Epidurals and Spinals (Applegate) Flashcards
What are the absolute indications for a spinal/epidural needle anesthesia?
There are none.
How many segments are in each vertebral section?
Cervical - 7 Thoracic - 12 Lumbar - 5 Sacral -5 Coccyx - 4
What are the benefits of spinal/epidural anesthesia?
-Blunts stress response to surgery -Decreases intraoperative blood loss -Lower incidence of post-op thromboembolic events -Decrease morbidity and mortality in high risk surgical patients -Extend analgesia into the post op period (better than with long term opoioids)
You can palpate these structures along a patient’s back. If they are rotated, it may indicate scoliosis or abnormal spinal physiology. You may need to adjust the angle of your approach accordingly, usually by 5-10 degrees. What structures are these?
Transverse processes (2, 1 on each side). Spinous process can also help you (middle)
What is a common method of clinically determining the end of cervical vertebrae and the beginning of thoracic vertebrae?
A good way of determining the border between C7-T1 is to look for spinal movement. –> C7 will move but T1 will not.
What is the most prominent cervical vertebrae?
C7
What is the landmark for T12?
Find the posterior portion of the last rib and palpate towards midline.
What is the landmark for the level of L4-L5?
Find the top of the iliac wings and palpate towards midline.
What is below the arachnoid?
subarachnoid space (also cauda equina from L2-L5)
What are the ligaments in the spine from order of most superficial to the deepest?
What is the most ubiquitous material in the epidural space?
Epidural fat - resides mostly in the posterior epidural space.
What can give you a false loss of resistance in the epidural space? What are the clinical implications of this in relation to drug administration?
You can potentially experience a false loss of resistance due to epidural fat in the posterior epidural space.
This epidural fat acts as a sink, changing the metabolism of your drugs (esp the fat soluble meds like fentanyl, which are going to persist much longer in the epidural space than lipid insoluble meds like morphine)
What lasts longer in the epidural space? Fentanyl or morphine? Why?
Fentanyl, due to its higher lipid solubility
What are the meningeal layers? List them in order of most superficial to deepest.
Dura, Arachnoid, Pia
What is the plica medianis dorsalis?
A midline connective tissue connecting the dura mater to ligamentum flavum
Describe the arachnoid mater and its function in anesthesia.
It is a delicate avascular membrane composed of cells and tight junctions.
It acts as an anatomical barrier for drugs moving between the epidural and spinal space.
What meningeal layer are you in if you see CSF from your needle?
The subarachnoid space.
Hence a spinal block can also be called a subarachnoid block.
What are arachnoid granulations?
Sites for material in the subarachnoid space to exit the CNS.
What is CSF produced by?
Choroid plexus cells found in the 3rd and 4th ventricles
How much CSF is produced an hour?
20-25 mL/hr
Describe the movement of CSF in relation to systole and diastole. How is it removed?
Systole displaces CSF caudally into the spinal cord
Diastole displaces CSF rostrally into the cranium
CSF is removed by arachnoid villi
What are the two classes of needles used in spinal/epidural placement?
Sharp (cutting)
Blunt (pencil-point)
What is an example of a sharp/cutting needle in spinals/epidurals placement? What are its disadvantages?
A Quincke needle
These needles cause tissue tearing so are not used as often.
What are two examples of blunt (pencil-point) needles in spinals/epidurals?
What are they characterized by?
Whitacre and Sprotte
Local Anesthetics come out of the side of the needle as opposed to the front of the needle like in sharp/cutting type needles.
Note:whitacre has a smaller opening for injection.
Why must we be careful with antiseptics in regional blocks?
All antiseptics are neurotoxic
What is parethesia?
If a patient experiences parethesia, what should you do? Why?
Parasthesia is an abnormal sensation of hands or feet (esp one of burning)
Consider starting over again if patient experiences parethesia. The catheter may be rubbing against a nerve rootlet (avoid nerve damage). You may also risk having a one-sided epidural.
What should you remember when managing a continuous spinal according to Dr. Applegate?
Do not leave the room. Next provider may mistake the spinal for an epidural and give a massive dose.
What length should you thread the catheter once you are in the epidural space? Why?
Avoid threading beyond 5 cm into the epidural space.
>5 cm of threading risks knot formation or unintentional penetration into subarachnoid space.
What should you remember when doing a combined spinal epidural block? (CSE)
Hint: think interaction between epidural and spinal block level
Meds in the epidural space will raise your spinal block level.
When is a paramedian/lateral approach usually considered?
When calcification of spinal processes due to arthiritis (or other conditions) blocks your midline approach.
In a paramedian approach, how should you adjust your needle?
Go 1 cm lateral of midline and angle your needle ~15 degrees medial.
What are the pharmacological considerations with spinals? Epidurals?
Spinals: block height, onset, duration
Epidurals: block spread, onset, duration
What is a barbotage and what do we use it for?
Repeated injection and spiration of a fluid.
Used in spinals to confirm subarachnoid placement (CSF swirl is good)
What characeristics of LA determines the block height of a spinal?
Dose, concentration, volume, and baricity
What is our usual spinal dose for a 70 kg pt for lidocaine and bupivicaine?
40 mg lidocaine, 15 mg bupivicaine
What aspects of our technique can influence block height?
Our chosen site of injection, speed of injection, direction of needle bevel (where our LA will be injected), and addition of vasoconstrictor
What is baricity in spinal anesthesia?
The ratio of the densities of LA:CSF.
Therefore, if a local anesthetic is isobaric, it has the same density as CSF.
Hypobaric meds rise in the CSF.
If you are injecting an isobaric LA in a spinal, what will effect the height?
Dose. Volume and concentration will not effect block height if dose is held constant.
With injection of hyper or hypobaric LA into a spinal, what important factors will influence the ultimate block height?
Baricity and gravity (Gravity until it becomes isobaric as it spreads through the CSF and equilibrates)
With hyperbaric LA, what is the most important factor in ultimate block height?
CSF volume: if it is small, it will not take a lot of hyperbaric LAs to push level of block towards the head (not good considering that you’re using hyperbaric LAs to keep the height low)
Make sure your pts are not terribly hypovolemic!
What pharmacological trait is the most important in determining osnet time of spinals?
pKa of LAs
What is the onset of spinals usually? How long does it take to reach peak block height?
A few minutes.
Depends on the LA (lidocaine and mepivacaine takes 10-15 min, while tetracaine and bupivicaine takes >20 min)
What are the main factors influencing the duration of a spinal?
- Choice of LA used
- Dose given
- Height of block (isobaric LA produces longer blocks than hyperbaric)
- Addition of adrenergic agonists
In spinals, how long do commonly used LAs usually last? (Procaine, Lidocaine, Bupivicaine)
Procaine: 90-120 min
Lidocaine, Mepivacaine: 140-240 min
Bupi, Tetracaine: 240-380’
What is the most important determinant of spread in epidural blocks?
What are some other important determinants?
Injection site.
Other important considerations: drug dose, volume given
Pt considerations: age (greater spread in older adults), pregnancy (greater spread at term and early stages), extreme height variations ( titrate slowly)
What is the usual onset of epidurals? Time to peak effects?
How can you speed up onset?
5 minutes (onset begins at local dermatome level)
Time to peak effects depends on LA but lidocaine = 15-20 minutes, bupi = 20-25 minutes
You can speed onset by increasing dose of LA (will also effect potential motor block)
Most important determinant of duration in epidural blocks is..?
What are some other considerations?
Type of LA used. 2% lid = 160-200 min, 0.5% bupi = 300-460 min
Other considerations: drug dose, use of adrenergic agonists (decreases drug clearance)
What are the pros and cons of using adrenergic agonists in epidurals and spinals?
Pros: can be used as a stress test to see if you are in IV
Increases duration of block by decreasing drug clearance
Can decrease spread of block
Cons: Can cause spinal ischemia via vasoconstriction
What is the differential nerve blockade phenomenon?
Nerve fibers serving different functions display varying sensitivity to the same LA blockade
This is due to differences in nerve fiber diameter (for example, touch and proprioceptive receptors persist despite ablation of pain receptor signals)
What would you expect the CV effects of a spinal block to be?
Sympathetic block: HoTN (vaso/venodilation) that leads to decreased preload, CO, VR, and SVR
Bradycardia (cardioaccelerator fibers @ T1-T4) that leads to deceased VR
What would you expect the CV effects of an epidural to be, with and without epinephrine?
No Epi: decreased SV, CO, SVR, MAP
With Epi: Increased SV, CO, more pronounced decrease in SVR, MAP due to beta 2 agonism
What are the respiratory effects of spinals/epidurals?
Increased ventilatory response to hypercapnia
Possible abdominal and intercostal muscle paralysis can impair ventilatory functions (however, usually pt just loses sensation of ability to breathe despite breathing fine due to knockout of sensation from their intercostal muscles)
If you notice dyspnea despite normal or elevated minute ventilation, suspect muscle paralysis!
Easy test: normal speaking voice? ventilation is probably normal
What are the GI effects of spinals and epidurals?
Increased secretions, sphincter relaxation, and bowel constriction (leads to pooping)
Nausea (esp in blocks above T5, if pt is HoTN or has h/o motion sickness, or had opioids pre med)
Symptoms due to unopposed parasymp activity (vagus nerve)
Effects of spinals/epidurals on stress response?
Decreases the stress response/cortisol release
What are possible complications of spinals/epidurals?
Backaches
PDPH (postdural puncture headache)
Hearing loss (transient, 1-3 days)
LAST (local anesthesia systemic toxicity), total spinal, Neurologic injury
Why does PDPH occur? How can we diagnose it?
It is due to loss of CSF from the injection site.
PDPH is a positional headache, so patient will feel better laying down.
What are the treatments for PDPH?
Bed rest and analgesics
Caffeine
Epidural blood patch* (sterile blood injected into epidural space, very effective)
What are symptoms that can indicate a total spinal? How can you treat it?
Symptoms: profount HoTN and brady, respiratory arrest
Rx: Vasopressors, atropine, fluids, MV
What are signs of TNS (Transient Neurologic Syndrome)?
What are the risk factors?
What is it usually due to?
What is it usually treated with?
Intense back pain is the most common manifestation
Risk factors: outpatient status, lithotomy, phenylephrine added to tetracaine
Usually due to lidocaine administration
*Pain usually resolves within 72 hrs spontaneously. Can also be treated with NSAIDs (common).
What is the most neurotoxic local anesthetic that we use in spinals/epidurals?
Lidocaine
What are signs of an epidural hematoma? Treatment?
Numbness and LE weakness
Needs surgical intervention within 8 hours or pt will lose motor function
What are the contraindications to spinal/epidural blocks?
Pt refusal (Absolute)
HoTN or shock
High ICP
Extreme coagulopathy
Sepsis
Infection at puncture site
Neurologic disease
Aortic stenosis
If a pt is on heparin, is it okay to place a spinal/epidural? How about LMWH?
If it is subQ or LMWH, then generally yes.
With LMWH, wait 10-12 hrs if given prophylactically, or 24 hours if given therapeutically before placing the block.
Remove the catheter 10-12 hrs after placement (prevention of bleeding out) and restart on therapy 2 hrs after removal of catheter
