Causes:
There are a number of reasons why a catheter may tear. These include:
1. the use of undue force in removing a catheter which is trapped between the vertebral spinous processes or is knotted in the epidural space (Chapter 75);
2. shearing of the catheter by the needle when attempts are made to withdraw the catheter through the Tuohy needle;
3. nicking of the catheter by a barb on the bevel of the needle;
4. shredding of the catheter if the needle is advanced over the catheter after the catheter has been placed ;
5. weakness of the catheter produced by imperfections in manufacture; or
6. damage to a catheter occurring after placement (eg. fraying by pinching between two vertebral processes) (1, 3, 7, 8, 9).
Diagnosis:
Radio-opaque epidural catheters are easier to locate radiologically than non-radio-opaque ones but, paradoxically, they have a lower tensile strength than standard clear catheters (Chapter 42). It makes little sense to use a catheter which is more liable to fracture on the grounds that the broken segment can be more easily located after the incident! In fact, even a radio-opaque fragment may be impossible to locate radiologically because the surrounding structures are radio-dense.
Another drawback of some radio-opaque catheters is the problem of diagnosing inadvertent intravascular or dural puncture because it is more difficult to visualise CSF or blood through an opaque catheter.
Ultrasonographic Iocalisation of torn catheters is singularly unrewarding but xeroradiography, computerised tomography (CT) scanning or magnetic resonance imaging (MRI) may prove more fruitful.
Successful Iocalisation of the catheter segment by medical imaging is no guarantee that the task of finding the missing segment at subsequent surgery will be made any easier.
Prevention:
1. The force required to remove a catheter should be minimal. If resistance is encountered, a number of simple manoeuvres have been described to enable removal of the catheter without stretching or tearing (Chapter 75).
2. Needles should be checked for barbs on the bevel and the catheter for manufacturing defects before insertion.
3. No more than about 5cm of catheter should be advanced into the epidural space to reduce the risk of kinking, curling up or knotting (2).
4. Catheters should never be withdrawn through the metal needle.
5. Catheters of high breaking strain (tensile strength) (Table 42.1) and of a sufficient diameter (eg. 16 or 18G epidural) should be obtained from a reputable, reliable manufacturer.
Management:
Epidural catheters are inert and should not produce a foreign body reaction. In most cases, segments of catheter are best left alone because surgical removal can produce more harm than good (5). Foreign bodies in the epidural space are not likely to migrate (although this is not impossible).
There are three situations where a policy of non-interference and reassurance does not apply:
1. where infection or symptoms supervene,
2. if the spinal catheter fragment is sitting partially intrathecally and is acting as a wick which allows persistent CSF leakage (6), or
3. if the proximal end of the segment is known to be located very close to the skin such that it can be retrieved simply through a superficial incision (7).
In the majority of situations the mother can be managed expectantly and reviewed periodically to ensure that there is no discomfort, infection or radiculopathy.
Conclusion: The best intentions and the exercise of utmost care can still result in tearing of the catheter. In only in a small proportion of cases is it prudent to attempt to remove the offending retained portion of catheter.
References:
1. Moerman N, Porcelijn T, Deen L. A Broken Epidural Catheter. Reg Anesthesie (Springer-Verlag) 3:17-18, 1980.
2. Dawkins M. An Analysis of the Complications of Extradural and Caudal Block. Anaesthesia 24:554. 1969.
3. Tio T, Macmurdo S, McKenzie R. Mishap with an Epidural Catheter. Anesthesiolgy 50:3:260-262. 1979.
4. Herrera M, Hsia T, Becker T. Migration of Teflon Mesh from Abdominal Wall into Large Bowel. NY State J Med 76:452. 1976.
5. DeVera H, Ries M. Complications of Continuous Spinal Microcatheters: Should We Seek Their Removal if Sheared? Anesthesiol 74:794, 1991.
6. Pasquariello C, Betz R. A Case for the Removal of the Retained Intrathecal Catheter. Anesth. Analg 72:562, 1991.
7. DeArmendi A, Ryan J, Chang H, et al. Retained Caudal Catheter in a Paediatric Patient. Paed Anaes 2:325-327, 1992.
8. Chun L, Karp M. Unusual Complications from Placement of Catheters in the Caudal Canal in Obstetrical Anesthesia. Anesthesiol 36:71-72, 1968.
9. Simpson P. Defective Epidural Cannulae. Anaes 36:72, 1981.