Blockage of indwelling urinary catheters: the roles of urinary composition, the catheter, medication and diet.

The aim of this work was to study factors related to the blockage of indwelling urinary catheters. There were 40 patients with indwelling catheters, 20 of whom had catheters that blocked frequently. The other 20 were trouble free at the time of our study. The type and gauge of catheter and frequency of events were recorded. Urine samples for biochemical analysis comprised 24-hour collections, morning specimens on up to 10 different days and 5-8 samples at different times during the same day. Chemical analysis of debris removed from blocked catheters showed it to consist of mixed phosphates of calcium and magnesium, thus being similar to urinary stones that may be seen in spinal cord injury patients. Patients with frequent catheter blockage had significantly elevated urinary pH and ammonium and calcium concentrations. Discriminant analysis gave 78-94% separation of catheter blocking patients from nonblockers depending on the type of sample. We conclude that bacterial urease activity and urinary calcium concentration are the most important factors in catheter blockage. Elevation of urinary pH following ingestion of effervescent preparations, drug- or diet-induced increases in urinary calcium or magnesium excretion and inadequate or erratic fluid intake may be avoidable contributing factors.