Pennsylvania State University :NURSING Acute Kidney Injury NCLEX Review
Acute Kidney Injury
What is Acute Kidney Injury? It is the SUDDEN decrease in r... [Show More] enal function that will lead to the buildup of waste in the blood, fluid overload, and electrolyte imbalances. AKI can be reversible.
Basics about the kidneys:
Role of the kidneys? Filters the blood which creates a filtrate called urine. In addition, the kidneys regulate electrolyte levels, removes waste, and excessive fluid in the body. The kidneys normally do NOT filter blood cells or proteins.
An adult normally voids 1-2 liters of urine per day.
How do the kidneys create urine? Via the nephrons in the kidneys (the heart also plays a role in this, specifically the blood flow given by the heart to supply the kidneys with blood).
Each kidney contains millions of nephrons. Each nephron receives fresh blood from the heart via an afferent arteriole.
The nephron consists of two main parts:
• Renal Corpuscle (function is to FILTER the blood and create filtrate..hence urine)
o Bowman ’s capsule
• Renal Tubule (function is to REABSORB and SECRETE substances IN or OUT of the filtrate with the assistance of the peritubular capillaries)
• Proximal Convoluted Tubule
• Loop of Henle
• Distal Convoluted Tubule
• Collecting Tubule
*In conclusion, there is the flow of substances back in forth from the nephron to the peritubular capillaries (circulation) until the filtrate is how the body wants it, and then it will leave the body as urine. Therefore, the tubules are crucial in deciding what should stay or go back into circulation.
HOWEVER, when the nephrons are damaged as in INTRARENAL failure this mechanism is damaged and the patient will experience electrolyte imbalances, decreased glomerular filtration rate, decreased urinary output, azotemia (increase of BUN and creatinine in the blood…waste products).
Urine consists of:
• Ions: sodium, chloride, calcium, potassium, magnesium, phosphate, bicarbonate
Lab work for determining kidney function:
• *Creatinine: is a waste product from muscle breakdown and is solely filtered from the bloodstream via the glomerulus and is NOT reabsorbed or secreted within the nephron. Therefore, the rate of filtration of creatinine by the
glomerulus helps us to determine the efficiency of the kidneys, which is why we collect blood levels to measure creatinine levels.
Normal Creatinine level 0.6-1.20 mg/dL
Increasing Creatinine in the body = the kidneys are NOT filtering properly
• Creatinine clearance: the amount of blood the kidneys can make per minute that is free of creatinine.
Normal creatinine clearance: 85-125 mL/min (female) & 95-140 mL/min (men)
A creatinine clearance value along with age, sex, weight, race can help determine the
GFR (glomerular filtration rate).
• Glomerular Filtration Rate: rate of blood flow through the kidneys (ml/min). This shows how well the glomerulus is filtering the blood….great for determining kidney function.
Normal GFR in adults: 90 or higher ml/min (remember this depends on the patient’s age, weight, creatinine, sex, and race)
Normal GFR = normal urine output, normal BUN and creatinine, normal electrolyte and water balance
Decreased GFR = low urinary output along with an increase in waste products in the blood (creatinine and BUN), electrolyte/fluid imbalances, and buildup of fluid
• BUN (blood urine nitrogen): urea (measured as blood urea nitrogen) is a waste product from protein breakdown in the liver. It is secreted in the blood and filtered out through the kidneys.
Normal BUN: 6-20 mg/dL (in AKI this level becomes greater than 20 mg/dL)
Causes of Acute Renal Failure
Prerenal Injury: issue with perfusion to the kidneys (any injury BEFORE the kidneys)
• This leads the kidney function to decrease. The kidneys are deprived of nutrients to function properly and the amount of blood it can filter. This can eventually lead to intrarenal damage where nephrons become damaged.
What can lead to decreased perfusion to the kidney?
• Issues with the heart in conditions that decrease cardiac output as with an acute myocardial infarction. In this condition, the heart muscle is damaged and can’t pump sufficient amounts of blood to the kidney.
• Other causes: massive bleeding (internally or externally), dehydration (hypovolemia…diarrhea, vomiting), burns etc.
Intrarenal Injury: damage to the nephrons of the kidney (injury in WITHIN the kidneys)
• When the nephrons are damaged the kidneys can’t filter the blood, maintain electrolyte levels, and remove excessive waste and fluid from the body.
What can lead to the damage of the nephrons in the kidneys?
• Nephrotoxic drugs: NSAIDS
o Antibiotics “aminoglycosides
o Chemo drugs
o Contrast dyes used in procedures
• Infection “glomerulonephritis”
Postrenal Injury: blockage in the urinary tract after the kidneys to the urethra (injury found AFTER the kidneys)
• This prevents urine from draining out of the kidneys, which leads to build up pressure and waste in the kidney and decreases their function.
What can cause a blockage in this area?
• Renal calculi
• Enlarged prostate
• A bladder doesn’t empty properly due to neuro damage “stroke”
Stages of Acute Kidney Injury
• Initiation: a cause creates injury to the kidney and then signs and symptoms start to appear which leads to the next stage. This stage lasts a few hours to several days.
• Oliguric: *some patients skip this stage and go straight into the diuresis stage Urine output will be less than 400 ml/day
Glomerulus is NOT filtering the blood properly: DECREASED GFR which will lead to the following signs and symptoms you will see in the patient:
• Increased BUN and CREATININE: neuro changes, itching
o NURSING Role: low protein diet (WHY? Remember urea is a waste
product from protein break down in the liver), safety
• Increased Potassium (hyperkalemia) >5.1 meq/L: due to the nephrons decreased ability to excrete potassium. It builds up in the blood and the patient is at risk for a significant cardiac event
o NURSING Role: restrict potassium-rich foods, monitor EKG for changes (tall peaked T-waves, Wide QRS and prolonged PR interval), monitor lab values…may be ordered to give Kayexalate orally or rectally to remove extra potassium out of the blood), place on cardiac monitor to watch rhythm.
• Increased fluid in the body: edema, at risk for fluid overload (pulmonary, cardiac issues: hypertension)
o NURSING Role: restrict fluid intake, STRICT I and O’s, daily weights every day, assess swelling, heart sounds, lung sounds (crackles), monitoring respiratory rate and oxygen saturation, neuro status
• Metabolic acidosis: blood pH less than 7.35 due to the decrease in the excretion of hydrogen ions by the nephrons. Patient may be confused and have
kussmaul breathing. This is deep and rapid breathing. The respiratory system is trying to compensate by blowing off carbon dioxide (which is an acid) to help increase the blood’s pH.
o NURSING Role: monitor respiratory and neuro status, safety
• Mild hyponatremia (can be normal): diluted from fluid overload and decreased ability of the nephron to reabsorb sodium
• High phosphorus and low calcium: nephron can’t regulate phosphate and calcium levels
• Highly concentrated urine: high urine specific gravity >1.020
How long does this stage last? A week to 2 weeks. It is important this stage is as short as possible because the longer the patient stays in this stage the more of a risk of long term damage to the kidneys.
Treatment: dialysis…this is where the blood will be filtered through a special machine that will act as the nephron to remove excessive waste, water, and electrolytes from the body.
Nephrons can’t concentrate urine (so it can’t regulate water and electrolyte levels yet) but they can filter out waste. So, what will be found highly concentrated in the urine? WASTE…specifically urea.
This will cause OSMOTIC DIURESIS.
The patient will be voiding out an excessive amount of urine (3-6 Liters/day) due to osmotic diuresis. This occurs from the high amounts of urea in the newly filtered filtrate.
NURSING Role: strict I and O’s, daily weights, monitor for signs and symptoms of dehydration, HYPOVOLEMIA, hypotension.
As the GFR improves (still abnormal) this will allow the BUN and CREAT to decrease but the levels will still be abnormal. Therefore, the patient’s azotemia will start resolving, and the patient will become more alert and oriented.
Other signs and symptoms of this stage:
Hypokalemia: per MD order may give supplements and IV fluids to prevent dehydration
Urine diluted: low urine specific gravity <1.020
Lasts a week to 3 weeks
Starts when GFRreturns to normal and the kidneys start to function normally.
Urine output returns to normal along with BUN and creatinine, and electrolytes level. Therefore, the body is able to maintain these values.
This stage can last a year or more, and it depends on the amount of damage done to the kidney and the patient’s age.
Some patients are unable to progress to the recovery phase and instead develop Chronic Kidney Disease. [Show Less]