Penile block; field block for circumcision

Anatomy

The sensory nerves of the penis are derived from the terminal branches of the
internal pudenda! nerves. The dorsal nerves of the penis travel beneath the
pubic bone, one on each side of the midline, lying against the dorsal surface of
the corpus cavernosum. The skin at the base of the organ is supplied by the
ilio-inguinal and perhaps the genitofemoral nerves. In addition, the posterior
scrotal branches of the perinea! nerves run para-urethrally to the ventral surface
and fraenum, so four nerves have to be blocked.

This is a satisfactory alternative to extradural sacral block, with fewer
complications.

Technique

An intradermal and subcutaneous ring weal is raised around the base of the
penis; the subcutaneous infiltration should precede the intradermal. The
dorsal nerve is next blocked on each side by injecting 5 ml of solution into
the dorsum of the organ just below but not deep to the symphysis so that the
needle point lies against the corpus cavernosum. If the needle pierces the corpus
cavernosum, pain is experienced and blood can be aspirated. For the ventral
injection of the para-urethral branches, the penis should be pulled upwards and
2 ml of solution injected near the base of the organ into the groove formed by
the corpora cavernosa and the corpus spongiosum. Infiltration of 5 ml of 1%
plain lignocaine or 0.5% plain bupivacaine into each dorsal nerve provides
good postoperative analgesia (Fig. above). In infants, smaller volumes are
used. Postoperative pain can be relieved by repeated penile block in awake
patients, even in children, without undue discomfort.
Adrenaline must not be used lest necrosis of tissue results, as the arteries of
the penis are end-arteries.

The smallest possible needle is used to prevent haematoma formation. If
one begins, pressure is applied for 5 min to stop it. Subpubic injection must be
avoided.

Lignocaine spray, EMLA or amethocaine gel, applied topically gives useful
relief for pain following circumcision.