Renal Failure
- Acute Kidney Injury (Acute Renal Failure)
- Chronic Kidney Disease (Chronic Renal Failure)
Acute Kidney Injury (Acute Renal Failure)
Summary
AKI (formerly more commonly Acute Renal Failure, but now more correctly AKI) is a sudden decline in renal function significant enough to produce uraemia, and also often oliguria – a urine output of <400ml/day. It normally occurs over a period of days or week, and is often reversible. Diagnosis is usually based on serum urea and/or creatinine levels.
Severe AKI is defined as a creatinine level of >500umol/L
Acute renal failure is a medical emergency and can cause death.
Epidemiology
AKI superimposed on CRF comprises 50% of community-acquired cases that are admitted to hospital. The approximate incidence of AKI is 180 per 1 million; before the age of 50, this value is 17 per 1 million, but as high as 950 per 1 million in those over 80.
Causes
These can be divided into three main categories: prerenal, intra-renal and post-renal. There may be multiple causes of SKI in an individual patient. In the hospital situation, the most common cause of AKI is
sepsis.
Prerenal causes – here, there is impaired blood flow to the kidney, and this may be a result of hypovolemia, ↓BP, ↓CO, vascular disease, or a combination of any of these.
Clinical signs are probably more important than laboratory tests in the determination of prerenal causes, and those that suggest prerenal uraemia are history of blood/fluid loss,
sepsis leading to vasodilation, cardiac disease,
postural hypotension, weak, rapid pulse and low JVP
Intra-Renal causes
- Acute tubular necrosis (ATN) – by far the most common cause of AKI where toxicity and/or ischaemia results in ↓GFR
- Nephrotoxicity – caused by aminoglycosides, contrast nephropathy
- Renal parenchymal disease – a result of ATN
Investigations
- Urine dipstick
- Urine microscopy – look particularly for the presence of red cell casts and red cells.
- Blood tests – U+E’s (particularly Cr and K+, FBC, free haemoglobin and myoglobin.
- Kidney function is monitored through urine output analysis and creatinine clearance monitoring – creatinine clearance monitoring is the ideal, i.e. it is a more precise indication of GFR than serum urea monitoring alone!
- Check if the patient is on any nephrotoxic drugs.
Management
This is based on careful monitoring of signs and symptoms, e.g. treatment of hypovolaemia whilst avoiding fluid overload, and seeking specialist help if
hyperkalaemia, pulmonary oedema, bleeding, acidosis or
sepsis are present.
This is indicated if any of the following cannot be controlled: fluid overload,
hyperkalaemia, hypocalcaemia, metabolic acidosis,
pericarditis, uremic symptoms,
GFR <15ml/min/1.73 m2, or poisoning. Different options include haemodialysis,
peritoneal dialysis,
haemofiltration, and
renal transplantation.
Definition
Acute renal failure is a sudden decline in renal function significant enough to produce uraemia, and also often oliguria – a urine output of <400ml/day, which is the minimum volume required to remove waste products from the blood.
Uraemia – this is where there is enough urea in the blood to cause clinical symptoms, which may include anorexia and lethargy, and later, possible decrease in mental capacity leading to coma. The term azotaemia is sometimes used to describe levels of urea above normal but not high enough to cause clinical signs.
It normally occurs over a period of days or week, and is often reversible.
Diagnosis is usually based on serum
urea and/or creatinine levels.
Acute renal failure is a medical emergency and can cause death.
The distinction between acute and chronic can sometimes be difficult to make. In some cases, acute renal failure may present on top of a history of chronic disease.
Be suspicious of ARF – particularly in the elderly! A combination of low muscle mass, and low dietary meat
