Abstract
PURPOSE:
To evaluate the effect of catheter connections on drainage catheters’ flow rate.
MATERIALS AND METHOD:
The in vitro model used commercially available catheters (8.5-F, 10.2-F, 12-F, and 14-F), connections- Luer-lok (2.33 mm inner diameter), and stopcocks (1.33 mm, 2.00 mm, and 2.67 mm inner diameters), water, ultrasound gel, textured vegetable protein (TVP) 2 mm particles, and collection bags. Plain water, viscous fluid (30% ultrasound gel solution in water), or water/viscous fluid with TVP were placed in collection bags and drained by gravity through each of the catheters and each connection. The flow rate was measured, recorded, and compared for each catheter and each connection as well as to the control flow rate of the catheters without connections. Ten one-minute trials were performed, and the mean flow rates were analyzed using Student T-test and Pearson correlation coefficient.
RESULTS:
Flow rate was significantly decreased in the 12-F and 14-F catheters with all stopcock and Luer-Lok connections with both water and viscous fluids. There was no significant reduction in flow for the 8.5-F and 10.2-F catheters with the 2.00 mm, 2.33 mm, and 2.67 mm connections; flow rate was significantly decreased in the 8.5-F and 10.2-F catheters with the 1.33 mm connection. A majority of trials with particulate fluid became occluded, and no consistent pattern between connections could be made.
CONCLUSION:
This in vitro study suggests that stopcock and Luer-Lok connections limit catheter flow rate when their inner diameter is less than that of the drainage catheter.
Keywords: Percutaneous drainage, Drainage catheter, Interventional radiology, Percutaneous abscess drainage, Stopcock
Introduction
Image-guided percutaneous drainage (PD) of intraabdominal abscesses is among the most common procedure performed by interventional radiologists and is the standard of care for the majority of intraabdominal fluid collections (1). One recent study querying the Medicare part B procedural databases showed that as many as 79% of abdominal abscesses are managed by interventional radiologists (2). Despite how frequently PD is performed, there is considerable variability in catheter selection, size, number, and route (3). Despite this variability, PD is typically universally successful with suggestive curative and partial successes of over 85% (4).
Catheter diameter is a factor that has been the focus of several in vitro investigations (5–8) and few clinical reports (9, 10). Catheter connectors, such as stopcocks and Luer-Lok, are connections are devices that connect commercial catheters to drainage reservoirs. These connections may be the smallest diameter in the drainage system, potentially impeding flow.
The purpose of our study was to evaluate the effect of catheter connections on drainage catheters’ flow rate.
Materials and methods
This was an in vitro laboratory study that did not require institutional review board approval. All experiments were conducted in a basic science laboratory. Materials in this study included commercial drainage catheters (Cook Medical, Inc., Indiana), commercial stopcocks and a Luer-Lok (Cook Medical, Inc., Indiana), both water and non-viscous fluids, and an ad hoc drainage system that was created to measure fluid flow through catheters and stopcock or Luer-Lok connections (Fig. 1).
Figure 1.
In vitro drainage system model.
Various sizes of single lumen percutaneous drainage catheters - sizes 8.5-, 10.2-, 14.0-French, and the multi-purpose 12.0-F size catheter were interrogated. The outer and inner diameters and amount and dimensions of drainage holes of each catheter are listed in Table 1. Three stopcock connections were used: low-pressure, standard, and high-pressure three-way stopcock (Fig. 2), with their respective inner diameters listed in Table 2.
Table 1.
Characteristics of drainage catheters used in experiments.
| Catheter (Fr) | Outer diameter (mm) | Inner diameter (mm) | # of side holes | Side hole diameter (mm) |
|---|---|---|---|---|
| 8.5 | 2.83 | 1.67 | 5 | 3×1 |
| 10.2 | 3.40 | 2.30 | 5 | 5×2 |
| 12.0 | 4.00 | 3.00 | 6 | 4×3 |
| 14 | 4.67 | 4.00 | 5 | 4×2 |
Figure 2.
A, B, C, D: Connections consisted of A) a 2.67mm inner diameter stopcock, B) a 2.33mm inner diameter Luer-lok (top and side view), C) a 2.00mm inner diameter stopcock, and D) a 1.33mm inner diameter stopcock
Table 2.
Characteristics of catheter connection used in experiments. Stopcocks are named according to their commercial designations. High and low pressure refers to their grading for angiographic use. The standard model is marketed as a generic multipurpose stopcock.
| Connection | Inner diameter (mm) | |
|---|---|---|
| A | Low pressure stopcock | 2.67 |
| B | Luer-lok | 2.33 |
| C | Standard stopcock | 2.00 |
| D | High-pressure stopcock | 1.33 |
Note – this table is meant to be displayed in conjunction with Figure 2.
Four types of fluids were used to test drainage efficiency: water, viscous fluid, water with particulate matter, and viscous fluid with particulate matter. Viscous fluid was a 30% dilution of ultrasound gel at a viscosity of 12 mPa sec. Fifteen grams of textured vegetable protein, <2 mm in size, was then added to the water and viscous fluid to create particulate matter.
The drainage model was constructed with a source reservoir (a 540 mL urine leg bag) above a catheter and a collection container. Each of the four fluids was drained by gravity through the catheters, both without a stopcock connection (control) and with the stopcock connections and collected into the measuring container. The liquids flowed for 1 minute through the catheter into the measuring container in a total of 10 trials for each unique set up. After draining liquids with particles, the catheter was flushed with air to prevent blockage and ensure accurate results after each trial.
The flow rate of the control was compared with that of the stopcock connections to calculate the drainage difference (% decrease ± standard deviation [SD]) between the two volumes. Data were compared using Student t-test and Pearson correlation coefficient. A P value < 0.05 was considered to be significant. A correlation coefficient (r) of r ˃ 0.8 was considered a strong correlation.
Results
Flow rate was significantly decreased in the 12-F and 14-F catheters with all stopcock and Luer-Lok connections with both water and viscous fluids (P <0.001 in all comparisons). There was no significant reduction in flow for the 8.5-F and 10.2-F catheters with the 2.00 mm, 2.33 mm, and 2.67 mm connections (P >0.05 in all comparisons). Flow rate was significantly decreased in the 8.5-F and 10.2-F catheters with the 1.33 mm connection (P <0.05 for all comparisons). The majority of trials with particulate fluid became occluded and, given the inconsistencies, no consistent pattern between connections could be made due to lack of inferential statistical analysis. Between the different catheter sizes, flow rate for both water and viscous fluid significantly increased when the catheter size increased in all connection groups (P <0.01 in all comparisons).
In the 12.0-F and 14-F groups, all connections significantly reduced the flow rate of water and viscous fluid, the difference negatively correlating with the size of the stopcock. The high-pressure stopcock reduced flow of water by 36% and 48% respectively, and of viscous fluid by 26% and 41% respectively, showing a strong negative correlation between with the size of the catheter and the flow rate (r=−0.984 for water, r= −0.957 for viscous fluid). The bigger the catheter, the more the high-pressure stopcock obstructed flow. Particulate fluids entirely or partially blocked all catheters, with and without connections (Table 3).
Table 3.
Average flow rate (mL/min) of water and 30% diluted ultrasound gel (viscous fluid) with particulate matter (TVP) with control and different connections. The number of occluded trial and unpredictability of which catheters and connection devices would become occluded prevented summarizing the data with descriptive statistics and analyzing with inferential statistics. The data are presented to illustrate the inconsistencies, which may be indicative the occlusive nature and unpredictability of particulate matter/debris.
| Catheter size (Fr) | Control | Luer-lok (2.67mm) | Low pressure (2.33mm) | Standard (2.00mm) | High pressure (1.33mm) |
|---|---|---|---|---|---|
| Water and TVP | |||||
| 8.5 | occluded in 3/10 trials | occluded in 5/10 trials | occluded in 3/10 trials | occluded in 8/10 trials | occluded in 2/10 trials |
| 10.2 | occluded in 1/10 trials | occluded in 8/10 trials | 55±41 | 69±35 | occluded 10/10 trials |
| 12.0 | 23 ±30 | occluded in 6/10 trials | occluded in 7/10 trials | 33±54 | occluded in 9/10 trials |
| 14.0 | 6±2 | occluded in 7/10 trials | 41±38 | occluded in 6/10 trials | occluded in 3/10 trials |
| Viscous fluid and TVP | |||||
| 8.5 | occluded in 4/10 trials | occluded in 2/10 trials | occluded in 4/10 trials | occluded in 4/10 trials | occluded in 5/10 trials |
| 10.2 | occluded in 1/10 trials | 27±25 | occluded in 1/10 trials | occluded in 1/10 trials | occluded 1/10 trials |
| 12.0 | occluded in 2/10 trials | occluded in 1/10 trials | occluded in 3/10 trials | occluded in 5/10 trials | occluded in 6/10 trials s |
| 14.0 | 9±9 | occluded in 1/10 trials | 10±8 | occluded in 2/10 trials | occluded in 7/10 trials |
| 14.0 | 6±2 | occluded in 7/10 trials | 41±38 | occluded in 6/10 trials | occluded in 3/10 trials |
Note. The number of occluded trial and unpredictability of which catheters and connection devices would become occluded prevented summarizing the data with descriptive statistics and analyzing with inferential statistics. The data are presented to illustrate the inconsistencies, which may be indicative the occlusive nature and unpredictability of particulate matter/debris.
Discussion
The current data demonstrates that stopcocks and catheter connections impede flow from a drainage catheter when the connections internal diameter is smaller than that of the drainage catheter. Studies have shown that flow through drainage catheters complies with Poiseuille’s law, with the inner diameter being the most important variable. Poiseuille’s law states that the flow rate (Q) is directly related to the pressure difference (Δp) between the ends of the catheter and the catheter radius (r) to the fourth power, and it is inversely related to the catheter length (L) and the viscosity coefficient (η) of the fluid drained (Q = πΔpr4/8ηL) (11). Several in vitro studies have demonstrated that catheters with a larger inner lumen diameter outperformed those with a smaller diameter, especially when draining a viscous solution (7, 8). Hoyt et al. compared drainage of double lumen to single lumen catheters in vitro (5). While double and single lumen catheters of the same size have equivalent outer diameters, a double lumen catheter has an additional lumen to provide for simultaneous irrigation and aspiration, decreasing the effective inner diameter of the drainage catheter. The study showed that single lumen catheters performed as well or better than double lumen catheters when draining fluids of varying viscosities.
Furthermore, other variables in Poiseuille’s law have been shown to have effects on catheter flow, such as catheter length, pressure differences, and viscosity. For example, Lee et al. (8) demonstrated that shorter lengths in catheters did improve drainage in vitro, while Macha et al. (6) showed no correlation of catheter length with drainage efficiency in vitro. A study on the number of drainage side holes, which relates to length of the catheter, suggested that beyond a critical side hole number threshold, adding more distal side holes does not improve catheter drainage efficiency (3).
Yet, while larger-French catheters have proportionately greater flow, the flow of drainage may be impeded at the level of the stopcock, where the diameter of the system is smallest (12). Larger-French catheters are most affected, due to the greater discrepancy between luminal diameter and stopcock size. Park et al. showed in an in vitro model that standard commercial stopcocks decreased catheter drainage efficiency of water by 13–42% (6). In the present study, when the diameter of the stopcock was similar to the diameter of the catheter there was no significant impendence in flow for fluids without particulate matter. For maximum drainage efficiency of viscous fluids, the diameter of the stopcock should be no smaller than the catheter. Particulate matter may occlude the system at the level of the stopcock. In our study, a majority of the trials with particulate fluid became occluded. Interestingly, prior in vitro studies have demonstrated smaller diameter catheters perform better over time compared to larger catheter in draining fluid with particulate matter (12). Smaller sideholes in smaller catheters may act as a filter to prevent larger particulate matter from entering the lumen; however, it is unknown if this translates to clinical percutaneous drainage. Due to the inconsistencies of trials becoming occluded with particulate matter in the present study, which precluding inferential statistical analyses, we are unable to support or refute these observations from prior studies.
The present study tested threaded connector catheters and connectors, which screw into one another. Some commercial large bore drainage catheters (e.g., 20-F Thal-Quick and Gordan catheters; Cook Medical) use barbed (also called ‘Christmas tree’) adaptors that are wedged into the catheter hub, rather than the screw-and-receiver configuration of smaller diameter catheters. Other connection devices in percutaneous drainage are used in clinical practice. Although other connecting devices were not specifically tested in the present study, Poiseuille’s law would suggest a point in the system that constricts the radius of the drainage system (i.e., is the point of smallest diameter) would impede flow.
Limitations of this study include are reflective of its in vitro methodology. Commercial catheters were used in this study and we were able to delineate the effect of catheter connections with water. Viscous fluid with debris was simulated using ultrasound gel and TVP. These are not perfect analogues to pus in abscesses and debris in abscesses and necrotizing peripancreatic collections with debris. We simulated their use in a short period of time, whereas clinically these catheters would remain in the patient for days to weeks. The design of the ad hoc drainage system has its limitations. Gravity drainage was used instead of suction. Prior in vitro drainage catheter experiments demonstrate that both gravity and suction drainage act according to Poiseuille’s law (3, 6–8, 12). The drainage system was designed to simulate the initial drainage of an undrained intraabdominal collection in which the volume and pressure decreases as it may in an initial percutaneous drainage. Although it does not take into account intraabdominal pressure, similar in vitro methodologies have been used to simulate collection managed by drainage catheters (3, 8, 12). Regardless, our study provides valuable information to the ability for the ability of catheter and their connections to evacuate fluid collections at the initial drainage. Designing clinical studies would help to substantiate our findings. Although daily output and volume drained at the initial procedure are metrics often documented, the time that the initial volume took to accumulate would be a helpful measurement in designing such a clinical study.
In conclusion, this in vitro study suggests that stopcock and Luer-Lok connections limit catheter flow rate when their inner diameter is less than that of the drainage catheter. Increasing inner luminal diameter of connections may improve drainage catheters flow rate.
Acknowledgements:
The authors thank Travon Taylor, Alicia Thomas, Erin Rogers, Bruana Williams, Anna Li, and Alan Sticker for their contributions to generating the study data.
Footnotes
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Conference Presentation:
This study was presented at the 2015 SIR Annual Scientific Meeting as: Sticker A, Li H, Ballard D, D’Agostino H. In Vitro Evaluation of Percutaneous Drainage Catheters: Flow Related to Connections and Liquid Characteristics. Oral Presentation presented at: Society of Interventional Radiology 2015 Annual Meeting Medical Student Days Program; Atlanta, GA.
Disclosures: Dr. D’Agostino has served as paid speaker for Cook Medical. Dr. Ballard and Dr. D’Agostino are coinventors of an alternative stopcock design as detailed in the patent application below. This is not referred to in the current study: Hamidian Jahromi A, Ballard DH, Weisman JA, D’agostino HRV. Medical stopcock valve. Google Patents; 2016. Available from: http://www.google.com/patents/WO2015112803A1
Conflicts of Interest Statement
Author 4 has served as paid speaker for Cook Medical.
Author 1 and Author 4 are coinventors of an alternative stopcock design, which is not referred to in the current study: Medical stopcock valve. Patent Application. Google Patents; 2016. Available from: http://www.google.com/patents/WO2015112803A1
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