Acute Renal Failure

Also known as acute kidney injury.

It is defined as sudden decrease in kidney function resulting in failure to maintain acid base, fluid and electrolyte balance and excrete nitrogenous wastes.

                In the absence of kidney functions serum creatinine rises 1-1.5 mg/dl in a day. It can increase rapidly in conditions like rhabdomyolysis.

RIFLE Criteria:

It describes progressive stages of acute kidney disease.

RISK: 1.5 fold increase in serum creatinine or decline in urine output to 0.5ml/kg/hour over 6 hours.

INJURY: two fold increase in serum creatinine or decline in urine output to 0.5ml/kg/hour over 12 hours

FAILURE: threefold increase in serum creatinine or decline in urine output to 0.5ml/kg/hour over 24  hours

LOSS: persistent AKI or complete loss of kidney function for more than 4 weeks

ESRD:  need for renal replacement therapy (RRT) for more than 3 months

SIGN AND SYMPTOMS

·         Mostly nonspecific

·         While present they are due to uremia or its underlying cause

·         Uremia can cause nausea, vomiting, malaise, altered sensorium, encephalopathy, astrexis

·         HTN may occur

·         Hypovolemia associated with pre-renal causes and hypervolemia with intrinsic or post renal causes

·         Pericardial effusion with pericardial effusion rub may be present and it can result in crdiac tamponade.

·         Crepts can be present due to hypervolemia

·         Arrhythmias may occur with hyperkalemia

·         Bleeding or clotting disorders may be present.

    CAUSES:

     1. PRERENAL CAUSES

These are most common & due to decreased perfusion of kidneys which may be due to:

·         Decrease  intravascular volume

·         Change in vascular resistance

·         Low cardiac output

Decrease  intravascular volume

                Hemorrhage

                GI losses

                Dehydration

                Excessive dieresis

                Burns

                Pancreattis

                Trauma

                Extravascular space sequestration

                Peritonitis

Changes in vascular resistance

                Sepsis

                Anaphylaxis

                Anesthesia

                Afterload reducing drugs

                NSAIDS

                Renal artery stenosis

                Epi, Nepi, high dose dopamine, anesthetic drugs

Low cardiac output

                CHF

                Cardigenic shock

                Cardiac tamponade

                Pulmonary embolism

     2. POST RENAL CAUSES

They are least common cause of ARF but must be excluded due to their reversibility.

They occur when urine flow from the kidneys is obstructed. Obstruction leads to increase in intraluminal pressure which can cause renal parenchymal damage. Causes include:

                BPH

                Urethral obstruction

                Bladder obstruction

                Bladder, prostate & cervical cancers

                Reteroperitoneal fibrosis

                Neurogenic bladder

                Blood clots

                Papillary necrosis of kidney

     3. INTRINSIC RENAL CAUSES

It is considered if pre- & post-renal causes have been excluded. The sites of injury are

tubules, interstitium, vasculature & glomeruli. Causes include:

Acute tubular necrosis

Vasculitis

Malignant HTN

Cholesterol emboli

HUS

TTP

Interstitial nephritis

Hepato-renal syndrome

LABORATORY FINDINGS:     

·         Elevated BUN and serum creatinine

·         Urine analysis may show casts or sediments related to specific disorder

·         Hyperkalemia from impaired renal K excretion

·         Anion gap and non anion gap metabolic acidosis

·         Hyperphospahtemia

·         ECG- peaked T waves, PR prolongation, QRS widening and a long QT segment can occur with hypocalcmia.

·         USG- may show obstruction due to stones, prostate or carcinoma

·         CT scan for reteroperitoneal fibrosis.

·         PT/APTT should be done.

TREATMENT:

                Pre-renal causes:

                                Depends entirely on the cause

                                Maintain euvolemia

                                Monitor serum potassium

                                Avoid nephrotoxic drugs

               

                 Post-renal causes:

                                Immediate catheterization

                                Removal of obstruction

                                Watch for volume replacement as post abstructive dieresis.