Fig. 29.1
Surface anatomy and needle insertion points for intercostal nerve block
Midaxillary line: This line is drawn longitudinally from the midpoint of the axilla and is used in younger children (younger than 10 years). At this more lateral location, the nerves are separated from the parietal pleura by the internal intercostal muscle.
Scapular line: this line is drawn downward at the inferior angle of the scapula. The insertion site is immediately medial to the scapula or along the scapular line. This line is more suitable for older children (older than 10 years) and adolescents.
Ribs: The lower border of each rib marks the needle puncture site for the nerve of the same level.
Nipples and sternum (anterior block).
Needle insertion typically occurs at the intersection of the midaxillary line (for children <10 years old) or scapular line (for children >10 years old) or immediately medial to the scapula (Fig. 29.1). For the 11th intercostal nerve and the subcostal nerve (T12), the puncture point will be medial to the scapular line, with the length of the corresponding rib determining the point. Although an anterior approach has been described [1], it is rarely indicated and will not be discussed here.
29.2.3 Needle Insertion
The same procedure will be repeated at all levels to be blocked. Posterior blocks are described here.
Most anesthesiologists prefer to stand on the side that allows their dominant hand to hold the syringe at the caudal end of the patient.
A short-beveled needle with a length of no longer than 3 cm should be used to allow maximum appreciation, or “feel,” of the tissue resistances and to avoid trauma.
Generally, 22G–24G needles will be used. A Tuohy needle will allow a catheter to be placed for continuous blocks.
Plastic tubing should be placed between the needle and syringe containing the local anesthetic solution in order to avoid needle disturbances from chest movements during respiration.
Starting with the lowest rib, the index finger of the cephalad hand retracts the skin overlying the rib in a cephalad direction.
With the bevel of the needle directed cephalad, insert the needle, maintaining a constant 20° cephalad angulation.
After contact is made with the inferior border of the rib, withdraw the needle slightly, and release the cephalad traction slowly.
The cephalad hand takes over the needle and syringe, and the needle is allowed to “walk down” to below the rib at the same angle.
Advance the needle slightly (2–3 mm) while maintaining the cephalad angle.
Maintaining pressure on the syringe will allow a loss of resistance to be felt upon penetration of the intercostal space.
29.2.4 Local Anesthetic Application
The needle is placed within the intercostal space, inferior to the overlying rib, and after obtaining a negative aspiration test, 0.5–1 mL (depending on the patient) of local anesthetic solution is injected. The lower volume is typically used in patients under the age of three. Since larger volumes may produce a more effective block, the solution should be diluted with normal saline to avoid overdose.
Since absorption of local anesthetic by the blood is high at the intercostal space, peak plasma levels of local anesthetic are reached after injection, and high toxicity potential exists. To reduce the solution’s absorption, the use of epinephrine is advised, although a maximum dose of 4 μg/kg, with typical concentrations of 1:400,000, is used. Incremental injection with frequent aspiration is an additional measure to avoid toxicity.
A shorter duration block will be achieved when using lidocaine (0.25–1 %), while longer duration (up to 16–18 h) will be attainable with bupivacaine (0.125–0.25 %).
Clinical Pearl
Despite frequent concern about the incidence of pneumothorax with intercostal blocks, this complication is rare in experienced hands. This depends primarily on maintaining strict safety features of the described technique. Emphasis should be placed on absolute control of the syringe and needle at all times, particularly during injection.
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