[The effect of the Tuohy cannula on the positioning of an epidural catheter. A radiologic analysis of the location of 175 peridural catheters].

UNLABELLED: The aim of this study was to determine at which lumbar spinal level the tips of different epidural catheters may be located following insertion through cranially directed Tuohy needles. Previous studies varied with respect to materials and methods and may have left the false impression that different types of catheters are necessary or actually more advantageous for particular needs. MATERIALS AND METHODS: One hundred seventy-five trauma patients scheduled for surgery on their lower extremities received continuous epidural anesthesia. With the patient in a sitting position, a midline lumbar puncture was made and one of six different plastic catheters advanced 5 cm beyond the tip of the Tuohy needle. Postoperatively the catheters were filled with Iopamidol and ap X-rays taken of the lumbar spine. The catheter tips were declared to be "cranial" if they were more than 2 cm above, "caudal" if they were more than 2 cm below, and "equal to" if they were within 2 cm of the puncture site. RESULTS: Of the 175 documented catheter tips 47.7% assumed a cranial position, 9.2% were in a caudal position, and 43.4% remained within the level of insertion. A statistical analysis comparing catheter tip location among the six epidural catheter models tested did not reveal any significant differences. DISCUSSION: In a clinically controlled study based on the Tuohy principle of inserting catheters through a needle with a Huber point, different epidural catheter models were inserted into the lumbar epidural space and their locating radiologically documented. It was shown that 52% of the epidural catheters that had been advanced 5 cm into the lumbar epidural space through a cephaled-directed Tuohy needle did not reach the intended spinal level cranial to the puncture site. The results are similar to those of earlier studies, which were not systematic and involved a variety of methods and materials. One reason for the unreliable ascension of the catheter tips may be the many structures within the epidural space which may dislodge and divert the catheters during advancement. In addition, it has sometimes been observed that a change in the patient's position may cause a spinous process cranial to the puncture site to exert pressure and traction on the catheter, partially dislodging it. It must thus be concluded that the use of a Tuohy needle cannot guarantee cranial ascension of an epidural catheter in the lumbar epidural region.