Acute kidney injury

Acute kidney injury is a spectrum of injuries to the kidneys which can result from a number of causes. It is a clinical syndrome rather than a biochemical diagnosis. It is characterised by a decline in renal excretory function over hours or days, that can result in failure to maintain fluid, electrolyte and acid–base homeostasis (National Institute for Health and Care Excellence (NICE), 2023a).

The signs and symptoms of acute kidney injury vary according to the exact cause of the injury, and can include:

• raised serum creatinine
• reduced urine output

Signs can occur over a short space of time. Other signs and symptoms commonly associated with acute kidney injury include:

• hyperkalaemia
• acidaemia
• uraemia
• low urine output, anuria or urine retention
• pulmonary oedema
• hypertension or hypotension
• altered level of consciousness
• nausea and vomiting
• diarrhoea (Ellis, 2013a; Lewington, 2023)

There are three classifications of acute kidney injury and several causes within each classification. Understanding the aetiology of the acute kidney injury is important in planning the treatment of people affected by the condition and any longer-term management.

The three classifications of acute kidney injury are:

• pre-renal
• renal (intrinsic)
• post-renal (Ellis, 2013b)

Pre-renal acute kidney injury occurs when the blood supply to the kidneys is reduced, causing the glomerular filtration rate to fall as a result of hypoperfusion such that the urine output is less than 400 mL/day. Causes of pre-renal acute kidney injury include:

• blood loss
• other fluid loss or vascular depletion (eg burns, diarrhoea and vomiting)
• hypotension, for example from trauma, sepsis, medication
• reduced cardiac output (eg myocardial infarction, arrhythmia)
• medications (eg angiotensin-converting enzyme inhibitors) (ACE inhibitors)
• renal artery stenosis
• pulmonary embolism

Intrinsic acute kidney injury occurs when there is damage to the kidney, such as to the:

The 10 most significant risk factors for acute kidney injury are:

1. being older (over 65 years old)
2. having co-morbidities (eg hypertension and/or diabetes)
3. using certain medications (eg non-steroidal anti-inflammatory drugs)
4. having a history of chronic kidney disease 
5. dehydration from whatever cause
6. sepsis
7. biochemistry (raised markers of renal disease on hospital admission)
8. urinalysis (current or previous proteinuria and/or haematuria)
9. weight (anorexia or obesity)
10. nutritional status ( eg malnourished)

The key to the diagnosis of acute kidney injury is understanding the causes to identify the correct classification, which is also important for establishing treatment. The criteria by which acute kidney injury is adjudged in the UK are:

• a rise in serum creatinine level of 26 micromol/litre or more in less than 48 hours
• a 50% or more increase in serum creatinine levels, either proven or presumed, within 7 days
• a reduction in urine output to under 0.5 mL/kg/hour for more than 6

Acute kidney injury is managed by removing or reversing the cause, where this is possible (Ellis, 2013a). This requires a structured and thorough approach to the assessment of the individual patient, which then indicates the treatment required:

1. Undertake holistic clinical assessment and investigations to identify past medical history as well as any contributing illnesses or other factors. Failing to understand the patient’s current physiological status may mean their risk of death is increased. Some bedside observations, such as fluid balance, blood pressure, weight, pulse and temperature enable a rapid indication of their state of health including dehydration and sepsis.
   
   Blood tests are necessary to include urea and electrolytes and estimated glomerular filtration rate; fundamental to staging the acute kidney injury and enabling early management of electrolytes (eg potassium). A full blood count may indicate issues such as anaemia (which may indicate the presence of chronic kidney disease).
   
   Erythrocyte sedimentation rate and/or C-reactive protein can detect inflammatory disease or infection which should be treated according to what is found. Blood cultures may be indicated where infection or sepsis are thought to be present as they enable the informed use of antimicrobial therapy.
   
   
   
   
   
   

Ellis P. Back to basics: acute kidney injury III. J Renal Nurs. 2013a;5(3):148-149. https://doi.org/10.12968/jorn.2013.5.3.148 

Ellis P. Back to basics: acute kidney injury. J Renal Nurs. 2013b; 5(1): 38-39. https://doi.org/10.12968/jorn.2013.5.1.38 

Ellis P, Jenkins K. An overview of NICE guidance: Acute Kidney Injury. Br J Nurs. 2014;23(16): 904-906. https://doi.org/10.12968/bjon.2014.23.16.904 

Fenoglio R, Sciascia S, Baldovino S, Roccatello D. Acute kidney injury associated with glomerular diseases. Curr Opin Crit Care. 2019;25(6): 573-579. https://doi.org/10.1097/MCC.0000000000000675 

Kellum JA, Lameire N, Aspelin P et al. Kidney disease: improving global outcomes (KDIGO) acute kidney injury work group. KDIGO clinical practice guideline for acute kidney injury. Kidney international supplements. 2012;2(1):1-38. https://doi.org/10.1038/kisup.2012.1 

Lewington A. Best practice: acute kidney injury. 2023. https://bestpractice.bmj.com/topics/en-gb/3000117 (accessed 13 November 2023)

Mahon A, Jenkins K, Burnapp L. Oxford handbook of renal nursing. Oxford: Oxford University Press: 2013

National Institute for Health and Care Excellence. Acute kidney injury. 2023a. https://cks.nice.org.uk/topics/acute-kidney-injury/ (accessed 13 November 2023)

National Institute for Health and Care Excellence. Acute kidney injury: prevention, detection and management. 2023b.