Page 240 - Medicine and Surgery

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236 Chapter 6: Genitourinary system

required with regular review to ensure that the patient Indications for urgent dialysis
does not become fluid overloaded. Central venous Persistent hyperkalaemia >6 mmol/L despite medical
pressure measurement may be helpful, but should therapy
not be relied upon over clinical assessment espe- Severe acidosis
cially in the presence of cardiac or pulmonary disease. Refractory pulmonary oedema
Urinary catheterisation is not always required, and Pericarditis, cardiac tamponade, encephalopathy
carries a risk of introducing infection. Urine output (flap)
should increase in response to filling. If it does not, Rapidly progressive renal failure
and the patient is well filled, then there is likely to be
concomitant renal ARF. If blood pressure remains low Prognosis
despite filling (such as due to cardiac insufficiency, Depends on underlying cause and concomitant medical
sepsis), then additional treatment, usually inotropic conditions. Oliguric ARF has a higher mortality.
support is needed with specialist help.
Once the patient is normovolaemic intravenous flu- Acute tubular necrosis (ATN)

ids should be reduced to maintenance levels to avoid
precipitating fluid overload. Definition
In fluid overload, or in oliguric renal failure high doses Necrosis of renal tubular epithelium as caused by hypop-

of furosemide may be effective in causing a diuresis. erfusion of the kidneys and certain toxins.
However, there is no good evidence that furosemide
speeds the recovery from renal failure, and it should Aetiology
be avoided in those thought to have pre-renal failure. Themaincausesarehypoperfusion,i.e.thecausesofpre-
Pulmonary oedema which does not respond to renal failure (more common) and toxins (see Tables 6.3

diuretics may have to be treated initially with and 6.4).
vasodilators (intravenous GTN, diamorphine) and
ventilatory support including non-invasive ventila- Pathophysiology
tion,buttheonlydefinitivetreatmentishaemodialysis The renal medulla is particularly susceptible to is-
or haemofiltration. chaemia, because of high metabolic activity. In addi-
tion, in shock renal blood flow is particularly likely to
Hyperkalaemia suffer because of constriction of renal vessels due to
Treatseverehyperkalaemia(K>6.0mmol/L)urgently

to avoid cardiac arrhythmias (see page 7).
Table 6.4 Causes of acute tubular necrosis
Stop any drugs that cause high potassium (ACE-

inhibitors, spironalactone). Causes of ATN Examples
Hypoperfusion
General measures Hypovolaemia Severe burns, haemorrhage,
Amultidisciplinary approach is required, involving
diarrhoea
physiotherapists, nurses and nutritionists. Intravascular hypovolaemia, e.g.
nephrotic syndrome
Monitor fluid in/out, daily weight (this is a useful,

Diuretics
accurate way of monitoring fluid balance). Impaired cardiac output Cardiac failure
Low salt and potassium diet. Ensure adequate Septic shock

nutrition. Toxin induced
Endogenous Haemoglobinuria, myoglobinuria,
Review all medication for dosages in renal failure.

hepatic toxins, uric acid,
Consider prophylaxis against gastrointestinal bleed- Bence–Jones protein

ing. Exogenous Drugs, e.g. antibiotics, NSAIDs,
Referral to a renal physician should be considered if
cytotoxics
there are red cell casts or heavy proteinuria, if the di- X-ray contrast
Organic solvents: chloroform,
agnosis is unclear or if there is acute-on-chronic renal
carbon tetrachloride
failure.