Acute Kidney Injury/Rhabdo Flashcards
Functions of the Kidney
Regulation of ionic composition
Sodium, potassium, calcium, chloride, phosphate
Regulation of blood pH, osmolarity, and glucose
Regulation of blood volume
Conserving or eliminating water
Regulation of blood pressure
Secreting renin
Release of erythropoietin & calcitriol
Excretion of wastes
Nitrogenous waste products (ammonia, uric acid, urea, creatinine, and amino acids), excess quantities of salts and water
Major Function of the Kidney
Filter blood plasma and separate wastes from the useful chemicals
Eliminates the wastes in urine while returning the useful chemicals to the bloodstream
Renal Corpuscle
Component of each nephron
Site where blood filtration begins
Passive process by high hydrostatic pressure of the glomerular capillaries
Consists of:
Glomerulus (cluster of capillaries)
Bowman’s capsule
Two-layered capsule that encloses the glomerulus
Blood flows into the glomerulus via the afferent arterioles → water and solutes pass through the capillary endothelium, through the basement membrane, and through the epithelium → Bowman’s space → renal tubule
Remaining blood leaves the glomerulus through efferent arterioles
Glomerular Filtration Rate (GFR)
General and dependent on
The volume of fluid filtered by the kidneys in a minute
Measure of your kidney function
Dependent upon:
The net filtration pressure
Vasodilation of the afferent arterioles mediated by prostaglandins
Vasoconstriction of the efferent arterioles mediated by angiotensin II
Available surface area for filtration
Filtration membrane permeability
Angiotensin II vasoconstricts the glomerular arterioles; greater effect on the efferent arterioles than the afferent arterioles → increased glomerular filtration pressure
Increased circulating volume from the affects of aldosterone → increased blood pressure and renal perfusion
Angiotensin II stimulates the release of antidiuretic hormone (ADH), which will reabsorb water from the collecting ducts → increased circulating blood volume and renal perfusion
Renal Tubule
Duct that leads away from the glomerular capsule
Divided into 4 regions:
Proximal convoluted tubule (PCT)
Nephron loop
Distal convoluted tubule (DCT)
Collecting duct
Each has a unique absorptive properties
Acute Kidney Injury (AKI)
general and epi
Characterized by abrupt deterioration in kidney function (within 48 hours) based on an elevation in serum creatinine level with or without reduction in urine output
Spectrum of injury from mild to advanced → requiring renal replacement therapy
Often reversible
Classified as pre-renal, intrinsic/intra-renal, or post-renal
Epidemiology:
7% of hospitalized patients
2/3 of ICU patients → Mortalityis 50%‒70% in AKI associated withsepsis and multiple organ failure
Previously referred to as acute renal failure (ARF) and acute renal insufficiency
AKI
Staging Criteria
Kidney Disease: Improving Global Outcomes (KDIGO) criteria for AKI
Stage 1
≥ 0.3 mg/dL increase in serum creatinine within 48 hours,or
Increase in serum creatinine > 1.5–1.9 times baseline in the past 7 days,or
Urine volume/urine output < 0.5 mL/kg/hr for 6–12 hours
Stage 2
Serum creatinine 2.0‒2.9 times baseline,or
Urine volume/urine output < 0.5 mL/kg/hr for ≥ 12 hours
Stage 3
Serum creatinine 3 times baseline,or
Serum creatinine ≥ 4 mg/dL,or
Initiation of renal replacement therapy,or
Decrease in estimatedGFR
< 35 mL/min/1.73 m2in individuals < 18 years of age,or
Urine volume/urine output < 0.3 mL/kg/hr for ≥ 24 hours,or
Anuria for ≥ 12 hours
DONT MEMORIZE
Multiple staging systems for AKI
Staging is based on serum creatinine, urine output, and/or changes in GFR
Kidney Disease: Improving Global Outcomes (KDIGO) criteria is the currently preferred staging system
Other staging systems:
Risk, Injury, Failure, Loss, and End-stage kidney disease (RIFLE) classification system
The Acute Kidney Injury Network (AKIN) criteria
International Renal Interest Society (IRIS) guidelines for AKI (Grade I-V)
AKI
RF
Older age >75 years
Hypovolemia – dehydration or blood loss
Nephrotoxic drugs
Rhabdomyolysis
Sepsis
Chronic disease:
Diabetes mellitus
Liver failure
Heart failure
Kidney disease (acute on chronic kidney injury)
AKI
Pre-renal Causes
Most common type of AKI
70% of community-acquired cases
Caused by decreased renal perfusion
Reduced circulating volume (GI losses, blood loss, diuretic use, osmotic diuresis – DKA, insensible loss – burns)
Reduced cardiac output (heart failure)
Systemic vasodilation (septic shock)
Medications
ACE inhibitors, ARBs, NSAIDs
Obstruction of the renal artery (thrombosis/embolus, stenosis, or aneurysm)
Pre-renal cause
NSAIDs
Vasodilation of the afferent arterioles mediated by prostaglandins
NSAIDs block the production of prostaglandins → vasoconstriction and possible AKI
Vasoconstriction of the efferent arterioles mediated by angiotensin II
ACEi/ARBs block the effects of angiotensin II (vasoconstriction) → vasodilation of the efferent arterioles (renal protective)
In patients with renal artery stenosis, the introduction of an ACEi/ARBs can lead to a drop in glomerular filtration pressure
AKI
Intrinsic/Intra-renal Causes
Caused by direct damage to the glomeruli and/or tubulointerstitial structures
Acute tubularnecrosis(ATN)
Damage to the tubular cells
Caused by a lack of blood flow to the kidneys and nephrotoxic agents
Acute interstitial nephritis
Inflammatory cell infiltration into the kidney interstitium
Caused by medications,infections, orautoimmune diseases
Vascular disease
Atherosclerosis and vasculitis
Glomerular disease
Glomerulonephritis (presents withhematuria) or nephrotic syndrome(presents withproteinuria)
AKI
Post-renal Causes
Caused by inadequate drainage of urine distal to the kidneys (obstruction) leading to back pressure on the kidneys and hydronephrosis
May occur at any point in its course from therenal pelvisto theurethra
Causes of obstruction
Urinary calculi
Benign prostatichyperplasia (BPH) or prostate cancer
Bladder outlet obstruction
Urethral stricture
Gynecologic tumors (ovarian cancer, uterinefibroids,cervical cancer)
A single stone will lead to AKI in a patient with 1 functioning kidney, but unlikely in patients with 2 functioning kidneys
Effects of AKI on Electrolytes & Acid-Base Balance
Hyperkalemia
Due to decreased renal excretion ofpotassium
Increases theprobability ofcardiac arrhythmias
Hyperphosphatemia
Due to decreased renal excretion ofphosphate
Metabolic acidosis
Inability of thekidneysto excreteacids
Exacerbateshyperkalemia
Increases theprobabilityofcardiac arrhythmias