BOO is a clearly defined urodynamic diagnosis. The most widely accepted diagnosis of obstruction is by the use of the Abrams-Griffiths (AG) number and its associated nomogram. The AG number can be derived from conventional cystometry by the following equation:
If the AG number is less than 20, the patient is unobstructed. If the result is between 20 and 40, the result is said to be equivocal, whereas if it is over 40, the patient has BOO (Abrams 1997;Chapple andMacDiarmid2000).
In male patients above the age of 40, BOO is typically caused by BPE, although other causes exist, as outlined above (other causes of BOO are also discussed in Sect. 11.2.5). In most examples, it tends to be a progressive problem, and serial cystometry in these patients will show progressive increases in voiding pressures with an associated reduction in maximum urine flow rates.
In cases caused by BPE, there may be a critical point beyond which the patient is unable to generate a sus tained detrusor contraction sufficient to overcome the outlet resistance, and it is at this point that they may present in AUR. In many cases presenting acutely, however, this information is unknown, and cannot easily be derived in the acute setting.
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