Acute kidney injury after surgery: causes, warning signs and recovery

The kidneys filter waste products from the blood and balance fluid and salts. The NHS explains that acute kidney injury (AKI) is when something suddenly causes the kidneys to stop working as well as they should. Kidney Research UK adds that it is a sudden upset to the kidney that is not necessarily a physical injury, and that it can cause partial or complete loss of kidney function that is temporary or longer lasting.

When it occurs after an operation it is often called post-operative AKI. It is not a single disease with one cause. It is a label for a drop in kidney function in the days after surgery, and the reasons vary from person to person. For most people it is picked up and treated in hospital, often before they notice anything themselves.

Kidney Research UK lists reduced blood supply to the kidney, caused by bleeding, heart failure, infection and dehydration, as a cause of AKI and gives an operation as an example of when this can happen. The NHS lists infections or sepsis, dehydration, low blood pressure or blood loss, blockages, long-term kidney, heart or liver conditions, certain medicines, and the contrast dye used in some scans among the causes.

NICE guidance on AKI says the risk should be assessed before surgery and be included in the routine discussion of the risks and benefits of the operation. It notes that increased risk is associated with:

• emergency surgery, especially when there is sepsis or low fluid volume

• surgery inside the abdominal cavity (intraperitoneal surgery)

• chronic kidney disease, with those with an eGFR below 60 at particular risk

• diabetes, heart failure and liver disease

• age 65 or older

• use of drugs that can cause or worsen kidney injury around the time of surgery, in particular NSAIDs after surgery

The NHS stresses that many people with AKI do not get symptoms, particularly if it is mild. When symptoms do occur, the NHS lists:

• peeing a lot less than usual

• feeling very thirsty

• feeling sick or being sick

• swollen feet or legs

• feeling tired, dizzy, confused or sleepy

• feeling breathless, especially when lying down

The NHS says to ask for an urgent GP appointment or get help from NHS 111 if you think you may have symptoms of AKI. After an operation, you will normally be monitored in hospital, and nurses will watch your urine output and fluids. Tell staff if you are passing much less urine than usual, are very thirsty, or feel confused or breathless.

Kidney Research UK says the most obvious sign is a reduction in the amount of urine passed, particularly with severe illness or a recent operation, but it also notes that some people with AKI, especially when caused by back pressure from a blockage, continue to pass normal amounts. A normal urine volume does not rule it out.

The NHS says AKI is diagnosed with a blood test that checks creatinine, a waste product made by the muscles and removed by the kidneys. A higher level than usual means the kidneys are not working as well as they should. NICE advises comparing the creatinine with the person’s baseline.

Doctors may also ask for a urine sample, ask how often you have been peeing, and check your pulse and blood pressure. Depending on the suspected cause, the NHS says you may have an ECG or scans such as an X-ray, CT scan or ultrasound. Kidney Research UK adds that doctors measure urine output per hour, test the urine for signs of infection, inflammation, protein or blood, and in some cases carry out a kidney biopsy.

If AKI is severe or the cause is unclear, the NHS says you may be referred to a kidney specialist (nephrologist) or admitted to hospital.

Treatment depends on how severe the injury is and what is causing it. The NHS says it may be given in hospital and may include medicine to treat an infection, raise blood pressure, reduce swelling or calm the immune system, stopping or changing any medicine that could be causing damage, fluids through a drip, a catheter to drain urine, and surgery to remove a blockage.

Kidney Research UK describes close monitoring of fluid in and out, extra fluids if you are short of fluid, stopping drugs such as ibuprofen until kidney function improves, and treatments to relieve blockages. If AKI is severe, the NHS says a machine can do the kidneys’ work of cleaning the blood (dialysis), usually just for a few days or weeks until the kidneys recover.

The NHS says AKI is serious and can be life-threatening if not treated, but many people recover fully within a few weeks with no long-term effects. If the AKI is more serious, recovery can take several months. You will have regular blood tests and check-ups afterwards to make sure the kidneys are working as expected.

Some people are left with permanent kidney damage, causing chronic kidney disease. The NHS says this is more likely if the AKI was severe or you already have other long-term health problems. Kidney Research UK adds that chronic kidney disease can also develop two to three years after an episode, and that a small proportion do not recover and reach end-stage kidney disease.

NICE says people who have had AKI, or their carers, should be given information about long-term treatment options, monitoring, self-management and support.

If you have had AKI before or are at higher risk because of age or medication, the NHS advises staying hydrated, so your pee is pale and regular throughout the day, especially in hot weather or when being sick or having diarrhoea. It also advises speaking to a doctor before taking any new medicines or supplements, and knowing the symptoms to watch for.

Before a future operation, tell the surgical and anaesthetic team that you have had AKI. This allows them to take account of it in planning fluids and in choosing painkillers.

AKI is usually detected and managed within the hospital where you had your operation, whether NHS or private. If you need intensive treatment such as dialysis, this is arranged by the hospital caring for you. Follow-up blood tests are usually arranged through your GP. Tell any clinician who treats you that you have had AKI.