The presence of helical flow can suppress areas of disturbed shear in parameterised models of an arteriovenous fistula

Areas of disturbed shear that develop following arteriovenous fistula (AVF) creation are believed to trigger the onset of intimal hyperplasia (IH), leading to AVF dysfunction. The presence of helical flow can suppress the flow disturbances that lead to disturbed shear in other areas of the vasculature. However, the relationship between helical flow and disturbed shear remains unevaluated in AVF. In this study, computational fluid dynamics (CFD) is used to evaluate the relationship between geometry, helical flow, and disturbed shear in parameterised models of an AVF characterised by four different anastomosis angles. The AVF models with a small anastomosis angle demonstrate the lowest distribution of low/oscillating shear and are characterised by a high helical intensity coupled with a strong balance between helical structures. Contrastingly, the models with a large anastomosis angle experience the least amount of high shear, multidirectional shear, as well as spatial and temporal gradients of shear. Furthermore, the intensity of helical flow correlates strongly with curvature (r = 0.73, P < .001), whereas it is strongly and inversely associated with taper (r = −0.87, P < .001). In summary, a flow field dominated by a high helical intensity coupled with a strong balance between helical structures can suppress exposure to low/oscillating shear but is ineffective when it comes to other types of shear. This highlights the clinical potential of helical flow as a diagnostic marker of exposure to low/oscillating shear, as helical flow can be identified in vivo with the use of ultrasound imaging

Cryopreservation of porcine urethral tissue: storage at − 20◦C preserves the mechanical, failure and geometrical properties

Cryopreservation is required to preserve the native properties of tissue for prolonged periods of time. In this study, we evaluate the impact that 4 different cryopreservation protocols have on porcine urethral tissue, to identify a protocol that best preserves the native properties of the tissue. The cryopreservation protocols include storage in cryoprotective agents at − 20 ◦C and − 80 ◦C with a slow, gradual, and fast reduction in temperature. To evaluate the effects of cryopreservation, the tissue is mechanically characterised in uniaxial tension and the mechanical properties, failure mechanics, and tissue dimensions are compared fresh and following cryopreservation. The mechanical response of the tissue is altered following cryopreservation, yet the elastic modulus from the high stress, linear region of the Cauchy stress – stretch curves is unaffected by the freezing process. To further investigate the change in mechanical response following cryopreservation, the stretch at different tensile stress values was evaluated, which revealed that storage at − 20 ◦C is the only protocol that does not significantly alter the mechanical properties of the tissue compared to the fresh samples. Conversely, the ultimate tensile strength and the stretch at failure were relatively unaffected by the freezing process, regardless of the cryopreservation protocol. However, there were alterations to the tissue dimensions following cryopreservation that were significantly different from the fresh samples for the tissue stored at − 80 ◦C. Therefore, any study intent on preserving the mechanical, failure, and geometric properties of urethral tissue during cryopreservation should do so by freezing samples at − 20 ◦C, as storage at − 80 ◦C is shown here to significantly alter the tissue properties

Mechanical and morphological characterisation of porcine urethras for the assessment of paediatric urinary catheter safety

Paediatric urinary catheters are often necessary in critical care settings or to address congenital anomalies  affecting the urogenital system. Iatrogenic injuries can occur during the placement of such catheters, highlighting  the need for a safety device that can function in paediatric settings. Despite successful efforts to develop devices  that improve the safety of adult urinary catheters, no such devices are available for use with paediatric catheters.  This study investigates the potential for utilising a pressure-controlled safety mechanism to limit the trauma  experienced by paediatric patients during inadvertent inflation of a urinary catheter anchoring balloon in the  urethra. Firstly, we establish a paediatric model of the human urethra using porcine tissue by characterising the  mechanical and morphological properties of porcine tissue at increasing postnatal timepoints (8, 12, 16 and 30  weeks). We identified that porcine urethras harvested from pigs at postnatal week 8 and 12 exhibit morpho?logical properties (diameter and thickness) that are statistically distinct from adult porcine urethras (postnatal  week 30). We therefore utilise urethra tissue from postnatal week 8 and 12 pigs as a model to evaluate a pressure-controlled approach to paediatric urinary catheter balloon inflation intended to limit tissue trauma during  inadvertent inflation in the urethra. Our results show that limiting catheter system pressure to 150 kPa avoided  trauma in all tissue samples. Conversely, all of the tissue samples that underwent traditional uncontrolled urinary  catheter inflation experienced complete rupture. The findings of this study pave the way for the development of a  safety device for use with paediatric catheters, thereby alleviating the burden of catastrophic trauma and life  changing injuries in children due to a preventable iatrogenic urogenital event.  </p

In vivo ureteroscopic intrarenal pressures and clinical outcomes: a multi-institutional analysis of 120 consecutive patients

  Objectives To evaluate the pressure range generated in the human renal collecting system during ureteroscopy (URS), in a large patient sample, and to investigate a relationship between intrarenal pressure (IRP) and outcome. Patients and Methods A prospective multi-institutional study was conducted, with ethics board approval; February 2022–March 2023. Recruitment was of 120 consecutive consenting adult patients undergoing semi-rigid URS and/or flexible ureterorenoscopy (FURS) for urolithiasis or diagnostic purposes. Retrograde, fluoroscopy-guided insertion of a 0.036-cm (0.014″) pressure guidewire (COMET™ II, Boston Scientific, Marlborough, MA, USA) to the renal pelvis was performed. Baseline and continuous ureteroscopic IRP was recorded, alongside relevant operative variables. A 30-day follow-up was completed. Descriptive statistics were applied to IRP traces, with mean (sd) and maximum values and variance reported. Relationships between IRP and technical variables, and IRP and clinical outcome were interrogated using the chi-square test and independent samples t-test.   Results A total of 430 pressure traces were analysed from 120 patient episodes. The mean (sd) baseline IRP was 16.45 (5.99) mmHg and the intraoperative IRP varied by technique. The mean (sd) IRP during semi-rigid URS with gravity irrigation was 34.93 (11.66) mmHg. FURS resulted in variable IRP values: from a mean (sd) of 26.78 (5.84) mmHg (gravity irrigation; 12/14-F ureteric access sheath [UAS]) to 87.27 (66.85) mmHg (200 mmHg pressurised-bag irrigation; 11/13-F UAS). The highest single pressure peak was 334.2 mmHg, during retrograde pyelography. Six patients (5%) developed postoperative urosepsis; these patients had significantly higher IRPs during FURS (mean [sd] 81.7 [49.52] mmHg) than controls (38.53 [22.6] mmHg; P  Conclusions A dynamic IRP profile is observed during human in vivo URS, with IRP frequently exceeding expected thresholds. A relationship appears to exist between elevated IRP and postoperative urosepsis.</p

A prospective multi-institutional evaluation of Iatrogenic urethral catheterization injuries

Objectives:  To perform a multi-institutional investigation of incidence and outcomes of urethral trauma sustained during attempted catheterization. Patients & Methods: A prospective, multi-center study was conducted over a designated 3-4month period, incorporating seven academic hospitals across the UK and Ireland. Cases of urethral trauma arising from attempted catheterization were recorded. Variables included sites of injury, management strategies and short-term clinical outcomes. The catheterization injury rate was calculated based on the estimated total number of catheterizations occurring in each center per month. Anonymised data were collated, evaluated and described. Results:  Sixty-six urethral catheterization injuries were identified (7 centers; mean 3.43months). The mean injury rate was 6.2±3.8 per 1000 catheterizations (3.18–14.42/1000). All injured patients were male, mean age 76.1±13.1years. Urethral catheterization injuries occurred in multiple hospital/community settings, most commonly Emergency Departments (36%) and medical/surgical wards (30%). Urological intervention was required in 94.7% (54/57), with suprapubic catheterization required in 12.3% (n=7). More than half of patients (55.56%) were discharged with an urethral catheter, fully or partially attributable to the urethral catheter injury. At least one further healthcare encounter on account of the injury was required for 90% of patients post-discharge. Conclusions:  This is the largest study of its kind and confirms that iatrogenic urethral trauma is a recurring medical error seen universally across institutions, healthcare systems and countries. In addition, urethral catheter injury results in significant patient morbidity with a substantial financial burden to healthcare services. Future innovation to improve the safety of urinary catheterization is warranted. </p