Penile Block
The penis is mainly supplied by the two dorsal nerves of the penis
that are terminal branches of the pudendal nerves. Its proximal part receives a
few sensory fibers from the ilioinguinal and genitofemoral nerves. Its ventral aspect,
up to the frenulum, is partially supplied by sensory fibers derived from the perineal
nerve.[268]
Each dorsal nerve passes under the
pubic bone, runs within the subpubic space and then through the substance of the
suspensory ligament, accompanies the dorsal artery of the penis at the inner aspect
of Buck's fascia (close to the corpora cavernosa), and ends in the glans penis.
During its course, it gives off numerous branches to the corpora cavernosa, the skin
of the penis, the glans, and the frenulum. The only safe approach to the dorsal
nerves of the penis is within the subpubic space, a pyramidal space limited by the
perineal membrane and symphysis pubis (above), the pelvic part of the corpora cavernosa
(laterally and below), the suspensory ligament, and the superficial fascia of the
abdomen. At this level, the fascia superficialis divides into two layers. The superficial
layer's layer is loose, fatty, and areolar. The deep
Figure 45-20
Perineal or pudendal nerve block, indicating the ischial
tuberosity (1).
layer's structure is membranous, thin but resistant, and aponeurotic. It is also
called Scarpa's fascia and is continuous with the
fascia of the penis or Buck's fascia.
Penile blocks are recommended for surface operations on the penis,
foreskin (i.e., circumcision), and glans. They are suitable for providing long-lasting
pain relief when performed at the end of surgery for hypospadias repair, but they
are not usually sufficient for the surgery itself, which is best completed under
caudal anesthesia. Because the penis is supplied by terminal arteries, epinephrine
must not be added to the anesthetic solution. The technique is performed
with the patient placed in the supine position.[269]
The penis is pulled down by manual traction or by taping, and two sites of punctures
are marked 0.5 to 1 cm below the symphysis pubis and lateral to the midline ( Fig.
45-21
). A 30-mm-long needle,
Figure 45-21
Penile block through the subpubic space.
the bevel of which is not too short because Scarpa's fascia is not easily traversed
due to its elasticity (a caudal or a neonatal lumbar tap needle is ideal), is inserted
almost perpendicular to the skin ( Fig.
45-14
) with a slight slope medially and caudally until it pierces Scarpa's
fascia with a characteristic give at a distance of 10 to 25 mm, regardless of the
age and weight of the patient. Because the subpubic space is frequently divided
into two separate compartments by a medial division (the suspensory ligament of the
penis), a two-injection technique is preferable. The volume of 0.5% bupivacaine
without epinephrine to be injected is 0.1 mL/kg per
side up to a maximum of 5 mL per side. The intrinsic vasoconstrictive properties
of ropivacaine may raise some worries concerning its use for this block; temporary
ischemia of the glans penis occurring 40 minutes after dorsal penile nerve block
with 0.75% ropivacaine has been reported in one patient.[270]
Several other techniques for penile blocks have been reported. Most of them approach
the dorsal nerves at the proximal part of the penis when they run between Buck's
fascia and the outer surface of the corpora cavernosa, but these techniques are dangerous
and should not be used in children. A safer alternative consists of performing a
subcutaneous ring of local anesthetic at the base of the penis. This technique requires
relatively large amounts of local anesthetic (2 mg/kg of bupivacaine) and fails to
provide adequate analgesia in 20% of patients. Topical anesthesia occasionally can
be used as an alternative to penile blocks for urethral meatotomy or neonatal circumcision,
but the quality of analgesia is less than that obtained from penile blocks.[271]
