Dialysis and its complications
Once a patient’s glomerular filtration rate (GFR) falls below 15 ml/ min/1.73m2 they require renal replacement therapy (RRT), either haemodialysis (HD), peritoneal dialysis (PD) or transplantation. Both haemo-and peritoneal dialysis are associated with specific complications, in addition to the general complications associated with ESRF.
Complications related to vascular access
Vascular access is required to administer HD. For acute HD, this may be achieved using a temporary central dialysis catheter (which can be used for a week or so). Temporary catheters are often placed in the femoral vein, although this may compromise the vessel for future use during transplantation.
In the medium term, vascular access can be provided via a tunnelled central catheter, which can last for a number of months. The main complication of tunnelled lines is infection, including:
1. Exit site infections
2. Tunnel infections
3. Infective endocarditis.
4. These are commonly caused by skin-colonising staphylococci. The presence of active infection precludes the patient from transplantation, as the addition of immunosuppression may be life threatening.
5. Other line-related complications include the following.
6. Line insertion-related – pneumothorax and/or vascular injury.
7. Thrombosis – a large thrombus can sometimes form on the tip of the catheter, which can become infected. These often form in the right atrium, and their removal may require open cardiac surgery.
8. Central vein stenosis – particularly with subclavian vein catheters and catheters that remain in situ for prolonged periods (months or even years).
For patients on HD, the vascular access of choice is an arteriovenous fistula (AVF). These are formed by joining the radial or brachial artery with the cephalic vein and they provide vascular access without the presence of indwelling catheter (therefore lowering the risk of infection). Ideally, the cephalic and brachial veins of either arm should not be used for cannulation or venepuncture in patients approaching ESRF in anticipation of their later use for AVF formation.
Occlusion/thrombosis of an AVF can occur if the patient becomes hypotensive on dialysis, if they are hypercoagulable or have a stenosis of the draining vein; thrombosis is also common following transplantation, either due to peri-operative hypotension or the removal of the uraemic inhibitory effect on platelet aggregation. The AV fistula itself may become aneurysmal or steal blood from the circulation, rendering the distal limb ischaemic.
To achieve adequate RRT, most patients will need to undergo haemodialysis for 3–4 hours, three times a week. This involves a journey to the local dialysis centre, which may be some distance from the patient’s home. If they are reliant on ‘hospital transport’, the whole process can take the best part of a day, making it dif- ficult for the patient to maintain full-time employment.
Fluid balance can be a particular problem in anuric patients on dialysis, many of whom struggle to restrict their fluid intake to the necessary 500–750 ml/24 hours. Such patients often need to have 2–3 litres removed during their dialysis session, which can result in peri-dialysis hypotension and leave them feeling totally exhausted.
In summary, haemodialysis can replace some of the functions of the kidney, but carries specific morbidities and imposes significant restrictions on a patient’s quality of life.
Peritoneal dialysis complications
PD involves the placement of a catheter into the peritoneal cavity. This is tunnelled underneath the skin to limit the translocation of infectious organisms from the surface into the peritoneum. The catheter is used to instil 1–2 litres of dialysate into the abdominal cavity via one of two methods.
1 Manual method: continuous ambulatory peritoneal dialysis (CAPD). The patient manually connects a bag of PD fluid to the dialysis catheter via a transfer set and instils fluid into the perito- neal cavity using gravity. The fluid is then drained out (again using gravity) after a dwell period of several hours. This procedure is repeated three or four times a day.
2 Automated method: automated peritoneal dialysis (APD). This refers to all forms of PD employing a mechanical device to assist in the delivery and drainage of the dialysate, usually overnight. The main advantage of APD is that it allows freedom from all procedures during the day.
The PD fluid needs to be similar in composition to interstitial fluid, and hypertonic to plasma in order to achieve fluid removal. Glucose is used as an osmotic agent and solutions of differing strengths are used, depending on how much ultrafiltration (fluid removal) is required.
The main complication of PD is the development of infection, (‘PD peritonitis’). Patients usually present with abdominal pain and the drainage of cloudy PD fluid from the abdomen. Gram- positive organisms cause up to 75% of all episodes of peritonitis, mainly Staphylococcus epidermidis or, more seriously, S. aureus. The latter can be associated with a more severe illness, which may be life threatening. Treatment is with intraperitoneal and systemic antibiotics; catheter removal may be required. Patients with active PD peritonitis should be temporarily suspended from the trans- plant waiting list until resolution of infection.
Encapsulating peritoneal sclerosis (EPS) is a well-recognised, although uncommon, complication of long-term PD, occurring in 1–5% of patients. Macroscopic changes in the peritoneum can be seen after relatively short periods of PD, particularly ‘tanning’ of the peritoneum. Patients who remain on PD for a number of years can develop more extensive peritoneal thickening, with superimposed fibrous tissue encasing the bowel. Clinical features include vomiting and distension (secondary to bowel obstruction), blood-stained effluent and ultrafiltration failure. Radiological features include peritoneal thickening and calcification, with the develop- ment of the so-called ‘abdominal cocoon’. Risk factors include multiple episodes of peritonitis and long duration of dialysis. The main treatment is to avoid EPS by stopping PD when dialysis adequacy declines, or when evidence of peritoneal sclerosis is noted on CT. EPS, if present, should be treated before listing for transplantation; malnourishment due to EPS is a contraindication to transplantation. EPS can present post-transplantation.
Mortality on dialysis
The complications of ESRF, together with those associated with dialysis, have a significant impact on patient survival. On average, a 50-year-old commencing haemodialysis has a 50% 5-year survival. This can be significantly improved by transplantation.