Ultrasound image of the brachial plexus in the supraclavicular location, a needle is seen injecting a pool of local anesthetic
A 50 kg patient receives a supraclavicular peripheral nerve block in the preoperative area for anesthesia and postoperative pain for open reduction and internal fixation of an ulnar fracture on the left arm. The patient received a total of 20 cc of 0.5% ropivacaine during the block (See Fig. 58.1). 55 min later, the surgery starts and the patient complains of pain in the area of the surgery.
Based on the ultrasound image above what is the most likely cause of the patient’s pain?
How would you supplement the block?
Are there other reasons for pain during surgery?
Should a continuous nerve catheter been placed?
Do additives in the block mixture have a role?
Most probably this patient experienced ulnar sparing due to poor distribution of the injection to the lower trunk . This occurs commonly when the injection is made superficial to the plexus and does not cover the lower trunk (in the “eight ball corner pocket,” which is the area formed by the angle between the brachial plexus and first rib).
These patients will report adequate motor and sensory block over the median, radial, and musculocutaneous distribution; however, the area of the ulnar nerve, and medial cutaneous nerve of the forearm retain sensation and function.
Time permitting, the block could be supplemented by placing more local anesthetic in the “eight ball corner pocket,” since the patient could safely still receive more local anesthetic .
The maximum dose of ropivacaine in this patient is 150 mg (3 mg/kg). So we could safely repeat the block targeting the area of interest and inject up to another 10 cc of ropivacaine 0.5%.
Awake patients might complaint of tourniquet pain. All patients experience neuropathic pain after a few minutes of a tourniquet being inflated to 100 mmHg above the systolic blood pressure. With enough time this manifests as pain, sometimes severe in awake patients, or a sympathetic response in patients under general anesthesia.
Other reasons for pain are due to surgical stimulation in the area covered by the intercostobrachial nerve, the upper, inner aspect of the upper arm, which is not routinely covered by brachial plexus blocks. This area can be anesthetized with a field block of the medial side of the arm or a PECS II (pectoralis nerves) block.
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