**1. Introduction**

Long-term hemodialysis (HD) is dependent on reliable vascular access (VA), which is the lifeline of a patient. We have come a long way in the chronic HD treatment due to advances in VA. Starting from Scribbner's shunt to single-lumen HD catheters in the femoral vessels to double-lumen non-tunneled non-cuff HD catheters, to tunneled cuff catheters (TCC), and to early stick arteriovenous grafts; all for urgent start HD. Over the years, we also moved the catheters from subclavian veins (SCV) to internal jugular veins (IJV), for VA in the upper part of the body, basically for access draining to the superior vena cava (SVC). Unfortunately, the non-cuffed HD catheters became a tool to continue HD for a prolonged period (a practice very commonly encountered in the part of the world where the author is working, mainly due to nonavailability of VA expertise) in the absence of matured arteriovenous fistula (AVF) or graft. This led to injury to the vessel wall, leading to thrombosis and central vein occlusion and compromised VA for HD due to central venous stenosis (CVS). Even the TCCs are associated with CVS. Two major factors

implicated in development of CVS are venous trauma resulting from cannulation of central veins and hemodynamic stress secondary to high flow due to access site AVF, causing central venous disease (CVD).

AVF is the gold standard of VA. Ideally, all patients starting HD should have AVF in place, but that is not possible. In 2015, 80% of patients were using a catheter at HD initiation, a rate that has changed only marginally since 2005, and at 90 days after the initiation of HD, 68.5% of patients were still using catheters [1, 2]. Late referral by nephrologists to surgeons has been an underappreciated cause of initiation of HD with central catheters. [3]. There are situations when a patient has multiple AVF failures, in the upper limbs. It then becomes a challenging situation to provide dialysis to these patients with a reliable access. The problem is further compounded in patients with prior central vein HD catheters, resulting in CVD. CVS is considered to be common in patients on hemodialysis, but its exact prevalence is not known. The CVS may have occurred due to insertion of central catheters, PICC, or pacemaker leads. Due to direct contact of these devices with the wall of the central veins, and the constant movement, both lateral (like a pendulum) and cephalocaudal direction associated with breathing and the cardiac cycle cause endothelial injury. Pathological examinations of central veins obtained at autopsy have shown that even short-term catheters are associated with foci of local intimal injury with endothelial denudation and adherent thrombus [4].

In patients with AVF, development of CVS is partly related to turbulent blood flow and neointimal hyperplasia (NIH). Infection related to prior catheter insertion may also be responsible for CVS. Extrinsic compression, either musculoskeletal or arterial, can be contributing to CVS.

However, in an otherwise healthy person, the CVS hardly, if ever, causes problems. The problem comes to light when an AVF or graft is placed on the ipsilateral side where there is presence of CVS. It also gets recognized when a fresh attempt is made to insert cuffed or non-cuffed tunnel catheter in the central vein. We should realize that CVS leading to CVD is difficult to treat and often resistant to treatment. In CVD, VA for HD sometimes need to be abandoned, or in serious cases, the patient's life may be threatened. Therefore, one should strive for the ideal situation of catheter avoidance and central vein preservation and remember that prevention is ideal and better than cure.
