A Foley catheter is a flexible tube designed to drain urine from the bladder into a collection bag. It is used when individuals cannot urinate independently or during medical procedures. An inflatable balloon at the catheter’s tip secures it within the bladder, preventing dislodgement.
How Foley Catheters Are Measured
Foley catheter size is determined by the French (Fr) scale, also known as Charrière (Ch) or French Gauge (FG). This universal system indicates the catheter’s outer diameter. One French unit equals approximately 0.33 millimeters.
To calculate the outer diameter in millimeters, divide the French size by three; for example, a 15 Fr catheter is approximately 5 millimeters. While the French scale defines diameter, it does not specify length, which varies based on anatomical needs.
Common adult Foley catheter sizes typically range from 14 Fr to 18 Fr. For women, common sizes are 10 Fr to 12 Fr, often with shorter lengths due to anatomical differences. Men typically use 14 Fr to 16 Fr. Pediatric patients generally require smaller catheters, often 6 Fr to 10 Fr.
Identifying the Largest Available Size
Foley catheter sizes range from 6 Fr to 36 Fr. For routine urinary drainage, the largest standard sizes are typically 24 Fr or 26 Fr. Sizes beyond 28 Fr are usually reserved for specific medical situations.
Larger sizes (20 Fr to 36 Fr) are used for specialized applications. These include draining thick fluids, such as blood clots, or for continuous bladder irrigation. Three-way catheters for irrigation are generally 20 Fr or larger. Suprapubic catheters may also be larger, like 18 Fr or 20 Fr, depending on the patient’s condition.
Importance of Correct Catheter Sizing
Selecting the appropriate Foley catheter size is crucial for patient comfort, effective drainage, and minimizing complications. A catheter that is too small can cause urine leakage (bypassing) or inadequate drainage, increasing the risk of urinary tract infections. It may also lead to urethral injury during insertion.
Conversely, a catheter that is too large can cause discomfort and pain during insertion. An oversized catheter can also lead to urethral trauma, irritation, and stricture formation (a narrowing of the urethra). Prolonged use of an overly large catheter can result in pressure necrosis or erosion of the urethral meatus.
Healthcare professionals aim to use the smallest catheter diameter that effectively drains the bladder and accommodates patient needs. The decision on catheter size is a medical assessment, considering individual anatomy, the patient’s condition, and the specific purpose of catheterization.