Prerenal acute kidney injury (acute renal failure) - causes, symptoms & pathology

Osmosis from Elsevier
18 Jul 201606:02
EducationalLearning
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TLDRAcute kidney injury (AKI), previously known as acute renal failure (ARF), is a condition where kidney function rapidly declines, typically within days. It can be categorized into three types: prerenal, postrenal, and intrarenal AKI. The kidneys play a crucial role in regulating blood composition by filtering waste, balancing electrolytes, and maintaining water levels, also producing hormones. Blood enters the kidney through the renal artery, is filtered in the glomeruli, and the filtrate moves into the renal tubule, where reabsorption and secretion occur. Waste compounds like urea and creatinine are filtered, with some reabsorption back into the blood. The normal blood urea nitrogen (BUN) to creatinine ratio aids in diagnosing kidney function. Prerenal AKI occurs due to decreased blood flow to the kidneys, which can result from absolute or relative fluid loss, distributive shock, congestive heart failure, or renal artery issues. This leads to a reduced glomerular filtration rate (GFR), azotemia, oliguria, and activation of the renin-angiotensin system, causing increased reabsorption of sodium and water. Consequently, the BUN to creatinine ratio becomes greater than 20:1, urine sodium is less than 20 mEq/L, FENa is less than 1%, and urine concentration rises above 500 mOsm/kg. Understanding prerenal AKI is key to recognizing and addressing kidney function issues.

Takeaways
  • 🍂 **Acute Kidney Injury (AKI) Definition**: AKI is a rapid decrease in kidney function, previously known as acute renal failure (ARF), but now includes minor function declines.
  • 🧐 **Types of AKI**: AKI can be categorized into prerenal (before the kidneys), postrenal (after the kidneys), and intrarenal (within the kidneys).
  • 🔄 **Kidney Function**: Kidneys regulate blood composition by removing waste, maintaining electrolyte balance, controlling water levels, and producing hormones.
  • 🚰 **Blood Filtration**: Blood enters the kidney through the renal artery, is filtered in the glomeruli, and the filtrate moves into the renal tubule for further processing.
  • 🔁 **Reabsorption and Secretion**: Filtrate components can move back into the blood (reabsorption) or from blood to filtrate (secretion), with urea and creatinine being key waste compounds.
  • 📉 **BUN to Creatinine Ratio**: A normal ratio of blood urea nitrogen (BUN) to creatinine in the blood is 5-20:1, which is a diagnostic indicator for kidney function.
  • 🚨 **Prerenal AKI Causes**: It is caused by decreased blood flow to the kidneys, which can be due to absolute or relative fluid loss, or issues with the renal artery.
  • 🌊 **Glomerular Filtration Rate (GFR)**: A decrease in blood flow to the kidneys leads to a reduced GFR, resulting in less urea and creatinine being filtered and higher levels in the blood.
  • 🔍 **Azotemia and Oliguria**: Less blood filtration leads to azotemia (high nitrogen compound levels in blood) and oliguria (low urine output).
  • 🌀 **Renin-Angiotensin System Activation**: In response to decreased filtration, the renin-angiotensin system is activated, leading to aldosterone release and increased sodium and water reabsorption.
  • 🏥 **Diagnostic Indicators**: In prerenal AKI, urine sodium is typically less than 20 mEq/L, FENa (fractional excretion of sodium) is less than 1%, and urine concentration is greater than 500 mOsm/kg, often due to urea.
  • 📚 **Further Learning**: The video encourages viewers to explore more about postrenal and intrarenal AKI in subsequent videos.
Q & A

  • What is the medical term for a sudden decrease in kidney function that develops quickly?

    -Acute kidney injury (AKI) is the term used to describe a sudden decrease in kidney function that develops over a few days.

  • What was the previous term used to describe acute kidney injury?

    -The previous term used for acute kidney injury was acute renal failure (ARF).

  • How many types of AKI are there, and what are they?

    -There are three types of AKI: prerenal AKI, postrenal AKI, and intrarenal AKI.

  • What is the primary function of the kidneys?

    -The primary function of the kidneys is to regulate the components in the blood, including removing waste, maintaining electrolyte levels, regulating water balance, and producing hormones.

  • How does blood enter the kidney for filtration?

    -Blood enters the kidney through the renal artery and is filtered in tiny clumps of arterioles called glomeruli.

  • What is the process called when fluid or electrolytes move back from the filtrate into the blood?

    -The process is called reabsorption.

  • What are two waste-containing compounds that are filtered by the kidneys?

    -Two waste-containing compounds filtered by the kidneys are urea and creatinine.

  • What is the normal ratio of blood urea nitrogen (BUN) to creatinine in the blood?

    -The normal ratio of BUN to creatinine in the blood is between 5 and 20 to 1.

  • What is the term used to describe high levels of nitrogen-containing compounds in the blood due to decreased filtration by the kidneys?

    -The term is azotemia.

  • How does the renin-angiotensin system respond in a prerenal AKI situation?

    -In prerenal AKI, the renin-angiotensin system is activated, leading to aldosterone release by the adrenal glands, which signals the kidneys to reabsorb sodium.

  • What are the typical urine characteristics in a prerenal AKI situation?

    -In a prerenal AKI situation, urine typically has less than 20 mEq/L of sodium, a FENa (fractional excretion of sodium) of less than 1%, and a concentration greater than 500 mOsm/kg, mostly due to urea.

  • What are the common causes of prerenal AKI?

    -Common causes of prerenal AKI include major hemorrhage, blood loss, vomiting, diarrhea, severe burns, distributive shock, congestive heart failure, renal artery stenosis, and blockage by an embolus.

Outlines
00:00
🏥 Understanding Acute Kidney Injury (AKI)

Acute kidney injury (AKI) is a condition where kidney function rapidly declines, usually over a few days. It encompasses a range of kidney function impairments, from mild to severe, and was formerly known as acute renal failure (ARF). AKI is categorized into three types: prerenal, postrenal, and intrarenal, each indicating the location of the injury relative to the kidney. The kidneys' primary role is to regulate blood composition by filtering waste, maintaining electrolyte balance, and controlling water levels, while also producing hormones. Blood enters the kidney through the renal artery, is filtered in the glomeruli, and the filtrate either undergoes reabsorption or secretion. Key waste products like urea and creatinine are filtered, with some reabsorption occurring for urea. The normal blood urea nitrogen (BUN) to creatinine ratio aids in diagnosing kidney function. The filtrate ultimately becomes urine, excreted via the ureter, bladder, and out of the body, while the filtered blood drains into the renal vein. Prerenal AKI specifically results from decreased blood flow to the kidneys, which can stem from absolute or relative fluid loss, distributive shock, congestive heart failure, or issues with the renal artery itself. This leads to a reduced glomerular filtration rate (GFR), azotemia, oliguria, and activation of the renin-angiotensin system, resulting in increased reabsorption of sodium and water, higher BUN to creatinine ratios, and concentrated urine with low sodium excretion.

05:00
🔍 Recap and Further Exploration of AKI

The video concludes with a recap of prerenal acute kidney injury (AKI), emphasizing the reduced kidney function due to decreased blood flow. After providing a comprehensive understanding of prerenal AKI, the video encourages viewers to explore additional content on postrenal and intrarenal AKI through other videos. The video ends with a call to action for viewers to support the channel through Patreon donations, subscriptions, or by spreading the word on social media.

Mindmap
Keywords
💡Acute kidney injury (AKI)
Acute kidney injury, or AKI, refers to a sudden and rapid decline in kidney function, typically occurring within a few days. It is a critical condition that can lead to a range of health complications if not addressed. In the video, AKI is the central theme, as it discusses the different types and causes of kidney injury, as well as the implications for kidney function and overall health.
💡Acute renal failure (ARF)
Acute renal failure, or ARF, is an older term for what is now more broadly referred to as acute kidney injury (AKI). It specifically refers to a severe and sudden loss of kidney function. The video mentions that AKI is a more encompassing term that includes not just severe cases but also subtle decreases in kidney function.
💡Prerenal AKI
Prerenal AKI is a type of acute kidney injury that occurs due to a decrease in blood flow to the kidneys. It is caused by conditions that lead to a reduced supply of blood to the kidneys, such as significant blood loss, dehydration, or heart failure. In the video, prerenal AKI is discussed as one of the three main categories of AKI, with a focus on the mechanisms that lead to decreased kidney function in this case.
💡Glomeruli
Glomeruli are tiny clumps of arterioles within the kidneys where the initial filtration of blood occurs. They play a crucial role in the kidney's function by allowing the passage of waste and excess substances into the renal tubules, which will later form urine. The video explains that blood enters the glomeruli through the renal artery and is filtered, with the filtrate then moving into the renal tubule for further processing.
💡Glomerular filtration rate (GFR)
The glomerular filtration rate, or GFR, is a measure of how much blood the kidneys filter through the glomeruli each minute. It is an important indicator of kidney function. When there is a decrease in blood flow to the kidneys, as in prerenal AKI, the GFR also decreases, leading to less filtration of waste products like urea and creatinine.
💡Reabsorption
Reabsorption is the process by which certain substances, such as water and electrolytes, move back from the filtrate into the blood as it passes through the renal tubules. This is a key part of the kidney's function to maintain the body's balance of fluids and electrolytes. The video mentions that in prerenal AKI, the reabsorption of sodium and water increases, which contributes to the symptoms of the condition.
💡Urea
Urea is a waste product formed in the liver from the breakdown of proteins and is typically excreted by the kidneys. In the context of the video, urea is an important compound in understanding kidney function, as its levels in the blood can indicate the effectiveness of the kidney's filtration process. An increased reabsorption of urea in prerenal AKI leads to a higher blood urea nitrogen (BUN) to creatinine ratio.
💡Creatinine
Creatinine is another waste product that is filtered by the kidneys and excreted in urine. Unlike urea, creatinine is not significantly reabsorbed and thus provides a more stable measure of kidney function. The video discusses the normal ratio of blood urea nitrogen (BUN) to creatinine, which is a diagnostic tool for assessing kidney health.
💡Blood urea nitrogen (BUN)
Blood urea nitrogen, or BUN, is a measure of the amount of urea in the blood. The video explains that the normal BUN to creatinine ratio is between 5 and 20 to 1. In prerenal AKI, this ratio can become greater than 20:1 due to increased reabsorption of urea, which is a diagnostic clue for this type of kidney injury.
💡Oliguria
Oliguria refers to a condition where the production of urine is abnormally low. It is a common symptom of kidney dysfunction, including prerenal AKI. The video mentions that when the kidneys filter less blood due to decreased blood flow, less urea and creatinine are excreted, leading to oliguria.
💡Renal artery stenosis
Renal artery stenosis is a condition where the renal artery becomes narrowed, which can reduce blood flow to the kidneys. This is mentioned in the video as one of the causes of decreased blood flow that can lead to prerenal AKI. A narrowed renal artery can impair the kidney's ability to filter blood effectively.
Highlights

Acute kidney injury (AKI) is a condition where kidney function rapidly decreases, typically over a few days.

AKI is a broader term than acute renal failure (ARF), encompassing even subtle decreases in kidney function.

AKI can be categorized into three types: prerenal, postrenal, and intrarenal AKI, based on the location of the injury.

The kidney's role is to regulate blood composition, including waste removal and electrolyte balance.

Blood enters the kidney through the renal artery and is filtered in the glomeruli.

Reabsorption and secretion are processes where fluid and electrolytes move between the filtrate and blood.

Waste compounds like urea and creatinine are filtered by the kidneys, with some reabsorption occurring.

The normal BUN to creatinine ratio in the blood is between 5 and 20 to 1, which is a key diagnostic for kidney function.

The filtrate is converted into urine and excreted through the ureter, while filtered blood drains into the renal vein.

Prerenal AKI is caused by decreased blood flow to the kidneys, which can result from various factors.

Decreased blood flow can be due to absolute or relative loss of body fluid, or issues with the renal artery itself.

A decrease in glomerular filtration rate (GFR) leads to azotemia and oliguria in prerenal AKI.

The renin-angiotensin system is activated in prerenal AKI, leading to increased sodium and water reabsorption.

In prerenal AKI, the BUN to creatinine ratio is often greater than 20:1 due to increased urea reabsorption.

Urine sodium is typically less than 20 mEq/L, and the FENa is usually less than 1% in prerenal AKI.

The urine is more concentrated in prerenal AKI, often with a specific gravity greater than 500 mOsm/kg.

Prerenal AKI is characterized by the kidneys not functioning at full capacity due to reduced blood flow.

Further understanding of postrenal and intrarenal AKI is provided in additional videos.

Transcripts

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Acute Kidney InjuryRenal FunctionPrerenal AKIPostrenal AKIIntrarenal AKIKidney HealthMedical EducationBlood FiltrationElectrolyte BalanceHealth AwarenessUrine AnalysisFluid Regulation