The EAU guidelines on Neurogenic Bladder state that urodynamic investigations should be carried out at least every 1-2 years on neurogenic patients in order to protect the upper tracts. The results of urodynamic investigations are used to make decisions regarding safe bladder management. Our local practice is to use a lubricating gel for insertion ofurodynamic catheters which includes a local anaesthetic (lidocaine) and an anti-septic (chlorhexidine). In a small cohort of our spinal cord injured (SCI) patients there is a discrepancy between the urodynamic results including cystometric capacity (CC), leakage and maximum detrusor pressure (MDP) and the patient reported bladder volumes and leakage. We hypothesised that the active ingredients in the lubricating gel may be triggering exaggerated reflex responses in some SCI patients which contributed to the discrepancy. In some of the identified patients we have performed repeat cystometry using lubricating gel with no added ingredients.

The study used mixed methods; a retrospective analysis and a prospective evaluation. The clinical records of patients who underwent urodynamics in our centre were searched to identify patients who were potentially sensitive to active ingredients in lubricating gel, based on a discrepancy between urodynamic findings and reported bladder function. These patients were then prospectively followed and repeat cystometry was performed using a gel without active ingredients.

16 patients with ANLUTD were identified as potentially sensitive to active ingredients in lubricating gel based on previous urodynamic results. 2 were female and 14 male. They all had a SCI with a level ranging from C3 to L2. 7 had a complete SCI and 9 had an incomplete SCI. 12 were managing their bladder with intermittent self-catheterisation and either anti-muscarinic or beta3 adrenergic agonists and 4 were voiding on urge. 2 had previously had a bladder augmentation. All urodynamic investigations were carried out with 8 Fr catheters and using room-temperature saline infused at a rate of 30 ml/min. All patients had a reported functional bladder volume that exceeded the CC measured during urodynamics. The range of patient reported functional volumes was 300-1000 ml however, the range of CC on urodynamics was 70-200 ml when using lubricating gel with active ingredients. The range of MDP during urodynamics was 15-100 cmH2O. One patient arrived for urodynamics with 500 ml in the bladder (which was drained at the start of the test) but could only hold 80 ml before there was an NDO contraction with MDP 50 cmH2O and urethral leakage at which point the test was abandoned. Although most patients have impaired sensation due to their SCI, some reported that they had some strange urethral sensations during the test. To date 7 patients  have had repeat urodynamics using lubricating gel without active ingredients. The range of CC during the repeat urodynamics was 240 -710 ml and the range of MDP 20-42 cmH2O.

Comparison of the urodynamic results of patients who underwent urodynamics using lubricating gel with and without active ingredients showed that the urodynamics without active ingredients gave results that correlated much better with patient reported bladder function with regard to CC and a reduction in MDP.

Although the number of patients that we identified as possibly sensitive to the active ingredients in the gel is a small subset of the SCI population, we believe that it is important that they are identified as this may reduce the potential for over-treatment based on urodynamic investigation results as compared to reported bladder function. 
Although to date we cannot prove that the active ingredients in the lubricating gel were the single cause of unrepresentative urodynamic results, we will continue to use lubricating gel without active ingredients on those patients who we believe may be sensitive. The sensitivity may be more pronounced in this group of patients compared to a non-SCI population as they already have exaggerated reflex responses due to the nature of the SCI. The potential risk of not using gel with active ingredients is that there may be an increase in post-investigation urinary tract infection although this has not been investigated.