Ultrasound for the Clinical Management of Vascular Access Cannulation and Needle Position in Hemodialysis Patients

Abstract

A native arteriovenous fistula (AVF) is the vascular access of choice for hemodialysis (HD) treatment. Compared with other types of vascular access such as grafts and central venous catheters, it functions longer and is associated with a lower risk of complications. The aim of the study described here was to assess, in an HD population, the position of the fistula needles during an HD session and evaluate the role of ultrasound in the management of AVF puncture. Forty-five consecutive chronic HD patients with an AVF or an arteriovenous vascular graft were included in the study for ultrasound evaluation. Each patient underwent an ultrasound evaluation during HD treatment to assess the position of the needles inside the vascular access. The ultrasound evaluation revealed that 81.8% of the traditional needles were incorrectly adjacent to the vessel walls, in the absence of clinical symptoms or hemodynamic alterations detectable on the dialysis monitor. A greater frequency of malpositioning has been observed for needles in the arterial portion of the vascular access, closer to the anastomosis. The absence of clinically detectable signs of venipuncture-related complications does not ensure correct positioning of the needles within the AVF. Ultrasound evaluation may not only resolve suboptimal cannulation problems of new or complicated vascular accesses but may also be useful in the prevention of acute and chronic damage to the AVF.

Introduction

Hemodialysis (HD) is the most frequent dialytic modality, being chosen by 70% of patients with end-stage renal disease. Adequate treatment requires a well-functioning vascular access. A native arteriovenous fistula (AVF) represents the vascular access of choice for HD patients owing to the lower incidence of complications and longer survival compared with grafts and central venous catheters (Gibson et al. 2001; NKF-K/DOQI 2001).

Optimal cannulation of AVFs is very important for the survival of the vascular access. Cannulation of the vessel causes a microtrauma that can result in hyperplasia of the intima and lead to vasal stenosis (Hsiao et al. 2010). Over time, repeated punctures in the same area result in a weakened vessel wall that results in the formation of aneurysms (Lee et al. 2006). Moreover, the insertion of the needle inside the wall causes hematomas (a complication present in 35% of cannulations) and clots, which are associated with an increased risk of fistula thrombosis and loss of access (Lee et al. 2006). It is generally recommended that the needle be placed on the venous access in the same direction as the blood flow (co-current). This reduces the formation of hematomas and the development of pseudoaneurysms during removal of the needle (Ball 2005) and minimizes bleeding because closure of the vessel flap facilitates hemostasis at the endothelial wall. The needle at the arterial access can be positioned in both co-current and counter-current directions. Recent studies, however, have found that retrograde positioning counter-current improves blood flow dynamics (Fulker et al. 2013), although the risk of bleeding is increased owing to the failure of vessel wall tissue to close the wall. Some authors recommend directing the needle tip anteriorly to prevent infiltration at the level of the anterior vessel wall, avoiding rotation of the needle inside the vessel, which can lead to trauma (Fulker et al. 2013). In clinical practice, different choices are adopted by different centers, and methods based on personal experience are used with no unambiguous recommendations for the practice of vascular access puncture.

Intimal hyperplasia and shear stress of the wall are two other important aspects of vascular access function and are the primary causes of stenosis of the AVF. After formation and maturation of an AVF, the consequent hemodynamic alterations in the vessel wall are correlated with new changes in parietal tension, shear stress, that are not correctly perceived by the endothelium. These changes may, in fact, result in reductions (Meyerson et al. 2001), oscillations (Keynton et al. 2001) or excessive increases in wall shear stress (Fry 1968), inducing mechanical alterations of the vascular endothelial layer and local activation of inflammation, finally leading to cellular and tissue alterations and intimate hyperplasia.

In addition to the turbulent flow present within the AVF, the use of extracorporeal circulation determines a further perturbation in blood flow caused by the impact of needle flow at the arterial and venous levels. Blood flow generated by the needles during the extracorporeal circulation has a direct effect on endothelial function. This flow may, in fact, induce changes in the blood flow or disturbance of AVF flow, resulting in the appearance of turbulent components at the vessel wall. This phenomenon changes the shear stress to which endothelial cells are subjected. This alteration is also heightened when the direction of venous needle flow is not perfectly co-current with respect to the natural flow of the AVF, but is oriented toward the vessel wall. The same alteration can be observed if the venous needle induces turbulence in the blood flow owing to incorrect positioning.

The diameter of the needle and the direction of vessel cannulation entail alterations in the dynamics of flow inside the vessel that can affect the damage induced by the general hemodynamic alterations in the fistula. Studies have reported that the needle alters blood flow dynamics after insertion, modifying wall stress and flow turbulence (Huynh et al. 2007). Furthermore, Fulker et al. (2017) recently reported that positioning of the needle tip at the level of the posterior wall of the vessel causes a large increase in wall shear stress, while significant secondary flows are generated if the needle is positioned at the level of the anterior wall. On the basis of this evidence, it is easy to deduce how positioning of the needle tip away from the vessel wall can minimize vessel damage, greatly limiting shear stress and turbulent secondary flow.

The use of ultrasound in evaluating both the arterial and venous sides of the AVF has improved survival of patients with AVFs, because acute and chronic complications are rapidly detected and corrected, and useful information is obtained for follow-up (Zamboli et al. 2012).

In the study described here, we aimed to assess the role of ultrasound in the optimal clinical assessment of AVF cannulation by evaluating positioning of HD needles during standard HD sessions.