How does NICE NG148 define acute kidney injury?

A rise in serum creatinine of 26 micromol/L or greater within 48 hours, a 50% or greater rise known or presumed to have occurred within the past 7 days, or a fall in urine output to less than 0.5 ml/kg/hour for more than 6 hours in adults.

What are the KDIGO stages by creatinine ratio?

The NHS England algorithm endorsed by NG148 flags stage 1 at a ratio of 1.5 to 1.99, stage 2 at 2.0 to 2.99, and stage 3 at 3.0 or more or a creatinine above 354 micromol/L.

When does NICE say to ultrasound the kidneys in AKI?

Within 24 hours when there is no identified cause or a risk of urinary tract obstruction, and within 6 hours when pyonephrosis is suspected. Ultrasound is not routinely needed once the cause has been identified.

Which drugs should be stopped in a surgical patient with AKI?

NG148 names NSAIDs, aminoglycosides, ACE inhibitors, angiotensin receptor blockers and diuretics as drugs that cause or worsen kidney injury, and says consider temporarily stopping ACE inhibitors and ARBs during diarrhoea, vomiting or sepsis.

How is severe hyperkalaemia treated?

The UK Kidney Association guideline recommends 10 units of soluble insulin with 25 g glucose for moderate or severe hyperkalaemia, adds nebulised salbutamol 10 to 20 mg for severe hyperkalaemia (6.5 mmol/L or more), and gives intravenous calcium at a 6.8 mmol dose, equivalent to 30 ml of 10% calcium gluconate, when the ECG is affected.

AKI in Surgical Patients: CST Interview Clinical Station Answer

Q: What are the indications for urgent renal replacement therapy?

NG148 lists hyperkalaemia, metabolic acidosis, symptoms or complications of uraemia such as pericarditis or encephalopathy, fluid overload and pulmonary oedema, when any of these is not responding to medical management. The decision is based on the whole patient.

Acute kidney injury in a surgical patient is almost always pre-renal, from hypovolaemia, sepsis or a nephrotoxic drug, and NICE NG148 defines it by a creatinine rise of 26 micromol/L or more within 48 hours, a 50% rise within 7 days, or a urine output under 0.5 ml/kg/hour for more than 6 hours. The CST answer is to find and treat the cause, stop the nephrotoxins, stage the injury, treat hyperkalaemia and know the referral rules.

Key takeaways

According to NICE NG148, AKI is detected by a creatinine rise of 26 micromol/L or more within 48 hours, a 50% or greater rise within 7 days, or urine output below 0.5 ml/kg/hour for more than 6 hours.
The NHS England AKI algorithm, which NG148 cites, stages by the creatinine ratio: 1.5 to 1.99 is stage 1, 2.0 to 2.99 is stage 2, and 3.0 or more, or a creatinine over 354 micromol/L, is stage 3.
NG148's risk factors include chronic kidney disease with an eGFR under 60, heart failure, liver disease, diabetes, previous AKI, hypovolaemia, nephrotoxic drugs, contrast within the past week and age 65 or over.
NG148 says offer urgent ultrasound within 24 hours when there is no identified cause or a risk of obstruction, and within 6 hours when pyonephrosis is suspected.
NG148 says refer immediately for renal replacement therapy when hyperkalaemia, metabolic acidosis, uraemic complications, fluid overload or pulmonary oedema are not responding to medical management, and base that decision on the whole patient, not an isolated value.
The UK Kidney Association grades hyperkalaemia as mild at 5.5 to 5.9 mmol/L, moderate at 6.0 to 6.4 and severe at 6.5 or more.

How do I recognise acute kidney injury in a surgical patient?

AKI is recognised from the creatinine trend and the urine output, not from symptoms, which is why NG148 asks hospitals to have systems that flag oliguria of under 0.5 ml/kg/hour when the early warning score does not include it. On a surgical ward the first sign is usually a catheter bag that has not filled.

What does NICE NG148 say the risk factors are?

Chronic kidney disease, with an eGFR under 60 ml/min/1.73 m2 carrying particular risk
Heart failure, liver disease, diabetes and a history of AKI
Hypovolaemia, and oliguria under 0.5 ml/kg/hour
Drugs that cause or worsen kidney injury: NSAIDs, aminoglycosides, ACE inhibitors, angiotensin receptor blockers and diuretics
Iodine-based contrast within the past week
Age 65 years or over

In practice a 74-year-old on ramipril and a diuretic, who had gentamicin at induction and a contrast CT yesterday, and who has been vomiting since, carries almost every risk factor on the list. That is the typical CST scenario.

What is the immediate management from A to E?

Immediate management of AKI is ABCDE with a focus on circulation and potassium: assess volume status, correct hypovolaemia with a crystalloid bolus under NICE CG174, get a venous gas for potassium and acid-base, and put the patient on a cardiac monitor if the potassium is raised.

Circulation: pulse, blood pressure, capillary refill, jugular venous pressure, and a 500 ml crystalloid bolus over less than 15 minutes if the CG174 indicators of hypovolaemia are present
Circulation: catheterise and measure hourly urine output; check the catheter is not blocked before calling it oliguria
Disability: a venous gas for potassium, bicarbonate and lactate, and a glucose
Exposure: the drug chart, for every nephrotoxin to stop, and the fluid balance chart, for the losses you have not replaced

According to NICE NG148, consider temporarily stopping ACE inhibitors and angiotensin receptor blockers in adults with diarrhoea, vomiting or sepsis until the condition has stabilised. Stop NSAIDs, and ask pharmacy to dose-adjust everything else.

Which investigations stage and explain the injury?

The investigations are serial urea, creatinine and electrolytes to stage the injury, a urine dipstick to look for an intrinsic cause, and an ultrasound of the urinary tract when the cause is unclear or obstruction is possible. NG148 says the ultrasound is within 24 hours in those cases, and within 6 hours if pyonephrosis is suspected.

How is AKI staged?

The NHS England algorithm that NG148 endorses compares the current creatinine with a reference value. A ratio of 1.5 to 1.99 is stage 1, 2.0 to 2.99 is stage 2, and 3.0 or more, or an absolute creatinine over 354 micromol/L, is stage 3. A rise of more than 26 micromol/L within 48 hours triggers an alert on its own.

NG148 adds that haematuria and proteinuria on the dipstick, without infection or catheter trauma, should make you think of acute nephritis and involve nephrology. Do not routinely ultrasound once the cause is clear.

What is the definitive management?

Definitive management is treating the cause: restoring volume, controlling sepsis with source control, relieving obstruction, and withdrawing nephrotoxins. Most surgical AKI recovers once perfusion is restored, provided the insult is not repeated.

How is hyperkalaemia treated?

The UK Kidney Association guideline grades hyperkalaemia as mild at 5.5 to 5.9 mmol/L, moderate at 6.0 to 6.4 and severe at 6.5 or more. For moderate or severe hyperkalaemia it recommends 10 units of soluble insulin with 25 g of glucose, and for severe hyperkalaemia it adds nebulised salbutamol at 10 to 20 mg. Where the ECG is changed, intravenous calcium at a 6.8 mmol dose, which is 30 ml of 10% calcium gluconate, protects the myocardium.

Hyperkalaemia that does not respond to medical treatment is one of NG148's indications for immediate referral for renal replacement therapy, alongside metabolic acidosis, uraemic complications such as pericarditis or encephalopathy, fluid overload and pulmonary oedema.

When do I escalate, and who do I call?

Escalate to the surgical registrar for any AKI, and involve nephrology or critical care according to NG148's rules. The guideline separates immediate referral for renal replacement from a discussion within 24 hours.

Immediately, to a nephrologist or critical care: any indication for renal replacement therapy that is not responding to medical management
Within 24 hours, discuss with a nephrologist: a possible diagnosis needing specialist treatment such as vasculitis or myeloma, AKI with no clear cause, inadequate response to treatment, complications, stage 3 AKI, a renal transplant, or CKD stage 4 or 5
Urology, immediately: upper tract obstruction with pyonephrosis, a single kidney, or bilateral obstruction
Do not refer when there is a clear cause responding promptly to treatment

That said, NG148 is explicit that the decision to start renal replacement rests on the patient as a whole, not on an isolated urea, creatinine or potassium. Say that sentence; it is the one the panel wants.

How do I prevent AKI in the next patient?

Prevention is a risk assessment at admission, fluid balance that is kept up to date, nephrotoxins held during acute illness, and an eGFR from the past 6 months checked before contrast. NG148 says consider stopping ACE inhibitors and ARBs before contrast in patients with an eGFR under 30, and discuss patients on renal replacement with nephrology before contrast without delaying emergency imaging.

What is the interviewer listening for?

The NG148 definition stated as numbers: 26 micromol/L in 48 hours, 50% in 7 days, 0.5 ml/kg/hour for 6 hours
Volume assessed and corrected before anything else, with the catheter checked
The drug chart reviewed and the nephrotoxins named
The staging ratios and the ultrasound timings
The renal replacement indications, and the whole-patient sentence

What are the common mistakes?

Giving a diuretic for oliguria in a dry patient
Leaving the ACE inhibitor and the NSAID on the chart
Calling it AKI when the catheter is blocked
Quoting a potassium value as the trigger for dialysis rather than the response to treatment
Forgetting that contrast yesterday is a cause today

How this comes up at the CST interview

The CST management and clinical station scores a structured approach, knowledge, prioritisation and communication. AKI tests whether you assess volume before treating numbers, whether you know the NG148 thresholds, and whether you can explain a referral rule to a registrar on the phone.

coresurgeryinterview has 299 questions with AI-marked spoken practice, and its oliguric post-operative patient scenario rewards exactly this order: catheter, volume, drugs, potassium, staging, referral.

Acute Kidney Injury in Surgical Patients: Prevention, Staging and Management