Anesth Analg 2005;101:1528-1530
© 2005 International Anesthesia Research Society
doi: 10.1213/01.ANE.0000181006.36917.3E
REGIONAL ANESTHESIA
An In Vitro Comparison of the Electrical Conducting Properties of Multiport Versus Single-Port Epidural Catheters for the Epidural Stimulation Test
Ban C. H. Tsui, MD, MSc, FRCP*, and
Corey K. C. Sze
*Department of Anesthesiology and Pain Medicine, University of Alberta, Edmonton, Alberta, Canada; Faculty of Engineering, University of Alberta, Edmonton, Alberta, Canada
Address correspondence and reprint requests to Ban C.H. Tsui, MSC, MD, FRCP(C), Department of Anesthesiology and Pain Medicine, 8–120 Clinical Sciences Building, University of Alberta, Edmonton, Alberta, Canada T6G 2G3. Address electronic mail to btsui{at}ualberta.ca.
 |
Abstract
|
|---|
Effective conduction of electricity through a catheter is essential for the success of the epidural stimulation test. In this in vitro study we examined the electrical conductivity of single and multiport epidural catheters (with and without embedded metal elements) after being primed with normal saline. Seven different types of 19-gauge catheters (n = 5), either single-port or multiport catheters, with or without embedded metal elements, were studied. The proximal end of each epidural catheter was connected to the cathode of a nerve stimulator via an electrode adapter. The catheter, primed with normal saline, was placed at the bottom of a syringe filled with 5 different volumes of saline (1, 2, 3, 4 and 5 mL) and attached to an electrode adapter. The voltage of the peripheral nerve stimulator was measured using an oscilloscope. The electrical resistance between the proximal and distal end of the catheter was calculated using Ohm’s Law. In catheters without metal elements the electrical resistances were too high to be measured. In catheters that had metal elements, the mean electrical resistances of the same catheter design (single-port or multiport) were similar. However, the electrical resistances of the multiport metal reinforced epidural catheters were significantly lower (P < 0.05) than the single-port metal coil reinforced epidural catheters. The volume of saline in the syringe had no impact on the measured electrical resistances. This study suggests that multiport metal reinforced epidural catheters have low electrical resistances and, thus, are a reasonable alternative to single-port catheters for transmitting sufficient current for performing the epidural stimulation test. On the other hand, epidural catheters without metal elements (single-port or multiport) are not suitable for performing the stimulation test.
|
Introduction
|
|---|
The use of epidural electrical current (1–10mA) to confirm epidural catheter location is a useful technique in pediatric patients (1–3). All previous studies on the epidural stimulation test used single-port metal-coil reinforced epidural catheters (Flexitip, Arrow International, Reading, PA) (1–3). However, multiport catheters with similar metal elements are now available. Because there is clinical evidence suggesting that multiport catheters provide a more even spread of local anesthetic within the epidural space (4,5), it is important to examine the suitability of these multiport catheters for transmitting sufficient current when performing the epidural stimulation test. This in vitro study examines if multiport epidural catheters, with or without metal elements, can transmit sufficient current (10 mA) for the epidural stimulation test.
|
Methods
|
|---|
Five samples of 7 different 19-gauge epidural catheters were studied: 1) single-port nylon catheters from Becton-Dickinson (Deseret Medical, Sandy, UT); 2) multiport nylon catheters from Becton-Dickinson; 3) single-port metal reinforced catheters from Arrow International; 4) single-port metal reinforced catheters from B. Braun (Bethlehem, PA); 5) multiport metal reinforced catheters from B. Braun; 6) single-port metal reinforced catheters from Portex (Sims, Markham, Ontario, Canada); and 7) multiport metal reinforced catheters from Portex. The proximal end of the epidural catheter was connected to the cathode of a nerve stimulator via an electrode adapter (Johans ECG Adapter, Arrow International Inc.). To try to mimic situations in which a catheter tip would be located at varying distances from the nerve, the syringe was filled with 5 different volumes of normal saline (1, 2, 3, 4, and 5 mL) and the catheter tip was placed at the bottom of the syringe (Fig. 1). We ensured that all ports were immersed in the fluid. The syringe was in turn attached to an electrode adapter. The intensity of current delivered by the nerve stimulator was calibrated before the experiments. The stimulator was set at an intensity of current of 10 mA, a pulse width of 0.2 ms, and a frequency of 1 Hz. The current output of the peripheral nerve stimulator was measured using a factory-calibrated oscilloscope (Tektronix Inc., Beaverton, OR). The electrical resistance was calculated using Ohm’s Law (r = V/I), where V was the measured voltage (volts) and I was the current output from the nerve stimulator (MaxiStim® Model ST5; Life-Tech, Inc., Stafford, TX). Data are presented as mean ± sd. A one-way analysis of variance test, followed by a post hoc Turkey-Kramer multiple comparisons test was performed. Statistical significance was determined as P < 0.05.
|
Results
|
|---|
The electrical resistances of the various single-port and multiport epidural catheters are summarized in Table 1. A decrease in voltage could not be measured in the nylon catheters from Becton-Dickinson, probably because of their high electrical resistances. For all other catheters with metal elements, the electrical resistances of these catheters remained constant (i.e., no change), despite changing the volume of saline in the syringe from 1 to 5 mL. The electrical resistances of the multiport catheters from B. Braun were significantly (P < 0.05) less than single port catheters from Arrow, B. Braun, and Portex. Multiport catheters from Portex also demonstrated the same statistically significant result (P < 0.05). However, there was no statistically significant difference among the different single-port catheters or among the different multiport catheters.
|
Discussion
|
|---|
This is the first in vitro study to examine the electrical conductivity of single and multiport epidural catheters (with and without embedded metal elements) after they had been primed with normal saline. Multiport metal reinforced catheters are a reasonable alternative to single-port 19-gauge metal reinforced catheters for transmitting sufficient current (10 mA) for performing the epidural stimulation test. On the other hand, regular nylon epidural catheters without metal elements (single-port or multiport) are not suitable for performing the stimulation test.
In the original technique described by Tsui et al. (6,7), the stimulating current (0.2 ms; 1 Hz) was conducted through the injected normal saline into the epidural space via an electrically conducting metal coil embedded in the catheter. Although saline can conduct electric current, the high impedance of this fluid through the lengthy, narrow epidural catheter hinders the flow of current. Any air lock within the lumen will also deter current flow. As all portable nerve stimulators have limited voltage ranges, low electrical resistance catheters are essential to allow sufficient current (10 mA) to be conducted from the source to the tip for performing the epidural stimulation test. This was evident in this experiment where the high electrical resistance regular nylon epidural catheters (single-port or multiport) could not transmit adequate current (Table 1).
Our results demonstrated that the volume of saline in the syringe had no impact on the measured electrical resistance between the two conducting points. This may be because the narrow catheter opening accounted for most of the electrical resistance and was therefore not significantly affected by small volume changes in the highly conductive normal saline. In contrast, the additional holes in the new multiport metal-coil reinforced catheters allowed several contact metal points for the conducting saline and, thus, significantly decreased the electrical resistance of these catheters compared with single-port catheters. Therefore, as regards electrical conduction, new multiport metal reinforced catheters are a reasonable alternative to 19-gauge metal reinforced catheters for transmitting sufficient current to perform the epidural stimulation test. Conventional plastic catheters are not suitable for performing the epidural stimulation test.
|
Footnotes
|
|---|
Supported, in part, by a Clinical Investigatorship Award, Alberta Heritage Foundation for Medical Research, Alberta, Canada.
Accepted for publication May 31, 2005.
|
References
|
|---|
- Tsui BC, Seal R, Koller J, et al. Thoracic epidural analgesia via the caudal approach in pediatric patients undergoing fundoplication using nerve stimulation guidance. Anesth Analg 2001;93:1152–5.[Abstract/Free Full Text]
- Tsui BC, Finucane B. Verifying accurate placement of an epidural catheter tip using electrical stimulation. Anesth Analg 2002;94:1670–1.[Free Full Text]
- Tsui BC, Wagner A, Cave D, Kearney R. Thoracic and lumbar epidural analgesia via the caudal approach using electrical stimulation guidance in pediatric patients: a review of 289 patients. Anesthesiology 2004;100:683–9.[ISI][Medline]
- D’Angelo R, Foss ML, Livesay CH. A comparison of multiport and uniport epidural catheters in laboring patients. Anesth Analg 1997;84:1276–9.[Abstract]
- Dickson MA, Moores C, McClure JH. Comparison of single, end-holed and multi-orifice extradural catheters when used for continuous infusion of local anaesthetic during labour. Br J Anaesth 1997;79:297–300.[Abstract/Free Full Text]
- Tsui BC, Finucane B. Epidural stimulator catheter. Tech Reg Anesth Pain Manage 2002;6:150–4.
- Tsui BC, Gupta S, Finucane B. Confirmation of epidural catheter placement using nerve stimulation. Can J Anaesth 1998;45:640–4.[Abstract/Free Full Text]
Top
Abstract
Introduction
