Patients undergoing elective thoracic surgery, abdominal surgery, or having rib fractures who will have placed a thoracic epidural catheter to manage their perioperative analgesia.

With an US-guided parasagittal oblique approach, the interlaminar space at the union between laminas and spinous processes at the predefined insertion level will be identified. A skin wheal will be raised with 3 mL of lidocaine 1%. Afterward, an 18-gauge Tuohy epidural block needle will be advanced under direct US vision until the tip is insinuated between the laminas and anchored to the flavum ligament. Then the needle will be attached to a low resistance syringe prefilled with saline solution and advanced until LOR to injection is confirmed. Then a 20-Gauge epidural catheter will be inserted 3-5 cm beyond the needle tip inside the epidural space and the needle removed.

After fifteen minutes of local anesthetic administration (4- mL dose of lidocaine 2% with epinephrine 5 μg/mL ), an investigator will apply ice to the T1 to L4 dermatomes bilaterally. The criterion standard for success will be the presence of an epidural block, defined as a block to ice in at least 2 dermatomes bilaterally. If operators could not advance the catheter past the needle tip after 2 attempts despite a 180-degree rotation of the bevel between the first and second attempts, epidural blocks will be considered failures.

Number of blocked dermatomes after injection of local anesthetics through the epidural catheter.