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Pigtail Catheters Used for Percutaneous Fluid Drainage: Comparison of Performance Characteristics¹

¹ From the Department of Radiology, Duke University Medical Center, Durham, NC. From the 2002 RSNA Annual Meeting. Received April 7, 2005; revision requested June 7; revision received August 1; final version accepted September 6. Address correspondence to D.B.M., 3405 Storey Lake Dr, Tyler, TX 75707 (e-mail: doug{at}machas.net).

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION APPENDIX ADVANCES IN KNOWLEDGE References

 
Purpose: To compare the performance characteristics of various single-lumen all-purpose pigtail drainage catheters.

Materials and Methods: The following parameters were compared: flow rates between catheters of the same size, whether changing the fluid viscosity has any effect on catheter comparisons, the effect on flow of leaving an open three-way stopcock in the drainage pathway, the tendency of the catheters to kink, and catheter patency after kinking, as measured according to flow. All-purpose 8.0-, 8.3-, and 8.5-F (collectively referred to as 8-F); 10.0-, 10.2-, and 10.3-F (collectively referred to as 10-F); and 12.0-F pigtail drainage catheters from three manufacturers were evaluated. Data were compared by using two-tailed t tests after normal distributions were confirmed. P < .05 was considered to represent a significant difference.

Results: At comparison of the 8-F catheters, the C.R. Bard catheters demonstrated better flow rates than the Cook and Boston Scientific devices. Among the 10-F catheters, there were no significant differences in the flow rates of fluid with viscosity equivalent to that of water between the C.R. Bard and Boston Scientific catheters; however, both these catheter types demonstrated significantly (P < .05) better flow rates than the Cook devices. Among the 12-F catheters, the C.R. Bard catheters demonstrated significantly (P < .05) better flow rates than the other two catheter types. Changing the fluid viscosity caused no changes in comparison results. In all catheter groups, the presence of a stopcock significantly (P < .05) impaired flow. None of the evaluated catheters demonstrated a clear advantage in terms of patency or susceptibility to kinking.

Conclusion: At comparison of the in vitro performances of catheters from different manufacturers, the C.R. Bard 8.0-F and Cook 10.2-F catheters had comparable flow rates, and flow rates through the C.R. Bard and Boston Scientific 10.0-F catheters were comparable to flow rates through the Cook and Boston Scientific 12.0-F catheters. Varying viscosity had no effect on comparisons of catheter flow rates; however, a stopcock between the vacuum source and the catheter was noted to impair flow rates in all brands and sizes of evaluated catheters.

© RSNA, 2006

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION APPENDIX ADVANCES IN KNOWLEDGE References

 
Percutaneous catheter drainage catheters are commonly used for the treatment of fluid collections of varied causes in the chest, abdomen, and pelvis. Predicting a successful drainage procedure is a complex and multifactorial process based on the size, location, character, and configuration of the abscess. Other important factors include the selected drainage technique, the composition and viscosity of the abscess contents, the catheter configuration (ie, sump, dual lumen, or single lumen), and the lumen size (1–21). The only controllable and variable factor other than operator technique, guidance modality, and timing is the choice of catheter used. The flow of various body fluids through catheters has been demonstrated to follow the Poiseulle law: The flow rate (F)—that is, the volume of fluid flowing per unit of time—is proportional to the pressure difference (p) between the ends of the pipe and the radius to the fourth power (r⁴): F = pr⁴/8Lµ, where L is the length of the pipe and µ is the coefficient of viscosity, a constant variable of the given fluid (4,22).

Investigators in a prior study compared the effectiveness of single- and double-lumen catheters in vitro and suggested that single-lumen catheters perform better and are more cost effective than dual-lumen devices (2). Another study revealed that single-lumen catheters work as effectively as sump-type catheters (16). For more viscous fluids, catheters with larger bores enable more rapid drainage, and on a theoretic and experimental basis, the addition of urokinase or streptokinase decreases viscosity and increases the rate of flow of purulent material (4,23). The model and size of the all-purpose drainage catheter(s) used to perform ultrasonographically or computed tomography–guided catheter placement are most often selected according to operator familiarity and/or institutional preference. The purpose of our study was to compare the performance characteristics of all-purpose single-lumen pigtail drainage catheters made by different manufacturers.

	MATERIALS AND METHODS

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Catheters
A total of 100 catheters and various testing supplies were provided by three vendors: Cook (Bloomington, Ind), C.R. Bard (Covington, Ga), and Boston Scientific (Natick, Mass). We received no financial aid from the manufacturers and had control of the data and information submitted for publication. The following pigtail drainage catheters were evaluated: 8.5-, 10.2-, and 12.0-F all-purpose Cope-type catheters (Cook); Navarre 8.0-, 10.0-, and 12.0-F nitinol-reinforced pigtail catheters (C.R. Bard); and Meditech 8.3-, 10.3-, and 12.0-F regular pigtail catheters and 12.0-F nephrostomy catheters with absorbable tips (Boston Scientific). The full names and further descriptions of the catheters used are given in the Appendix.

The following parameters were compared: flow rates between catheters of the same size, whether changing fluid viscosity would have any effect on the catheter comparisons, the effect on flow of leaving an open three-way stopcock in the drainage pathway, the tendency of the catheters to kink, and catheter patency after kinking, as measured according to flow.

The total 100 catheters were studied. Their inner diameters, outer diameters, and lengths are listed in the Table. Ten catheters of each size from each vendor were tested by using a 30 mm Hg vacuum source (Vacuum Regulator; Ohmeda, Columbia, Md) to measure flow rates. A suction value of 30 mm Hg was selected after preliminary testing revealed that commonly used Jackson-Pratt bulb drains (Cardinal Healthcare, McGaw Park, Ill), which we routinely use in our practice, generate 30–50 mm Hg of suction when they are initially set up.

View larger version (25K): [in this window] [in a new window] [Download PPT slide]   Figure 1: Diagram of flow rate testing.

Stopcock Testing
It is not uncommon for a two- or three-way stopcock to be routinely used in the catheter pathway, primarily to facilitate Jackson-Pratt bulb or drainage reservoir exchanges and routine catheter flushing. Thus, a test to compare flow rates in the same catheter with and without the stopcock in place was devised. For "stopcock-present" testing, the two-way stopcock that comes packaged with the drain connector tubing kit (REF 22–910; Boston Scientific) that we routinely use was placed in the drainage pathway. Then, for each catheter group, flow rates were evaluated under the same conditions underwhich the previous flow rate determinations without the stopcock present were made. In addition, with use of a micrometer, the internal diameters of three-way stopcocks from various manufacturers were evaluated: Abbott Intralock, REF 42383–01 3W (Abbott Laboratories, Abbott Park, Ill); Namic Morse, REF 70055003 (Boston Scientific); and Baxter Large-Bore 3-Way, REF 2C6202 (Baxter, Deerfield, Ill). One author (D.B.M.) performed all of the stopcock tests.

Flow Rates and Statistical Analysis
The flow rates achieved with each catheter group (n = 10) were evaluated at statistical analysis. Statistical analysis software (SPSS for Windows, version 6.0, SPSS, Chicago, Ill; Statgraphics Plus, version 5.0, Statistical Graphics, Herndon, Va) was used to evaluate the data. Normal distributions were achieved, as confirmed by using measures of skewness and kurtosis, and, thus, one-way analysis of variance between means was used to study the data. If a significant difference between the three main catheter size groups (8, 10, and 12 F) was found, individual two-tailed t-test comparisons between catheter groups were performed. P < .05 was considered to indicate a statistically significant difference.

Susceptibility to Kinking and Statistical Analysis
To evaluate the catheters' susceptibility to kinking, we constructed an apparatus (Fig 2) that would bend the catheters around gauge pins of gradually decreasing radius until a visible kink formed. Thus, a smaller kinking radius was better. Each catheter was tested at the following three locations, which represented the equidistant imaginary junctions between each quarter length of the catheter: at the imaginary junction between the proximal quarter length of the catheter and the distal three-fourths of the catheter, at the imaginary junction in the middle of the catheter length, and at the imaginary junction between the distal quarter length of the catheter and the proximal three-fourths of the catheter. The value of merit was determined to be the minimal radius (at any site) at which the catheter would not kink. One author (D.B.M.) performed all of the kink radius tests. The distributions were analyzed according to measures of skewness and kurtosis to ensure a normal distribution, and the means were compared by using t tests, with P < .05 indicating significance.

View larger version (21K): [in this window] [in a new window] [Download PPT slide]   Figure 2: Diagram of kink susceptibility testing. R = radius of gauge pin.

View larger version (169K): [in this window] [in a new window] [Download PPT slide]   Figure 3: Reproducible kink apparatus.

	RESULTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION APPENDIX ADVANCES IN KNOWLEDGE References

View larger version (27K): [in this window] [in a new window] [Download PPT slide]   Figure 4: Graph illustrates comparison of flow rates for normal saline solution (NS), which has low viscosity, among all catheter groups.

View larger version (26K): [in this window] [in a new window] [Download PPT slide]   Figure 5: Graph illustrates comparison of flow rates for oil, which has high viscosity, among all catheter groups.

View larger version (22K): [in this window] [in a new window] [Download PPT slide]   Figure 6: Comparison of normal saline flow rates achieved with 12-F Meditech catheters with an absorbable tip (Tip Present), without an absorbable tip (Regular), and with the absorbable tip dissolved.

View larger version (28K): [in this window] [in a new window] [Download PPT slide]   Figure 7: Effects of stopcock use on average flow rate, in milliliters per second. Cook catheters: 8.5 F (C8), 10.2 F (C10), and 12.0 F (C12). Navarre catheters: 8.0 F (N8), 10.0 F (N10), and 12.0 F (N12). Meditech catheters: 8.3 F (M8), 10.3 F (M10), and 12.0 F (M12).

View larger version (15K): [in this window] [in a new window] [Download PPT slide]   Figure 8: Comparison of minimal kink radii, in millimeters, for 8-F catheters.

View larger version (16K): [in this window] [in a new window] [Download PPT slide]   Figure 9: Comparison of minimal kink radii, in millimeters, for 10-F catheters.

View larger version (17K): [in this window] [in a new window] [Download PPT slide]   Figure 10: Comparison of minimal kink radii, in millimeters, for 12-F catheters.

View larger version (27K): [in this window] [in a new window] [Download PPT slide]   Figure 11: Effects of kinking on normal saline flow rates. Cook catheters: 8.5 F (C8), 10.2 F (C10), and 12.0 F (C12). Navarre catheters: 8.0 F (N8), 10.0 F (N10), and 12.0 F (N12). Meditech catheters: 8.3 F (M8), 10.3 F (M10), and 12.0 F (M12).

	DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION APPENDIX ADVANCES IN KNOWLEDGE References

 
Percutaneous pigtail catheters are now used extensively for abscess drainage. To our knowledge, before the present study, the performance characteristics of the described single-lumen all-purpose pigtail catheters from different manufacturers had not been evaluated comparatively in an in vitro or in vivo setting.

The nitinol reinforcement of Navarre catheters gives these devices a thinner wall that has the same outer diameter and a larger inner diameter compared with the walls of the other catheters of the same diameter (ie, French). This design gives these catheters higher flow rates with both low- and high-viscosity fluids compared with the flow rates possible with the Meditech and Cook devices of the same size. The only exception is that the Meditech 10.3-F catheter had flow rates comparable to those of the Navarre 10.0-F device. Interestingly, flow rates for the Navarre 8-F catheter were comparable to those for the Cook 10.2-F catheter, and Navarre and Meditech 10-F catheter flow rates were comparable to Cook and Meditech 12-F catheter values. Varying viscosity had no effects on the results of comparisons among the catheters.

The flow rates were directly comparable to the inner diameters of the various catheters listed in the Table. According to the Poiseulle law, catheter length is a theoretic component of flow rate, with shorter catheters having an advantage over longer ones. The differences in catheter length (Table) were minor and did not correlate with differences in catheter flow rates, as was predicted according to the Poiseulle law. This is because a catheter's inner diameter, owing to the radius to the fourth power, has a much greater effect on flow rates than its length.

The use of a stopcock between the vacuum source and the catheter is noted to impair flow rates and is thus best avoided, unless a large-bore stopcock is used. In the current study, the presence of a standard stopcock between the vacuum source and the catheter resulted in significantly decreased flow rates for the 8-, 10-, and 12-F catheters and thus reduced the advantage yielded by the larger lumen. This result was probably secondary to a bottleneck effect created by the bore of the stopcock, which, among the several stopcocks tested, was smaller than the internal diameters of the bores of even the small 8-F catheters. As a result of these data, in our department we began using a large-bore stopcock (Baxter Large-Bore 3-Way 2C6202) that measures 2.6 mm in diameter internally, which is similar to the internal diameters of the 12-F catheter lumina. Although we did not perform repeat testing of the flow rates achieved with this stopcock, it seems reasonable to assume that using a bore with an internal diameter that is at least equivalent to that of the drainage catheter will not result in decreased flow rates. Incidentally, the bore of the drain connector tubing that we use (REF 22–910) also has a substantially larger inner diameter than the 12-F catheter lumina.

We thought that the nitinol reinforcement of the Navarre catheters, while increasing flow rates as a result of a thinner reinforced wall and a larger internal lumen, would increase the relative stiffness of the catheters and thus worsen their susceptibility to kinking when transverse forces were applied. However, no group of catheters offered a clear advantage in terms of susceptibility to kinking. The nitinol wall reinforcement of 10-F Navarre catheters acts to maintain the patency of the devices after kinking. Again, however, no catheter group offered a clear advantage in terms of patency after kinking, according to flow rates measured in catheters with 90° kinks. After more severe—specifically, 180°—kinking, which seems unlikely to occur in vivo, the Navarre nitinol catheters demonstrated significantly better patency than did the Cook and Meditech devices.

A weakness of this study is that it was a solely in vitro catheter study in which only one of many factors used to predict successful percutaneous drainage was evaluated. However, catheter choice is one of the few factors involved in percutaneous drainage that is controllable. Also, the evaluations and results in this study apply to only those fluids with viscosities of up to 200 mPa · sec and thus may not be applicable to thicker pus with greater viscosity. The viscosity of pus ranged from 6 to 470 mPa · sec in one study; however, the fluid sample with a viscosity of 470 mPa · sec was an outlier and the mean pus viscosity was 70 mPa · sec (23).

Another limitation was that the studied material did not include particulate matter. Also, we did not evaluate gravity drainage of pus, which is a technique used in some institutions, although not in ours except in cases of large or recurrent fluid collections. Unlike suction-type drains, which rely on the negative pressure at the catheter output, gravity drains rely on positive pressure from within the patient relative to the outside atmospheric pressure to generate flow. When the Poiseulle law regarding flow in a tube is considered, the difference in mechanism between gravity and suction-type drains translates to a change in only one variable: p, the difference in absolute pressure between the ends of the tube. The remaining variables are unchanged. Although our comparisons did not include models of flow generated by a positive pressure system, we do not believe that the described differences in flow rates between the catheters would change with the use of such a system.

The drainage catheters available from Uresil (Skokie, Ill) and InterV (Dartmouth, Mass) were not available for our evaluation. Also, the study did not include evaluations of 14- and 16-F catheters, which are not used in our practice. It should be noted, however, that Gobien et al (6) found no significant differences in the success rates achieved with percutaneous drainage procedures between catheters of different sizes. There are other factors related to catheter performance—specifically, the biomaterials used to construct the devices and a catheter's susceptibility to clogging as a function of internally applied coatings, which can have a major effect on catheter performance. However, these factors were not assessed in this study. A technique developed by Lee et al (1) represents a quantitative method of evaluating flow resistance through indwelling catheters in vivo by monitoring the pressure at the catheter hub during saline infusion. This technique is promising for future in vivo comparisons of catheters.

In summary, the flow rates achieved with the Navarre 8.0-F catheters were comparable to those achieved with the Cook 10.2-F devices, and the flow rates achieved with the Navarre and Meditech 10.0-F catheters were comparable to those achieved with the Cook and Meditech 12.0-F devices. Although varying viscosity had no effect on comparisons among the different catheters, a standard stopcock placed between the vacuum source and the catheter was noted to impair flow rates for all brands and sizes of catheters. The comparison of these all-purpose drainage catheters and the study of the effects of using a stopcock revealed differences and findings that may be of interest to the reader and help in choosing a catheter for use in drainage procedures.

	APPENDIX

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION APPENDIX ADVANCES IN KNOWLEDGE References

 
The following are a list and descriptions of the catheters tested in this study:

1. Ultrathane Cope-type loop multipurpose drainage catheters (Cook): Cook REF ULT8.5–38-25-P-6S-MCL, 8.5 F, 25 cm, six side holes; Cook REF ULT10.2–38-25-P-6S-MCL, 10.2 F, 25 cm, six side holes; Cook REF ULT12.0–38-25-P-6S-MCL, 12.0 F, 25 cm, six side holes.

2. Meditech Flexima regular all-purpose drainage catheter sets with locking pigtail (Boston Scientific): Meditech REF 27–134, 8.3 F; Meditech REF 27–135, 10.3 F; Meditech REF 27–138, 12.0 F.

3. Meditech Flexima regular nephrostomy catheter system with locking pigtail and TempTIP (Boston Scientific): Meditech REF 28–121, 12.0 F, 25 cm.

4. Navarre universal drainage catheters with nitinol (C.R. Bard): Navarre REF NNU8LPT, 8.0 F, 30 cm; Navarre REF NNU10LPT, 10.0 F, 30 cm; Navarre REF NNU12LPT, 12.0 F, 30 cm.

	ADVANCES IN KNOWLEDGE

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION APPENDIX ADVANCES IN KNOWLEDGE References

 

• Changing fluid viscosity has no effect on the comparison of catheters.
  
• With all catheter sizes, leaving an open three-way stopcock in the drainage pathway impairs flow.
  
• None of the catheters tested offers an advantage in terms of susceptibility to kinks.
  
• None of the catheters tested offers an advantage in terms of patency after kinking.
  

	FOOTNOTES

 
Authors stated no financial relationship to disclose.

Author contributions: Guarantors of integrity of entire study, D.B.M., R.C.N.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, D.B.M., R.C.N.; experimental studies, D.B.M., R.C.N.; statistical analysis, D.B.M., R.C.N.; and manuscript editing, all authors

	References

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION APPENDIX ADVANCES IN KNOWLEDGE References

 

1. Lee KH, Han JK, Kim KG, et al. Clogging of drainage catheters: quantitative and longitudinal assessment by monitoring intracatheter pressure in catheters and rabbits. Radiology 2003;227:833–838.[Abstract/Free Full Text]
2. Hoyt AC, D'Agostino HB, Carrillo AJ. Drainage efficiency of double-lumen sump catheters and single-lumen catheters: in vitro comparison. J Vasc Interv Radiol 1997;8:267–270.[Medline]
3. Lee SH, vanSonnenberg E, D'Agostino HB, Tanenbaum L. Laboratory analysis of catheters for percutaneous abscess drainage. J Minim Invasive Ther 1994;3:233–237.
4. Park JK, Kraus FC, Haaga JR. Fluid flow during percutaneous drainage procedures: an in vitro study of the effects of fluid viscosity, catheter size, and adjunctive urokinase. AJR Am J Roentgenol 1993;160:165–169.[Abstract/Free Full Text]
5. Haaga JR, Weinstein AJ. CT-guided percutaneous aspiration and drainage of abscesses. AJR Am J Roentgenol 1980;135:1187–1194.[Abstract]
6. Gobien RP, Stanley JH, Schabel SI, et al. The effect of drainage tube size on adequacy of percutaneous abscess drainage. Cardiovasc Intervent Radiol 1985;8:100–102.[CrossRef][Medline]
7. vanSonnenberg E, Mueller PR, Ferrucci JT Jr. Percutaneous drainage of 250 abdominal abscesses and fluid collections. I. Results, failures, and complications. Radiology 1984;151:337–341.[Abstract/Free Full Text]
8. Mueller PR, vanSonnenberg E, Ferrucci JT Jr. Percutaneous drainage of 250 abdominal abscesses and fluid collections. II. Current procedural concepts. Radiology 1984;151:343–347.
9. American College of Radiology. Percutaneous catheter drainage of infected intra-abdominal fluid collections. In: ACR appropriateness criteria. Reston, Va: American College of Radiology, 1999.
10. Gazelle GS, Mueller PR. Abdominal abscess: imaging and intervention. Radiol Clin North Am 1994;32:913–932.[Medline]
11. vanSonnenberg E, Ferrucci JT, Mueller PR, Wittenberg J, Simeone JF. Percutaneous drainage of abscesses and fluid collections: technique, results, and applications. Radiology 1982;142:1–10.[Abstract/Free Full Text]
12. Bouali K, Magotteaux P, Jadot A, et al. Percutaneous catheter drainage of abdominal abscess after abdominal surgery: results in 121 cases. J Belge Radiol 1993;76:11–14.[Medline]
13. vanSonnenberg E, Wing VW, Casola G, et al. Temporizing effect of percutaneous drainage of complicated abscesses in critically ill patients. AJR Am J Roentgenol 1984;142:821–826.[Abstract/Free Full Text]
14. Bufalari A, Giustozzi G, Moggi L. Postoperative intraabdominal abscesses: percutaneous versus surgical treatment. Acta Chir Belg 1996;96:197–200.[Medline]
15. Lang EK, Springer RM, Giorioso LW, Cammarata CA. Abdominal abscess drainage under radiologic guidance: causes of failure. Radiology 1986;159:329–336.[Abstract/Free Full Text]
16. Rothlin MA, Schob O, Klotz H, Candinas D, Largiader F. Percutaneous drainage of abdominal abscesses: are large-bore catheters necessary? Eur J Surg 1998;164:419–424.[CrossRef][Medline]
17. Lambiase RE, Deyoe L, Cronan JJ, Dorfman GS. Percutaneous drainage of 335 consecutive abscesses: results of primary drainage with 1-year follow-up. Radiology 1992;184:167–179.[Abstract/Free Full Text]
18. American College of Radiology. ACR practice guideline for specifications and performance of image-guided percutaneous drainage/aspiration of abscesses and fluid collections (PDAFC) in adults. In: Practice guidelines and technical standards, 2003. Reston, Va: American College of Radiology, 2003; 319–326.
19. Society of Cardiovascular and Interventional Radiology Standards of Practices Committee. Quality improvement guidelines for adult percutaneous abscess and fluid drainage. J Vasc Interv Radiol 1995;6:68–90.[Medline]
20. Jaques P, Mauro M, Yankaskas B, Piggott B. CT features of intraabdominal abscesses: prediction of successful percutaneous drainage. AJR Am J Roentgenol 1986;146:1041–1045.[Abstract/Free Full Text]
21. Belair M, Gianfelice D, Lepanto L. Computed tomographic abscessogram: a useful tool for evaluation of percutaneous abscess drainage. Can Assoc Radiol J 1998;49:336–343.[Medline]
22. Pfitzner J. Poiseuille and his law. Anaesthesia 1976;31:273–275.[Medline]
23. Simpson G, Roomes D, Heron M. Effects of streptokinase and deoxyribonuclease on viscosity of human surgical and empyema pus. Chest 2000;117(6):1728–1733.[Abstract/Free Full Text]

This Article Abstract Figures Only Full Text (PDF) Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Macha, D. B. Articles by Nelson, R. C. Search for Related Content PubMed PubMed Citation Articles by Macha, D. B. Articles by Nelson, R. C.