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.
Haemodialysis complications
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.
Other complications
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.
