentanyl) to a LA do? (3 things)
- Shortens the onset (makes it work quicker)
- Increases the level
- Prolongs the duration of a regional block.
When an opioid is added to a LA, a selective action at the _____ _____ of the spinal cord modulates pain transmission.
dorsal horn
Adding an opioid to a LA, action is _______ with the action of the local anesthetic.
synergistic
Why would you add precedex or clonidine to a LA?
to prolong the block (up to 72hrs)
T/F: true allergic reactions are rare
True
Must be differentiated from non-allergic responses such as syncope and vaso-vagal reaction.
Describe allergic reactions to Amides
essentially devoid of allergic potential.
If a methyl-paraben preservative is used, it may produce allergic reaction in someone allergic to PABA.
Describe allergic reactions to Esters
may cause allergic reaction due to metabolite similar in structure to PABA.
Also may produce allergic reaction in persons sensitive to sulfonamides or thiazide diuretics.
Is there cross sensitivity between esters and amides?
NO, if allergic to one class, give the other
How does systemic toxicity occur?
accidental intravascular injection or overdose of local anesthetic
What are ways to minimize systemic toxicity?(4 things)
Aspiration prior to injection (if you get block back DO NOT inject)
Use of epi-containing solutions for test dose
Will see tachycardia
Use of small incremental volumes to establish the block
5 check, 5 check
Use of proper technique during IV regional
Bier block
What are symptoms of CNS toxicity?
Lightheadedness
Tinnitus
Metallic taste
Visual disturbance
Numbness of tongue and lip
May progress to: Muscle twitching Loss of consciousness Grand mal seizure Coma
What should you do it a patient starts to complain of any S/S of CNS toxicity?
STOP injecting
In a periperal nerve block, they should not get lightheadedness tinnitis, etc
When someone arrests from systemic toxicity, why won’t normal drugs work?
Because we are blocking all the Na channels with our LA. We need to give lipids and do compressions until level of block comes down.
What LA has the highest seizure threshold?
What LA has the lowest seizure threshold?
Procaine
Bupivicaine (more likely to see seizures)
What do you need to do if a patient start to have seizures with a LA?
blow off CO2
Midazolam 1-2 mg
Thiopental 50-200mg
Propofol
Amin 100% O2
What is the clinical presentation to cardiovascular toxicity from a LA?
Decreased contractility
Decreased conduction
Loss of vasomotor tone
CV collapse
What are the 2 most CV toxic LAs?
bupivacaine (MOST) & etidocaine
Treatment of CV toxicity
Administer O2
Support the circulation with volume, vasopressors, and inotropes
ACLS if indicated
Treat V-tach with cardioversion
Prolonged cardiopulmonary resuscitation may be required until the cardiotoxic effects subside with drug redistribution. (up to 45 minutes)
For CV toxicity, what is the dose of lipid emulsion?
1.5 ml/kg over 1 min
Drip 0.25 ml/kg/min
repeat bolus q3-5 min for a Max 3 ml/kg
What 2 monitoring devices MUST be on before putting a block in?
pulse ox and BP cuff
T/F: Research suggests that post-op morbidity and possibly mortality may be reduced when neuraxial blockade is used, either alone or in combination with general anesthesia.
True
Name some benefits of using an Neuraxial blockade
REDUCED INCEDENCE OF venous thrombosis pulmonary embolism cardiac complications vascular graft occlusion respiratory depression and pneumonia blood loss and transfusion allows earlier return of GI function
How is a Neuraxial Blockade accomplished?
by injecting local anesthetic solution into the cerebral spinal fluid within the subarachnoid/intrathecal space.
Why do you use less LA when performing a neuraxial blockade in the subarachnoid space?
because injecting it right where nerves are
Indications for a spinal
Surgery of lower abdomen
Surgery of lower extremities
Surgery on perineum
Skin infection at the site of injection increases the risk of meningitis or epidural abscess. Aseptic technique MUST be adhered to. Other factors that increase the risk of infection include skin conditions such as
psoriasis, underlying sepsis, diabetes, immunologic compromise, steroid therapy, history of HIV or herpes simplex virus
What is the most common causative organism in the epidural abscess?
phylococcus aureas (MRSA)
How is an epidural abscess diagnosed and treated?
diagnosed by MRI, early aggressive surgical intervention and antibiotics.
According to Levi, what is the ONLY ABSULUTE CONTRAINDICATION to a spinal
Pt refusal
guidelines for anticoagualted patients:
ASA/NSAIDS
no contraindication
guidelines for anticoagualted patients:
Heparin
place catheter 1 hour prior to administering heparin
Catheters should be pulled when heparin activity is at a minimal level. Ie. An hour before the next dose
guidelines for anticoagualted patients:
Clopidogrel & abciximab
discontinue 7 days preop
guidelines for anticoagualted patients:
Xarelto
discontinue 3 days preop
What are the herbal subelements that can effect blood clotting?
“G” Herbals
Gingo, Ginsing
Fish oil
What S/S would have you concerned for a Spinal or epidural hematoma
New onset weakness to lower limbs and sensory deficit
New onset back pain
New onset bowel or bladder dysfunction
OR
Spinal never wears off (very nervous at 5 hrs)
What must happen for the best outcome of a spinal hematoma
Must diagnose and surgically decompress hematoma within 8 hours for best outcome
Or become paraplegic
Will need emergent MRI
Risk of permanent neurologic damage
Spinal anesthesia
Epidural anesthesia
Spinal anesthesia 1-4.2 : 10,000
Epidural anesthesia 0-7.6 : 10,000
Dermatomes C6 C8 T4 T7 T10
T1-T4
C3,4,5
C6 - thumbs C8 - pinky T4 - nipple line T7 - xiphoid T10 - belly button
T1-T4 - cardiac accelerators (above bradycardia, treat with atropine/epi)
C3,4,5 - diaphragm
Level required for surgery
Lower extremities Hip Vagina/uterus Bladder/prostate Lower extremities/TQ Testis/ovaries Lower intraabdominal Other intraabdominal
Lower extremities T12 Hip T10 Vagina/uterus T10 Bladder/prostate T10 Lower extremities/TQ T8 Testis/ovaries T8 Lower intraabdominal T6 Other intraabdominal T4
How many vertebra
cervical vertebra thoracic lumbar sacral coccygeal
7 cervical vertebra 12 thoracic 5 lumbar 5 sacral 4 coccygeal
Why is the lumbar a good place to insert a needle to enter spinal canal?
spinal processes are straight
Thoracic spinal processes are angled, what does this mean
you need to enter the spinal canal at a deep angle
The sacral region is all fused, what type of block is this
caudal block
connects apices of spinous processes.
Supraspinous ligament
connects the spinous processes.
Interspinous ligament
connects the caudal edge of the vertebra above to the cephalad edge of the lamina below
Ligamentum flavum
When doing a midline approach, what is the order that the needle will pass though
Skin, subcutaneous tissue, supraspinous ligament, interspinous ligament, ligamentum flavum
The spinal canal extents the length of the spinal cod during fetal life, but end at _____ at birth
L3
Spinal cord moves progressively cephalad eventually reaching the adult position of ____ by 2 years of age.
L1 (conus medularis is here)
The conus medularis, lumbar, sacral, and coccygeal nerve roots branch out distally to form the
Cauda Equina
Spinal needles are placed below ___ as the mobility of spinal nerves reduces the danger of needle trauma.
L2
Where is the Pia mater located?
against the spinal cord
What is the dura mater?
tough fibrous sheath running the length of the cord.
What is the arachnoid?
lies between the dura and the pia mater.
What is total volume of CSF (brain and ventricles)
Volume of CSF in the spinal canal
~140 ml
30-80 ml.
CSF is continuously formed at a rate of
500 ml/day
20.8 ml/hr
CSF is formed predominantly by the _____ _______ of the cerebral ventricles.
choroid plexuses
Normal CSF pressure?
10-20 cm H2O pressure.
Factors affecting spinal (subarachnoid block):
Drug Dose - the level of anesthetic varies directly with the _____ of local anesthetic used.
dose
Factors affecting spinal (subarachnoid block):
Drug Volume: – the greater the volume of injected drug, the _____ the spread within the CSF.
Farther
Factors affecting spinal (subarachnoid block):
Turbulence of CSF – turbulence ______ the spread of the drug and the level of blockade obtained.
increases
What are some ways to create turbulence?
Rapid injection Barbotage (aspirate, push....) Coughing Excessive pt. movement Increased intra-abd pressure Spinal curvature Baricity
Hyperbaric solutions are the most common local anesthetic solution for spinal anesthesia. How is this achieved?
by adding glucose (dextrose) 5-8% to the drug.
> 1.0015
How do Hyperbaric solutions settle down?
Due to gravity
Hypobaric solutions will flow to the highest part of the CSF volume. How is a hybobaric solution achieved?
By adding sterile water
<0.999
What would a hypobaric solution be for?
Perineal procedures in prone – jackknife.
What is the theoretical advantage of isobaric solution?
predictable spread through CSF independent of patient position.
It will remain where injected
True/False: Increasing the dose of an isobaric anesthetic will affect duration of anesthetic more than spread to higher dermatome.
True
Describe the Quincke needle and what its advantage is
has a cutting bevel tip
hold the bevel direction parallel to the longitudinal dural tissue fibers to minimize the rick of PDPH.
Describe the whitacre sprotte needle
pencil point tip, holes on side
Describe the rtie marx needle
Pencil point tip, more round holes on side
Describe the touhy needle
Epidural needle 17-18 guage, rounded at the top
What are the sizes of the spinal needles?
What size do we normally use?
22-29 gauge and in lengths of 3.5 - 5 inches
25-27 gauge 3.5 inch needle
Recent dada suggest using a _________________ - less PDPH, drag less contaminants into subdermal tissue, pierce the dura with a clearly perceptible “click” or POP not appreciated as easily with cutting tip
noncutting tip needles (pencil point )
Positioning: Lateral - how is patient laying?
Knees drawn up to chest and chin flexed downward to chest to obtain maximal flexion of spine.
When patient is laying in the lateral position for a spinal, what way will they be laying for a hypobaric solution? for a hyperbaric solution?
Affected side up if using hypobaric technique
affected side down if hyperbaric technique.
What is the line called between the top of the iliac crests, where is this anatomically?
tuffiers line, aligns with L4
Positioning: sitting - how is the patient positioned?
Head and shoulders are flexed downward onto the trunk with patients back close to the edge of the table
Who is the sitting position for spinal anesthetics good for?
obese patients
Sitting position is used in conjunction with hat type of spinal anesthetic?
hyperbaric
What position are patients place in while awake when prone? What anesthetic is this good for?
prone jackknife while awake
Used with hypobaric solutions
surgeries on rectum, perineum, anus
When advancing the needle through the midline approach, how if the needle positioned?
Needle is advanced through the skin in the same plane as the spinous processes with a slight cephalad angulation toward the intralaminar space.
When do you use the paramedian approach?
Useful in patients who cannot be maximally flexed or whose intraspinous ligaments are ossified.
When advancing the needle through the paramedian approach, how if the needle positioned?
Spinal needle is placed 1-1.5 cm lateral to midline of selected interspace.
Needle is aimed medially and slightly cephalad and passed lateral to the supraspinous ligament.
What spaces can spinal anesthesia be administered?
L2-L3, L3-L4, or L4-L5.
DONT go above L2
When preparing for a spinal, clean a large area with
antiseptic solution.
Avoid contamination of spinal kit with antiseptic solution – this is
potentially neurotoxic.
Infiltrate skin at intended spinal puncture site with
1% lidocaine solution. (25 gauge needle)
Insert the needle so that its bevel is ______ to the fibers that run longitudinal to reduce the incidence of post – dural puncture headache.
Parallel
Advance needle until increased resistance is felt as it passes the _____ _____. A sudden _____ or loss of resistance is felt as the needle is advanced beyond this ligament.
ligamentum flavum.
“Pop”
Remove the stylet from the needle. Correct placement is confirmed by ___________ into the hub of the needle.
Free flow of CSF
____________ occurring with placement of the needle requires immediate withdrawal of the needle and repositioning.
Paresthesia (shooting pain)
The hub of the needle may be rotated in __________ until good flow is established.
90-degree increments
After you connect the syringe with the LA to the needle, _______ confirms free flow of CSF. Drug is _______ injected. __________ of CSF at end of injection confirms the needle tip is still in the __________ space. The needle is gently removed and the patient is placed in the desired position.
aspiration
slowly
Re-aspiration
subarachnoid
The ascending anesthetic level is assessed using ______ or _______
pinprick or alcohol swab.
Blood pressure, heart rate and respirations are closely monitored how often until patient is deemed stable.
(at least once a minute)
Fixation of local anesthetic takes approximately
20 minutes.
Differential neural blockade:
_____ fibers conveying _______ impulses are more easily blocked than larger sensory and motor fibers.
Smaller C
autonomic
The level of autonomic blockade therefore extends two or three segments _____ the sensory blockade.
above
Fibers conveying ______ are more easily blocked than larger motor fibers.
Sensory blockade therefore extends two or three segments above motor blockade.
sensation
Neural Blockade
______ >_______>______
Autonomic > sensory> motor
Hypotension is proportion to the degree of _______ block achieved. Sympathetic block dilates both arteries and veins ______ the level of the block
proportional
below
Why will hypotension be more profound in the younger patient than older patients
elderly arteries are more atherosclerotic and won’t dilate as much
T/F: HR changes significantly with spinal
False
Heart rate does not change significantly in most patients. (baroreceptor in neck still okay)
Significant bradycardia does occur in 10-15% of patients.
When does the risk of bradycardia increase?
Risk of bradycardia increases with increasing sensory levels of anesthesia.
Block of cardio-accelerator fibers T1-T4.
To help prevent a CV response to a spinal, what should you do?
Fluid load with 500-1000cc IV prior to spinal blockade if history allows. (15 ml/kg)
Treatment for a CV response
Oxygen mask Vasopressors Atropine (0.4-0.8) Epinephrine CPR
What is the agent of choice for symptomatic brady and hypotension with a spinal
ephedrine is a mixed alpha and beta agonist
Cardiovascular effects ______________
and steps taken to minimize the degree of
hypotension and bradycardia.
should be anticipated
Are pulmonary changes with spinals common?
usually minimal.
C3,4,5 are still okay
This will take away the sensation of breathing
What patients respiratory status may be affected with a spinal
Pts. with chronic lung disease who rely upon accessory muscles of respiration to actively inspire or exhale may be affected. These muscles will be impaired below the level of the block.
won’t be able to cough
The clinically important factors that can be controlled by the anesthetist are:
- Total dose of anesthetic
- Site of injection
- Baricity of the drug (drug choice)
- Position or posture of the patient after injection
What are some complications of spinal anesthetic? (7)
Failure of block Postdural puncture headache High spinal Nausea Urinary retention Hypoventilation Backache
When you give an epidural, you stop just prior to the _____.
dura
this is a potential space
Epidural space
In the lumbar region the epidural space is
_____ wide at midline.
In the mid-thoracic region the epidural space is _____ wide.
5-6mm
3-5mm
Local anesthetic placed in the epidural space acts directly on the _________ _________ _________ located in the lateral space.
spinal nerve roots
True/False: Onset of block for epidural is slower and intensity is less.
True
Need to give more drug than with spinal (has to soak through all layers)
Anesthesia develops in a segmental manner and ______ blockade can be achieved.
selective (between 2 areas)
spinals block from level of injection down to toes
Epidural anesthesia can be titrated to deliver _____ or ______
analgesia or anesthesia
Epidural anesthesia : Horizontally, medication spreads to the ____ ____, where it diffuses into the CSF and achieves analgesia/anesthesia
dural cuffs
Epidural anesthesia: Longitudinally, medication spreads in a ______ direction, with possible site of action along the paravertebral nerve trunks, intradural spinal roots, dorsal and ventral spinal roots, the dorsal root ganglia, the spinal cord, and the brain.
Cephalad
Epidural anesthesia is ______ dependent
diffusion
Relatively large volumes of local anesthesia must be used to achieve anesthesia. How much is used for an epidural?
How much is used for a spinal?
20 ml
2-3 min
Epidural Anesthesia takes significantly longer to achieve because medications get to the subarachnoid space by the process of
diffusion
The needle should always enter the epidural space in the _____ irregardless of approach used for access, as the space is widest here and the risk of puncturing epidural veins, spinal arteries, or spinal nerve roots is decreased.
midline
Technique for lumbar epidural:
Use a long, 25 gauge needle to infiltrate local into the ______ and _____ ligaments.
Advance epidural needle through the supraspinous and interspinous ligaments in a slightly cephalad direction until it comes to lie within the “rubbery” ______ _______
Use either the loss of resistance technique or the hanging drop technique to locate the _____ _____
supraspinous and Interspinous
ligamentum flavum
Epidural space
Technique for thoracic epidural:
Used to provide anesthesia for upper _____ and _____ regions.
Requires _____ dose of local anesthetic.
Placement considerations are similar to those for lumbar epidural.
Insert epidural needle in a more cephalad direction due to sharp ______ angulation of the thoracic vertebral spinous processes.
abdominal and thoracic
smaller
downward
Epidural test dose:
A test dose of local anesthetic is given to verify correct needle location.
The test dose consists of ___ of local with ______
This will have little effect if placed in the epidural space.
If placed in the CSF, will rapidly behave like a spinal. What symptoms?
If injected into an epidural vein, a ______ increase in HR will be seen.
3 ml local, 1:200,000 epi.
numb, heavy legs
20-30%
Does positioning have an effect on epidural blockade?
NO, it is not placed in the CSF
For an epidural block, all solutions should be injected in increments of ____ ml, every 3 minutes and titrated to the desired anesthetic level. With loading doses and intermittent injections, _______ of the catheter should occur before any injection.
3-5
aspiration
Addition of epi 1;200,000 to 1:400,000 solution ______ systemic uptake, resulting in lower plasma levels of the local anesthetic and _______ of its duration of action.
slows
prolongation
Sympathetic nervous system blockade with epidural spinal.
Onset of sympathetic block is slower with decreased incidence of abrupt ____
hypotension
As with spinal anesthesia sympathetic block can result in a reduction in preload, a decrease in cardiac output and a decrease in BP.
Side effects of epidural spinal
Backache
Post dural puncture headache PDPH
Trauma with catheter removal
PDPH is 1-2% , inadvertent tear of dura by 17g touhy needle makes a large dural perforation and is referred to as a “wet tap” , when a wet tap happens the rate of PDPH increases to 75%
