Nephrology Flashcards
(39 cards)
What should you think of if a urine dipstick is heme-positive but the microscopic examination is negative for RBCs?
Myoglobinuria
How do you confirm myoglobinuria?
Urine ammonium sulfate test - precipitates hemoglobin (Hgb) but not myoglobin
What are some clinical situations that can cause an elevated BUN:Cr?
Can indicate prerenal azotemia:
- Low flow and increased reabsoprtion
- heart failure
- cirrhosis
- nephritic syndrome
- or true intravascular volume depletion
Can result from increased protein breakdown:
- increased protein uptake
- GI bleed
- TPN
- or catabolic states (corticosteroid intake)
What does an FEna <1 usually signify?
early AGN; prerenal azotemia
FEna = [(Una x Pcr) / (Ucr x Pna)] x 100; cannot be used if diuretics have been used
Total body water (TBW) varies and depends upon what factors?
- Gender
2. Percentage of body fat
What are the 2 important regulators of ADH secretion from the posterior pituitary?
- Osmoreceptors in the hypothalamus
2. Volume (stretch) receptors in the left atrium (and possibly in the pulmonary veins) and blood vessels
How do you calculate maintenance fluids and electrolytes for a 24-hour period?
Fluids:
- First 10 kg: 100cc/kg
- Second 10 kg (10 kg-20kg): 50 cc/kg
- Remaining weight >20 kg: 20cc/kg
Electrolytes:
- NaCl: 2-3 mEq/100 ml per 24 hours
- K: 1-2 mEq/100 ml per 24 hours
What causes hyperosmolar hyponatremia?
Osmotic shift due to glucose and mannitol, diluting plasma Na+
For each 100-increment increase in glucose over 100mg/dL, how do you correct the serum Na?
For each 100-increase in glucose over 100mg/dL, the [Na+] decreases by 1.6
What are the causes of low-volume, hypoosmolar hyponatremia?
Loss of both water and Na+, but more Na+ than water:
- Diuretics
- GI losses (vomiting, diarrhea)
- Third spacing fo fluid
- Adrenal insufficiency (Addison disease)
- Sodium-losing nephropathies
What are the causes of high-volume, hypoosmolar hyponatremia?
Patients typically have dependent edema and possibly JVD
- Edema forming states: heart failure, cirrhosis, and nephrotic syndrome
- Kidney failure: acute or chronic
What are the most common drugs that cause SIADH (Syndrome of Inappropriate Antidiuretic Hormone)?
- NSAIDs
- SSRIs
- Carbamazepine and oxcarbazepine
- Psychotropic drugs (Haloperidol, amitriptyline)
- IV Cyclophosphamide
- Vincristine and vinblastine
- Cisplatin
- Ecstasy
- Chlorpropamide
Which endocrinopathies must be rules out in all patients with hyponatremia?
Hypothyroidism and glucocorticoid deficiency
- Can have low serum osmolalities and high urine osmolalities
What is the suggested rate of correction for severe hyponatremia?
Never exceed 10 mEq/L over 24 hours; 0.5mEq/L per hour
Under what conditions is osmotic demyelination syndrome most likely to occur?
Chronic, severe hyponatremia (Na <115 for >2 days) whose sodium is corrected rapidly (>10 mEq/L over 24 hours)
What does hypernatremia indiciate?
Water deficit
What is the usual serum Na in a patient with DI who has access to water?
Normal or borderline-high serum sodium levels
What K derangement can be seen in Cushing syndrome?
Hypokalemia
Know the effects of NSAIDs on serum K.
NSAIDs decrease renin release, thus increasing K+ concentration.
NSAIDs make hyporeninemic states worse.
Addison disease causes what type of K derangement?
Hyperkalemia
What are important causes of pseudohyperkalemia?
Hemolyzed specimen, thrombocytosis (>450k), LEUKOCYTOSIS (>100k)
What ECG changes are seen with hyperkalemia?
peaked T wave and short QT interval, progressive lengthening of PR and QRS intervals, loss of P wave+QRS widening into sine wave, v fib or cardiac standstill.
What is special about the treatment of hyperkalemia in patients taking digoxin?
Do not give IV calcium to a patient taking Digoxin, can enhance effect of med
What must be checked in all patients with renal potassium wasting?
Magnesium; comorbid magnesium deficiency causes renal potassium wasting
