Final answer:
The most commonly used self-retaining urethral catheter is the Foley catheter, which stays in place with an inflated balloon to allow for continuous urine drainage.
Step-by-step explanation:
The most commonly used self-retaining urethral catheter is a Foley catheter. This type of catheter has a balloon near the end that is inflated with sterile water once the catheter is correctly positioned within the bladder. This inflation holds the catheter in place and allows for continuous drainage of urine from the bladder. The Foley catheter is often used during surgeries, for patients who are bedridden, or in those who cannot void urine naturally due to medical conditions or postoperative recovery.