Acute Renal Failure
Renal failure depicts a group of
diseases that may be associated with decreased GFR and manifested by retention
of BUN and creatinine. Acute renal failure is defined
as a rapidly (over a period of days) increasing
creatinine level or decreasing urine output.
Causes of acute renal failure is caused by failure of the kidneys to
perform their normal functions due to:
- Prerenal - Problems affecting the flow of blood before it reaches
- Postrenal - Problems affecting the movement of urine out of the kidneys
- Renal - Problems with the kidney itself that prevent proper filtration
of blood or production of urine
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This is by far the most common type of acute renal failure. Your kidneys
do not receive enough blood to filter. Prerenal failure can be caused by
the following conditions:
- Dehydration - From vomiting,
diarrhea, water pills, or blood loss
- Disruption of blood flow to the kidneys - From a variety of causes
- Drastic drop in blood pressure - From major surgery, severe injury
or burns, or infection in the bloodstream (sepsis)
- Blockage or narrowing of a blood vessel leading to the kidneys
- Heart failure or heart attacks
- Liver failure
There is no actual damage to the kidneys with prerenal failure. With
appropriate treatment, it usually can be reversed.
Postrenal renal failure is sometimes referred to as obstructive renal
failure, since it is often caused by something blocking elimination of urine
produced by the kidneys. This problem also can be reversed.
At the ureter level, this condition can be caused by the following:
- Kidney stone
At the bladder level, the following conditions can cause obstruction:
- Kidney stone
- Enlarged prostate (the most common cause)
- Blood clot
- Bladder cancer
- Neurologic disorders of the bladder
Treatment consists of relieving the obstruction. Once the blockage is
removed, the kidneys usually recover in 1-2 weeks if there is no infection
or other problem.
Primary renal damage is the most complicated cause of renal failure.
Renal causes of acute kidney failure can be subdivided into those affecting
the filtering system of the kidney, those affecting the blood supply in
the kidney, and those affecting kidney tissue.
Some of the kidney problems that can cause kidney failure include the
- Blood vessel diseases
- Blood clot in a vessel in the kidneys
- Injury to kidney tissue and cells
- Acute interstitial nephritis
- Acute tubular necrosis
ARF passes through two phases 1.
Destructive phase: oliguric and non-oliguric 2. Reconstructive phase: could
ARF due to pre-renal or renal causes (esp. ATN) usually
presents as oliguric renal failure passing through the
3 phases of pathology:
Intitiation phase: due to the initiating
insult on the kidney.
Maintenance phase: maintenance of oliguria
Recovery phase: due to recovery of renal
ARF due to other causes as partial obstruction may
present as polyuria.
ARF due to postrenal obstruction may present as anuria.
is manifested by the rise of serum creatinine.
The next step is to
if chronic or acute renal failure.
Then exclude if postrenal then identify
if pre-renal or renal. If
renal identify what type of intrisic renal disease ? if no diagnosis is
reached then by exclusion the diagnosis is ATN.
1. Prerenal azotemia
creatinine ratio > 40
decreased < 20
excretion of Na is <1%
is > 500
2. Renal azotemia
creatinine ratio < 20
decreased > 40
excretion of Na is >1%
is > 350
These findings can be
altered by diuretic use and urine sample should be taken before institution
of diuretic use.
3. Postrenal azotemia
Post-renal azotemia develops only if the obstruction is bilateral or
affects a solitary functioning kidney. During the early stages of obstruction,
continued glomerular filtration leads to increased intra-luminal pressure
proximal to the site of obstruction. As a result, there is gradual distension
of the proximal ureters, renal pelvis and calyces and fall in glomerular
filtration which will be evident by renal ultrasound.
N.B.: the level of creatinine in serum has nothing
to do with whether the ARF is oliguric, anuric or non-oliguric: it is an
indication that tubular function is lost as creatinine is not filtered-
it is secreted. K+ and H+ are retained even in nonoliguric renal failure
due to the same principal (they are both secreted and not filtered).
Treatment of acute renal failure usually should be
conservative and largely supportive. It requires careful and precise management.
All patients will require close monitoring, many of them within intensive
Supportive care includes stabilizing the patient, monitoring input and output
strictly, weighing daily, determining electrolyte values frequently, preventing
sepsis via reducing the number of intravenous lines and removing an indwelling
Therapy for prerenal failure
Rapid volume replacement and treatment of the underlying
condition that resulted in prerenal failure are the cornerstones of therapy.
Initial fluid administration of isotonic saline (0.9%) or 5% albumin (10
to 20 mL/kg per dose) should be used to restore intravascular volume. This
can be both a diagnostic and a therapeutic trial. Fluid administration also
can convert oliguric to nonoliguric renal failure in its early stage.
Therapy for postrenal failure
Therapy for postrenal failure includes removal of obstruction
by decompression or diversion of the urinary tract, stabilization of electrolyte
abnormalities, management of postobstructive diuresis, and therapy for voiding
dysfunction and for urinary tract infection. Surgical intervention will
require urologic consultation. The site of the obstruction will determine
the approach: placement of a Foley catheter, vesicostomy, ureteral catheters
(stents), or nephrostomy tubes.
Therapy for established renal failure
Maintaining Balance of Fluid and Electrolytes
In a euvolemic state, fluid intake, including water generated from endogenous
metabolism (insensible fluid gain), is balanced by fluid output.
Kidney failure in any form can present as hypertension and hypertensive
encephalopathy. It is essential to lower the blood pressure quickly and
safely. The blood pressure should be reduced by at least 25% within 1 hour
with an antihypertensive medicine whose onset of action is rapid. It is
advisable to start with one antihypertensive medicine and increase the dose
to its maximum recommended level. Therapy is individualized and needs titration.
In most cases, hypertension is the result of sodium and fluid retention,
but other factors, such as activation of the renin-aldosterone-angiotensin
II and/or the alpha-adrenergic system, may have roles in kidney failure.