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Percutaneous nephrostomy catheters: Drainage flow and retention strength
ADULT UROLOGY
PERCUTANEOUS NEPHROSTOMY CATHETERS: DRAINAGE FLOW AND RETENTION STRENGTH BENJAMIN K. CANALES, KARI HENDLIN, MATTHEW BRAASCH, CHRISTOPHER ANTOLAK, AVINASH REDDY, BESMA ODEH, AND MANOJ MONGA
ABSTRACT Objectives. To evaluate the impact of percutaneous nephrostomy catheter configuration on drainage flow and retention strength. Methods. The Cook nephrostomy 16F (symmetric balloon), Bardex Council 16F (eccentric balloon), Microvasive Flexima 14F (pigtail), and Bardex Malecot 16F (flange) nephrostomy catheters were attached to an artificial renal pelvis (12-in.-round latex balloon). The balloon was subsequently filled with either 60 mL of water or orange juice with pulp, and gravity drainage of this fluid was recorded as flow into a flowmeter. Using a Force Five Model FDV-100 force gauge, the retention strength was tested by measuring the force required to pull the nephrostomy catheter through an 8-mm hole in a 35-mm-thick biologic tissue specimen (bologna). Results. The maximal flow rate using both orange juice and saline was significantly greater for the Cook nephrostomy than for the Microvasive Flexima, Bardex Malecot, and Bardex Council catheters (P ⱕ0.016). The average flow rate using saline for the Cook nephrostomy catheter was significantly greater than for all other catheters (P ⱕ0.02) and was significantly greater than for the Microvasive Flexima and the Bardex Council catheters (P ⱕ0.036) using orange juice. The retention strength was strongest for the Cook nephrostomy catheter (3.41 ⫾ 0.14 lb) compared with the Bardex Council (1.75 ⫾ 0.1), Microvasive Flexima (1.35 ⫾ 0.3), and Bardex Malecot (0.29 ⫾ 0.03) catheters. In addition, the Microvasive Flexima catheter resulted in greater maceration of the biologic tissue after forceful dislodgement. Conclusions. The results of this study have demonstrated that the Cook nephrostomy catheter combines strong drainage flow and strong retention strength during in vitro testing. Clinical evaluations of the ease of use and patient comfort are warranted. UROLOGY 66: 261–265, 2005. © 2005 Elsevier Inc.
P
ercutaneous tube drainage of the kidney was first described in 1955.1 Percutaneous nephrostomy tubes (PNTs) are now routinely used by radiologists and urologists for a wide range of clinical situations in which optimization of renal drainage is critical. Recent investigations for percutaneous nephrolithotomy have centered on adaptation of the procedural technique to improve efficacy and decrease
M. Monga is a study investigator funded by Boston Scientific, Cook Urological, and Bard Urological. From the Department of Urologic Surgery, Veterans Affairs Health Care System; and Department of Urologic Surgery, University of Minnesota School of Medicine, Minneapolis, Minnesota Reprint requests: Manoj Monga, M.D., Department of Urology, University of Minnesota School of Medicine, 420 Delaware Street Southeast, MMC 394, Minneapolis, MN 55455-0392. E-mail: [email protected] Submitted: December 2, 2004, accepted (with revisions): March 8, 2005 © 2005 ELSEVIER INC. ALL RIGHTS RESERVED
morbidity. These studies have included the development of minipercutaneous nephrolithotomy,2– 4 the use of a smaller PNT,5–7 or a tubeless approach in select patients after completion of nephrolithotomy.4,8 For tubeless percutaneous nephrolithotomy, careful patient selection is important for success, as this approach limits reentry for second-look nephroscopy, postoperative bleeding, or ureteral obstruction.8 Successful PNT drainage at the completion of percutaneous nephrolithotomy requires adequate drainage flow to prevent urinary obstruction or the development of intrarenal clots. Adequate retention strength to prevent inadvertent dislodgement of the catheter is also important, because inadvertent removal has been reported to be as high as 30% in some studies.9,10 In this study, we evaluated the impact of percutaneous catheter configuration on drainage flow and retention strength in an in vitro model. 0090-4295/05/$30.00 doi:10.1016/j.urology.2005.03.030 261
FIGURE 1. Tip configuration, cross-sectional area, and catheter lengths of Bardex Malecot, Bardex Council, Cook nephrostomy, and Microvasive Flexima catheters.
MATERIAL AND METHODS The Cook nephrostomy 16F (Cook Urological, Spencer, Ind), Bardex Council 16F (CR Bard, Covington, Ga), Bardex Malecot 16F (CR Bard), and Microvasive Flexima 14F (Boston Scientific, Natick, Mass) PNTs were used in this study (Fig. 1). The largest size available for the Flexima catheter is 14F.
RETENTION STRENGTH Bologna has been used as a homogenous biologic tissue that is easily available for repetitive and reproducible testing.11 Two 8-oz. packages of bologna (35 mm thick) were frozen to ⫺80°C. Twenty-one separate, 8-mm-diameter holes spaced evenly apart were then drilled through the length of the bologna using a 5/16-in. drill bit. All plastic bologna wrappings were removed, except for a small rim of plastic casing around the peripheral edge of the surface, and the bologna was allowed to thaw overnight in a refrigerator. For testing, individual catheters were inserted through a bologna hole centered above the gap between two wooden tables (Fig. 2). After insertion, the retention balloons of the Cook nephrostomy and Bardex Council catheters were inflated with 3 mL water. After insertion of the Boston Scientific Flexima catheter, the retention coil was tightened and locked. A handheld Force Five Model FDV-100 force gauge was secured to the lower portion of the catheter and used to pull the catheter tip through the bologna. This procedure was repeated five times for each catheter using a new hole in the bologna for each trial, and the maximal force readings were recorded (Fig. 3). Statistical analysis was performed using commercially available software. P ⬍0.05 was considered significant.
DRAINAGE For drainage testing, the balloons of the Cook nephrostomy catheter and Bardex Council tip catheter were inflated with 3 mL water, and the coil of the Flexima pigtail catheter was tightened and secured with the tension string. A 12-in.-round 262
latex balloon (Betta Products) was attached proximal to the retention balloon, coil, or flange of the catheter with a rubber band and filled manually with a syringe using the drainage port. Danuser et al.12 reported that the mean preoperative pyelocaliceal volume of hydronephrotic kidneys (primary ureteropelvic junction obstruction) was 64 ⫾ 33 mL. We attempted to replicate this by filling our artificial renal pelvis reservoir (balloon) with 60 mL of water. Air in the pelvis and drainage port was aspirated, and the catheter tip was manually centered in the fluid contents of the balloon. The catheter-pelvis unit was then placed on a level platform with the drainage port over the flow meter. The syringe was removed, and the results of the average and maximal drainage flow (in millimeters per second) were recorded using the Urodyn 1000 Flow Meter (Medtronic-Dantec, Allendale, NJ). The artificial renal pelvis reservoir was manually emptied of residual water between trials. To replicate the clinical scenario of blood or debris, the test was then repeated using 60 mL Tropicana “Some Pulp” premium orange juice. Each test was repeated a total of five times for each catheter.
RESULTS The retention strength was significantly stronger for the Cook nephrostomy catheter (3.41 ⫾ 0.14 lb) compared with the Bardex Council (1.75 ⫾ 0.1), Microvasive Flexima (1.35 ⫾ 0.3), and Bardex Malecot (0.29 ⫾ 0.03) catheters (P ⬍0.001; Fig. 3). In addition, the Microvasive Flexima resulted in greater maceration of the biologic tissue after forceful dislodgement (Fig. 2). Using 60 mL normal saline, the maximal drainage flow rate was significantly greater for the Cook nephrostomy (3.6 ⫾ 0.4 mL/s) than the MicrovaUROLOGY 66 (2), 2005
FIGURE 2. Retention strength setup and results. Bard Malecot catheter (1) placed through 8-mm opening in biologic tissue and graduated force applied with Force Five force transducer (2) until catheter pulled through tissue. Maceration of tissue after forceful extraction noted with Bard Council (A), Bard Malecot (B), Microvasive Flexima (C), and Cook nephrostomy catheter (D).
FIGURE 3. Tube retention strength.
sive Flexima (2.6 ⫾ 0.2 mL/s), Bardex Malecot (2.5 ⫾ 0.2 mL/s) and Bardex Council (1.6 ⫾ 0.2 mL/s) catheters (P ⬍0.0003; Fig. 4). The average drainage flow rate was significantly greater for the Cook nephrostomy catheter (2.4 ⫾ 0.3 mL/s) than the Bardex Malecot (2.0 ⫾ 0.2 mL/s, P ⫽ 0.02), Microvasive Flexima (1.8 ⫾ 0.1 mL/s, P ⫽ 0.003), or Bardex Council (1.3 ⫾ 0.2 mL/s, P ⫽ 0.0001; Fig. 5). Using 60 mL orange juice with pulp (to represent potential debris in the efflux), the maximal drainage flow rate was significantly greater for the Cook nephrostomy (4.6 ⫾ 1.25 mL/s) than for the Bardex Malecot (2.5 ⫾ 0.9 mL/s, P ⫽ 0.016), Microvasive Flexima (2.1 ⫾ 0.62 mL/s, P ⬍0.01), and Bardex Council (1.4 ⫾ 0.48 mL/s, P ⬍0.001) catheters (Fig. 4). The average drainage flow rate was significantly greater for the Cook nephrostomy catheter (1.6 ⫾ 0.43 mL/s) than for the MicrovaUROLOGY 66 (2), 2005
FIGURE 4. Maximal drainage rate (Qmax) with 60 mL sterile water (dots) and 60 mL orange pulp (crosshatched lines).
sive Flexima (1.0 ⫾ 0.32 mL/s, P ⫽ 0.036) and the Bardex Council (0.8 ⫾ 0.11, P ⬍0.01; Fig. 5). A small, but nonsignificant statistical difference was found between the Cook nephrostomy and Bardex Malecot catheters (1.1 ⫾ 0.2 mL/s, P ⫽ 0.077). COMMENT The PNTs available for placement include nonballoon (pigtail or flange) or balloon (symmetric or eccentric-placed) catheters. Because maximizing the drainage flow may prevent urinary obstruction 263
FIGURE 5. Average drainage rate (Qave) with 60 mL sterile water (dots) and 60 mL orange pulp (crosshatched lines).
or the development of intrarenal clot in the postoperative period, we decided to evaluate the maximal and average drainage rates with four commercially available PNT designs. Similarly, adequate retention strength to prevent inadvertent dislodgement of the catheter is an important property that can be attributed to catheter design. We evaluated this property through an 8-mm opening, similar to what one would anticipate at the completion of standard percutaneous nephrolithotomy in which the percutaneous tract was dilated to 10 mm in size. Small-bore nephrostomy drainage after urologic procedures has recently been shown to result in less postoperative pain,5–7,13 urinary extravasation,6 and hospital stay7 than large-bore drainage. A study by Joshi et al.14 also reported less discomfort from nephrostomy tubes than from doublepigtail ureteral stents for ureteral obstruction. Because these reports indicated that more physicians are using smaller PNTs for drainage, we selected four small-bore catheters (14F to 16F) for study inclusion. Although some have suggested that larger tubes are important to tamponade the nephrostomy tract, to our knowledge, this theory has never been proven. In addition, a 34F tube would be required to tamponade the 34F (outer diameter) nephrostomy tract, and proponents of large-bore catheters typically use only a 24F or 26F catheter. When considering the flow of a liquid through a tube, the rate of flow is equal to the change in pressure (driving pressure) times a fourth power dependence on the radius divided by the viscous resistance (Poiseuille’s law). This resistance depends linearly on the viscosity of the liquid and the length of the tube. In our study, the cross-sectional area should be the greatest variable with regard to flow followed by the length of the catheters. How264
ever, the catheter with the largest surface area (Malecot) did not have the greatest flows. This suggests that not only the cross-sectional area and catheter length, but also catheter tip, hole, balloon design, and wall properties may be important flow variables to consider when choosing a PNT. Although the Cook nephrostomy and Bardex Council catheters are of similar size and distal tip hole configuration, the flow rates with the Cook nephrostomy were significantly greater. This suggests that the balloon configuration (eccentric versus symmetric) or catheter shaft hole positioning (two holes opposing each other with the Bardex, two holes separated by 1.5 cm with the Cook) may affect the resistance and flow through the tube. The greater retention strength of the Cook catheter may reflect differences in balloon material or configuration. Pigtail catheters are the smallest catheters, ranging in size from 5F to 14F. The “Cope loop” pigtail catheter has a nylon string between the last side hole and the catheter tip. By placing tension on the string during tube insertion, the pigtail locks and self-retains in a tight coil, obviating the need for anchoring skin sutures.15 This nylon string lock must be subsequently released or cut to uncoil the stent and allow it to be removed. Nylon stringlocking pigtails have been reported to cause renal parenchymal injury, especially when placed in small, undilated systems.15 We found that forceful removal of the locked Flexima catheter, representing the clinical situation of inadvertent catheter dislodgement, resulted in the most maceration of the biologic tissue. Malecot or flange catheters deploy a mushroomstyle tip within the renal calix, averting the concern for caliceal obstruction and facilitating removal. Despite this design, cases of tissue bridge formation over the flanges, requiring endoscopic removal, have been reported.16,17 Traditionally, Malecot catheters have been used to provide largebore drainage after percutaneous renal surgery, because the lack of a balloon port means a larger catheter lumen compared with balloon catheters of the same size. Despite the larger cross-sectional area, we were surprised to find that the Malecot catheter had significantly lower maximal flow rates using both saline and pulp compared with the Cook nephrostomy tube and significantly lower average flow rates for saline. This was likely a reflection of catheter length and possibly of tip configuration. In addition, the self-retaining mechanism of the Malecot proved less secure than the pigtail or balloon catheters (P ⬍0.001). Balloon catheters include the Foley, Council, Couvelaire, and Argyle. Council catheters are most commonly used as they have a terminal hole allowing insertion or exchange over a guidewire. CathUROLOGY 66 (2), 2005
eter balloons may occlude one or more calices, depending on placement,18 or may increase postoperative flank pain with overdistension. Although the results of our study have demonstrated that the drainage properties of the Cook nephrostomy tube in an in vitro model of the renal pelvis were superior to those of other catheters tested, it is important to emphasize that our model does not address the impact of the balloon design on caliceal drainage. CONCLUSIONS The results of this study have shown that the Cook nephrostomy catheter (16F, symmetric balloon) combined both strong drainage flows and strong retention strengths in our in vitro testing. Clinical evaluations of the ease of use and patient comfort are warranted. REFERENCES 1. Goodwin WE, Casey WC, and Wolf W: Percutaneous trocar (needle) nephrostomy in hydronephrosis. JAMA 157: 891– 894, 1955. 2. Chan DY, and Jarrett TW: Mini-percutaneous nephrolithotomy. J Endourol 14: 269 –272, 2000. 3. Monga M, and Olgevie S: Minipercutanous nephrolithotomy. J Endourol 14: 419 – 421, 2000. 4. Feng MI, Tamaddon K, Mikhail A, et al: Prospective randomized study of various techniques of percutaneous nephrolithotomy. Urology 58: 345–350, 2001. 5. Pietrow PK, Auge BK, Costa DL, et al: Pain after percutaneous nephrolithotomy: impact of nephrostomy tube size. J Endourol 17: 411– 414, 2003.
UROLOGY 66 (2), 2005
6. Maheshwari PN, Andankar MG, and Bansal M: Nephrostomy tube after percutaneous nephrolithotomy: large bore or pigtail catheter? J Endourol 14: 735–737, 2000. 7. Liatsikos EN, Hom D, Dinlenc CZ, et al: Tail stent versus re-entry tube: a randomized comparison after percutaneous stone extraction. Urology 59: 15–19, 2002. 8. Bellman GC, Davidoff R, Candela J, et al: Tubeless percutaneous renal surgery. J Urol 157: 1578 –1582, 1997. 9. Mahaffey KG, Bolton DM, and Stoller ML: Urologist directed percutaneous nephrostomy tube placement. J Urol 152: 1973–1976, 1994. 10. Farrell TA, Wallace M, and Hicks ME: Long-term results of transrenal ureteral occlusion with use of Gianturco coils and gelatin sponge pledgets. J Vasc Interv Radiol 8: 449 – 455, 1997. 11. Monga M, Gawlik A, and Durfee W: Systematic evaluation of ureteral access sheaths. Urology 63: 834 – 836, 2004. 12. Danuser H, Ackermann DK, Bohlen D, et al: Endopyelotomy for primary ureteropelvic junction obstruction: risk factors determine the success rate. J Urol 159: 56 – 61, 1998. 13. Desai MR, Kukreja RA, Desai MM, et al: A prospective randomized comparison of nephrostomy drainage following percutaneous nephrolithotomy: large bore versus small bore versus tubeless. J Urol 172: 565–567, 2004. 14. Joshi HB, Adams S, Obadeyi OO, et al: Nephrostomy tube or “JJ” ureteric stent in ureteric obstruction: assessment of patient perspectives using quality of life survey and utility analysis. Eur Urol 39: 695–701, 2001. 15. Paul EM, Marcovich R, Lee BR, et al: Choosing the ideal nephrostomy tube. BJU Int 92: 672– 677, 2003. 16. Koolpe HA, and Lord B: Eccentric nephroscopy for the incarcerated nephrostomy. Urol Radiol 12: 96 –98, 1990. 17. Sardina JI, Bolton DM, and Stoller ML: Entrapped Malecot nephrostomy tube: etiology and management. J Urol 153: 1882–1883, 1995. 18. Watson G: Problems with double-J stents and nephrostomy tubes. J Endourol 150: 1267–1270, 1993.
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PERCUTANEOUS NEPHROSTOMY CATHETERS: DRAINAGE FLOW AND RETENTION STRENGTH BENJAMIN K. CANALES, KARI HENDLIN, MATTHEW BRAASCH, CHRISTOPHER ANTOLAK, AVINASH REDDY, BESMA ODEH, AND MANOJ MONGA
ABSTRACT Objectives. To evaluate the impact of percutaneous nephrostomy catheter configuration on drainage flow and retention strength. Methods. The Cook nephrostomy 16F (symmetric balloon), Bardex Council 16F (eccentric balloon), Microvasive Flexima 14F (pigtail), and Bardex Malecot 16F (flange) nephrostomy catheters were attached to an artificial renal pelvis (12-in.-round latex balloon). The balloon was subsequently filled with either 60 mL of water or orange juice with pulp, and gravity drainage of this fluid was recorded as flow into a flowmeter. Using a Force Five Model FDV-100 force gauge, the retention strength was tested by measuring the force required to pull the nephrostomy catheter through an 8-mm hole in a 35-mm-thick biologic tissue specimen (bologna). Results. The maximal flow rate using both orange juice and saline was significantly greater for the Cook nephrostomy than for the Microvasive Flexima, Bardex Malecot, and Bardex Council catheters (P ⱕ0.016). The average flow rate using saline for the Cook nephrostomy catheter was significantly greater than for all other catheters (P ⱕ0.02) and was significantly greater than for the Microvasive Flexima and the Bardex Council catheters (P ⱕ0.036) using orange juice. The retention strength was strongest for the Cook nephrostomy catheter (3.41 ⫾ 0.14 lb) compared with the Bardex Council (1.75 ⫾ 0.1), Microvasive Flexima (1.35 ⫾ 0.3), and Bardex Malecot (0.29 ⫾ 0.03) catheters. In addition, the Microvasive Flexima catheter resulted in greater maceration of the biologic tissue after forceful dislodgement. Conclusions. The results of this study have demonstrated that the Cook nephrostomy catheter combines strong drainage flow and strong retention strength during in vitro testing. Clinical evaluations of the ease of use and patient comfort are warranted. UROLOGY 66: 261–265, 2005. © 2005 Elsevier Inc.
P
ercutaneous tube drainage of the kidney was first described in 1955.1 Percutaneous nephrostomy tubes (PNTs) are now routinely used by radiologists and urologists for a wide range of clinical situations in which optimization of renal drainage is critical. Recent investigations for percutaneous nephrolithotomy have centered on adaptation of the procedural technique to improve efficacy and decrease
M. Monga is a study investigator funded by Boston Scientific, Cook Urological, and Bard Urological. From the Department of Urologic Surgery, Veterans Affairs Health Care System; and Department of Urologic Surgery, University of Minnesota School of Medicine, Minneapolis, Minnesota Reprint requests: Manoj Monga, M.D., Department of Urology, University of Minnesota School of Medicine, 420 Delaware Street Southeast, MMC 394, Minneapolis, MN 55455-0392. E-mail: [email protected] Submitted: December 2, 2004, accepted (with revisions): March 8, 2005 © 2005 ELSEVIER INC. ALL RIGHTS RESERVED
morbidity. These studies have included the development of minipercutaneous nephrolithotomy,2– 4 the use of a smaller PNT,5–7 or a tubeless approach in select patients after completion of nephrolithotomy.4,8 For tubeless percutaneous nephrolithotomy, careful patient selection is important for success, as this approach limits reentry for second-look nephroscopy, postoperative bleeding, or ureteral obstruction.8 Successful PNT drainage at the completion of percutaneous nephrolithotomy requires adequate drainage flow to prevent urinary obstruction or the development of intrarenal clots. Adequate retention strength to prevent inadvertent dislodgement of the catheter is also important, because inadvertent removal has been reported to be as high as 30% in some studies.9,10 In this study, we evaluated the impact of percutaneous catheter configuration on drainage flow and retention strength in an in vitro model. 0090-4295/05/$30.00 doi:10.1016/j.urology.2005.03.030 261
FIGURE 1. Tip configuration, cross-sectional area, and catheter lengths of Bardex Malecot, Bardex Council, Cook nephrostomy, and Microvasive Flexima catheters.
MATERIAL AND METHODS The Cook nephrostomy 16F (Cook Urological, Spencer, Ind), Bardex Council 16F (CR Bard, Covington, Ga), Bardex Malecot 16F (CR Bard), and Microvasive Flexima 14F (Boston Scientific, Natick, Mass) PNTs were used in this study (Fig. 1). The largest size available for the Flexima catheter is 14F.
RETENTION STRENGTH Bologna has been used as a homogenous biologic tissue that is easily available for repetitive and reproducible testing.11 Two 8-oz. packages of bologna (35 mm thick) were frozen to ⫺80°C. Twenty-one separate, 8-mm-diameter holes spaced evenly apart were then drilled through the length of the bologna using a 5/16-in. drill bit. All plastic bologna wrappings were removed, except for a small rim of plastic casing around the peripheral edge of the surface, and the bologna was allowed to thaw overnight in a refrigerator. For testing, individual catheters were inserted through a bologna hole centered above the gap between two wooden tables (Fig. 2). After insertion, the retention balloons of the Cook nephrostomy and Bardex Council catheters were inflated with 3 mL water. After insertion of the Boston Scientific Flexima catheter, the retention coil was tightened and locked. A handheld Force Five Model FDV-100 force gauge was secured to the lower portion of the catheter and used to pull the catheter tip through the bologna. This procedure was repeated five times for each catheter using a new hole in the bologna for each trial, and the maximal force readings were recorded (Fig. 3). Statistical analysis was performed using commercially available software. P ⬍0.05 was considered significant.
DRAINAGE For drainage testing, the balloons of the Cook nephrostomy catheter and Bardex Council tip catheter were inflated with 3 mL water, and the coil of the Flexima pigtail catheter was tightened and secured with the tension string. A 12-in.-round 262
latex balloon (Betta Products) was attached proximal to the retention balloon, coil, or flange of the catheter with a rubber band and filled manually with a syringe using the drainage port. Danuser et al.12 reported that the mean preoperative pyelocaliceal volume of hydronephrotic kidneys (primary ureteropelvic junction obstruction) was 64 ⫾ 33 mL. We attempted to replicate this by filling our artificial renal pelvis reservoir (balloon) with 60 mL of water. Air in the pelvis and drainage port was aspirated, and the catheter tip was manually centered in the fluid contents of the balloon. The catheter-pelvis unit was then placed on a level platform with the drainage port over the flow meter. The syringe was removed, and the results of the average and maximal drainage flow (in millimeters per second) were recorded using the Urodyn 1000 Flow Meter (Medtronic-Dantec, Allendale, NJ). The artificial renal pelvis reservoir was manually emptied of residual water between trials. To replicate the clinical scenario of blood or debris, the test was then repeated using 60 mL Tropicana “Some Pulp” premium orange juice. Each test was repeated a total of five times for each catheter.
RESULTS The retention strength was significantly stronger for the Cook nephrostomy catheter (3.41 ⫾ 0.14 lb) compared with the Bardex Council (1.75 ⫾ 0.1), Microvasive Flexima (1.35 ⫾ 0.3), and Bardex Malecot (0.29 ⫾ 0.03) catheters (P ⬍0.001; Fig. 3). In addition, the Microvasive Flexima resulted in greater maceration of the biologic tissue after forceful dislodgement (Fig. 2). Using 60 mL normal saline, the maximal drainage flow rate was significantly greater for the Cook nephrostomy (3.6 ⫾ 0.4 mL/s) than the MicrovaUROLOGY 66 (2), 2005
FIGURE 2. Retention strength setup and results. Bard Malecot catheter (1) placed through 8-mm opening in biologic tissue and graduated force applied with Force Five force transducer (2) until catheter pulled through tissue. Maceration of tissue after forceful extraction noted with Bard Council (A), Bard Malecot (B), Microvasive Flexima (C), and Cook nephrostomy catheter (D).
FIGURE 3. Tube retention strength.
sive Flexima (2.6 ⫾ 0.2 mL/s), Bardex Malecot (2.5 ⫾ 0.2 mL/s) and Bardex Council (1.6 ⫾ 0.2 mL/s) catheters (P ⬍0.0003; Fig. 4). The average drainage flow rate was significantly greater for the Cook nephrostomy catheter (2.4 ⫾ 0.3 mL/s) than the Bardex Malecot (2.0 ⫾ 0.2 mL/s, P ⫽ 0.02), Microvasive Flexima (1.8 ⫾ 0.1 mL/s, P ⫽ 0.003), or Bardex Council (1.3 ⫾ 0.2 mL/s, P ⫽ 0.0001; Fig. 5). Using 60 mL orange juice with pulp (to represent potential debris in the efflux), the maximal drainage flow rate was significantly greater for the Cook nephrostomy (4.6 ⫾ 1.25 mL/s) than for the Bardex Malecot (2.5 ⫾ 0.9 mL/s, P ⫽ 0.016), Microvasive Flexima (2.1 ⫾ 0.62 mL/s, P ⬍0.01), and Bardex Council (1.4 ⫾ 0.48 mL/s, P ⬍0.001) catheters (Fig. 4). The average drainage flow rate was significantly greater for the Cook nephrostomy catheter (1.6 ⫾ 0.43 mL/s) than for the MicrovaUROLOGY 66 (2), 2005
FIGURE 4. Maximal drainage rate (Qmax) with 60 mL sterile water (dots) and 60 mL orange pulp (crosshatched lines).
sive Flexima (1.0 ⫾ 0.32 mL/s, P ⫽ 0.036) and the Bardex Council (0.8 ⫾ 0.11, P ⬍0.01; Fig. 5). A small, but nonsignificant statistical difference was found between the Cook nephrostomy and Bardex Malecot catheters (1.1 ⫾ 0.2 mL/s, P ⫽ 0.077). COMMENT The PNTs available for placement include nonballoon (pigtail or flange) or balloon (symmetric or eccentric-placed) catheters. Because maximizing the drainage flow may prevent urinary obstruction 263
FIGURE 5. Average drainage rate (Qave) with 60 mL sterile water (dots) and 60 mL orange pulp (crosshatched lines).
or the development of intrarenal clot in the postoperative period, we decided to evaluate the maximal and average drainage rates with four commercially available PNT designs. Similarly, adequate retention strength to prevent inadvertent dislodgement of the catheter is an important property that can be attributed to catheter design. We evaluated this property through an 8-mm opening, similar to what one would anticipate at the completion of standard percutaneous nephrolithotomy in which the percutaneous tract was dilated to 10 mm in size. Small-bore nephrostomy drainage after urologic procedures has recently been shown to result in less postoperative pain,5–7,13 urinary extravasation,6 and hospital stay7 than large-bore drainage. A study by Joshi et al.14 also reported less discomfort from nephrostomy tubes than from doublepigtail ureteral stents for ureteral obstruction. Because these reports indicated that more physicians are using smaller PNTs for drainage, we selected four small-bore catheters (14F to 16F) for study inclusion. Although some have suggested that larger tubes are important to tamponade the nephrostomy tract, to our knowledge, this theory has never been proven. In addition, a 34F tube would be required to tamponade the 34F (outer diameter) nephrostomy tract, and proponents of large-bore catheters typically use only a 24F or 26F catheter. When considering the flow of a liquid through a tube, the rate of flow is equal to the change in pressure (driving pressure) times a fourth power dependence on the radius divided by the viscous resistance (Poiseuille’s law). This resistance depends linearly on the viscosity of the liquid and the length of the tube. In our study, the cross-sectional area should be the greatest variable with regard to flow followed by the length of the catheters. How264
ever, the catheter with the largest surface area (Malecot) did not have the greatest flows. This suggests that not only the cross-sectional area and catheter length, but also catheter tip, hole, balloon design, and wall properties may be important flow variables to consider when choosing a PNT. Although the Cook nephrostomy and Bardex Council catheters are of similar size and distal tip hole configuration, the flow rates with the Cook nephrostomy were significantly greater. This suggests that the balloon configuration (eccentric versus symmetric) or catheter shaft hole positioning (two holes opposing each other with the Bardex, two holes separated by 1.5 cm with the Cook) may affect the resistance and flow through the tube. The greater retention strength of the Cook catheter may reflect differences in balloon material or configuration. Pigtail catheters are the smallest catheters, ranging in size from 5F to 14F. The “Cope loop” pigtail catheter has a nylon string between the last side hole and the catheter tip. By placing tension on the string during tube insertion, the pigtail locks and self-retains in a tight coil, obviating the need for anchoring skin sutures.15 This nylon string lock must be subsequently released or cut to uncoil the stent and allow it to be removed. Nylon stringlocking pigtails have been reported to cause renal parenchymal injury, especially when placed in small, undilated systems.15 We found that forceful removal of the locked Flexima catheter, representing the clinical situation of inadvertent catheter dislodgement, resulted in the most maceration of the biologic tissue. Malecot or flange catheters deploy a mushroomstyle tip within the renal calix, averting the concern for caliceal obstruction and facilitating removal. Despite this design, cases of tissue bridge formation over the flanges, requiring endoscopic removal, have been reported.16,17 Traditionally, Malecot catheters have been used to provide largebore drainage after percutaneous renal surgery, because the lack of a balloon port means a larger catheter lumen compared with balloon catheters of the same size. Despite the larger cross-sectional area, we were surprised to find that the Malecot catheter had significantly lower maximal flow rates using both saline and pulp compared with the Cook nephrostomy tube and significantly lower average flow rates for saline. This was likely a reflection of catheter length and possibly of tip configuration. In addition, the self-retaining mechanism of the Malecot proved less secure than the pigtail or balloon catheters (P ⬍0.001). Balloon catheters include the Foley, Council, Couvelaire, and Argyle. Council catheters are most commonly used as they have a terminal hole allowing insertion or exchange over a guidewire. CathUROLOGY 66 (2), 2005
eter balloons may occlude one or more calices, depending on placement,18 or may increase postoperative flank pain with overdistension. Although the results of our study have demonstrated that the drainage properties of the Cook nephrostomy tube in an in vitro model of the renal pelvis were superior to those of other catheters tested, it is important to emphasize that our model does not address the impact of the balloon design on caliceal drainage. CONCLUSIONS The results of this study have shown that the Cook nephrostomy catheter (16F, symmetric balloon) combined both strong drainage flows and strong retention strengths in our in vitro testing. Clinical evaluations of the ease of use and patient comfort are warranted. REFERENCES 1. Goodwin WE, Casey WC, and Wolf W: Percutaneous trocar (needle) nephrostomy in hydronephrosis. JAMA 157: 891– 894, 1955. 2. Chan DY, and Jarrett TW: Mini-percutaneous nephrolithotomy. J Endourol 14: 269 –272, 2000. 3. Monga M, and Olgevie S: Minipercutanous nephrolithotomy. J Endourol 14: 419 – 421, 2000. 4. Feng MI, Tamaddon K, Mikhail A, et al: Prospective randomized study of various techniques of percutaneous nephrolithotomy. Urology 58: 345–350, 2001. 5. Pietrow PK, Auge BK, Costa DL, et al: Pain after percutaneous nephrolithotomy: impact of nephrostomy tube size. J Endourol 17: 411– 414, 2003.
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6. Maheshwari PN, Andankar MG, and Bansal M: Nephrostomy tube after percutaneous nephrolithotomy: large bore or pigtail catheter? J Endourol 14: 735–737, 2000. 7. Liatsikos EN, Hom D, Dinlenc CZ, et al: Tail stent versus re-entry tube: a randomized comparison after percutaneous stone extraction. Urology 59: 15–19, 2002. 8. Bellman GC, Davidoff R, Candela J, et al: Tubeless percutaneous renal surgery. J Urol 157: 1578 –1582, 1997. 9. Mahaffey KG, Bolton DM, and Stoller ML: Urologist directed percutaneous nephrostomy tube placement. J Urol 152: 1973–1976, 1994. 10. Farrell TA, Wallace M, and Hicks ME: Long-term results of transrenal ureteral occlusion with use of Gianturco coils and gelatin sponge pledgets. J Vasc Interv Radiol 8: 449 – 455, 1997. 11. Monga M, Gawlik A, and Durfee W: Systematic evaluation of ureteral access sheaths. Urology 63: 834 – 836, 2004. 12. Danuser H, Ackermann DK, Bohlen D, et al: Endopyelotomy for primary ureteropelvic junction obstruction: risk factors determine the success rate. J Urol 159: 56 – 61, 1998. 13. Desai MR, Kukreja RA, Desai MM, et al: A prospective randomized comparison of nephrostomy drainage following percutaneous nephrolithotomy: large bore versus small bore versus tubeless. J Urol 172: 565–567, 2004. 14. Joshi HB, Adams S, Obadeyi OO, et al: Nephrostomy tube or “JJ” ureteric stent in ureteric obstruction: assessment of patient perspectives using quality of life survey and utility analysis. Eur Urol 39: 695–701, 2001. 15. Paul EM, Marcovich R, Lee BR, et al: Choosing the ideal nephrostomy tube. BJU Int 92: 672– 677, 2003. 16. Koolpe HA, and Lord B: Eccentric nephroscopy for the incarcerated nephrostomy. Urol Radiol 12: 96 –98, 1990. 17. Sardina JI, Bolton DM, and Stoller ML: Entrapped Malecot nephrostomy tube: etiology and management. J Urol 153: 1882–1883, 1995. 18. Watson G: Problems with double-J stents and nephrostomy tubes. J Endourol 150: 1267–1270, 1993.
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