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234 Chapter 6: Genitourinary system

Draining system (the renal pelvis, ureters and bladder 3 Reduced production of 1, 25-dihydroxycholecalci-

outflow) – postrenal. ferol, which can lead to low calcium, and reduced
Morethanonetypemayco-exist,asprerenalorpostrenal excretion of phosphate causes hyperphosphataemia.
failure can lead to parenchymal involvement. High phosphates cause pruritus (itching), chronic
In prerenal failure, the kidney is not damaged but renal failure leads to renal osteodystrophy.

functionally compromised due to ischaemia, so re- 4 Anaemia (normocytic, normochromic) can occur
versal of the cause leads to prompt recovery of renal reduced erythropoietin production.
function, although in some cases correction can be The presentation of renal failure may be asymptomatic
difficult. (diagnosed on blood tests), with symptoms and signs of
In renal failure, there is evidence of parenchymal dis- acute renal failure or the more insidious symptoms of

ease. There may be a pre-existing prerenal factor, chronic renal failure.
which led to renal damage. Recovery may be possible,
though if the disease is severe and scarring results, full Acute renal failure
functional recovery is unlikely.
With postrenal failure as with prerenal failure, Definition

early treatment can avert irreversible damage to the Adeterioration of renal function (loss of GFR) over a
kidneys. If left undetected for some time, for example period of days to weeks.
one kidney is first affected without causing symptoms,
then the other precipitates renal failure, there may be Aetiology/pathophysiology
permanent loss of function. The causes may be divided into prerenal, renal and
postrenal, whilst they all have different mechanisms, the
Renal failure causes result is loss of the three functions of the kidney: fluid
1 Arise in serum concentrations of urea, creatinine, hy- and electrolyte balance, excretion of waste products and
drogen ions (causing a metabolic acidosis) and potas- toxins, and hormone synthesis (see Table 6.3).
sium (hyperkalaemia). The rate at which these rise
depends on a number of factors, including how Clinical features
catabolic the patient is, i.e. the rate of tissue break- The main clinical features are usually those of the under-
down, in particular muscle breakdown causes a lying cause together with symptoms and signs caused by
marked rise in potassium. Uraemia (a term used to the renal failure. Acute renal failure (ARF) may be dif-
describe raised urea and creatinine) is associated with ficult to differentiate from chronic renal failure (CRF)
anorexia, nausea, vomiting and increased bleeding without a recent onset in symptoms of an underlying
tendency (due to a reduction in platelet function). cause, e.g. loin pain, a previous serum creatinine mea-
Neurological effects include confusion, myoclonus surement or further investigations.
and lowered seizure threshold. It is thought that urea In asymptomatic patients, ARF may be detected by
and creatinine are not directly responsible for the ob- arise in plasma creatinine or abnormality on urine
servedclinicalfeaturesbutthatthereareotheruraemic dipstick.
toxins which rise in parallel with urea and creatinine. Reduced urine output or a change in urine appear-
2 Loss of the kidneys’ ability to manage salt and water. ance. Complete anuria is only seen with bladder out-
Oliguria (urine output <15 mL/hour or <400 mL/ flow obstruction, bilateral (or unilateral in a single
24hour) is common, but doesnot occur with all causes functioning kidney) ureteric obstruction.
of renal failure. This can cause fluid overload, i.e. Loin pain – this is suggestive of a renal stone (or
peripheral oedema and pulmonary oedema, partic- other cause of obstruction), pyelonephritis or renal
ularly in those with impaired cardiac function, the infarction.
elderly, and those given excessive amounts of intra- Anorexia, vomiting, fever, malaise, hiccoughs, con-
venous fluids in order to try and reverse a preceding fusion, seizures.
hypovolaemic state. Water retention can lead to Hyperventilationmaybeduetohypoxiaorrespiratory
hyponatraemia. compensation for metabolic acidosis.