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o
Fractional excretion of Na – FeNa – this test is
reliable for determining reabsorptive capacity of
tubules (amount of Na that escapes in urine relative
to amount that was filtered in first place). The volume
of anything that is found in the urine (UV of x)
divided by the amount filtered (measured by Glomerular
Filtration Rate multiplied by serum concentration of
that substance) equals the fractional excretion of
substance x.
§
Fractional excretion of x: UV/ (Glomerular Filtration
Rate*serum concentration of x)
o
Urine osmolality – intact kidney that isn’t receiving
enough blood will have concentrated urine
ŕ
urine osmolality will be high (ex. pre-renal Acute Renal
Failure). With Acute Tubular Necrosis, urine can’t be
concentrated
ŕosmolality
will be low. Another way to look at this is the U/P osm
ratios.
Complications of Acute Renal Failure and Uremic Syndrome
-
metabolic complications
o
hyponatremia – low serum sodium concentration
§
usually mainly deals with water balance (not sodium);
can mean patient is overhydrated or that the patient
can’t excrete solute free water appropriately
o
hyperkalemia – high potassium concentration
§
potentially lethal complication because high potassium
can cause cardiac arrhythmias that stop the heart and
kill the patient
o
hypocalcemia and hyperphosphatemia
§
serum phosphate is high because it mainly involves a
renal rate of excretion
§
calcium and phosphate are reciprocally related, as
phosphorus goes up, calcium goes down
§
hypocalcemic tetany can be seen in untreated patients
·
Classic peripheral neurologic findings of hypocalcemia
include Chvostek sign and Trousseau sign.
o
Chvostek sign: Tap over the facial nerve about 2 cm
anterior to the tragus of the ear. Depending on the
calcium level, a graded response will occur: twitching
first at the angle of the mouth, then by the nose, the
eye, and the facial muscles.
o
Trousseau sign: Inflation of a blood pressure cuff above
the systolic pressure causes local ulnar and median
nerve ischemia, resulting in carpal spasm.
o
hypermagnesemia
§
magnesium is excreted through the kidney
§
hypermagnesemia is iatrogenic most of the time because
it is very effective in management of pre-eclampsia
(hypertension in pregnancy or immediately after
pregnancy accompanied by edema and proteinuria). So,
overly aggressive obstetricians can precipitate renal
failure in their patients.
o
hyperuricemia – not lethal in short term
o
metabolic acidosis – will be talked about in the
acid-base lecture
-
cardiovascular complications
o
Increase in total body sodium with expansion of ECF
volume which makes the patients prone to pulmonary and
peripheral edema, cardiac arrhythmias, and pericarditis
§
when
there is a problem excreting Na+, there is an increase
in ECV (extra cellular volume) and this can lead to
congestive heart failure. Don’t give renal failure
patients saline because they have a problem secreting
Na+ to begin with
§
pericarditis can occur, but is less common now because
patients are dialyzed – pericarditis occurs when there
is a fibrinous deposition of material between
pericardial surfaces (visceral and parietal pericardium)
·
diagnosis of pericarditis is made clinically by the
presence of a pericardial friction rub (you can mimic
this sound by covering your ear with your hand and
scratching the back of your hand with your index finger)
·
the
danger of pericarditis is that the two layers of the
inflamed pericardium can separate (clinically, the rub
can no longer be heard), and blood can accumulate in
this space (cardiac tamponade). This is more likely in
patients with uremia (renal failure patients).
-
neurologic complications
o
metabolic encephalopathy
§
physical finding of ‘liver’ flap is seen in patients
with this complication – asterixis – pathological
neurologic sign which is elicited by having the patient
extend their arms with their elbows straight and
hyperextend the wrist, patient may move hand back and
forth (flap) which is a positive ‘liver’ flap or
flapping tremor
o
neuromuscular irritability – twitching that isn’t tetany
o
seizures
o
coma
-
hematologic complications
o
anemia – because of decreased secretion of
erythropoietin
o
bleeding tendency secondary to defective platelet
function
o
impaired white cell function and decreased immune
response, subject to infections
-
gastrointestinal complications – GI tract is often first
system affected
o
submucosal hemorrhages seen in kidney when viewed
microscopically
o
uremic toxins (unidentified compounds that are not urea
or creatinine) can cause uremic gastritis or enteritis
o
uremic gastritis, enteritis, and colitis with:
§
nausea
§
vomiting
§
diarrhea
§
bleeding
-
infectious complications
o
pneumonia
o
urinary tract infections
o
wound infections
o
line
sepsis
o
bacteremia
-
multi-organ failure syndrome – renal failure developed
due to profound sepsis or trauma, may be due in some
cases to pure uremic syndrome
Management of Acute Renal Failure
-
accurate volume assessment at time of diagnosis is
mandatory/necessary
-
fluid challenge and repletion if appropriate
-
fluid restriction and loop diuretic if appropriate
-
sodium and potassium restriction
-
maintain nutrition, transfuse if necessary
-
avoid nephrotoxins if possible – adjust dose of
nephrotoxic medications if they are absolutely necessary
Renal replacement therapy (popular term for dialysis)
-
dialysis can be conventional or continuous
-
dialytic therapy may be necessary if medical therapy
fails or is not feasible
o
uremic syndrdome
o
metabolic acidosis
o
CHF
and fluid overload
o
refractory hyperkalemia
Prognosis of Acute Renal Failure
-
study comparing Korean war gunshot/trauma victims who
did not have access to dialysis to Vietnam war injured
veterans who did have access to dialysis shows that
there was no difference in mortality
o
dialysis is important, but only permits you to get
better if your underlying condition allows it
-
remember that Acute Renal Failure is a complication of
many things, but ability to recover depends on your
condition/health before renal failure sets in
o
prognosis is variable and depends on:
§
age
§
severity underlying conditions
§
degree of catabolism
§
number of co-morbid organ failure
§
control of sepsis
§
mortality may be as high as 70% in ICU – this is
due to severity of underlying conditions
Summary of Acute Renal Failure
-
very
common, particularly in ICU hospital patients who have a
significant mortality
-
it
is important to be aware of risk factors, to diagnose
properly, to manage complications, and support the
patient pending recovery of renal function
o
underlying conditions are very important in determining
outcome of patients (an important risk factor to
consider)
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