ACUTE RENAL FAILURE

•	Definition.
•	Causes.
•	Approach.
•	Investigations.
•	Management.

Definition

1.	Acute renal failure: an abrupt deterioration in parenchymal renal function which is usually reversible over a period of days or weeks.

2.	Classification:

Type	GFR	Urine output	
Oliguric	5 ml / min / 1.73m2	< 300 ml/ m2/Day	
Non-oliguric	5 – 15 ml / min / 1.73m2	Normal	

Causes

1.	Prerenal:

a.	Congestive heart failure.

b.	Volume depletion / dehydration:

i.	GI loss: GIT haemorrhage, vomiting, diarrhoea.

ii.	renal loss: renal diseases causing polyuria and loss of fluids.

c.	3rd space loss:

i.	hypoalbuminaemia states.

ii.	physical causes: burns, peritonitis, crush injuries.

iii.	peripheral dilatation: sepsis.

2.	Renal:

a.	Glomerulonephritis:

i.	acute nephritic syndrome: post-infectious GN, lupus nephritis, Henoch – Schonlein nephritis, IgA nephropathy.

ii.	rapidly progressive GN.

b.	Vascular:

i.	haemolytic-uraemic syndrome: triad of acute renal failure, microangiopathic haemolytic anaemia and thrombocytopenia following acute gastroenteritis, pneumonia, UTI.

ii.	renal vein thrombosis in neonates following sepsis.

c.	Interstitial nephritis:

i.	allergies.

ii.	postinfectious.

iii.	fulminating pyleonephritis.

iv.	papillary necrosis due to aspirin.

d.	Acute tubular necrosis:

i.	untreated / undiagnosed prerenal conditions.

ii.	nephrotoxins: gentamicin, heavy metals.

iii.	pigment injuries: intravascular haemolysis due to G6PD deficiency.

Approach

1.	Outline:

a.	Confirming presence of renal failure.

b.	Excluding other causes of uraemia.

c.	Excluding chronic renal failure.

d.	Differentiation between prerenal, renal and postrenal causes.

2.	Renal failure should be considered in any child presenting with:

a.	Oliguria: urine output < 300 ml/m2/day.

b.	Anuria.

c.	Acidosis: Kussmaul breathing.

d.	Haematuria, proteinuria.

e.	Hypertension.

f.	Symptoms of obstructive uropathy.

g.	Symptoms of renal tubular dysfunction.

h.	Anaemia of unknown cause.

3.	Features suggesting chronicity:

a.	History:

i.	history of polyuria, polydipsia and enuresis.

ii.	past history of renal disease.

iii.	family history of hereditary nephritis, e.g. Alport’s, polycystic kidney.

b.	Physical examination:

i.	short stature and growth failure.

ii.	sallow complexion.

iii.	anaemia.

c.	Investigations:

i.	bone scan: renal osteodystrophy.

ii.	ultrasound: small kidneys.

4.	Differentiation between prerenal, renal and postrenal causes

a.	Principles:

i.	exclusion of postrenal disease.

ii.	differentiate between prerenal and renal disease.

b.	Exclusion of postrenal disease:

i.	symptoms of obstructive uropathy: hesitancy, frequency, dysuria, terminal dribbling.

ii.	ultrasound, MCU, isotope scan.

c.	Clinical parameters:

Prerenal disease	Renal disease	
Dehydration & decreased BP	Normal hydration and BP	
Normal potassium level	Hyperkalaemia	
No acid-base abnormalities	High anion-gap acidosis	

d.	Urinary segments indicative of renal disease

i.	distorted RBCs & casts: GN.

ii.	raised WBC: pyelonephritis.

iii.	raised eosinophils: interstitial nephritis.

iv.	crystals: crystalluria.

e.	Urine electrolytes and osmolality

Parameter	Prerenal	Renal	
U specific gravity	> 1.020	< 1.010	
U osmolality	> 500 mOsmol/L	< 350	
U Na	< 20 mmol/L	> 40 mmol/L	
FE Na	< 1%	> 1%	
U Cl	< 25 mmol/L	> 25 mmol/L	
FE Cl	< 1%	> 1%	
U:P Osm	High 	Low	
U:P urea	High	Low	
U:P creat	High	Low	
RFI	< 1	> 1	
U: urine, P: plasma, FE: fractional excretion, RFI: renal failure index.

f.	Fluid and diuretic challenge:

i.	prerequisites: patient not fluid overloaded and there are no obstructive lesions in urinary tract.

ii.	correct dehydration state and hypovolaemia by saline / plasma / blood infusion: i/v 20ml / kg / normal saline or plasma over 30 – 60 min.

iii.	diuretics: i/v frusemide 2 – 5 mg/kg.

iv.	observe urine output: good output – prerenal disease; oliguria still persists – renal disease with acute tubular necrosis.

Investigations

1.	Confirmation of diagnosis of renal failure:

a.	Glomerular filtration rate:

i.	in health the GFR remains constant due to intrarenal regulatory mechanisms. 

ii.	in disease, with a reduction in intrarenal blood flow, damage to or loss of glomeruli, or obstruction to the free flow of ultrafiltrate along the tubule, the GFR will fall and the ability to eliminate waste material and to regulate the volume and composition of body fluid will decline.

iii.	this will manifest as a rise in the blood level of urea or the plasma level of creatinine and in a reduction in measured GFR.

b.	ARF is detected by a rising plasma urea and creatinine.

c.	Serum creatinine:

i.	in normal circumstances, serum creatinine is a good indicator of GFR as it is much less dependent on diet but is more related to age, sex and muscle mass.

ii.	normal values: 70 – 150 mol/L. 

iii.	in children, the creatinine level is usually lower than in adults; for every year of life, creatinine increases by 10 mol/L.

c.	Serum urea:

i.	the level of urea depends on both the GFR and the production rate, the latter is heavily influenced by protein intake and tissue catabolism.

ii.	therefore, serum urea is not an accurate indicator of GFR or renal function as compared to serum creatinine.

iii.	normal values: 2.5 – 6.7 mmol/L.

iv.	if urea is greatly raised out of proportion to creatinine consider dehydration or hypercatabolic states.

2.	Exclude CRF and assess etiology of ARF:

a.	UFEME: 

i.	RBC: > 1 rbc / mm3 or > 5 rbc per high power flim of fresh, unspun, mid-stream urine indicates haematuria and is abnormal.

ii.	WBC: > 10 wbc / mm3 in fresh, unspun mid-stream urine samples is abnormal and indicates an inflammatory reaction within the urinary tract.

iii.	casts: granular casts occur with glomerular and tubular disease while red-cell casts indicate renal disease; white cell casts may be seen in acute pyelonephritis.

iv.	bacteria: the demonstration of bacteria on Gram staining of the centrifuged deposit of a clean-catch mid-stream urine is highly suggestive of urinary infection.

b.	Urinary electrolytes and osmolarity.

c.	Renal ultrasound, IVU, MCU:

i.	to visualize the kidneys to detect masses, renal size and presence of obstructive uropathy and reflux nephropathy.

ii.	exclude CRF and (small kidneys) and postrenal causes of CRF.

3.	Assess for complications of ARF

a.	FBC.

ii.	UE, Ca, PO4, uric acid.

iii.	infection screen: CXR, urine culture.

iv.	ABG.

v.	ECG if hypokalaemia is present. 

Management

1.	Objective: the prime goal of management of ARF is maintenance of body homeostasis while awaiting improvement in renal function when the underlying cause has been treated or spontaneously resolved.

2.	General measures: good nursing, regular oral toilet, chest physiotherapy, consistent documentation of fluid intake and output and measurement of daily body weight to assess fluid balance changes.

3.	Maintaining homeostasis

Problem	Treatment	
Fluid overload	•	Fluid restriction.
•	Aim: loss of 0.5 – 1% body weight / day.	
Excess in nitrogenous waste	•	Patients with non-oliguric ARF: high dose diuretics.
•	Adequate caloric intake.
•	Restrict protein intake to 1g / kg /day.	
Electrolytes

Dilutional hyponatraemia	

•	Fluid and salt restriction.
•	Patient is usually edematous.	
Hypovolaemic hyponatraemia	•	Na replacement: 0.6 x BW x Na def.
•	True salt loss occurs in interstitial nephritis, diarrhoea, etc.
•	Patient is usually dehydrated.	
Hyperkalaemia	•	Oral resin exchange.
•	IV NaHCO3: as soon as acidosis is treated, K will be excreted.
•	IV Ca gluconate: stabilizes membrane of cardiac muscle.
•	IV 50% glucose: push K into cells.
•	IV 50% glucose + insulin.
•	Early dialysis if refractory to above measures.	
Hypocalaemia	•	PO4 restriction
•	PO4 binders: CaCO3
•	Calcium supplements once PO4 is lowered. 	
Metabolic acidosis	•	IV NaHCO3 (NaHCO3 =  0.3 x BW x base deficit).
•	Dialysis if refractory. 	
Hypertension	•	Diuretics.
•	Anti-hypertensive drugs: sodium nitroprusside, nifedipine in acute crisis.	
Convulsions / coma	•	Treat underlying problem: electrolyte abnormalities, uraemia, hypertension, intracranial haemorrhage.
•	Anticonvulsants may be used.	
Pericarditis	•	Dialysis.	
Anaemia	•	Exchange transfusion in neonates.
•	Dialysis and transfusion.	
Infection	•	Antibiotics as indicated.
•	Beware of nephrotoxic drugs such as aminoglycosides and cephalosporins.	

4.	Indications for dialysis

a.	Hyperkalaemia: > 7 mmol/L.

b.	Acidosis: HCO3 < 10 mEq/L.

c.	Severe fluid overload: CCF, pulmonary edema, hypertension.

d.	Uraemia: urea > 300 mg/dL with deterioration of general condition, esp. encephalopathy.

e.	Hypercatabolic states where urea increases by > 10mmol/day.

f.	Options for dialysis:

i.	peritoneal dialysis.

ii.	intermittent haemodialysis combined with ultrafiltration.

iii.	intermittent haemofiltration.

iv.	continuous arteriovenous or venovenous haemofiltration.

v.	haemodiafiltration.

5.	Treatment for underlying disease

Disease	Treatment	
Cardiac failure	•	Diuretics.
•	Inotropes.	
Volume depletion	•	Replacement therapy.	
Hypoalbuminaemia states	•	Albumin and diuretics.	
SLE, nephritis.	•	Steroids	
Pyelonephritis	•	Antibiotics	
Obstructive uropathy	•	Surgery.