Insertion length and resistance during advancing of epidural catheter

The migration of an epidural catheter into the intravascular and subarachnoid spaces sometimes occurs. This study was designed to investigate where the resistance was felt during the advancing of the catheter into the epidural space and whether the length of catheter advanced in the epidural space affected the incidence of catheter migration.

One hundred and twenty women, American Society of Anesthesiologists (ASA) 1 or 2, scheduled to undergo lower abdominal surgeries with epidural anesthesia were randomly assigned to two groups according to the length of the epidural catheter advanced; 4 cm (n = 60) or 8 cm (n = 60). The length where resistance to advancing the catheter was perceived was recorded in all patients, and the incidence of aspiration of blood or cerebrospinal fluid (CSF) was obtained. Further, the catheters removed 48 h after surgery were scrutinized for their bending sites.

Resistance was felt in 83 (69.2%) patients and the mean length in the epidural space at which resistance was found was 2.5 +/- 1.2 cm. Blood was aspirated in 9 (7.5%) patients when resistance to advancing the catheter was overcome, but CSF was aspirated in no patient. A distal bend was observed 2.4 +/- 1.3 cm from the tip of the catheter, and the sites of bending were correlated with the length where resistance was encountered. An additional proximal bend was observed in 35 (58%) patients in the 8-cm group, and in 2 patients (3%) in the 4-cm group (P < 0.001), probably due to coiling of the catheter.

At approximately 2.5 cm in the epidural space, advancing an epidural catheter causes resistance. Further advancing past this point may cause migration of the catheter into the vessels, or the coiling of the catheter.