Aims of study:
Detrusor instability is a common complaint among women. Anecdotal reports suggest that alkalinising urine may improve symptoms of frequency and urgency, and intravesical administration of sodium bicarbonate has been shown to increase bladder capacity in patients with detrusor instability1. There is some evidence that women with detrusor instability may have a lower urinary pH than those with stable bladders2. This study was designed to determine whether alkalinising urine would improve symptoms in women with detrusor instability.

Methods:
A randomised double-blind controlled study of the effect of placebo versus sodium bicarbonate was conducted among women with urodynamically proven detrusor instability. The dose of sodium bicarbonate used in the study was determined from a pilot study among volunteers, and was the dose that increased the mean daily pH by 1. The study lasted four weeks and consisted of a baseline week, a week of either 5.4 gms sodium bicarbonate or placebo, a washout week and a final week of either 5.4 gms sodium bicarbonate or placebo. All women took both placebo and sodium bicarbonate, but they were randomised to the order in which they took these. Urinary diaries including information concerning episodes of urgency and leakage were kept during all weeks apart from the washout week. Women tested their urinary pH with labsticks three times a day during the study. A 24 hour pad test was completed at the end of each week as well as a short symptom questionnaire. General linear models were fitted to the data after log transformation. Baseline readings and correlations between observations on the same patient were allowed for within the model and F-statistics were used to test for differences between sodium bicarbonate and placebo.

Results:
35 women completed the study. The mean age of the women was 49 years (range 23 to 71 years). The mean daily pH was 6.1 for the baseline week, 6.1 for the placebo week and 6.9 for the week when sodium bicarbonate was taken. Table 1 shows the mean number of daily episodes of urgency and wetting, frequency and 24 hour pad weights. The difference in 24 hour pad weights was the only statistically significant result with increased leakage occurring in the week that sodium bicarbonate was ingested. There was no difference in the quality of life impact of urinary symptoms for either group with the mean impact of their urinary symptoms on their daily life reported as "somewhat" for the period of the study. Type your text within this frame. If 2nd page is needed use Abstract Form A-2. Category No. (Please choose one) Abstract No. International Continence Society 30th Annual Meeting Tampere Hall, Tampere, Finland o 28 - 31 August, 2000 Author(s): LV Swithinbank1,C Rogers2, J Ellis Jones1, P Abrams1 Table 1: comparing the mean number of daily episodes of urgency and wetting, frequency and pad weights. The means reported are geometric rather than arithmetic means in view of the log transformation of the data.

Conclusions:
It is a common belief that urinary pH may affect detrusor instability, and the variation between the pH of infused fluids and urine has been proposed as the reason for the presence of increased detrusor contractility during ambulatory monitoring when compared with routine cystometry. However, our study has not confirmed this belief, as increasing urinary pH had no effect on the symptoms associated with detrusor instability, apart from the 24 hour pad weight. The number of wetting episodes did not change with treatment and therefore the clinical significance of this result is unclear. Urinary pH alone does not therefore appear to be related to the symptoms of detrusor instability. We feel that this is important clinical information as it negates the advice often given to patients with urinary frequency.

References:
1 Br J Urol 1987 60: 516-518 2 Neurourol 1990 9: 331-332