NSG 539 PHARMACOLOGY OF NEURAXIAL LAS | MECHANISM
OF ACTION, DOSING & ADVERSE EFFECTS | EXAM PREP
2026/2027
1. Site of action of LAs in subarachnoid space: -Subarachnoid space: myelinated preganglionic
fibers of the spinal nerve roots
-also inhibit neural transmission in the superficial layer of the spinal cord
2. Site of action of LA in the epidural space: -diffuse through the dural cuff before they block the
nerve roots
-also leak through intervertebral foramen’paravertebral area
3. Factors that significantly affect spinal anesthesia spread: Controllable:
-Baricity of LA
-Patient position during block placement
-Dose
-Site of injection
Non-controllable:
-Volume of CSF
-Density of CSF
4. Factors that do not significantly affect spinal anesthesia spread: -Barbotage
-Increased intra-abdominal pressure (coughing, labor)
-Speed of injection
-Addition of a vasoconstrictor
-Weight
-Gender
5. Baricity: ratio of specific gravity of LA to patient CSF
6. Isobaric: Solutions that have the same density of CSF and have a baricity of 1.0000; resists
extensive spread
, from site of injection
7. Hyperbaric: solutions that are more dense than CSF Solutions; gravitates downwards
8. Hypobaric: solutions are less than CSF or float to the highest anatomic position possible
9. CSF specific gravity: 1.004-1.009
10. Hyperbaric additive: 10% dextrose (sp.gravity >1.009)
11. Hypobaric additive: sterile water (sp. gravity <1.004)
12. A patient receives a hyperbaric solution in the L4 interface and lays supine,
where will the solution move to?: slide down the lumbar lordosis and eventually pool in the
sacrum
and the thoracic kyphosis
13. A sitting patient receives a hypobaric solution. Where will the solution move
to?: brain (bad idea)
14. A patient receives a hypobaric solution and is placed supine. Where will the
solution move?: Lumbar region; won't go to cervical region because it first sinks into the thoracic
kyphosis
15. Order of nerve fibers blocked by LA: autonomic ’ sensory ’ motor
16. Sympathetic spinal blocks are how many dermatomes higher than sensory
blocks?: 2-6
17. Sensory spinal blocks are how many dermatomes higher than motor
blocks?: 2
18. A alpha fibers: -12-20µm
-Heavily myelinated
-Skeletal muscle (motor) and proprioception
-fast velocity
-blocked 4th
19. A beta fibers: -5-12µm
OF ACTION, DOSING & ADVERSE EFFECTS | EXAM PREP
2026/2027
1. Site of action of LAs in subarachnoid space: -Subarachnoid space: myelinated preganglionic
fibers of the spinal nerve roots
-also inhibit neural transmission in the superficial layer of the spinal cord
2. Site of action of LA in the epidural space: -diffuse through the dural cuff before they block the
nerve roots
-also leak through intervertebral foramen’paravertebral area
3. Factors that significantly affect spinal anesthesia spread: Controllable:
-Baricity of LA
-Patient position during block placement
-Dose
-Site of injection
Non-controllable:
-Volume of CSF
-Density of CSF
4. Factors that do not significantly affect spinal anesthesia spread: -Barbotage
-Increased intra-abdominal pressure (coughing, labor)
-Speed of injection
-Addition of a vasoconstrictor
-Weight
-Gender
5. Baricity: ratio of specific gravity of LA to patient CSF
6. Isobaric: Solutions that have the same density of CSF and have a baricity of 1.0000; resists
extensive spread
, from site of injection
7. Hyperbaric: solutions that are more dense than CSF Solutions; gravitates downwards
8. Hypobaric: solutions are less than CSF or float to the highest anatomic position possible
9. CSF specific gravity: 1.004-1.009
10. Hyperbaric additive: 10% dextrose (sp.gravity >1.009)
11. Hypobaric additive: sterile water (sp. gravity <1.004)
12. A patient receives a hyperbaric solution in the L4 interface and lays supine,
where will the solution move to?: slide down the lumbar lordosis and eventually pool in the
sacrum
and the thoracic kyphosis
13. A sitting patient receives a hypobaric solution. Where will the solution move
to?: brain (bad idea)
14. A patient receives a hypobaric solution and is placed supine. Where will the
solution move?: Lumbar region; won't go to cervical region because it first sinks into the thoracic
kyphosis
15. Order of nerve fibers blocked by LA: autonomic ’ sensory ’ motor
16. Sympathetic spinal blocks are how many dermatomes higher than sensory
blocks?: 2-6
17. Sensory spinal blocks are how many dermatomes higher than motor
blocks?: 2
18. A alpha fibers: -12-20µm
-Heavily myelinated
-Skeletal muscle (motor) and proprioception
-fast velocity
-blocked 4th
19. A beta fibers: -5-12µm
