A post void bladder scan is a non-invasive method of assessing bladder volume using ultrasonography and should be undertaken on first contact with all individuals (with consent).
Why perform a bladder scan?
The aim of the post void bladder scan is to identify if the individual is emptying their bladder effectively when voiding, or if the volume of any residual urine left is significant.
Although urinary catheterisation has long been regarded as the gold standard in determining an accurate post void residual (PVR) urine volume, it is invasive, sometimes uncomfortable, and carries a risk of infection or urethral trauma. It may still be used to determine PVR if a bladder scanner is not available or a client is not suitable for bladder scanning.
Bladder scanning has advantages over many other interventions, such as intermittent catheterisation, for measurement of post void residual volume, as it is simple and causes no discomfort to the patient/client.
In order to perform bladder scanning, health professionals must undergo training and be deemed competent to perform a bladder scan.
When a bladder scanner is available, estimation of residual urine or confirmation of effective bladder emptying should be a standard component of a continence assessment.
Note: Frailty, age or dementia are not reasons to not perform a bladder scan.
Clinical Practice Point. Remember that some individuals can present with a normal voiding pattern but have a significant post void residual.
A bladder scan needs to be completed at the first contact to enable prompt referral if a high bladder capacity/residual volume is identified. A delay could result in the individual suffering long term bladder damage with potential associated complications.
If residual urine is found in the bladder discuss this with the individual, request them to try to void again and re-scan.
Measuring post void residual (PVR) urine volume
At least three consecutive scans are recommended to ensure a correct reading, as there can be wide variations in PVR in any one patient/client.
- A PVR of below 100ml is considered ‘normal’ for any adult. This PVR may be higher in a frail older adult and cause no symptoms
If the PVR is between 100-200ml give advice to promote more effective bladder emptying – sit down with feet well supported, take time, lean forward, use double voiding. Arrange to repeat scan in 1-2 weeks.
The bladder will function more effectively if the correct toilet posture and technique is followed
- If the PVR is over 200ml discuss the scan results and the individual’s bladder diary information with a medical/specialist practitioner
- A PVR of 250ml is more significant if the voided volumes are low, 80-100ml than if they are higher 200-250ml - because it may indicate an outflow obstruction and/or underactive bladder
- Urgent discussion is required for high post void residuals 500-1000+ ml
- If the bladder stretches to hold volumes over 1000ml the detrusor muscle is very likely to become permanently damaged, resulting in an atonic bladder.
Clinical Practice Point. Note - the 1000ml is the volume voided + the residual volume. i.e. if the person voids 400ml and has a PVR of 740ml, their bladder is holding 1140ml.
Difficulties in voiding to request
If the person is unable to empty their bladder try to identify when they last voided and what they have had to drink.
Estimate how much urine they think they will have in their bladder and then undertake the bladder scan. If a repeat scan is indicated, talk to the individual and carers and try to arrange to scan when you think they may have voided.
Some individuals are unable to void to request, this may be related to a neurological problem or dementia. Some individuals with dementia can hold for significant periods of time; they may only void 1-2 times daily and pass large volumes.
Clinical indicators for a bladder scan
For the clinician, these are:
- Part of a continence assessment
- To confirm urinary retention
- To identify incomplete bladder emptying
- To assess post void residual urine volume
- In a trial without catheter (TWOC), to prevent bladder distension
- To assess bladder volume if indwelling catheter not draining
- To determine bladder volume in a client with decreased urine output.
For the patient/client, these are:
- In a bladder retraining program, it determines the need to void based on bladder volume and not time
- To assess effectiveness of mechanical bladder emptying
- To identify level of bladder sensation related to bladder volume
- To identify if adverse side effects of urinary retention are present such as with medications, e.g. anticholinergics
- As a standard investigation for at-risk groups (e.g. neurological disease, diabetes) when presenting with urinary problems
Bladder scanner limitations
Use of a bladder scanner may not be appropriate in all situations, including:
- If the patient/client has gross or morbid obesity
- If severe abdominal scarring is present
- If abdominal staples or tension sutures are in situ
- If an infectious abdominal wound is present (unless scan head protected with a condom)
Check the manufacturer’s recommendations
- For pregnant women
- For babies/infants
- For women in the immediate post partum period
- Identification of true anatomical detail of the bladder
Inaccurate bladder scan recordings may occur if:
- A cracked, broken or unclean scan head is used
- The wrong type of conduction gel is used
- Inadequate amount of gel on the scan head is used
- The battery is flat
- The scan head is incorrectly positioned
- There is movement of the scan head while operating the machine
- The wrong gender is identified before scanning
- The operator uses a poor technique
- Regular service and calibration is not carried out as per manufacturer’s recommendations
- The person is incorrectly positioned (ie not supine)
- Excessive body hair prevents conduction
- The person is obese
- Part of the bladder extends outside of the scanned region (e.g. if a large hernia or diverticula is present)
- Bladder contents have a density other than water e.g. blood clots, mucous, etc.
- There is altered anatomy such as a displaced organ/prolapse
- Ascites or fluid collection is in the abdominal cavity
Performing a bladder scan
The bladder scanner is a non-invasive method of assessing bladder volume using ultrasonography.
The patient/client is asked to void and the volume is measured.
The probe is then placed externally on the abdomen over the site of the bladder. It has a motorised scanning head with an ultrasonic transducer that transmits sound waves which are reflected from the bladder to the transducer.
The data is then transmitted to a computer in the unit which calculates the bladder volume, and may display an image of the bladder.
It is important to measure PVR immediately after voiding to ensure accuracy, as there is additional renal output of 1-14ml of urine per minute. The voided volume and PVR should both be recorded.
Documentation should be thorough, concise, legible and accountable and should identify:
- The reasons for using the bladder scanner and patient consent
- Patient/client’s name, consent and date and time the bladder scan was performed
- Results of physical assessment prior to bladder scanning
- Volume of void before bladder scanning and time elapsed since voiding
- Results of bladder scan (include a printout for patient/client records, if available)
- Who was notified of the results of the bladder scan
- Patient/client’s response to procedure
- Follow up plan
All of the following articles are available from the Nursing Times website. If you do not have organisational access you may like to register for guest access where you will get a limited number of free Nursing Times articles. You can follow the link from individual articles.
1. Rigby D, Housami FA. Using bladder ultrasound to detect urinary retention in patients. Nursing Times. 2009;105:21 [Cited 1 August 2018] Available from: https://www.nursingtimes.net/clinical-archive/continence/using-bladder-ultrasound-to-detect-urinary-retention-in-patients/5001853.article
2. Addison R. 2000. Bladder ultrasound. Nursing Times. September 28 2000;96:9;9-50. [Cited 29 August 2018] Available from: https://www.nursingtimes.net/bladder-ultrasound/205952.article
3. Addison R. 2000. A guide to bladder ultrasound. Nursing Times. October 5 2000;96:40;14-15. [Cited 29 August 2018] Available from: https://www.nursingtimes.net/clinical-archive/infection-control/a-guide-to-bladder-ultrasound/205641.article
© Association for Continence Advice. CC BY-NC 4.0