A. Continuous Axillary Blocks
Patient Position: Supine, with the arm to be blocked abducted at 90°.
Indications: Anesthesia and postoperative analgesia for elbow, forearm, and hand surgery.
Needle Size and Catheter: 18-gauge, 25-, 38-, or 50-mm insulated introducer needle and 20- or 21-gauge catheter.
Skin–Nerve Distance: 1.5 cm at one year, increasing to 2.5 cm or more in adolescents (Fig. 58-1). Distance from skin to axillary nerve sheath also depends on patient's weight.
Volume and Infusion Rate: (Table 58-1); maximum initial bolus volume of ropivacaine 0.2%. Dosage of ropivacaine 0.2% for continuous infusion: 0.4 to 0.5 mg/kg/h.
Anatomic Landmarks: The axillary artery in the axilla crease is identified. The insertion point is directly next to the artery at the lateral border of the axillary crease.
Approach and Technique: In an appropriately anesthetized/sedated child the needle is inserted directly next to the artery, pointing almost parallel to the artery in a proximal direction with a 30° to 45° angle to the skin. As appropriate muscle twitches in the hand are still present at a current of 0.5 mA, the local anesthetic solution is slowly injected after negative aspiration for blood. Maintaining the introducer needle in the same position, the catheter is threaded 2 cm beyond the needle tip (Fig. 58-2). The introducer needle is removed and the catheter is secured in place with benzoin and a transparent adhesive dressing.
Figure 58-1. Skin–nerve distance, axillary approach.
1. At this level, there are no vital structures and it is a perfect approach for beginners in pediatric peripheral nerve blocks.
2. By introducing the needle more distally from the axilla crease, the catheter can be placed close to a specific nerve that needs to be anesthetized.
3. Because of shoulder mobility the axillary catheter is easily dislocated.
4. To prevent easy dislocation, the catheter can be tunneled by inserting a longer needle subcutaneously at the midhumeral level toward the axillary crease. Only when the needle is close to the axillary crease, look for nerve stimulation.
5. In obese children, ultrasound guidance facilitates this approach.
6. This approach can be used to rescue an incomplete continuous infraclavicular block. Ulnar distribution is sometimes missed by the infraclavicular approach.
7. Ultrasound can be used to localize the axillary nerves, to position the needle, and to verify that the local anesthetic is injected via the catheter around the nerves.
8. A stimulating catheter can be used in older children.
Figure 58-2. Axillary catheter placement.
Table 58-1. Maximal Initial Volume Bolus of Ropivacaine 0.2%
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