Urinary catheters tend to block when bio®lm from urease-producing organisms build up on the catheter surface. This is a locally-occurring process that in¯uences and is in¯uenced by the composition of the urine. In this work we relate urine pH and calcium to catheter blockage and suggest how to reduce the rate of encrustation. Sixty patients with indwelling urinary catheters were studied, 26 of them being troubled by frequent blockage of their catheters, 34 of them not. A series of small urine samples were collected during a 24 h period. Urinary pH and calcium concentration were combined into discriminant functions designed to separate Blockers from Non-blockers and achieved a 95% correct classi®cation. The results indicate that a high and uniform rate of¯uid intake is mandatory for the patient with a tendency for catheter blockage. Excessive total¯uid intake may be avoided by attention to uniformity. Other avoidable risk factors include: excess dietary calcium from certain protein supplements and antacids; excess dietary magnesium from certain beverages and antacids; alkali from eervescent tablets; excess dietary citrate from some fruit juices and cordials; intermittent dehydration from alcohol ingestion. Less tractable risk factors include infection of the urinary tract with urease-positive organisms, hypercalciuria of immobilisation, hyperhydrosis and postural oliguria. The processes involved in catheter encrustation and blockage provide a model for the formation of calculi in spinal cord injured patients. Therefore the above considerations may also be relevant to the management of stone disease in paraplegic and tetraplegic patients.

Heterotopic ossification (HO) occurs in 4-49% of patients with spinal cord injury, but the cause of the complication has not been established. The aim of this study was to investigate clinical factors related to the occurrence of HO. The incidence of HO was determined in 91 consecutive patients with traumatic lesions of the spinal cord who had been admitted to the National Spinal Injuries Centre for management and rehabilitation. Clinical data were analysed. Clinically apparent HO occurred only in 10 of 56 patients in whom the start of passive movements to their paralysed limbs was delayed until 7 days or more from time of injury. The findings of this study are consistent with the view that HO occurs as a result of trauma induced by passive movements carried out on joints where contractures have started to develop.

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.

The aim of this work was to identify factors related to the length of stay of patients admitted to this centre for rehabilitation. The study involved 200 patients admitted within one year of onset of a spinal cord lesion. Clinical and laboratory data were recorded. Length of stay was related to the level of the spinal cord lesion and whether it was complete or incomplete. The length of stay was increased in patients in whom anaemia or hypoalbuminaemia occurred; the cause of these conditions was not always evident. We conclude that attention directed towards recognising and treating the cause of anaemia or hypoalbumin aemia may be expected to shorten the time required for rehabilitation in this centre.

Oliguria in patients following spinal cord injury was first mentioned in 1649, but has since been referred to only occasionally. The work detailed here was completed 30 years ago but is reported because of the lack of any comparable study and because suitable patients are not now readily available. A total of 27 water load tests were carried out on 20 patients. The test included measurement of serum osmolality to confirm absorption of ingested water. Impaired response to the water load was obtained in 17 tests: 12/13 between 1 and 5 days after onset of the cord lesion and 5/14 more than 2 weeks after injury. The possibilities that oliguria was due to dehydration, failure to absorb ingested water, hypotension or renal failure are discounted.In the first few days after injury, oliguria may be due to release of antidiuretic hormone as part of the metabolic response to trauma. The impaired response seen later is discussed in relation to possible neural and hormonal mechanisms. There is a need for further study of factors influencing water excretion in tetraplegic and paraplegic patients.

Attention to volume and variability of fluid intake by the patient should have a major impact on the incidence of blockage of the indwelling urinary catheter.

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The urinary excretions of citrate, inorganic orthophosphate and pyrophosphate, silicate and urate were measured in 17 paraplegic patients with renal calculous disease associated with urinary infection, in 16 paraplegics with no history of urinary calculus and in 14 healthy control subjects. The paraplegics excreted less citrate, orthophosphate and pyrophosphate than the control subjects. The stone-formers excreted more urate than the paraplegics without stone disease, but less than the control subjects. There were significant positive correlations between urinary orthophosphate and pyrophosphate and between urinary silicate and 24-h urine volume. The possible roles of increased urate and diminished excretion of citrate and inorganic pyrophosphate in the aetiology of renal calculosis in paraplegic patients deserve further investigation.