15. Renal Disease Flashcards
Function of the kidneys
- Elimination of metabolic waste and non-essential materials
- Fluid balance, electrolyte balance, and composition
- Maintenance of acid/base levels
- Secretion of renin by the juxtaglomerular cells
- Secretion of erythropoietin, conversion of vitamin D, calcium and phosphorus homeostasis
- Regulation of blood pressure
How is renal function measured?
Glomerular Filtration Rate (GFR)
Estimated with a formula that includes age, lean body weight, and serum creatinine.
GFR for adult male 130 mL/min
GFR for adult female 120 mL/min
Chronic kidney disease occurs when GFR is reduced by at least 50mL/min or when it is lower than 60 mL/min/1.73m2
GFR is commonly measured using body’s clearance of creatinine (by-product of muscle metabolism exclusively filtered through glomeruli making it a good indicator of renal function).
Define Acute Renal Failure
Acute Kidney Injury
How is it diagnosed
The loss of renal function over hours to days that results in disturbances in fluid, electrolyte, and acid-base homeostasis.
Diagnosis based on serum creatinine increase by more than 0.5 mg/dL or serum creatinine concentration rise of more than 25% in a patient with chronic kidney disease and a reduction in GFR by 50%
BUN levels also helpful but less reliable due to other distracting factors (GI bleeding, increased protein intake, low urine output/dehydration, catabolic drugs like steroids and tetracycline).
What is the most accurate estimate of renal function?
24-hour urine collection
Used to compare differences in plasma to urine creatinine and nitrogen levels.
How is acute renal failure classified? (3)
Prerenal azotemia: conditions that cause a fall in GFR because of reduced glomerular perfusion pressure (BUN:CR >20:1 and a FENA <1%)
Intrinsic renal failure: direct damage to structures of the kidney
Post renal failure: obstruction from either upper or lower urinary tract
Pre-renal causes of AKI
60% of AKI
- Hypovolemia (hemorrhage, diarrhea, diuretics)
- Hypotension (cardiac failure, sepsis, dehydration)
- Drugs (ACE-inhibitors, NSAIDs)
Renal (intrinsic) causes of AKI
30% of AKI
- Acute tubular necrosis (toxic, septic, ischemic)
- Toxins: ethylene glycol, contrast dye, myoglobinuria, NSAIDs, aminoglycosides, amphotericin B
- Ischemia: embolism, dissection, cardiovascular surgery, severe blood loss, severe hypotension
- Sepsis: acute interstitial nephritis (edema and inflammation of the renal interstitium - PCN, diuretics, cimetidine, NSAIDs)
Post-renal (obstructive) causes of AKI
10% of AKI
- Renal vein occlusion
- Urinary tract obstruction
- Anticholinergic-associated bladder dysfunction from anesthetic agents or antihistamines
Labs for evaluation of Acute Renal Failure
CBC with diff
CMP
Coagulation profile
Urinalysis
Urine electrolytes
FENa: fractional excretion of sodium in urine (measure differences between sodium and creatinine in the plasma and urine)
Urinalysis findings in ARF
Brown granular casts and epithelial cells represent ischemia or nephrotoxic ARF
Heme in the absence of red blood cells represents rhabdomyolysis
Eosinophils associated with fever, rash, peripheral eosiniphelia represents AIN
Red cell casts, protein, RBC represent glomerulonephritis
Urinalysis is NORMAL/ABNORMAL in pre-renal and post-renal ARF
Normal
Management of ARF
Discontinue NSAIDs (inhibit synthesis of prostaglandins, which are vital in the maintenance of renal blood flow and GFR)
Short-term discontinuation of ACE inhibitors and ARBs (inhibit actions on afferent arterioles and worsen ARF)
Avoid radiocontrast dye
Treat underlying cause (eliminate causative agents, aggressive hydration, if obstructive, relieve obstruction)
Dialysis is last resort if fluid overload, significant electrolyte imbalance, acid-base imbalances.
Urinalysis is NORMAL/ABNORMAL in renal (intrinsic) ARF
Abnormal
Stages of Chronic Renal Failure and GFR
- Slight kidney damage, normal or increased filtration (GFR >90)
- Mild decrease in kidney function (60-89)
- Moderate decrease in kidney function (30-59)
- Severe decrease in kidney function (15-29)
- Kidney failure/ESRD (<15)
Co-morbidities and sequelae in patients with CRD
- Cardiovascular: causes up to 50% mortality in ESRD patients. Dislipidemia, CAD, CHF, LVH, Hypertension (chronically elevated ATII).
- Anemia: anemia of chronic disease due to altered and decreased production of erythropoietin.
- Platelet dysfunction (qualitative defect, inc. risk bleeding)
- GI: nausea/vomiting, inc. risk of ileus and aspiration
- Glycemic control: many have DM (may be causative factor leading to CKD)
- Infection: impaired phagocytosis, neutrophil chemotaxis, and malnutrition.
- Secondary hyperparathyroidism
- Electrolyte disturbances (inability to secrete potassium, hydrogen ions) - metabolic acidosis
- Uremia
