Anesth Analg 2003;97:1524-1526
© 2003 International Anesthesia Research Society
REGIONAL ANESTHESIA
Tensile Strength of 19- and 20-Gauge Arrow Epidural Catheters
Ban C. H. Tsui, MD MSc, FRCP, and
Brendan Finucane, MB ChB, FRCP
From the Department of Anesthesiology and Pain Medicine, 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, University of Alberta Hospitals, 3B2.32 Walter Mackenzie Health Science Centre, 8440–112 Street, Edmonton, Alberta, Canada T6G 2B7. Address email to btsui{at}ualberta.ca
 |
Abstract
|
|---|
There are no data about the mechanical properties of the 20-gauge reinforced Arrow epidural catheter, which has a similar design to the 19-gauge reinforced Arrow catheter. In this study, we compared the mechanical properties of 19- and 20-gauge Arrow epidural catheters at 22°C and 37°C. The distal 12 cm of each catheter was suspended in an enclosed chamber maintained at either 22°C or 37°C. A pair of forceps was applied to each catheter 5 cm from the distal end (fixed site). Another pair of forceps was applied 15 cm from the catheter tip (traction site). The catheter was pulled. At 22°C, the mean fracture force was 2.24 kg (range, 1.96 – 2.41 kg) for 5 19-gauge catheters and 2.17 kg (range, 2.04–2.41 kg) for 5 20-gauge catheters. At 37°C, the mean force was 1.98 kg (range 1.84- 2.15 kg) for 5 19-gauge catheters and 1.99 kg (range, 1.81–2.09 kg) for 5 20-gauge catheters. There were no significant differences in tensile strength between the two different gauge catheters at either temperature. All the 19-gauge catheters fractured at the same "fixed site" at both temperatures. All the 20-gauge catheters elongated at the "fixed site" but fractured at the "traction site." We conclude that using the smaller-gauge catheter (20-gauge) is not associated with a more frequent rate of fracture.
IMPLICATIONS: The 20-gauge Arrow epidural catheters had similar tensile strengths as the 19-gauge epidural catheters but fractured at the traction site rather than at the fixed site. Thus, the 20-gauge Arrow catheter may be a reasonable alternative to the 19-gauge Arrow catheter.
|
Introduction
|
|---|
The reinforced Arrow epidural catheter has the advantages of ease of insertion and an infrequent incidence of associated paresthesias and epidural vein cannulation (1). The 19-gauge variety of this catheter fractures occasionally on removal (2–4). However, there are no data regarding the mechanical properties of the 20-gauge reinforced Arrow epidural catheter, which has a similar design to the 19-gauge catheter. This study compared the mechanical properties of 19-gauge and 20-gauge Arrow epidural catheters at 22°C ("room" temperature) and 37°C ("body" temperature).
|
Methods
|
|---|
We studied 10 samples of both 19- and 20-gauge reinforced Arrow epidural catheters (FlexTip Plus, Arrow International, Reading, PA). The distal 12 cm of the catheter was suspended in an enclosed plastic chamber with temperatures maintained at either 22°C ("room" temperature) or 37°C ("body" temperature) using the Fisher Anesthesia Humidifier (Model MR720, Fisher and Paykel Health Care, Laguna Hills, CA) for 15 min before each experiment (Fig. 1). The plastic chamber was made from a shortened endotracheal tube (size 7.5). A pair of forceps was fixed and applied to the catheter 5 cm from the catheter tip (fixed site) via the plastic chamber, simulating a catheter trapped by a vertebral structure in a patient. Another pair of rubber-sleeved forceps was applied just outside of the enclosed chamber (not shown in Fig. 1) 15 cm from the catheter tip (traction site). The traction force was applied and measured using a digital hand-held scale (ProGuide Digital Scale, Rapala V M C Corp, Oshawa, Ontario, Canada). The traction site simulates the site where the catheter would be pulled during removal. The catheter was pulled slowly, and the force required to fracture the catheter was recorded. The site of fracture was also noted.
|
Results
|
|---|
The mean force required to fracture 19- and 20-gauge epidural catheters at 2 different temperatures is shown in Figure 2. At 22°C, the mean fracture force was 2.24 kg (range, 1.96 – 2.41 kg) for 5 19-gauge catheters and 2.17 kg (range, 2.04–2.41 kg) for 5 20-gauge catheters. At 37°C, the mean force was 1.98 kg (range, 1.84- 2.15 kg) for 5 19-gauge catheters and 1.99 kg (range, 1.81–2.09 kg) for 5 20-gauge catheters. There were no significant differences in tensile strength between the two different gauge catheters at either temperature. All 19-gauge catheters fractured at the same site (5 cm from the distal end) at both temperatures. All 20-gauge catheters elongated at the 5 cm site but fractured at the site where the force was applied (Fig. 3).
|
Discussion
|
|---|
Although the incidence of fracture of epidural catheters during removal is unknown, it appears to be infrequent (2–4). We have routinely used both 19- and 20-gauge Arrow epidural catheters and have never encountered a case of breakage during several years of use in our institution, although we are aware of one case within our community. This is the first study to examine the tensile strength and fracture site of 19- and 20-gauge Arrow epidural catheter at both 22°C ("room" temperature) and 37°C ("body" temperature).
Previous studies have suggested that the mean force required to remove an epidural catheter from a patient ranges between 0.17 to 0.32 kg and the maximum withdrawal force is 1.17 kg (5,6). Thus, the findings in this study, showing that the mean fracture force required to break either of these catheters was much more than the maximum reported withdrawal force required, indicate that these catheters would be unlikely to fracture under normal clinical circumstances.
Although this study has limitations and the results may not accurately reflect the rare occurrence of a difficult catheter extraction in a clinical setting, we attempted to simulate the clinical situation. First, we applied a pair of forceps to fix the catheter in an enclosed chamber maintained at 37°C, simulating a catheter trapped by a vertebral structure in a patient. Second, we applied another rubber-sleeved forceps to pull the catheter outside the chamber at 22°C, simulating traction applied by anesthesiologists when removing epidural catheters from patients. A digital hand-held scale was attached to the pulling forceps to measure the tensile strength accurately. Because the speed of stretching the catheter may also affect how the catheter fractures, we applied gentle and steady traction with a speed similar to that used by anesthesiologists when removing epidural catheters from patients.
Despite slightly reduced tensile strength of both 19-gauge and 20-gauge catheters at the higher temperature (37°C), there were no significant differences in tensile strength observed between the two different gauge catheters at the two temperatures studied. This may be because of the inner stainless steel coil of the Arrow catheters that provide some of the tensile strength and are not affected by minor temperature changes. One of the important findings in this study was the difference in the location of the fracture sites of 19 and 20-gauge catheters. The 20-gauge catheter had a similar tensile strength to the 19-gauge catheter but fractured at the traction site rather than at the fixed site. This observation concurs with previous clinical reports and an in vitro study showed that the common breakage site of the 19-gauge catheter was at the fixed site where the inner metal coil was less dense (2). Based on this observation, we speculated that the likelihood of an accidental fracture beneath the skin would be less likely with a 20-gauge catheter than with a 19-gauge catheter.
Another important advantage of using a 20-gauge in preference to a 19-gauge catheter is that one can use a smaller gauge Tuohy needle (18-gauge versus 17 or 16-gauge). Although there is no clear evidence to support improved outcomes by using smaller epidural needles, one would intuitively expect less discomfort and a reduced potential for postdural headache. Nevertheless, caution is required when interpreting clinical implications of these in vitro results.
|
Acknowledgments
|
|---|
Supported, in part, by a Clinical Investigatorship Award from the Alberta Heritage Foundation for Medical Research, Alberta, Canada.
|
References
|
|---|
- Banwell BR, Morley-Forster P, Krasue R. Decrease incidence of complications in parturients with the Arrow (FlexTip Plus) epidural catheter. Can J Anaesth 1998; 45: 370–2.[Abstract/Free Full Text]
- Asai T, Yamamoto K, Hirose T, Taguchi H, et al. Breakage of epidural catheters: a comparison of an arrow reinforced catheter and other nonreinforced catheters. Anesth Analg 2001; 92: 246–8.[Abstract/Free Full Text]
- Ates Y, Yucesoy CA, Unlu A, et al. The mechanical properties of intact and traumatized epidural catheters. Anesth Analg 200; 90: 393–9.
- Nishio I, Sekiguchi M, Aoyama Y, et al. Decreased tensile strength of an epidural catheter during its removal by grasping with a hemostat. Anesth Analg 2001; 93: 210–2.[Abstract/Free Full Text]
- Morris GN, Warren BB, Hanson EW, et al. Influence of patient position on withdrawal forces during removal of lumbar extradural catheters. Br J Anaesth 1996; 77: 419–20.[Abstract/Free Full Text]
- Boey SJ, Carries LES. Withdrawal forces during removal of lumbar extradural catheters. Br J Anaesth 1994; 73: 833–5.[Abstract/Free Full Text]
Accepted for publication June 25, 2003.
Top
Abstract
Introduction
