TABLE 1.

Epidural electrical stimulation test (Tsui test)

Catheter location	Motor response	Current
Subcutaneous	None	NA
Subdural	Bilateral (many segments)	<1 mA
Subarachnoid	Unilateral or bilateral	<1 mA
Epidural space against nerve root	Unilateral	<1 mA
Nonintravascular	Unilateral or bilateral	1 mA to 10 mA (threshold current increases after local anesthetic is injected)
Intravascular	Unilateral or bilateral	1 mA to 10 mA (no change in threshold current after local anesthetic is injected)

Confirmation of catheter placement in the epidural space is recieved once obtaining either a bi- or unilateral motor response, and when the threshold current is 1 mA to 10 mA initially and increases with injection of local anesthetic