Oliguria can be a sign of hypovolaemia and acute renal failure. Fluid balance must be accurately monitored so deficits can be corrected and complications prevented
Phil Jevon, PGCE, BSc, RN, is resuscitation officer/clinical skills lead, Manor Hospital, Walsall.
Jevon P (2010) How to ensure patient observations lead to effective management of patients with oliguria. Nursing Times; 106: 7, early online publication.
Fluid balance is essential for normal functioning of the body. Oliguria (poor urine output) is usually associated with low circulatory blood volume (hypovolaemia), and can be a sign that a patient is acutely ill and deteriorating. Early warning scoring systems should identify the condition so that appropriate interventions can be undertaken to restore urine output and protect renal function.
Keywords Oliguria, Patient observation, Hypovolaemia
- This article has been double-blind peer reviewed
Competencies relating to monitoring urine output
Nurses and healthcare assistants should be able to record fluid input and output accurately.
Registered nurses responsible for patients should be able to:
- Interpret fluid balance;
- Administer intravenous fluids as prescribed;
- Insert a urinary catheter (Department of Health, 2008).
Fluid balance is essential for normal functioning of the body. It helps to maintain body temperature, cell shape, and assists in the transportation of nutrients, gases and waste products (Docherty and Coote, 2006).
Disturbance in fluid balance during episodes of critical illness occur for a number of reasons including:
- Disruption to normal physiological mechanisms such as hypernatraemia (elevated sodium levels in the blood);
- Disease processes for example, acute renal failure;
- Side-effects of treatment for example, diuretic therapy.
Oliguria (poor urine output) is a common sign of critical illness and is associated with poor fluid intake or excessive fluid loss. This article discusses the assessment and management of oliguria associated with hypovolaemia (low circulatory blood volume).
The condition is defined as the production of abnormally small amounts of urine - 100-400mls of urine in 24 hours (Smith, 2003). Definitions of abnormal urine output are listed in Box 1. It can be a sign that the patient is acutely ill and deteriorating (Jevon, 2008) and is usually associated with hypovolaemia (low circulatory blood volume) caused by restricted fluid intake or excessive fluid loss (Docherty and Coote, 2006). The causes of oliguria are listed in Box 2.
Early warning scoring (EWS) systems should identify oliguria so that timely and appropriate interventions are carried out to re-establish urine output and protect renal function (Jevon, 2008). This may prevent further deterioration and progression to acute renal failure (Ahern and Philpot, 2002) which is a life-threatening condition commonly associated with critical illness (Gwinnutt, 2006).
Box 1. Definitions of abnormal urine output
- Oliguria: 100-400ml in 24 hours;
- Anuria: <100ml in 24 hours;
- Absolute anuria: 0ml in 24 hours.
Source: Docherty and Coote, 2006; Smith, 2003.
Absolute anuria is rare and is usually associated with a blocked urinary catheter (Adam and Osborne, 2005; Ahern and Philpot, 2002).
Box 2. Causes of oliguria
Requirements for normal urine output include:
- Adequate renal perfusion (Smith, 2003);
- Normal renal function;
- No obstruction to the flow of urine (Jevon, 2008).
Causes of oliguria
- Pre-renal: for example, hypovolaemia, hypotension;
- Renal: for example, acute tubular necrosis;
- Post renal: for example, ureteric stone, retention of urine (Jevon, 2008).
Monitoring fluid balance
Fluid balance is defined as the appropriate balance of fluid input and output over 24 hours. The fluid input over 24 hours in an average person should be approximately 2500ml (1500ml as liquid, 800ml in ingested food and 200ml as a bi-product of food metabolism). Fluid output should be the same volume - 1500ml urine, 800ml of insensible loss such as sweating, and 200ml in faeces (Marcovitch, 2005).
During critical illness fluid input and output should be monitored following local EWS protocols and the following should be recorded:
- Oral intake;
- Urine output;
- Wound and nasogastric drainage;
- All drug and fluid infusions (Adam and Osborne, 2005).
A positive fluid balance occurs when input exceeds output. This can occur when a patient’s IV fluids administration regime is increased to rectify fluid volume deficits and dehydration.
A negative fluid balance is when output exceeds input, for example, following treatment of fluid overload with diuretics (Brooker and Waugh, 2007). It is important to accurately monitor fluid balance in the critically ill patient so that deficits in fluid balance can be corrected and further complications prevented.
It is important to identify the cause of oliguria as early as possible so the most appropriate treatment can be instigated before complications occur (Jevon, 2008). The most common cause in the critically ill patient is hypovolaemia.
Absolute anuria is rare and is most likely to be caused by a blocked catheter (Ahern and Philpot, 2002).
Occasionally oliguria can occur because patients have difficulty passing urine in hospital due to embarrassment and this should be considered when other causes have been eliminated.
Patients should be assessed following the Resuscitation Council (UK)’s systematic ABCDE (airway, breathing, circulation, disability, exposure) approach to the assessment of critically ill patients (Resuscitation Council UK, 2006) to ascertain whether they are critically ill. Ensure appropriate senior help is called if necessary following local EWS protocols.
- In critically ill patients, start prescribed emergency oxygen (Jevon, 2010a) and ensure they have a clear airway and are breathing adequately;
- In hypotensive patients, position them in a supine position if this is tolerated (Jevon, 2010b);
- Insert a urinary catheter to monitor output (Smith, 2003);
- In patients with a urinary catheter, ensure the oliguria is not caused by a mechanical problem for example, blocked or kinked catheter tubing;
- Exclude retention of urine as the cause of oliguria (Gwinnutt, 2006);
- Arrange for IV cannulation to administer an intravenous fluid challenge and monitor its effect on urine output. It may be necessary to repeat the challenge (see Box 3);
- Attempt to establish the cause of the oliguria. Perform a urinalysis (dark concentrated urine and a high specific gravity (SG >1.030) are features of volume deficit (Brooker & Waugh, 2007)).
- Blood tests should be taken to monitor serum sodium, potassium, urea and creatinine levels. It may be necessary to measure urine volume over 24 hours to assess fluid and electrolyte balance.
- Regularly monitor fluid balance in combination with vital signs. Complete the EWS chart following local protocols.
- Ask the doctor to review the use of nephrotoxic drugs, for example, non steroidal anti-inflamatory drugs (NSAIDs), gentamicin and ciclosporin as these may need to be discontinued;
- Seek medical advice for patients on diuretic therapy as this may need to be omitted if they are hypovolaemic.
Box 3. Fluid challenge
Oliguria caused by hypovolaemia can be reversed if a fluid challenge is immediately administered (Smith, 2003).
This is a key treatment intervention aimed at preventing acute renal failure in the general ward setting (Docherty and Coote, 2006).
The aim of a fluid challenge is to produce a significant and rapid increase in plasma volume which will stabilise the patient’s condition. This procedure should be carried out while expert help is being sought (Gwinnutt, 2006).
- An isotonic crystalloid such as 0.9% normal saline is normally infused (Doherty and Coote, 2006).
- Fluids containing dextrose are not used for initial resuscitation because they are rapidly distribute throughout the intracellular and extracellullar fluid compartments in the body, with very little remaining in the circulation (Gwinnutt, 2006).
- A fluid challenge (usually 500mls) is administered over approximately 15 minutes; the patient is closely monitored for signs of improvement, for example, increased urine output, decreased respiratory and pulse rates, a rise in blood pressure and improved level of consciousness (Gwinnutt, 2006).
- The fluid bolus may need to be repeated.
Oliguria could indicate critical illness and it is important to assess the patient following the ABCDE approach and maintain an accurate fluid balance chart. Nurses should be aware of other causes of oliguria including blocked catheters or urinary retention and exclude these during initial assessment of the patient. If no other causes of oliguria can be identified, patient embarrassment about urination while in hospital may be causing the condition.
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