Marco conceptual

I. Strategy

1. Identify the functional derangement. This requires a high index of suspicion. (N.B. Beware of non-oliguric acute renal failure) 2. Define and neutralise immediate life threatening or potentially life

threatening events eg. Pulmonary oedema, hyperkalaemia, severe acidosis 3. Delineate the cause. Remember to exclude a surgical obstruction

4. Plan long term management such as preventing future identical insults, etc

II. Conservative medical management 1. Fluid management:

• One of the hallmarks of acute renal failure is a marked reduction in urine production ( <400 mls/24 hours). However, non-oliguric renal failure can also occur.

• In established renal failure, the strategy is fluid restriction. However, in the pre-renal phase, fluid replacement and correction of intravascular volume contraction is important.

• Accurate clinical judgement of intravascular volume is required.

Assessment of intravascular volume can be achieved by:

i. Estimating from history the quantum of loss.

ii. Determining loss in body weight.

iii. Assessing clinically the percentage of dehydration eg. skin tugor, etc.

iv. Measuring the pulse volume and blood pressure.

v. Putting in a central line to measure central venous pressure (CVP).

• Hypovolaemia should be corrected . Any hypotension must be quickly corrected with fluid challenge, or if there is no volume deficit, the use of an appropriate inotrope is advocated.

• Patient with volume deficit:

I. IN HYPOTENSIVE PATIENTS:

• Fluid challenge with 250 ml of normal saline over 15 mins may be given. If CVP measurement does not increase by 2 cm repeat fluid challenge (up to 500-1000ml of NS may be required). Stop if CVP measurement increase to satisfactory level ie 5-10cm H2O (NB:-Patient in severe shock may have an initial high CVP due to central venous spasm).

• If a good blood pressure is obtained, and good urine flow is

established (>40 mls/hour), continue with a slower fluid replacement regimen.

• If volume is restored, and blood pressure is still low, use an appropriate inotrope (eg dopamine titrated to less than 10 mcg/kg/min).

• If volume is restored, with good blood pressure, but urine outflow is poor (less than 40 mls/hour), start IV frusemide as described below.

• IV frusemide can be given either by slow bolus of 40-120mg repeated as necessary or infusion (dilute in NS) at a rate of 10-60mg/hr with maximal daily dose of 2g. Large doses of IV frusemide for prolonged period may cause hearing loss.

• If volume is restored, with good blood pressure, and the use of both frusemide and inotrope do not induce adequate urine output, restrict fluid to 500 mls/24 hours plus measured losses. Avoid potassium and food rich in potassium. Keep a strict intake and output chart.

II. IN NORMOTENSIVE PATIENTS:

• Fluid challenge should also be given to correct fluid deficit. If good urine flow is established (>40ml/hr), continue with slower fluid replacement regimen. If volume is restored but urine outflow is poor (<40ml/hr), start IV frusemide as described above.

• Patient without volume deficit:

Start IV frusemide and if necessary with an inotrope as above. If urine flow cannot be induced, restrict fluid.

2. Dietary modification:

• Protein - 0.5gm/kg/day (normal to high protein intake if dialysis is in place).

• NaCl - 2-4g/day.

• Calaric intake - 35-50 kcal/kg/day.

• Potassium - 40mmol/day (if dialysed).

N.B. Nutrition is a vital area of management and should be given a high priority.

3. Blood pressure:

• Hypotension should be corrected with volume expansion or vasopressors, depending on the patient’s intravascular volume status.

• Hypertension should be treated appropriately, with the blood pressure controlled at a rate depending on the clinical situations.

4. Hyperkalaemia should be treated promptly (see section on hyperkalaemia). Successful diuresis or dialysis are the only definite methods of removing potassium from the body; all other methods shift potassium between body fluid compartments.

5. Metabolic Acidosis:

• Metabolic acidosis of pH <7.2 or with HCO3 <10mmol/l should be treated with NaHCO3. A rough estimation of the amount required can be

calculated from the following formula:

0.5 X Body weight (kg) X Base deficit

# 1ml of 8.4% NaHCO3 provides 1 mmol/l of NaHCO3.

# Base deficit = 24 - Actual HCO3.

• In practice the treatment is usually ‘titrated’ slowly by infusing bicarbonate (eg. 1ml of 8.4% NaHCO3 per kg BW over 30 min) and regularly checking the plasma pH & HCO3. It is safer to under correct the deficit.

6. Drug dosages:

• Dosages of agents excreted by kidney must be adjusted for the level of renal function. Refer to drug information documents for accurate dosing.

7. Infection:

• Appropriate antibiotics should be given. Irrespective of the degree of renal impairment or the route of drug metabolism, a “loading” dose is

mandatory, followed by appropriate adjustment in dosage/frequency of dosing, to maintain a therapeutically efficacious and safe level.

8. Gastrointestinal haemorrhage should be treated appropriately.

Prophylaxis with H2 antagonist or similar drugs may be given.

9. Anaemia: Packed cells are transfused when anaemia is symptomatic. Aim for slow correction to a “functionally accepted level” rather than a normal level.

10. Hyperalimentation:

• In hypercatabolic patient, hyperalimentation should be started when the patient is more stable.

• If instituted in oliguric patients, it will necessitate more frequent dialysis or some of the continuous dialysis hemofiltration methods.

• The best and safest feeding route is oral; tubes placed in the intestinal tract are less desirable; IV feeding is the most dangerous.

11. Other measures:

• Abdominal ultrasound should be done to measure renal size and exclude obstructive uropathy.

• A renal biopsy may be indicated to establish a treatable renal cause, if pre-and post-renal causes pre-and abdominal infection have been excluded.

III. Dialysis

• Dialysis is best started early (eg when BU is around 35 mmol/l and creatinine around 600 umol/l).

• Dialysis is most often prescribed every other day or as frequently as necessary.

• In severely catabolic patients (crush injury, burns), daily dialysis (usually haemodialysis) may be required.

• It is generally accepted that in patient with ARF, dialysis therapy should be used as often as necessary to maintain BU of <30mmol/l.

1. Indications for initiating dialysis are:

• BU >35mmol/l.

• Severe hyperkalaemia (>6.5mmol/l).

• Severe metabolic acidosis (pH <7.2).

• Volume overload +/- pulmonary oedema not responsive to diuretics.

• The development of uraemic symptoms eg. CNS (asterixis,

neuromuscular irritability, somnolence, coma, seizures), GI (nausea and vomiting, haemorrhage) symptoms.

• Oliguria (urinary output <5ml/kg per day) or anuria (no urinary output for 12 hr).

N.B. Do not wait for the “critical number” to appear before initiating dialysis if the renal function is deemed to deteriorate. Early dialysis results in lessmorbidity and mortality.

2. Type of dialysis:

• The type of dialysis therapy for a particular patient - haemodialysis vs peritoneal dialysis - depends on the clinical situation.

• Patients with severe tissue breakdown (eg. rhabdomyolysis, trauma, burns, sepsis, postoperative) have enhanced urea production and usually require haemodialysis.

• In other types of ARF in which the catabolic component is less prominent, peritoneal dialysis may be adequate.

IV. Treatment of specific conditions 1. Acute intersitital nephritis.

• The suspected causative agent(s) should be stopped.

• When renal impairment is minor, recovery is the rule, and dialysis is usually not indicated.

• In more severe cases, high dose, short term prednisolone therapy (60mg/day for 1-2 weeks) may speed recovery of renal function.

• Renal function replacement therapy may occassionally be necessary

2. Primary renal disease, systemic diseases and vascular diseases.

Disease Therapy

Acute poststreptococcal

glomerulonephritis No specific therapy unless very severe.

Penicillin therapy indicated for 10 days Goodpasture's

syndrome/anti GBM GN

Plasmapheresis + Pulse IV

methylprednisolone 1g daily for 3 days followed by prednisolone 1g/kg/day and cyclophosphamide 2 mg/kg/day

Pauci-immune rapidly progressive GN (ANCA associated microvasculitis)

IV pulse methylprednisolone followed by oral prednisolone 1 mg/kg/day and cyclophosphamide 2 mg/kg/day

SLE Prednisolone 1-2mg/kg/day with or

without initial IV methylprednisolone 1g od for 3 days +/- cyclophosphamide 2 mg/kg/day or azathioprine 2-3mg/kg/day

Subacute bacterial

endocarditis Antibiotics (note use of possible nephrotoxic antibiotics) Henoch-schonlein purpura No specific therapy

Malignant hypertension Antihypertensives. Control blood pressure to a safe but NOT normal level within a twenty four hour period.

Dialysis, if required D. Footnotes

1. D Cockcroft formula:

Creatinine clearance (ml/min)

= (140-age in years) x (wt in kg) * 72 x serum creatinine in mg/dl

* For women multiply by 0.85

2. Fractional excretion of sodium (FENa) is the per cent of the filtered sodium which is eventually excreted.

FENa (%) = Urine Na x Plasma creatinine x 100 Plasma Na Urine creatinine In normal subject FENa is <1%.