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OverviewAetiologyPathophysiologyClinical features and red flagsInvestigationsDifferential diagnosisManagementComplicationsMonitoring and follow-upSpecial situationsCommon pitfallsQuestionsSources
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Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.

Acute kidney injury and hydration in frailty

Medicine of older adults · UK scope · Sources checked 27 Aug 2026 · Clinical review pending

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AKI with life-threatening complication

Severe hyperkalaemia, pulmonary oedema, refractory acidosis, uraemic encephalopathy or pericarditis, anuria, shock or an infected obstructed urinary tract requires immediate specialist treatment and possible renal replacement therapy.

Action: Use ABCDE and ECG, treat hyperkalaemia and pulmonary oedema immediately, measure bladder volume and urine, obtain urgent renal, electrolyte and gas tests, stop further nephrotoxic exposure and involve nephrology or urology without delaying decompression or critical care.

Overview

Detect acute kidney injury despite low muscle mass and non-specific decline, distinguish hypovolaemia from congestion and obstruction, and restore perfusion safely while adjusting medicines, nutrition and community monitoring.

Compare creatinine with reliable previous values and record urine output. NICE uses an increase of at least 26 micromol/L within 48 hours, at least 50% within seven days, or oliguria below 0.5 mL/kg/hour for more than six hours to detect AKI in adults. A frail person with low muscle mass may have severe filtration impairment at a modest absolute creatinine.

Establish tempo and causes: vomiting, diarrhoea, fever, bleeding, reduced intake, urinary symptoms, surgery, contrast, heart failure, liver disease and recent medicine change. Ask who provides drinks and whether dysphagia, cognition, toileting fear or dependence limits access. Check weight trajectory and fluid balance records rather than relying on the word dehydrated.

Examine both sides of the fluid question. Hypovolaemia features include reduced perfusion, postural symptoms and losses; congestion features include raised jugular venous pressure, oedema, crackles, increasing oxygen need and weight gain. They can coexist in heart failure with poor arterial perfusion. Bedside ultrasound can support selected decisions but does not replace integrated examination and response.

Practice

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Medicine of older adultsOriginal SBA

AKI with fluid overload

An older adult with acute kidney injury has raised JVP, peripheral oedema, crackles and increasing oxygen requirement. What is the best immediate fluid interpretation?

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Sources and review status5 sources · checked 27 Aug 2026 · clinical review pending+
Sources

Sources and review status

National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.

  • NICE NG148 acute kidney injuryDetection, obstruction imaging, medicines, referral and post-AKI care.
  • NICE CG174 intravenous fluid therapyResuscitation, maintenance, frailty modification and monitoring.
  • NICE NG5 medicines optimisationReconciliation, adjustment and safe transitions.
  • UK Kidney Association hyperkalaemia guidelineEmergency potassium assessment and treatment pathways.
  • British Geriatrics Society CGA HubFrailty, hydration access, function and community planning.

Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes

Authoring stateComplete draftClinical stateAwaiting reviewJurisdictionUnited Kingdom

Investigate severity and mechanism. Repeat renal and electrolytes, bicarbonate, glucose, FBC and relevant infection or bleeding tests. Use ECG for potassium concern and blood gas for severe acidosis or shock. Urinalysis for blood and protein can identify an intrinsic pattern. Send microscopy, immunology or myeloma tests with nephrology input when findings support glomerular, interstitial or systemic disease.

Assess obstruction promptly. Palpate and bladder-scan after voiding when retention is possible, reviewing prostate, pelvic, neurological, constipation and anticholinergic factors. NICE recommends urgent urinary tract ultrasound within 24 hours when AKI has no identified cause or obstruction risk, and within six hours when pyonephrosis is suspected. An infected obstructed system requires immediate urological decompression.

Treat shock or hypovolaemia with isotonic crystalloid and frequent reassessment. NICE adult IV-fluid guidance uses a 500 mL bolus over less than 15 minutes for resuscitation, while frailty, heart failure and CKD may warrant smaller aliquots and earlier senior review. After each aliquot reassess pressure, perfusion, lungs, oxygen, urine and oedema; stop blind repetition when response is absent or congestion appears.

Prescribe maintenance from weight, oral intake, ongoing loss and disease. NICE suggests less routine maintenance—approximately 20 to 25 mL/kg/day water and lower sodium or potassium provision—for older or frail people and those with renal or cardiac impairment, with clinical adjustment. Replace abnormal losses separately. Fluid charts are prescriptions and need recorded delivery and response.

Review medicines systematically. Stop NSAIDs and avoid further nephrotoxic exposure when possible. Temporarily pause ACE inhibitors or ARBs during vomiting, diarrhoea or sepsis until the condition stabilises, unless a senior clinical reason favours continuation. Review diuretics against congestion rather than the creatinine alone. Hold or modify metformin, SGLT2 inhibitors and other agents under current sick-day and product guidance and adjust all renally cleared doses.

Treat complications. Use the current emergency hyperkalaemia pathway for ECG change or significant potassium, with cardiac membrane stabilisation, intracellular shift and removal strategies as indicated. Pulmonary oedema needs oxygen or ventilatory support and decongestion rather than routine fluid. Refractory hyperkalaemia, acidosis, uraemic complications, overload or poisoning prompts urgent nephrology and renal replacement discussion.

Maintain nutrition, mouth care, mobility and delirium prevention while balancing fluid restrictions and support. A person who cannot reach a drink needs an administration plan rather than an instruction to drink. Speech and language and dietetic input adapts dysphagia support. Avoid prolonged catheterisation solely to measure urine once stability allows safer monitoring.

At discharge, state baseline, peak and latest creatinine, AKI stage, cause, outstanding tests, urine and volume status, medicine changes and restart dates. Arrange repeat kidney and electrolyte testing according to recovery and risk, assess albuminuria and CKD after stabilisation, and explain when vomiting, diarrhoea, reduced urine, breathlessness or medicine uncertainty requires help.

Key points

  • Diagnose AKI by creatinine change or urine output using current NICE criteria; a value inside the laboratory range can still represent AKI.
  • First-line assessment reviews previous renal results, urine output, losses, sepsis, bleeding, obstruction, heart failure, medicines and recent contrast or procedures.
  • Examine perfusion and congestion together: blood pressure, refill, mucosa, postural symptoms, jugular venous pressure, oedema, lungs, weight and bladder.
  • Measure post-void residual and obtain renal ultrasound urgently when obstruction is possible or the cause remains unclear under NICE criteria.
  • Urinalysis helps identify blood and protein patterns; send microscopy and renal serology only when intrinsic disease is clinically plausible.
  • For hypovolaemic resuscitation, NICE CG174 uses 500 mL isotonic crystalloid over under 15 minutes, with smaller cautious aliquots and immediate reassessment when frailty, heart or kidney disease limits tolerance.
  • Do not give fluid for a raised creatinine automatically; congested heart failure often needs decongestion rather than hydration.
  • Review NSAIDs, ACE inhibitors, ARBs, diuretics, metformin, SGLT2 inhibitors, anticoagulants, opioids, gabapentinoids and antimicrobials against current physiology and indication.
  • Temporary medicine withholding needs a written restart trigger; failure to restart beneficial treatment after recovery creates long-term harm.
  • After AKI, document cause, peak and recovery, repeat kidney and electrolyte testing, review albuminuria and provide recurrence and sick-day education.

Aetiology

01

Reduced renal perfusion

Dehydration, bleeding, sepsis, hypotension and low cardiac output reduce filtration before structural kidney injury develops during prolonged insult.

02

Intrinsic kidney injury

Ischaemic or toxic tubular injury, glomerulonephritis, interstitial nephritis and vascular disease damage renal tissue directly through different mechanisms.

03

Urinary obstruction

Prostate disease, pelvic mass, stones, neurogenic bladder, constipation and anticholinergics impair outflow and raise upstream pressure.

04

Medicine-associated risk

NSAIDs, ACE inhibitors, ARBs, diuretics, contrast and renally cleared toxic medicines interact with illness and volume state.

Pathophysiology

  1. 1
    Filtration pressure failure

    Low arterial pressure or altered afferent and efferent arteriolar tone reduces glomerular filtration during physiological stress.

  2. 2
    Tubular and inflammatory injury

    Prolonged ischaemia, toxins and inflammation damage tubular cells, impair concentration and propagate intrarenal obstruction and inflammation.

  3. 3
    Postrenal pressure

    Outflow obstruction transmits pressure to nephrons and causes filtration loss, infection risk and permanent damage when prolonged.

  4. 4
    Low-muscle-mass concealment

    A small creatinine rise can represent substantial filtration loss because frailty and sarcopenia lower baseline creatinine production.

  5. 5
    Volume-treatment tension

    Hypovolaemia needs perfusion restoration while heart failure and reduced excretion make excessive sodium and water cause respiratory compromise.

Clinical features and red flags

Hypovolaemic AKI

Losses, poor intake and reduced perfusion occur without convincing venous or pulmonary congestion.

Congested cardiorenal pattern

Oedema, raised venous pressure, weight gain and lung congestion accompany worsening renal function.

Obstructive patternRed flag

Retention, anuria, palpable bladder or hydronephrosis directs urgent drainage and imaging.

Intrinsic renal pattern

Blood, protein, casts, rash or systemic inflammation suggests glomerular, interstitial or vascular disease.

Medicine accumulationRed flag

New sedation, bleeding, hypoglycaemia or neurotoxicity follows renal decline without an intentional dose change.

Dialysis-level complicationRed flag

Refractory potassium, acidosis, pulmonary oedema or uraemic symptoms requires immediate nephrology assessment.

Red flags requiring action

  • ECG change, muscle weakness or rapidly rising potassium requires emergency hyperkalaemia treatment and monitoring.
  • Anuria, painful bladder, hydronephrosis or sepsis with obstruction requires urgent urinary drainage and specialist care.
  • Hypoxia, crackles, raised venous pressure or pulmonary oedema means further routine fluid may be dangerous.
  • Hypotension, mottling, raised lactate or ongoing losses requires urgent resuscitation with repeated response assessment.
  • Haematuria, proteinuria, systemic rash, low platelets or inflammatory features raises intrinsic renal disease needing specialist investigation.
  • Confusion, reduced intake, falls or medicine accumulation may be the first clinical expression of AKI in frailty.

Investigations

  1. 01
    Serial creatinine and urine outputFirst stepFirst line
    Why
    Diagnose, stage and follow AKI first line.
    Interpretation and limitations
    Compare with reliable baseline and weight-adjusted urine output; low muscle mass can hide severe filtration reduction.
  2. 02
    Fluid and perfusion assessment
    Why
    Distinguish hypovolaemia from clinically important congestion.
    Interpretation and limitations
    Integrate pressure, refill, JVP, oedema, lungs, oxygen, weight, losses and response rather than using one sign.
  3. 03
    Urinalysis and microscopy
    Why
    Screen for intrinsic and obstructive clues.
    Interpretation and limitations
    Blood and protein or casts support renal inflammation, while infection and catheter trauma can confound results.
  4. 04
    Electrolytes, gas and ECG
    Why
    Detect life-threatening metabolic and cardiac AKI complications.
    Interpretation and limitations
    Potassium, bicarbonate and ECG guide emergency treatment; severity and trend matter more than waiting for symptoms.
  5. 05
    Post-void residual and renal ultrasound
    Why
    Identify lower or upper tract obstruction.
    Interpretation and limitations
    Bladder-scan promptly and use urgent ultrasound timing based on pyonephrosis risk, uncertain cause and obstruction probability.
  6. 06
    Medicine and exposure review
    Why
    Find nephrotoxicity and dose accumulation.
    Interpretation and limitations
    Record NSAIDs, haemodynamic agents, contrast, antimicrobials, anticoagulants and renally cleared CNS or diabetes drugs with last doses.
  7. 07
    Directed intrinsic-disease tests
    Why
    Investigate a renal inflammatory phenotype.
    Interpretation and limitations
    Select serology, electrophoresis, imaging or biopsy with nephrology when urine, systemic and trajectory findings justify them.

Differential diagnosis

01

Chronic kidney disease

Historical creatinine, albuminuria, kidney size and trajectory distinguish chronic impairment from superimposed acute decline requiring a separate cause.

02

Hypovolaemia

Loss history, thirst, postural symptoms, poor perfusion and fluid response support reduced effective circulating volume as the principal mechanism.

03

Congested cardiorenal syndrome

Raised venous pressure, oedema, pulmonary congestion and weight gain indicate kidney dysfunction during fluid overload rather than dehydration.

04

Obstructive uropathy

Retention symptoms, palpable bladder, hydronephrosis or anuria directs bladder scanning, ultrasound and urgent drainage before permanent damage occurs.

05

Drug-related creatinine change

Haemodynamic medicines, trimethoprim and changing muscle production affect creatinine differently from structural renal injury and need context-specific interpretation.

Management

01First-line AKI sequenceConfirm, assess danger and find mechanismFirst stepFirst lineCreatinine rises, urine falls or frailty presents with possible renal accumulation.+
  1. 1Compare baseline and current creatinine and urine output and assess potassium, acidosis, overload, uraemia and shock.
  2. 2Examine perfusion and congestion, review losses, sepsis, bleeding, medicines and obstruction and obtain targeted urine and imaging tests.
  3. 3EscalationTreat the cause and complication, adjust exposure and record a fluid, urine, laboratory and escalation plan.
02Cautious fluid routeTest and reassess the perfusion responseHypovolaemia or shock is plausible without dominant pulmonary congestion.+
  1. 1Use isotonic crystalloid in the guideline resuscitation dose or smaller frailty-appropriate aliquot with a clear physiological target.
  2. 2Reassess blood pressure, refill, consciousness, lungs, oxygen, urine and oedema immediately after every bolus.
  3. 3Stop repeated fluid when congestion appears or response is absent and seek senior haemodynamic or critical-care support.
03Obstruction routeRelieve pressure before irreversible damageRetention, anuria, pelvic disease or hydronephrosis is possible.+
  1. 1Perform bladder scan and catheterise confirmed acute lower retention with appropriate monitoring and urology criteria.
  2. 2Arrange urgent ultrasound and immediate urology for infected obstruction, solitary kidney or upper-tract compromise.
  3. 3Treat constipation and medicine or prostate contributors and create a catheter removal or long-term drainage plan.
04Recovery and restartPrevent recurrent AKI and accidental undertreatmentKidney function and acute illness begin to stabilise.+
  1. 1Review creatinine, electrolytes, volume and the ongoing indication for every withheld or dose-adjusted medicine.
  2. 2Restart beneficial treatment in a staged monitored manner when physiology permits and communicate exact ownership.
  3. 3Arrange post-AKI bloods, urine albumin and CKD assessment and provide practical sick-day and hydration guidance.
Key medicines and prescribing safety1 treatment · regimens, roles and cautions+
Restores circulating volume in clinically assessed hypovolaemia or shock while cause treatment proceeds.

Isotonic crystalloid for hypovolaemic resuscitation

Give 500 mL intravenously over less than 15 minutes under NICE adult IV-fluid guidance; use smaller aliquots and earlier senior review when frailty, heart failure or kidney disease narrows fluid tolerance.

Reassess perfusion, lungs, oxygen, JVP, oedema and urine after every bolus; avoid routine repetition for congested cardiorenal disease or established pulmonary oedema.

Complications

01

Hyperkalaemia and arrhythmia

Reduced potassium excretion, acidosis and tissue breakdown can cause conduction disturbance and cardiac arrest without preceding muscular symptoms.

02

Fluid overload

Impaired sodium and water excretion causes oedema, hypertension, pulmonary congestion and hypoxic respiratory failure during ongoing replacement.

03

Medicine accumulation

Opioids, gabapentinoids, anticoagulants, antibiotics and glucose-lowering medicines can produce sedation, bleeding, neurotoxicity or hypoglycaemia after clearance falls.

04

Delirium and functional decline

Uraemia, dehydration, treatment disruption and bed rest cause confusion, falls, poor intake and prolonged dependency after the acute biochemical problem resolves.

05

Chronic kidney progression

Incomplete recovery and recurrent AKI accelerate CKD, cardiovascular risk and future vulnerability to acute illness and medicine toxicity.

Monitoring and follow-up

  • Repeat creatinine, potassium, bicarbonate and other electrolytes at a frequency matched to stage and trajectory.
  • Record urine output accurately during instability and remove unnecessary catheterisation once safer monitoring is feasible.
  • Trend pressure, refill, weight, lungs, oxygen, JVP and oedema during fluid or diuretic treatment.
  • Review every renally cleared or nephrotoxic medicine after each material change in kidney function.
  • Document withheld medicines, restart thresholds, responsible clinician and post-restart laboratory timing.
  • Track cognition, intake, swallowing, mobility and access to fluids during acute and community recovery.
  • After AKI, repeat renal testing, assess albuminuria and review whether CKD coding and nephrology follow-up are required.

Special situations

Normal range can conceal AKI

A small creatinine rise within reference limits can represent major filtration loss in sarcopenia.

Oedema does not prove perfusion

A person can have total-body fluid excess while effective arterial circulation and kidney perfusion remain poor.

Fluid is a monitored treatment

Every bolus needs an indication, target and stop point just like a vasoactive medicine.

Obstruction may be painless

Neuropathy, dementia and chronic retention can remove the expected suprapubic pain and urge.

A temporary hold needs an exit

Beneficial heart and kidney treatment is often lost when restart ownership is absent at transition.

Common pitfalls

  1. 01

    Excluding AKI because creatinine remains within the laboratory reference range.

  2. 02

    Calling every raised creatinine dehydration without examining congestion and obstruction.

  3. 03

    Giving repeated fluid boluses without documenting response and lung findings.

  4. 04

    Using an empty bladder scan to exclude upper-tract obstruction.

  5. 05

    Continuing renally cleared sedatives or anticoagulants at the previous dose without review.

  6. 06

    Stopping diuretics automatically in congested heart failure because creatinine rose.

  7. 07

    Withholding ACE inhibitor or ARB indefinitely after the acute indication has resolved.

  8. 08

    Discharging without post-AKI bloods and medicine restart ownership.