Week 13: Chp 62: Acute Kidney Injury Flashcards
What is Acute kidney Injury?
condition characterized by an acute, rapid loss of renal function
- a rapid and progressive azotemia, an accumulation of nitrogenous waste products such as urea, nitrogen, and creatinine and progressive increases in potassium
- oliguria may be present
- uremia may be present
- is reversible if addressed in a responsive and timely manner
Modifiable risk factors
sepsis, administration of contrast media, and exposure to nephrotoxins
Oliguria
a reduction of urine output to 400 mL/day
- may be present in acute kidney injury
- may be at risk for CKF (chronic kidney failure) if circulating fluid volume is not returned to normal
Uremia
renal function decline that involves multiple body systems
3 Major categories of Acute Kidney Injury (AKI)
- Prerenal causes
- Intrarenal causes
- Postrenal causes
Prerenal Causes
most common cause of AKI
- result of external factors (those that are not related to the anatomical structures of the urinary system) that reduce renal blood flow and lead to decreased glomerular perfusion and filtration
- prerenal causes: hypovolemia, decreased cardiac output, decreased peripheral vascular resistance, and vascular obstruction (these can affect circulation)
Decreased Renal Perfusion affects the clearance of what?
waste products
-known as Azotemia (inability to get rid of waste products)
Azotemia
happens when your kidneys can not get rid of enough nitrogenous waste
-affects clearance of waste products
What affects circulation?
hypovolemia, decreased cardiac output, decreased peripheral vascular resistance, and vascular obstruction
>these are prerenal causes
What happens when the renal system senses the decrease in perfusion?
the renin-angiotensin-aldosterone system (RAAS) is stimulated
-the RAAS is a compensatory mechanism that conserves sodium and water in order to maintain blood pressure
-the result is low urine output with an increase in BUN and creatinine (ratio of 10:1) and an inability of the kidneys to conserve sodium
>if renal perfusion remains compromised and compensatory mechanisms fail, intrarenal damage to renal tissue may occur
Intrarenal causes
involve direct damage to the renal parenchymal tissues, resulting in impaired nephron functioning
Nephron
functional unit of the kidney
-any direct assault to the nephron significantly compromises the perfusion and filtration of waste products
Damage to Nephron occurs as a result from?
prolonged ischemia, exposure to nephrotoxins such as aminoglycoside antibiotics, contrast dye used in imaging studies, hemoglobin released from hemolyzed RBCs, or myoglobin released from necrotic muscle cells
Complications of nephrotoxins
cause crystallization or damage to the epithelial cells of the tubules
Complications if hemoglobin and myoglobin
block the tubules and cause renal vasoconstriction
Causes of AKI (intrarenal)
-acute glomerulonephritis and acute tubular necrosis (ATN)
Intrarenal causes: Acute tubular necrosis
intrarenal condition caused by ischemia, nephrotoxins, or pigments and accounts for 90% of all intrarenal cases
-the ischemia of the basement membrane and tubular epithelium seen in ATN result in a decreased GFR
-is reversible if identified early and appropriate measures are taken
>nephrotoxic agents such as aminoglycoside antibiotics are the causative factor; removal of these aids in reversing the disease process
Postrenal Causes
involve the mechanical obstruction of the lower urinary tract (the ureters, bladder, and urethra)
-as the urine leaves the kidneys, flow is obstructed at some point at the ureters or below, causing reflux into the renal pelvis, impairing kidney function
>post renal causes include: BPH, prostate cancer, calculi, trauma, and tumors
>potential for intrarenal damage is reversible if obstruction is removed
Postrenal causes include?
BPH, prostate cancer, calculi, trauma, or tumors
Which is a prerenal cause of AKI?
A. acute glomerulonephritis and neoplasms
B. septic shock and nephrotoxic injury from medications
C. pyelonephritis and calculi formation
D. hypovolemia and myocardial infarction
D. hypovolemia and myocardial infarction
(prerenal = result of external factors that reduce renal blood flow and lead to decreased glomerular perfusion and filtration)
Four Phases of Acute Kidney Injury
- Initiating phase
- Oliguric phase
- Diuretic phase
- Recovery phase
Phases of AKI: Initiating phase
“onset”, is the beginning phase of the insult, continuing until signs and symptoms appear
-can last for hours to days
-triggering events arise from prerenal conditions; decrease in circulating volume, resulting in an equal decrease in tissue oxygenation
-compensatory mechanisms cause the release of angiotensin II, aldosterone, norepinephrine, and antidiuretic hormone to preserve the blood flow to essential organs
-vasoconstriction occurs along with sodium and water retention
-decrease in urine output, high specific gravity of urine and a low urine sodium concentration is observed
>if prerenal cause is corrected, the condition is reversible
Phases of AKI: Oliguric phase
a urine output below 400 mL/day
-when urine output decreases because of renal tissue damage
-urine with a fixed specific gravity (between 1.007 and 1.010) and a high sodium concentration (>40 mEq/L[>40 mmol/L])
> a high sodium concentration with a fixed specific gravity indicates intrarenal damage that does not respond to the compensatory mechanism of RAAS
-increases in BUN/creatinine, electrolyte abnormalities, acidosis, and fluid overload as a result of decreased GFR
-phase may last up to 14 days or longer depending on initiation of treatment
-the loner the oliguric phase lasts, the poorer the prognosis
Phases of AKI: Diuretic phase
occurs when the cause of AKI has been corrected
- there is an osmotic diuresis resulting from high urea levels
- urine output increases from 1 to 3 L to 3 to 5 L a day
- patient may experience severe fluid loss as a result of increased urination, leading to dehydration and causing electrolyte imbalances
- phase can last from 1 to 3 weeks
- as this phase ends, acid-base, electrolytes, BUN, and creatinine levels begin to normalize
Phases of AKI: Recovery phase
begins as the kidney begins to return to its regular excretory function
- the basement membrane is restored, and the GFR increases up to 70 to 80% of normal
- fluid and electrolyte balance normalize
- phase can last from several months to 1 year