Medical devices should ideally aim for the best performance and the highest levels of safety they can achieve. For bladder management through catheterization, this primarily means optimal bladder emptying and, at the same time, reducing adverse events such as mucosal microtrauma, which may lead to UTI4,9,27,28. While advancements have been made in recent years by improving catheter materials and coatings and moving towards single-use rather than reusable catheters10,17,19,29,30, other parameters and processes related to UTIs have not been studied as extensively. Many factors increase the patient's risk of developing a UTI when performing CIC; among them are incomplete or improper voiding reflected in high post-void residual urine volumes and mucosal microtrauma10,11,31.
As suggested by a recent ex vivo study, higher than desirable residual volumes may be explained by obstruction of flow caused by mucosal suction during voiding18. Specifically, a suction event and resulting flow-stop may be misinterpreted as the bladder being empty, thus leaving residual urine and potentially uropathogens in the bladder. Subsequently, repositioning of the catheter would be required to continue the voiding process. It has been documented that in practice CIC is sometimes associated with higher than ideal post-void residual volumes11–14.
The latter UTI contributing factor mentioned above, microtrauma, can result from mucosal suction through the catheter drainage holes, which may cause damage to the urothelial barrier32. In the case of CECs, the process leading to mucosal microtrauma is related to a hydrodynamically-generated negative-pressure gradient when the bladder tissue approaches and closes the eyelets, leading to negative pressure peaks at the site of the eyelets and subsequent transient suction of the urothelium18,32,21.
In order to tackle the two related issues described here, namely incomplete drainage and microtrauma due to suction events, a new IC has been developed. What differentiates it from a CEC is, primarily, the design of the drainage area. While in a typical IC the drainage area consists of 2 usually elongated, ellipse-like eyelets placed near the tip of the catheter, in the new MHZC these eyelets are replaced by over 80 micro-holes positioned in the same area where the eyelets would be in a conventional device. The micro-holes of the MHZCs tested in this study had diameters ranging from 0.4 to 0.7 mm whereas the ellipsoid-like eyelets on conventional catheters have sizes of around 4 mm (major axis) by 1.5 mm (minor axis)32.
The two types of ICs (MHZC and CEC) were tested in a previously developed ex vivo porcine LUT model. The CEC used as control here was the one that proved superior to other CECs in a previous study conducted in the same porcine LUT model18. The outcomes of interest reported in the current study were flowrate and residual volume at the first flow-stop, as indicators of catheter performance, as well as instances of mucosal suction related to potential safety issues, but also to risk of flow obturation. The impact of parameters such as diameter of micro-holes, catheter insertion depth, and simulated intra-abdominal pressure mimicking sitting and standing positions was analyzed in the study. However, irrespective of these parameters, the MHZCs outperformed the conventional eyelet catheter in all of the experiments.
Two aspects are noteworthy, namely the very low residual volumes and the negligible mucosal suction attained with the MHZC. The residual volumes at the first flow-stop when using the MHZC were significantly lower than for the CEC in all cases, with values below 6 mL for the new device and typically around 40 mL when the CEC was used. This is indicative of the potential this new catheter design has to reduce the risk of UTI by decreasing the post-void residual urine volume to values that do not pose a threat for infection development10,11. From a different perspective, what this also means is that with the MHZC the first flow-stop occurred when all the urine from the bladder was drained and therefore was caused by the bladder being empty. By contrast, with the CEC the first flow-stop could take place, as previously shown18, not due to an empty bladder, but because of catheter obstruction, requiring subsequent repositioning of the device to complete the voiding.
Furthermore, the reduced incidence of mucosal suction episodes with the MHZC, or even lack thereof, with the 0.4 mm hole diameter, is suggestive of a different behavior of the device during voiding, compared to the CEC, where suction events were common (over 80% of catheterizations ex vivo). A deeper understanding of these differences was gained by measuring the pressure inside the catheter during bladder emptying and through endoscopic studies in the ex vivo model and also in vivo, in living pigs. As shown previously18 during voiding with a CEC the bladder mucosa may get suctioned into the eyelets and block the draining process. The endoscopy experiments conducted in the MHZC, however, show a different behavior, with the bladder gradually folding around the catheter tip and slowly covering the micro-holes, without obstructing flow. The lack of such suction events with the MHZC was further confirmed by the pressure profile inside the device during voiding, as a relatively constant pressure was recorded throughout the process. By contrast, the pressure profile of the CEC had sharp peaks, of up to 500 mbar, when suction events occurred, as shown previously18 and confirmed in this study.
This study has certain limitations related to the lack of in vivo validation of flow-rates and residual urine and not assessing the mucosal trauma directly, through histological examinations. Nevertheless, the use of a validated porcine LUT model that closely resembles the human bladder is an important strength of the presented work. Furthermore, the previous use of the same model in the study of different CECs further strengthens the validity of the results.
The overarching conclusion of the current study is that the new catheter design, with over 80 micro-holes replacing the traditional 2 eyelets of conventional ICs, improves flowrates, reduces post-void residual volumes to values in the ideal range, and virtually eliminates suction events in a complex ex vivo bladder model. Furthermore, endoscopy analysis provided valuable insight that improved the understanding of how the voiding process of the MHZC differs from that of the conventional IC. By eliminating flow-stops resulting from eyelet obstruction, the need to reposition the catheter in practice is also eliminated, consequently reducing the risk of trauma inflicted by mechanically moving the device during catheterization. Collectively, the results of this study indicate a superior performance of the MHZC compared to the state-of-the-art CEC design on the key parameters of drainage efficiency and safeguarding of the bladder mucosa. Considering the association of these adverse effects with IC-related UTI, a lower risk of UTI when using this catheter is likely as well.