9/12 Spinal Anesthesia – Flashcards
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Define Spinal Anesthesia
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Consists of the temporary interruption of nerve transmission within the subarachnoid space produced by injection of local anesthetic solution into csf.
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Terms associated with spinal anesthesia.
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1. neuraxial block 2. subarachnoid block 3. intrathecal injection
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Spinal and epidural blocks are known collectively as....
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central neuraxial blockade (cnb), because they involve the placement of local anesthetic solution onto or adjacent to the spinal cord.
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Advantages of spinal anesthesia
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1. Can perform on patients with full stomachs 2. Use with patients with anatomic distortions of the upper air way. 3. TURP 4. Obstetrics 5. May be simpler and faster 6. Decreased post-op pain 7. Can use a continuous infusion post-op 8. More cost effective
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Spinal anatomy
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33 vertebrae -7 cervical -12 thoracic -5 lumbar -5 sacral -4 coccygeal
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High points on spine
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C5 and L5
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Low points on spine
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T5 and S2
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What are the four curves on the spine?
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1. Cervical 2. Thoracic 3. Lumbar 4. Sacral
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C1 is known as
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atlas
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C2 is known as
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axis
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What is the first palpable spinous process?
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C2
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What is the most prominent vertebrae?
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C7
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What anatomy can be used to locate T7?
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The tip of the scapula when patients arms are at their sides.
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The spinal cord in the adult begins and ends where?
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Begins: Foramen Magnum Ends: L1
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The spinal cord in the newborn begins and ends where?
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Begins: Foramen Magnum Ends: L3 newborn up to 20 months
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What is the terminal end of the spinal cord called?
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Conus Medullaris
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What anchors the spinal cord in the sacral region?
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Filum Terminale
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What is Cauda Equina
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Nerve group of lower dural sac
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What are the ligaments of the vertebral column?
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1. Supraspinous ligament 2. Intraspinous ligament 3. Ligamentum flavum
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Supraspinous ligament
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Extends from C7 to the sacrum. It is composed of collagen and is broad and thick in the lumbar region. The tips of the spinous processes are joined together by the supraspinous ligament.
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Interspinous ligament
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Extends the full length of the spinal column. It is broad and thick in the lumbar region.
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Ligamentum flavum
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Also known as the yellow ligament
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Longitudinal ligaments
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Anterior and posterior ligaments that bind the vertebral bodies together.
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Spinal meninges
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Membranes the spinal cord, nerve roots and csf are enclosed in.
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What are the meninges from outermost to innermost?
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1. Dura mater 2. Arachnoid mater 3. Pia mater
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Dura mater
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1. Outer most layer 2. Fibrous 3. Runs longitudinally 4. Collagenous and elastic 5. Compressible 6. Ends at S2
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Arachnoid mater
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1. Middle layer 2. Non vascular 3. Ends at S2 4. Delicate 5. Nonvascular
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Pia mater
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1. Inner most layer 2. Highly vascular
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Sub Arachnoid space
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Lies between the arachnoid and pia and is where medications are injected.
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A midline fold that tents posteriorly when air or fluid is injected into the dural sac is known as...
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Plica mediana dorsalis
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What is the filum terminale?
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The terminal thread of the pia mater and anchors the spinal cord and spinal dura.
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What are the 3 divisions of the subarachnoid space?
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1. Cranial (surrounding the brain) 2. Spinal (surrounding the spinal cord) 3. Root (surrounding the dorsal and ventral spinal nerve roots)
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CSF
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1. Contained between the arachnoid and pia maters. 2. Forms 500ml/per day or 21ml/hr 3. 100ml in vertebral canal 4. Majority (49.9ml) in the area of the cauda equina below the level of T11-T12.
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Where is csf formed?
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choroid plexus
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What is the pH of csf?
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7.32
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What is the major electrolyte found in csf?
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Na
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How many pairs of spinal nerves are there?
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31
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In the cervical region the spinal nerves exit ____ the vertebrae.
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above
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Below the cervical region the spinal nerves exit ____ their corresponding vertebrae.
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below
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The cauda equina is also known as the...
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"horses tail"
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Cauda equina
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The lumbar and sacral nerve roots extend beyond the termination of the spinal cord at the lower border of L1 and form the cauda equina at the lower border of the dural sac. Anchored in the sacral region. Especially sensitive to local anesthetics because only covered by a thin layer of pia.
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How long is the adult spinal cord?
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41-48cm
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What is the weight of the spinal cord?
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24-36g
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What is the diameter of the spinal cord?
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1cm
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What is the tapered end of the spinal cord called and where is it located?
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Conus medullaris at L1
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What is the primary inhibitory neurotransmitter in the spinal cord?
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Glycine
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The majority of blood flow to the spinal cord comes from....
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2 posterior arteries 1 anterior arteries
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Where is the anterior spinal artery formed?
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Vertebral artery at the base of the skull.
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Where is the origin of the posterior spinal arteries?
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The posterior inferior cerebellar arteries.
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How much blood supply does the posterior artery contribute to the spinal cord?
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1/3
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How much blood supply does the anterior spinal artery contribute to the spinal cord?
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2/3
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What is the largest artery that feeds the spinal nerve "rootlets"?
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Radicularis magna (artery of Adamkiewicz)
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What does the radicularis magna artery supply blood to?
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The lumbar portion of the cord.
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How do you ensure the radicularis magna is intact after lumbar laminectomy?
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By having the patient move their legs after the surgery.
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The wake up test monitors what portion of the spinal cord?
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The ventral portion which is supplied by the anterior spinal artery.
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Somatosensory evoked potentials monitor what portion of the spinal cord?
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Dorsal portion.
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When choosing a local anesthetic for spinal anesthesia make sure it says what on the vial?
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FOR SPINAL USE ONLY PRESERVATIVE FREE.
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Vasoconstrictors do what to the duration of action of a spinal block?
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Prolong it.
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What factors effect distribution of spinal blocks?
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1. Site of injection 2. Shape of spinal column 3. Patient height 4. Angulation of needle 5. Volume of csf 6. Characteristics of local anesthetic 7. Dose 8. Volume 9. Patient position during and after.
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What are 3 factors that the anesthetist can control in regards to effects of distribution of LA?
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The characteristics of local anesthetic. 1. Density 2. Specific gravity 3. Baracity
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What determines anesthesia level of LA?
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Patient position.
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Uptake of anesthetic occurs by _____.
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diffusion
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2 ways elimination determines duration of a block.
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1. Lipid solubility decreases vascular absorption 2. Vasoconstriction can decrease rate of elimination
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The decision about which local anesthetic to use depends on what?
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The intensity of motor block verses sensory block and the desired duration of the anesthetic.
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Drugs that can be added to prolong the duration of anesthesia, intensify the block, and prevent post-op pain without prolonged recovery from the LA are...
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1. Morphine 0.1-0.4cmg (duramorph) 2. Fentanyl 10-25mcg 3 Sufentanil 2.5-10mcg 4. Epinepherine 0.2-0.3mg 5. Phenylepherine 2-5mg 6. Clonidine 15-45mcg 7. Precedex 3mcg
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Where are the alpha 2 receptors found?
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The substantia gelatinosa of the dorsal horn of the spinal cord.
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Clonidine does what to a sensory block?
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Prolongs
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What drug is a hydrophilic opioid that provides post-op pain relief for up to 24 hours?
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Morphine
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Complications of using morphine in spinal anesthesia.
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1. It spreads rostrally to the level of the brainstem and delayed respiratory depression can occur up to 24 hours after the injection. 2. Side effects: N/V, pruritus, and resp. depression 3. Not advisable to use in elderly patients due to resp depression.
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Why do fentanyl and sufentanil rapidly penetrate the spinal cord?
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Because they are lipophilic
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Unlike morphine rostral spread may be....
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immediate, causing resp. depression within 20-30min after injection.
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What scenarios are are appropriate for the use of fentanyl and sufentanil?
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Ambulatory settings, relief of labor pain, c-sections, and arthroscopic surgeries of lower extremities.
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Where is the mechanism of action in spinal anesthesia?
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The spinal nerve roots and in the dorsal root ganglia.
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The spinal cord itself takes up LA by diffusion through...
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the pia mater.
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In contrast to small nerve roots, large nerve roots may be the most...
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resistant to LA.
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Factors affecting the uptake of local anesthetics from the csf.
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1. Concentration of the LA. 2. Point of diffusion from higher to lower concentration. 3. Drug goes down a concentration gradient. 4. Surface area of neural tissue exposed to csf. 5. Lipid content of the nerve.
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Spread of LA in spinal anesthesia.
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1. Determined by diffusion and the baracity of the LA compared to the density of the csf. 2. Spread determines the level of anesthesia, what areas are anesthetized. 3. The concentration of LA decreases the further you are from the site of injection. 4. Fewer molecules become available to cause nerve blockade the further you get from the site of injection.
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Order of spread in spinal anesthesia.
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1. cauda equina 2. laterally to the nerve rootlets and nerve roots 3. spinal cord
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Primary targets of spinal anesthesia
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1. rootlets 2. roots 3. spinal cord
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Order of nerve fiber blockade
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1. B fibers 2. C and A delta fibers 3. A gamma fibers 4. A beta fibers 5. A alpha fibers
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B fibers
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1. Responsible for venodilation and hypotension 2. Preganglionic sympathetic fibers. 3. Most sensitive to LA 4 Efferents=motor
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C fibers
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1. Sensory fibers (produce sensation to cold) 2. First blocked sensory fibers and remain blocked longest. 3. Carry sensation of throbbing pain and temperature. 4. Afferents=sensory
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A delta fibers
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1. Carry sensations of sharp prickling pain and temperature. 2. Afferents=sensory
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A gama fibers
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1. Sharp pain, loss of muscle tone 2. Are the second sensory fibers to be blocked. 3. Efferents=motor
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A beta fibers
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1. Proprioception (position sense) and touch 2. The last sensory fibers blocked and the first to recover. 3. Detect touch 4. Afferent and efferent=sensory and motor
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A alpha fibers
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1. Proprioception (position sense) 2. Largest fibers and hardest to block 3. Least sensitive to LA 4. Adjust skeletal muscle force and length. 5. Efferent=motor
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Venodilation reduces:
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1. Venous return 2. Stroke volume 3. CO 4. BP
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T1-T4 blockade causes...
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unopposed vagal stimulation which leads to bradycardia.
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What is the best way to treat hypotension r/t spinal anesthesia?
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Physiologically, Volume, Large bolus 1 liter 30 minutes prior to spinal placement.
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What is the more effective pharmacologic treatment for hypotension r/t spinal anesthesia?
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Ephedrine superior to neosynepherine.
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Bainbridge reflex
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A decrease in venous return and reduction in right atrial filling, the frequency of action potentials from stretch receptors to the right atrium and great veins is diminished, which leads to a reflex decrease in HR.
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Total spinal anesthesia
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Occurs when LA spreads high enough to block the entire SC and occasionally the brain stem during either spinal or epidural anesthesia.
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If a patient becomes nauseous within 5 minutes after a spinal anesthetic, the likely cause is....
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Central hypoxia due to low CO.
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Treatment for hypotension r/t spinal anesthesia.
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1. Elevate legs or t-berg no greater than 20 degrees only if it has been 20 minutes after LA administration. 2. O2 3. IVF 4. Ephedrine 10-15mg
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Why shouldn't you use IVF with glucose?
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Glucose can act as a diuretic and worsen the hypotensive situation.
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What are the dosing increments for epi use in severe bradycardia r/t spinal anesthesia?
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5mcg
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LA effects on respiratory center in a high spinal.
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1. Decreased FRC 2. Paralysis of abdominal muscles 3. Intercostal muscle paralysis 4. Apnea due to hypoperfusion of respiratory center.
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T or F. You should have a urinary catheter placed before or after performing a spinal.
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T.
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Endocrine affects of spinal anesthesia
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Causes activation of the rennin-angiotensin-aldosterone system.
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GI effects of spinal anesthesia
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Small intestine contraction and has unopposed vagus nerve activity. Sphincters are relaxed and peristalsis in normally active.....code brown
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Thermoregulation in spinal anesthesia.
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Shivering is common, caused by a decrease in core body temp, r/t redistribution of blood flow. can be averted by the use of a fluid warmer and warm blankets.
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The 4 P's of spinal placement
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1. Preparation 2. Position 3. Projection 4. Puncture
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Absolute contraindications to spinal anesthesia.
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1. Patient refusal 2. Infection at the site of injection 3. Dermatologic conditions 4. Septicemia or bacteremia 5. Shock or severe hypovolemia 6. Major abnormal clotting 7. Increased ICP 8. Lack of skill of the anesthesia provider 9. Allergy to LA 10. Unknown length of surgery 11. Abruptio placentae
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Relative Contraindications to spinal anesthesia
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1. Deformities of the spinal column 2. Preexisting disease of the spinal cord 3. Chronic headache or backache 4. Inability to achieve spinal fluid in 3 attempts 5. Stenotic valvular lesions 6. Tramp stamp
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Other relative contraindications to spinal anesthesia.
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1. Tattoos must be soaked in for 6 months or 180days 2. Major surgical procedure above umbilicus 3. Blood in csf that does not clear 4. Uncooperative patient 5. Preexisting neurologic deficits 6. Abnormal EKG Mobitz I or II and 3 degree HB
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Controversial decisions to do spinal include...
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1. Prior back surgery at the site of injection. 2. Inability to communicate with the patient 3. Prolonged or complicated operation 4. Major blood loss 5. Compromising respiration 6. Severe aortic or mitral stenosis which is an absolute contraindication is some texts
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Complications associated with spinal anesthesia
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1. Failed block 2. Back pain (most common) 3. Spinal head ache
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Spinal head ache
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1. More common in women in ages 13-40 2. Larger needle size increases severity 3. Onset typically first or second day post-op
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Tx for spinal head ache
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1. Bed rest 2. Fluids 3. Caffeine 4. Blood patch
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Sitting position
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1. With legs hanging over side of bed 2. Have the patient hug a pillow 3. Put feet up on a stool (no wheels) 4. Assistant MUST keep the patient from swaying 5. Curve back like a "C", Halloween cat, Shrimp, Cannon ball 6. Baricity
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Lateral Decubitus (left/right) position
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1. Needs to be parallel to the edge of the bed 2. Legs flexed up to abdomen 3. Forehead flexed down toward knees
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Jack-knife position
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1. Chosen for ano-rectal surgery 2. CSF will not drip from hub of needle 3. Use hypobaric solution
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The midline approach for a spinal, the needle passes through what tissues in order from outermost to innermost.
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1. Skin 2. Sub Q 3. Supraspinous ligament 4. Interspinous ligament 5. Ligamentum flavum 6. Epidural space 7. Arachnoid mater
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The paramedian approach for a spinal, the needle passes through the same tissues as in the midline approach except....
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supraspinous and interspinous ligaments
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Paramedian approach is also known as...
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Taylor approach
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How long will it take for a block of tetracaine or marcaine to set up enough where you can check a level according to the text?
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5-10min
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Fluid test for CSF return.
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1. Clear 2. Free flow 3. Aspiration 4. Litmus paper 5. Urine dip stick 6. Temperature 7. Taste will be salty
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Analegesia
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Lack of pain
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Anesthesia
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Lack of feeling
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Successful motor block of lumbar is indicated by...
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The patients inability to raise their legs.
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When assessing sensation of spinal block and dermatones...
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The dermatone immediately caudad to the dermatone in which a sharp sensation is elicited is the dermatone representing the highest level of analgesia.
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Dermatone
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Is an area of skin that is mainly supplied by a single spinal nerve.
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How many cervical nerves?
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8
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How many thoracic nerves?
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12
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How many lumbar nerves?
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5
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How many sacral nerves?
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5
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C4 clavicle
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Chest surgery
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T4-T5 nipples
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upper abdominal surgery
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T6-T8 xiphoid
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intestinal surgery, appendectomy, gynecologic pelvic surgery, ureter and renal pelvic surgery
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T8 lower border of rib cage
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abdominal surgery
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T10 umbilicus
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transurethral resection, obstetric vaginal delivery, hip surgery
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L1 inguinal ligament
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transurethral resection, if no bladder distention, thigh surgery, lower limb amputation
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L2-L3 knee and below
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foot surgery
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S2-S5 perineal
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perineal surgery, hemorrhoidectomy, anal dilation
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Key dermatones and levels
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C1-C2 Oops! C3-5 keep the diaphragm alive T1-T4 cardioaccelerator T4 nipple line T6 xiphoid process T10 umbilicus S2-4 keep the penis off the floor
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Sympathetic block is how many dermatomes higher than the sensory block?
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2-6
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Motor block is how many dermatomes lower than the sensory block?
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2
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Plt count should be what for a spinal?
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>50,000 at a minimum prefer 100,000
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Heparin
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1. Reverse with FFp or protamine 2. IV discontinued 4 hrs prior to block 3. SQ can block 1hr prior to to dose 4. Do not dc cath until 4 hrs after heparin dc and obtain normal lab values.
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Lovenox
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1. No reversal 2. Stop 10 days prior to surgery 3. Post-op dc cath 2hrs prior or 10 hrs after the first dose.
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Coumadin
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1. Reverse with Vit K or FFP 2. Stop 7 days prior to surgery 3. Check PT INR=<1.5
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Plavix
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1. No reversal 2. Stop 5-10 days prior to surgery
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NSAIDS
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1. No reversal 2. May be safe for regional block 3. Ideal to stop 5 days prior to surgery
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ASA
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1. No reversal 2. Stop 7-10 days prior to surgery
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PDPH (post dural puncture headache)
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1. More frequent in women and younger patients 2. Highest incidence in OB patients 3. The earlier the onset the more severe it will be and harder to relieve the symptoms
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What is the hallmark sign of PDHP?
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Headache that is relieved immediately by lying flat and immediately severe when sitting up.
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Other signs of PDPH.
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1. N/V 2. Neck stiffness 3. Auditory and visual symptoms
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TX for PDPH
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1. 1L IV bolus with 500mg caffeine added to solution 2. Epidural blood patch
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What is the maximum number of blood patches that may be placed?
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2
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How much time should elapse between 1st and 2nd blood patch if a 2nd patch needed?
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24hrs
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What is the success rate for a blood patch in relieving PDPH?
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95%
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5 factors that increase the likelihood of PDPH
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1. Younger as compared to older patients 2. More in females as compared to males 3. Larger needle = bigger risk 4. Pregnant vs nonpregnant 5. Hx of multiple punctures
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Major factors associated with spinal cord injury in the maplractice claims study in the 1990's were...
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Blocks for chronic pain management and systemic anticoagulation in the presence of neuraxial block.
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In a comparison study of closed claim files 1980-1999 hematoma was the most common cause of neuraxial injuries, and the majority of cases were associated with....
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Intrinsic or Iatrogenic coagulopathy.
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What concentration of LA should be used for spinals?
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<5%
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What should you do if the patient experiences sustained parasthesia?
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STOP, reposition or pull out the needle and move to a different spot or determine if you should continue to attempt the block.
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Cauda equina syndrome
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Is characterized by bowel and bladder dysfunction together with evidence of injury to multiple nerve roots. Hyperbaric 5% lidocaine most common LA associated with syndrome.
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Causes of cauda equina syndrome
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1. Direct needle trauma 2. Spinal cord ischemia from neurotoxic drugs and chemicals. 3. Introduction of bacteria into the subarachnoid or epidural space. 4. Long term intrathecal catheter.
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Characteristics of Transient Neurologic Syndrome
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Pain radiating to the legs without sensory or motor deficits after the resolution of a spinal. Symptoms usually resolve within several days. Typically occurs in outpatient cases where hips or knees were flexed such as lithotomy which causes additional stretch on the nerve roots.
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Treatment of Transient Neurologic Syndrome
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Analgesia, IV narcs 2mg morphine or 50mcg fentanyl. If symptoms persist out of hospital motrin and moist heat.
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Spinal hematoma
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Needle or catheter trauma to epidural veins often causes minor bleeding in the spinal canal and is usually harmless.
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What is the incidence of spinal hematoma for epidurals?
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1:150,000
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What is the incidence of spinal hematoma for spinals?
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1:220,000
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Risk factors for spinal hematoma?
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1. bleeding disorders 2. anticoagulation 3. inserting and removing the needle for the block.
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What is the top priority to prevent permanent neurological sequelae from spinal hematomas?
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Rapid dx and intervention.
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Symptoms of spinal hematoma
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Sharp back and leg pain with a progression to numbness and motor weakness and/or sphincter dysfunction.
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What is the time period required for hematoma decompression in spinal hematomas?
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8-12hrs
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Meningitis and arachnoiditis
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Infection of the subarachnoid space can occur as a result of contamination of equipment or injected solutions and introduction of organisms from the skin.
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Symptoms of meningitis and arachnoiditis
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fever, severe h/a, ams, and neck stiffness.
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Most common causitive organisms of meningitis and arachnoiditis.
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1. strep pneum. 2. Hamemophilus influenza 3. nesseria meningitides 4. e. coli 5. listeria monocytogenes
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Delayed depression of ventilation by opioids is due to
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Cephalad spread of opioid in csf to respiratory centers on the surface of the medulla.
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What is the time frame for delayed depression of ventilation with opioids in spinal anesthesia?
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6-12hrs
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Delayed depression of ventilation is much more likely to occur when the opioid is injected where?
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Subarachnoid space
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Early depression of ventilation is more likely to occur when an opioid is injected where?
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Epidural space.
