The technique of caudal epidural block involves palpation,
identification and puncture.1 Patients are evaluated
for any epidural block, and the indications and relative and absolute
contraindications to its performance are identical. A full complement of
noninvasive monitors is applied, and baseline vital signs are assessed. One
must decide whether a continuous or single-shot technique will be employed.
For continuous techniques, a Tuohy-type needle with a lateral facing orifice
Several positions can be used in adults, compared with the lateral
decubitus position in neonates and children. The lateral position is
efficacious in pediatrics because it permits easy access to the airway when
general anesthesia or heavy sedation has been administered prior to
performing the block. In pediatric patients, blocks may be performed with
the patient fully anesthetized; the same is not recommended for older
children and adults. In adults, the prone position is the most frequently
utilized, but the lateral decubitus position or the knee–chest (also known
as knee–elbow) position may be employed. In the prone position, the
procedure table or operating room table should be flexed, or a pillow may be
placed beneath the symphysis pubis and iliac crests to produce slight
flexion of the hips. This maneuver makes palpation of the caudal canal
easier. The legs are separated with the heels rotated outward to smooth out
the upper part of the anal cleft while relaxing the gluteal muscles. For
placement of caudal epidural block in the parturient, the woman is in the
lateral (Sim position) or in the knee–elbow position.
A dry gauze swab is placed in the anal cleft to protect the anal area
and genitalia from povidone-iodine (Betadine) or other disinfectants
(especially alcohol) used to sterilize the skin. The skin folds of the
buttocks are useful guides in locating the underlying sacral hiatus.
Alternatively, a triangle may be marked on the skin over the sacrum, using
the posterior superior iliac spines (PSIS) as the base, with the apex
pointing inferiorly (caudally). Normally, this apex sits over or immediately
adjacent to the sacral hiatus. The hiatus is marked and the tip of the index
finger is placed on the tip of the coccyx in the natal cleft while the thumb
of the same hand palpates the two sacral cornua located 3–4 cm more
rostrally at the upper end of the natal cleft. The sacral cornua may be
identified by gently moving the palpating index finger from side to side
(Figure 15–2). The palpating thumb should sink into the hollow
between the two cornua, as if between two knuckles of a
fist.1 A sterile skin preparation and draping of the
entire region is performed in the usual fashion.
Technique of palpating the midline over the sacral
hiatus. The palpating index and middle fingers are spread
over the fifth sacral vertebral body. The sacrococcygeal ligament lies
directly beneath the palpating fingers.
A small-gauge 1.5-in. needle is then utilized to infiltrate the skin
over the sacral hiatus using 3–5 mL of 1–1.5% plain lidocaine HCl
(Figures 15–3, 15–4, and 15–5). If fluoroscopy is utilized, a lateral
view is obtained to demonstrate the anatomic boundaries of the sacral canal.
We routinely leave the local anesthetic infiltration needle in situ for this
view, since it demonstrates whether the approach is at the appropriate level
for subsequent advancement of the epidural needle. With fluoroscopy, the
caudal canal appears as a translucent layer posterior to the sacral segments
(Figure 15–6). The median sacral crest is visualized as an opaque
line posterior to the caudal canal. The sacral hiatus is usually visualized
as a translucent opening at the base of the caudal canal. The coccyx may be
seen articulating with the inferior surface of the sacrum.
Technique of skin infiltration using a fine-bore
needle and local anesthetic. The needle is inserted first above, and then into the
substance of the sacrococcygeal ligament.
The fine-bore needle has been left in place, having
engaged the sacrococcygeal ligament.
A longer, firmer infiltration needle for local
anesthetic injection is now advanced through the sacrococcygeal ligament to
anesthetize that structure and the overlying subcutaneous tissues.
Lateral fluoroscopic image depicting the 17-gauge
extracatheter device correctly seated in the caudal epidural space.
Once the tissues overlying the hiatus have been anesthetized, a 17- or
18-gauge Tuohy-type needle is inserted either in the midline or, using a
lateral approach, into the caudal canal (Figures 15–7 and 15–8). A
feeling of a slight “snap” may be appreciated when the advancing needle
pierces the sacrococcygeal ligament. Once the needle reaches the ventral
wall of the sacral canal, it is slowly withdrawn and reoriented, directing
it more cranially (by depressing the hub and advancing) for further
insertion into the canal (Figure 15–9). We utilize the
anteroposterior view once the epidural needle is safely situated within the
confines of the canal, and the epidural catheter is advanced cephalad. In
this projection, the intermediate sacral crests appear as opaque vertical
lines on either side of the midline. The sacral foramina are visualized as
translucent and nearly circular areas lateral to the intermediate sacral
crests. The presence of intestinal gas may obfuscate the recognition of
these structures. A syringe loaded with either air or saline containing a
small air bubble is attached to the needle, and the loss-of-resistance
technique is used to establish entry into the epidural space.
The 17-gauge needle has been advanced from the skin into
the sacral hiatus through the sacrococcygeal ligament. Usually, when
fluoroscopy is not available to verify correct needle placement, a syringe
loaded with air or saline is attached to the needle and the
loss-of-resistance technique is employed to identify the epidural space, as
for conventional lumbar or cervical epidural injections.
Skeletal specimen demonstrating the needle introducer
from the 17-gauge extracatheter device situated correctly in the caudal
epidural space, traversing the sacrococcygeal ligament (removed) and
entering the sacral hiatus (lateral view).
Caudocranial view of the 17-gauge extracatheter device
situated correctly through the sacrococcygeal ligament into the sacral
- The needle tip should stay below the S2 level to avoid tearing the
- The needle should never be advanced in the space to the full length of the
- The skin corresponding to about 1 cm inferior to the PSIS indicates the S2
level (caudalmost extension of the dura mater).
- The dural sac extends lower in children than in adults, and epidural needles
should be very carefully advanced no deeper than the S3 or S4 level in this
A “whoosh” test has been described for identifying correct needle
placement in the caudal canal. This characteristic sound has been noted
during auscultation of the thoracolumbar region during the injection of 2 to
3 mL of air into the caudal epidural space.20 The test has
been modified in pediatrics, wherein local anesthetic, and not air
injection, is auscultated during the performance of the block. Of the
108 patients with a successful block in one study, 98 had a positive test, with
no false-positive results.21 Once the correct placement of
the needle is confirmed, a catheter is inserted into the desired location
(depth) (Figure 15–10), and its position confirmed
fluoroscopically when desired (Figures 15–11 and 15–12).
A continuous catheter with a stylet in place is
shown. The catheter is advanced through either the short over-the-needle
catheter that was left in situ (shown), or through a 17–18-gauge steel
needle placed in the canal.
Anteroposterior fluoroscopic image depicting proper
placement of the needle. The patient's hardware from previous fusion surgery
is also seen.
Lateral fluoroscopic image depicting radiopaque
contrast medium in the caudal and lower lumbar epidural spaces. The image
shows considerable spread, both anteriorly and posteriorly, following the
injection of 2 mL of dye.
- In pediatric patients, electrical stimulation has been used to
ascertain correct needle placement in the caudal canal. Anal sphincter
contraction (corresponding to stimulation of S2-S4) can be sought with a
current of 1–10 mA.22
- If the needle has been inserted correctly, it will swing easily from side to
side at the hub while the shaft is held
like a fulcrum at the sacrococcygeal
membrane and the tip moves freely in the sacral canal.
- If cerebrospinal fluid (CSF) is aspirated through the needle, it should be
withdrawn and injection should not be undertaken.
- If blood is aspirated, the needle should be withdrawn and reinserted until
no blood is apparent at the hub.
- When injection of air (or saline) for the loss-of-resistance technique
results in a bulging over the sacrum, the needle tip most probably lies
dorsal to the sacrum in the subcutaneous tissues.
- If the needle tip is subperiosteal, the injection will meet with significant
resistance, and the patient will find this to be a most unpleasant
experience. The cortical layer of the sacral bone is often quite thin,
particularly in infants and older subjects, and puncture of cancellous bone
is relatively easy, especially if force is exerted while advancing the needle. The sensation of entering cancellous bone is
not unlike penetrating
the sacrococcygeal membrane; there is a feeling of resistance that is
suddenly overcome and the needle advances more freely and subsequent
injection is unhampered.
Injected solutions may be absorbed very rapidly by bone marrow and toxic
drug reactions result. In this situation, pain is typically noted over the
caudal part of the sacrum during the injection. If this occurs, the needle
should be withdrawn slightly and rotated on its axis until it can be
reinserted in a slightly different direction.23–25
If injection is made anterior to the sacrum (between the sacrum and coccyx),
it is possible to perforate the rectum, or, in parturients, the baby's head
may be injured. This limits the use of caudal block in laboring women once
the presenting part has descended into the perineum. Inadvertent venous
puncture also may occur, and the incidence of this has been reported to be
Caudal block may be used with a single-shot or continuous catheter
technique. For continuous block, the catheter may be advanced anterogradely
(conventionally) or retrogradely. Continuous caudal block may be performed
in retrograde fashion using needle insertion into the lumbar epidural space,
but directed inferiorly instead of superiorly. In one study of 10 patients,
epidural catheters were advanced through 18-gauge Tuohy-type epidural
needles in retrograde fashion from the L4-L5 interspace. This technique was
associated with a 20% failure rate with the catheter going into the
paravertebral or retrorectal spaces, despite easy epidural space
entry.27 Using the conventional approach, a Huber-tipped
Tuohy needle is used as a conduit to pass the epidural catheter into the
canal. This needle has a skilike tip that limits its being caught or
snagged on the sacral periosteum. The needle is inserted with its shoulder
facing anteriorly and its orifice dorsally. Alternatively, a standard 16- or
17-gauge catheter-over-needle assemblage (angiocatheter) may serve as the
introducing needle for subsequent catheter placement. The catheter is
advanced with fluoroscopic guidance, especially when it is performed for
chronic pain management in failed back surgery syndrome. The catheters
should be advanced gently, since there have been reports of dural puncture
with rapid or aggressive advancement. The lateral and anteroposterior views
should be obtained to demonstrate placement of the catheter in the epidural
space (lateral view, see Figure 15–6) and to follow its path in a cephalad
or cephalolateral direction (anteroposterior view, see Figure 15–11). When
the desired level is attained, iodinated nonionic contrast media may be
injected, followed by the injection of local anesthetics, corticosteroids or
adjuncts (Figures 15–13 and 15–14). We usually do not
advance the catheter higher than the level of the L4 vertebral body,
although we have occasionally advanced it to the L1 or L2 level. Some
authorities suggest avoiding advancement more than 8–12 cm cephaladly.
A syringe loaded with radiopaque contrast medium is
attached to the continuous catheter or catheter system in place in the
caudal epidural space. Injection of mixture of local anesthetic or
corticosteroid medication (or both) into a continuous catheter placed into
the caudal epidural space.
Anteroposterior fluoroscopic image depicting
radiopaque contrast medium in the epidural space, beneath the patient's
hardware from previous fusion surgery. In the face of previous spinal
surgery, with or without hardware implantation, caudal epidural block may be
significantly safer than conventional epidural block, since it obviates the
need to penetrate the surgical scar.
|Spread of local anesthetic solutions injected into the caudal epidural space
is influenced by injected volume, speed of injection, and patient position.|