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Skills: Assessing continence with bladder ultrasound

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VOL: 103, ISSUE: 19, PAGE NO: 44
Ray Addison
BSc, FETC, CertHEd, RN, is nurse consultant in bladder and bowel dysfunction, Mayday University Hospital, Croydon.
Addison, R. (2007) Assessing continence with bladder ultrasound. Nursing Times; 103: 19, 44–45

Ray Addison outlines the principal uses of portable bladder ultrasound and reminds readers of the importance of reviewing the results of this investigation with other clinical investigations and the patient’s health status.

Using a portable bladder ultrasound machine may be a simple task but its application is complex. An HCA can undertake a portable bladder ultrasound but it is the interpretation of the results that requires a wider knowledge and higher level of competence.

Problems with micturition affect a patient’s quality of life and health status. Interventions must therefore aim to improve these two variables and be guided by careful risk assessment. For example, a portable ultrasound may reveal a large residual volume of urine in a patient’s bladder but this may not affect her or his quality of life or health and treatment may not be necessary (see case studies).

Voiding problems

Patients may complain of voiding problems including hesitancy, intermittency, frequency and poor stream. However, some patients may be asymptomatic but have serious complications.

Complications of voiding problems include compromised renal function and renal failure caused by back pressure of urine in the bladder, which leads to dilation of the ureters and renal congestion (hydronephrosis). This results in the accumulation of toxic waste products in the bloodstream, which can cause sickness, skin irritation and confusion.

Detrusor failure can occur when the bladder has been stretched to accommodate a residual volume of urine or it may occur due to the effort required by the bladder muscles to expel urine past an outflow obstruction. Detrusor failure may not be resolved even when the cause of the outflow problem has been removed, for example by a prostatectomy, and residual urine volume accompanied by symptoms of poor bladder emptying may occur after surgery.

Risk assessment

Nurses need to consider the risk of any intervention they undertake (NMC, 2004). Portable bladder ultrasound is a very low-risk activity compared with catheterisation to estimate a residual volume of urine in the bladder, although catheterisation remains the gold standard. There are risks associated with using portable bladder ultrasound results alone to decide on interventions such as intermittent self-catheterisation.

A residual urine status model can provide a framework for the healthcare professional to rationalise clinical decisions, care planning and interventions (Box 1).

The health professional reviewing the results of a portable bladder ultrasound needs to consider:

Is the volume of residual urine found on ultrasound significant? Under 100ml is insignificant, between 100ml and 500ml could be significant and over 500ml is very significant;
Is there a diagnosed, undiagnosed or suspected cause for the residual urine?;
Is the voiding problem likely to be curable or incurable? If the patient has multiple sclerosis, the voiding problem is incurable but, in a male with an enlarged prostate, it may be curable;
Is the urinary retention acute or chronic? This may influence how urgently interventions are required;
Does the patient have symptoms that are linked to the voiding problem and associated urinary retention? These may include hesitancy, poor stream, intermittent stream, urgency and frequency and may have a direct effect on quality of life;
Is the urinary retention having an effect on the patient’s health status? Assessing this will include a review of renal function.
Portable bladder ultrasound can also be used as part of continence assessment. Other uses include:

Assessment of catheter-related problems. It is possible to see an inflated catheter balloon in the bladder using certain ultrasound machines;
Identifying bladder neck elevation and relaxation during a pelvic floor education programme;
Evaluating the effect of anticholinergic medication on voiding function, particularly with patients who have bladder instability associated with a neurological condition.
If residual urine is found in a healthy woman with no underlying neurological condition, a catheter should be inserted to ensure the fluid observed is urine. If fluid is still present following catheterisation an ovarian cyst may be suspected and an urgent referral should be made to a gynaecologist.

Accuracy

False readings can be obtained with volumes over 1,000ml and under 100ml (Ouslander et al, 1994). Other reasons for false readings include:

Foley catheter in the bladder;
Intravesical mass;
Bladder has an unusual shape (Coombes and Millard, 1994);
Ovarian cyst;
Obesity (Resnick, 1995);
Advanced pregnancy;
Altered position or shape of the bladder following surgery (such as hysterectomy);
Severe constipation;
Incorrect positioning of patient during the bladder ultrasound;
Blood clots in the bladder;
Bladder stones.
Some patients may be very distressed by a residual volume of urine of 300ml while others will have no problems with a residual volume of 700ml. If a patient is distressed, it is advisable to insert a urinary catheter regardless of volume. The value of bladder ultrasound is that it helps to identify the cause of the patient’s symptoms.

Conclusion

A residual urine volume on its own means very little and a symptom and patient profile combined with blood chemistry, urinalysis and urinary tract ultrasound provide a more holistic assessment and will aid any decisions about interventions.

References:

Coombes, G.M., Millard, R.J. (1994) The accuracy of portable ultrasound scanning in the measurement of residual urine volume. Journal of Urology; 152: 6, part 1, 2083–2085.

NMC (2004) Professional Code of Conduct. London: NMC.

Ouslander, J.G. et al (1994) Use of a portable ultrasound device to measure post-void residual volume among incontinent nursing home residents. Journal of the American Geriatric Society; 42: 11, 1189–1192.

Resnick, B. (1995) A bladder scan trial in geriatric rehabilitation. Rehabilitation Nursing; 20: 4, 194–203.

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