acute renal failure by dr. rafique
DESCRIPTION
Lecture by Dr. RafiqueTRANSCRIPT
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Functions of Kidneys 1: Formation of urine (maintain fluid
balance).
2: Maintain Ionic composition of the body
and H+ concentration. (Homeostasis)
3: Endocrinal functions: Production of
Renin and Erythropoietin.
4: Activation of Vitamin D.
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GLOMERULAR FILTERATION RATE (GFR)
Def.: Amount of glomerular filtrate formed in all nephrons by both kidneys /min.. In normal male adult , the average GFR is 125 ml/min, or 180 liters/day.
Normally 99% of filtrate is reabsorbed in the renal tubules and the remaining 1% passes into urine
GFR = (K ×height in cm) /Serum creatinine
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Acute renal failure in children
Abrupt reduction in kidney function & rapid
decline in GFR over several hours / days.
It results in the disturbance of renal
physiological functions including :
I. Impairment of nitrogenous waste product excretion(azotemia).
II. Loss of water and electrolyte regulation.
III.Loss of acid-base regulation.
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Prerenal causes or ARF
Prerenal azotemia results from either:
A- Volume depletion due to:
Bleeding (surgery, trauma, GIT).
GIT fluid loss (vomiting, diarrhoea).
Urinary (diuretics, diabetes insipidus)
Cutaneous losses (burns).
B-Decreased effective arterial pressure :
Heart failure, shock, or cirrhosis.
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Intrinsic renal causes of ARF
Vascular : Thrombosis (arterial & venous). Hemolytic-uremic syndrome (HUS). Malignant hypertension. Vasculitis e.g. HSP. Glomerular: Acute glomerulonephritis ( AGN). Tubular and interstitial disease : (ATN) results from ischemia due to decreased renal perfusion or injury from tubular nephrotoxins. Nephrotoxic agents: -Aminoglycosides. -Amphotericin B. - Contrast agents. -Heme pigments.
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All causes of prerenal azotemia can progress to ATN if renal perfusion is not restored and/or nephrotoxic insults are not withdrawn
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Post-renal causes of ARF Bilateral urinary tract obstruction .
Urinary tract obstruction, due to posterior urethral valve.
chronic obstructive uropathies.
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CLINICAL PRESENTATION
Tachycardia, dry mucosa, sunken eyes, low BP & decreased skin turgor suggest hypovolemia.
Dysentery with oliguria (<500 ml/1.73 m2 /day in children & <1 ml/kg / h in infants) or anuria (absent urine/<0.5ml/kg/h) is consistent with HUS
H/O pharyngitis or impetigo, a few weeks prior to the onset of gross hematuria suggests post-infectious glomerulonephritis (AGN)
Nephrotic syndrome, heart failure & liver failure may result in oedema and other signs of specific organ dysfunction.
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CLINICAL PRESENTATION -Cont..
Hemoptysis suggests pulmonary-renal syndrome.
Skin findings: malar rash, petechiae, and/or joint pain , systemic vasculitis, such as SLE or HSP
Anuria or oliguria: in a newborn suggests a major congenital malformation or genetic disease, like posterior urethral valve, b/l renal vein thrombosis or AR kidney disease.
In the hospital, ATN due to hypotension or nephrotoxic medications (such as aminoglycosides or amphotericin-B).
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Symptoms of uremia
Lethargy
Anorexia
Pericarditis
Neuropathy
Nausea and vomiting
Pruritis
Dyspnea
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EVALUATION & Dx. OF ARF Serum creatinine .
Serum BUN/creatinine ratio .
Urinalysis.
Urine Na .
Fractional excretion of Na.
Urine osmolality and urine output.
Renal imaging.
Fluid challange.
Others:
CBC, serum Na, K, P and blood gases.
ECG
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Value of urinalysis in Dx. of ARF
Normal urine : prerenal disease, urinary tract obstruction.
Muddy brown/granular & epithelial cell casts: ATN.
Red cell cast: glomerulonephritis.
Pyuria (WBCs), granular, waxy casts & proteinuria: tubular or interstitial disease or UTI.
Hematuria and pyuria: acute interstitial nephritis, glomerular disease, vasculitis, obstruction, and renal infarction.
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Urine sodium excretion
Measurement of the urinary Na is helpful in distinguishing renal from prerenal ARF due to effective volume depletion.
above 30 - 40 meq/l. ATN (renal)
below 10 meq/l. pre renal ARF
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Fractional excretion of Na (FENa)
This is defined by the following equation:
UNa x PCr FENa (percent) = —————— x 100 PNa x UCr
UCr & PCr : urine and plasma creatinine .
UNa & PNa : urine and plasma sodium .
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FENa - screening test that differentiates
between prerenal and renal ARF
< 1 % suggests prerenal disease.
1 -2 may be seen with either disorder.
> 2 % usually indicates ATN (renal cause).
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Urine osmolality :
urine osmolality below 350 m-osmol/kg suggest renal aetiology.
urine osmolality above 500 mosmol/kg is highly suggestive of prerenal cause.
Urine volume :
low (oliguria) in prerenal disease due to the combination of sodium and water loss.
Patients with ATN may be either oliguric or nonoliguric .
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Response to volume repletion ( fluid challenge)
H/O fluid loss & signs of hypovolemia/oliguria
-give I/V fluid to dif. b/w prerenal ARF & (ATN)
Fluid infusion is contraindicated in obvious volume overload or heart failure.
Normal saline (20 ml/kg) in 20 - 30 min. which can be repeated if necessary.
Restoration of adequate urine flow and improvement in renal function with fluid resuscitation is consistent with prerenal disease.
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Additional Lab. Measurements
CBC : Microangiopathic hemolysis & thrombocytopenia with ARF confirms HUS
Anti-neutrophil cytoplasmic antibodies (ANCA), (ANA), anti-(GBM) antibodies, ASOT, hypocomplementemia.
Elevated serum levels of aminoglycosides : Eosinophilia : Interstitial nephritis. Elevated uric acid :May also induce ARF.
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K:Due to oligurea or high K diet like dates, citrus fruits & increased tissue breakdown.
P : Once GFR falls below threshold, low P excretion- resulting hyperphosphatemia.
Ca: Due to hyperphosphatemia, low GIT
Ca absorption due to low Vit.D3 production .
Acid-base balance: metabolic acidosis .
Additional Lab. Measurements
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Renal imaging
Renal ultrasonography:
All children with ARF of unclear etiology.
Follow up of renal size and parenchyma .
Diagnosing urinary tract obstruction or
occlusion of the major renal vessels.
Renal biopsy: When noninvasive evaluation unable to establish correct Dx. & etiology
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LAB. STUDIES TO D/D PRE-RF& ATN
Pre-renal Failure
Urine Na excretion:<10 m mol/l (low)
FENa :< 1 %
Urine osmolality > 500
mosmol/l(serum+100)
U/P creatinine > 40
U/P urea >8 (high)
Urine sp. g. high >1.020
+ve fluid challenge test
ATN (renal cause)
> 40 m mol/l (high)
> 2 %
<350 m osmol/Kg
< 20
U/P urea <3 (low)
Fixed 1.010-1.020
-ve fluid challenge test
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Prevention of ARF
Close monitoring of serum levels of nephrotoxic drugs.
Adequate fluid repletion in hypovolemia.
Aggressive hydration and alkalinization of the urine prior to chemotherapy.
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Management of ARF
Maintenance of electrolyte and fluid balance
Adequate nutritional support.
Avoidance of life-threatening complications e.g. hyperkalemia, acidosis, hypertension, CCF
Treatment of the underlying cause .
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Mx. of fluid & electrolyte disturbancesHyperkalemia
Serum K > 7.0 meq/l is life-threatening & needs immediate attention and follow up by ECG:
1- I/V calcium , glucose + insulin infusion, NAHCo3 , beta agonists nebulization to promote extracellular K movement into the cells.
2-Kayexalate, an anion exchange resin, can remove excess K
3-Adjust K intake.
4- Renal replacement therapy if medical management fails to improve hyperkalemia.
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Acidosis
Sodium bicarbonate in life-threatening acidosis or hyperkalemia.
Serum NaHCo3 levels > 14 meq /l or arterial pH >7.2 do not require immediate intervention.
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Intravascular volume
Child with ARF may be hypo/ eu/ hypervolemic (including pulmonary edema and heart failure).
Appropriate evaluation of volume status and treatment to maintain euvolemia.
Insert urinary catheter.
If no response to diuretics after restoration of I/V volume (CVP), stop diuretics and start fluids as insensible water loss plus urine output only.
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Hypertension: result of hypervolemia. Use antihypertensives.
Nutrition :
Adequate calories to promote recovery.
If sufficient calories cannot be achieved with oliguria / anuria without causing hypervolemia, then renal replacement therapy is recommended.
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Renal replacement therapyINDICATIONS:
1) Signs and symptoms of sever uremia .
2) Azotemia (BUN > 80 - 100 mg/dl).
3) Severe fluid overload refractory to medical therapy .
4) Severe electrolyte abnormalities (eg. hyperkalemia and acidosis) that are refractory to supportive medical therapy
5) Nutritional support in oliguria / anuria.
6) Severe uncontrolled hypertension.
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Renal Replacement Therapy
Hemodialysis, peritoneal dialysis (PD), and continuous renal replacement therapy(CAPD).
The choice of modality is influenced by
-clinical presentation and
-status of the patient including
. presence of multi-organ failure
. indication for renal replacement
therapy.
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Prognosis of ARF The prognosis of ARF depends upon :
Etiology.
Age of the patient.
Clinical Picture.
Status of the patient.
Hypotension and need for inotropic
support during renal replacement therapy are significant poor predictors for patient survival.
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