Neuraxial Anesthesia

Question 1

How many of each kind of vertebrae are there?

Answer 1

• Cervical (7)
• Thoracic (12)
• Lumbar (5)
• Sacral (5) fused
• Coccygeal (4) fused

Question 2

Where are the high curves and the low curves in the spine?

Answer 2

• High
  
  • C5
  • L3
• Low
  
  • T5
  • S2

Question 3

What are the 5 ligaments of the spine?

Where are they located?

What is their purpose?

Answer 3

• Supraspinous: C5- sacrum
• Interspinous: entire length
• Ligamentum flavum
  
  • foramen magnum to the sacral hiatus
  • tough wedge-shaped ligament composed of elastin
  • thickest in the midline (3-5 mm at L3)
  • called “yellow ligament”
• Posterior longitudinal ligament: posterior surface of vertebral bodies (C2- sacrum)
• Anterior longitudinal ligament: anterior surface of vertebral bodies (C1-sacrum)
• **Purpose of all ligaments is to stabilize the spine

Question 4

What are the spinal meninges?

Answer 4

• Protective membranes that are continuous with the cranial meninges
• Dura Mater- the thick outer layer
  
  • begins at foramen magnum and ends caudally at the S2/Dural sac
• Arachnoid mater- thinner and pressed up against the dura
  
  • principal physiologic barrier for drugs moving between the epidural space and the spinal cord
  • ends at S2- delicate and nonvascular
• Pia- very thin and right against the spinal cord
  
  • separated from arachnoid mater by the CSF in the subarachnoid space

Question 5

Where does the spinal cord start and finish?

How many nerves does it have?

Answer 5

• Foramen magnum to conus medullaris
  
  • terminates anywhere from T12 to L2
  • Usually L1
  • sometimes L3 in peds
• 31 pairs of spinal nervs, each with anterior and posterior root

Question 6

How do you remember what the anterior and posterior spinal nerve roots do?

Answer 6

SAD DAVE

Question 7

What is a spinal cord segment?

What is a dermatome?

Answer 7

• Segment- the portion of the spinal cord that gives rise to all the rootlets of a single spinal nerve
• Dermatome- skin area innerved by a spinal nerve and its segment

Question 8

What are the noteworthy dermatomes?

Answer 8

• C6- thumb
• C7- 2nd and 3rd finger
• C8- 4th and 5th fingers
  
  • Phrenic nerve innervating diaphragm
• T4- nipple
  
  • cardiac accelerators T1-T4
• T6- xiphoid
• T8- last rib
• T10- umbilicus

Question 9

CSF

Volume

Rate produced

specific gravity

Answer 9

• 150 ml in the subarachnoid space
• volume replaced 3-4x/day
• 21 ml produced per hour by choroid plexus
• Specific gravity: 1.004- 1.008

Question 10

How is blood supplied to the spinal cord?

Answer 10

• One anterior spinal artery and two posterior spinal arteries
  
  • these arteries are from branches off the aorta
  • the posterior arteries have better continuity of blood supply than anterior

Question 11

What are the physiological differences of a Sub-Arachnoid Block (SAB) and an epidural?

Answer 11

• SAB- LA is injected into CSF to directly bathe the nerve root; rapid onset of block
  
  • autonomic blockade 2-6 levels above sensory blockade; motor blockade 2 below sensory
• Epidural anesthesia- LA is injected into epidural or caudal space and diffuses through the dural cuff before bathing the nerve root; slower onset
  
  • approx 5 minute onset
  • autonomic blockade same level as sensory blockade; motor blockade 2-4 levels below sensory blockade
  • not as dense of a block
  • good option if pt will not tolerate the large drop in autonomic response of the SAB

Question 12

What is the goal of a neural blockade?

Answer 12

• Goal: blockade of nociceptive impulses
  
  • it will block all impulses regardless of fiber type
    
    • autonomic
    • sensory
    • proprioception
    • motor

Question 13

Which nerve type are highly sensitive to blockade?

intermediate?

resistant to LA blockade?

Answer 13

• Autonomic nerves are highly sensitive with rapid onset
• Sensory nerves have intermediate sensitivity
• Motor nerves are more resistant to LA and have slower onset

Question 14

What are the advantages of neuraxial anesthesia?

(7)

Answer 14

• decreased incidence of DVT, cardiac morbidity and death
• decreased lower extremity vascular graft occlusion, due to vasodilation which increases tissue blood flow below level of blockade
• decreased incidence of PNA
• decreased stress response
• avoids airway manipulation
• decreased incidence of PONV
• intra and postoperative pain relief

Question 15

What are the disadvantages of neuraxial anesthesia?

(4)

Answer 15

• hypotension
• delayed case start
• failure rate depends on experience
• not a benign anesthetic

Question 16

Things to consider when choosing a neuraxial technique: (7)

Answer 16

• Anatomy
• Age: younger ppl are easier because the spaces between vertebrae get smaller with age
• pregnancy
• pathophysiology/comorbidities
• sensory level required vs adverse physiological effects
• length of procedure: a spinal gives about 2 hours, can be prolonged a bit with vasoconstrictor and decadron added
• post-op analgesia needs

Question 17

What are contraindications for neuraxial anesthesia?

(13)

Answer 17

• patient refusal (the only absolute contraindication)
• infection at injection site
• bacteremia
• septicemia
• increased ICP
• clotting defects/anticoagulant therapy
• severe hemorrhage or hypovolemia
• CNS disease/meningitis
• hysteria/inability to remain still for block placement
• valvular lesions with fixed stroke volume
  
  • severe AS/MS and hypertrophic cardiomyopathy
• difficult airway
• full stomach
• peripheral neuropathies