Acute Renal Failure

By:

Dr.Leena Hafeez

Definition

Sudden and usually reversible loss of renal function which develops over days or weeks accompanied by reduction in urine volume.

Etiology

The etiology of ARF can be divided into 3 categories.

PRE-RENAL RENAL POST RENAL

Etiology of AcuteRenal Failure(Overview)

Pre Renal Acute Renal Failure

Causes: Pre-renal causes of ARF include

Heart Failure.

Blood/Fluid loss as in major surgery,trauma,dehydration

sec. to severe diarrhea and vomiting.

Renal artery stenosis/Occlusion.

Diseases Affecting the arterioles.

Pathogenesis:

In circumstances which dec the perfusion pressure(Heart failure,Shock,Hypovolemia),Kidneys maintain their perfusion by constriction of renal vasculature and selective constriction of efferent arterioles

Drugs like NASIDs and ACE inhibitors affect these compensatory mechanisms.

Prolonged hypo perfusion and drug toxicity halt these compensatory mechanisms leading to acute decline in GFR

History and physical Examination

History: History of Vomiting,Diarrhea,Surgery or Trauma with blood loss and history of medications including diuretics,NSAIDs, ACE inhibitors, and ARBs may be present.

Examination: Physical signs of poor peripheral perfusion may be present. Orthostatic hypotension,Tachycardia,Reduced jugular venous pressure, decreased skin turgor, and dry mucous membranes are often present in prerenal azotemia

Intrinsic Acute Renal Failure

CausesIntrinsic causes of Acute renal failure include

Acute tubular necrosis:

May occur as a result of Ischemia,sepsis or

Nephrotoxic drugs.

Glomerular diseases:

Primary or Secondary glomerulonephritis

Vascular diseases:

E.g. Vasculitis or malignant hypertension

Pathogenesis of ATN Ischemia,Nephrotoxic agents(drugs and bacteria) or a

combination of these two can cause damage to the

tubular cells leading to their necrosis. Tubular cells shed

and block the tubular lumen along with interstitial edema.

Tubular cells regenerate from the basement membrane

resulting in recovery of renal function if the patient is

supported in the recovery phase.

Nephrotoxic drugs leading to ATN include

I. Aminoglycosides

II. Cisplatin

III. Amphotericin B

Post renal Acute Renal Failure

Causes:

Post renal ARF occurs secondary to any obstruction in the urinary tract

which include:

Renal stones

Tumors

Benign prostatic hyperplasia

Fig:Post Renal Causes of ARF

History and Physical Examination

Colicky flank pain radiating to the groin suggests acute ureteric

obstruction.

Nocturia and urinary frequency or hesitancy can be seen in prostatic disease.

Abdominal fullness and suprapubic pain can accompany massive bladder enlargement.

Definitive diagnosis of obstruction requires radiologic investigations.

Phases of Acute Renal Failure

Phases Acute Renal Failure is divided into 4 phases

Initiation Phase:

Oliguric phase:

Lasts 7-14 days. Urine output <400ml/day.

Diuretic Phase:

Urine output can reach up to 2500ml/day. Adequate fluid replace

required for good recovery

Recovery Phase:

GFR returns to normal. Renal parameters decline towards the normal

range

Investigations

Blood Counts Full Blood Count:

Anemia may show CKD

Low platelets may indicate DIC and sepsis

Urea and Creatinine:

Daily raise may exceed up to 5mmole/day

Serum Electrolytes:

Hyperkalemia

Albumin:

Low Serum Albumin in nephrotic syndrome and sepsis

Urine Analysis

Proteinuria may indicate glomerular disease

Hematuria shows obstructive lesions, stone or glomerulonephritis

Leucocytes may show infection

Crystals can be specific of drugs or uric acid

Radiological Investigations

Ultrasound:

Small kidneys suggest CKD, Asymmetric kidneys in renal vascular

diseases. Site of obstruction may be seen in post renal causes.

Doppler Ultrasound:

To rule out renal artery stenosis

X-ray Chest:

Pulmonary edema in fluid overload

Nuclear Scans:

I. DMSA Scan

II. DPTA Scan

Renal Artery stenosis

Specific Investigations:

Renal Biopsy:

For glomerular diseases, interstitial nephritis

Serology:

For infections like post streptococcal glomerulonephritis,

Leptospirosis.

Management

Management1.Treat the underlying cause:

Pre renal failure:

Restore the blood volume by transfusing Blood, Plasma or isotonic

saline carefully monitoring CVP and PWP

Renal Cause of ARF:

I. ATN responds to restoration of renal perfusion

II. Immunosuppressive therapy for glomerulonephritis

Post renal cause:

Prompt relive of obstruction restores the renal functions.

Management2.Fluid and Electrolyte Balance:

Strict monitoring of Intake and output

Daily fluid intake should be equal to output+500ml

Additional replacement required in case of abnormal losses like Diarrhea and Vomiting.

3.Hyperkalemia:

Potassium concentration >6mmole/L can cause serious

arrthymias.Immediate intervention required

4.Metabolic Acidosis:

Restoration of blood volume will correct acidosis. Treat with sodium

bicarbonate(50ml of 8.4%) in severe cases.

Management5.Proteins and energy Intake:

Protein restriction to less than 40g/day.

Major source of energy should be fats and carbohydrates

Enteral and parenteral nutrition may be required in patients with hyper catabolic states(e.g. burns and sepsis)

6.Infection Control:

Prompt diagnosis and treatment with antibiotics required

7.Avoidance of nephrotoxic drugs:

NSAIDS and ACE inhibitors may prolong ARF and should be avoided.

8.Renal replacement therapy:

May be required as supportive management

Prognosis

Prognosis of ARF depends upon the severity of Underlying cause

In Uncomplicated ARF secondary to hemorrhage and Drugs mortality is low

ARF associated with Serious Infections and MOF mortality is 50-70%

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