5.5 Caudal Block

Question 1

What are your analgesic options for a child who is booked for hypospadias surgery?

Answer 1

Multimodal analgesia (WHO ladder)

• Simple analgesics
• NSAIDS
• Opioids—oral/IV
• Wound infiltration
• Nerve blocks—dorsal penile block/caudal block

Question 2

What is the nerve supply of the scrotum and penis?

Answer 2

Scrotum
* Anterior 1/3—ilioinguinal nerve (L1)

• Posterior 2/3—perineal nerve (S2)
• Lateral—posterior cutaneous nerve of thigh (S3)

Penis
* Dorsal nerve of penis (S2,3,4)

• Ilioinguinal nerve (L1)

Question 3

What are the indications of caudal block?

Answer 3

It is the commonest regional technique in children and the first means of
administering local anaesthetic in the epidural space dating back as early
as 1901.

1. Acute pain
2. Chronic pain

3.

Question 4

Acute pain

Answer 4

• Surgical:
  To cover area innervated by lower lumbar and sacral roots.

In younger children, the caudal block effectively covers T10-S5,

although only sacral roots are blocked in older children and adults.

Caudal anaesthesia is also recommended for upper abdominal surgery,
but higher doses are needed to attain a high block

° Elective:
anorectal,
genitourinary procedures—
inguinal hernia, hypospadias, orchidopexy, circumcision

° Emergency:
testicular torsion, strangulated hernia

2. • Nonsurgical:
     To provide sympathetic block in vascular insufficiency of
     lower extremities secondary to vasospastic disease,
     unrelieved perineal pain in labour (historical)

Question 5

2. Chronic pain

Answer 5

• Complex regional pain syndromes (CRPS)
• Lumbar radiculopathy secondary to herniated discs and spinal stenosis
• Backache with sciatica after failed conservative or surgical treatment
• Coccydynia
• Diabetic polyneuropathy

Question 6

Cancer pain

Answer 6

• Primary genital, pelvic, and rectal malignancy
• Bony metastasis to the pelvis

Question 7

What are the advantages of caudal over lumbar epidural analgesia?

Answer 7

1. Onset:

The onset of perineal anaesthesia and muscle relaxation
after caudal anaesthesia is rapid compared to epidural.

2. Extent:
   It is good for ankle and foot surgery
   as it covers S1 reliably,
   whereas the lumbar epidural
   fails to block S1 in 10%–20% of patients.
3. Indications:
   Can be performed where lumbar epidural cannot be done,
   especially after spinal surgeries.
4. Complications:
   The incidence of postdural puncture headache (PDPH) is
   negligible.
5. Caudal epidural uses a larger volume of local anaesthetic compared to the
   lumbar epidural, and there is a similar failure rate due to anatomical variation.

Question 8

Describe the anatomy relevant to caudal anaesthesia.

Answer 8

1. Sacrum (Latin for sacred)
   is believed to have played a key part in ancient
   pagan sacrificial rites and also it was thought as the last bone of the body
   to decay and the body resurrects around it.
2. It is a triangular bone
   composed of five fused sacral vertebrae
   forming a median crest.
3. Sacral hiatus is a triangular defect
   in the lower part of the posterior wall of
   sacrum formed by the failure of the fifth
   sacral laminae to fuse in the midline.
4. It is bounded above by the fused laminae of S4,
   laterally by the margins of the deficient laminae of S5,
   inferiorly by the posterior surface of the body of S5,
   and covered posteriorly by the dense sacrococcygeal ligament

(formed from supraspinous ligament,
interspinous ligament,
ligamentum flavum).

5. It is about 5 cms above the tip of the coccyx.
6. Sacral canal is the prismatic cavity
   running through the length of the sacrum
   following from the lumbar spinal canal and
   terminating at the sacral hiatus.
7. The left and right lateral walls of the canal
   contain the four intervertebral foramina.

Question 9

What are the contents of sacral canal?

Answer 9

1. • Terminal part of dural sac ending at S1–S3
2. • Sacral and coccygeal nerves making up cauda equina
3. • Sacral epidural veins end at S4 but may extend throughout the canal
4. • Filum terminale
     final part of spinal cord, which does not contain nerves
5. • Epidural fat
     loose in children and fibrosed close-meshed texture in adults

Question 10

Describe the technique of performing the block.

Answer 10

Preparation:

Informed consent,
intravenous access,
monitoring,
resuscitation equipment,
and equipment needed for the block.

Full asepsis:
Similar to any central neuraxial block.

Personnel:
Trained anaesthetist and skilled assistant.

Calculation:
Calculate the local anaesthetic dose using the Armitage
regimen.

Question 11

Describe the technique of performing the block.

Prep

Answer 11

Preparation:

Informed consent,
intravenous access,
monitoring,
resuscitation equipment,
and equipment needed for the block.

Full asepsis:
Similar to any central neuraxial block.

Personnel:
Trained anaesthetist and skilled assistant.

Calculation:
Calculate the local anaesthetic dose using the Armitage
regimen.

Question 12

Armitage regimen

Answer 12

• Drug: 0.25% L—Bupivacaine
• Dose:

Infraumbilical operation – 0.5 mL/kg

Lower thoracic operation – 1 mL/kg

Higher thoracic operation – 1.25 mL/kg

• In our patient: 0.5 mL/kg of
  0.25% L—Bupivacaine

Question 13

Describe the technique of performing the block.
Positioning

+ Locating Space

Answer 13

Position:
The lateral position is efficacious in paediatrics because it permits
easy access to the airway when general anaesthesia has been administered.

Prone position is preferable in adults,
as the caudal space is made prominent
by internal rotation of the ankles.

Landmarks: Locate the sacral hiatus.

• The sacral hiatus forms the apex of an equilateral triangle drawn joining
  posterior superior iliac spines.
• When the curve of the sacrum is followed in the midline with the tip of the
  finger from the tip of the coccyx, the sacral hiatus is felt as a depression.

Question 14

Describe the technique of performing the block.

Procedure

Answer 14

Procedure:

1. A 22 G short beveled cannula is inserted
   at 45 degrees until a ‘click’ is felt,

indicating the sacrococcygeal ligament has been pierced.

2. Then the needle is directed cephalad
   at the angle approaching the long axis of sacral canal.
3. Careful aspiration for blood or CSF should be performed before
   injection of local anaesthetic although negative aspiration does not always
   exclude intravascular or intrathecal placement.
4. For this reason,
   the cannula is left in place whilst the drugs are being drawn,
   thus giving adequate time for the passive flow of CSF/blood
   with any inadvertent puncture.
5. After confirming position, drugs are injected slowly.
6. Test to confirm: Introduction of small amounts of air would produce
   subcutaneous emphysema if the needle were superficial. A ‘whoosh’
   sound is heard when a stethoscope is placed further up the lumbar spine in
   successful blocks

Question 15

What are the additive drugs that can be used along with the local anaesthetics whilst performing a caudal block?

Answer 15

Preservative-free additives are used to prolong the duration of analgesia,

improve the quality of the block,
and reduce the unwanted side effects.

Opioids—
fentanyl, morphine, and diamorphine:

Injection of opioids enables provision of analgesia
due to a local action of the opioid at the spinal cord
level rather than due to systemic absorption.

It increases the duration of the block
by up to 24 hours,

but at the expense of nausea, pruritus, urinary
retention, and late respiratory depression.

Question 16

Newer Additives

Answer 16

The use of opioids has been replaced by

clonidine and ketamine as they significantly
prolong the duration of ‘single-shot’ caudal injections
with minimal risk of side effects.

The addition of clonidine to plain bupivacaine 0.25%
can extend the duration of postoperative analgesia by 4 h,

whereas ketamine and bupivacaine are even more effective,
providing analgesia for up to 12 h.

The main side effects of epidurally administered clonidine are
hypotension, bradycardia, and sedation.

Question 17

Dose + MOA

Clonidine

Ketamine

Answer 17

Clonidine (1–2 mcg/kg):
α2 adrenoceptor agonist.
It acts by stimulating the descending
noradrenergic medullospinal pathway,
thereby inhibiting the release of
nociceptive neurotransmitters in the dorsal horn of spinal cord.

S(+)Ketamine (0.5–1 mg/kg):
NMDA receptor antagonist that binds to a
subset of glutamate receptor and decreases
the activity of dorsal horn neurons.

Question 18

What are the complications of this block?

Answer 18

Serious or catastrophic complications are rare
and can be related to the procedure
or the drug injected.

• Absent/patchy block
• Subcutaneous injection
• Hypotension
• Urinary retention
• Intravenous or intraosseous injection—seizures and cardiac arrest
• Dural puncture—resulting in total spinal block if not recognised
• Rectal perforation
• Sepsis
• Haematoma

Question 19

What are the differences in the anatomy of the caudal epidural space between adults and
children?

Answer 19

Adults
* Dura ends at S2.

• Sacral fat pad, making it difficult to feel hiatus.
• Epidural fat is dense,
  making it difficult to achieve a high block.
• Sympathetic blockade causes pronounced hypotension

____________________________________________________________

Children
* Dura ends at S4 at birth.

• No fat and thus easy anatomy.
• Epidural fat is loose, so drug spreads well.
• Delay in autonomic maturation,
  so there is cardiovascular stability.