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Published online before print April 10, 2003, 10.1148/radiol.2281020245
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(Radiology 2003;227:833-838.)
© RSNA, 2003

Experimental Studies

Clogging of Drainage Catheters: Quantitative and Longitudinal Assessment by Monitoring Intracatheter Pressure in Catheters and Rabbits1

Kyoung Ho Lee, MD, Joon Koo Han, MD, Kwang Gi Kim, PhD, Youngro Byun, PhD, Chang Jin Yoon, MD, Seung Ja Kim, MD and Byung Ihn Choi, MD

1 From the Department of Radiology, Institute of Radiation Medicine, Clinical Research Institute (K.H.L., J.K.H., C.J.Y., S.J.K., B.I.C.) and Interdisciplinary Program in Medical and Biological Engineering, Clinical Research Institute (K.G.K.), Seoul National University College of Medicine, Seoul National University Hospital, 28 Yongon-dong, Chongno-gu, Seoul 110-744, Korea; and Department of Materials Science and Engineering, Kwangju Institute of Science and Technology, Gwangju, Korea (Y.B.). Received March 29, 2002; revision requested June 11; final revision received November 5; accepted November 19. Supported in part by Korean Ministry of Health and Welfare grant HMP-98-G-2-034. Address correspondence to J.K.H. (e-mail: hanjk@radcom.snu.ac.kr).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 
PURPOSE: To develop a method for the quantitative and longitudinal assessment of clogging in drainage catheters and to confirm the validity of the method.

MATERIALS AND METHODS: Intracatheter pressure was measured during the infusion of saline at a rate of 0.1–3.0 mL/sec in nine catheters with different internal diameters. With the data obtained, a fitting equation between the intracatheter pressure and internal diameter was derived on the basis of the Poiseuille law. To confirm the validity of this measurement method, four drainage catheters were inserted into the peritoneal cavity in each of 15 rabbits. Intracatheter pressures at infusion rates of 0.1 and 0.5 mL/sec were monitored for 14 days, while the degrees of catheter clogging were graded on the basis of the different frequencies of manual irrigation: one, two, or three times per day. Repeated measures analysis of variance was used to determine the statistical significance of differences in pressure between different irrigation frequencies.

RESULTS: Pressure was measured successfully throughout the experiment except in three rabbits with dislodged catheters. Three to 14 days after catheter insertion, the pressures were significantly lower in catheters with higher irrigation frequencies than in those with lower irrigation frequencies (P < .05). The effective internal diameter of each catheter could be monitored by means of the derived fitting equation.

CONCLUSION: This method can be used to quantitatively measure the degree of clogging of a drainage catheter. It can also be used for comparative or longitudinal in vivo studies concerning the effectiveness of drainage procedures or catheter development.

© RSNA, 2003

Index terms: Abscess, percutaneous drainage, 70.21 • Animals • Catheters and catheterization, technology, 70.21 • Experimental study, 70.21


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 
In the past decade, computed tomography– and sonography-guided percutaneous drainage of abscesses and fluid collections has become a widely used, safe, and effective technique. Various factors can hinder or delay the successful drainage of abscesses, such as the location and configuration of the abscess (1–3), the nature of the infecting organism, host resistance (4), fistulous connections, and viscosity of the abscess contents (5). Several procedure-related factors can also influence the patency of the drainage tube. A number of methods for preventing catheter clogging have been proposed, including the use of irrigations and large-lumen or sump-type catheters (6). However, catheter clogging is still encountered frequently during various drainage procedures.

We have been working on the development of anticlogging drainage catheters with new biomaterials and drug-delivery technologies in recent years. During this work, we found that no recognized method has been reported for objective evaluation of the effectiveness of catheter drainage. The purpose of this study was to develop a method for the quantitative and longitudinal assessment of clogging in drainage catheters and to confirm the validity of the method.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 
Principle
The flow of fluids, including pus (5), through a drainage catheter is governed by the Poiseuille law (7), which describes the rate of laminar flow of fluid (or gas) through a cylindric structure. For drainage catheters, the Poiseuille law is expressed by the following equation:

where Q is the flow rate, Pr is the pressure gradient between the two ends of the catheter, r is the radius of the catheter, L is the length of the catheter, and {eta} is the viscosity of the fluid. If the fluid is infused at a constant rate by using an infusion pump, the resistance of a given catheter can be expressed as a function of the intracatheter pressure (Pr) because all other variables remain constant (Fig 1). Furthermore, the effective internal diameter (ID) of a drainage catheter, which is influenced by the clogging effect in vivo, can be calculated if other variables are known.



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  		Figure 1. Diagram of pressure measurement system. A catheter, a pressure-monitoring device, and an infusion pump are connected with a three-way stopcock. If the fluid is infused at a constant mean rate (Q) of the infusion pump, the resistance (R) of a given catheter can be expressed as a function of the intracatheter pressure (P).

 
With the method used in this study, a prerequisite is that the infusion pump (A-50 B-1; Nemoto Kyorindo, Tokyo, Japan) must maintain a constant infusion rate when the intracatheter pressure is high. We confirmed the constant rate in a separate experiment. The cumulative volume infused was increased linearly at a preset infusion rate from 0.1 to 3.0 mL/sec until the intracatheter pressure exceeded the measurable limit (350 mm Hg) of the pressure-monitoring device (Siredoc 60; Siemens Medical Systems, Erlangen, Germany), which was a standard patient monitor. In the present study, laminar flow was presumed for all measurements, and every precaution was taken to ensure that catheters were aligned to avoid kinking or distortion of the lumen.

In Vitro Experiment
A series of unused angiographic and drainage catheters with different IDs were connected to the measurement system, as illustrated in Figure 1, and the intracatheter pressure was measured during the infusion of saline at a rate from 0.1 to 3.0 mL/sec (C.J.Y., S.J.K.). This in vitro experiment was performed (a) to verify that the measurement system discriminated adequately between catheters with different IDs, (b) to allow the derivation of a standard curve (or equation) between the intracatheter pressure and the effective ID, and (c) to determine the infusion rate to be used in the animal experiment. The 48 combinations of IDs and infusion rates are summarized in Table 1. If the ID of each catheter was not provided by the manufacturers, it was measured with image analysis software (UTHSCSA ImageTool, version 2.03; University of Texas Health Science Center, San Antonio, Tex), and digitally captured images of a magnified cut surface were obtained by using a stereomicroscope (SZ 11; Olympus Optical, Tokyo, Japan).


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  		TABLE 1. Catheter and Infusion Rates Tested in in Vitro Experiment

 
We measured the ID of each catheter five times and calculated the mean after discarding the highest and lowest values. All catheters were carefully cut at the shaft to a fixed length of 30 cm. After infusion was initiated, the intracatheter pressure gradually increased until it reached a plateau (determined with consensus between the two observers) in 5–15 seconds; this plateau indicated that a steady state had been reached between inflow from the infusion pump and outflow from the catheter tip. To minimize measurement error, intracatheter pressure was measured five times for each combination. The mean value was calculated after the highest and lowest values had been discarded. The pressure-monitoring device was set to zero by opening the system to air before each measurement.

Standard Equation
For the measurement system used in this study, the Poiseuille law equation can be written as follows:

where Pr (in millimeters of mercury) is intracatheter pressure, Q (in milliliters per second) is infusion rate, and D (in French) is ID of catheter because the length was fixed to 30 cm and the viscosity of water is 1.002 x 10-3 Ns/m2 at 20°C (8).

On the basis of Equation (2), a fitting equation was derived to describe the intracatheter pressure as a function of the infusion rate and ID. This process included empirical modification of Equation (2) by trial and error (K.G.K.) and iterative nonlinear curve fitting (Origin, version 6.1; OriginLab, Northampton, Mass) with the in vitro experimental data for 48 combinations.

The fitting equation was modified as follows:

where k1, k2, k3, k4, and k5 are coefficients. The error range of this fitting equation was represented by k1. With this equation, the relationship between the ID and the intracatheter pressure was plotted at each infusion rate. These curves were compared with the ideal curves generated by the Poiseuille equation (Eq [2]). The fitting equation was also used to calculate the theoretic effective IDs of catheters in the animal experiment.

Animal Experiment
All animal experimental protocols were approved by the animal research committee at our institution and were performed at the Clinical Research Institute. Fifteen New Zealand White rabbits (body weight, 2.5–3.0 kg) were used for the experiment. Animals were sedated with an intramuscular injection of 12-15 mg per kilogram of body weight of ketamine hydrochloride (Ketalar; Yuhan Yanghang, Seoul, Korea) and 2 mg/kg of xylazine hydrochloride (Rompun 2%; Bayer Korea, Seoul, Korea). After the abdominal wall was shaved and prepared, four standard 8-F drainage catheters (Jungsung) with length of 30 cm and ID of 5.07 F were inserted into the peritoneal cavity of each rabbit, with the Seldinger method and fluoroscopic guidance (C.J.Y.). Efforts were made to place the tips of the four catheters in the same region of the peritoneal cavity. During the follow-up period, the catheters were left in place, and animals were kept in a specially designed restraint cage in the laboratory to prevent the catheters from being dislodged accidentally. Each day, 200 mg of cefazolin sodium (Cefamezin; Dong-a Pharmacy, Seoul, Korea) and 15 mg of gentamicin sulfate (Gentamicin; Korea United Pharmacy, Seoul, Korea) was administered intramuscularly to prevent peritonitis.

To grade the degrees of catheter clogging, each of the four catheters inserted into an animal was irrigated manually with 10 mL of sterile saline at a different frequency (zero, one, two, or three times per day). With the method described in the in vitro experiment, intracatheter pressure was measured for each catheter at baseline and 3, 7, 10, and 14 days after insertion by infusing sterile saline at rates of 0.1 and 0.5 mL/sec, consecutively. These infusion rates were predetermined on the basis of results in the in vitro experiment to ensure that the maximum intracatheter pressure was within the measurable range of the pressure-monitoring device. Measurement procedures were conducted together by two radiologists (C.J.Y., S.J.K.), who were blinded to the irrigation frequency. Measurements were obtained from the four catheters in each animal in random order. From the intracatheter pressure, we were able to calculate the effective ID by using the fitting equation derived on the basis of results in the in vitro experiment. Changes in effective ID during the 14-day follow-up period were plotted for each irrigation frequency.

Microscopic Analysis
After the study was completed, the catheters were removed, and the animals were returned to laboratory cages; there were no complications. The surface morphology of the catheters after withdrawal was examined with stereomicroscopy and scanning electron microscopy (DS130-C; Akashi, Tokyo, Japan) at an accelerating voltage of 20 kV (K.H.L., C.J.Y.), after the catheters were prepared in a standard manner (9). Two catheters were selected randomly for each irrigation frequency, and representative segments were prepared for stereomicroscopic and scanning electron microscopic examinations of their internal surfaces.

Statistical Analysis
The data obtained in the animal experiment were analyzed to determine whether the intracatheter pressure was related to the irrigation frequency by means of repeated measures analysis of variance. A P value of less than .05 was considered to indicate a statistically significant difference. Statistical analysis was not performed with the stereomicroscopic or scanning electron microscopic data.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 
In Vitro Experiment
Intracatheter pressures at each combination of infusion rate and ID are summarized in Figure 2.



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  		Figure 2a. Graphs show results of the in vitro experiment and theoretic curves. (a, b) Relationship between ID of a catheter and intracatheter pressure (P). Colors of the plots and curves indicate a specific preset infusion rate. In a, red = 0.1 mL/sec, blue = 1.0 mL/sec, orange = 2.0 mL/sec, and black = 3.0 mL/sec. In b, red = 0.5 mL/sec, blue = 1.5 mL/sec, and black = 2.5 mL/sec. Data are plotted separately in a and b to avoid crowding. Plots indicate the pressures measured in 48 combinations of catheter IDs and infusion rates. Solid curves were generated by fitting Equation (4) derived from the data (plots), and the dotted curves represent the ideal curves generated by the Poiseuille equation (Eq [2]). Note agreement between the data, fitting curves, and ideal curves. A log10 scale was used to plot P on the y axis.

 


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  		Figure 2b. Graphs show results of the in vitro experiment and theoretic curves. (a, b) Relationship between ID of a catheter and intracatheter pressure (P). Colors of the plots and curves indicate a specific preset infusion rate. In a, red = 0.1 mL/sec, blue = 1.0 mL/sec, orange = 2.0 mL/sec, and black = 3.0 mL/sec. In b, red = 0.5 mL/sec, blue = 1.5 mL/sec, and black = 2.5 mL/sec. Data are plotted separately in a and b to avoid crowding. Plots indicate the pressures measured in 48 combinations of catheter IDs and infusion rates. Solid curves were generated by fitting Equation (4) derived from the data (plots), and the dotted curves represent the ideal curves generated by the Poiseuille equation (Eq [2]). Note agreement between the data, fitting curves, and ideal curves. A log10 scale was used to plot P on the y axis.

 
Standard Equation
The coefficients k2, k3, k4, and k5 were determined to be 152.089, 0.1799, 5.372, and 136, respectively, by means of iterative nonlinear curve fitting. The error range of fitting Equation (3), which is represented by k1, was 1.000 ± 0.014 (SD), 0.987 ± 0.061, 1.217 ± 0.045, 1.102 ± 0.034, 1.029 ± 0.022, 0.931 ± 0.029, and 0.730 ± 0.063 at infusion rates of 0.1, 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 mL/sec, respectively. By taking k1 to be 1, the fitting equation can be written thus:

Figure 2 illustrates the theoretic curves that describe the relationship between ID and intracatheter pressure, according to fitting Equation (4) and the Poiseuille equation (Eq [2]).

Animal Experiment
In three of the 15 rabbits, one or more catheters became dislodged within 4 days of follow-up, and these three rabbits were excluded from the analysis. When the infusion rate was 0.5 mL/sec, the absolute intracatheter pressure could not be measured in all combinations because it sometimes exceeded the measurable limit (350 mm Hg) of the pressure-monitoring device. In these cases, the intracatheter pressure was regarded as 350 mm Hg for statistical analysis. This out-of-range inaccuracy occurred in 16 catheters from day 7 after insertion: 10 catheters with an irrigation frequency of zero times per day (four catheters from day 7, five from day 10, and one from day 14), five catheters with an irrigation frequency of one time per day (three catheters from day 10 and two from day 14), and one with an irrigation frequency of two times per day (from day 14).

Figures 3 and 4 illustrate changes in the intracatheter pressure and the effective ID, respectively, during the 14-day follow-up for each irrigation frequency. Three to 14 days after catheter insertion, the intracatheter pressure was significantly lower in catheters with higher irrigation frequencies than in those with lower irrigation frequencies. Table 2 summarizes the results of statistical analysis of intracatheter pressure differences at each irrigation frequency for each observation during 14-day follow-up.



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  		Figure 3a. Graphs show intracatheter pressure changes in 12 rabbits during the 14-day follow-up. Pressure was measured during the infusion of sterile saline at rates of (a) 0.1 and (b) 0.5 mL/sec. The degree of catheter clogging was graded on the basis of the different frequencies of manual irrigation: {blacksquare} = zero, {blacktriangleup} = one, {blacktriangledown} = two, and {diamondsuit} = three times per day. Plots indicate means, and error bars represent the standard errors of means. In b, pressures exceeding the measurable limit (350 mm Hg) of the pressure-monitoring device were regarded as 350 mm Hg. Note that degrees of catheter clogging were discriminated by means of the pressure measurement system illustrated in Figure 1. A log10 scale was used to plot pressure on the y axis.

 


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  		Figure 3b. Graphs show intracatheter pressure changes in 12 rabbits during the 14-day follow-up. Pressure was measured during the infusion of sterile saline at rates of (a) 0.1 and (b) 0.5 mL/sec. The degree of catheter clogging was graded on the basis of the different frequencies of manual irrigation: {blacksquare} = zero, {blacktriangleup} = one, {blacktriangledown} = two, and {diamondsuit} = three times per day. Plots indicate means, and error bars represent the standard errors of means. In b, pressures exceeding the measurable limit (350 mm Hg) of the pressure-monitoring device were regarded as 350 mm Hg. Note that degrees of catheter clogging were discriminated by means of the pressure measurement system illustrated in Figure 1. A log10 scale was used to plot pressure on the y axis.

 


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  		Figure 4a. Graphs show changes in the effective ID of drainage catheters in 12 rabbits during the 14-day follow-up. Data were calculated from the pressure measurement (Fig 3) at infusion rates of (a) 0.1 and (b) 0.5 mL/sec by means of fitting Equation (4). Degrees of catheter clogging were graded on the basis of the different frequencies of manual irrigation: {blacksquare} = zero, {blacktriangleup} = one, {blacktriangledown} = two, and {diamondsuit} = three times per day. Plots indicate means, and error bars represent the standard errors of means. Note that the degree of catheter clogging (effective IDs) is monitored comparatively.

 


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  		Figure 4b. Graphs show changes in the effective ID of drainage catheters in 12 rabbits during the 14-day follow-up. Data were calculated from the pressure measurement (Fig 3) at infusion rates of (a) 0.1 and (b) 0.5 mL/sec by means of fitting Equation (4). Degrees of catheter clogging were graded on the basis of the different frequencies of manual irrigation: {blacksquare} = zero, {blacktriangleup} = one, {blacktriangledown} = two, and {diamondsuit} = three times per day. Plots indicate means, and error bars represent the standard errors of means. Note that the degree of catheter clogging (effective IDs) is monitored comparatively.

 

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  		TABLE 2. Results of Statistical Analysis of Differences in Pressures at Each Irrigation Frequency in 12 Rabbits during 14-day Follow-up

 
Microscopic examination of the catheters after they were withdrawn showed multifocal plugging of the side holes and catheter lumen with white jellylike pieces of tissue debris of various sizes and frequencies. Results of histopathologic examination revealed that this tissue debris was inflammatory exudate that consisted of lymphocytes, plasma cells, neutrophils, and some eosinophils among a background of delicate fibrillary collagenous material. Results of scanning electron microscopic examination revealed that this tissue debris had irregular surfaces (Fig 5), but the catheter surfaces remained smooth in other areas without debris.



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  		Figure 5a. Images show internal surfaces of drainage catheters after the catheters were withdrawn. (a) Stereomicroscopic image shows debris that plugs the catheter side holes and lumen, which were irrigated one time per day. (b) Scanning electron microscopic image shows a catheter that was irrigated two times per day. Note the irregular surface caused by the debris (D). (Original magnification, x170.)

 


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  		Figure 5b. Images show internal surfaces of drainage catheters after the catheters were withdrawn. (a) Stereomicroscopic image shows debris that plugs the catheter side holes and lumen, which were irrigated one time per day. (b) Scanning electron microscopic image shows a catheter that was irrigated two times per day. Note the irregular surface caused by the debris (D). (Original magnification, x170.)

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
 
In this study, we evaluated a method with application of the Poiseuille law for the quantitative and longitudinal assessment of catheter clogging during percutaneous drainage procedures. We verified the validity of this method in two ways: (a) by performing an in vitro experiment, in which a series of catheters with different IDs were used to simulate various degrees of obstruction and (b) by observing the results in an in vivo experiment, in which the degree of clogging was graded according to the irrigation frequency. Furthermore, our results show that the effective ID of a drainage catheter can be estimated in vivo by means of the mathematically based approach used in our study.

To our knowledge, no method has been reported for evaluating the effectiveness of drainage procedures and the catheters used in such procedures. Our efforts to develop anticlogging drainage catheters in recent years have demonstrated to us that there is a need for an objective method of quantifying catheter clogging.

We previously determined the degree of catheter clogging in animal models by means of measurement of catheter weight changes, microscopic morphologic analysis of side holes and luminal surfaces, scanning electron microscopy, or measurement of the infusion rate through a catheter after it was withdrawn. In our experience, morphologic analysis is not an effective method because it is labor intensive and tends to result in sampling error and because it is practically impossible to prepare the catheters without losing debris. For these reasons, we did not statistically analyze stereomicroscopic and scanning electron microscopic data in this study. These methods to determine the degree of catheter clogging necessitated prolonged experimental cycles and required the use of many animals for multiple observation times; these factors resulted in the unavoidable loss of animals and catheters.

With the method we developed for the current study, however, several catheters could be followed over time in one animal, which provided quantitative and comparative information about temporal characteristics of the obstruction process or anticlogging effect. This feature is critical for the evaluation of drainage procedures or for the development of new drainage catheters with anticlogging effects (ie, those involving novel biomaterials or drug-delivery systems). Furthermore, the method used in this study does not preclude analyses of weight or morphologic changes after catheter withdrawal. This method might also be used in clinical studies because the amount of saline injected is small (less than 10 mL per catheter in this study); that amount is not enough to significantly increase the pressure inside the abscess cavity.

However, the method used in this study has several limitations. (a) Despite the advantage of allowing direct assessment of flow through a catheter in vivo, the direction of the infused flow during the measurement is opposed to the direction of natural drainage. This might be a substantial limitation because debris inside a drainage system can act as a one-way check valve. (b) The Poiseuille law can be applied only if an assumption is made that narrowing of the lumen is diffuse (7), but this assumption does not reflect the real situation. In cases of multifocal severe obstruction, the flow dynamics become more complex.

With the Poiseuille law, we derived a fitting equation from the in vitro experimental data and used the equation to calculate the effective ID of catheters in the animal experiment. However, this method also has several limitations. For example, in the animal experiment, the ID of catheters was 5.07 F, but the ID of the same catheters calculated from the baseline measurement was approximately 3.5 F. This discrepancy might be attributed to multiple factors. (a) Intracatheter pressure for a given catheter in vivo can be variable since it is influenced by many factors, including the respiratory cycle, abdominal pressure, and locations of side holes relative to adjacent anatomic structures. (b) Catheters used in the in vitro experiment had only one end hole. (c) Mechanical properties, such as the compliance materials, were not considered in this study. We believe, however, that these limitations are not important if the method is used for comparing the degrees of catheter clogging between different catheters.

We found a discrepancy between the curves generated by the fitting Equation (4) and those generated by the Poiseuille equation (Eq [2]). Furthermore, intracatheter pressure was found to be proportional to the square of the infusion rate and not to the infusion rate, as indicated by fitting Equation (4). This discrepancy might be attributed to technical factors or to the fact that the system is not modeled perfectly by the Poiseuille law. The reasons for these differences remain unknown, and further study is required.

In summary, we propose a method for in vivo evaluation of the effectiveness of a drainage catheter, which is based on the application of the Poiseuille law. With this method, the flow resistance of a catheter can be determined quantitatively; thus, it offers a means of quantifying the degree of clogging or the anticlogging effect of drainage catheters. This method can be used for comparative and longitudinal studies concerning the evaluation of drainage procedures or the development of new catheters.

Practical application: By applying the noninvasive method used in this study, flow resistance through multiple drainage catheters can be compared over time in one animal, which provides quantitative information about the gradual obstruction of catheters. This information is critical for the evaluation of drainage procedures or development of new catheters with anticlogging effects, such as those made with novel biomaterials and drug-delivery systems. Furthermore, this method does not preclude analyses based on weight or morphologic changes after the catheter is withdrawn.


   ACKNOWLEDGMENTS
 
We thank Hyuk Jae Choi, Myoung Soo Kim, RT, and Hyun Jung Lee, RT, for their technical assistance in animal preparation. We are grateful to Myoung Jin Jang, PhD, for her help with the statistical analysis.


   FOOTNOTES
 
Abbreviation: ID = internal diameter

Author contributions: Guarantor of integrity of entire study, B.I.C.; study concepts, K.H.L., Y.B.; study design, K.H.L., J.K.H., K.G.K., C.J.Y.; literature research, S.J.K.; experimental studies, C.T.Y., S.J.K., K.H.L.; data acquisition, K.H.L., C.J.Y., S.J.K.; data analysis/interpretation, C.J.Y., S.J.K.; manuscript preparation, K.H.L., J.K.H., S.J.K.; manuscript definition of intellectual content, C.J.Y., K.G.K., Y.B.; manuscript editing, B.I.C.; manuscript revision/review and final version approval, B.I.C., J.K.H.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 

  1. Haaga JR, Weinstein AJ. CT-guided percutaneous aspiration and drainage of abscesses. Am J Roentgenol 1980; 135:1187-1194.[Abstract]
  2. 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]
  3. 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.[Abstract/Free Full Text]
  4. Dawson SL, Mueller PR, Ferrucci JT, Jr. Mucomyst for abscesses: a clinical comment. Radiology 1984; 151:342.[Free Full Text]
  5. 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. Am J Roentgenol 1993; 160:165-169.[Abstract/Free Full Text]
  6. Han JK. Percutaneous abdominal abscess drainage. In: Han MC, Park JH, eds. Interventional radiology. Seoul, Korea: Ilchokak, 1999; 707-714.
  7. Pfitzner J. Poiseuille and his law. Anaesthesia 1976; 31:273-275.[Medline]
  8. Frazini JB, Finnemore EJ, eds. Fluid mechanics with engineering applications Appendix A. 9th ed. Boston, Mass: McGraw-Hill, 1997; 764-765.
  9. Moon HT, Lee YK, Han JK, Byun Y. A novel formulation for controlled release of heparin-DOCA conjugate dispersed as nanoparticles in polyurethane film. Biomaterials 2001; 22:281-289.[CrossRef][Medline]



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