Acute Renal Failure (ARF)

1st September, 2006

Summary

The human kidney constitutes only 1% of body mass yet renal blood flow equates to approx. 20% of the resting cardiac output. i.e. typically 1200mls of blood per minute The functional unit of the kidney is the nephron.

The main functions of the kidney are:
  • Excretion of waste products such as urea & creatinine
  • Selective reabsorption to control electrolyte balance
  • Water balance
  • Acid - base control (along with buffers and respiratory system)
  • Endocrine functions:
    • Erythropoietin (essential for red blood cell production)
    • Renin

Acute Renal Failure refers to the sudden failure of the kidney to produce urine of sufficient quality to prevent a rise in the level of nitrogenous metabolites, urea and creatinine and other waste products in the blood, to maintain normal electrolyte and fluid balance. The diagnosis is made from a rapidly rising urea and creatinine and a reduction in urine production over a period of hours or days.

Causes of acute renal failure - classified below:

Pre Renal: occurs as a result of renal hypoperfusion which usually responds well to rehydration

Renal: in critically ill patients other insults such as infection, hypoxia, drugs etc. may convert a simple problem of poor perfusion into one of acute tubular necrosis where there is structural damage to the renal parenchyma. The patient may not die from renal failure although this may be present at the time of death. There is a high mortality in patients who develop ARF in the context of other severe illness.

Post Renal (obstructive): The most common cause of obstructive uropathy in men is prostate

Clinical Signs and symptoms:

Oliguria and anuria: ARF is normally associated with oliguria (24 hour urine volume less than 400 mls) and possibly anuria (24 hour urine volume less than 100 mls) although it can occur with a wide range of urine output.

Uraemia: failure to eliminate the waste products of protein metabolism leads to a symptomatic serum rise of waste products normally found in the urine.

Electrolyte disturbances: Hyperkalaemia, metabolic acidosis

Fluid overload

Other: GI disturbances, hiccoughs / itching skin, thirst, dry mouth, candida infections, confusion, convulsions and coma

Hyperkalaemia:

The normal serum level of potassium is 3.5 - 5mmols/L. Potassium levels may elevate in acute renal failure mainly due to reduced renal excretion. The effects of hyperkalaemia can be dangerous and myocardial irritability and possible cardiac arrest can be seen.

ECG monitoring is a necessity. The main ECG signs of hyperkalaemia tend to be:

  • Peaking of the T wave
  • Widening of the QRS complex
  • Possible cardiac arrest rhythms

Management of Acute Renal Failure

Acute Renal Failure is a medical emergency. Renal function may be reversible in a large number of cases and so prompt assessment and treatment is essential to maximize the chances of recovery. The underlying cause of the ARF should be identi­fied and treated as soon as possible.

Closely screen at risk patients: It is essential that nurses identify at risk patients, such as those with pre-existing renal disease or receiving nephrotoxic drugs and also patients where there may be a reversible cause such as haemorrhage.

Ultrasound examination and abdominal x-ray are important to exclude obstruction. Urine ‘dipstick’testing may also be useful in determining the nature of the ARF

Fluid status: It is important to distinguish pre renal failure from established renal failure by establishing the fluid status of the patient. A number of observations may help:

  • Jugular Venous Pressure (JVP): Is often raised in fluid overload
  • Lying and standing Blood Pressure: A marked postural fall is a good sign of hypovolaemia
  • Lungs: The presence of crepitations due to pulmonary oedema may indicate fluid overload
  • Central Venous Pressure (CVP): A central line may be inserted as this is often a good indicator of fluid status. Low readings are often seen in hypovolaemia and higher readings in fluid over­load.
  • Chest x-ray: The presence of cardiomegaly and pulmonary oedema may indicate fluid overload
  • General observations: e.g. dry tongue, poor perfusion

If dehydration is suspected an intravenous fluid challenge e.g. 250mls of colloid is given while the patient is closely observed for signs of overload.

If the blood pressure is low despite correcting fluid status intravenous Inotropic drugs such as dobutamine may be considered. This is usually commenced at a rate of 2.5 – 5micrograms per KG per minute and titrated to BP response. Dopamine intravenous infusion at a rate of 2 micrograms per KG per minute may improve renal perfusion although its effectiveness remains controversial. Care should be taken when administering Dopamine via peripheral lines as infiltration may lead to local tissue necrosis.

If fluid overload is suspected consider diuretic as this may increase amount of fluid loss but will not necessarily improve renal function.

A strictly accurate fluid balance must be kept and it may be necessary to impose a fluid restriction that takes account of any insensible loss e.g. sweating.

Nutritional support is very important and may require enteral feeding. Adequate calories must be provided to minimize the breakdown of body protein that can lead to further rises in urea and creatinine.

Managing hyperkalaemia:

Firstly ensure the accuracy of result as it may be abnormal due to sample haemolysis. Remember that correcting the potassium ultimately depends on restoring homeostasis. It is important to identify and discontinue any contributing medication.

Measures to temporarily reduce potassium:

Hypertonic (50ml 50%) glucose and 15u Actrapid IV over 15 minutes ~ may reduce K+ by 1 mmol in 1 hour and lasts 2 hours. Remember that intravenous hypertonic glucose may be irritant to veins and a vein that ensures good flow should be selected for cannulation.

Calcium Gluconate 20% 10mls IV ~ the ECG normalizes rapidly although the effect may be relatively short lived.

Exchange resins ~ Resonium 15 grams four times daily oral or rectally. Simple laxatives may be equally effective in increasing gastrointestinal loss of potassium.

Consider haemodialysis particularly if hyperkalaemia is refractory to treatment or if there is pulmonary oedema and a severe or worsening metabolic acidosis.

Observations:

  • Strictly accurate 24 hour fluid balance
  • Daily weight: if possible. This offers a good indication of fluid status
  • 1 - 2 hourly vital signs
  • CVP recording
  • ECG monitoring and daily 12 lead
  • Biochemistry & haematology

Infection: patients are particularly vulnerable to infections from their invasive lines and urinary catheters. Meticulous hand washing is essential whenever dealing with these.

Anaemia: reduced production of erythropoietin and dilution may reduce the red blood cell count.

Most Nurses will encounter patients with Acute Renal Failure throughout their career. It is a medical emergency that requires prompt assessment and intervention if the patient is to survive.

For training courses in Renal Disease and other clinical skills visit www.cb-training.com

Further reading:

  1. Davidson AM, Cameron JS et al,, Oxford Textbook of Clinical Nephrology. 2nd ed. Oxford University Press 1998
  2. Brady HR, Singer CG. Acute Renal Failure. Lancet 1995; 346:1533-40