To the Editor:-The "migration" of epidural catheters into undesirable locations is well-documented in the literature. The three most commonly reported sites of catheter misplacement are intravascular, subdural, and subarachnoid. However, most of these reports provide details consistent with introduction of the Tuohy needle, either partially or completely, into these spaces prior to the placement of the catheter. Others have reported what appeared to be a block produced by a normally functioning epidural catheter which, after a few subsequent bolus doses, "suddenly" produced a far more extensive block, i.e., from lumbar to cervical. To our knowledge, only one instance of an epidural catheter perforating into the subdural space after functioning normally for a prolonged period of time (4 days) has been reported. [1]We report an apparent delayed perforation into the subarachnoid space involving the new soft FlexTip PlusO epidural catheter (Arrow International).

The patient was a 66-yr-old woman with malignant mesothelioma presenting for thoracotomy and pleural decortication. Multiple attempts were made to place an epidural catheter in the T7-T8 interspace using the "loss of resistance" technique and normal saline. At no time did we note paresthesias, blood, or cerebrospinal fluid (CSF). A catheter was threaded but subsequent doses of local anesthetic failed to confirm placement in the epidural space. The surgery proceeded under general anesthesia without incident. Several hours after surgery, a repeat attempt at catheter placement at T11-T12 resulted in an obvious subarachnoid puncture. A second successful atraumatic attempt was made at T10-11. With the Tuohy needle bevel oriented cephalad, another Arrow FlexTip Plus catheter was threaded without resistance to about 15 cm at the skin and secured. Aspiration of the catheter yielded no fluid. A test dose of 5 ml of 2% lidocaine with 1:200,000 epinephrine was injected slowly producing a gradual decline in blood pressure (BP) from 124/82 to 95/47 mmHg and moderate resolution of her pain. A detailed neurologic examination was not performed. Our Acute Pain Service (APS) began an epidural infusion of 0.125% bupivacaine plus hydromorphone 6 mg/ml at 14 ml/h. Approximately 2.5 h later the patient was transferred to a "step-down" unit for further observation. At this time the patient was comfortable with a sensory deficit to cold from T4to L1, coughing effectively, and performing deep-breathing maneuvers easily. She did not report any extraordinary sensations of numbness or demonstrate any muscle weakness.

Our APS examined the patient the next morning and found her to be alert and oriented with motor and sensation to light touch intact. Except for mild pruritus and nausea controlled with intravenous promethazine 6.25 mg, she was comfortable. When examined that afternoon there was no change in her condition. Sometime that evening the patient's husband recalled that she was more somnolent and seemed weaker. At about 02:00 the next day, the nurse found the patient barely responsive with a respiratory rate of 6 breath/min. She was not moving her extremities. Her O2saturation was 86%, and her BP was 80/50 mmHg with a heart rate of 78 beats/min. Her pupils were 2 + and reacted sluggishly. The epidural infusion was stopped and 100% O2by mask, 1 l of crystalloid and intravenous naloxone 0.4 mg was administered by the nursing staff. The patient quickly aroused, and her sensorium cleared. Her upper and lower extremities were paralyzed. Sensation to pinprick was absent from the C6dermatome and below. Aspiration of the epidural catheter did not return any fluid until it was withdrawn 3-4 cm whereupon a few ml of clear fluid was obtained. Unfortunately the fluid was discarded without analyzing for CSF. The catheter was removed before radiographic determination of its true position could be obtained. Appropriate concentrations of drug in the remaining epidural infusate was verified by our pharmacy. Over the next several hours, the patient's strength and sensation recovered in a manner consistent with the recession of a local anesthetic-induced block. She never complained of a headache. The patient was discharged from the hospital without any sequelae.

The final position of our catheter was never determined with certainty because neither CSF was aspirated nor radiographic evidence obtained. However, on clinical grounds, it is difficult to explain the transition of a purely analgesic state to one marked by quadriplegia and depressed consciousness without proposing subarachnoid deposition of our 0.125% bupivacaine [center dot] 6 mg sup -1 [center dot] ml sup -1 hydromorphone infusate. It is generally appreciated that, theoretically, any epidural catheter can penetrate the dura. The new catheter by Arrow does not appear to be an exception in spite of its flexibility.

J. Michael Jaeger, Ph.D., M.D.

Assistant Professor of Anesthesiology and Neurological Surgery

Melissa L. Madsen, M.D.

Resident in Anesthesiology

Department of Anesthesiology; University of Virginia Health Sciences Center; Box 10010; Charlottesville, Virginia 22906-0010

(Accepted for publication June 23, 1997.)

Hartrick CT, Pither CE, Pai U, Tomsick TA: Subdural migration of an epidural catheter. Anesth Analg 1985; 64:175-8.