The coiling length of thoracic epidural catheters: the influence of epidural approach angle

Thoracic epidural catheters are used for anaesthesia and postoperative analgesia. Usually, epidural catheters are placed without confirmation of their position despite frequent reports of complications as a result of malposition. In this study, we evaluated the threading length of thoracic epidural catheters without coiling and assessed the influence of two different epidural approach angles on the threading length without coiling.

Eighty-three patients scheduled for thoracotomy were enrolled and randomly allocated into the acute angle group and the obtuse angle group. In both groups, skin insertion was performed at the T8-9 intervertebra level. Epidural access was performed under fluoroscopy using a paramedian approach at the T7-8 level in the acute angle group and at the T6-7 level in the obtuse angle group, and an end-hole 19-gauge epidural catheter was inserted. Coiling length, defined as the length of the catheter within the epidural space when any part of the catheter just begins to head caudally, was measured in both groups.

The coiling length was 7.4(4.4) cm (95% CI 6.0-8.7 cm) in the obtuse angle group compared with 4.9(3.3) cm (95% CI 3.8-6.0 cm) in the acute angle group (P = 0.005).

Approaching the thoracic epidural space with an obtuse approach angle provides longer coiling length. We recommend that an obtuse approach angle should be used to maximize the chance of the catheter reaching the intended level with minimum risk of coiling.