Clogging of Drainage Catheters: Quantitative and Longitudinal ...

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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 Drainage catheter Jungsung 9 5.38 No Yes Yes Yes Yes Yes Yes Drainage catheter Jungsung 10 6.74 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
Page 1: Radiology Kyoung Ho Lee, MD Joon Ko
Page 5 and 6: Radiology Figure 4. Graphs show cha

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