Acute kidney injury (AKI) is common in the UK, with a reported prevalence of 15% among people admitted as emergencies to hospitals (National Institute for Health and Care Excellence (NICE), 2021a). Community acquired AKI is even more prevalent at approaching 600/100 000 population, although in the absence of blood testing this figure is probably inaccurate (NICE, 2021a). One study reports an incidence rate across the UK of approximately 150/10 000 of the population per year (Sawhney et al, 2018).
The truth is no one is certain what the prevalence or incidence rates for AKI are, because they cannot easily be measured. What is known is that the incidence of AKI is on the increase and that this increase is likely to be related to the increased age of the population and attendant increase in the prevalence of chronic conditions, which contribute to the risk of acquiring AKI (Yokota et al, 2018). Therefore, practice nurses need to be aware of the signs and symptoms of AKI, as well as the characteristics of people most at risk from it. Sometimes people still term AKI as acute renal failure, although this terminology is no longer in mainstream use.
This article will describe what AKI is, its signs and symptoms, causes, types and how it is diagnosed. It will consider the issues practice nurses might want to think about in its management in the community and when people affected by it should be referred onward for secondary or tertiary care management.
Definition
NICE (2021a) define AKI as:
‘a spectrum of injury to the kidneys which can result from a number of causes. It is a clinical syndrome rather than a biochemical diagnosis… It is characterized by a decline in renal excretory function over hours or days that can result in failure to maintain fluid, electrolyte, and acid-base homeostasis.’
Signs and symptoms
The signs and symptoms of AKI vary according to the exact cause of the injury, but in the community the presenting signs will usually include the patient complaining of a reduced urine output. This presentation is most often a result of the fact that the patient has an active infection, such as influenza or gastroenteritis (Semogas et al, 2019). AKI is also a frequent sequelae of COVID-19 infection and is generally associated with poor outcomes (Diebold et al, 2021). Practice nurses might begin to suspect a diagnosis of AKI in patients who present to the practice with viral diseases, and therefore might consider, where other signs and symptoms suggest it, screening patients for AKI.
The signs and symptoms of AKI, including oliguria, have a rapid onset and also include (British Medical Journal, 2022):
- Raised serum creatinine
- Hyperkalaemia
- Acidaemia
- Uraemia
- Anuria/urine retention
- Pulmonary oedema
- Hypertension/hypotension (AKI cause dependent)
- Altered level of consciousness.
Risk factors
The National Confidential Enquiry into Patient Outcome and Death (NCEPOD, 2009) identified the ten most important risk factors for AKI as being:
- Older age
- The presence of co-morbidities (commonly hypertension and/or diabetes)
- The use of some medications (eg non-steroidal anti-inflammatory drugs (NSAIDs))
- The presence of chronic kidney disease (CKD)
- Dehydrated, regardless of the cause
- Septic
- Raised serum biochemistry (markers of renal disease) on hospital admission
- Unusual urinalysis, eg proteinuria and/or haematuria either current or historic
- Of an unhealthy weight (over or underweight)
- Of a poor nutritional status, eg malnourished.
Causes and classifications
There are a large number of potential causes of AKI, many of which are obvious, while others are more subtle. The causes of AKI give rise to the classifications of AKI; an understanding of the cause and classification of a particular presentation of AKI will provide the practice nurse with useful clues as to its management. Understanding the aetiology of AKI is also important in considering issues like primary care follow-up and long-term patient management, eg AKI that is associated with CKD will require close monitoring in the long-term.
The three classifications of AKI, which are derived from the underlying causes, are (NICE, 2021a):
- Pre-kidney
- Intrinsic kidney
- Post-kidney.
Pre-kidney
Pre-kidney AKI refers to AKI that occurs as a result of a reduction in the blood supply to the kidneys. A reduction in the blood supply to the kidneys results in a reduction in the glomerular filtration rate secondary to hypoperfusion. A characteristic of pre-kidney AKI is oliguria of less than 400 ml/day.
The potential causes of pre-kidney AKI include anything which contributes to hypoperfusion and includes (BMJ, 2022):
- Haemorrhage
- Hypovolaemia, eg burns, diarrhoea and vomiting
- Hypotension, eg from trauma, sepsis, medication (eg antihypertensive and over diuresis)
- Heart failure
- Medications exacerbating disease, eg angiotensin converting enzyme inhibitors (ACEI) in renal artery stenosis
- Liver disease (hepatorenal syndrome).
Some of these mechanisms of injury are clear at presentation and may cause the practice nurse to suspect AKI in the presence of signs and symptoms suggestive of AKI.
Intrinsic
Intrinsic AKI occurs when there is damage to any of the structures contained in the kidneys themselves. This includes the blood vessels, glomeruli, interstitial cells or the renal tubules. Intrinsic AKI is often multifactorial in aetiology. Acute tubular necrosis, rapidly progressing glomerulonephritis and interstitial nephritis are the leading aetiologies of intrinsic AKI (BMJ, 2022). Other causes of intrinsic AKI include (Ellis, 2013a):
- Autoimmune diseases, eg glomerulonephritis
- Damage relating to medications, eg penicillin, NSAIDs, cytotoxics and radio-contrast
- Malignant hypertension
- Vasculitis
- Myeloma.
These presentations of AKI may only be obvious once a primary diagnosis is clear. Sometimes the initial presentation of AKI causes the investigations, which uncovers one of the above diseases.
Post-kidney
As the name suggests, post-kidney AKI is characterised by anything causing AKI in the structures after the bladder. Post-kidney obstruction to the outflow of urine from the kidneys or the bladder will over time cause damage upstream in the kidneys themselves. Prostatic disease and kidney stones are widely known causes of post-kidney AKI, while other causes the practice nurse might come across include (Mahon et al, 2013; BMJ, 2022):
- Bladder cancers
- Strictures
- Urinary tract infections (UTIs) (ascending)
- Blood clots
- Ganglions
- Medications, eg acyclovir, anticholinergics.
Often discomfort and a palpable bladder will point the practice nurse towards a diagnosis of post-kidney AKI.
Diagnosis
Understanding the diagnosis of AKI, and initially most importantly the classification, is helpful in establishing what early treatment is needed. For example, fluid replacement is indicated in pre-kidney AKI, while in post-kidney AKI it may exacerbate matters until the obstruction is relieved.
In the UK, the diagnosis of AKI, classification excepted, is made with reference to the following criteria (Ellis and Jenkins, 2014):
- A rise in serum creatinine of greater than or equal to 26 micromol/L in less than 48 hours
- An increase in serum creatinine of 50% or more, either proven or presumed, within 7 days
- A reduction in urine output to under 0.5 ml/kg/hour for more than 6 hours in adults or 8 hours in children
- A 25%, or greater, decrease in estimated glomerular filtration rate (eGFR) in children and young people within the past 7 days.
As well as the various classifications of AKI and the presence or absence of the above diagnostic criteria, AKI may be staged as shown in Table 1 (Kidney Disease Improving Global Outcomes (KDIGO), 2012).
Table 1. Staging of acute kidney injury
| Stage | Criteria |
|---|---|
| 1 | Creatinine 1.5 to 2 times the baseline level, or creatinine rise to more than 26 micromol/L, within 48 hours |
| 2 | Current creatinine 2 to 3 times the baseline level |
| 3 | Current creatinine 3 or more times the baseline level, or 1.5 times baseline and more than 354 micromol/L |
Management
The key to management of AKI in the primary care setting is the removal, or reversal, of its cause, if possible (Ellis, 2013b). This requires the practice nurse to undertake a structured and thorough assessment of the patient and therefore generally requires:
- The nurse to consider the patient's past medical history, especially any recent illness or injury. An elderly man with mild CKD, diabetes and a recent history of diarrhoea and oliguria might suggest pre-kidney AKI; while the same man presenting with a distended bladder and a recent history of frequency, urgency and dysuria is more likely to be affected by a post-kidney AKI
- The nurse will need to undertake a holistic clinical assessment to identify the extent of the problem and any other underlying issues. Basic observations such as blood pressure, pulse and temperature checks might uncover issues with the patient's state of hydration, presence of infection or even the presence of sepsis (Nutbeam and Daniels, 2022)
- If the patient is not so unwell that they need to be referred to hospital (see later), the practice nurse may consider ordering blood tests including urea and electrolytes and eGFR which will help provide a stage for the AKI if present. This is especially indicated in those patients identified as at high risk of AKI (Royal College of General Practitioners (RCGP), ND)
- Erythrocyte sedimentation rate (ESR) and/or C-reactive protein (CRP) tests may be indicated where infection is thought to be present, although sepsis needs immediate referral to a hospital setting in most cases (Nutbeam and Daniels, 2022)
- Urinalysis can be useful in excluding some diagnoses and potentially commencing the patient on treatment for a UTI if indicated (NICE, 2021b).
Where AKI stage 1 is suspected and while blood results are awaited, and the patient is otherwise well, treatment in primary care may include the provision of antibiotics and advice and support about increasing fluid intake. The RCGP (ND) recommend when such an approach is adopted, that if the patient remains unwell after 48-72 hours, the blood tests are repeated.
Patients who are facing a potential diagnosis of AKI may be very scared (Mahon et al, 2013) and have the right to be told about the illness and be involved in decision making related to it (NICE, 2019). This requires the practice nurse to ensure they explain the likely causes and consequences of AKI and the decision making about management in primary care or onward referral.
Referral
NICE (2021a) are clear that not all people affected by AKI need to be referred to hospital, with some AKI being treatable in the community. When the practice nurse is thinking about referral from primary to secondary or tertiary care, they should take account not only the type and severity of the AKI but also the presence and severity of the other comorbidities affecting the patient.
Table 2 shows when urgent admission to hospital with same day referral is usually necessary, subject to clinical judgement (NICE, 2021a).
Table 2. Criteria for urgent same day referral to hospital
| Affected by a probable stage 3 acute kidney injury (AKI) |
| Affected by a cause which requires management in the hospital setting, eg acute obstruction and/or kidney infection |
| Affected by an AKI where the cause is not discernible |
| At risk of obstruction because of an underlying diagnosis, eg prostatic disease, cancer of the pelvis, recurrent urinary tract infections |
| Obviously septic (Nutbeam and Daniels, 2022) |
| Hypovolaemic and in need of fluid resuscitation |
| Deteriorating clinically and giving cause for concern and the need for closer monitoring |
| Suffering from a complication of AKI which is potentially life threatening, eg encephalopathy. |
As ever, there is a degree of clinical interpretation which needs to be applied to the referral criteria, which will be informed by the patient's age and comorbidities, the nurse's experience of their care needs and the clinical support available within the general practice.
Long-term complications
Some people who have a diagnosis of AKI will die; the mortality rates cited in the UK suggest 18% of people die within 30 days of an AKI diagnosis (UK Renal Registry, 2020). Some people will never recover full kidney function after an episode of AKI, with some developing CKD as a result of the AKI, and some having had CKD prior to the episode of AKI but having worse kidney function afterward (BMJ, 2022).
As well as monitoring kidney function in AKI survivors, the practice nurse may be required to consider what medications were stopped when the person was acutely unwell and whether these should be restarted (RCGP, ND). People who have had AKI and now have CKD will also need monitoring in the long-term in the same way as other people with CKD (Ellis, 2021), which may include instigating kidney protective measures such as strict blood pressure control and referral to a nephrologist (BMJ, 2021).
There is increasing evidence to suggest that people who have recovered from AKI may be at a greater life-time risk of recurrent AKI, cardiovascular disease and even cancer (James et al, 2020). With this additional knowledge, the practice nurse may need to consider the provision of lifestyle advice including the avoidance of nephrotoxic medications, as well as cardiovascular risk management among AKI survivors (Gameiro et al, 2021).
Conclusion
This article has identified that AKI is a common presentation in primary care, especially among patient groups who are at high risk. Practice nurses need to have a suspicion of AKI among high-risk patients who present with some of the signs and symptoms of AKI including issues like oliguria. While stage 1 AKI in otherwise well patients may be treated in the community, higher stages of AKI and AKI in at risk individuals should be referred to secondary and tertiary care settings without delay.
The management of AKI is usually predicated by removal or reversal of causality, where this is possible, and may, in mild cases, be as simple as relieving dehydration or outflow obstruction. The management of patients who have recovered from AKI is complicated by the additional disease burden risks they face, with many requiring life-long monitoring and management of additional risks like hypertension.
The practice nurse can play an important role in the recognition, diagnosis, acute management and subsequent long-term management of people affected by AKI and therefore should be aware of the risk factors and signs and symptoms.
KEY POINTS:
- Some individuals carry an increased risk of acute kidney injury (AKI), eg the elderly
- AKI is characterised by a rapid decline in the kidney's excretory functions
- Signs and symptoms of AKI include a reduced estimated glomerular filtration rate (eGFR), oliguria and altered states of consciousness
- AKI is classified by the main root causes and staged by severity
- Primary care management of AKI is limited to reversal of low-grade AKI, with the rest referred into secondary care
- People who recover from AKI require life-long monitoring
CPD REFLECTIVE PRACTICE:
- Can you identify the risk factors for AKI among the patient groups you care for?
- What are the key signs and symptoms which a patient might present with which might make you suspicious that they have AKI?
- What factors might trigger you referring a patient with suspected AKI for immediate hospital care?
- How might you change your practice around the management of AKI survivors after having read this article?