Epidural stimulation test vs epidural ECG test for checking epidural catheter placement

E-mail: btsui{at}ualberta

Editor—It is with great interest that I read the excellent literature review of pain management techniques for pediatric practice by Lonnqvist and Morton.1 However, I should like to point out that the statements regarding epidural stimulation testing are not entirely correct.

I agree with the authors' statement that by using epidural electrocardiography (ECG) test, it is possible to determine correct threading placement after administering neuromuscular blocking agents or epidural anesthetics.1 It is true that epidural ECG technique will not exclude a catheter lying at the appropriate segmental level in the subarachnoid space or intravascularly.2 However, the statement ‘neither of the two techniques described by Tsui will exclude a catheter lying at the appropriate segmental level but not in the subarachnoid space or intravascularly’ is incorrect and misleading concerning the epidural stimulation test.3 For epidural stimulation testing, our previous studies have demonstrated that a low current between 1–10 mA applied through the epidural catheter results in a motor response indicating the catheter is in the epidural space.3 If the catheter is located in the subarachnoid space, the motor response found resultant of electrical stimulation is a positive segmental motor response (<1 mA).3 If the catheter is located in the subdural space, electrical stimulation results in a multiple segmental motor response (<1 mA).4 Subarachnoid and subdurally positioned epidural catheters elicit motor responses with a lower threshold current (<1 mA) because the stimulating catheter is very close or in direct contact with highly conductive cerebrospinal fluid (CSF).4 5 The electrical stimulation technique can also exclude a catheter lying intravascularly; the stimulation test will result in the electrical current remaining or returning to baseline threshold current (1–10 mA) in the situation of intravascular placement, even after local anesthetic injection.5 Thus, we believe that the newly introduced epidural stimulation test can provide objective and practical information regarding epidural catheter location including subarachnoid and intravascular placement.

B. C. H. Tsui

Edmonton, Canada

References

1 Lonnqvist PA, Morton NS. Postoperative analgesia in infants and children. Br J Anaesth 2005; 95: 59–68[Free Full Text]

2 Tsui BCH, Seal R, Koller J. Thoracic epidural catheter placement via the caudal approach in infants by using electrocardiographic guidance. Anesth Analg 2002; 95: 326–30[Abstract/Free Full Text]

3 Tsui BC, Gupta S, Finucane B. Confirmation of epidural catheter placement using nerve stimulation. Can J Anaesth 1998; 45: 640–4[Abstract]

4 Tsui BC, Gupta S, Emery D, Finucane B. Detection of subdural placement of epidural catheter using nerve stimulation. Can J Anaesth 2000; 47: 471–3[Abstract/Free Full Text]

5 Tsui BC, Gupta S, Finucane B. Detection of subarachnoid and intravascular epidural catheter placement. Can J Anaesth 1999; 46: 675–8[Abstract]





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