To the Editor:-Jaeger and Madsen recently presented a case of delayed subarachnoid migration of an epidural catheter. [1]Diagnosis was based on a late onset of phenomena suggestive for subarachnoid block (SAB), even though initially the block appeared to be epidural. Unfortunately, the diagnosis was not confirmed by analysis of aspirated fluid or radiographic determination of catheter position. There may, however, be another explanation for the described event.

The authors state that their first attempt at catheter placement at T11-T12 resulted in an obvious subarachnoid puncture. At the second, successful attempt at T10-T11, an Arrow FlexTip Plus catheter was inserted with the Tuohy needle bevel oriented cephalad. More than 24 h after establishing a normal epidural block, the patient was found with what appeared to be a high SAB caused by intrathecal local anesthetic (LA) and opioids. The authors attribute this to a delayed subarachnoid migration of the catheter. However, it is possible that the catheter was still in the epidural space. It was demonstrated for both lumbar [2]and thoracic [3,4]epidural anesthesia that roughly 50% of catheters inserted through a cephalad-oriented Tuohy needle are directed in caudad direction. The close proximity of the orifice (the Arrow FlexTip catheter is an end-hole catheter) to the preexistent dural puncture site may then have permitted large amounts of local anesthetic and opioid to enter the subarachnoid space and cause a SAB. After an epidural infusion at a rate of 14 ml/h for over 24 h, the few ml of clear fluid that could be aspirated from the catheter may have been either LA/opioid solution, cerebral spinal fluid, or a combination of both. It is unfortunate that the authors did not record the amount of centimeters that the catheter was advanced beyond the Tuohy needle tip. The stated 15 cm marking at the skin is not of any importance without knowledge of the skin-dura distance in this particular patient.

Although in this case there was no laboratory or radiographic evidence to support either the theory above or the authors' theory, epidural catheter insertion one level cephalad of an inadvertant dural puncture site may not always prevent epidural solution from entering the subarachnoid space. This was demonstrated in a case report by Van Zundert and Scott, in which a patient died after lumbar epidural administration of a large amount of LA, one level cephalad of an earlier dural puncture site. [5]Diagnosis was confirmed during autopsy by determination of high levels of LA in the cerebrospinal fluid and location of the catheter in the epidural space.

W. Anton Visser, M.D.

Clinical and Research Fellow; Department of Anaesthesia; University of British Columbia; 910 W. 10th Avenue; Vancouver, British Columbia; Canada

(Accepted for publication January 20, 1998.)

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