18 – Anatomy and Spinal Anesthesia

Where is LA injected in spinal anesthesia?
-CSF contained within the subarachnoid (intrathecal) space

Where is LA injected in epidural anesthesia?
-the space that lies within the vertebral canal but outside or superficial to the dural sac

Does caudal anesthesia represent a type of spinal or epidural anesthesia?
-special type of pidural anesthesia in which LA solution is injected into the caudal epidural space through a needle introduced through the saral hiatus.

Advantages of spinal anesthesia over epidural:
-takes less time to perform
-causes less discomfort during placement
-requires less local anesthetic
-produces more intense sensory and motor block
-correct placement of needle confirmed by backflow of CSF

Advantages of epidural anesthesia?
-decreased risk of post-dural puncture headache (assuming a negligible incidence of inadvertent dural puncture)
-a lower incidence of systemic hypotension
-the ability to produce a segmental sensory block
-greater control over the intensity of sensory anesthesia and motor block achieved by adjustment of LA concentration
-the routine placement of catheters for epidural anesthesia imparts additional benefit by allowing titration of the block tot he duration of surgery
-Catheter allows long-term administration of LA or opioid-containing solutions (or both

the vertebral (spinal) canal extends from what to what?
-foramen magnum to sacral hiatus
-contains spinal cord and nerve roots

What is important about he kyphosis and lordosis of the spinal canal
-influences distribution of LA solution in the SA space
-has little effect on the spread of LA solutions in the epidural space

what are the components of a vertebra?
-anterior vertebral body and posterior arch
-the posterior arch is created by fusion of lateral cylindrical pedicles with two flattened posterior laminae
-a transverse process extends out laterally at each junction of the pedicale and laminae
-a single spinous process projects posteriorly from the juntio of the two laminae.
-each pedicle is notched on its superior and inferior surfaces, and when two adjacent vertebrae are articulated, these notches form the intervertebral foramina through which the spinal nerves emerge

How man true vertebrae are there? where are they located
24
-7 cervical
-12 thoracic
-5 lumbar

How many false vertebrae are there? where are they located
5 – fused t form the bony sacrum

thus the sacrum and coccyx are dital extensions of the vertebral column, and the sacral canal is a continuouation of the vertebral canal through the sacrum.

what structures do you advance through when placing an epidural? Spinal?
Skin –> supraspinous ligament –> interspinous ligament –> ligamentum flavum (“pop”) –> Epidural fat

Epidrual fat –> Dura mater/arachnoid (“pop) –> Spinal

Good images on page 254 and 255

what is the sacral hiatus?
-fused lamina of the fourth and fifth sacral vertebrae

in what percentage of adults is the sacral hiatus absent
-8%, thereby preventing entry through the sacrococygeal ligament into the sacral canal and performance of caudal anesthesia

what ligament do you go through when performing caudal anesthesia
sacrococygeal

Sacral landmarks:
1. iliac crest
2. bony knob at the lower end of the neck
3. lower wing of the scapula
4. Posterior superior iliac spine
1. transverses the body of the L4 vertebra
2. C7
3. T7
4. S2

what is the most caudal limit of the dural sac in adults?
-about S2 (PSIS)

Describe the development of the spinal cord and its growth
-begins at the rostral border of the medulla and, in the fetus, extends the entire length of the vertebral canal (all the way to S2)
-b/c of disproportionate growth of neural tissue and the vertebral canal, the spinal cord generally terminates around the third lumbar vertebra at birth and at the lower border of the first lumbar vertebra in adults

what happens to the spinal nerves b/c of the disproportionate growth?
-spinal nerves become progressively longer and more closely aligned with the longitudinal axis of the vertebral canal

what is the conus?

where does it begin in newborns? adults?

-roots are ariented parallel to this axis and resemble a horse’s tail – from which the name cauda equine is derived
-nerve roots of the cauda equine move relatively freely within the CSF, a fortunate arrnagment that permits them to be displaced rather than pierced by and advancing needle

newborn – conus at L3 vertebra body
Adult – conus at L1 vertebra body

what are the meninges?
-in addition to the CSF, there are 3 meninges layers of connective tissue that protect the spinal cord

what are the 3 meninges layers? characteristics?
1. Dura – outermost
2. Arachnoid – closely adherent to the inner surface of the dura
3. Pia – innermost layer

Dura:
1. originates where?
2. terminates where?
3. Characteristics?
1. foramen magnum as an extension of the inner (meningeal) layer of cranial dura
2. terminates between S1 and S4.
3. tough fibroelastic membrane that provides structural support and a fairly impenetrable barrier that normally prevents displacement of an epidural catheter into the fluid-filled subarachnoid space

Arachnoid Membrane:
1. characteristics?
2. Function?
3. Relationship to each other
1. More delicate than the dura,
2. serves as the major pharmacologic barrier preventing movement of drug fromt he epidural to the subarachnoid space
**conceptually, the dura provides support and the arachnoid membrane imparts impermeability

3. b/c te dura and arachnoid are closely adherent, a spinal needle that penetrates the dura will generally pass through the arachnoid membrane

Pia:
1. characteristics?
2. what is the denticulate ligament?
1. highly vascular structure closely applied to the cord that forms the inner border of the sufarachnoid space

2. along the lateral surface between the dorsal and ventral roots, an extension of the pia membrane forms the denticulate ligament
-a dense serrated longitudinal projection that provides lateral suspension through its attachement tot he dura

Pia:
3. what happens to the pia as the spinal cord tapers to form the conus medullaris
3. the pia continues inferiorly as a thin filament, the filum terminale
-distally, the filum terminale becomes enveloped by the dura at the caudal termination of the dural sac (generally around S2) and continuous inferiorly to attach to the posterior wall of the coccyx

Spinal Nerves:
1. where do spinal nerves originate?
-along the dorsolateral and ventrolateral aspect of the spinal cord, rootlets emerge and coalesce to form the dorsal (afferent) and ventral (efferent) spinal nerve roots)

2. distal to the dorsal root ganglion, these nerve roots merge to form how man pairs of spinal nerves? Number by location?
31
-8 cervicle
-12 thoracic
-5 lumbar
-5 sacral
-1coccygeal

3. location of sensory fibers in spinal nerves? effect on pt position and type of LA used
-b/c the sensory fibers traverse the posterior aspect of the subarachnoid space, they tend to lie dependent in a supine pt, thus makingthem particularly vlnerable to hyperbaric (heavier than CSF) solutions containing ocal anesthetic

4. what happens as nerves pass through the intervertebral foramen?
-they become encased by the dura, arachnoid, and pia, which form the epineurium, perineurium, and endoneurium, respectively

5. what happens to the dura as the spinal nerves pass through the intervertebral foramen?
-becomes thinned in this area (often called the dural sleeve), thereby facilitating penetration of LA.

Spinal Nerves: Preganglionic Sympathetic Nerve Fibers:
1. originate where?
2. Leave spinal cord where?
3. How do they leave the spinal nerve?
4. How do they rejoin the spinal nerve?
1. intermediolateral gray columns of the thoracolumbar cord
2. leave with ventral nerve roots passin tinto the spinal nerve trunks
3. they then leave the nerve via the white rami communicates and project to the paravertebral sympathetic ganglia or more distant sites (adrenal medulloa, mesenteric and celiac plexus)
4. after a cholinergic synapse (nicotinic) in the autonomic ganglia, the postsynaptic sympathetic nerve fibers join the spinal nerves via the gray rami communicantes and innervate diverse adrenergic effector sites

Cervical Nerve:
1. the first cervical nerve passes where?
2. where do the 7th cervical nerve pass
3. 8th cervical nerve
1. between the occipital bone and the posterior arch of the first cervical vertebra (atlas), and this relationship continues
2. passes above the seventh cervical vertebrae
3. the eighth cervical nervepasses between the seventh cervical vertebra and the first thoracic vertebra.
**Below this point, each spinal nerve passes through the inferior notch of the corresponding vertebra

Subarachnoid Space:
1. Location?
2. Contents?
3. what produces CSF?
4. is the spinal and carnial arachnoid spaces continuous?
1. between the arachnoid and the pia
2. CSF
3. choroid plexus of the lateral, third, and fourth ventricles
4. yes, carnail nerve can be blocked by local anesthetic migrating into the CSF above the foramen magnum

Epidural Space:
1. location
2. composition
3. bound cranially by what? Caudally? Anteriorly? Posteriorly? Lateral?
1. between the dura and the wall of the vertebral canal
2. irregular column of fat, lymphatics, and blood vessels
3.
Cranially – foramen magnum
Caudally – sacrococcygeal ligament
Anteriorly – posterior longitudinal ligamne
Posteriorly – both the ligamentum flavum and the vertebral lamina
Laterally – vertebral pedicles

Epidural Space:
4. Is the epidural space a closed space?
5. where is the depth of the epidural space the largest (size of epidural space)? Smallest
4. NO – communicates with the paravertebral spaces by way of the intervertebral foramina.
5.
largest – about 6 mm – midline at L2. is about 4-5 mm in the midthoracic region
Smallest – where the lumbar and cervical enlargements of the spinal cord (T9-T12 and C3-T2, respectively) encroach n the epidural space with roughly 3 mm left between eh ligamentum flavum and the dura

**There is controversy regarding whether the epidural space has compartments or is continuous

Blood Vessels: Arterial
1. arterial supply of spinal cord
1. two posterior arteries, a single anterior artery

Blood Vessels: Arterial
2. where do the posterior spinal arteries arise from? are areas supplies by posterior arteries relatively protected from ischemic damage?
2. emerge from the crania vault and supple the dorsal (sensory) portion of the spinal cord
-b/c they are paired and have rich collateral anastomotic links from the subclavian and intercostal arteries, this area of the spinal cord is relatively protected from ischemic damage.

Blood Vessels: Arterial
3. anterior spinal arteries – origination? at risk for ischemic changes?
3. originates from the vertebral artery and supplies the ventral (motor) portin of the spinal cord
-receives branches from the intercostal and iliac arteries, but these branches are variabl in number and location
-More susceptible to ischemia

Blood Vessels: Arterial
4. what is the Artery of Adamkiewicz?
4. the largest anastomatic link with the anterior spinal artery,
aka. the radicularis magna
-arises from the aorta in the lower thoracic or upper lumbar region
-most commonly – is on the left and enters the vertebral canal through the L1 intervertebral foramen.

Blood Vessels: Arterial
5. what is the function of the artery of Adamkiewicz?
-critical to blood supply of the lower two thirds of the spinal cord
-damage to this artery during surgy on the aorta (anortic aneurysm resection) or by a strapy epidural needle will produce characteristic bilateral lower extremity motor loss (anterior spinal artery syndrome)

Blood Vessels: Venous
1. what drains the contents of the vertebral canal? where are these veins located?
1. vertebral venous plexus
-prominent in the lateral epidural space and ultimately empty into the azgos venous system

Blood Vessels: Venous
2. what is the azygos venous system?
2. enters the chest, arches over th right lung, and then empties into the superior vena cava

Blood Vessels: Venous
3. what is the effect of a tumor or increased intra-abdominal pressure that compress the vena cava and epidural placement
– blood is diverted from the inferior vena cava and engorges veins n the epidural space, which increases the likelihood of accidental vascular cannulation during attempted epidural anesthesia.
-in addition, b/c the vertebral veins are enlarged, the effective volume of the epidural space is reduced, thereby resulting in greater longitudinal spread of injected local anesthetic solutions

Preoperative preparation of neuraxial anesthesia:
1. serious, but rare, complication
2. more common, but less severe?
1. nerve damage, bleeding, infection
2. postdural puncture headache. possibility of failed block.

what are the absolute contraindications to neuraxial anesthesia?
1. pt refusal
2. infection at the site of planned needle puncture (bacteremia is not an contraindication)
3. elevated ICP
4. bleeding diathesis

Neuraxial anesthesia and infection
-bacteremia not a contraindication
-benefit of epidural outweighs the small risk of infection from bactermia
-make sure appropriate antibiotic therapy has been initiated before the block – may decrease the risk of infection

Is preexisting neuroogic disease a absolute or relative contraindications?
Relative
-make sure there is an benefit before performing in pt with multiple sclerosis. Local anesthetic toxicity can be confused for multiple sclerosis exascerbation

in what heart conditions should neuraxial anesthesia be cautiously used?
-mitral stenosis, idiopathic hypertrophic subaortic stenosis, and aortic stenosis intolerant of acute decrease in SVR
“Full, Fast, Forward”

where can you reference regarding neuraxial anesthesia and abnormal coagulations?
American Society of Regional Anethesia and Pain Medicine. www.asra.com

what must be in place before performing a spinal
– IV
– Standard monitors

what is important about the selection of interspace used for a spinal?
-the interspace selected for spinal anesthesia has considerable impact on the distribute of anesthetic within the subarachnoid space.
-for example, the likelihood of a “failed spinal” increases as interspaces that are more caudal are used, with up to a 7% incidence occurring when the L4-L5 interspace is selected.

How high is it generally accepted to go with a spinal?
-rostral interspaces are associated with higher success rates, this benefit must be balanced against the potential for traumatic injury to he spinal cord
-the spinal cord in adults usually lies between the L1 and L2 vertebrae.
-spinal anesthesia is not ordinarily performed above the L2-L3 interspace.

What percentage of adults have a spinal cord that extends beyond the L2 vertebrae?
-2% of adults have a spinal cord that extends beyond the L3 vertebrae.

what is the problem with using the iliac crest as a landmark?
-the conceptual line that is often used to identify L4 vertebra often results in selection of an interspace that is one or more levels higher than believed

1. what are the two types of spinal needles commonly used?
2. what gauges are often used?
1. open-ended (beveled or cutting)
closed tapered-tip pencil-point needle with a side port

2. 22-25 gauge

the incidence of PDPH directly correlates with what?
-size of the needle

in what age of pt is PDPH more likely to occur in?
-younger
-24 or 25-gauge pencil point needle is often selected.

what are the differences of the pencil-point versus the open needle
Pencil-Point (Whitacre or Sprotte)
Open-ended (Quinke)

Pencil-point needle requires more force to insert
-but provides better tactile feel of the various tissues encountered as the needle is advanced
-less incidence of PDPH.

what are the 3 approaches for a spinal anesthetic
1. midline
2. paramedian
3. taylor

Midline Approach:
1. technique?
2. layers passed through by the needle
3. how are dura fibers oriented
1. identify the upper border the the inferior spinous process. Pierce the skin and then advance in a slight cephalic direction
2. skin, SubQ, supraspinous ligament, interspinous ligament, ligamentum flavum, and the epidural space –> pierce the dura/arachnoid
3. largely oriented along the longitudinal aixs of the dural sac

what is important about the orientation of the dural fibers?
-orienting the bevel of a cutting needle parallel to this axis tends to spread rather than cut th fibers, which may reduce the risk for PDPH

Paramedian Approach
1. technique
2. most common error?
3. what is the first resistance encountered in this technique
1. insert needle typically 1 cm lateral to the midline, varies in the rostra-caudal plane according to the pt’s anatomy and anesthesia provider’s preference.
2. underestimate the distance to the subarachnoid space and direct the needle too medially, with resultant passage across the midline
3. needle bypasses the supraspinous and interspinous ligaments, and the ligamentum flavum will be the first resistance

Taylor Approach:
1. described by who? Why?
-urologist John A. Taylor – paramedian technique to access the L5-S1 interspace
– Though generally the widest interspace, it is often inaccessible from the midline b/c of the acute downward orientation of the L5 spinous process

Taylor Approach:
2. technique?
-spinal needle is passed from a point 1 cm caudad and 1 cm medial to the PSIS and advanced cephalad at a 55-degree angle with a medial orientation based on the width of the sacrm (See picture on 265)
-technically challenging but very useful b/c it is minimally dependent on pt flexion for successful passage of the needle into the subarachnoid space.

what should be done if blood-tinged CSF is seen?
-occasionally blood-tinged CSF initially appears at the hub of the needle. If clear CSF is subsequently seen, the spinal anesthetic can be completed.
-conversely, of blood-tinged CSF continues to flow, the needle should be removed and reinserted.

what should be done if paresthesia is experienced
-spinal anesthesia should NEVER be administered in the presence of paresthesia. The occurrence of a paresthesia during needle placement mandates withdrawal of the needle

in which needle, cutting or pencil point, can the needle to adjusted to direct the direction of LA injectin?
Pencil-Point: the side port can be positioned to encourage the desired distribution of local anesthetic solution within the suarachnoid space, which is generally cephalad.

-the position of cutting edge needle makes no difference.

the distribution of local anesthetic solution in CSF is influences principally by what 3 factors?
1. the baricity of the solution
2. contour of the spinal canal
3. position of the pt in the first few minutes after injection of LA solution into the subarachnoid space.

the duration of LA in a spinal depends on what 2 factors?
1. drug selected
2. presence or absence of a vasoconstrictor (epinephrine or phenylephrine)

During recovery, anesthesia regresses in what fashionn
-from the highest dermatome in a caudad direction

Baricity – what is the most commonly selected LA soultino for spinal anesthesia?
-hyperbaric – achieved by the addition of glucose (dextrose)

what is the pricinple advantage of hyperbaric solution
-greater cephalad spread of anesthesia

what are the commercially available hyperbaric solutions
1. 0.75% bupivacaine with 8.25% glucose
2. 5% lidocaine with 7.5% glucose
3. Tetracaine
–formulated as a 1% plaine solution, most often used as a 0.5% solution with 5% glucose.
-achieved by dilution of anesthetic with an equal volume of 10% glucose.

what anatomy factor is important in determining the subarachnoid distribution of hyperbaric local anesthetic solutions
-contour of the vertebral canal
-for example, in the supine horizontal position, the pt’s thoracic and sacral kyphosis will be dependent relative the the peak created by the lumbar lordosis.
-anesthetic delivered cephalad to this peak will thus move towards the thoracic kyphosis,w hich is normally around T6-T8
Placing the pt in a head-down (Trendelenburg) position will further accentuate this cephalad spread of LA solution and help ensure an adequate level of spinal anesthesia for abdominal surgery.

Do hypobaric solutions have much of a clinical use
No

What happens with isobaric solution when injected in the subarachnoid space?
-it undergoes limited spread

Isobaric solution – advantages?
-more profound motor block and more prolonged duration of action than achieved with equivalent hyperbaric local anesthetic solutions. B/c the distribution of local anesthetic is not affected by gravity, spinal anesthesia can be performed w/out concern that the resultant block might be influenced by pt position.

what clinical circumstances are well suited for isobaric solution?
-perennial or lower extremity procedures, as well as surgery involving the lower part of the trunk (hip arthroplasty, inguinal hernia repair)

does isobaric solution result in a segmental anesthesia?
-although spread of local anesthetic solution may be limited caudally, subarachnoid injections does nt produce segmental anesthesia b/c the nerves innervating more caudad structures are vulnerable to block as the pas through the region of high local anesthetic oncentrations

How does adding epinephrine to a spinal anesthesia increase the duration of action?
-reduction in spinal cord blood flow, which decreases loss of local anesthetic fromt e perfused areas and thus increases the duration of exposure to local anesthetic?

Epinephrine results in the largest increase of duration of action of what local anesthetic? why?
TETRACAINE – produces intense vasodilation

the effect of lidocaine is more modest

bupivacaine actually decreases both spinal cord and dural blood flow

what has the addition of epinephrine to lidocaine for spinal anesthesia been questioned?
-b/c of reports of nerve injury attributed to spinal lidocaine, and epinephrine may increase lidocaine neurotoxicity.

Epinephrine has been associated with significant “fluelike” side effects when coadministered with spinal _________
chloroprocaine

what opioid when added to spinal anesthesia doesn’t necessitate admission to hospital for monitoring of respiratory depression?
what is the common dose
Fentanyl – 25 mcg added to spinal anesthesia

how does opioid added to spinal local anesthetic produce analgesia?
-effect is mediated at the dorsal horn of the spinal cord, where opioids mimic the effect of endogenous enkephalins.

what are the characteristics of local anesthetics to consider when deciding which to use?
1. duration of action
2. potential side effects
3. differences in relative intensity of sensory and motor block

what anesthetic is best suited for short-duration spinal anesthesia?
Lidocaine

Lidocaine:
1. duration of action
2. More motor or sensory
3. positive characteristics?
1. 60-90 minutes
2. excellent sensory anesthesia and fairly profound motor block
3. above features, also positive recovery profile

Lidocaine:
4. what are the 2 major side effects of spinal lidocaine?
1. neurotoxicity
2. transient neurologic symptoms

Lidocaine:
5. Neurotoxicity?
-despite a long history of apparent safe use subsequent reports of major and minor complications associated with spinal lidocaine have tarnished its reputation and jeopardized its continued use
-at first thought to happen with only continuous spinal anesthesia and resulting high amounts of lidocaine. Has since been determined to occur after single shot

***Current suggestion –> reduction in lidocaine dose from 100 mg to 60-75 mg and dilution of the commercial formulation of 5% lidocaine with an equal volume of saline or CSF before subarachnoid injection

Lidocaine:
6. what is Transient neurologic symptoms? what increases your risk for this?
-pain or dysesthesia in the back, buttocks, and lower extremities
– lithotomy, knee arthroscopy and outpatient status

**the etiology of transient neurologic symptoms is not established, but their occurrence has reinforced dissatisfaction with lidocaine and general interest in alternative local anesthetics for short-duration spinal anesthesia

what are the alternatives to lidocaine for short duration spinal anesthesia?
1. Mepivacaine – probably has an incidence of transient neurologic symptoms less than lidocaine and may offer some benefit
2. Procaine – has very short duration of action, the incidence of nausea is relatively frequent, and yet the incidence of TNS is probably only marginally better
3. Chloroprocaine – next slides

Chloroprocaine – use in spinal anesthesia?
-low-dose (40-60 mg) preservative-free chloroprocaine – excellent short-duration spinal anesthesia with little, if any, risk for TNS

Chloroprocaine
1. can epinephrine be added?
2. Can opioids and clonidine be added?
1. no for spinal anesthesia – has sideffects
2. yes for fentanyl and clonidine – provide the expected enhancement of chloroprocaine spinal anesthesia

what local anesthetics are used for long duration spinal anesthesia?
Bupivacaine and tetracaine

**although ropivacaine has been used as a spinal anesthetic, the advantages over bupivacaine are not obvious

1. what are the concentrations of bupivacaine
2. what are the concentrations of tetracaine?
1. 0.75% solution with 8.25% glucose for hyprbaric anesthesia
2. Tetracaineis prepared as 1% plain solution, which can be diluted with glucose, saline, or water to produce hyperbaric, isobaric, or hypobaric solution, respectively.

the recommended dose for bupivacaine and tetracaine is similar – what is it? duration of actin?
5-20 mg, durations of action 90-120 minutes

what is the difference in motor vs sensory blockade of the two?
Bupivacaine – more sensory than motor
Tetracaine – slightly more pronounced motor block

can epinephrine be added to tetracaine to increase the duration of action of spinal anesthesia?
-no, results in a significant incidence of TNS

Documentation of anesthesia level:
1. time for spinal anesthesia to develop?
2. what fibers are affected first
3. how should anesthetic level be tested?
4. level of SNS anesthesia vs level of sensory block? vs level of motor block.
1. 30-60 seconds
2. nerve fibers that transmit cold sensation (C and A delta) are among the first to be blocked
3. early indication of level of a spinal anesthetic can be obtained by evaluating the pt’s ability to discriminate temperature changes a s produced by “wetting” the skin with an alcohol sponge. in the area blocked by the spinal anesthetic, the alcohol produces a warm or neutral sensation rather than the cold perceived in the unblocked areas.
4. level of SNS > level sensory > level of motor

what time frame is most critical for adjusting the level of anesthesia?
first 5-10 minutes

Sensory level anesthesia necessary for surgical procedures:
1. hemorrhoidectomy
2. foot surgery
3. lower extremity surgery
4. Hip surgery, TURP, Vaginal delivery
5. lower abdominal surgery, appendectomy
6. upper abdominal surgery, C-section
1. S2-S5
2. L2-L3 (knee)
3. L1-L3 (inguinal ligament)
4. T10 (umbilicus)
5. T6-T7 ( xiphoid process)
6. T4 (nipple)

Segmental levels and significance of sensory block:
1. Fifth digit
2. Inner aspect of the arm and forearm
3. apex of the axilla
4. Nipple
5. Tip of the xyphoid
6. Umbilicus
7. inguinal ligament
8. Outer aspect of the foot
1. C8: all cardiaccelerator fibers blocked
2. T1-T2: some degree of cardioaccelerator block
3. T3: easily determined landmark
4. T4-T5: Possibility of cardioaccelerator block
5. T7: Splanchnic fibers (T5-L1) may be blocked
6. T10: SNS block limited to legs
7. T12: no SNS block
8: S1: Confirms block of the most difficult root to anesthetize

what is the order of nerves anesthetized by LA in subarachnoid space?
First – unmyelinated (sympathetic) fibers
Second – larger myelinated (sensory and motor) fibers

dermatome comparison between sympathetic fibers and sensory fibers
SNS block typically exceeds the somatic sensory block by two dermatomes
this estimate may be conservative, with SNS block somties exceeding somatic sensory block by as many as sic dermatomes, which explains why systemic hypotension may accompany even low sensory levels of spinal anesthesia

what is the physiology behind pts experiencing dypnea after receiving a spinal anesthetic?
dyspneic despite adequate ventilation/c of inadequate sensation of breathing from loss of proprioception in the abdominal and thoracic muscles
alveolar oxygenation is the same

SNS block above what level inhibits GI SNS stimulation
above T5 –> unopposed PSN activity –> contracted intestines and relaxed sphincters
contracted ureters

is there a difference in perioperative mortality rate between regional anesthesia and general inrelatively healthy pts scheduled for elective surgery?
no

what neurologic complications can occur after spinal anesthesia?
1. Trauma – either directly provoked by a needle or catheter or indirectly by compression from hematoma or abscess
2. TNS – unclear etiology – don’t inject LA when paresthesia are present to avoid nerve injury

what % of pts receiving spinal anesthesia experience hypotension (systolic <90)? Why?
1/3 of pts

Modest hypotension (e.g., <20 mm Hg) is probably due to decreases in systemic vascular resistance More intense hypotension (>20 mm Hg) probably is the result of decreases in venous return and cardiac output.

the degree of hypotension often parallels the sensory level of spinal anesthesia nd the intravascular fluid volume status of the patient.

what are the treatment options for spinal induced hypotension
1. Restoration of venous return and increase cardiac output
–internal autotransfusion – tilt table down 5-10 degrees
–IV hydration

2. Sympathomimetics

does tilting the table down 5-10 degrees effect level of anesthesia
-facilitates venous return without greatly exaggerating cephalad spread of spinal anesthetic.

what are the first line sympathomimetics for spinal induced hypotension
1. ephedrine
2. phenylephrine
3. Epinephrine – when first two fail, to avid cardiac arrest from severe hypotension

**Phenylephrine – increases SVR but may decrease CO and does not correct the decreased venous return contributing to the spinal anesthesia
In the past, phenylephrine was contraindicated in parturients b/c of possible detrimental effects on uterine blood flow, which has not been confirmed.

what percent of pt’s experience bradycardia after a spinal?
-10-15%

what are the two possible causes of bradycardia after spinal?
1. block of cardioaccelerator fibers originating from T1 through T4
2. decreased venous return (Bezold-Jarisch reflex)

how is severe bradycardia and asystole treated?
Stepwise fashion: Aggressive stepwise escalation of treatment
1. ephedrine, 5 to 50 mg IV
2. atropine, 0.4-1.0 mg IV
3. epinephrine 0.05 to 0.25 mg IV

development of profound bradycardia or asystole –> 1.0 mg IV of epinephrine

what is the basic physiology behind a postdural puncture headache
-hole in dura results in loss of CSF at a rate exceeding production
-loss of CSF causes downward displacement of the brain and resultant stretch on sensitive supporting structures
-Pain results form distension of the blood vessels, which must compensate for the for the loss of CSF b/c of the fixed volume of the skull

how long after a spinal does a PDPH manifest
12-48 hrs after transgression of the dura, but can occur immediately even up to severe months after the event

what are the characteristic features of PDPH
-POSTURAL COMPONENT: it appears or intensifies with sitting or standing iand is partially or completely relieved by recumbency.
this feature is so distinctive that it is difficult to consider the diagnosis in its absence.

where is a PDPH felt
-occipital or frontal (or both) and usually described as dull or throbbing.

what associated symptoms might be experienced
N/V, anorexia, and malaise

why might pt’s experience ocular disturbances: manifested by diplopia, blurred vision, photophobia, or “spots” with a PDPH
stretch of CNs, most likely CN VI

Which pt’s are at high risk for PDPH? Low risk?
High Risk
-after puberty (age is important risk factor)
-Females, even it not pregnant
-hx of PDPH

Low Risk:
Children

How are PDPH treated?
Initial treatment – convervative:
-bed rest, IV fluids, analgesics, and possibly caffeine (500 mg IV

Definitive treatment:
-blood patch – 15-20 mL

at what level should a blood patch be given?
near or preferably below the site of initial puncture b/c there is preferential cephalad spread.

how long should pt lay flat after blood patch?
2 hrs

Blood patch – what is responsible for immediate relief and long term relif
immediate – volume effect of injected blood
Long-term – sealing or “patching” of dural tear.

High Spinal Anesthesia – your pt develops apnea and loss of consciousness after spinal anesthesia – what is the reason?
-often attributed to ischemic paralysis of the medullary ventilator centers b/c of profound hypotnsion and associated decreases in cerebral blood flow. Also LA effect above the foramen magnum.

what is the treatment for high or total spinal anesthesia
1. maintenance of the airway and ventilation
2. support circulation with sympathomimetics and IV fluid administration
3. Pts placed in head-down position to facilitate venous return
**an attempt to limit the cephalad spread of LA solution in CSF by placing pt’s in a head-up position is not recommended b/c this position with encourage venous pooling, was well as potentially jeopardizing cerebral blood flow, which may contribuate to medullary ischemia
4. Tracheal intbuation

why does nausea occur with spinal anesthesia
-systemic hypotension sufficient to produce cerebral ischemia
-Treat with sympathomimetic drugs

Spinal anesthesia and urinary retention
-Spinal interferes with innervation of the bladder
-large amounts of fluid –> bladder distension if no foley
-IVF needed to maintain preload, prevent hypotension and asystole
-inclusion of epinephrine in spinal will increase the time of urinary retention

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