A Challenge for Nephrologists—Increasing Fistula Maturation Rates, Reducing Fistula Maturation Time, and Decreasing Dialysis Catheter Prevalence in the United States

Tunneled dialysis catheters are simultaneously a benefit and burden for hemodialysis patients. The infectious and vascular complications of catheters are well documented. Despite this, prevalence of catheter use in the US hemodialysis population remains high and could be due in part to increased efforts to create arteriovenous (AV) fistulas in most new end-stage renal disease patients. The editorial argues that creating fistulas instead of prosthetic grafts is the correct approach and that inadequately diagnosed and treated primary fistula failure is a major cause of excessive and prolonged catheter dependency. An understanding of AV fistula physiology and the treatable causes of primary fistula failure are key to maximizing the percentage of created fistulas that are successfully used for dialysis. Diagnosis of fistula malfunction based on history, physical examination, and hemodynamic and angiographic evaluation is discussed, and treatment strategies presented. A major emphasis is placed on early primary fistula failure recognition and intervention. It is the author's contention if adequate vein and artery are selected for initial fistula construction nearly all fistulas should eventually function adequately to support dialysis and sooner than previously appreciated by utilizing an array of percutaneous and surgical therapies. Fistula malfunction is a unique problem within the spectrum of vascular disease and therefore demands that patients are treated by physicians with demonstrated expertise and experience.     

Longitudinal Assessment of Hemodynamic Endpoints in Predicting Arteriovenous Fistula Maturation

Arteriovenous fistula (AVF) nonmaturation is currently a significant clinical problem; however, the mechanisms responsible for this have remained unanswered. Previous work by our group and others has suggested that anatomical configuration and the corresponding hemodynamic endpoints could have an important role in AVF remodeling. Thus, our goal was to assess the longitudinal (temporal) effect of wall shear stress (WSS) on remodeling process of AVFs with two different configurations. The hypothesis is that early assessment of hemodynamic endpoints such as temporal gradient of WSS will predict the maturation status of AVF at later time points. Two AVFs with curved (C‐AVF) and straight (S‐AVF) configurations were created between the femoral artery and vein of each pig. Three pigs were considered in this study and in total six AVFs (three C‐AVF and three S‐AVF) were created. The CT scan and ultrasound were utilized to numerically evaluate local WSS at 20 cross‐sections along the venous segment of AVFs at 2D (D: days), 7D, and 28D postsurgery. These cross‐sections were located at 1.5 mm increments from the anastomosis junction. Local WSS values at these cross‐sections were correlated with their corresponding luminal area over time. The WSS in C‐AVF decreased from 22.3 ± 4.8 dyn/cm² at 2D to 4.1 ± 5.1 dyn/cm² at 28D, while WSS increased in S‐AVF from 13.0 ± 5.0 dyn/cm² at 2D to 36.7 ± 5.3 dyn/cm² at 28D. Corresponding to these changes in WSS levels, luminal area of C‐AVF dilated (0.23 ± 0.14 cm² at 2D to 0.87 ± 0.14 cm² at 28D) with attendant increase in flow rate. However, S‐AVF had minimal changes in area (0.26 ± 0.02 cm² at 2D to 0.27 ± 0.03 cm² at 28D) despite some increase in flow rate. Our results suggest that the temporal changes of WSS could have significant effects on AVF maturation. Reduction in WSS over time (regardless of initial values) may result in dilation (p < 0.05), while increase in WSS may be detrimental to maturation. Thus, creation of AVFs in a specific configuration which results in a decline in WSS over time may reduce AVF maturation failure.     

Accessory Veins in Nonmaturing Autogenous Arteriovenous Fistulae: Analysis of Anatomic Features and Impact on Fistula Maturation

The appropriate management of nonmaturing arteriovenous (AV) fistulae continues to be a controversial issue. While coil embolization of accessory side‐branch veins can be performed to encourage maturation of nonmaturing AV fistulae, the true efficacy and optimal patient population are not well understood. Fistulagrams performed on nonmaturing AV fistulae were retrospectively reviewed in 145 patients (86 males, median age 63 years) for the presence of accessory veins. Fistula and accessory vein measurements were obtained, as were rates of eventual fistula maturation after accessory vein coil embolization. Of 145 nonmaturing fistulae, 49 (34%) had a stenosis without any accessory veins, 76 (52%) had a stenosis and one or more accessory veins, and 20 (14%) had an accessory vein without concurrent stenosis. Eighteen AV fistulae had one or more accessory veins without coexisting stenosis. Nine fistulae had a caliber decrease immediately downstream from the accessory vein. Coil embolization of dominant accessory veins with a caliber decrease immediately downstream (n = 6) resulted in a 100% eventual fistula maturation rate versus 67% for fistulae without this configuration (n = 6, p = 0.15). Accessory vein size was not correlated with maturation rates (p = 0.51). The majority of nonmaturing fistulae with accessory veins had a coexisting stenosis. Higher maturation rates may result with selected anatomic parameters, although additional studies with more robust sample sizes are needed prior to definitive conclusions.     

Colosplenic Fistula: a Highly Unusual Colonic Fistula

Discussion

Internal fistulization of the colon to other organs, such as the urinary bladder, vagina, or small bowel is a relatively common complication associated with inflammatory diseases such as diverticulitis, Crohn disease, as well as neoplasia such as colorectal cancer or lymphoma. However, fistulization of the colon to the spleen is an exceedingly rare condition described by few in the literature.     

Knot in a thoracic epidural catheter

We report a case of impossible injection into a thoracic epidural catheter associated with a difficult withdrawal of this catheter after its introduction on the T3-T4 level. Thanks to a gentle and continuous traction, the catheter was finally successfully removed without being broken, but presented a simple knot at 13 mm from its end. No neurological complication was observed later on. This complication happened during the introduction of the catheter at the thoracic level where anatomic conditions are less favorable for this kind of complication to happen than at the lumbar level. We have been probably confronted with a catheter taking an abnormal direction due to an anatomic structure. This case shows us that knots in an epidural catheter are also possible on the high thoracic level and that its ascent within the epidural space must happen without any resistance.     

Improved Cumulative Survival in Fistulas Requiring Surgical Interventions to Promote Fistula Maturation Compared with Endovascular Interventions

Due to high nonmaturation rates, arteriovenous fistulas (AVF) frequently require intervention(s) to promote maturation. Endovascular or surgical interventions are often undertaken to salvage nonmaturing AVFs. The objective of this study was to compare the impact of surgical versus endovascular interventions to promote AVF maturation on cumulative AVF survival. We evaluated 89 patients with new AVF placement from a Veterans Affairs population over a 5‐year period. Of these, 46 (52%) required intervention(s) to achieve successful maturation for dialysis: 31 patients had surgical revisions and 15 patients had endovascular repairs. We compared cumulative survival between AVFs requiring no intervention, surgical revision, and endovascular intervention to promote AVF maturation. Cumulative survival was longer in AVFs receiving surgical intervention compared with angioplasty to promote AVF maturation (p = 0.05). One‐year cumulative survival was 86% vs. 83% vs. 40% for no intervention vs. surgery vs. angioplasty, respectively. In AVFs that required interventions to promote maturation, AVFs with surgical intervention had longer cumulative survival compared with those AVFs with endovascular intervention. AVFs with surgical intervention to promote maturation had similar 1‐year cumulative survival to those AVFs that did not require intervention to promote maturation.     

Towards a Better Laparoscopic Knot: Using Knot Quality Scores to Evaluate Three Laparoscopic Knot-Tying Techniques

Objective:

In the past, knot-tying techniques have been evaluated and compared, but there has been a scarcity of objective scoring systems in these comparison studies. Using an objective scoring system, we aimed to compare 3 types of knots: intracorporeal flat-square knots, intracorporeal slip-square knots, and extracorporeal square-knots for their Knot Quality Scores (KQS) and their rates of slippage.

Materials and Methods:

Three surgeons tied 100 knots in the 3 knot categories. The knots tied were evenly distributed amongst the 3 surgeons with each surgeon contributing at least 30 knots. These knots were tied in a nonrandomized fashion. Forces were measured using a tensiometer and an objective scoring system, the Knot Quality Score (KQS), which is used to compare the knot''s strength and rates of slippage.

Results:

Median KQS scores of the 3 groups were not all the same. The median KQS and variance for the extracorporeal square knot group was 0.32 and 0.0079, respectively. For the intracorporeal slip-square knot group, the median KQS and variance was 0.28 and 0.00017, respectively. Lastly, for the intracorporeal flat-square knot group, the median KQS and variance was 0.33 and 0.0075, respectively. Follow-up analysis revealed that the KQS medians (0.32 versus 0.28) of the extracorporeal square-knots and intracorporeal slip-square knot groups were significantly different (P<0.0001). The medians of the intracorporeal slip-knot and intracorporeal flat-square knot groups (0.28 versus 0.33) were also statistically significantly different (P<0.0001). There was no statistically significant difference in KQS scores between extracorporeal square-knots and intracorporeal flat-square knots.

Conclusion:

Extracorporeal square-knots and intracorporeal flat-square knots can tolerate better distraction forces and thus have higher median KQS scores compared with intracorporeal slip-square knots.