For Bladder Stones, Scope Size Matters

I cystoscopically removed a 5 cm stone in a teenager with neurogenic bladder status post bladder augmentation:

I decided to do this cystoscopically — and not open or percutaneously — because of obesity and prior history of bladder augmentation, and because I was able to use a large caliber cystoscope in her (23 French).

Cystoscopic, percutaneous or open approach for bladder stones?

When it comes to deciding the approach, the key is to determine what is the largest cystoscope that you would be able to get in the patient. A larger cystoscope will allow you to take care of the stone exponentially faster compared to a smaller scope.

It took me 80 minutes to remove the 5 cm stone shown above through the urethra using a 23 Fr cystoscope and a 1000-micron laser fiber.

Now bear with me for some interesting calculations

A 5 cm stone has a volume of approximately 65 cm3. The 23 Fr cystoscope has a diameter of 7.7 mm. A 5 cm stone can be broken into 277 spherical stone fragments each measuring 7.7 mm in diameter. Now let’s say it takes 80 minutes to remove 277 fragments of stones:

For a 17 Fr cystoscope, the fragments would have to be 5.7 mm in diameter in order to pass. The same 5 cm stone will need to be broken down into 686 fragments, each 5.7 mm in diameter. If removing 277 took 80 minutes, then removing 686 would take 198 minutes or 3.3 hrs:

Using the same logic, here are the calculations for a 13 and 8 Fr cystoscopes:

Although we could argue whether 3.3 hrs is too much cystosocopic time, few would want to spend 7 hrs using a 13 Fr scope and only someone that should not be licensed to practice medicine would spend 32 hrs with an 8 Fr scope trying to remove a 5 cm stone.

In other words, if you cannot get a >17 fr scope in a patient with a 5 cm stone, you need to consider open or percutaneous approaches.

Cystoscopic time to remove various sizes of stones

I did the same calculations as above for stone sizes 1, 2, 3 and 4 cm. The numbers below are in minutes:

Based on the table above, I think the cutoff for a 13 Fr scope would be a 3 cm stone and for an 8 Fr scope a 2 cm stone.

Percutaneous approach

The percutaneous approach can provide a lumen of 5 mm (15 Fr), 10 mm (30 Fr) or 12 mm (36 Fr) — if using a 5, 10 or 12 mm laparoscopic trocar.

The one disadvantage of the percutaneous approach is the lack of the “gravity factor” which allows the stones to fall out of the scope into the pouch. The gravity factor is huge in my opinion; when I did the 5 cm stone I only had to basket a few fragments at the end since the great majority were just washed out through the scope by filling the bladder to capacity and then removing the lens letting the water and stones flow down the cystoscope sheath into the pouch.

To compensate for the lack of the “gravity factor”, the patient could be tilted towards one side.

What really makes the percutaneous approach go fast is the Cyberwand. This miraculous 3.75 mm stone-crusher-sucker will go through a 5 mm step trocar with visualization accomplished through the urethra or catheterizable channel using a small scope.

 

Open approach

If a large cystoscope or CyberWand are able to be used, then it becomes hard to justify opening the patient to save oneself 30-60 minutes of operating time. From the perspective of the patient, I would rather be asleep for another 1-2 hrs than undergo an open procedure, especially in patients that have had multiple abdominal surgeries or are obese. However, no one can be faulted for choosing the open approach since its fast, reliable and safe.

 

Conclusions

The above numbers are “back of the envelope” calculations that can be used as a rough guide to decide on the approach to remove a bladder stone. Factors such as previous operations, obesity, size of the stone, and more importantly scope size will determine the best operation for the patient.

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