Knotting of an Epidural Catheter Like a Tie

To the editor: Knotting of the catheter has been reported as a very rare complication of epidural anesthesia, with an estimated incidence of 0.0015%(1). Simple and double knots (2,3) have been previously reported. We recently experienced a new type of epidural catheter knot. A labor epidural was administered in a healthy 27-yr-old G1P1 woman using a 17-gauge Tuohy needle at the L2-3 interspace. The catheter was initially threaded 9 cm beyond the tip of the Tuohy needle and no resistance was encountered. However, after the removal of the needle, resistance occurred and the catheter could not be easily withdrawn. Despite the initial resistance, the use of a steady force allowed removal of the catheter, without obvious stretching. The patient remained pain free during the catheter removal and because she was awake and no anesthetic had been administered it was assumed that the catheter had not knotted around any nerves (4). No neurological sequela developed. On examination, we found a knot 2.5 cm from the tip that looked like a tie (Fig. 1). It has been suggested that to avoid knotting, epidural catheters should not be inserted more than 5 cm into the epidural space. However, many anesthesiologists thread the epidural catheter more than 7 cm into the epidural space during initial insertion and then subsequently withdraw the catheter to the desired depth, thus ensuring that a sufficient amount of epidural catheter will remain in the epidural space after needle removal. In addition, a knot developing in a catheter that was inserted <3 cm has also been reported (2), so factors other than catheter depth may also be responsible for knotting. Although we are not suggesting that force great enough to break a catheter should ever be used, we were successful in this case by using a gentle but constant force despite the presence of a small knot. Should continuous traction have failed, we would have taken the patient to radiology for further evaluation. We suggest that further study is necessary and that manufacturers should endeavor to design needles and catheters with specific properties that avoid this rare but potentially dangerous complication.Figure 1: Knotting of an epidural catheter like a tie.Mazen A. Karraz, MD