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Identification of the thoracic epidural space by the running infusion drip technique

Beirut, Lebanon

To the Editor:

Location of the thoracic epidural space between T3 and T7 is difficult because of the extreme caudad angulation of the long posterior spinous processes at these levels. Also, above L2, the epidural space gradually becomes smaller because of the size of the spinal cord.

The loss-of-resistance technique is the most frequently used method for locating the epidural space. However, because of the difficulty of identification of the epidural space in the thoracic region as well as the possibility of inadvertent dural puncture resulting in intrathecal administration of the local anesthetic and/or spinal cord injury, an objective technique for identification of the thoracic epidural space must be considered as an alternative for the subjective loss-of-resistance technique.

Thirty years ago, I reported the use of the running infusion technique for identification of the lumbar epidural space.¹ The technique has also proved to be very useful for identifying the thoracic epidural space. Patients are positioned in the sitting position and, after scrubbing and draping the skin, a Tuohy epidural needle is inserted in the midlle line at the desired thoracic level, with an upward angulation of 45–60 angle to the skin. The needle is advanced through the skin, subcutaneous tissue, supraspinous ligament and interspinous ligament. The stylet is then removed, and the sterile end of a saline infusion drip tubing is carefully connected to the hub of the needle. The drip is then left open. The infusion sometimes drips slowly when the tip of the needle is in the loose interspinous ligament. However, when the needle engages the ligamentum flavum, marked resistance is felt and the infusion always stops running. The needle is then advanced very slowly through the ligamentum flavum. As soon as the bevel of the needle enters the epidural space, the infusion starts to flow, thus identifying the epidural space (Figure). The rate of the drip varies from patient to patient, due to possible variations in the epidural pressure. Entry into the space is usually associated with a "give way" feeling and advancement of the needle is stopped immediately. The infusion is then detached from the needle. If no cerebrospinal fluid drips from the needle, injection of 3 mL of lidocaine plus epinephrine 1:200,000 is used as a test dose. The injection without resistance, as well as the absence of tachycardia or spinal anesthesia confirm proper epidural localization.

View larger version (93K): [in this window] [in a new window]   FIGURE A saline infusion set is positioned approximately one metre above the site of proposed epidural anesthesia and connected to the hub of the epidural needle. As soon as the needle pierces the ligamentum flavum, and enters the peridural space, the infusion starts to drip due to the hydrostatic pressure difference between the infusion and the peridural space.

Reference

1 Baraka A. Identification of the peridural space by a running infusion drip. British Journal of Anaesthesia 1972; 44: 122.[Free Full Text]

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