ACUTE KIDNEY INJURY
Acute kidney injury
(AKI) is the abrupt loss of kidney function, resulting in the retention of urea
and other nitrogenous waste products and in the dysregulation of extracellular
volume and electrolytes. The term AKI has largely replaced acute renal failure
(ARF), reflecting the recognition that smaller decrements in kidney function
that do not result in overt organ failure are of substantial clinical relevance
and are associated with increased morbidity and mortality. Currently, there is
no universally accepted definition of ARF in clinical practice: in fact, more
than 30 definitions for ARF are reported in the medical literature. The term
ARF is now reserved for severe AKI, usually implying the need for renal
replacement therapy. The
diagnostic criteria for AKI is based on an increase in serum creatinine or the
presence of oliguria. Two important criteria used most widely are RIFLE and
AKIN criteria.
EPIDEMIOLOGY:
ARF is an
uncommon condition in the community-dwelling, generally healthy population,
with an annual incidence of approximately 0.02%. In individuals with preexisting CKD, however,
the incidence may be as high as 13%. In nonhospitalized patients, dehydration,
exposure to selected pharmacologic agents such as contrast media, and the presence
of heart failure are associated with an increased risk of ARF. Additionally,
trauma, rhabdomyolysis, vessel thrombosis, and drugs are common culprits in the
development of ARF. The
hospitalized individual is at high risk of developing ARF; the reported
incidence is 7%
ETIOLOGY:
The causes of ARF can be divided
into broad categories based on the anatomic location of the injury associated
with the precipitating factor(s). They are :
1.Prerenal:
Dehydration, Hemorrhages,
Anaphylaxis, Sepsis, Bilateral renal artery stenosis, Excessive antihypertensive
use.
2. Intrinsic:
Vasculitis, Polyarteritis nodosa, Accelerated
hypertension, glomerular damage, SLE, Acute tubular necrosis, acute
interstitial nephritis.
Bladder outlet obstruction ,Abdominal
cancers,nephrolithiasis, Retroperitoneal fibrosis , infections.
PATHOPHYSIOLOGY:
Signs : edema; urine
may be colored or foamy; orthostatic hypotension in volume-depleted patients,
the presence of acute or chronic hypertensive kidney disease.
Laboratory
Tests
: Elevations in the serum potassium, BUN, creatinine, and phosphorous, or a
reduction in calcium and the pH (acidosis).
The clinical findings are different based on
the cause of the ARF.
An increased serum WBC count may be present.
Urine microscopy can reveal cells, casts, or
crystals.
Renal ultrasonography or cystoscopy may be
needed to rule out obstruction; renal biopsy is rarely used, and is reserved
for difficult diagnoses.
PREVENTION
AND MANAGEMENT :
The goals are (a) to prevent ARF,
(b) avoid or minimize further renal insults that would worsen the existing
injury or delay recovery, and (c) provide supportive measures until kidney
function returns. The patient should receive guidance regarding their optimal
daily fluid intake (approximately 2 L/day) to avoid dehydration, and if they
are to receive any treatment that can pose a risk for insult to the kidney
(e.g., chemotherapy or uric acid nephropathy).
Normal saline may prevent most of
the preventable events.
Giving low-dose dopamine infusions
(≤2 mcg/kg/min) for the prevention of ARF is a surprisingly common practice
given the paucity of data to support its use.
The use of diuretics to prevent
nephrotoxicity may actually result in intravascular volume depletion and
thereby increase the risk of ARF.
Once acute renal failure is
established, the cause is known, and any specific therapy implemented,
supportive care is the mainstay of ARF management regardless of etiology.
RRT may be necessary to maintain
fluid and electrolyte balance while removing accumulating waste products.
The slow process of renal recovery cannot
begin until there are no further insults
to the kidney. Typically, IV fluid
challenges are initiated with 250 to 500 mL of normal saline over 15 to 30
minutes with an assessment after each challenge of the patient’s volume status.
Nutrition :
There are two major constraints
concerning the nutrition of patients with AKI: •
Patients may be anorexic, vomiting
and too ill to eat;
Oliguria associated with renal failure limits
the volume of enteral or parenteral
nutrition that can be given safely.
In all situations, protein is
usually supplied as 12–20 g/day of an essential amino acid formulation,
although individual requirements may vary.
