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Can J Anaesth. 1999 Jul;46(7):675-8.

Detection of subarachnoid and intravascular epidural catheter placement.

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Department of Anesthesiology and Pain Medicine, University of Alberta and affiliated Hospitals (University of Alberta Hospital and Royal Alexander Hospital), 3B2.32 Walter Mackenzie Health Sciences Centre, Edmonton, Canada.



To report the detection of subarachnoid and intravascular catheter placement using nerve stimulation through an epidural catheter.


Electrical stimulation (1-10 mA) was applied through the catheter. A positive motor response (truncal or limb movement) indicated that the catheter was in the epidural space. Absence of a motor response indicated that it was not. A low milliamperage (<1 mA) with bilateral response indicated subarachnoid placement. Intravascular catheter placement was indicated by a positive response to the test, which remains at or returns to the baseline levels (i.e. prior to any local anesthetic injection), despite the administration of local anesthetics. In the first patient, the test confirmed subarachnoid catheter placement during attempts at continuous spinal anaesthesia even though CSF could not be aspirated. Bilateral motor response in the legs was observed at 0.2 mA. In the second patient, inadvertent subarachnoid placement was detected during attempted lumbar epidural block by observing bilateral motor response in the legs at 0.3 mA. In the third patient, intravascular placement was suspected and confirmed by failure to obliterate the motor response despite repeated local anesthetic injection.


The new test provides objective information in managing epidural catheters when their position is uncertain.

[Indexed for MEDLINE]

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