Complications related to regional anesthesia using either epidural or spinal catheters are well described and are generally associated with unintentional intrathecal injection of drugs meant to be administered in the epidural space, or in the case of intrathecal catheters, unintentional injection of medicines which should not be delivered into the spinal canal (1, 2, 3). However, a described, but uncommon, complication of both epidural and intrathecal catheterisation is separation of the catheter tip during removal (4, 5, 6).
Currently, the standard of care which applies to retention of a segment of epidural catheter within the epidural space is to leave the broken segment in place if no symptoms occur and then follow up with neurologic examination (Chapter 104). However, if a small-diameter continuous spinal catheter becomes separated within the intrathecal space, it is not unreasonable to perform an exploration of the intrathecal space and to retrieve the broken segment of the spinal catheter (11). As intrathecal catheters have become smaller and smaller in diameter, not only has the use of these catheters increased in popularity, but so has the chance of separation of the catheter tip when the device is withdrawn.
Of the studies relating to the tensile strength of catheters, three are of relevance to those who perform regional anesthesia (8, 9, 10):
Study 1. Tensile strengths of epidural catheters in vitro.
Study 2. Tensile strengths of micro-catheters used for continuous spinal anesthesia in vitro.
Study 3. Force necessary to withdraw an epidural catheter in vivo.
Study 1. The tensile strength and elongation before failure of six commonly used epidural catheters was investigated. This test was performed using an 'Instron' universal testing instrument and both load-to-failure as well as catheter elongation were measured (Table 42.1). It should be noted that a 19 Gauge (ga) nylon catheter by Pharmaseal gave the greatest margin of safety when considering separation of a catheter tip. In fact, the 19ga Pharmaseal nylon catheter offered nearly a 2kg margin of safety before breakage when compared with a 20ga Teflon epidural catheter. Also of note was the elongation factor where, once again, the 19ga Pharmaseal catheter performed best in that it had a greater than 1,000 percent elongation before failure occurred. This adds to the margin of safety of the catheter in that once it is seen to stretch, the patient can be repositioned in order to permit removal of an intact catheter.
Study 2. The second evaluation involved seven continuous spinal micro-catheters including 24ga, 28ga and 32ga devices. Testing done on these particular catheters was the same as for the epidural catheters described in Study 1. There was no significant difference in the tensile strength or extent of elongation of any of the catheters tested. The range in which breakage occurred was 0.45 - 0.51 kg. The force needed to break a 20ga epidural catheter measured nearly 3kg indicating a six-fold difference in break forces between spinal micro-catheters and conventional 20ga epidural catheters.
Study 3: This study was an in vivo determination of the force of manual extraction of lumbar epidural catheters in postpartum patients. Results of this study indicated that there was a considerable margin of safety between actual in vivo force needed to extract lumbar epidural catheters and measured in vitro tensile strengths. The in vitro breaking strength of a 20ga nylon epidural catheter has been measured at 3kg which was more than 1.4kg greater than the highest level recorded in the in vivo manual extraction study. However, the in vitro breaking force in spinal micro-catheters has been measured at 0.4 - 0.5kg. This breaking point lies within the in vivo ranges noted in this study regardless of body position when an epidural catheter is removed. Furthermore, body position during catheter removal must be considered because the force needed to remove an epidural catheter in the sitting position is considerably greater than that for the lateral decubitus position. Figure 42.1 describes ounces of pull needed to extract catheters in the lateral decubitus and sitting positions. These forces are also compared to those required to break a spinal microcatheter.
Figure 42.2 integrates all the data from the three studies described and supports the following recommendations:
(1) Care must be used when spinal micro-catheters are being extracted from a patient because the chance for breakage is real;
(2) Using the lateral decubitus position when removing an epidural catheter is recommended as this results in the least force of extraction (Chapter 75); and finally,
(3) if the catheter separates within the epidural space, leave the broken segment in place and follow up with neurological examination as needed. However, if a spinal microcatheter separates within the intrathecal space, surgical exploration with retrieval of the tip of the catheter is required to avoid future neurologic problems (Chapter 104).
References:
1. Murphy TM: Spinal, epidural, and caudal anesthesia. In: Miller RD (ed). Anesthesia,
2nd edition.
New York, Churchill Livingstone. 1986
2. Bromage PR: Epidural Analgesia. Philadelphia. WB Saunders, 1978, pp 664-666
3. Cousins MJ. Bromage PR: Epidural neural blockade. In: Cousins MJ, Bridenbaugh PO (eds). Neural Blockade in Clinical Anesthesia and Management of Pain, 2nd ed, JB Lippincott Co, Philadelphia,1988. p 336
4. Moerman N. Porcelijn T, Deen L: A broken epidural catheter. Reg Anesthesie (Springer-Verlag) 3:17-18, 1980.
5. Hurley R J, Lambert DH. Continuous spinal anesthesia with a microcatheter technique: preliminary experience. Anesth Analg 1990:70:97-102
6. Tio TO, Macmurdo SD, McKenzie R: Mishap with an epidural catheter. Anesthesiology 1979;50:260-262
7. Ley SJ, Jones BR: Strength of continuous spinal catheters. Anesthesia and Analgesia 1991:394-6
8. Blackshear RH, et al. Comparison of tensile strength of seven types of epidural catheters. Anesthesiology 1990;73(3A);A961
9. Wissler RN, Blackshear RH: Tensile strength of spinal microcatheter. Anesthesiology 73:A505, 1990.
10. Blackshear RH, Gravenstein N, Radson E: Tension applied to lumbar epidural catheters during removal is much greater with patient sitting versus lying. Anesthesiology 1991; 75:A833
11. De Vera HV, Ries M. Complication of continuous spinal microcatheters: Should we seek their removal if sheared? (Letter) Anesthesiology 1991 74:794