Porth's Essentials of Pathophysiology, 4e

664

Kidney and Urinary Tract Function

U N I T 7

Treatment The goals of treatment for neurogenic bladder disorders focus on preventing bladder overdistention, urinary tract infections, and potentially life-threatening kidney dam- age. The methods used in treatment are individualized based on the type of neurologic lesion that is involved; information obtained through the health history, includ- ing fluid intake; report or observation of voiding pat- terns; presence of other health problems; urodynamic studies when indicated; and the ability of the person to participate in the treatment. Treatment methods include catheterization, bladder training, pharmacologic manip- ulation of bladder function, and surgery. Catheterization involves the insertion of a small- diameter latex or silicone tube into the bladder through the urethra. The catheter may be inserted on a one- time basis to relieve temporary bladder distention, left indwelling (i.e., retention catheter), or inserted intermit- tently. The methods used for bladder retraining depend on the type of lesion causing the disorder. Methods used to supplement bladder retraining include monitoring fluid intake to control urine volume and osmolality and prevent urinary tract infections, developing scheduled times for urination, and using body positions that facili- tate micturition. Pharmacologic manipulation includes the use of drugs to alter the contractile properties of the bladder, decrease the outflow resistance of the internal sphinc- ter, and relax the external sphincter. Antimuscarinic drugs decrease detrusor muscle tone and increase blad- der capacity in persons with spastic bladder dysfunc- tion. 7 Cholinergic drugs that stimulate parasympathetic receptors provide increased bladder tone and may prove helpful in the symptomatic treatment of milder forms of flaccid neurogenic bladder. Muscle relaxants may be used to decrease the tone of the external sphincter. Intravesical injection of medications such as capsaicin and resiniferatoxin, which are specific C-fiber afferent neurotoxins, may be used to decrease bladder hyperac- tivity. Botulinum toxin type A injections may be used to produce paralysis of the striated muscles of the external sphincter in persons with neurogenic overactive bladder. The effects of the injection last about 6 months, after which the injection must be repeated. 12 Among the surgical procedures used in the man- agement of neurogenic bladder are sphincterectomy, reconstruction of the sphincter, and resection of the sacral reflex nerves that cause detrusor overactivity or the pudendal nerve that controls the external sphinc- ter. 12 Extensive research is being conducted on meth- ods of restoring voluntary control of the storage and evacuation functions of the bladder through the use of implanted electrodes. Urinary Incontinence Urinary incontinence represents the involuntary loss or leakage of urine. It can occur without the person’s knowledge; at other times, the person may be aware of the condition but be unable to prevent it. A number of

conditions can lead to incontinence, which is a common problem, particularly in older adults. 8,16–19 Types and Causes of Incontinence Urinary incontinence is commonly divided into three main types: stress incontinence, urge incontinence, and mixed incontinence, which is a combination of stress incontinence and urge incontinence. Other types of incontinence include overflow incontinence, which is a term used to describe leakage of urine associated with urinary retention, and nocturnal enuresis, which is the involuntary loss of urine during sleep. Post-micturition dribble and continuous urinary leakage are other forms of incontinence. 17-20 Stress Incontinence. Stress incontinence represents the involuntary loss of urine that occurs when, in the absence of detrusor muscle action, the intravesical pressure exceeds the maximum urethral closure pres- sure. 21–24 Among the proposed causes of stress inconti- nence are changes in the anatomic relationship between the bladder and the urethra, so that increases in intra- abdominal pressure are unevenly distributed to the urethra. 8,19 Stress incontinence, which is a common problem in women of all ages, occurs as the result of weakness or disruption of pelvic floor muscles leading to poor sup- port of the vesicourethral sphincters. Except during the act of micturition, intraurethral pressure is normally greater than intravesical pressure. The pressure dif- ference between the urethra and bladder is known as the urethral closure pressure . If intra-abdominal pres- sure increases as it does during actions such as cough- ing, laughing, or sneezing, and if this pressure is not equally transmitted to the urethra, then incontinence occurs. Diminution of muscle tone associated with nor- mal aging, childbirth, or surgical procedures can cause weakness of the pelvic floor muscles and decrease the urethral closure pressure, resulting in stress inconti- nence by changing the relationship between the bladder base and the posterior urethral junction. Another cause of stress incontinence is intrinsic urethral deficiency, which may result from congenital sphincter weakness, as occurs with meningomyelocele. It also may be acquired as a result of trauma, irradia- tion, or sacral cord lesions. Stress incontinence in men may result from trauma or surgery to the bladder outlet, as occurs with prostatectomy. 19,24 Neurologic dysfunc- tion, as occurs with impaired sympathetic innervation of the bladder neck, impaired pelvic nerve innervation to the intrinsic sphincter, or impaired pudendal nerve innervation to the external sphincter, may also be a con- tributing factor. Urge Incontinence. Urge incontinence is the involun- tary loss of urine associated with a strong desire to void (urgency). 8,19 It is often associated with overactive blad- der, which the International Continence Society defines as “urinary urgency, usually accompanied by frequency and nocturia, with or without urinary incontinence, in