Spinal Anesthesia (pt 1)

Question 1

What is Spinal Anesthesia?

Answer 1

Reversible chemical blockade of neuronal transmission by a local anesthetic injected into the Cerebral Spinal Fluid (CSF).

Question 2

Where do the actions of spinal anesthesia occur?

Answer 2

On anterior and posterior nerve roots as they pass through the CSF to peripheral nerves
-To a lesser extent, on the spinal cord itself
-Temporary interruption of sensory, autonomic, and motor nerve fibers renders the patient insensitive to surgical stimulation.

Question 3

Immediately after spinal nerves exit via the intervertebral foramen, they divide into _____ ?

Answer 3

Ventral and Dorsal Primary Rami.
-DPR: supply skin and muscles of the back
-VPR: supply anterior lateral muscles, skin of neck and trunk and limbs.
Both also contribute a small nerve to sympathetic ganglia.
Joint together eventually to form plexi in a specific region

Question 4

What are Dermatomes?

Answer 4

Areas of the skin that are innervated by a specific nerve root.
-Help to determine where a block is working
-Help to understand where injury/pain is coming from

Question 5

What nerve forms the dermatomes of the face?

Answer 5

Ophthalmic, Maxillary, and Mandibular divisions of the Trigeminal Nerve

Question 6

What dermatome level is C4?

Answer 6

Clavicle

Question 7

What dermatome level is C8?

Answer 7

Little finger

Question 8

What dermatome level is T4?

Answer 8

Nipple

Question 9

What dermatome level is T6 - T8?

Answer 9

Xiphoid, lower rib cage

Question 10

What dermatome level is T10?

Answer 10

Umbilicus

Question 11

Above ___ is a high spinal, which causes what symptoms?

Answer 11

T2
-Severe hypotension, dyspnea, respiratory arrest

Question 12

What dermatome level is T12?

Answer 12

Last rib

Question 13

Explain how/why Differential Nerve Blockade works?

Answer 13

The anatomy of the nerve root accounts for differential sensitivity of nerve types to local anesthetic.
-Small diameter nerve fibers are found close to the nerve root surface (Shorter diffusion path of LA)
-Large diameter nerve fibers are found deep to the nerve bundle (longer diffusion path of LA)

Question 14

Which fibers are more sensitive to local anesthetic blockade?

Answer 14

Large myelinated fibers are more sensitive to local anesthetic blockade than smaller myelinated and unmyelinated fibers.

Question 15

What order are fibers blocked in (A, B, C, etc)?

Answer 15

1) B Fibers
2) C Fibers
3) A Delta Fibers
4) Larger A Gamma (muscle spindles), A Beta (Touch, pressure)
5) A Alpha (Proprioception, motor) fibers are last.

Question 16

What fibers are found at the outside of the root?

Answer 16

B Fibers
-Preganglionic sympathetic efferents
-Autonomics. This is why the first thing you’ll see with a block is a drop in BP.

Question 17

What fibers are found immediately inferior to B Fibers?

Answer 17

C and A-Delta fibers
-C: Pain
-A Delta: Pain, temperature
-Pain, temperature, and touch afferents
-Post ganglionic sympathetics

Question 18

What is the order of sensitivity with large myelinated to unmyelinated?

Answer 18

Large Myelinated > Smaller myelinated > unmyelinated
-Once it gets to them, the large myelinated fibers are very sensitive

Question 19

What are other factors that contribute to a differential nerve block?

Answer 19

-Myelination
-Nodes of Ranvier
-Size of fibers
-Location depth
-Na and K Channels on each nerve

Question 20

Sympathetic blockade (BP changes is 1st sign) is usually ___ segments higher than ____ blockade (temp, light touch, pain), which is usually ____ or greater segments before ____ blockade.

Answer 20

Sympathetic blockade (BP changes is 1st sign) is usually 2 segments higher than Sensory blockade (temp, light touch, pain), which is usually 2 or greater segments before Motor blockade.

-Sometimes, sympathetics can go up to 6 segments higher (bad).
-Could end up having a bigger block than what you thought.

Question 21

How do you assess your patient for sensory block?

Answer 21

-Loss of temperature sensation from cool alcohol swab is most sensitive indicator of initial onset of sensory block
-Sharp/broken tongue depressor is most accurate for overall sensory block
-Decrease in BP may be first sign it’s working (B fibers)
-Loss of sensation to cold (alcohol swab) occurs before sharp and at a higher level (C, A-Delta)
-Initial motor block is myelinated A Beta & A Gamma fibers
-Profound block is A Alpha

Question 22

What are the 2 most important factors that impact the Spinal (Intrathecal) Level?

Answer 22

-Baricity
-Patient position

Question 23

How do you determine baricity?

Answer 23

In relation to the specific gravity of CSF (1.004-1.008).
-Hypobaric: Less baricity than CSF (floats up)
-Isobaric: stays where it is injected
-Hyperbaric: most frequently used. Sinks

Question 24

What are the highest points of the spinal curve?

Answer 24

-Cervical & Lumbar Lordosis
-C3 and L3 high points

Question 25

What are the lowest points of the spinal curve?

Answer 25

-Thoracic and Sacral Kyphosis -T6 and S2 low points

Question 26

What other factors affect the height of a spinal block?

Answer 26

-Age -Height (if very tall, can increase dose as more distance to travel) -Weight: Obese/Pregnant have decreased intrathecal space (less dose) -Technique of injection: site, direction of needle/bevel, rate of injection (barbotage) - controversial -Spinal Fluid (rate of circulation, volume, pressure - coughing and straining) -LA: Amount, concentration, volume, vasoconstrictors (slow down how fast it is absorbed) MOST IMPORTANT is baricity and patient position!!!!

Question 27

How does age impact your height of spinal block?

Answer 27

-Ligamentum Flavum gets tougher -Intrathecal space is more compressed -**Higher spread of Local Anesthetic**

Question 28

What is the baricity of CSF?

Answer 28

1

Question 29

What is the baricity of hypobaric solutions?

Answer 29

-Tetracaine 0.33% / water = 0.9977 -Lidocaine 0.5% / water = 0.9985

Question 30

What is the baricity of isobaric solutions?

Answer 30

-Tetracaine 0.5% / 50% CSF = 0.9995 -Lidocaine 2% / water = 1.003 -Bupivicaine 0.5% / water = 0.999

Question 31

What is the baricity of hyperbaric solutions?

Answer 31

-Tetracaine 0.5% / 5% dextrose = 1.0133 -Lidocaine 5% / 7.5% dextrose = 1.0265 -Bupivicaine 0.5% / 8% dextrose = 1.0207 -Bupivicaine 0.75% / 8% dextrose = 1.0227

Question 32

What is specific gravity?

Answer 32

The ratio of a density of a substance to the density of water -Affected by proteins, glucose, uremia -temperature can affect it -Spec grav of CSF = 1.0069

Question 33

What is the definition of baricity?

Answer 33

The resting position of 2 fluids with differing specific gravities.

Question 34

What is the primary objective of neuraxial anesthesia? **

Answer 34

-To block afferent fibers located in the Dorsal Roots -Motor and sympathetic fibers are close and they get blocked as they pass through the ventral root.

Question 35

Why is Lidocaine 5% not used anymore for Spinal Anesthesia (SAB)?

Answer 35

-Potential to cause transient neurological syndrome (TNS) -Can cause Cauda Equina syndrome (permanent)

Question 36

Which is the most cardiotoxic local anesthetic?

Answer 36

Bupivicaine -May need lipids to reverse

Question 37

List some common preservatives added to local anesthetics.

Answer 37

-Parabens (high allergy/anaphylaxis potential) -Sulfites (neurotoxic) -EDTA (muscle pain, can cause tetany in paraspinous muscles)

Question 38

T/F: it's ok to use preservative containing, multi-use vials for spinals.

Answer 38

FALSE -Want preservative free, single dose vials for anything going in the spine. -Multi-use can be used for PNB, but not for spinals.

Question 39

What is the MOA of local anesthetics?

Answer 39

-Limit the sodium channels and stop the propagation of a nerve impulse. -Small amounts act directly on the spinal cord itself by way of diffusion through the pia mater (slow process) -LA can find its way to the cord via the Virchow-Robin Spaces

Question 40

What are Virchow-Robin Spaces?

Answer 40

Insertion sites of tiny blood vessels on the spinal cord where local anesthetics can get around the sides of them and act directly on the cord.

Question 41

The more _____ soluble the drug, the more it can penetrate the membrane and get to the roots (site of action).

Answer 41

Lipid soluble.

Question 42

Why is Epinephrine added to local anesthetics?

Answer 42

-Alpha 1 agonist -Produces direct analgesia when placed on the cord -Increases duration of LA by causing constriction of blood vessels (slows absorption of local) -Usual dose is 0.1-0.2 mL of Epi 1:1000 for spinal (Epi Wash)

Question 43

Epinephrine has the greatest effect on which local anesthetic?

Answer 43

**Greatest effect on Tetracaine** Then Lidocaine, then Bupivicaine.

Question 44

What is the dose of Phenylephrine added to Spinals?

Answer 44

-Pure Alpha 1 Agonist -0.5 - 2 mg

Question 45

What is the purpose of adding Clonidine to Local Anesthetics?

Answer 45

-Alpha 2 Agonist Activity -High lipid solubility -Local anesthetic effects -Prolongs DOA

Question 46

Why is NaHCO3 added to local anesthetics?

Answer 46

To increase the pH to decrease the onset (quicker)

Question 47

Describe Opioids added to a Spinal

Answer 47

-Stimulate opioid receptors in the brainstem (Substantia Gelatinosa) and Spinal Cord -Mu receptors are responsive to Morphine, Meperidine, Sufentanil, Fentanyl, and Alfentanil -Mu 2 receptors are responsible for dec HR, RR, Euphoria -SEs: N/V, itching, urinary retention

Question 48

What is the opioid reversal?

Answer 48

Naloxone - competitive antagonist

Question 49

What is the number 1 complaint of opioid additives to Local Anesthetics?

Answer 49

Itching (especially in OB)

Question 50

Why is Fentanyl widely used as an additive to local anesthetics?

Answer 50

-It adheres to lipoproteins in the spinal cord due to its high lipid solubility -Less drug available to diffuse to respiratory centers -Dose: 10-25 mcg -Onset: 5-10 min -DOA: 2-4 hours -Can be used in combo with morphine

Question 51

What is important to know regarding Morphine added to local anesthetics?

Answer 51

-Use preservative free for spinals! -Hydrophilic and not highly bound to spinal cord, so it moves around (can hit respiratory centers) -Be very careful - administer only if patient is being monitored -Onset: 60-90 min -DOA: 6-8 hours -Dose: 0.1 - 0.5 mg (spinal) -Won't be able to give more opioids for breakthrough pain -Caution with risk of delayed respiratory depression**

Question 52

For Upper abdominal surgery, what Dermatome level do you want to block?

Answer 52

T4

Question 53

For intestinal, gyn, and urologic surgeries, what Dermatome level do you want to block?

Answer 53

T6

Question 54

For a TURP, what Dermatome level do you want to block?

Answer 54

T10

Question 55

For a vaginal delivery or hip surgery, what Dermatome level do you want to block?

Answer 55

T10

Question 56

For thigh surgery and lower leg amputations, what Dermatome level do you want to block?

Answer 56

L1

Question 57

For Foot and Ankle surgery, what Dermatome level do you want to block?

Answer 57

L2

Question 58

For perineal and anal surgery, what Dermatome level do you want to block?

Answer 58

S2-S5 (saddle block)