Use of Magnesium Sulfate to Reduce Catheter-Related Bladder Discomfort after Transurethral Bladder Surgery

Magnesium sulfate is a widely used mineral salt supplement in the treatment of a spectrum of conditions. Absorbed in the gastrointestinal tract from our diets and the fourth most abundant cation in the human body, magnesium itself helps maintain ion balance across the cellular membrane, while also acting as a cofactor in multiple biochemical pathways (1) and serving a vital function in neurochemical transmission and muscular contractions. Magnesium sulfate as a treatment currently holds many Food and Drug Administration (FDA) approvals, while also serving numerous off-label uses for a variety of clinical situations, such as after surgery. FDA-improved indications include constipation, hypomagnesemia, and the prevention of seizures in eclampsia/preeclampsia, while non-FDA-approved indications span acute asthma exacerbations, torsades de pointes during advanced cardiac life support (ACLS), and as a tocolytic to prevent preterm labor. To this end, magnesium sulfate administration can be oral, intramuscular, intraosseous, or intravenous. Every 1 gram of magnesium sulfate contains 98.6 mg of elemental magnesium, which can be combined with dextrose 5% or water to form administration-ready intravenous solutions. This said, magnesium-related adverse effects,  such as nausea or vomiting, headache, lethargy, flushing, hypotension, and respiratory depression, may occur at higher blood concentrations of magnesium (2). 

Clinically, transurethral bladder surgery is the gold standard operational intervention to resect a bladder tumor (3). Patients require large-diameter urinary catheters postoperatively (4), frequently resulting in discomfort as a consequence of involuntary muscle contraction. Particularly, catheter-related bladder discomfort above a moderate grade, which is frequently intolerable and requires treatment, is reported among 38-57% of patients with urinary bladder catheters in situ in the post-anesthesia care unit (PACU) (5). Various agents such as ketamine, tramadol, butylscopolamine, and lidocaine have been studied for the prevention of catheter-related bladder discomfort (6,7). In this context, magnesium sulfate too has recently been shown to effectively minimize catheter-related bladder discomfort after transurethral bladder surgery, in particular by relaxing smooth muscle (8). 

Indeed, a landmark 2020 randomized, double-blind, placebo-controlled study from Korea assessing 120 patients recovering from transurethral resection of bladder found that magnesium sulfate substantially reduced discomfort, shrinking the number of patients who required treatment to two. Specifically, magnesium sulfate successfully reduced the incidence of catheter-related bladder discomfort at 0, 1, and 2 hours postoperatively. It also significantly boosted postoperative patient satisfaction, as assessed on a seven-point Likert scale (8). In this study, a 50 mg/kg loading dose of intravenous magnesium sulfate was administered for 15 min, followed by an intravenous infusion of 15 mg/kg/h during the intraoperative period.  

Since only one large study was conducted, it will be necessary to replicate these results across different settings and among different patient cohorts. In addition, further studies are warranted to evaluate the optimal magnesium dose required for the prevention of catheter-related bladder discomfort among patients who required a large-diameter urinary catheter. Further studies are also warranted to confirm the optimal timing required.  

In conclusion, in addition to its wide-ranging applicability in a number of other clinical contexts, magnesium sulfate is emerging as a very promising method of reducing catheter-related bladder discomfort after transurethral bladder surgery. 

References 

1.  Hicks MA, Tyagi A. Magnesium Sulfate. StatPearls; 2020 May 8. PMID: 32119440

2.  Costello R, Wallace TC, Rosanoff A. Magnesium. Vol. 7, Advances in Nutrition. American Society for Nutrition; 2016. p. 199–201.  

3.  Choi WJ, Baek S, Joo EY, Yoon SH, Kim E, Hong B, et al. Comparison of the effect of spinal anesthesia and general anesthesia on 5-year tumor recurrence rates after transurethral resection of bladder tumors. Oncotarget. 2017;8(50):87667–74.  

4.  Hu B, Li C, Pan M, Zhong M, Cao Y, Zhang N, et al. Strategies for the prevention of catheter-related bladder discomfort: A PRISMA-compliant systematic review and meta-analysis of randomized controlled trials. Vol. 95, Medicine (United States). Lippincott Williams and Wilkins; 2016.  

5.  Xiaoqiang L, Xuerong Z, Juan L, Mathew BS, Xiaorong Y, Qin W, et al. Efficacy of pudendal nerve block for alleviation of catheter-related bladder discomfort in male patients undergoing lower urinary tract surgeries: A randomized, controlled, double-blind trial. Med (United States). 2017 Dec 1;96(49). doi: 10.1097/MD.0000000000004859.

6.  Kim DH, Park JY, Yu J, Lee SA, Park S, Hwang JH, et al. Intravenous Lidocaine for the Prevention of Postoperative Catheter-Related Bladder Discomfort in Male Patients Undergoing Transurethral Resection of Bladder Tumors: A Randomized, Double-Blind, Controlled Trial. Anesth Analg. 2020;131(1):220–7.  

7.  Nam K, Seo JH, Ryu JH, Oh AY, Lee T, Park HP, et al. Randomized, clinical trial on the preventive effects of butylscopolamine on early postoperative catheter-related bladder discomfort. Surg (United States). 2015 Feb 1;157(2):396–401.  

8.  Park JY, Hong JH, Kim DH, Yu J, Hwang JH, Kim YK. Magnesium and bladder discomfort after transurethral resection of bladder tumor: A randomized, double-blind, placebo-controlled study. Anesthesiology. 2020;133(1):64–77.