[Incidence and risk factors for calculi formation in patients treated with augmentation cystoplasty or intestinal substitution].
OBJECTIVE: Bladder stones have been observed more frequently in patients undergoing bladder augmentation or substitution than in the normal population. We analyzed the etiological factors influencing bladder stone formation in patients submitted to the foregoing procedures. METHODS: Between December 1986 and October 1994, 12 augmentation cystoplasties with detubularized ileum or colon (group I) and 24 substitution ileocystoplasties (group II) were performed. None of the patients were known to have urinary stone formation. The possible causes of bladder stone formation were analyzed in both patients groups. The patients were evaluated for urinary infection, post micturition bladder residue, urinary pH, and stone forming metabolic alterations in blood or urine. The latter consisted in determining the blood levels of creatinine, calcium, uric acid and phosphorus and the 24-hr urine levels of calcium uric acid, phosphorus, creatinine, urea, oxalic acidi citric acid and magnesium. The statistical analysis consisted of an unweighted logistic regression test and a chi square test between each of the above variables and the existence of bladder stones. RESULTS: In group I, 10 patients revealed recurrent urinary infections, 0 showed a significant post-micturition bladder residue, a pathologically alkaline pH was observed in 2 and the metabolic study of blood and urine revealed alterations in 9 patients. In group II, 18 patients revealed recurrent urinary infection, 13 patients had post-micturition bladder residue, a pathologically alkaline pH was observed in 1, and the metabolic study of blood and urine revealed alterations in 13 patients. The statistical analysis using the unweighted logistic regression test showed no significant relation between any of the parameters and the presence of stones, for the substitution group pr augmentation group. However, the chi-square test to determine the relation between the different varikables and the existence of stones, showed a statistically significant relation between an elevated urinary pH, recurrent urinary infection, post-micturition bladder residue and bladder stone formation for groups I. Concerning the type of suture employed, some degree of relation between the use of non-resorbable suture and stone formation was found, although it was not statistically significant. CONCLUSION: We can therefore conclude that urinary pH, recurrent urinary infection annd post-micturition bladder residue, and probably use of nonreabsorbable suture, are among the etiological factors that we should avoid and treat in order to prevent the formation of bladder stones in patients undergoing augmentation or substitution cystoplasty.