Nephrology: Prerenal and Postrenal

Question 1

Acute Renal Failure

Answer 1

• rapid rise in BUN or creatinine
• can occur serveral hours, days, or weeks
• hours: rhabdomyolysis, contrast (afferent tubules constrict)
• days: aminoglycosides (space the intervals - toxicity based on troughs not peaks, also ototoxicity), burgers syndrome
• weeks: post-streptococcal

Question 2

Azotemia

Answer 2

• renal insufficiency
• not severe enough for dialysis
• GI bleeding or increased protein diet can cause artificial increase in BUN

Question 3

Uremia

Answer 3

requires dialysis

severe acidoisis, fluid overload

altered mental status

hyperkalemia

anemia

hypocalcemia (1,25 dihydroxy not made, can’t absorb calcium)

pericarditis (uremia bathing pericardium)

infections (neutrophils can’t degranulate with uremia)

increased superficial bleeding (platelets alpha and dense granules cannot degranulate. give ddavp (desmopressin - causes release of VWF and factor 8)

Question 4

Pre-renal

Answer 4

decreased perfusion

kidney normal

all causes of shock - burns, decreased volume, decreased albumin, decreased cardiac output, third spacing

renal artery stenosis (kidney thinks it is hypotension)

decreased urine sodium (body holding on to Na)

increased urine osmolality is high (other things besides Na like urea, less water, more concentrated)

use specific gravity on dip-stick to measure urine osmolality if no protein in urine

extremely high circulating aldosterone (thinks hypotension)

dx: BUN to creatinine ratio of 20:1 (urea has more time to be reabsorbed because of slow flow, creatine still secreted at same rate)

Question 5

Post-renal

Answer 5

stones - must be in bladder or both ureters (other kidney takes care of things if only one ureter) only need 1/3 of one kidney for normal operation

kidney is normal

GFR primarily driven by hydrostatic pressure in glomerular capillary

if pressure in bowman’s space increases, decreases GFR

causes:
stones, bilateral strictures, bladder cancer, BPH, retroperitoneal fibrosis (bleomycin, methotrexate), neurogenic bladder (diabetes, MS)

creatinine rises when 70-80% of renal function is lost

decreased urinary sodium

dx: big bladder, hydronephrosis, sonogram
tx: put in catheter

Question 6

Creatinine

Answer 6

closest thing to measuring GFR

slightly overestimates GFR because of 10% secretion

rises at rate of .5 - 1.0 per day in complete renal failure (anuric)

Question 7

Acute Tubular Necrosis

Answer 7

BUN/creatinine ratio 10:1

Question 8

Hepatorenal Syndrome

Answer 8

intense vasoconstriction of afferent arterioles

like Pre-renal azotemia

just because of liver failure

fix the liver, kidney will be fine

Question 9

ACE inhibitors

Answer 9

vasodilation of efferent arterioles

transient GFR decrease

still good for kidneys though because it decreases pressure inside the glomerulus and protects the kidneys

• intraglomerular hypertension is biggest factor for kidney damage

Question 10

Angiotensin

Answer 10

constricts the efferents

increases GFR

Question 11

Prostaglandins

Answer 11

prostaglandins vasodilate afferents (increasing GFR), so NSAIDS decrease GFR (only problem for old people with bad kidneys, diabetics,hypertension)

Question 12

Hepatopulmonary Syndrome

Answer 12

similar to hepatorenal syndrome

renal failure is secondary to pulmonary disease

marked change in oxygen saturation with changes in position - orthodeoxia (sitting up causes decrease oxygenation…. weird)