Spinal Anesthesia Flashcards
What is the most important thing to have before administering your spinal?
patent IV
What are two other important things to have (besides patent IV) before you administer your spinal?
suctionability to provide positive pressure ventilation
What is the order of anatomical structures traversed by a spinal needle?
- skin2. subcutaneous fat and tissue3. supraspinous ligament4. interspinous ligament5. ligamentum flavum6. epidural space7. dura8. subarachnoid space
What is the bottom of the spinal cord called?
conus medularis
What is the name of the ligament that goes from conus medularis to sacrum?
filum terminale
What is the dura mater?
outermost, tough fibrous tube that runs longitudinally from foramen magnum to S2-3
What is CSF supposed to look like?
clear and colorless
What is the function of CSF?
mechanical buffer to protect brain and spinal cord
How much CSF does the body produce per hour?
21 mL/hour or 500 mL/day
How much CSF is in an adult?
150 mL
How much CSF is in the subarachnoid space?
20-35 mL
What is the specific gravity of CSF?
1.003-1.009
What is the order of nerve fiber onset with a spinal?
BC and AdeltaAgammaAbetaAalpha
What are the most common interspaces for dural puncture?
L2-3 or L3-4
What are the two needle approaches?
midline and paramedian
What landmark helps you identify L4?
intercrestal line that runs between the iliac crests
What does hyperbaric mean?
LA solution is heavier than CSF, add glucose to LA
What does isobaric mean?
LA solution is same as CSF, mix LA with CSF
What does hypobaric mean?
LA solution is lighter than CSF, mix LA with sterile water
Where is spinal anesthesia thought to take place?
anterior and posterior nerve roots as they pass through the CSF on their way to the periphery
What is spinal anesthesia?
REVERSIBLE chemical blockade of neuronal transmission produced by the injection of a local anesthetic drug into the CSF contained within the subarachnoid space
What are some advantages of spinal anesthesia?
- ideal technique for procedures involving the lower abd, pelvis/perineum and lower extremities- anesthetized patient can remain fully conscious or may be sedated- appropriate choice of agents can provide exceptional postoperative analgesia- when used with “light general” can be used for upper abd and thoracic cases- surgical stress reduced by afferent block and can speed patient’s recovery- reduces risk of venous thrombosis and overall blood loss by reducing arterial and venous pressure- small dose of local anesthetic required minimizes chance of systemic uptake
Can spinal anesthesia be used for a patient with a full stomach?
yes, but have plan B in case spinal fails
What postoperative complications does spinal anesthesia decrease the incidence of?
nausea/vomitingsedationcognitive impairmentwound pain
What is the #1 disadvantage of spinals?
sympathetic blockade that occurs virtually 100% of the time because it is relatively easy to block small autonomic fibers
What are some disadvantages of spinal anesthesia?
- Intense motor blockade that can last longer than the procedure- post-dural puncture headache- urinary retention- “takes too long”
Spinal anesthesia is strongly advocated for with what pathophysiology?
pulmonary disease, although if pulmonary disease is really bad general may allow better gas exchange
What is a common fear of patients undergoing spinal anesthesia?
being “awake,” minimize their fear with your preoperative interview and reassure that pre and intra operative medications will be provided
What type of surgeries/indications would be ideal with spinal anesthesia?
- major intra/abd procedures can be accomplished with high level T4 block-well managed SAB may be safer for the patient with a full stomach- urological procedures (TURP)- obstetrical procedures- minimal effect on metabolism (safer for liver disease, kidney disease, diabetes)- reduced systemic blood pressure may reduce risk of venous thrombosis and overall blood loss
What are absolute contraindications to spinals?
- patient refusal- infection at injection site- coagulopathy or other bleeding diathesis- severe hypovolemia- severe aortic or mitral valve stenosis- increased ICP
What are relative contraindications to spinals?
- uncooperative patient, psychiatric disease- septicemia/bacteremia- preexisting neurological deficit- chronic backache or headache- stenotic valvular lesions- severe spinal deformity
What are controversial issues with deciding whether or not to use spinal anesthesia?
- prior back surgery- inability to communicate with the patient- complicated surgical procedures (long duration, major blood loss, respiratory compromise)
If a patient had an allergy to local anesthetics would you still do a spinal?
Yes, but use an amide local anesthetic
What would be some considerations with a spinal in a patient with untreated hypertension?
Could be volume depleted and have severe hypotension after spinal
What is important to remember about getting informed consent for a spinal?
- they should understand the advantages and disadvantages of the procedure- SAB should be adequate for the procedure but you cannot guarantee it- indicate risks and potential complications- indicate the patient appears to understand and accept- give the patient time to ask questions- do not attempt to dissuade a patient who has been counseled and agreed to a general anesthetic- **Documentation does not exonerate you from acts of carelessness or negligence
What premeds/fluids can you give before giving a spinal?
versed for anxiety and amnesia, but do not oversedate the patientcan also adminiser 500-1500 mL of a balanced salt solution to help protect against hypotension
What supportive meds should you have ready when doing a spinal?
- benzo or propofol- succ- atropine- ephedrine or phenyl
What monitors should be on the patient when doing a spinal?
EKGblood pressurepulse ox
How is the body of the thoracic vertebrae shaped?
heart shaped
How is the body of the lumbar vertebrae shaped?
kidney-shaped
What is the name of the space between the vertebrae you are trying to identify for needle placement?
laminar foramen
After you insert your needle and it feels “sandy” or “grainy,” what anatomical structure is your needle hitting?
lamina
Which vertebrae has spinous processes that are long and angulated downward?
thoracic vertebrae
Which vertebrae has spinous processes that are blunt and horizontal?
lumbar vertebrae
What is the most important thing that allows you to have a successful spinal?
proper position
What is the arachnoid mater?
middle layer, delicate, nonvascular and ends at S2
What is the pia mater?
- delicate, highly vascular, and covers spinal cord- subarachnoid space lies between the pia and arachnoid mater (CSF found here)- holds blood supply that feeds spinal cord- do NOT want to puncture
Which nerve fiber is responsible for motor and proprioception?
A alpha
Describe the size and myelination for A alpha fibers.
heavy myelinationbig diameter (6-22 micrometers)
Which nerve fibers are responsible for motor, proprioception, touch and pressure?
A beta
Describe the size and myelination for A beta fibers?
moderate myelinationbig diameter (6-22 micrometers)
Which nerve fibers are responsible for muscle tone?
A gamma
Describe the myelination and size of A gamma fibers?
moderate myelination and medium sized at 4-6 micrometers
Which nerve fibers are responsible for pain, touch, and cold?
A delta
Describe the myelination and size of A delta fibers?
light myelination and smaller at 1-4 micrometers
Which nerve fibers are responsible for preganglionic sympathetic stimulation?
B fibers
Describe the size and myelination of B fibers.
light myelination and small at 0.5-2 micrometers
Which nerve fibers are responsible for pain, touch, warm, and cold?
C fibers
Describe the size and myelination of C fibers.
no myelinationvery small at 0.5-1.3 micrometers
What positions can be used for a spinal?
lateral decubitussittingprone
At what levels can a dural puncture be done?
any level between L2 and S1
Before prepping and draping, what 4 things should you make sure you had before beginning?
- patient IV- blood pressure cuff is on patient- resuscitation drugs and necessary equipment are available and in working order- inform the patient about what to expect throughout the procedure
If someone is assisting you with the patient in the lateral decubitus position, where should you tell them to place their hands?
have them hold the back of the patients neck and the back of their legs to optimize their fetal position and keep the spine in proper alignment
What can you NEVER injection into the CSF?
anything with preservatives
What % tetracaine do you use for spinals?
0.5%
What percent lidocaine do you use in spinals?
2% plain or 5% in 7.5% dextrose
What percent bupivacaine do you use in spinals?
0.5%
Tetracaine 0.5% in water would be have what kind of baricity?
hypobaric
Tetracaine 0.5% in D5W would have what kind of baricity?
hyperbaric
What type of solutions migrate to the most dependent areas of the spine?
hyperbaric
What are four of the most important things that can influence your spinal level?
- baricity- position of patient (during injection, immediately after injection)- drug dosage- site of injection
What are other factors that can influence your spinal level?
- age- CSF volume (inverse correlation)- curvature of spine (abnormal curves)- drug volume- intra-abdominal pressure- needle direction- patient height- pregnancy
What type of technique should you use to put in a spinal?
aseptic
What is important to do when injecting local anesthetic to be used for the skin wheal?
make sure you are not injecting the wrong solution; double check which solution is for the skin and which is for the CSF
What type of syringe and needle should you use to make an intradermal wheal of local anesthetic?
3 mL syringe and 25 or 27 gauge needle
Where should you insert the spinal needle if using a 25 gauge or smaller needle?
place an “introducer” needle through the skin wheal in the midline of the lower third of the interspace
What causes you to feel the 2 “pops” as you advance your needle?
penetration of the ligamentum flavum (epidural space) and the dura/arachnoid membranes (subarachnoid space)
Once you feel your 2nd pop and you know you are in the subarachnoid space, what should you do?
remove the stylet and observe the inside of the needle hub for return of clear CSF
Once you know you passed through the dura and are in the subarachnoid space because you see clear CSF, you attach the syringe with the local anesthetic to the hub and then what should you do?
turn the syringe gently (90 degrees) and secure it to the needle, aspirate small volume of CSF to confirm that your needle tip is still in the subarachnoid space
When aspirating CSF into a syringe that is already filled with clear local anesthetic, how do you know that you are aspirating CSF?
it will have a distinct swirl because CSF has a less dense specific gravity
If you want a bilateral block, what should you do after removing the needle and introducer?
return the patient to the supine position immediately and elevate the patient’s head
If you want a unilateral block, what should you do after removing the needle and introducer?
leave the patient in the lateral position for at least 3 minutes then return them to a supine position and elevate the patient’s head
What are the 3 needle types?
QuinckeWhitacreSprotte
If your needle is touching the superior crest of the spinous process below the interspace, where should you direct the needle?
more cephalad
If your needle is touching the inferior surface of the spinous process above the interspace, where should you redirect your needle?
more caudad
If your needle is repeatedly striking bone, what should you do?
needle is striking the lamina and is not midline, remove the needle and reassess landmarks and positioning
What happens if you obtain CSF after placing the needle but your patient has paresthesias?
- stop advancing the neelde- leave the needle and stylet in place- if the paresthesia resolves then continue with the injection- if the paresthesia does not resolve then remove and reposition the needle
What happens if you patient has paresthesias and you have not confirmed placement with CSF?
likely extradural, remove and reposition the needle
What if you are unable to obtain CSF?
reinsert the stylet and slowly advance the needle an additional 1 to 2 mm, attempt to aspirate CSF, repeat these steps until CSF is identified
What is a good common practice to do after puncture of the dura?
insert the needle an additional 1 mm to ensure the needle bevel is entirely subarachnoid
What happens if you have no CSF, no paresthesia, and have not hit bone?
may have traversed both the dorsal and anterior surfaces of the dura, remove the stylet and attach a small syringe, gently aspirate the syringe as you slowly withdraw the spinal needle, may get CSF as the needle tip is withdrawn into the subarachnoid space
If you punctured both sides of the dura, what does the patient have an increased risk of?
PDPH
What happens if you have frank blood in the CSF that does not clear?
needle tip is likely in an epidural vein so you would need to withdraw and reposition
What happens if you have blood-tinged CSF?
allow CSF to flow for several seconds or aspirate until it clears, inject local anesthetic
What two types of nerve fibers are we trying to block with a spinal?
Adelta and C fibers
Is the drug concentration for spinals greater or less than the minimum concentration to block all nerve fiber types?
greater than minimum concentration
Is the block of autonomic fibers (B) rapid or slow?
rapid
What can occur with a block of autonomic (B) fibers?
- hypotension - severity depends on the level of the block- T4 level blocks cardio-accelerator fibers and produces bradycardia- precipitous drop in BP may be first sign block is “setting up”- N/V with low BP
What nerve fibers are affected next after B autonomic fibers?
A delta and C fibers (pain and temperature), loss of ability to discriminate temperature and light touch, level of temperature discrimination loss correlates well with level of sensory (pain) loss
What nerve fibers are blocked next after A delta and C fibers?
A alpha, A beta, and A gamma (motor, proprioception, touch, and pressure) which causes surgical muscle relaxation and patient may continue to feel “pressure”
How often do you have to check the progress of the block?
every 2-3 minutes
What can you use to check the progress of the block and determine the dermatome level?
alcohol sponge or pinprick
What should you monitor frequently after administering a spinal?
- assess progress of the block- check blood pressure- assess cognitive function
Are the degree of physiologic changes and extent of the CNS exposed to local anesthetic directly or indirectly related?
directly related
What is one way to control to some degree the distribution or spread of the local anesthetic?
Adjusting the horizontal level of the OR table
The upper limit of the autonomic block is generally ___ dermatomes higher than the level of the sensory block.
2
The upper limit of the motor block is generally ___ dermatomes below the level of the sensory block.
2
What is a saddle block?
S2 to S5, little effect on the autonomic nervous system, used for surgery on the perineum, perianal area and external genitalia
What is a low spinal?
T10, blocks sacral nerves and the lower lumbar roots, used for cystoscopies, TURP, lower extremity vascular and orthopedic procedures not requiring a tourniquet, urethra, vagina, cervix, and vaginal delivery
What is the most common level for a spinal?
T4, permits abdominal and lower extremity procedures (testicular procedures, inguinal herniorraphy, ureter and renal pelvic procedures, appendectomy, ovarian cystectomy, C-section, vaginal hysterectomy and lower extremity orthopedic procedures requiring a tourniquet)
What is a high spinal?
C8, jargon for a block higher than T2
What position would be optimal for an obese patient?
sitting position - provides better flexion of the vertebral column and adipose tissue is less likely to distort anatomical landmarks
When would you want to use a paramedian (lateral) approach?
useful when the patient cannot flex the lumbar spine (prior lumbar spine surgery, rheumatoid arthritis, hip or upper leg trauma)
What is the technique for a paramedian (lateral) approach?
- skin wheal 1 cm lateral and 1 cm caudad to the spinous process above the selected interspace- advance the spinal needle medially and cephalad toward the midline (needle passes through the paraspinal muscles to the ligamentum flavum to the dura; avoids supraspinous and interspinous ligaments)
What is the lumbosacral “taylor” approach?
- modification of the paramedian approach- uses the largest opening tot he spinal canal L5-S1- identify the posterior superior iliac spine- make a skin wheal 1 cm medial and 1 cm caudad to the spine- insert the needle 45-55 degrees medial, cephalad and parallel to the dorsal surface of sacrum toward the midline of the lumbosacral foramen
What is a continuous spinal?
ability to provide prolonged anesthesia and postoperative analgesia
Who are continuous spinals usually used for and why?
elderly patients due to PDPH risk
What needles do you use for a continuous spinal?
- puncture the dura with a 17 gauge epidural needle and passage of a 19 to 20 gauge catheter through the needle into the subarachnoid space
How do you administer local anesthetic for a continuous spinal?
small incremental doses of local anesthetic are given until the desired level is reached; incremental doses slow onset of hypotension and total dose to achieve a specific level same as for single injection
Why would you add vasoconstrictors to your local anesthetic?
constricts blood vessels of the spinal cord and dura slowing absorption into the blood which will prolong the duration, and possibly the intensity of the LA
What concentration and volume of epi would you add to your local anesthetic?
0.1-0.2 mL at 1:1000 solution
Which LA does epi have the greatest effect with?
tetracaine
How much phenyl do you add to LA?
0.05-0.2 mL of 1% solution (0.5-2 mg)
Which LA does phenyl have the greatest effect with?
tetracaine
What happens when clonidine is injected with LA?
has synergistic effect with LA
When would it be useful to add clonidine to your LA?
when epi is contraindicated
What are the common intrathecal opioids?
fentanylmorphinesufentanilmeperidine
Why would you use opioids with LA?
provides better analgesia than with either drug alone
What is the dose of fentanyl when mixing it with LA?
12.5-25 mcg mixed with LA
What is the onset of intrathecal fentanyl?
5-10 minutes
What is the duration of intrathecal fentanyl?
2-4 hours
Is intrathecal fentanyl lipid soluble?
yes, binds to elements of the spinal cord and therefore has less drug available to diffuse to the respiratory centers
Is morphine lipid soluble?
no, not bound to lipid elements in spinal cord and drifts freely in CSF
Can morphine cause respiratory depression and if so, when?
yes, in approx 6-8 hours can drift as high as the respiratory center
What is the dose of intrathecal morphine?
0.25-0.5 mg mixed with LA
What is the onset of intrathecal morphine?
60-90 minutes
What is the duration of intrathecal morphine?
18-27 hours
What are some complications of intrathecal morphine?
itching, urinary retention and delayed respiratory depression
What are some complications of spinal anesthesia?
MANY complications…- hypotension- intercostal muscle paralysis- apnea/phrenic nerve paralysis- paresthesias- subarachnoid or epidural hematoma- meningitis/epidural abscess- aseptic (chemical) meningitis- cauda equina syndrome- new nervous system lesion- exacerbation of preexisting neurologic disease- N/V- urinary retention- post dural puncture headache
What concentration of bupivacaine is commonly used?
0.75% in dextrose
What dose of bupivacaine 0.75% would you use for surgery on the perineum or lower limbs?
4-10 mg
What dose of 0.75% would you use for surgeries on the lower abdomen?
12-14 mg
What dose of 0.75% bupivacaine would you use for surgeries on the upper abdomen?
12-18 mg
How long will bupivacaine last without epi?
90-120 minutes
How long will bupivacaine last with epi?
100-150 minutes
What things should you include in the anesthesia record after administering a spinal?
- monitors applied- NC oxygen- position- betadine prep and sterile drape- L3-4 identified- skin wheal with 2 mL of 1% lidocaine- 18 G introducer placed midline at L3-4 interspace- 24 G sprotte needle x # of passes, (+) CSF, (-) parathesia (-) blood- cc’s of local anesthetic injected after (+) swirl- patient placed supine (or kept in sitting if doing saddle block)- final level
