Clogging of Drainage Catheters: Quantitative and Longitudinal ...

Radiology 

Kyoung Ho Lee, MD 

Joon Koo Han, MD 

Kwang Gi Kim, PhD 

Youngro Byun, PhD 

Chang Jin Yoon, MD 

Seung Ja Kim, MD 

Byung Ihn Choi, MD 

Index terms: 

Abscess, percutaneous drainage, 

70.21 

Animals 

Catheters and catheterization, 

technology, 70.21 

Experimental study, 70.21 

Published online before print 

10.1148/radiol.2281020245 

Radiology 2003; 227:833–838 

Abbreviation: 

ID internal diameter 

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). 

Clogging of Drainage Catheters: 

Quantitative and Longitudinal 

Assessment by Monitoring 

Intracatheter Pressure in 

Catheters and Rabbits 1 

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 

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. 

© 

RSNA, 2003 

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. 

833

Radiology 

MATERIALS AND METHODS 

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: 

Q Prr4 

8L , (1) 

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 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. 

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). 

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: 

Pr 5.628 1012 Q 

 

6,000 

D 4 , (2) 

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 10 3 Ns/m 2 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: 

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). 

Pr k 1 Q 2 10 10 k 2 e Q/k3 k 4 

 

6,000 

D 4 , 

k 5 

(3) 

where k 1 , k 2 , k 3 , k 4 , and k 5 are coefficients. 

The error range of this fitting 

equation was represented by k 1 . 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 

834 Radiology June 2003 Lee et al

TABLE 1 

Catheter and Infusion Rates Tested in in Vitro Experiment 

Radiology 

Catheter Name 

Manufacturer 

Outer 

Diameter 

(F) 

ID (F) 

Infusion Rate (mL/sec) 

0.1 0.5 1.0 1.5 2.0 2.5 3.0 

Microferret-18 infusion 

catheter Cook, Bloomington, Ind 3 1.58 Yes No No No No No No 

Tempo angiographic 

catheter Cordis, Miami, Fla 4 2.86 Yes Yes Yes Yes No No No 

Torcon NB Advantage 

angiographic catheter Cook 5 3.12 Yes Yes Yes Yes Yes Yes Yes 

Drainage catheter Jungsung, Seongnam, Korea 7 3.88 Yes Yes Yes Yes Yes Yes Yes 

Envoy guiding catheter Cordis 6 4.35 No Yes Yes Yes Yes Yes Yes 

Drainage catheter Jungsung 8 5.07 No Yes Yes Yes Yes Yes Yes 



Simple-Loc Locking 

Loop (MSL) Cook 12 7.33 No No Yes Yes Yes Yes Yes 

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 

In Vitro Experiment 

Intracatheter pressures at each combination 

of infusion rate and ID are summarized 

in Figure 2. 

Standard Equation 

The coefficients k 2 , k 3 , k 4 , and k 5 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 k 1 , 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 k 1 to be 1, 

the fitting equation can be written thus: 

Q 2 10 10 

152.089 e Q/0.1799 5.372 

Pr 

6,000 

D 4 

. 

136 

(4) 

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 outof-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 effec- 

Volume 227 Number 3 Clogging of Drainage Catheters: Assessment of Intracatheter Pressure 835

Radiology 

tive 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. 

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. 

Figure 2. 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 log 10 scale was used to plot P on the y axis. 

DISCUSSION 

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 

Figure 3. 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: zero, Œ one, two, and 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 log 10 scale was used to plot pressure on the y axis. 

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 


Radiology 

Figure 4. 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: zero, Œ one, two, 

and 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. 

TABLE 2 

Results of Statistical Analysis of Differences in Pressures at Each Irrigation 

Frequency in 12 Rabbits during 14-day Follow-up 

Irrigation 

Frequency 

(no. of times daily) 

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 

No. of Days after Catheter Insertion 

0 3 7 10 14 

Saline infusion rate, 

0.1 mL/sec 

0 vs 1 .964 .101 .011* .001* .001* 

0 vs 2 .995 .076 .001* .001* .001* 

0 vs 3 .965 .028* .001* .001* .001* 

1 vs 2 .960 .894 .392 .103 .042* 

1 vs 3 .929 .573 .059 .001* .001* 

2 vs 3 .970 .666 .299 .036* .019* 

Saline infusion rate, 

0.5 mL/sec 

0 vs 1 .987 .029* .001* .001* .001* 

0 vs 2 .746 .008* .001* .001* .001* 

0 vs 3 .813 .002* .001* .001* .001* 

1 vs 2 .734 .644 .084 .013* .001* 

1 vs 3 .800 .332 .008* .001* .001* 

2 vs 3 .931 .611 .340 .013* .001* 

Note.—Data are P values obtained by means of repeated measures analysis of variance. 

* P .05. 

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 oneway 

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 de- 

Volume 227 Number 3 Clogging of Drainage Catheters: Assessment of Intracatheter Pressure 837

Radiology 

grees 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 

Figure 5. 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, 170.) 

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. 

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