Limited Access Sites Research Articles

Estimating the Geological Structure and Transport Properties of Denied and Limited Access Sites

AbstractOnsite measurements are the standard for establishing geological conditions and related transport properties. However, making direct measurements is not always possible, either because a location is too remote, too vast, or access is outright denied. The latter is typically the case at nuclear test sites, or military installations. Here we describe a systematic method to characterize geology and estimate fracture width, spacing, tortuosity, permeability, and porosity at locations where direct measurements cannot be made. Fractures are treated as fractals with their respective fractal dimensions determined using surface images. Tortuosity in the geological matrix (i.e., bulk media) is determined using rock class with the latter also being used to determine distributions for permeability and porosity. The approach is tested using areal images and rock class for the Nevada Test Site and validated by comparison to field and core measurements. Past work has shown that testing a nuclear weapon underground can affect not only the migration time for gases to the surface but also their isotopic ratios. Accurately modeling gas transport and isotopic fractionation requires knowledge of the geology. However, suspected tests are typically conducted at sites to which the international community has no access.

The Transaxillary Approach via Prosthetic Conduit for Transcatheter Aortic Valve Replacement With the New-Generation Balloon-Expandable Valves in Patients With Severe Peripheral Artery Disease.

Background: The left subclavian artery (LSA) is an infrequently used alternative access route for patients with severe peripheral artery disease (PAD) in patients who underwent transcatheter aortic valve replacement (TAVR). We report a new endovascular approach for TAVR combining an axillary prosthetic conduit-based access technique with new-generation balloon-expandable TAVR prostheses.Methods and Results: Between January 2020 and December 2020, 251 patients underwent TAVR at the West German Heart and Vascular Center. Of these, 10 patients (3.9%) were deemed to be treated optimally by direct surgical exposure of the left or right axillary artery via a surgically adapted prosthetic conduit. All procedures were performed under general anesthesia. One procedural stroke occurred due to severe calcification of the aortic arch. No specific complications of the subclavian access site (vessel rupture, vertebral, or internal mammary ischemia) were reported. Two minor bleedings from the access site could be treated conservatively. No surgical revision was necessary.Conclusion: The axillary prosthetic conduit-based access technique using new-generation balloon-expandable valves allows safe and successful TAVR in a subgroup of patients with a high risk of procedural complications due to severe peripheral vascular disease. Considering the increasing number of patients referred for TAVR, this approach could represent an alternative for patients with limited access sites.

An Inexpensive Cardiovascular Flow Simulator for Cardiac Catheterization Procedure Using a Pulmonary Artery Catheter.

Cardiac catheterization associated with central vein cannulation can involve potential thrombotic and infectious complications due to multiple cannulation trials or improper placement. To minimize the risks, medical simulators are used for training. Simulators are also employed to test medical devices such as catheters before performing animal tests because they are more cost-effective and still reveal necessary improvements. However, commercial simulators are expensive, simplified for their purpose, and provide limited access sites. Inexpensive and anatomical cardiovascular simulators with central venous access for cannulation are sparse. Here, we developed an anatomically and physiologically accurate cardiovascular flow simulator to help train medical professionals and test medical devices. Our simulator includes an anatomical right atrium/ventricle, femoral and radial access sites, and considers the variability of arm position. It simulates physiological pulsatile blood flow with a setting for constant flow from 3 to 6 L/min and mimics physiological temperature (37°C). We demonstrated simulation by inserting a catheter into the system at radial/femoral access sites, passing it through the vasculature, and advancing it into the heart. We expect that our simulator can be used as an educational tool for cardiac catheterization as well as a testing tool that will allow for design iteration before moving to animal trials.

Salvage Antibiotic-Lock Therapy in Critically Ill Pediatric Patients

Salvage Antibiotic-Lock Therapy in Critically Ill Pediatric Patients

Strategies for Hemodialysis Access: Where to Start, Where to Go Next

Complications of vascular access are the most common cause of hospitalization for patients with end stage renal disease. Physicians involved in the placement and maintenance of hemodialysis access must have a long-term strategy for sequential placement of autogenous fistulas and synthetic grafts to preserve limited access sites. Although many principles involving hemodialysis access surgery are widely accepted, significant controversies exist regarding optimal access strategies. Autogenous access is generally preferred over prosthetic grafts. The nondominant upper extremity is the preferred site of initial access. Cuffed catheters are discouraged for long-term vascular access unless no other options are present. Recent advances in forearm, upper arm, and femoral venous transpositions have facilitated the performance of increased numbers of autogenous access procedures. Nevertheless, substantial numbers of patients on chronic hemodialysis require prosthetic arteriovenous grafts. Although the Kidney Disease Outcomes Quality Initiative of the National Kidney Foundation has provided general guidelines for access creation, considerable controversy remains regarding the optimal choice of prosthetic graft material and configuration. We present a strategy for the sequential placement of arteriovenous fistulas, venous transpositions, and arteriovenous grafts to guide the surgeon in the management of these often challenging patients.

Direct US-guided Puncture of the Innominate Veins for Central Venous Access

Maintenance of functioning venous access is recognized as the Achilles heel of long-term hemodialysis treatment. In patients who require catheter-directed hemodialysis, the internal jugular veins are recognized as the optimal veins for insertion of dialysis catheters. When these sites are no longer available, alternative venous access sites are required. The authors describe two hemodialysis patients with limited access sites in whom hemodialysis catheters were successfully inserted directly into the innominate veins with use of ultrasound-guided punctures.

A quality improvement program for hemodialysis vascular access.

The effective delivery of dialysis requires repeated reliable access to the central circulation capable of providing rapid extracorporeal blood flow. Unfortunately, this access to the circulation continues to be the "weak link" in the effective delivery of long-term hemodialysis therapy. This will likely become an even greater problem in the future as increasing numbers of patients with limited access sites secondary to advanced age and atherosclerosis enter the end-stage renal program. Therefore, the preservation of these limited vascular access sites is imperative. Vascular access thrombosis is the leading cause of graft loss and venous stenosis is the major cause of graft thrombosis. Early detection of venous stenosis through careful inspection of the graft combined with measurements of venous outflow pressure and urea recirculation can identify venous access stenosis. Identification of these lesions combined with preemptive repair improves dialysis efficiency and preserves vascular access. When these techniques are used, a dramatic impact on dialysis fistula patency and function can be seen.

Axillary and subclavian vein stenosis: percutaneous angioplasty.

Twenty-nine percutaneous balloon dilations of the axillary and subclavian veins were performed in 19 patients. Stenoses occurred in typical locations of anatomic narrowing or at sites of previous trauma. The initial success rate was 76%, with a 1-year patency rate of 35% and a 2-year patency rate of 6%. Angioplasty can be performed on an outpatient basis with a very low rate of significant complications and can be repeated numerous times to keep a vein patent for many years. This procedure is especially valuable in dialysis patients who have limited access sites.