The switch from 16 Fr to 18 Fr is a smart move for Dave's situation—the larger internal diameter (about 0.7 mm wider) provides better flow capacity and reduces blockage risk when dealing with sediment-heavy urine. The 100% silicone material is also an excellent choice for his needs.

Why 18 Fr Helps with Sediment

The 18 Fr catheter offers approximately 19% less resistance to flow compared to 16 Fr, which means:

• Sediment and crystals pass through more easily before they can accumulate and form blockages
• Faster drainage reduces the time urine sits in the catheter, giving crystals less opportunity to settle and stick
• Larger lumen accommodates thicker, more concentrated urine without clogging as quickly

This is precisely why 18 Fr catheters are specifically recommended for patients with:

• History of frequent catheter blockage (which Dave now has)
• Thick urinary sediment (his problem)
• Hematuria (blood in urine) or debris

The Trade-off: Rigidity and Comfort

You're right that the 18 Fr is less flexible. This happens because:

• Larger diameter catheters have thicker walls to maintain structural integrity
• 100% silicone catheters are inherently more rigid than latex or hydrogel-coated options—they're thin-walled but firm

The increased stiffness can cause:

• More urethral irritation or discomfort, especially during insertion
• Greater risk of bladder spasms
• Potential for urethral trauma if not properly positioned

However, given Dave's enlarged prostate (3× normal size), the firmer catheter may actually negotiate past the obstruction more reliably than a softer one would. The urethra passes through the prostate, and a stiffer catheter can sometimes navigate this narrowed passage better.

Why 100% Silicone is the Right Choice

Despite the rigidity, all-silicone catheters are ideal for Dave because they:

• Resist encrustation better than other materials—crucial for someone forming sediment rapidly
• Are biocompatible and cause less tissue reaction over time
• Have larger internal drainage lumens relative to their outer diameter (thin-walled design)
• Last longer without degrading, especially important if he needs long-term catheterization

The Real Solution Still Lies in Hydration

While the larger catheter buys more time before blockage, it doesn't solve the root cause. Dave's poor hydration is still creating:

• Supersaturated urine that crystallizes easily
• Alkaline pH (if bacteria are present) that accelerates precipitation
• Slow urine production that allows sediment to settle

Even with an 18 Fr silicone catheter, if Dave continues to hydrate poorly, he'll likely still experience blockages—they'll just take longer (perhaps 3-4 weeks instead of 2 weeks). The care team should monitor whether this size actually extends the time between changes or if more frequent changes are still needed.

Would it be possible to work with Dave on increasing his fluid intake? Sometimes strategies like setting specific drinking schedules, offering preferred beverages, or using visual reminders can help elderly patients who've lost their thirst sensation. That combined with the 18 Fr silicone catheter would give him the best chance of avoiding these frustrating early blockages.