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Chapter 6: Disorders of the kidney 233

Blood Blood
from patient to patient

Semipermeable
membrane

Replacement fluid in
(can be less than
haemofiltrate
to treat fluid overload)

Haemofiltrate out
e.g. 1000 mL/hour
Figure 6.4 Principles of haemofiltration.

Bacterial infection of the tunnelled catheter and of Henle and collecting ducts. There is a large degree of
bacterial peritonitis are the most common serious com- redundancy in the kidney, so many nephrons may be lost
plications. Patients with PD peritonitis present with ab- beforethereisanoticeablechangeinfluidandelectrolyte
dominal pain (80%), ‘cloudy bags’, fever and nausea, balance, and even more before there are symptoms of
vomiting and diarrhoea without classical signs of peri- renal failure.
tonitis. This can be treated by adding antibiotics to the It is useful when considering the causes of renal failure
peritoneal dialysate. In the longer term, PD may become to divide the kidney into three parts (see Fig. 6.5).
unable to adequately dialyse a patient, as the peritoneal Blood supply (aorta, renal arteries etc.) – prerenal.
membrane fails. Parenchyma (the ‘meat’ of the kidney, consisting of
nephrons and interstitium) – renal.
Disorders of the kidney

Prerenal
Renal failure e.g. hypovolaemia, GI
bleed, cardiac failure,
Definition hypotension
Renal failure is defined as a reduction in the glomerular
filtration rate (GFR), which leads to a loss of the ability
of the kidney to perform its functions properly.
The kidneys have three important functions:
1 Fluid and electrolyte balance, including acid–base bal-
ance.
Postrenal (obstruction)
2 Excretion of waste products and many drugs and tox- e.g. ureteric stone
ins. prostatic hypertrophy,
Renal
3 Hormone synthesis (such as erythropoeitin, vitamin malignancy
e.g. glomerular disease,
D and renin). tubulointerstitial disease,
Anormal kidney has 1 million nephrons. The nephron is vasculitis, hypertension
the basic unit of the kidney. It consists of the glomerulus
and its associated vascular supply and the tubules, loop Figure 6.5 Causes of renal failure.