Acute Renal Failure

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
Pre-renal
(↓renal blood flow) / ↓cardiac output, ↓effective artery volume, sepsis, Hypovolemia, cirrhosis (hepato-renal syndrome)
Drug : ACEi, NSAID, Contrast dye, cyclosporine
Renal
(intrinsic renal damage) / Acute tubular necrosis (ATN)
-Ischemia: progression of any prerenal process toxins
-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
(Obstruction of urine) / Bladder neck: BPH, prostate cancer, neuropathy, anticholindergic medication
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)

-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)

=Metabolic acidosis -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
mmHg / 6-8
mmHg / 9-11
mmHg / 12-14
mmHg / 15-17
mmHg / 18-20
mmHg / 21-22
mmHg / >22
mmHg
I-O
cc/H / 175
cc/H / 125
cc/H / 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.