Response Patterns to the Electric Stimulation of Epidural Catheters in Pregnant Women: A Randomized Controlled Trial of Uniport Versus Multiport Catheters
Authors: Patel Ruchira , Arzola Cristian , Petrounevitch Vitali , Balki Mrinalini , Downey Kristi , Tsui Ban C. H. , Carvalho Jose C. A. 
Published: April 2016

BACKGROUND:
The transcatheter electric stimulation test (Tsui test) can be performed at the bedside to confirm the correct placement of a wire-reinforced epidural catheter within the epidural space. The most commonly observed motor response with a uniport epidural catheter placed in the lumbar area is the unilateral contraction of the lower limbs. Wire-reinforced multiport catheters have recently been introduced into clinical practice; however, the characteristics of the Tsui test with such catheters are unknown. We designed a randomized controlled trial to test the hypothesis that the incidence of a bilateral response to the Tsui test would be higher with a multiport catheter, with all other characteristics of the test remaining unchanged.

METHODS:
We recruited laboring women requesting epidural analgesia. The epidural catheter placement was performed in a standard fashion, assisted by ultrasound, aiming at the L3-L4 interspace. Patients were randomly allocated for the placement of either a 19-G uniport or a 19-G multiport wire-reinforced catheter. The Tsui test (frequency 2 Hz; pulse width 0.2 millisecond) was performed immediately after securing the catheter (baseline) and at 5 minutes after a test dose with 3 mL lidocaine 2%. The current output was increased from zero until motor activity was detected up to a maximum of 20 mA. Subsequently, an initial loading dose of 10 mL bupivacaine 0.125% and 50 μg fentanyl was administered. The sensory block level to ice was assessed bilaterally at 20 minutes after injection of the loading dose. The primary outcome was the motor response pattern to the electric stimulation of the epidural catheter, either unilateral or bilateral; secondary outcomes included minimal current intensity needed to elicit a motor response at baseline and 5 minutes after the test dose, sensory block level and incidence of symmetrical sensory block at 20 minutes after injection of the loading dose, pain scores before the test dose and at 20 minutes after the loading dose, and need for catheter replacement within 2 hours of completion of the loading dose.

RESULTS:
Sixty-three women were assessed for eligibility and 46 were randomly allocated equally to each group. Three patients were excluded, resulting in 21 subjects in the multiport group and 22 subjects in the uniport group. Patient characteristics in both groups were similar. The incidence of unilateral motor response to the Tsui test was 95.2% (20/21) and 95.5% (21/22) in the multiport and uniport groups, respectively (rate difference 0.22%; 95% confidence interval, for the difference −29.2 to 29.2%; P = 0.99). The minimal current intensity (mean ± SD) required to produce a motor response at baseline was 5.4 ± 3.5 mA and 5.4 ± 4.1 mA in the multiport and uniport groups, respectively (P = 0.98). The sensory block levels to ice on the left and right, as well as pain scores at 20 minutes, were similar in both groups. No epidural catheters were resited.

CONCLUSIONS:
The Tsui test produced a high percentage of unilateral motor response in women with both uniport and multiport wire-embedded catheters. A larger study is necessary to confirm that there is no clinically significant difference in the motor response patterns between the 2 catheter types.