Bladder outflow obstruction

Bladder outflow obstruction

This is a urodynamic concept based on the combination of low flow rates in the presence of high voiding pressures. It can An essay on the shaking palsy in 1817. be diagnosed definitively only by pressure–flow studies. This is because symptoms are relatively non-specific and can result from detrusor instability , neurological dysfunction and weak bladder contraction. Even low measured peak flow rates (<10– 12 /uni00A0 mL/s) are not absolutely diagnostic because, in addition to BOO, weak detrusor contractions or low voided volumes (owing to instability) can be the cause. Nonetheless, flow rates provide a useful guide for everyday clinical management. Urodynamically proven BOO may result from: /uni25CF BPH; /uni25CF bladder neck stenosis; /uni25CF bladder neck dyssynergia or functional bladder neck ob struction; /uni25CF bladder neck hypertrophy; /uni25CF prostate cancer; /uni25CF urethral stricture; /uni25CF functional obstruction due to neuropathic conditions. The primary e ff ects of BOO on the bladder are as follows: /uni25CF Urinary flow rates decrease : for a voided vol ume >200 /uni00A0 mL, a peak flow rate of >15 /uni00A0 mL/s is normal ( Figure 84.4 ); one of 10–15 /uni00A0 mL/s is equivocal; and one <10 /uni00A0 mL/s is low ( Figure 84.5 ). /uni25CF Voiding pressures increase : pressures >80 /uni00A0 cmH are high ( Figure 84.6 ); pressures between 60 and 80 /uni00A0 cmH O are equivocal; and pressures <60 /uni00A0 cmH 2 2 normal. The long-term e ff ects of BOO are as follows: /uni25CF The bladder may decompensate so that detrusor contrac - tion becomes progressively less e ffi cient and a residual - urine develops, leading to chronic retention. /uni25CF The bladder may become more irritable during filling with a decrease in functional capacity partly caused by detrusor overactivity (see Chapter 83 ), which may also be caused by neurological dysfunction or ageing, or may be idiopathic. Aside from symptoms, the complications of BOO are as follows: - /uni25CF Acute retention of urine is sometimes the first symptom of BOO. /uni25CF Chronic retention. In patients in whom the residual volume is >250 /uni00A0 mL or so ( Figure 84.7 ), the tension in the O 2 bladder wall increases owing to the combination of a large volume of residual urine and increased resting and filling O are bladder pressures (a condition known as high-pressure chronic retention). The increased intramural tension results in functional obstruction of the upper urinary

5 m/s 100 mL Volume Figure 84.4 Normal /f_l ow rate. The voided volume is well in excess of 350 mL, and the maximum /f_l ow rate is in excess of 25 mL/s. Flow 5 m/s 100 mL Volume 10 s Figure 84.5 Diagram of a low /f_l ow rate showing a rather low voided volume of about 200 mL, but with a markedly decreased /f_l ow rate. Such a /f_l ow rate could be caused by a urethral stricture, bladder out /f_l ow obstruction or a weak detrusor. O) 120 (200) 80 (100) 40 0 Detrusor pressure (cmH ₂ Scale change 20 10 0 1 2 Flow rate (mL s- /one.numerator ) 0 Time (min) Figure 84.6 Conventional urodynamic trace showing detrusor pres

sure during voiding (voided volume 340 mL). There has been a change in scale because the pressure was so high; voiding pressures are increased with a low /f_l ow rate. This is diagnostic of bladder out /f_l ow obstruction. Figure 84.7 An ultrasonogram showing a large postvoid residual urine.

( Figures 84.8–84.10 ). As a result, upper tract infection and renal impairment may develop. Such men may present with overflow incontinence, enuresis and renal insu ffi ciency . These symptoms should alert the doctor to the pr esence of this condition. /uni25CF Impaired bladder emptying. If the bladder decompensates with the development of a large volume of residual urine, urinary infection and calculi are prone to develop. /uni25CF Development of storage bladder symptoms secondary to BOO that can be irreversible if BOO is not treated. /uni25CF Haematuria. This may be a complication of BPH. Other causes must be excluded by carrying out urine culture, cytology , computed tomography (CT) urography and cystoscopy .