Intercostal Nerve Block
The thorax is supplied by the two main branches of the spinal
nerves, dorsal and ventral, which maintain a metameric disposition of sensory supply.
The intercostal nerves are the continuation of the ventral branches. They run within
the intercostal spaces along the lower border of the rib and are accompanied by an
intercostal vein (draining to the azygous venous system) and an intercostal artery.
The intercostal space is triangular in section, with a medial border formed by the
posterior intercostal and the innermost intercostal muscles and with a lateral border
formed by the external intercostal muscle.
An intercostal nerve block is obtained by injecting a local anesthetic
within the intercostal space and, provided several adjacent intercostal spaces are
infiltrated, adequate intraoperative and postoperative pain relief is obtained for
thoracotomy,[280]
liver transplantation, pleural
drainage, and management of rib fractures. This block must be avoided in patients
with impaired blood gas exchange, and it requires that patients be kept under intensive
medical observation because of the danger of clinically delayed pneumothorax. The
block is contraindicated for outpatient surgery.
The safest approach to the intercostal space is in the midaxillary
line, with the child lying semiprone and using a short, 22- or 20-gauge Tuohy needle
(intradermal needles are not appropriate). The needle, connected to a syringe with
interposition of an extension line, is inserted just below the lower border of the
upper rib at an 80-degree angle to the chest, pointing cephalad, until it contacts
the rib ( Fig. 45-24
). It
is then slightly withdrawn and, while continuous pressure is exerted on the barrel
of the syringe, redirected more caudad (to pass immediately below the rib) and dorsally
(to avoid pleural damage).[281]
LOR is felt at
entry into the intercostal space, where 1 mL of 0.125% to 0.25% bupivacaine with
1:400,000 epinephrine or 0.2% plain bupivacaine is injected. This block provides
8 to 18 hours of analgesia; 0.25% to 1% lidocaine or mepivacaine is also suitable,
but pain relief lasts no longer than 3 to 4 hours.
Several adjacent intercostal spaces have to be blocked to produce
adequate sensory block, multiplying the dangers of complications. Because systemic
uptake is considerable,
Figure 45-24
Intercostal nerve block, showing insertion of the needle
at an 80-degree angle to the skin (1) and caudal and dorsal redirection of the needle
(2).
almost equivalent to intravenous injection,[11]
[282]
only diluted solutions are suitable, and the
overall dose of bupivacaine should not exceed 2 mg/kg. The total dose of epinephrine
must not exceed 4 µg/kg. A catheter can be introduced in the intercostal space
located at the center of the area to be anesthetized to allow reinjections (This
can also be achieved intraoperatively by the surgeon.) Spread of a large volume
of anesthetic solution can reach distant intercostal spaces (even contralateral areas),
probably through the paravertebral space, providing in many patients adequate prolongation
of pain relief with a single injection. Anesthetic can also spread to the epidural
space. The patient should be admitted to the intensive care unit for careful monitoring
of respiratory function and for delayed pneumothorax.
