Can normal saline be used to fill the balloon of a Foley catheter? The experience of a prospective randomized study in China
Chi-Fai Ng md, Division of Urology, Department of Surgery, Prince of Wales Hospital, Shatin, Hong Kong SAR, China. Email: firstname.lastname@example.org
Background: Despite the lack of evidence, using normal saline for inflating the balloon of a Foley urethral catheter is frequently regarded as a cause for deflation failure. We have investigated the issue by comparing the rate of deflation failure of Foley catheter balloon, using either sterile water or normal saline as the filling solution.
Methods: Four thousand latex Foley urethral catheters (14 Fr) were randomly assigned to one of two groups: sterile water or normal saline. Each of the catheter balloons would then be inflated with 10 mL of the corresponding fluid. They were subsequently put in water baths at 37°C for 4 weeks. At the end of 4 weeks, all the balloons were deflated by people who were blind to the assignment of fluid inflated. Failure of deflation was defined as the balloon not being able to be deflated completely. The number of deflation failures was recorded and the amount of fluid aspirated from each balloon was also noted.
Results: Of the 4000 catheters, 17 (0.43%) were found to be defective and could not be used for the study. The remaining 3983 catheters were randomly allocated into the sterile water (2011) and normal saline (1972) groups. The failure rate of deflation for the sterile water group and normal saline group were 185 (9.2%) and 157 (8.0%), respectively, which was not statistically significant (P = 0.162).
Conclusion: There was no difference in the rate of deflation failure of latex Foley balloons by using either sterile water or normal saline as the filling solution.
Urethral catheterization is one of the most commonly performed invasive procedures for hospitalized patients. Among all types of urethral catheters, the Foley catheter is the most commonly used. It was designed by Dr Frederick Foley (1881–1966)1 and is characterized by the presence of an inflatable balloon for retaining the catheter inside the urinary bladder. Although they are very useful in patient management, they can also cause complications, such as retained catheters due to a failure to deflate the balloon. One of the frequently blamed causes for retained catheters is the use of fluids other than pure water for the inflation of the Foley balloon. This may result in the blockage of the balloon channel by solute crystal that has formed.2,3 Therefore health care personnel are advised that only pure water should be used for filling the balloon of the Foley catheter, because normal saline can result in crystal formation ending up in blockage of balloon channel. But there is a scarcity literature or scientific evidence to support this practice. Therefore, we designed a study to compare the rate of deflation failure of the Foley balloon using sterile water or normal saline as the filling solution.
Four thousand 14-Fr latex Foley urethral catheters (Foleycath, WRP Asia Pacific Sdn Bhd, Malaysia) were randomly assigned to one of two groups: sterile water or normal saline. Each of the catheter balloons would then be inflated with 10 mL of the corresponding fluid. They were subsequently put in water baths at 37°C for 4 weeks. Copper screws were tied to the tip of each of the catheters in order to maintain the balloon in an upright position inside the water bath. Only the balloon and the most distal part of the catheter were submersed under water, in order to mimic the actual situation in the bladder. The water baths were warmed by a warming coil and wrapped by aluminum foil to minimize heat loss. The temperature was checked four times per day by thermometers fixed in the water baths and was maintained at 37°C during the study period.
At the end of 4 weeks, all the balloons were deflated by people who were blind to the assignment of inflation fluid. Failure of deflation was defined as the balloon not being able to be deflated completely. The number of successful and unsuccessful deflations were recorded and the amount of fluid aspirated from each balloon was also noted. The results were then analyzed with Pearson's χ2 test and Student's T-test.
Of the 4000 catheters, 17 (0.43%) were found to be defective and could not be used for the study. The remaining 3983 catheters were randomly allocated into the sterile water (2011) and normal saline (1972) groups. The success and failure rate of deflation for the sterile water group were 1826 (90.8%) and 185 (9.2%), respectively, and 1815 (92.0%) and 157 (8.0%), respectively, for the normal saline group. Using Pearson's χ2 test, the 2-tailed P-value was 0.162, which was not statistically significant.
The mean volume of fluid aspirated from the sterile water and normal saline groups were 9.005 mL and 9.182 mL, respectively (Table 1). Using a 2-tail T-test, the t-value for the two means was less than 0.0001.
Table 1. The amount of fluid aspirated from the sterile water and normal saline groups
|Sterile water group||9.005||0.410|
|Normal saline group||9.182||0.326|
In this era of evidence-based medicine, we need to justify and support our clinical practice with scientific evidence. The belief that ‘only pure water should be used for filling the balloon of the Foley catheter, because normal saline can result in crystal formation ending up in blockage of balloon channel’ is not backed up by good evidence. However, it is still a common practice today. From a chemical point of view, the solubility of sodium chloride in water at 37°C is approximately 36 g per 100 mL of water,4 which is approximately 40 times greater than the concentration of normal saline (0.9%, that is, 0.9 g per 100 mL water). Therefore the chance of crystallization is quite low for normal saline at body temperature.
The results of a literature search on the types of fluid used for Foley catheter balloon inflation were surprisingly diverse. While some authors specifically mentioned saline,5 water or air6 for such purpose, others seemed not as concerned regarding the type of fluid used.7 No definite conclusion could be drawn from the literature. There is no proper study to support the use of preference of any one of these fluids over the others.
Latex Foley catheters, which were used in the present study, are the most commonly used urethral catheters in our daily practice. In fact, nearly all our deflation failures were related to the usage of latex Foley catheter. They are mainly used for temporary urine drainage, either for therapeutic indications or for monitoring. Most of them are kept in situ for a few days or, at most, a few weeks at a time. Therefore, the study period was set at four weeks, which would be long enough from a practical point of view. The specific arrangement of the Foley catheters in the water bath (only the balloon and distal part were being submersed in water and water temperature was kept at 37°C) was an attempt to mimic the actual in situ condition of the catheters as much as possible.
From the results of the present study, we found that there was no statistically significant difference in the failure rate of using either solution. In fact, a higher deflation failure rate was noticed in the sterile water group, 185 (9.2%) as compared with the normal saline group, 157 (8.0%). This supports that the use of normal saline for inflating Foley catheter balloon is not a cause of deflation failure.
The amount of fluid retrieved in the sterile water group (9.005 mL) is significantly less than that in the normal saline group (9.182 mL, t < 0.0001). The explanation for this is unclear. Whether this observation is related to a higher deflation failure rate in the sterile water group (though there is no statistical difference groups in the deflation rate between the two) may worth further investigation. It would also be interesting to examine the retrieved fluid microscopically to determine the actual rate of crystal formation in future studies.
The result of the present study is based on latex Foley catheters and it may not be applicable to Foley catheters made of different material. Since the Foley catheter material may also interact with the filling solution, it may be worthwhile to repeat the study using Foley catheters of different materials to determine the deflation failure rate among different filling solutions. This may help us to have a better understanding of the mechanism of deflation failure of Foley catheter balloons, which may eventually facilitate better design and choice of material of Foley catheters to minimize the balloon deflation failure.
The traditional advice of the exclusive use of water to fill the Foley catheter balloon has no scientific foundation and the use of normal saline for inflating latex Foley catheter balloon does not increase the rate of deflation failure.