What is Acute Kidney Injury (Kidney Failure)?
Acute kidney injury (AKI), previously referred to as acute renal failure, is a sudden and often reversible decrease in kidney function. However, signs of AKI may be subtle at first, with measures of functionality like urea and creatinine levels appearing normal. Early indications of AKI may primarily be a drop in the amount of urine produced. If untreated, AKI can lead to a build-up of water, sodium, and other substances in the body. It can also cause imbalances in body electrolytes. AKI is common, especially in hospitalized patients, and is seen in around 7% of hospital admissions and 30% of intensive care admissions.
There are various ways to determine if a patient has AKI, such as using the RIFLE, AKIN, or KDIGO criteria. The most commonly used method is the KDIGO criteria, which looks at increased creatinine levels, reduced urine output, or increased creatinine levels compared to a baseline measurement from the previous week.
The RIFLE criteria put kidney impairment into three categories – risk, injury, and failure – and two long-term outcomes – loss and end-stage renal disease. The category that shows the most severe impairment is used for classification. The AKIN criteria are similar but are also known as the ‘modified RIFLE’ criteria.
While the RIFLE and KDIGO methods may be more sensitive than the AKIN criteria, all three methods have shown similar effectiveness in predicting in-hospital death due to AKI.
What Causes Acute Kidney Injury (Kidney Failure)?
Glomerular filtration, the kidney’s process of filtering waste from blood, is influenced by the difference in pressure between the glomerulus (a network of tiny blood vessels) and Bowman’s space (a sac that holds the filtered urine). The pressure difference depends on the blood flow in the kidney, and changes according to the resistances of the incoming (afferent) and outgoing (efferent) blood vessels in the kidney. One common path that leads to Acute Kidney Injury (AKI), a sudden episode of kidney damage, is a reduction in renal blood flow. AKI is commonly divided into three types: prerenal, intrinsic renal (or intrarenal), and postrenal, each with their own specific causes.
Prerenal AKI is due to anything that lowers blood flow to the kidney. This can be part of a widespread lack of blood flow throughout the body, due to low blood volume or due to a specific lack of blood flow to the kidneys, such as from a narrowing of the kidneys’ arteries or a tear in the aorta. However, the function of the tubules (tubes where the urine passes) and glomerulus in the kidney tend to be normal at first. Some examples of how prerenal AKI can happen include blood loss, significant burns, vomiting, diarrhea, heart attack, septic shock, allergy shock, and medication side effects.
Intrinsic renal AKI occurs when there’s a problem with the glomerulus or the tubules, such as when they’re damaged or inflamed. Conditions like acute tubular necrosis and acute interstitial nephritis can cause intrinsic renal AKI. Prolonged lack of oxygen to the kidneys, severe infection, and substances that cause harm to the kidneys are common causes. The resulting damage to the kidney can lead to the release of substances that constrict blood vessels. If the cause of a prerenal injury lasts long enough, it can cause cellular damage and become an intrinsic renal injury. Some examples include drug reactions, infections, autoimmune conditions, and genetic conditions.
Postrenal AKI occurs when there’s a blockage that prevents urine from leaving the kidneys. This can lead to a buildup of urine, which then prevents new urine from being filtered. It’s important to know that a blockage affecting one kidney might not always lead to AKI, especially if it happens slowly, because the other kidney can make up for loss in function. If the blockage isn’t removed, it can lead to a serious condition called End Stage Renal Disease (ESRD). After the obstruction is removed, up to half of patients may experience increased urine production, which can cause severe complications like dehydration and electrolyte imbalances. The most common cause of postrenal AKI is a blockage of the urinary exit, often due to an enlarged prostate in older men, abnormalities in the pelvic structure in older women, and kidney stones in younger patients.
Kidney stones can block any part of the urinary system. The size and position of the stone decides whether it will cause AKI, and it’s a prominent cause in those with only one kidney. Some stones grow rapidly and often cause blockages. Other causes include tumors, blood clots, and nerve-related bladder problems. For older men, an enlarged prostate is often the cause of blockage. Conditions like fibrosis in the area behind the abdominal cavity, pregnancy, constipation, pelvic organ drop, tumors in the pelvic area, or a narrowed foreskin can also cause blockages.
Risk Factors and Frequency for Acute Kidney Injury (Kidney Failure)
Acute kidney injury (AKI) is often seen in patients who are in the hospital. In fact, in the United States, it’s present in 1% of all people when they’re first admitted to the hospital. The chance of getting AKI while you’re in the hospital ranges between 2% to 5%. It’s even higher in intensive care units, with up to 67% of patients getting it. As a result, this condition contributes to longer hospital stays and poorer patient outcomes.
- Acute kidney injury is frequently observed in hospitalized patients.
- In the United States, on admission, 1% of all hospital patients have it.
- The rate of developing AKI during a hospital stay is between 2% and 5%.
- In intensive care units, up to 67% of patients may develop AKI.
- AKI contributes to extended hospital stays and deteriorating patient health.
Signs and Symptoms of Acute Kidney Injury (Kidney Failure)
The assessment for Acute Kidney Injury (AKI) should focus on understanding the underlying cause and how quickly it has developed. This usually involves an in-depth examination of the patient’s history and physical condition. Any signals of insufficient blood volume, such as low blood pressure, or potential causes like vomiting or diarrhea, should be investigated. Over-the-counter drugs like NSAIDs could also be a contributing factor. It is necessary to distinguish between AKI and Chronic Kidney Disease (CKD), as both have different symptoms and CKD can also increase the risk of developing AKI. Usual symptoms of CKD include chronic tiredness, loss of appetite, frequent urination at night, disrupted sleep patterns, excessive urination, and itching. Further, one’s medical history could reveal existing health conditions that can help pinpoint the cause of AKI, such as liver disease or a history of blood clots that demanded blood thinners. Laboratory tests are not always sufficient to identify the cause of AKI, making patient history and physical examinations essential.
The most common causes of AKI in patients admitted to the hospital include:
- Acute Tubular Necrosis (ATN), accounting for 45%
- Prerenal disease, 21%
- AKI arising from CKD, 13%
- Urinary tract blockages, 10%
- Glomerulonephritis or vasculitis, 4%
- Acute Interstitial Nephritis (AIN), 2%
- Atheroemboli, 1%
Observing the patient’s urine output can also provide hints. For example:
- Scarce urination could indicate AKI.
- Sudden lack of urine may suggest an obstruction, inflammation of the kidney’s filters (glomerulonephritis), or restricted blood flow.
- Excessive urination could be a symptom of nephropathy after the removal of an obstruction, or acute interstitial nephritis, which affects the kidney tubules.
A thorough physical examination can yield critical clues about the cause of AKI. Checking how the patient’s blood pressure changes when they stand up can indicate low blood volume. Additionally, skin abnormalities like speckled patterns, fingertip ischemia, lupus rash, or purpuras could signify vasculitis, while a fever rash could indicate drug-induced AIN. Other signs to look for include marks from intravenous drug use, skin infarcts, and decreased skin elasticity, which signifies low blood volume.
Other physical traits such as yellowing of the eyes or skin in liver disease, issues with the heart and blood vessels, or cyanosis of the extremities might provide clues. Similarly, multiple myeloma presents with a specific type of eye abnormality, and diabetes may reveal specific changes in the retina. Other evidence such as joint swelling, heart murmurs, or irregular rhythm could be important as well. All these can help determine the cause of AKI.
Testing for Acute Kidney Injury (Kidney Failure)
When a condition called acute kidney injury (AKI) is suspected, a doctor will conduct a detailed evaluation to try and identify the cause. There are various types of kidney conditions that might be at play, including ones that occur before, within or after the kidney. The doctor will try to pinpoint when symptoms first started in order to better understand the cause; this is especially helpful when patients are in the hospital. For instance, any significant, sudden changes in creatinine levels likely mean that something happened in the 24-48 hours prior to trigger the condition.
One very common cause of AKI is iodinated contrast agents – chemicals sometimes used in medical scans. So, the doctor will always check if the patient recently done any medical scans that use such agents. Moreover, the physician will review any medications the patients are currently taking, and check whether the doses need to be adjusted. In some cases, even common medications can contribute to AKI.
People with AKI symptoms should have a comprehensive panel of tests, including a check of the electrolyte levels in their urine, which might help identify a cause. Other key tests include checks for proteins, osmolality (which shows the concentration of a solution), and albumin-to-creatinine ratios in the urine. It might be necessary for older patients to be tested for monoclonal gammopathy and multiple myeloma, which are conditions that can also cause AKI.
Besides, different imaging methods, such as ultrasound or CT scans, can help to rule out or confirm if AKI resulted from any blockages. Sometimes, under a microscope, the urine can reveal signs like brown casts or white blood cells, which are typical of certain AKI conditions.
Creatinine levels in the blood are usually checked to test for AKI, but other biomarkers might be more sensitive and show up earlier during AKI. Some examples include the plasma and urine levels of an enzyme called neutrophil gelatinase–associated lipocalin (NGAL) or binding proteins related to kidney injuries. However, tests for these biomarkers aren’t widely available and still need more research for validation.
In some instances, a kidney biopsy might be a valuable tool. This procedure, which involves taking a small piece of kidney tissue for examination, is mainly recommended when kidney function is rapidly declining without an apparent cause or when several potential causes are possible. Since this procedure involves some risks, such as bleeding, it should be performed carefully, especially in patients with coagulation disorders.
Finally, the doctor may also calculate some kidney function parameters to distinguish between different causes of AKI. However, these calculations aren’t always definitive, as many common medicines can affect the results. Therefore, there’s no reliable stand-alone test to identify AKI. The patient’s clinical presentation must always be considered in conjunction with the test results.
Treatment Options for Acute Kidney Injury (Kidney Failure)
Acute Kidney Injury (AKI), in which the kidneys suddenly stop working properly, can be difficult to diagnose since it can resemble other conditions. One method for determining whether AKI has resulted from process changes before the kidneys (prerenal) or damage to the kidney’s filters (Acute Tubular Necrosis or ATN), is through a fluid challenge. This involves closely monitoring the patient’s urine output and how their kidneys function after they’re hydrated. If the kidneys improve after hydration, this suggests the AKI is prerenal. However, if they have ATN or other types of intrinsic kidney damage, their recovery could take weeks to months. During this recovery phase, the use of diuretics (medications which increase urine output) might be necessary to prevent fluid overload.
Avoiding further harm to the kidneys is crucial. This can mean avoiding certain drugs that can harm the kidneys (nephrotoxic drugs) and adjusting dosages of medications for patients who have developed AKI. Regulating the intake of potassium and phosphorus in one’s diet is also usually suggested.
When the potassium levels in the blood become too high (hyperkalemia), immediate treatment is necessary. There are several options; these include eating a low potassium diet, administering certain medications that can lower potassium levels in your body, and in serious cases when other treatments have failed, dialysis may be considered.
Patients with AKI often experience fluid overload. This needs to be corrected quickly to avoid complications related to the lungs or heart. Usually, diuretics are used to restore normal fluid levels. In some instances, renal replacement therapy, which performs the role of the kidneys, may be required for a short period of time until kidney function recovers. This can include standard hemodialysis or a slower, continuous form of it for patients who may not handle regular dialysis well. Adjusting for other metabolic abnormalities may be part of the treatment regime too.
Additional treatments will depend on the cause of AKI. For example, certain medications might be prescribed for kidney issues related to liver conditions (hepatorenal syndrome) or heart problems (cardiorenal syndrome). For blockages beyond the kidneys (postrenal obstruction) due to benign prostatic hypertrophy or obstructive calculi, surgery might be necessary to relieve the obstruction.
What else can Acute Kidney Injury (Kidney Failure) be?
When trying to identify the cause of acute kidney injury (AKI), many different conditions must be considered. These could include kidney stones, long-term or sudden-onset kidney disease, low fluid levels in the body, internal bleeding in the stomach or intestines, decreased heart function, urinary tract infections, or blockage in the urinary tract.
In some rare cases, high levels of a substance called creatinine, a common marker used to measure kidney function, can increase not because of kidney disease but due to excessive consumption of protein or dietary supplements. This is important to keep in mind when trying to understand the reason behind a kidney injury.
What to expect with Acute Kidney Injury (Kidney Failure)
In most cases of prerenal AKI, which is a kind of kidney injury, patients can fully recover if the underlying issue is treated promptly. But, if this underlying issue persists, it may lead to ATN, another type of kidney damage that might not be fully reversible. Importantly, while each individual episode of kidney injury might see a complete or partial recovery, repeated episodes can progressively worsen kidney function.
Thus, it is very important to closely monitor these patients to ensure their kidney function returns to normal or until a new normal range is determined. The in-hospital death rate for AKI is around 40% to 50%, and for patients in intensive care units, it’s more than 50%. The following factors can affect the prognosis of patients:
- Older age
- Length of illness
- Fluid balance
- Use of drugs that increase urine production
- Decreased urine output
- Low blood pressure
- Need for medication to strengthen heart contractions
- Involvement of multiple organs
- Infection that spreads throughout the body
- Number of blood transfusions
In the long run, at least 12% to 15% of AKI patients might need permanent dialysis, a treatment to substitute the normal function of kidneys. The risk of death is higher in patients with high APACHE III scores, which is a system to measure the severity of disease, advanced age, and persistently elevated creatinine levels, which is an indicator of kidney function.
Possible Complications When Diagnosed with Acute Kidney Injury (Kidney Failure)
Acute Kidney Injury (AKI) can lead to several complications that may be associated with a higher risk of death. Some complications are directly tied to AKI, and these can be easily tracked. These include too much potassium in the blood (hyperkalemia), water retention causing swelling (volume overload), a harmful increase in acid in the body’s fluids (metabolic acidosis), and low sodium levels in the blood (hyponatremia). However, assessing the impact of other complications, such as inflammation and infection, on death rates linked to AKI is more challenging.
The most frequent complications of AKI include:
- Hyperkalemia: too much potassium in the blood which can cause irregular heart rhythms and, in serious cases, can be considered a medical emergency.
- Metabolic acidosis: a condition requiring a prescription of bicarbonate or citrate buffers to balance the body’s acid levels.
- Hyperphosphatemia: too much phosphate in the blood, usually prevented by reducing dietary consumption or using phosphate binder medications.
In addition to these, a patient may experience lung congestion due to fluid overload (pulmonary edema), and swelling due to the body’s inability to get rid of excess water (peripheral edema). This is particularly common during the low-urine-volume phase of Acute Tubular Necrosis (ATN), a specific type of AKI. It may require the use of diuretics or renal replacement therapy.
AKI can also lead to other organ-related complications such as:
- Cardiovascular issues: these include heart failure due to fluid overload (attributable to low-urine-volume AKI), irregular heart rhythms due to acidosis and electrolyte imbalances, cardiac arrest resulting from metabolic imbalance, heart attack, and inflammation of the heart’s lining (pericarditis).
- Gastrointestinal problems: these typically include nausea, vomiting, gastrointestinal bleeding, loss of appetite, and high amylase levels. When there is a suspicion of inflammation of the pancreas (pancreatitis), serum lipase levels should be checked.
- Neurologic signs from high urea levels in the blood (uremia): these may include lethargy, excessive sleepiness, disturbed sleep-wake cycle, and cognitive impairment.
Preventing Acute Kidney Injury (Kidney Failure)
For individuals who have developed a condition called Acute Kidney Injury (AKI), there are several important tips to help preserve kidney health. These include avoiding substances that can harm the kidneys (nephrotoxic agents) and staying safe from dehydration. The use of certain medications like Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) could lead to a kidney disorder, known as interstitial nephritis, that can result in AKI or worsen an existing case.
There are other medications, such as Angiotensin-converting enzyme inhibitors and angiotensin receptor blockers, which can interfere with how the kidneys function. The decision to use these medications for someone with AKI depends on their overall health condition and must be assessed on a case-to-case basis.
