central nervous system education

1. Central Neuroaxial Blockade

2. Introduction
• Anaesthesia that pertains to placing local
anaesthetics around the nerves of central
nervous system
• It includes
– Spinal anaesthesia or subarachnoid block
– Epidural
– Caudal blocks

3. History
• 1898 – first subarachnoid blockade in man was performed by Karl August
Bier using a cocaine solution
• Bier decided to experiment on himself and developed a postdural
puncture headache (PDPH)
• His assistant, Dr. Otto Hildebrandt, volunteered to have the procedure
performed.
• After injection of spinal cocaine into Hildebrandt, Bier conducted
experiments on the lower half of Hildebrandt's body. Bier described
needle pricks and cigar burns to the legs, incisions on the thighs, avulsion
of pubic hairs, strong blows with an iron hammer to the shins, and torsion
of the testicles.
• Hildebrandt reported minimal to no pain during the experiments;
however, afterward he suffered nausea, vomiting, PDPH, and bruising and
pain in his legs.
• Bier attributed the PDPH to loss of CSF and felt the use of small-gauge
needles would help prevent the headache.

4. History
• 1930 – 1950, spinal techniques were used
widely for anaesthesia
• The was declined in popularity
– Fear of toxicity
– Improvements of general anaesthesia

5. History
• 1901 – epidural anaesthesia was described by
Sicard and Cathelin
• Only became popular after World War II with
the introduction of amide local anaesthetic
agents and catheters that allowed
replenishment of the block
• Since 1960 – resurgence of these regional
techniques and now used widely

6. ANATOMY

7. Anatomy

8. Anatomy

9. Anatomy
• The vertebral column consists of
33 vertebrae:
– 7 cervical
– 12 thoracic
– 5 lumbar
– 5 sacral
– 4 coccygeal segments
• The vertebral column usually
contains three curves.
– The cervical and lumbar curves are
convex anteriorly,
– The thoracic curve is convex posteriorly.

10. Anatomy
• Five ligaments hold
the spinal column
together.
• Supraspinous
ligaments
• Interspinous ligaments
• Ligamentum flavum, or
yellow ligament
– connects the laminae
above and below
together.
• Posterior and anterior
longitudinal ligaments

11. Anatomy

12. Anatomy
• The three membranes that
protect the spinal cord are
–Dura mater
–Arachnoid mater
–Pia mater

13. Anatomy

14. Anatomy

15. Anatomy
• Spinal cord
– Ends at L1 in the adult
– Ends at L3 in the infant
– However, there are anatomical variations
that influence the level that the spinal
cord ends
– In the adult, it is generally safe to
place a spinal needle below L2,
unless there is a known anatomical
variation.
• Needle trauma to the cauda equina is
unlikely. Individual nerves of the cauda
equina are in a fluid environment and
not likely to be pierced by a needle.

16. Anatomy
• Subarachnoid space
– Contains cerebral spinal
fluid (CSF), spinal cord,
and conus medullaris
– In direct communication
with the brainstem
through the foramen
magnum and ends with
the conus medullaris at
the sacral hiatus

17. Anatomy
• Epidural space
– dural sac, the
spinal nerve
roots, the
extradural
venous plexus,
spinal arteries,
lymphatics
and fat

18. Anatomy
• Epidural space
– widest posteriorly
and at this point is
occasionally divided
by a fold of dura
mater into two or
three compartments
that do not always
communicate with
each other.
– The consequence of
this infrequent
abnormality may be
patchy analgesia after
an epidural
anaesthetic.

19. Anatomy
• Epidural space
– Prolongations of the dura surround the nerve
roots (dural cuffs) and fuse with them as they
traverse the intervertebral foraminae.

20. Anatomy
• Cerebrospinal fluid
– Clear fluid that fills the subarachnoid space.
– The total volume in the adult varies between 100-150 ml.
– CSF volume within the subarachnoid space is approximately 25-35 ml.
– Cerebral spinal fluid is continually produced at a rate of 450 ml per day
– Produced by the choroid plexuses, which are located in the lateral.
3rd, and 4th ventricles.
– The specific gravity of CSF ranges from 1.00028-1.001, playing a crucial
role in choosing the baracity of local anesthetic solution.
– CSF volume
• plays a role in patient to patient variability in relation to block height and
motor/sensory regression
• body weight is the only patient measurement that coincides with CSF volume.
This becomes important when administering neuraxial blockade to the obese
and during pregnancy. The amount of CSF is usually less

21. Surface Anatomy
• Spinal processes are
generally palpable and
define
• midline.
• Identifying the gluteal
crease may help identify
midline. This will not be
accurate if the patient has
scoliosis or other
deformities of the spine.

22. Surface anatomy
• In lumbar area, spinous
processes are almost
horizontal with flexion.
Needle placement will be in
a horizontal or slightly
cephalad direction.
• In the thoracic area, the
spinous processes are
slanted in a caudad
direction. With flexion,
needle need to be directed
more cephalad

23. Anatomical
landmark

24. Anatomical landmark
• Helpful landmarks for
lumbar epidural or
subarachnoid block
– A line drawn from the
top of the iliac crest is
known as “Tuffier’s”
line.
– This line generally
crosses the body of L4
or the L4-L5 interspace

25. Anatomy
• Spinal anesthetic - midline
approach
– Skin
– subcutaneous fat
– supraspinous ligament
– interspinous ligament
– ligamentum flavum
– dura mater
– subdural space
– arachnoid mater
– subarachnoid space

26. Anatomy
• Spinal anaesthetic -
paramedian approach
• Skin
• subcutaneous fat
• ligamentum flavum
• dura mater
• subdural space
• arachnoid mater
• subarachnoid space

27. Indications of neuraxial blockade
• Labour analgesia
• Caesarian section
• Orthopaedic procedures
• Perioperative analgesia
• Chronic pain

28. PHARMACOLOGY OF COMMONLY
USED AGENTS

29. Local anaesthetics
• Blokcs sodium channels of the nerve,
preventing depolarisation and conduction

30. Local anaesthetics

31. Local anaesthetics
• Baricity
• Hypobaric solutions
– less dense than CSF
– tend to rise against gravity
– made by adding distilled sterile water
– Patient positioning is important
• Isobaric solutions
– as dense as CSF
– tend to remain at the level at which they are injected
• Hyperbaric solutions
– more dense than CSF
– tend to follow gravity after injection
– Made by adding dextrose or glucose
– Patient positing is important

32. SPINAL ANAESTHESIA

33. Spinal anaesthesia
• Also known as subarachnoid block
• It occurs as a result of an intrathecal injection
of local anaesthetics

34. Indications
• Surgical procedures to the lower body

35. Mechanism of action
• Results in a rapid onset of block, usually within 3 minutes.
• Acts mainly at spinal nerve roots, although some effect is
possible at the cord itself.
• Subarachnoid block always blocks down to the sacral levels
and more reliably affects both sides of the body
• If the patient is seated
– Becomes a saddle block
– the local anaesthetic does not spread as far up the spinal canal,
extending no higher than the upper lumbar levels
– With this level of block it is possible to undertake pelvic
operations, but not intra-abdominal operations, and much of
the cardiovascular disturbance caused by blockade of the
thoracic sympathetic outflow is avoided.

36. Mechanism of action
• In a supine position
– local anaesthetic pools at about the level of the
third thoracic vertebra, the lowest point of the
thoracic kyphosis, providing reliable anaesthesia
for most lower abdominal operations.

38. Distribution of LA
• The three most important factors:
– Baricity of the local anesthetic solution
– Position of the patient during and just after
injection
– Dose of the anesthetic injected

39. Spinal needles

40. Spinal needles

41. Technique
• Sitting or lying on their side
• Back flexion opens the intervertebral spaces.
• Aseptic technique
• Aim to identify the L3/4, L4/5 or L5/S1 interspace (use Tuffier’s
line).
• The chosen interspace is infiltrated with local anaesthetic. The
spinal needle is inserted in the midline, aiming slightly cranially.
• Resistance increases as the ligamentum flavum is entered and when
the dura is encountered, with a sudden "give" as the dura is
pierced.
• Correct placement of the needle is confirmed by cerebrospinal fluid
at the hub.
• The paramedian approach requires less back flexion (may be limited
in certain patients).

42. Technique

43. EPIDURAL

44. Indications
• abdominal, pelvic and lower limb surgery
• analgesia to the lower limbs, abdomen and
thorax
– postoperative pain
– pain of labour
– treatment of chronic and terminal pain

45. Mechanism of action
• Slower in onset (10-20min)
• LA injected into the epidural space spread in cranial and caudal directions
from the level at which they are administered
• The drug bathes the nerve roots as they pass through the anterolateral
epidural space, but roots above and below the limit of spread of local
anaesthetic remain unaffected. This gives an epidural local anaesthetic
block a top and a bottom level of effect, with the site of injection
somewhere in between.

46. Mechanism of action
• There may be preferential spread of local
anaesthetic to one side of the spinal canal,
and when this occurs the level and intensity of
blockade on each side of the body can be
different.
• Occasionally single nerve roots are missed
altogether resulting in a patchy block.

47. Tuohy needle

48. Epidural set

49. Epidural Anaesthesia Technique

50. Epidural Anaesthesia Technique
• Midline or paramedian
• Must stop just before piercing the dura
• Loss of resistance technique
– Saline or air
– Needle with stylet is advanced until interspinous ligaments
– Stylet removed, syringe filled with air or saline is attached
to the hub of the needle

51. Epidural Anaesthesia Technique
• The needle is slowly advanced , milimeter by
milimeter with continuous attempts at injection
• As the tip of the needle just enters the epidural
space, there is sudden loss of resistance and
injection is easy
• Catheter is then inserted

52. COMBINED SPINAL EPIDURAL

53. Indications
• suitable whenever a rapid onset of analgesia is
required but the period of analgesia required
exceeds that of a single spinal injection
• this technique also allows for post operative
pain relief via epidural

55. CONTRAINDICATIONS

56. Contraindications
• Absolute
– Infection at the site of injection
– Patient refusal
– Coagulopathy or other bleeding diasthesis
– Severe hypovolaemia
– Increase intracranial pressure
– Severe aortic stenosis
– Severe mitral stenosis

57. Contraindications
• Relative
– Sepsis
– Uncooperative patient
– Preexisting neurological deficits
– Demyelinating lesions
– Stenotic valvular heart lesions
– Left ventricular outflow obstruction
– Severe spinal deformity

58. COMPLICATIONS

59. With excessive responses to
appropriately placed drug
• High neural blockade
• Cardiac arrest during spinal anaesthesia
• Urinary retention

60. With needle or catheter insertion
• Inadequate anaesthesia or analgesia
• Intravascular injection
• Total spinal anaesthesia
• Subdural injection
• Backache
• Postdural puncture headache
• Neurological injury
• Meningitis and arachnoiditis
• Epidural abscess
• Sheering of an epidural catheter

61. With drug toxicity
• Systemic toxicity
• Transient neurological symptoms
• Lidocaine neurotoxicity

62. THANK YOU