Vascular Access Simplified; second edition

Davies, Alun, H, Gibbons, Christopher, P

• Editore: tfm Publishing Ltd
• Anno: 2007
• ISBN:
  9781908986153
• Argomento: Medicina
• Categoria: Teoria, pratica e riferimenti medici

Winner of a COMMENDED AWARD in the Urology category of the 2008 BMA Medical Book Competition. Following on from the huge success of the first edition, this is the second edition which will not only update all previous chapters but also, it will have many additional chapters to add value over and above the first edition. The need for dialysis access surgery is growing rapidly as the population of patients with endstage renal failure expands. This book is aimed at those healthcare professionals involved in the care of patients undergoing dialysis. Vascular Access Simplified gives a comprehensive review of all aspects of adult dialysis access with a specific emphasis on haemodialysis. The text highlights some of the difference in practices of physicians in Europe and the USA. The contributors are allied professionals, physicians, radiologists, vascular and transplant surgeons who have a specific interest and are all committed to improving the quality of dialysis access.

Chapter 1

Vascular access in clinical practice

Christopher P Gibbons MA DPhil MCh FRCS
Consultant Surgeon, Morriston Hospital, Swansea, UK

Introduction

Access to the circulation is vital in many branches of medicine. In most cases a temporary route of access for delivering fluids or drugs to the venous system is all that is required. In other cases small quantities of venous or arterial blood must be withdrawn intermittently for haematological or biochemical analysis. Simple intravenous or arterial catheters are sufficient to accomplish these tasks. More specialised intravenous catheters introduced into the central veins are required for long-term intravenous feeding or for the administration of cytotoxic chemotherapy. By contrast, haemodialysis or haemofiltration requires the reliable withdrawal and return of blood to the circulation at high flow rates (preferably exceeding 300ml/min) on a regular basis.

The Scribner shunt was the first vascular access device used to allow circulation of blood from the arterial system through a dialyser to the venous system. This was used for several years but proved unreliable for long-term access because of repeated thrombosis and infection. It was also unpopular with patients because of its cumbersome extracorporeal tubing. The arteriovenous (AV) fistula, first introduced by Brescia and Cimino in 1966, involves the conversion of an accessible peripheral vein, usually in the upper limb, to a high flow vessel from which blood can be rapidly withdrawn and returned to the circulation via two needles introduced for each dialysis session. This dispensed with the need for extracorporeal tubing between dialyses and allowed greater freedom for patients undergoing chronic renal replacement therapy. However, the need for a period of maturation generally precludes the use of AV fistulae for acute dialysis. In the absence of a suitable superficial vein, prosthetic grafts run subcutaneously from an artery to a vein can be used, but they are usually reserved for secondary access because of poorer patency and greater infection rates.

The introduction of dual-lumen central venous catheters supplanted the Scribner shunt for emergency and short-term use. More recent modifications have included the incorporation of a Dacron cuff around the catheters, which enables long-term fixation in a subcutaneous tunnel and acts as a barrier to infection. Single-lumen catheters with a Dacron cuff have also proved useful for long-term intravenous feeding and drug administration.

Whilst the vast majority of vascular access procedures are performed for haemodialysis, the access surgeon may occasionally be called upon to create an AV fistula for patients requiring plasmapheresis, to insert a long- term catheter for intravenous feeding or implant an injection port for the infusion of chemotherapeutic agents.

Renal replacement therapy

Haemodialysis is the most prevalent mode of chronic renal replacement therapy and is now almost universally used for acute dialysis. Peritoneal dialysis is an effective alternative mode of therapy, which allows greater independence for some patients. Unfortunately, the effectiveness of peritoneal dialysis tends to reduce after several years because of changes that occur in the peritoneal membrane. Renal transplantation is the preferred mode of treatment for most patients as it allows a near normal lifestyle, albeit at the expense of long-term immunosuppression, but many patients will return to dialysis after irreversible acute or chronic rejection. Thus, patients with end-stage renal failure will often move from one modality of treatment to another.

When is dialysis needed?

Acute renal failure

Temporary or permanent haemodialysis via a central venous catheter is required when the kidneys fail acutely, regardless of the underlying cause. In some patients with acute renal failure, dialysis may be deferred or avoided by careful fluid restriction, and the control of acidosis and hyperkalaemia using intravenous bicarbonate, salbutamol or insulin and glucose combined with enteral resonium. When there is anuria or severe oliguria with fluid overload, gross metabolic acidosis, hyperkalaemia and a rising serum creatinine, acute haemodialysis via a central line will be required as a matter of urgency. In some patients, particularly those with fluid overload, for instance patients with multi-organ failure in the intensive care unit, continuous techniques involving haemofiltration and/or dialysis can be performed through a double-lumen central venous catheter.

In those patients with a treatable or spontaneously recoverable renal failure, dialysis may be discontinued as urine flow returns and serum biochemistry stabilises, but some will progress to require long-term renal replacement therapy. Once it is clear that renal recovery is unlikely, permanent vascular or peritoneal access should be created as soon as possible to minimise the use of central venous lines with their attendant increased risks of systemic infection and thrombosis. Central venous catheters are associated with a relative mortality risk of 1.7 in non-diabetics and 1.54 in diabetics in comparison to autogenous AV fistulae ¹. In the US, the National Kidney Foundation - Dialysis Outcomes Quality Initiative (NKF-DOQI) guidelines recommend that less than 10% of patients should be dialysed on lines beyond three months ².

Chronic renal failure

A third of patients with chronic end-stage renal failure present acutely or are referred within three months of the need for dialysis. Two thirds have progressive renal disease presenting with symptoms of malaise over a period of time or are discovered by routine biochemical tests during the investigation of hypertension, proteinuria or other medical problems. It is recommended by the UK Renal Association that patients should be referred to a nephrologist when the serum creatinine is 150-200µmol/l ³. The serum biochemistry and especially the creatinine clearance of such patients can then be monitored as an outpatient so that the need for dialysis may be anticipated. The actual start of dialysis may be primarily dependent on symptoms (e.g. malaise, nausea, anorexia, weight loss, itching), but is sometimes precipitated by an acute deterioration in biochemistry during intercurrent illness or by dehydration.

Nevertheless, dialysis is usually required at a plasma creatinine of 500-1500µmol/l or when the creatinine clearance falls much below 14ml/minute. Plotting biochemical indices of renal function, such as creatinine clearance, for each patient may give an approximate date at which dialysis is likely to be necessary (see Chapter 2). When the start of dialysis can be anticipated, permanent vascular access should be created well in advance to allow for maturation of an AV fistula or for further procedures in the event of failure of the initial access. Peritoneal dialysis catheters should be inserted between 2-4 weeks from the anticipated date of onset of dialysis.

Guidelines for vascular access timing

In the US, t...