Fluids and Acute Kidney Injury: Why Getting Fluid Balance Right Saves Lives

What Is Acute Kidney Injury?

Acute Kidney Injury (AKI) is a sudden decline in kidney function that develops over hours or days. In simple terms, it means that the kidneys are struggling to cope — whether with filtering waste, balancing fluids, or maintaining electrolyte stability.

According to internationally recognised guidance from Kidney Disease: Improving Global Outcomes (KDIGO), AKI is diagnosed when any of the following occur (KDIGO, 2012):

• An increase in serum creatinine of ≥26.5 µmol/L within 48 hours
• A rise in creatinine to 1.5 times the patient’s baseline within seven days
• Or urine output of less than 0.5 mL/kg/hour for at least six hours

These criteria exist for a reason. They are designed to help us recognise kidney injury early — while there is still time to intervene and prevent long-term damage.

In the UK, the National Institute for Health and Care Excellence (NICE) also emphasises that even small rises in creatinine matter, as they are linked to poorer outcomes if not acted upon promptly (NICE NG148, 2019).

But in real life, AKI rarely announces itself neatly through textbook numbers. More often, it appears quietly. It might start with a patient who is “just not drinking much today.” Or someone whose urine output is a little lower than usual. Or a blood result that has risen slightly, but not enough yet to cause alarm. On their own, these changes can seem insignificant. Together, they often tell a very different story.

Research shows that even modest increases in creatinine are associated with higher mortality and longer hospital stays (Lewington et al., 2013). In other words, what looks “mild” on paper can carry serious consequences if ignored.

Over the years, I have learned that AKI is often first picked up not in a blood result, but in a pattern.

A pattern in fluid charts.
A pattern in urine output.
A pattern in how the patient looks, feels, and behaves.

The National Confidential Enquiry into Patient Outcome and Death highlighted that delayed recognition of these early warning signs has contributed to avoidable harm in many patients (NCEPOD, 2009). That finding resonates deeply with everyday nursing practice.

Blood tests are important, of course. But they are only part of the picture.

Often, it is the overall clinical context — reduced intake, infection, hypotension, medication changes, increasing fatigue — that gives us the earliest clues. As nurses, we are uniquely placed to see that bigger picture because we are there, shift after shift, noticing what has changed.

AKI rarely appears suddenly without warning. Most of the time, it whispers before it shouts and learning to recognise those early whispers is one of the most powerful ways we protect our patients.

💡Clinical Insight

AKI rarely happens in isolation — it often develops in patients who are already physiologically vulnerable. Recognising cumulative risk factors such as age, comorbidities, medications and acute illness allows nurses to anticipate deterioration rather than respond to it retrospectively.

Fluids: More Than Just Documentation

Fluid balance is not a checkbox on a chart. It is an evolving narrative of how well a patient’s body maintains homeostasis.

Accurate fluid balance monitoring helps us understand:

• If a patient is adequately hydrated
• Whether the kidneys are perfusing effectively
• Whether fluid overload or dehydration is developing

According to the NICE guideline on AKI prevention, detection and management, ensuring adequate hydration is critical, particularly in patients at increased risk of AKI. Early oral hydration should be encouraged for at-risk adults, and addressing fluid status can help prevent deterioration.()

When fluid balance is poorly recorded, or trends are missed, early warning signs can be delayed — and by the time AKI is obvious on blood tests, the window for straightforward prevention may have passed.

💡Clinical Insight

Fluid balance is a clinical assessment tool, not just a charting task. Inaccurate recordings can create a false sense of stability, delaying intervention. Vigilance in monitoring intake, output, and trends over time is a critical safeguard against avoidable harm.

Balancing Dehydration and Fluid Overload

One of the most nuanced and challenging aspects of AKI care is finding the balance between dehydration and fluid overload. In theory, it sounds straightforward. In practice, it rarely is.

As nurses, we are often caring for patients whose fluid needs are constantly changing — influenced by infection, surgery, medications, pain, anxiety, and reduced appetite. What a patient needs in the morning can be very different from what they need in the afternoon. This is why fluid management is never a “set and forget” intervention.

Dehydration and AKI Risk

When a patient becomes dehydrated — whether through fever, vomiting, diarrhoea, poor oral intake, or increased insensible losses — renal blood flow is reduced. This decrease in renal perfusion limits the kidneys’ ability to filter waste products effectively and is one of the most common triggers for AKI.

Both international and UK guidelines identify hypovolaemia as a major preventable cause of kidney injury and emphasise the importance of early recognition and correction (KDIGO, 2012; NICE NG148, 2019).

In everyday practice, dehydration does not always look dramatic. It is often subtle. A patient may stop finishing their drinks. They may feel too nauseated to eat or drink. They may be reluctant to mobilise to the toilet and so limit their intake. Over time, these small changes can place significant strain on the kidneys.

Prompt assessment, encouragement of oral fluids where appropriate, and timely intravenous replacement remain fundamental components of early AKI management (NICE, 2019).

💡Clinical Insight

Both under-resuscitation and over-resuscitation can impair kidney recovery. The goal is not simply to “give fluids” but to restore effective circulation without tipping the patient into overload — a balance that requires ongoing reassessment rather than fixed plans.

Fluid Overload: A Competing Risk

At the other end of the spectrum, excessive fluid administration can be just as harmful — particularly in patients with cardiac disease, pre-existing kidney impairment, or reduced physiological reserve.

Fluid overload is associated with increased respiratory compromise, prolonged hospital stay, and poorer overall outcomes in patients with AKI (Hoste et al., 2013). It can quickly lead to pulmonary oedema, increased oxygen requirements, and delayed recovery.

KDIGO guidance recommends close monitoring of volume status, body weight, and clinical signs in patients receiving fluid therapy, alongside regular reassessment of ongoing need (KDIGO, 2012).

In practice, this means looking beyond the prescription. It means listening to lung sounds, observing work of breathing, reviewing oxygen needs, and checking for peripheral oedema. It means asking not only, “Can this patient have more fluid?” but also, “Do they still need it?”

The Nursing Role in Getting the Balance Right

This balancing act — correcting hypovolaemia without overwhelming the patient — sits at the heart of skilled nursing practice. It requires clinical judgement, ongoing assessment, and confidence to question when something does not feel right.

Research consistently identifies appropriate fluid management as a key determinant of AKI outcomes (Lewington et al., 2013; NCEPOD, 2009). Poorly tailored fluid therapy, whether too little or too much, increases the risk of deterioration.

Over time, I have learned that the safest approach is to think of fluids as a conversation with the patient’s body. We give something. We watch how they respond. We adjust. We reassess. And we escalate when needed.

There is rarely a perfect formula. But there is always a responsibility to remain attentive.

That attentiveness is what protects our patients.

The Importance of Urine Output

Urine output is one of the earliest and most sensitive indicators of evolving Acute Kidney Injury. In many cases, it begins to fall before creatinine levels rise, making it an invaluable early warning sign.

The KDIGO guidelines define sustained oliguria as urine output of less than 0.5 mL/kg/hour for six hours or more and include this as a key diagnostic criterion for AKI (KDIGO, 2012). This reflects strong evidence that reduced urine output is closely linked to worsening kidney function and poorer patient outcomes.

In everyday practice, however, urine output is not always monitored as consistently as it should be — particularly in patients who are not catheterised. Outputs may be estimated rather than measured, forgotten during busy shifts, or recorded retrospectively. Over time, these small gaps can obscure important trends.

The NICE recommends regular monitoring of urine output in patients who are acutely unwell or at risk of AKI, alongside fluid balance and physiological observations (NICE NG148, 2019).

From experience, I have learned that a sudden drop in urine output often reveals a story before blood results do. A patient who has been passing reasonable volumes suddenly slows down. Another begins to report that they “haven’t really been much today.” These are moments that deserve attention, not reassurance.

Reliable monitoring, thoughtful interpretation, and timely escalation when output declines remain some of the most effective ways nurses can protect kidney function.

💡Clinical Insight

Changes in urine output often signal renal stress before laboratory values change significantly. Monitoring trends across hours — not just total volumes — enables earlier recognition of declining perfusion and more timely escalation.

Medications and AKI Risk

Medications play a significant role in the development and progression of Acute Kidney Injury. Many drugs that are routinely prescribed in hospital and community settings can place additional strain on vulnerable kidneys — particularly during periods of dehydration, infection, or haemodynamic instability.

Common examples include:

• Non-steroidal anti-inflammatory drugs (NSAIDs)
• ACE inhibitors
• Angiotensin receptor blockers (ARBs)
• Certain antibiotics
• Contrast agents

Both KDIGO and NICE highlight medication-related nephrotoxicity as a major, potentially preventable contributor to AKI and recommend regular review of drug therapy in at-risk patients (KDIGO, 2012; NICE, 2019).

During acute illness, medications that are normally safe can become harmful. Reduced circulating volume, hypotension, and altered renal perfusion can all increase susceptibility to drug-induced kidney injury. This is why national guidance supports temporary withholding or dose adjustment of certain medicines during periods of acute physiological stress.

Research suggests that inappropriate continuation of nephrotoxic drugs during acute illness is associated with higher rates of AKI and poorer outcomes (Lewington et al., 2013).

In practice, nurses are often the first to recognise when medication regimens no longer match the patient’s current condition. A patient who is hypotensive, not eating or drinking, and becoming oliguric may still be receiving regular antihypertensives or NSAIDs. Noticing this mismatch and prompting review can prevent significant harm.

Medication safety in AKI is not solely about prescriptions. It is about ongoing assessment, communication, and advocacy — all central to professional nursing practice.

💡Clinical Insight

Periods of acute illness can temporarily change how the body tolerates certain medications. Nurses play a key role in identifying when usual prescriptions may become harmful and in prompting timely review to prevent avoidable kidney injury.

The Link Between Sepsis and AKI

Sepsis — the body’s overwhelming and dysregulated response to infection — is one of the leading causes of AKI in hospitalised patients. When infection triggers widespread inflammation, blood vessels become leaky, circulation becomes unstable, and blood pressure can fall. Together, these changes significantly reduce blood flow to the kidneys, placing them under immediate physiological stress.

Research consistently shows that sepsis-related circulatory failure and inflammatory injury are major contributors to the development of AKI (KDIGO, 2012; Lewington et al., 2013). For many patients, kidney dysfunction is one of the earliest signs that sepsis is progressing.

In practice, this often means that a patient who initially appears “just a bit unwell” can deteriorate rapidly. Reduced urine output, rising lactate, increasing oxygen requirements, and subtle changes in behaviour may appear before severe hypotension develops. These early changes deserve close attention.

Fluid resuscitation is a cornerstone of early sepsis management and is strongly supported by national and international guidance. The NICE recommends prompt intravenous fluid therapy to restore circulating volume and support organ perfusion in patients with suspected sepsis (NICE NG148, 2019).

However, evidence also highlights that fluid therapy in sepsis must be dynamic rather than fixed. While early fluids improve perfusion, excessive or prolonged administration can contribute to fluid overload and worsen outcomes, particularly in patients with evolving AKI (Hoste et al., 2013; KDIGO, 2012).

From a nursing perspective, this means that giving fluids is only part of the work. The real skill lies in watching how the patient responds. Does urine output improve? Is blood pressure stabilising? Are oxygen needs increasing? Are lung sounds changing?

I have learned that early improvement in sepsis does not always mean sustained recovery. Some patients respond well initially, only to deteriorate hours later if fluid balance, renal function, and observations are not closely monitored. Without ongoing reassessment, these secondary declines can be missed.

Sepsis and AKI rarely exist in isolation. They often evolve together, feeding into one another. Effective nursing care means recognising this relationship early and responding with vigilance, evidence-based practice, and timely escalation.

💡Clinical Insight

In septic patients, fluid resuscitation is essential — but ongoing reassessment is equally important. What begins as life-saving therapy can become detrimental if excess fluid accumulates and compromises organ function.

Documentation & Escalation: Safeguarding Patients

Good nursing documentation is not just about “doing the paperwork.” It is one of the most important ways we keep our patients safe.

When we clearly record fluid balance trends, changes in urine output, and rising creatinine levels, we are telling the patient’s story. We are illustrating how things change over time — not just what is happening in a single moment.

Patterns only become visible when they are written down consistently.

The NICE guideline on Acute Kidney Injury (NG148) highlights the importance of early recognition and timely referral when needed (NICE, 2019). This can only happen when concerns are properly documented and shared.

I have learned that good documentation supports good conversations. It helps during handovers. It strengthens referrals. It makes sure worries are taken seriously. Without it, important changes can be missed or minimised.

National reviews have shown that delayed recognition and escalation have contributed to avoidable harm in patients with AKI (NCEPOD, 2009). That is a sobering reminder that how we document really does matter.

Escalation should never wait for dramatic blood results. When urine output is dropping, fluid balance is persistently negative, or creatinine is slowly creeping up, those trends deserve attention — even if they are not yet “red flags.”

Just like in sepsis care, the key is learning to act on patterns, not single numbers.

Clear documentation and confident escalation protect patients. They also protect us as professionals. Most importantly, they help ensure that concerns are heard, acted upon, and never lost in the busyness of the ward.

💡Clinical Insight

Escalation should be triggered by evolving patterns, not just single abnormal results. Persistent positive balance, falling urine output, or rising weight over consecutive shifts warrants proactive communication before critical deterioration occurs.

Conclusion

Acute Kidney Injury is common, serious, and often preventable.

The science is clear: early recognition, careful fluid management, medication review, and timely escalation all improve outcomes (NICE, 2019; KDIGO, 2012). But the practice of this science happens at the bedside.

It happens when a nurse notices a fluid balance chart that doesn’t quite add up.
When urine output drops, someone decides not to ignore it.
When a creatinine rises slightly and is taken seriously rather than dismissed.

AKI rarely begins with a crisis. It begins with subtle changes.

Our role is to recognise those changes early, document them clearly, and act with confidence. That is not just good practice — it is professional responsibility.

Fluids may look simple. Fluid balance may seem routine. But in truth, they are powerful indicators of how well a patient is coping. And when we pay attention to them — really pay attention — we protect kidney function, improve recovery, and sometimes prevent avoidable harm.

That is the quiet strength of skilled nursing care.

Key Resources:

• Hoste, E.A.J., Maitland, K., Brudney, C.S., Mehta, R., Vincent, J.L., Yates, D., Kellum, J.A. and Myburgh, J. (2014) ‘Four phases of intravenous fluid therapy: a conceptual model’, Intensive Care Medicine, 40(2), pp. 188–197. https://doi.org/10.1007/s00134-013-3077-5
• Kidney Disease: Improving Global Outcomes (KDIGO) (2012) KDIGO Clinical Practice Guideline for Acute Kidney Injury. Available at: https://kdigo.org/guidelines/acute-kidney-injury/ (Accessed: 18 February 2026).
• Lewington, A.J.P., Cerdá, J. and Mehta, R.L. (2013) ‘Raising awareness of acute kidney injury: a global perspective’, Kidney International, 84(3), pp. 457–467. https://doi.org/10.1038/ki.2013.153
• National Confidential Enquiry into Patient Outcome and Death (NCEPOD) (2009) Adding Insult to Injury: A Review of the Care of Patients Who Died in Hospital with a Primary Diagnosis of Acute Kidney Injury. London: NCEPOD. Available at: https://www.ncepod.org.uk (Accessed: 18 February 2026).
• National Institute for Health and Care Excellence (NICE) (2019) Acute kidney injury: prevention, detection and management (NG148). Available at: https://www.nice.org.uk/guidance/ng148 (Accessed: 18 February 2026).
• National Institute for Health and Care Excellence (NICE) (2024) Sepsis: recognition, diagnosis and early management (NG51). Available at: https://www.nice.org.uk/guidance/ng51 (Accessed: 18 February 2026).
• NHS England (2014) Patient Safety Alert: Standardising the Early Identification of Acute Kidney Injury. Available at: https://www.england.nhs.uk/patient-safety (Accessed: 18 February 2026).
• Prowle, J.R., Bellomo, R. and Kellum, J.A. (2011) ‘Fluid management for the prevention and attenuation of acute kidney injury’, Nature Reviews Nephrology, 7(4), pp. 209–219. https://doi.org/10.1038/nrneph.2011.13
• Think Kidneys (2016) Guidelines for Medicines Optimisation in Patients with Acute Kidney Injury. Available at: https://www.thinkkidneys.nhs.uk (Accessed: 18 February 2026).
• Vincent, J.L. and De Backer, D. (2013) ‘Circulatory shock’, New England Journal of Medicine, 369(18), pp. 1726–1734.
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