BJU international · 1999
The physicochemical basis of urinary catheter encrustation.
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Choong S K, Hallson P, Whitfield H N, Fry C H
Аннотация
OBJECTIVES: To determine the relationship between urinary pH and Ca2+ solubility in urine samples from patients who experienced either frequent ('blockers') or infrequent ('nonblockers') catheter blockage by crystalline deposits of divalent cation salts.
MATERIALS AND METHODS: Fresh urine samples from 'blockers' and 'nonblockers' were collected and the ionic calcium concentration ([Ca2+ ]) measured using a Ca2+-selective electrode whilst the urinary pH was increased in 0.25 increments between 4.75 and 9.00. The pH at which crystallization occurred (nucleation) was determined and crystal composition analysed.
RESULTS: The mean (sd) voided urinary pH of catheter 'blockers' was significantly more alkaline than that from 'nonblockers', at 7.63 (0.64) and 5.97 (0.80), respectively (P=0. 001). The nucleation pH of catheter 'blockers' was significantly more acid than in 'nonblockers', at 7.43 (0.73) and 6.45 (0.65), respectively (P=0.005). Urine from 'blockers' had significantly more Ca phosphate and Mg ammonium phosphate crystals. 'Blockers' were further divided into two subsets with and without urease-based urinary tract infection; both showed a decrease in the nucleation pH.
CONCLUSION: In the urine from 'nonblockers' there is a wide safety margin between voided and nucleation pHs; this margin was less in the urine from 'blockers'. This reduction in the safety margin arises partly because the voided pH in those with a urinary tract infection is more alkaline. However, the decrease in the nucleation pH also suggests that a fundamental property of urine is altered, which reduces Ca2+ solubility at more neutral pH values. The long-term goal is to increase the nucleation pH of catheter 'blockers' and increase the margin of safety.
MATERIALS AND METHODS: Fresh urine samples from 'blockers' and 'nonblockers' were collected and the ionic calcium concentration ([Ca2+ ]) measured using a Ca2+-selective electrode whilst the urinary pH was increased in 0.25 increments between 4.75 and 9.00. The pH at which crystallization occurred (nucleation) was determined and crystal composition analysed.
RESULTS: The mean (sd) voided urinary pH of catheter 'blockers' was significantly more alkaline than that from 'nonblockers', at 7.63 (0.64) and 5.97 (0.80), respectively (P=0. 001). The nucleation pH of catheter 'blockers' was significantly more acid than in 'nonblockers', at 7.43 (0.73) and 6.45 (0.65), respectively (P=0.005). Urine from 'blockers' had significantly more Ca phosphate and Mg ammonium phosphate crystals. 'Blockers' were further divided into two subsets with and without urease-based urinary tract infection; both showed a decrease in the nucleation pH.
CONCLUSION: In the urine from 'nonblockers' there is a wide safety margin between voided and nucleation pHs; this margin was less in the urine from 'blockers'. This reduction in the safety margin arises partly because the voided pH in those with a urinary tract infection is more alkaline. However, the decrease in the nucleation pH also suggests that a fundamental property of urine is altered, which reduces Ca2+ solubility at more neutral pH values. The long-term goal is to increase the nucleation pH of catheter 'blockers' and increase the margin of safety.