Acute Kidney Injury Flashcards
What is the definition of acute kidney injury?
An abrupt (within 48 hours) reduction in kidney function, defined as:
• Increase in serum creatinine of > 0.3mg/dL OR
• % increase in serum creatinine of 50% OR
• Oliguria of 6 hours
What is the relationship between acute kidney injury and critical illness?
AKI is often found in critically ill patients
What are the 3 groups of AKI causes?
- Prerenal Azotemia
- Intrinsic Renal Disease
- Postrenal Obstruction
What are the causes of prerenal azotemia?
i. True hypovolemia
ii. Decreased effective circulating volume
iii. Renal artery stenosis/occlusion
iv. NSAID/ACE-I/ARB mechanism
What are the causes of intrinsic renal disease?
i. Vascular causes
ii. Glomerular disease
iii. ATN
iv. AIN
What are the causes of postrenal obstruction?
i. Bladder outlet obstruction
ii. Bilateral ureteral obstruction
iii. Unilateral ureteral obstruction in a solitary kidney
What are the 2 most common causes of AKI?
- Prerenal Azotemia
- Ischemic ATN
What can prerenal azotemia progress to if it is not corrected?
Ischemic ATN
What is prerenal azotemia?
It is an appropriate response to renal hypo perfusion that leads to a build up of nitrogen compounds in the blood
What are some of the causes of prerenal azotemia?
- Decreased ECV
- Renal artery stenosis
- Drug-induced impaired renal autoregulation
What is the normal renal response to drop in BP?
- Afferent vasodilation
- Efferent vasoconstriction
What is the effect of NSAIDs on the GFR?
NSAIDs decrease the GFR by causing afferent arterial vasoconstriction
What is the effect of ACE-I/ARBs on the GFR?
They do not affect the GFR that much. They dilate the efferent arterioles which has a protective effect.
What are some of the risk factors for postern disease?
- Older men with prostate disease
- Solitary kidney
- Intra-abdominal (pelvic) cancer
What are the 4 categories of intrinsic renal disease?
- vascular causes
- glomerular diseases
- acute interstitial nephritis
- acute tubular necrosis
What are some of the causes of ATN?
- Sepsis
- Surgery
- Nephrotoxic exposures
What is the major cause of intrinsic renal disease?
ATN
What are the classical features of ATN?
- Muddy brown urine
- Oliguric Phase (HTN/Hyperkalemia/Volume Overload)
- Polyuric Phase
What are the two types of ATN?
- Ischemic
- Toxic
What are some of the vascular causes of intrinsic renal failure?
- Vasculitis
- Thromboembolic disease
- HUS/TTP
- Malignant HTN
- Scleroderma renal crisis
What is the main vascular cause of intrinsic renal failure?
Malignant HTN - which causes impending/progressive organ dysfunction
What are the two class of acute interstitial nephritis (AIN) that lead to intrinsic renal failure?
Drug Associated (NSAIDs and antibiotics) Non-drug Associated (Infectious/Autoimmune)
What is the triad of signs in AIN?
Fever, peripheral eosinophilia, rash
Abdominojugular Reflex
Pushing on the umbilicus leads to jugular vein rising of more than 4 cm
What are signs that the body is too dry?
- Dry mucous membranes
- Skin tenting (only useful if positive in adults)
- Neck veins flat at 0 degrees
What are signs that the body is too wet?
- Abdominojugular reflux at 30-45 degrees
- S3 gallop
- Ascites
Prerenal Azotemia Urinanalysis
Hyaline Casts
Prerenal Azotemia Urine Specific Gravity
It will be high - 1.020
Prerenal Azotemia Osmolality
It will be high - greater than 500
Prerenal Azotemia FE of Na
It will be low - less than 1%
Prerenal Azotemia FE of Urea
Less than 35%
ATN Urinanalysis
Tubular Epithelial Casts
ATN Urine Specific Gravity
Low
ATN Osmolality
It will be low - less than 300
ATN FE of Na
Greater than 2%
ATN FE of Urea
Greater than 35%
What is the BUN:Cr ratio in prerenal azotemia?
Greater than 10:1
What is the BUN:Cr ratio in ATN?
10:1
What are the general indications for hemodialysis in acute kidney injury?
- Acidosis (severe and/or refractory)
- Electrolyte derangement (usually severe ↑K+)
- Intoxication syndrome (severe, dialyzable)
- Overload (significant pulmonary edema)
- Uremia (significantly symptomatic)
