Are anaesthetists sure of the catheter length inserted into the epidural space?

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We read with interest the article by Afshan et al. regarding the appropriate length of epidural catheter in the epidural space for postoperative analgesia [1]. This prompted us to question: are anaesthetists sure of the catheter length inserted into the epidural space? The length at which an epidural catheter is positioned affects both effectiveness and complications. A length of 3 cm can lead to catheter migration outside the epidural space, while a length of 7 cm can increase the likelihood of unilateral block or accidental venous puncture [2]. Afshan et al. suggested a catheter length of 5 cm is the most appropriate length to be left in the epidural space for successful pain management [1]. Incremental withdrawal of epidural catheters, 0.5–1 cm at a time, can be used to rescue catheters that have failed to achieve adequate analgesia. The markings on the epidural catheter guide anesthetists as to the length left in the epidural space. Depending on the manufacturer, the positions of these markings vary. Both Portex® (Smiths Medical International Ltd, Ashford, Kent, UK) and Perifix® (B. Braun Medical Ltd, Sheffield, UK) epidural catheters are commonly used at our institution. At first glance, their markings look similar if not the same (Fig. 1), but the Portex catheter has 1-cm markings with a double marking at 10 cm and a triple marking at 15 cm. The Perifix catheter has the double marking at 10.5 cm and the triple marking at 15.5 cm. In addition, the Perifix catheter has a bold, 5-mm long mark at 12.5 cm, which is the position at which the catheter begins to leave the epidural needle. Comparing these two brands of catheter side-by-side, one can also see that the centimetre markings begin at different distances along the catheters (1-cm difference), casting uncertainty over the actual distance these markings represent. Comparison of Portex and Perifix epidural catheters. Practitioners need to be aware of these differences, particularly trainees who rotate between different hospitals. This reinforces the importance of checking the manufacturers’ literature, since a small change in catheter length can make a big difference in the analgesic effect.