Acute renal failure
Definition
=ARF :
rapid decrease the renal function or urine output ↑Cr>0.5mg/dl, or ↑Cr>50%,
or ↓GFR>50%
=Oliguria : (urine output < 500 mL/d)
-is a frequent
-but not invariable clinical feature
(-50%).
=Anuria : urine output<100cc/day
=For purposes of diagnosis and management,
ARF are divided into three categories:
(1) Prerenal ARF, prerenal azotemia(-55%)
diseases/that cause renal hypoperfusion
without compromising integrity of renal parenchyma
(2) intrinsic renal ARF, renal azotemia (-40%)
diseases that directly involve renal parenchyma
(3) postrenal ARF, postrenal azotemia (-5%).
diseases associated with urinary tract obstruction
=History and physical :special attention to recent
procedures and medications, vital signs, volume status, sign of CHF, signs and
symptoms of obstruction, vascular disease or systemic disease
=Serum electrolyte, Na, BUN, Cr, Hb/Ht, uric acid,
=Urine evaluation: Na, Cr, osmolality, I/O, urinalysis, sediment, electrolytes and
osmolality, fractional excretion of Na (FeNa) =(UNa/PNa)/(UCr/PCr)
(need simultaneous serum electrolytes)
Pre-renal and oliguric ATN RF
診斷
U/P Cr
UNa
FENa (%) Uosmolality
Pre-renal RF
>40
<20
<1
>500
Intrinsic RF
<20
>40
>1
<350
=Renal ultrasonography
useful to r/o obstruction and evaluate
kidney size to estimate chronicity of RF
Category
Etiology
↓cardiac output, ↓effective artery volume, sepsis, Hypovolemia,
Pre-renal
(↓renal blood cirrhosis (hepato-renal syndrome)
flow)
Drug : ACEi, NSAID, Contrast dye, cyclosporine
Renal
Acute tubular necrosis (ATN)
(intrinsic renal
-Ischemia: progression of any prerenal process toxins
damage)
-Drug: aminoglycocydes, amphoterecin, Cisplatin, contrast dye
-Pigmets: (myoglobin, Hb), Crystal (Uric acid) or Proteins (IgG
light chains)
Acute interstitial nephritis (AIN)
-Allergic: β-lactamantibiotics, sulfa drugs, NSAIDs,
-Infection
-Infiltration (sarcoid, lymphoma)
-Auto immune (SLE)
-Vascular : renal artery stenoses(especially bilateral +ACEi)
thrombosis, hypertensive crisis, sclerderma
renal crisis
Cholesterol emboli, HUS/TTP
Acute glomerulonephritis (AGN)
Post-renal
Bladder neck: BPH, prostate cancer, neuropathy, anticholindergic
(Obstruction of medication
urine)
Ureteral : Malignancy, Lymphadenopathy, retroperitoneal fibrosis
Tubular : precipitation of crystals
=Renal biopsy: consider if suspect AGN
[rapid ↑in Cr, proteinuria (sometimes in the
nephrotic range), and an active urinary
sediment with hematuria and RBC casts.]
DD of Postrenal ARF
- Bladder catheterization
assessment of Lower tract obstruction
- Ultrasonography usually identifies
lower and upper tract obstruction
-IVP
-CT
Complications
- Volume overload( edema, congestive HF)
- hyperkalemia, hyperphosphatemia
- Uremia (encephalopathy, pericarditis,
nausea, vomiting)
Prevention and treatment of ARF
Management of ARF
Prerenal azotemia
I. Hemodynamic monitoring
-adequate volume expansion while
avoiding overexpansion
- assess and manage poor
cardiac function
-Invasive monitoring with a
central venous pressure or
pulmonary artery catheter
II. Fluid Challenge
-The quantity must be determined on an individual
basis, but typically 500-1000 ml normal saline is
infused over 30-60 minutes.
-If no response is obtained, volume infusion can
be followed by furosemide, 100-400 mg iv to
promote urine flow.
-Metolazone, 5-10 mg PO
-Furosemide 10mg-40mg/H continue drip
Management of Radiocontrast nephropathy:
=Risk factor of Radiocontrast nephropathy
(1)long term DM
(2)Pre-existing renal insufficiency (Cr>1.5)
(3)volume depletion
(4)multiple myeloma
(5)CHF
(6)>65y/o
=tends to be oliguric,
-serum Cr peaks in the first 72 hours.
-Hydration
-12-24 hours before contrast and
ending 12 hours after the contrast study.
-Infusion rates need to be individualized
-75-150 ml/hour of 0.45% saline, the
-goal being a slightly volume-expanded patient
with a high urine output.
-Acetylcystine
-1.5g/day (2pk qid/day)
- starting 1 day before procedure until 12hours
after procedure
III. Obstructive nephropathy in the upper or lower urinary tract may incite ARF
=Relief of obstruction
-Foley
-Surgery process
- If the post-obstructive diuresis appears excessive,
fluid and electrolytes should be replaced.
-The appropriate initial replacement fluid in such
cases is usually 0.45% saline.
Prevention and treatment of complications
=Intravascular volume overload
-Salt (1-2 g/d) and water restriction
(usually 1-1.5 L/d)
-Diuretics (usually loop blockers ± thiazide)
(lasix max dose=1g/day)
-Ultrafiltration or dialysis
Prevention and treatment of complications
=Hyponatremia
-Restriction of enteral free water intake
(<1 L/d)
-Avoid hypotonic intravenous solutions
(including dextrose solutions)
=Hyperkalemia
-Restriction of dietary K intake
(usually <40 mmol/d)
-Eliminate K* supplements and
K-sparing diuretic
-Potassium-binding ion-exchange resins
(e.g., Kyxalate)
=Metabolic acidosis
-Glucose (50 mL of 50 dextrose)
and insulin (10 units regular)
-Sodium bicarbonate
(usually 50-100 mmol)
-Calcium gluconate
(10 mL of 10 solution over 5 min)
-Dialysis (with low K* dialysate)
-Restriction of dietary protein
(usually 0.6 g/kg per day of
high biologic value)
-Sodium bicarbonate
(maintain serum bicarbonate
>15 mmol/L or arterial pH >7.15)
-Dialysis
=Nutrition
-Restriction of dietary protein (0.6 g/kgper day)
-Carbohydrate (100 g/d)
-Enteral or parenteral nutrition
(if recovery prolonged or pt very catabolic)
=Indications for dialysis
-Clinical evidence (symptoms or signs) of uremia
-Intractable intravascular volume overload
-Hyperkalemia or severe acidosis
resistant to conservative measures
-Prophylactic dialysis when
urea >100-150 mg/dL or
creatinine >8-10 mg/dL
Fluid control for CRRT
PAWP <6
6-8
9-11
12-14 15-17
mmHg mmHg mmHg mmHg mmHg
I-O
cc/H
175
cc/H
125
cc/H
18-20 21-22 >22
mmHg mmHg mmHg
75 cc/H 0 cc/H -50 cc/H -75
cc/H
-100
cc/H
-125
cc/H
Prescribing of medications
=Choice of agents
Avoid -other nephrotoxins,
-ACE inhibitors,
-cyclooxygenase inhibitors,
-radiocontrast unless
absolute indication
and no alternative agent
=Drug dosing
- Adjust doses and
frequency of
administration for
degree of renal impairment (CCr)
Management of the recovery phase of intrinsic and obstructive ARF
-careful monitoring of serum electrolytes,
volume status, urinary fluid and
electrolyte loss
-careful supplement of fluid and electrolyte when dehydration and electrolyte
imbalance.