sub arachnoid block in detail

1. MODERATOR ---- Dr. Saba Ahad
CConsultant department of anaesthesiology & critical care medicine
Presented by: Dr. Mohsin Farooq

2. Spinal anesthesia is also called as spinal
block or subarachnoid block (sab). SAB
is a regional anesthesia involving
injection of a local anesthetics into the
subarachnoid space.

3. 3
HAVE A BASIC UNDERSTANDING OF
• Anatomic structure of spine and
vertebra
•Anatomic structure of spinal cord
•Blood supply of spinal cord
•Features of neuraxial blockade
•Indications/ contraindications
•Patient evaluation and preparation
•Techniques
•Local anesthetics and factors effecting
spread
•complications

4. BRIEF HISTORY OF SPINAL ANAESTHESIA
 CSF DISCOVERED ---- by Domenico Catugno 1764
 CSF CIRCULATION---- by F . Magendie 1825
 FIRST SPINAL ANALGESIA--- by J Leonard Corning
1885
 FIRST PLANNED SPINAL ANAESTHESIA--- by
August Bier in 1891
 The epidural space was first described by Corning in
1901, and Fidel Pages first used epidural anaesthesia in
humans in 1921.

5. ANATOMY
Spine consists of 33 vetrtebrae
•cervical vertebrae (7)
•thoracic vertebrae (12)
•lumbar vertebrae (5)
•sacral vertebrae (5)
•coccygeal vertebrae (4 )

6. LUMBAR VERTEBRA

7. SPINAL CORD
ADULTS– approx L1(30%T12;10%L3)
CHILDREN--approx L3

8. ANATOMY
The spinal cord usually ends at the level of L1 in adults (at
T12 in 30% population and L3 in 10%) and L3 in
children.
Dural puncture above these levels is associated with a slight
risk of damaging the spinal cord and is best avoided.
Spinal cord give rise to 31 pairs of spinal nerves each
composed of anterior motor & posterior sensory nerve
roots.
Spinal nerves that extend beyond the end of spinal cord to
their exit site are called cauda equina
Extension of pia mater, filum terminale penetrates dura and
attaches terminal end of spinal cord to coccyx.

9. ARTERIAL SUPPLY OF SPINAL CORD
 Ant 2/3 of cord is supplied
by single ant.spinal artery
 Post 1/3 by pair of post
spinal arteries
 Additional :intercoastal
arteries thoracolumbar,one
of these is large called
artery of adamkiewiecz
(arteria redicualaris
magna) its injury can lead
to ant spinal artery
syndrome

10. DERMATOMES
A dermatome is an area of skin innervated
by a single spinal nerve and corresponding
cord segment.
 T4 – nipples
 T6 – xiphoid
 T10 – umblicus
 T12, L1 – inguinal
ligament , crest of ileum
 S2-S4 – perineum

11. Dermatomal Levels of Spinal Anesthesia
for Common Surgical Procedures
Procedure Dermatomal Level
Upper abdominal surgery(
appendicectomy)
LSCS
T4
Intestinal, gynecologic, and urologic
surgery
T6
TURP, Vaginal delivery of a fetus, and
hip surgery
T10
Thigh surgery and lower leg
amputations
L1
Foot and ankle surgery L2
Perineal and anal surgery S2 to S5 (saddle block)

12. Spinous processes are palpable over the spine and help to
define the midline
Landmarks:
• First palpable spinous process is C2
• Most prominent spinous process is C7
•Inferior tip of scapula T7
•Superior aspect of both iliac crest –
body of L4& L3L4 space
( TUFFIER’S LINE)
•Posterior superior iliac spine S2
•Sacral cornu S4S5

13. CONTRAINDICATIONS
ABSOLUTE
1. Patients refusal.
2. Coagulopathy.
3. Infection at site of
injection
4. Severe hypovolemia
5. Raised ICT
6. Allergy to drugs
7. Shock
8. severe AS or MS
RELATIVE
1. Uncooperative pt
2. Preexisting neurological
deficits(MS)
3. Demyelinating lesions
4. Severe spinal deformity
5. Infection at site remote
from injection
6. Sepsis
7. left ventricular outflow obs

14. BEFOREHAND:
 Proper history, examination & informed written
consent of patient.
 Remove your jewellery/watches/thorough scrubing,
sterile gown and masks.
 I.V access/fluids bolus if needed
 Drapes and antiseptic solution should be ready
 Emergency drugs /equipment/check anesthesia
machine.
 Ensuring that operating table tilts.
 Sedation if needed
 Monitoring
NIBP/SPO2/ECG
• EQUIPMENT FOR RESUSCITATION should be
readily available.

15. POSITION
LATERAL DECUBITUS: Most commonly used
Patient lie on their side at the edge of couch with their
knees flexed and pulled high against abdomen or chest
and neck flexed.

16. SITTING:
Patient should sit on the table with knees resting on the edge,
legs hanging over the side and feet supported by a stool below
Or
Patients sit with their elbows resting on their thighs or bed side
table or hugs a pillow with neck flexed.
Commonly used :
For saddle block anesthesia
Obese patients,
Pregnant patients,
Patients with abnormal spinal
curvatures

17. Jackknife (buie’s) position
.
 This position is used
for anorectal
procedures using
hypobaric anaesthetic
solutions.
 Patient should be in
prone position with OT
table flexed under his
flanks, just above the
iliac crests
.

18. 1.Midline approach
2.Paramedian approach
3.Lumbosacral or Taylors approach

19. PREPARATION:
•Hands and lower forearms scrubbed for at
least 3 minutes
•Sterile gloves,gown and mask put on.
•A large area of L-S spine should be painted
using antiseptic solution( chlorhexidine acc.
to ASoRA)
•Excess antiseptics removed after waiting for
some time for antiseptic to act
•Selection of space –using tuffier’s line as
landmark
•Raise a skin wheal with 2ml of 2% lignocaine
solution after negative aspiration for blood

20. MIDLINE APPROACH
After selecting desired interspace {L3-L4;L4-L5) by
palpating the depression between the spinous process
of the vertebra above and below the level in midline
infiltrate with local anesthetics should be kept parallel
to the longitudinal axis of the spine to avoid pain on
insertion.
Insert needle in midline with slight cephalad angulation
(10-15 degree). The subcutaneous tissue gives feeling
of little resistance to the needle, after that needle will
enter the supraspinous and interspinous ligaments.

21. As the needle meets the ligamentum flavam an increase
in resistance is encountered and on piercing it, loss of
resistance can be felt .The needle is advanced through
the epidural space and penetrates the dura (2nd
resistance loss “Pop”) and subarachnoid membrane.
Once needle is correctly placed in space
stabilize the spinal needle and attach the syringe by
grasping the hub of spinal needle with thumb and index
finger while propping the remaining fingers against the
patient’s back to provide support (bromage grip)
CSF is aspirated & LA injected <0.5ml/sec. After
completing CSF is again aspirated to confirm needle tip
remained in SAS while drug was deposited .

22. Layers traversed by the spinal
needle (posterior to anterior)
Skin
Subcutaneous tissue
Supraspinous ligament
Interspinous ligament
Ligamentum flavum
Epidural space
Duramater
Sub dural space
Arachnoidmater into the
Subarachnoid space

23. Problems during SAB
 If no CSF then either -needle orifice is blocked by
nerve root Or needle not in the space completely--
---rotate needle 90 degree or advance 1-2 mm
 If bone encountered------- at shallow depth
needle walking up…sup.spinous process> redirect
caudad & if at greater depth needle walking
down inf spinous process redirect cephalad.
 While redirecting -----withdraw tip into the
subcutaneous tissue.

24. PARAMEDIAN APPROACH:
 Useful when there is inability to flex the spine or
heavy calcified interspinous ligament, severe
arthritis, kyphoscoliosis, prior spine surgery
 Needle is inserted 1cm lateral to the spinous
process forming the lower border of desired
interspace angling 45◦ cephalad with 10◦ medial
angulation.
 The first resistance encountered is ligamentum
flavum.

25. TAYLOR’S APPROACH
(LUMBOSACRAL)
 Paramedian approach at L5-S1{Largest
interlaminar space}.
 Needle is inserted 1cm medial & 1cm inferior
to posterior superior iliac spine.
 Used when other approaches unfeasible and in
cases of spine fusion, arthritic spine,

26. SPINAL NEEDLES:
Three parts
 Hub
 Cannula
 Stylet
 Point of the cannula is beveled or pencil
pointed
 Outer diameter determine the gauge.
 Sized 22-29G.
 Length: 3.5 to 4 inches

27. PENCIL POINT TIP(with side
apertures)
BEVEL POINT TIP ( with cutting
edges)
Whitacre, Eldor, Marx ,Sprotte QUIINKE, Greene,Atraucan
Requires more force to insert, provide
better tactile “feel”
Requires less force to inset
Do not deflect from intended path. Deflect from the path.
Less chance of PDPH More chance of PDPH
Spinal needles are Classified on the design of
their tips :

28. Spinal needles
Beveled tips with cutting
edges
Pencil tip with side apertures

29. Drug preparation Perineum,
lower limbs
(mg) dose
Lower
abdomen
(mg)dose
Upper
abdomen
(mg)dose
Duration
(min)
procaine 10% solution 75 125 200 45
tetracaine 1% solution
in 10%
glucose
4-8 10-12 10-16 90-120
lidocaine 5% in 7.5%
glucose
25-50 50-75 75-100 60-75
bupivacaine 0.75% in
8.25%
dextrose
4-10 12-14 12-18 90-120
0.5% in 8%
dextrose
7.5 to 12.5 12.5-17.5 17.5-25 90-120
ropivacaine 0.2-1%
solution
8-12 12-16 16-18 90-120
Spinal anaesthetic agents

30. Adjuvants used
Opioids
 Fentanyl – 12.5 mcg
 Sufentanyl – 2.5 – 5
mcg
 Diamorphine – 0.3 mg
 Morphine – 0.1 – 0.2
mg
ADRENERGIC
AGONIST
 Phenylephrine(2-5mg)
 Epinephrine (.2-.3mg)
 Clonidine (75-150mg)

31. SEQUENCE & ONSET OF BLOCK
 Onset of block within few minutes irrespective of LA.
 Time to reach peak block ht. differs with LA.
 (bupivacaine & tetracaine >20min.)
 Sequence of onset depends on conc. of LA achieved,
duration of contact, size & myelination of nerve fibers.
CLINICALLY OBSERVED SEQUENCE
1. Sympathetic nervous system fibers (B fibers: vasodilation,
skin temp ↑)
2. Temperature & pain conduction (A delta& C fibers)
3. Proprioception & touch (Aγ & Aβ fibers)
4. Motor function (A alpha & β fibers)

32. DIFFERENTIAL NERVE BLOCK:
Occurs with both neuraxial & peripheral nerve block ;
Manifests as spatial separation in modalities blocked
in central neuraxial block.
 Sympathetic block extends 2 or more dermatomes
higher than sensory block , which in turn extends 2
dermatomes higher than motor block.
 In peripheral nerve block it is temporal phenomenon
sympathetic occurring first followed by sensory than
motor blockade.

33. TESTING THE LEVELS OF BLOCK
 Sympathetic block
 Dilatation of skin vessels
 Changes in the skin
temperature
 Hypotension
 Sweating
 Sensory block
 Pin prick using sterile
needle
 Loss of touch

34. Motor block
Modified Bromage scale of onset of motor
block

35. PHYSIOLOGICAL EFFECTS OF NEUROAXIAL BLOCK
CARDIOVASCULAR EFFECTS:
HYPOTENSION{30-40%}
 Due to blockade of sympathetic efferents(T5 –L1) ------
Venodilatation (↓preload)  pooling of blood
↓ VR > ↓ CO
Ateriolardilataion(↓afterload)  ↓ PVR
 Risk factors:
Age>40yrs
ACE inhibitor/ARB
Hypovolemia
Obesity
Concurrent GA

36. BRADYCARDIA (13%)
Blockade of sympathetic
cardioaccelerator fibers from T1-T4
segment.
Risk factors :
Block height
Age <50
Beta blockers

37.  Even with high thoracic levels, tidal volume is unchanged.
 A small decrease in vital capacity due to paralysis of abdominal
muscles necessary for forced exhalation & not due to decrease in
phrenic nerve or diaphragmatic function.
 Effective coughing & clearing of secretions may get affected with
higher levels of block.
• Rare respiratory arrest associated with spinal anaesthesia due to
hypoperfusion of respiratory centers in brain stem.
Patients with high block complain of dyspnoea despite
normal MV due to inability to feel chest wall motion.
Pulmonary effects:

38. Gastrointestinal function:
 Nausea and vomiting in upto 20% patients due to
gastrointestinal hyperperistalsis caused by unopposed
parasympathetic(vagal) activity.
 Vagal tone dominance results in small contracted gut
with active peristalsis & can provide excellent operative
conditions for some laproscopic procedures when used
as an adjunct to GA.
 Hepatic blood flow will ↓ with decrease in mean
arterial pressure.

39. Renal function:
 Renal function has a wide physiological reserve. ↓
in renal blood flow is of little physiological
importance.
 Neuraxial blocks are a frequent cause of urinary
retention as it effectively block sympathetic &
parasympathetic control of bladder.

40. ENDOCRINE & METABOLIC
 Inhibits metabolic & endocrine changes associated
with stress.
 Due to blockade of afferent sensory response from
surgical site.

41. Drug Factors Patients Factors Procedure Factors
Baricity of drug Age Needle position
Drug dosage CSF volume Speed of injection
Conc of drug injected Intraabdominal
pressure(obesity,pregnancy
Addition of vasoconstrictor
Curvature of spine Patient position
Fluid currents
 .
Factors Affecting the Level of BLOCK
height Spinal Anesthesia

42. Baricity
 Density of a solution in
relation to density of CSF at
370C
 Density of CSF is 1.0003 to
1.0005 at 370C
 Hypobaric solutions : raise
against gravity
 Isobaric solutions : tend to
remain in the same sight
where they are injected
 Hyperbaric solutions : tend to
follow gravity
ISOBARIC SOLUTIONS
Densities between
0.9998 and 1.0008
• Solutions are mixed
with physiological
saline
• Solutions with out
added glucose
• Bupivacaine,
ropivacaine,
levobupivacaine
• Spread not influenced
by position

43. .
HYPOBARIC SOLUTIONS HYPERBARIC SOLUTIONS
• Baricity less than
0.9998 at 370C
• Prepared by diluting
with distilled water
• Solutions at 370c with
baricity greater than
1.0008
• Made by addition of 5-
8% dextrose.

44. AGE
Spinal space become smaller with  age - distribution greater.
OBESITY/ PREGNANCY
• Increase intra-abdominal pressure
• Decrease subarachnoid space
SPINAL CURVATURE
• Abnormal curvature have an effect on technical aspects
Changes the contour of Subarachnoid space
 AMOUNT OF DRUG
• Increase amount- increase Duration
 EFFECT OF TEMPERATURE
• Decrease Temperature- increase Baricity

45. Problems withthe Block
If after 10 minutes the patient still has full power in the legs and
normal sensation, then the block has failed probably because
the injection was not intrathecal. Try again.
The block is one-sided or is not high enough on one side. lie the
patient on the side that is inadequately blocked for a few
minutes and adjust the table so that the patient is slightly "head
down".
SAB not high enough. tilt the patient head down while they are
supine (lying on the back), so that the solution can run up the
lumbar curvature. Flatten the lumbar curvature by raising the
patient's knees.
Block too high. The patient may complain of difficulty in
breathing or of tingling in the arms or hands. Do not tilt the
table "head up".

46. Continuous Spinal Anesthesia
Inserting a catheter into the subarachnoid space
increases the utility of spinal anesthesia by
permitting continuous or repeated drug delivery in
order to expand the level or duration of spinal
block , dural puncture is done with an epidural
needle. After that subarachnoid placement of the
needle and ascertaining free flow of csf ,the
catheter is threaded 2-3 cm in to the SAS .The
catheter should never be pulled back in to the needle shaft
because of the risk of shearing the catheter off into the
subarachnonid space
 If the catheter needs to be removed both needle
and catheter should be removed as a unit. 18 G
epidural needle &20 G epidural catheter are used

47. Combined spinal-epidural anesthesia
 CSE is useful technique by which a spinal block and
epidural catheter are placed simultaneously.
 Benefit: rapid onset,dense block
 This technique is done with special epidural needle
having separate lumen to accommodate spinal needle,
first a epidural needle is placed in epidural sace, and
then spinal needle is introduced through epidural needle
into SAS and desired drug is injected and spinal needle
removed and then epidural catheter is placed into
epidural space.

48. COMPLICATIONS/SIDE EFFECTS OF NEURAXIAL
ANESTHESIA
 Hypotension
 Postdural Puncture Headache (25%)
 High Spinal Anesthesia
 Total spinal anaesthesia
 Cardiac arrest
 Neurological complications (peripheral neuropathy,
TNS,CES)
 Arachnoiditis / Meningitis
 Spinal / Epidural Hematoma Formation
 Epidural Abscess
 Backache
 Hearing loss
 Urinary retension
 Pruritus
 shivering
 Systemic toxicity

49. HIGH NEURAL BLOCKADE AND TOTAL SPINAL ANAESTHESIA
Can occur both with spinal and epidural
Admins . Of an excessive dose, failure to reduce doses in
selected pts (elderly, pregnant, obese, very short) or
unusual sensitivity or spread of LA maybe responsible
Presents with dyspnea, numbness in upper extremities,
severe hypotension, bradycardia and respiratory
insufficiency and even apnea
Total spinal can occur following attempted epidural/caudal
anesthesia if there is inadvertent intrathecal injection
involving cranial neves.
TREATMENT---vasopressors, atropine ,fluids, oxygen
,assisted ventilation and even intubation and mechanical
ventilation may be needed

51. TRANSIENT NEUROLOGICAL SYMPTOMS AND CAUDA
EQUINA SYNDROME
 TNS or transient radicular irritation refers to pain
,dysesthesia or both in the legs or buttocks after spinal
anesthesia, resolving spontaneously within several
days
 Most common with hyperbaric lidocaine and after
surgery in lithotomy position
 CES characterized by bowel and bladder dysfunction
together with evidence of multiple nerve root injury,
assoc with use of continous spinal catheters and 5%
lidocaine

52. NEURAXIAL BLOCKADE IN SETTING OF ANTICOAGULANTS AND
ANTIPLATELET AGENTS---AMERICAN SOCIETY FOR REGIONAL
ANESTHESIA RECOMMENDATIONS
 Pts taking NSAIDS or receiving SC unfractioned heparin for DVT
prophylaxsis are not viewed as being at increased risk of spinal
hematoma
 DISCONTINUE---ticlopidine 2 weeks, clopidogrel for 1 week
,abciximab 24 to 48 hrs, eptifibate and tirofiban 4 to 8 hrs before
performing central neuraxial block.
 Pt who are fully anticoagulated or who are receiving thrombolytic
or fibrinolytic theraphy should not receive central neuraxial block
except in very unusual circumstances where other options are not
viable.
 Patients receiving IV heparin, should be delayed for 1hour after CNB
 Delay atleast 10 -12 hrs after last dose of LMWH
 Post op t/t with LMWH delay 12hrs after compl of surgery
 Removal of epi ,spi catheters should take place 10—12hrs after last dose
with subs dosing delay for atleast 2hrs.

53. Advantage of spinal over general
anaesthesia
 Less chance of deep vein thrombosis
 Less chances of PONV
 Early ambulation
 Less bleeding
 Better post operative pain control
 Decreased stress response
 Less respiratory and cardiovascular complications

54. .