Principles of Monitoring Renal Function
Renal function is the key indicator of the kidneys’ condition and should be monitored in all deteriorating or critically ill patients in order to:
- Monitor disease progress;
- Assess baseline measurements before starting treatment with certain drugs;
- Indicate the function of other systems, (e.g. cardiovascular system where low cardiac output will result in diminished urine output);
- Identify renal impairment.
This article will discuss the principles of monitoring renal failure.
The kidneys, located near the middle of the back, just below the rib cage, have several functions, which include:
- Secretion of hormones such as:
- Renin: controls the production of angiotensin and aldosterone-contributes to the regulation of blood pressure and fluid balance.
- Erythropoietin: synthesised in the kidney-it stimulates the bone marrow to produce red blood cells.
- It is responsible for the regulation and maintenance of:
- Fluid balance
- Electrolyte balance
- Acid-base balance
- Excretion of foreign materials such as drugs and by-products of metabolism, nitrogen, urea, creatinine.
- Maintenance of calcium and phosphorus balance, and activation of vitamin D.
(Tortora and Derrickson 2011)
Principles of Urinalysis
A urinalysis can provide healthcare professionals with valuable information about the patient’s health status. For example, urinalysis can provide indications of kidney disease, diabetes mellitus, liver disease, urinary tract infection (UTI) and general dehydration (Steggall 2007).
The Purpose of Urinalysis
- Screening for systematic diseases – such as renal conditions and diabetes mellitus;
- Diagnosis – confirm and exclude suspected conditions, for example, urinary tract infections (UTIs);
- Management and planning – to monitor the progress of an existing condition and plan programmes of care.
Appearance of Urine
The colour of urine can vary greatly. Normal urine varies in appearance from clear to straw coloured, and is practically odourless, but becomes turbid and smells of ammonia if left to stand (Bishop 2008; Snyder 2009).
Variations in appearance of urine include the following:
- Pale: urine is very clear and colourless. Causes include pharmacologically induced diuresis, or by diabetes insipidus / diabetes mellitus.
- Dark: urine is concentrated as seen in fluid depletion or contains conjugated bilirubin and jaundice (Jenkins and Johnson 2010).
- Orange: usually caused by specific medicines such as hydroxocobalamin rifampicin (Bishop 2008).
- Pink/Red: may indicate haematuria, though other causes include ingestion of certain foodstuffs like beetroot and blackberries (Bishop 2008).
- Cloudy: may indicate the presence of pus, protein or white cells and requires further investigation (Steggall 2007).
- Sediment: is particulate material and comprises products of broken-down cellular materials formed in the collection tubules. Urinary stasis promotes cast formation which is often present in prerenal disease.
- Frothy: may indicate significant proteinuria.
- Normal, freshly voided urine is practically odourless. If left to stand for several hours, it acquires a mild smell of ammonia (Bishop 2008).
- Infected urine has a ‘fishy’ smell (Bishop 2008).
- In patients with diabetes who have ketoacidosis or in patients who are anorexic or not eating, acetone is excreted in the urine causing the urine to smell uncharacteristically sweet (Steggall 2007).
A dipstick test of urine can accurately show the presence of a variety of substances such as protein, glucose, blood and ketones as well as the PH.
To ensure reliable results, the following procedures are recommended.
- Always use a fresh sample of urine collected in a clean, dry container.
- Observe sample for colour, appearance, smell and debris.
- Ensure that reagent strip is in date.
- Ensure that the whole of the reagent strip is immersed in the urine sample.
- Wipe off excess urine, place horizontal and compare reagent pads with the colour scale at time intervals stipulated by manufacturer, documenting results immediately.
- Safely discard strip and urine sample.
- Store reagent strips following the manufacturer’s recommendation
Significance of Urinalysis Results
- Glucose in urine indicates that blood glucose is raised and the consolidation of glucose in the plasma exceeds the renal threshold (Wilson 2005). The most common cause is diabetes mellitus.
- Ketones are by-products of fat metabolism (Snyder 2009) and are suggestive of excessive fat breakdown as in starvation, fasting and uncontrolled diabetes (Stegall 2007).
- Proteinuria is the presence of abnormally large quantities of protein, usually albumin. Persistent proteinuria is typically a sign of renal disease such as UTI.
- Haematuria (presence of blood) is associated with diseases of the kidney or urinary tract; it can also be present during menstruation (Wilson 2005).
- Nitrate is strongly indicative of infection (Jenkins and Johnson 2010) although negative results can’t rule out infection (Bishop 2008).
- White blood cells (pyuria) usually indicate an infection somewhere along the urinary tract (Snyder 2009) and is an indication for laboratory testing.
Principles of Urine Output Monitoring
- Urine output is frequently used as a guide to the adequacy of cardiac output (renal perfusion amounts to 25% of the cardiac output) (Gomersall and Oh 1997).
- The average urine output in a healthy adult is 1000-1500ml/day (Snyder 2009)
- All critically ill patients will require a urinary catheter to measure urine output and normally an hourly urine drainage bag attached.
- The urinary catheter should be closely monitored for blockages or occlusions.
- If urine output dramatically falls always consider mechanical obstruction first.
- Sometimes bladder washouts are indicated (intermittent or continuous).
Principle of Monitoring Fluid Balance
Monitoring fluid balance in critical illness is essential. Understanding of disease processes is essential because clinical conditions can deteriorate rapidly.
- Careful monitoring of the fluid balance chart (input and output) must be maintained.
- Monitoring the patient for signs of fluid loss/gain should also be undertaken.
- Daily measurement of serum sodium, potassium, urea and creatinine is required to assess fluid and electrolyte balance.
- Fluid balance charts from preceding few days should be compared with serum and urine urea and electrolyte values to help evaluate the patient’s response to fluid administration and guide the fluid regimen over the next 12-24 hours.
(Murphy and Byrne 2010)
Acute Renal Failure
Acute renal failure (ARF) is characterised by a rapid decrease in the kidneys’ ability to eliminate waste products, which result in an accumulation of urea and creatinine.
ARF can be classified according to precipitating factors. For example:
- Prerenal: caused by inadequate renal perfusion due to;
- A decreased intravascular volume such as dehydration, haemorrhage, hypovolemic shock (Murphy and Byrne 2010).
- Cardiovascular failure such as heart failure, myocardial infarction (MI), cardiogenic shock.
- Medicines such as angiotensin-converting enzyme (ACE) inhibitors, non-steroidal anti-inflammatory drugs (NSAIDS), anaesthetics.
- Decreased effective renal perfusion due to sepsis, cirrhosis, neurogenic shock.
- Intrinsic: occurs when there is structural damage to the renal parenchyma such as acute tubular necrosis (ATN). ATN occurs because of sustained renal hypoperfusion (Perkins and Kisiel 2005).
- Post-renal: caused by obstruction of urine drainage due to ureteral obstruction such as stones, blood clots, strictures (Holcombe and kern Feeley 2009).
Monitoring renal function is essential to the care of a deteriorating or critically ill patient. It can provide indications of the kidney functions as well as the performance of other major body systems.
- Bellomo, R 2009, ‘Acute renal failure’, in Bersten, AD & Soni, N (eds), Oh’s Intensive Care Manual, 6th edn, Elsevier, Philadelphia.
- Bishop, T 2008, ‘Urine testing: Urinalysis (urine testing) can provide valuable information about a patient’s condition, allowing the detection of systemic disease and infection (practise nurse trainer)’, Practice Nurse, vol. 35, no. 12, p. 18.
- Gomersall, C & Oh, T 1997, ‘Hemodynamic Monitoring’, in Oh, T (eds), Intensive care Manual, 4th edn, Butterworth Heineman, Oxford.
- Holcombe, D & Kern Feeley, N 2009, ‘Renal Failure’, in Gonce Morton, P & Fontaine, DK (eds), Critical care Nursing. A holistic approach, 9th edn, Wolters Kluwer Lippincott Williams & Wilkins, Philadelphia.
- Jenkins, PF & Johnson, PH 2010, Making sense of acute medicine, Hodder Arnold, London.
- Jevon, P & Ewens, B 2012, Monitoring The critically Ill patient, 3rd edn, Blackwell Publishing Ltd, Oxford.
- Murphy, F & Byrne, G 2010, ‘The role of the nurse in the management of acute kidney injury’, British Journal of Nursing, vol. 19, pp. 146-52.
- Perkins, C & Kisiel, M 2005, ‘Utilising physiological knowledge to care for acute renal failure’, British Journal of Nursing, vol. 14, no. 14, pp. 768-73.
- Snyder, KA 2009, ‘Anatomy and physiology of the renal system’, in Gonce Morton, P & Fontane, DK (eds), Critical care Nursing. A holistic approach, 9th edn, Wolters Kluwer Lippincott Williams & Wilkins, Philadelphia.
- Steggall, M 2007, ‘Urine samples and urinalysis’, Nursing standard, vol. 22, no. 14-16, pp. 42-5.
- Tortora, GJ & Derrickson, BH 2011, Principles of anatomy and physiology, 13th edn, Wiley Blackwell, Oxford.
- Wilson, LA 2005, ‘Urinalysis’, Nursing Standard, vol. 19, no. 35, pp. 51-4.