What is Perioperative Acute Kidney Injury?
Acute kidney injury (AKI) refers to a sudden drop in kidney function, often due to changes in blood flow or exposures to harmful substances. Medical professionals traditionally gauge kidney function through serum creatinine levels and urine output. However, during surgeries, these markers might not change until the kidney loses half of its filtering capacity or urine output decreases for different reasons. This has led to the division of AKI into two types: 1) subclinical AKI where lab results and urine output do not meet the current guidelines, and 2) functional AKI where lab results and urine output do follow the guidelines.
There are three main classifications of AKI: Acute Kidney Injury Network (AKIN), Risk, Injury, Failure, Loss, ESKD (RIFLE), and Kidney Disease Improving Global Outcomes (KDIGO). They essentially evaluate serum creatinine levels, glomerular filtration rate (GFR – a measure of kidney function) and urine output. The classification depends on certain criteria which are used to define whether the kidney function has been compromised.
AKIN, for example, classifies AKI if, within 48 hours, creatinine levels increase by 1.5 times, creatinine rises by 0.3 mg/dL or more, or urine output is less than 0.5 mL/kg/h for over 6 hours. RIFLE, on the other hand, defines AKI if in 7 days, creatinine doubles, GFR decreases by more than 50%, or urine output is below 0.5 mL/kg/h. KDIGO classifies AKI by an increase in serum creatinine levels within 48 hours or if urine output is less than 0.5mL/kg/h for 6 hours.
In comparing the timeline of AKI and acute kidney disease, the Acute Dialysis Quality Initiative Group explains that acute kidney injury occurs within 48 hours or less, while acute kidney disease is when AKI lasts 7 or more days.
Newly discovered biomarkers can detect AKI, even when traditional criteria are not met, which is referred to as “subclinical AKI.” These biomarkers can reveal kidney damage regardless of its filtration capability. On the other hand, traditional criteria like creatinine level and urine output represent the kidney’s filtration function rather than its structural damage and thus are termed “functional AKI.”
It could be easy to overlook AKI cases that do not match traditional criteria, but research shows that even a slight rise in creatinine levels during surgery is linked to a 50% increase in mortality and lengthier hospital stays.
Acute kidney injury after surgery (or perioperative AKI) is a serious but commonly overlooked issue in patients who recently had surgery. This is increasing in occurrence due to the aging population and the growing number of people with multiple health conditions. Post-surgery AKI elevates the risk of mortality in the short and long term, raises hospital costs, and uses up more healthcare resources compared to patients without post-surgery AKI. Detecting AKI early and starting appropriate treatments can help prevent it from progressing to chronic kidney disease, needing renal replacement therapies (RRT), and even death.
What Causes Perioperative Acute Kidney Injury?
Perioperative acute kidney injury (AKI) is a sudden worsening of kidney function that can happen within hours or days following surgery. The cause of perioperative AKI can be due to several factors, including:
- Blood flowing too quickly through the kidneys
- Body-wide inflammation caused by injury and surgical stress
- Use of nonsteroidal anti-inflammatory drugs (NSAIDS) during and after surgery
- Previously high levels of creatinine in the blood (>1.2 mg/dL), a substance that the kidneys usually remove
- Being older in age
- Having African American heritage
- Preexisting high blood pressure
- Existing active congestive heart failure
- Chronic kidney disease
Other risk factors that might contribute to perioperative AKI include having pulmonary disease, insulin-dependent diabetes, peripheral vascular disease, presence of ascites (excess fluid in the abdomen), high body mass index, and also suffering from active congestive heart failure.
Risk Factors and Frequency for Perioperative Acute Kidney Injury
Perioperative AKI, or sudden kidney damage or failure during or immediately after surgery, is a common but often overlooked medical problem. Certain groups of people are more at risk of perioperative AKI: these include people undergoing gastric bypass or liver transplant surgery, older adults, African-Americans, people with pre-existing conditions like CKD, hypertension, congestive heart failure, pulmonary disease, insulin-dependent diabetes, peripheral vascular disease, ascites, and those with a high body mass index.
It is estimated that this condition affects about 12% of hospital patients each year. In 2017, research indicated a shocking 2,147 cases of AKI per million people per year, with 30% to 40% of these cases seen in surgical patients. Among those undergoing surgery, patients undergoing cardiac surgery with the use of cardiopulmonary bypass are most at risk.
In a study of 39,369 surgical patients using specific AKI criteria, 6% were found to have perioperative AKI. Even a minor change in serum creatinine levels, a key marker of kidney health, showed a significant increase in death risk and an extended hospital stay by two days. Another study showed a mortality rate of 13.3% in patients with perioperative AKI compared to only 0.9% without. For patients undergoing cardiac surgery, it was found that between 25% and 30% experienced perioperative AKI.
Signs and Symptoms of Perioperative Acute Kidney Injury
Perioperative acute kidney injury, or a sudden decline in kidney function during or after surgery, often has nonspecific signs. The symptoms one might notice are dependent on how severe the kidney damage is, as well as the underlying cause, like low blood pressure or low blood volume. It’s been observed that low blood pressure during surgery can often lead to this condition. This can happen either before the cut is made, which is normally preventable, or after it, where it’s harder to avoid.
Low blood pressure after the cut is made can happen due to a variety of reasons, like blood loss, changes in pain sensation, patient positioning, or compression of blood vessels. Research shows that half of all patients experience low blood pressure during surgery, and this risk quadruples after the cut is made.
The symptoms of perioperative acute kidney injury are similar to kidney injuries from other causes and may include:
- Reduced urine output
- Nausea and vomiting
- Dizziness
- Swelling due to fluid buildup
Testing for Perioperative Acute Kidney Injury
Medical science continues to develop better ways of detecting Acute Kidney Injury (AKI) before it has a significant impact on the kidneys. One of these advancements involves the use of AKI biomarkers. Biomarkers are indicators of changes or events in the body. In this case, they alert us to early stress on the kidney tubules. These stresses can be triggered by intensive procedures, like surgeries or cardiopulmonary bypass. The presence of certain biomarkers can also suggest the underlying cause of the kidney damage as specific types are released in response to specific injuries. For example, specific biomarkers called TIMP-2 and IGFBP-7 are associated with the onset of kidney events, including death, long-term kidney dysfunction, and the need for dialysis.
NGAL, KIM-1, and Cystatin C are other biomarkers that researchers are studying. NGAL, in particular, is known to show an uptick in both blood and urine up to 24 hours before increased levels of creatinine. Creatinine is another indicator of kidney function which typically rises in the blood when there’s damage to the kidneys. So, an increase in NGAL before creatinine suggests it may be a useful early warning sign of kidney damage.
Cystatin C is another biomarker that scientists are looking at as a possible alternative to creatinine. It’s a small, charged molecule that’s filtered out of the bloodstream in the kidneys, where it’s then broken down by kidney cells. Since it’s usually not found in the urine of healthy people and has a short lifespan, it could be useful as an indicator of how well the kidneys are functioning and the health of the kidney cells.
However, there’s still work to be done in making these biomarkers more widely available outside of research settings. More studies are needed to confirm whether they can help detect early signs of kidney damage and assess kidney function before conventional indicators, such as creatinine levels and urinary output, begin to show abnormalities. This could lead to earlier diagnosis and treatment of AKI, which could potentially save lives and prevent further kidney damage.
Treatment Options for Perioperative Acute Kidney Injury
Finding a successful treatment for sudden kidney injury during or after surgery has been difficult. Although many agents showed promise, none have shown effectiveness in improved real-world medical care. When acute kidney injury happens during or after surgery, providing a goal-oriented treatment to achieve suitable heart function and oxygen delivery has shown to decrease death rates from kidney injuries.
Unfortunately, certain indicators of decreased kidney blood flow, such as the buildup of lactic acid or a drop in blood pressure during surgery, tend to show up late. To ensure proper blood flow to the kidneys, high volumes of fluids are often administered. If fluids aren’t enough, medications that enhance heart function (“inotropes”) may be necessary. Limiting fluids isn’t generally advised, since a generous fluid regimen is safer for patients.
Some medications have been debated for kidney injury treatment. For instance, dopamine was once thought to be helpful, but that hasn’t been proven in studies and current guidelines recommend avoiding dopamine for kidney injury.
The guidelines do support using diuretics (drugs that help to eliminate fluids from the body) to treat low blood volume, but they don’t seem to prevent kidney injury. Other medicines like fenoldopam and atrial natriuretic peptide (ANP) have shown potential to reduce the need for kidney treatment, but their usage is limited due to their ability to cause a drop in blood pressure.
Current kidney disease guidelines suggest specific methods to help prevent kidney injuries such as avoiding harmful substances, maintaining optimal blood volume to keep adequate blood pressures, watching blood sugar levels, and monitoring kidney function indicators. Early implementation of these methods can help to reduce the likelihood of kidney injury in post-surgery patients.
Prompt referral to a kidney specialist is crucial for managing acute kidney injury. Studies have found that delayed recognition of kidney injuries can lead to chronic kidney disease and lowered survival rates. Kidney treatment should be started immediately when progressive kidney injury is identified, or if there are life-threatening complications, such as severe fluid overload, metabolic disorders, or harmful changes in body salts.
In addition to standard treatments, some experimental strategies are being investigated to prevent kidney injury around the time of surgery. One technique called ‘remote ischemic preconditioning’ has shown potential. This process involves applying short periods of restricted blood supply to the limbs to prepare the body for long periods of restricted blood supply during surgery. Given its non-invasive nature and some promising initial results, this technique could be easily integrated into standard practice.
What else can Perioperative Acute Kidney Injury be?
It’s important to note that many conditions could lead to Acute Kidney Injury (AKI) after an operation, such as changes in blood flow, exposure to harmful substances, body-wide inflammation due to damage-associated molecular patterns (DAMP), and blockages in the urinary tract. If a patient has a reduced urine output or ‘oliguria’ – a key symptom of AKI, we should look into blockage in the urinary tract as a possible cause. Such blockages are commonly seen in patients who have undergone surgeries related to the colon, urinary tract, or female reproductive organs.
Moreover, drugs causing an inability to pass urine should also be ruled out. In a situation where a patient has a Foley catheter (a tube to drain urine from the bladder), it’s crucial to check if the catheter is blocked or kinked. It’s also worth considering if the body is making more of the antidiuretic hormone (which helps the body retain water, leading to less urine production) due to pain, nausea, or the surgical process itself. Another possible cause could be an increased secretion of aldosterone, a hormone that can cause the kidneys to retain sodium and water, increasing blood volume and thereby decreasing urine production.
What to expect with Perioperative Acute Kidney Injury
Perioperative AKI, or acute kidney injury during the perioperative period, is linked with a ten times higher risk of death. It also results in decreased chances of long-term survival and a greater likelihood of developing chronic kidney disease. This may lead to the need for regular hemodialysis after being discharged from the hospital.
The need for renal replacement therapy, a treatment option when the kidneys fail, as a result of AKI also independently increases the risk of death.
Possible Complications When Diagnosed with Perioperative Acute Kidney Injury
In simpler terms, if someone develops a kidney injury around the time of surgery (termed as “perioperative AKI”), they are at greater risk of developing long-term kidney disease. This might mean they need ongoing therapy to replace the functions the kidneys normally perform. The seriousness of the complications they may experience depends on the severity of the initial kidney injury. Below is a thorough list of potential complications someone with perioperative AKI may face:
- Hyperkalemia (too much potassium in blood)
- Hyperphosphatemia (high levels of phosphate in blood)
- Hyponatremia (low levels of sodium in blood)
- Hypermagnesemia (excessive magnesium in blood)
- Hypocalcemia (low levels of calcium in blood)
- Metabolic acidosis (too much acid in the body)
- Uremic encephalopathy (brain disorder due to waste build-up in the blood)
- Volume overload (too much fluid in the body)
- Hypertension (high blood pressure)
- Circulatory collapse (a severe, sometimes fatal, drop in blood pressure)
Preventing Perioperative Acute Kidney Injury
People who have suffered kidney damage during surgery should be advised on how to take care of their kidneys. This includes avoiding certain harmful agents that may further damage the kidneys. Some non-steroidal anti-inflammatory drugs (NSAIDs) can cause issues like reduced blood flow to the kidneys and inflammation, which can lead to or worsen kidney damage. Certain blood pressure medications, like Angiotensin-converting enzyme inhibitors and angiotensin receptor blockers can also affect the kidneys’ ability to control blood flow. However, it’s presently a topic of discussion whether or not to avoid these medications during the surgical period.
