Background

A bladder scan is a portable noninvasive ultrasound device that measures the volume of urine in the bladder by using ultrasound waves measured in three dimensions. The machine calculates a volume measurement of urine in the bladder without displaying an image on the screen. Bladder scans are used mostly during inpatient encounters to evaluate patients for urinary retention. Acute urinary retention (AUR) is defined as the inability to voluntarily pass urine, can cause severe pain, and is considered a medical emergency. Without prompt diagnosis and treatment, AUR can result in permanent damage to the kidneys and genitourinary system. AUR is more common in men than in women and is usually due to underlying benign prostatic hypertrophy (BPH). In women, urinary retention is usually due to pelvic organ prolapse or masses in the pelvis. The diagnosis of urinary retention is suspected when greater than 200 mL of urine is retained in the urinary bladder after the patient voluntarily voids. When the volume of urine in the bladder is greater than 100 mL, the bladder scan is 90% accurate compared with urinary bladder catheterization.

How to Use It

A bladder scan displays approximately how much urine is in the bladder at a given time. When the urine volume is measured after a patient voluntarily voids, it is called a postvoid residual (PVR), which is a marker for urinary retention. In addition to being used to diagnose urinary retention, it can be used to monitor urine volumes after an indwelling urethral catheter (i.e., Foley catheter) is removed for several hours to evaluate if the patient needs the catheter to be reinserted. It is also used in patients with decreased urine output to evaluate if the etiology is due to bladder outlet obstruction. Bladder scan has helped to minimize unnecessary catheterization and associated urinary tract infections. See Chapter 59: Urinary Catheters for more details about types and risks of catheters. See Chapter 23: Cultures – Urine for details about urinary tract infections. Bladder scans can be falsely elevated in patients with obesity, abdominal ascites, and anasarca; therefore, bladder volume in these patients may need to be confirmed with an ultrasound image of the urinary bladder.

How It Is Done

A handheld ultrasound device is used to measure the volume of urine remaining in the urinary bladder approximately 10 minutes after the patient voids. The machine scans the bladder in three dimensions and calculates a volume. The patient is positioned in the supine position. A small amount of ultrasound gel is applied to the ultrasound probe, and the probe scanner head is placed on the abdomen in the suprapubic area. No discomfort is usually experienced, and no sedation or anesthesia is required. The scan is initiated by pushing the button on the handle of the probe and the volume will be displayed on the screen in under a minute. Many facilities practice measuring the volume two to three times and then average the measurements to increase accuracy. There is no specific preparation needed prior to performing the exam in terms of diet or activity. A normal bladder scan PVR in a patient without urinary retention should be 50 mL or less.

Medication Implications

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  The bladder scan is noninvasive and there are no medications that need to be given prior or during the test.

  
  
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  There are no medications that need to be held prior to exam.

  
  
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  If the bladder scan reveals urinary retention, an indwelling urethral (i.e., Foley) catheter will likely need to be placed. Once the obstruction is alleviated with a catheter, the patient’s medications should be reviewed, as many medications can cause urinary retention.

  
  
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  The most common medications that cause urinary retention are anticholinergic medications and sympathomimetics (medications that stimulate the sympathetic nervous system). Anticholinergic medications cause urinary retention by reducing the contractility of the detrusor muscle, which is the main muscle in the wall of the bladder that causes voiding. It should be noted that many of these are available as over-the-counter (OTC) medications, so a thorough medication history that includes OTC medications should be performed.

  
  
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  Anticholinergic medications and opioids cause urinary retention by decreasing bladder sensation.

  
  
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  Categories of offending medications and some examples (not all inclusive) include:

  
  
  
  
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    Sympathomimetics (alpha adrenergic agents)—ephedrine, phenylephrine, pseudoephedrine

    
    
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    Tricyclic antidepressants—imipramine, nortriptyline, amitriptyline, doxepin

    
    
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    Antiarrhythmics (class 1a)—quinidine, procainamide, disopyramide

    
    
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    Anticholinergics—atropine, scopolamine, glycopyrrolate, oxybutynin, hyoscyamine, dicyclomine

    
    
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    Antiparkinsonian agents—trihexyphenidyl, benztropine, amantadine, levodopa, bromocriptine mesylate

    
    
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    Hormonal agents—progesterone, estrogen, testosterone

    
    
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    Antipsychotics—haloperidol, thiothixene, chlorpromazine, fluphenazine, prochlorperazine

    
    
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    Antihistamines—diphenhydramine, cyproheptadine, hydroxyzine, dimenhydrinate

    
    
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    Antihypertensive—hydralazine, nifedipine

    
    
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    Muscle relaxants—diazepam, baclofen, cyclobenzaprine

  
  
  
  
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  Urinary retention in men is most commonly caused by BPH and can result in significant symptoms (known as lower urinary tract symptoms [LUTS]), AUR, impairments to quality of life, and the need for surgical intervention. For decades, the pharmacologic management of LUTS included alpha-1 adrenergic antagonists and 5-alpha-reductase inhibitors but now also includes muscarinic receptor antagonists (anticholinergic) and phosphodiesterase-5 inhibitors. A systematic review and meta-analysis revealed that alpha-1 adrenergic antagonists, 5-alpha-reductase inhibitors, and phosphodiesterase-5 inhibitors all improve LUTS scores. Effects on maximum urinary flow, obstructive symptoms, and irritative symptoms were more varied among classes and combinations.

  
  
  
  
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    Alpha-1 adrenergic antagonists work by relaxing prostatic smooth muscle and improve symptoms by 3 months of daily use. Examples include tamsulosin, doxazosin, and terazosin

    
    
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    5-alpha-reductase inhibitors work by inhibiting the production of dihydrotestosterone (which causes prostate growth) and can take 6 months to years to demonstrate benefit on LUTS scores or AUR rates. Examples include finasteride and dutasteride

    
    
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    Muscarinic receptor antagonists (anticholinergics) improve storage-related symptoms in BPH (e.g., frequency, urgency) but have the concern of increasing the PVR or AUR rate based directly on their anticholinergic mechanism. Because of this concern, muscarinic receptor antagonists should be avoided in patients with a significantly elevated PVR, though the specific threshold varies by agent and study. Also, during treatment with these agents, it is reasonable to perform a bladder scan to monitor the medication’s effect on the PVR and assess risk for AUR. Examples include oxybutynin, tolterodine, and solifenacin

    
    
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    Phosphodiesterase-5 inhibitors are the newest treatment options for BPH, as they were originally used to treat erectile dysfunction. They work by regulating smooth muscle in the prostate. Examples include sildenafil, tadalafil, vardenafil, and avanafil