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.

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

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.

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.

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.

All causes of prerenal azotemia can progress to ATN if renal perfusion is not restored and/or nephrotoxic insults are not withdrawn

Post-renal causes of ARF Bilateral urinary tract obstruction .

Urinary tract obstruction, due to posterior urethral valve.

chronic obstructive uropathies.

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.

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).

Symptoms of uremia

Lethargy

Anorexia

Pericarditis

Neuropathy

Nausea and vomiting

Pruritis

Dyspnea

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

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.

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

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 .

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).

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 .

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.

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.

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

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

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

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.

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 .

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.

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.

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.

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.

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.

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.

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.