Venturi vs. peristaltic pumps have different advantages in conventional, femtosecond phaco
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With the new phacoemulsification machines, venturi and peristaltic pumps have reached substantially comparable surgical efficiency and safety. However, the intrinsic differences between the two pumps may better suit specific techniques and surgical styles, which may matter even more when performing femtosecond laser-assisted procedures, according to two surgeons.
“In the first phaco machines, the difference was huge. The venturi pump was very fast and aggressive, and many surgeons were afraid to use it. We were moving our first steps into this new way of doing cataract surgery, and venturi was a choice that required some temerity. The peristaltic pump allowed for a slower and more flexible approach to cataract surgery, with the techniques we had at the time. That’s why peristaltic pumps had a much faster and more widespread acceptance,” Alessandro Galan, MD, said.
In the following years, manufacturers worked at making venturi pumps less aggressive and safer and peristaltic pumps faster and more efficient.
“I have been a fan of venturi from the start because it is fast, efficient and immediately responsive. You press on the pedal, and things happen: Vacuum builds up and aspiration occurs immediately, with an extraordinary capturing followability. With peristaltic pumps, vacuum is activated by tip occlusion, resulting in a more gradual and controlled aspiration but at the cost of more time and manipulation. To me, the two systems are very much like a petrol car (the venturi) vs. a diesel car (the peristaltic), which you choose based on your driving preferences,” Galan said.
However, the technology of both types of pump has evolved to such an extent that differences are now minimal, and their safety and efficiency are comparable. Automated IOP control systems have minimized the risk for post-vacuum surge, chatter and anterior chamber loss, and some platforms offer a dual pump system, allowing surgeons to switch between the two modalities within the same procedure.
“I have seen and experienced all these changes. In our hospital department, we perform high volumes of cataract surgery, and companies are keen on us to try their platforms and progressive upgrades. I can honestly say that nowadays no machine is better than the other, though we may have preferences, based on our habits, attitudes and the techniques we use,” Galan said.
Best suited for specific techniques
Peristaltic systems work better for surgeons who use a stop-and-chop technique, consisting of two phases: sculpting a longitudinal groove in the nucleus to achieve a nucleus fracture and then aspirating the fragments. This is an easier approach, used by 80% of surgeons. Peristaltic also works better for surgeons who use the divide-and-conquer technique, in which cross grooves are performed. With both these techniques, two programs, with different vacuum, flow and phaco power settings, are required for the two phases.
“Venturi holds and aspirates at the same time and is therefore well-suited for the phaco chop technique, in which no sculpting is performed and the nucleus is bisected by direct chopping maneuvers. Then both halves are aspirated, and fragments are quickly captured,” Galan said.
Galan is a high-volume cataract surgeon who has never converted to femtosecond laser-assisted cataract surgery. In his hospital, an average of 5,500 cataract procedures are performed per year, using traditional phacoemulsification.
“Femto adds time and cost to the procedure for a result that is comparable. The only advantage is in the capsulotomy. For beginner surgeons this may be significant, but experienced surgeons feel just as confident performing the capsulorrhexis manually. In my view, it makes no sense in public hospitals, while it may be a very good marketing strategy for private clinics,” he said.
A different approach
Surgeons who convert to femtosecond laser-assisted cataract surgery often try to use the phacoemulsification techniques they have always used. They do not seem to realize that a lens that is micro-machined and fractured by the laser requires a substantially different approach, according to Wendell J. Scott, MD.
“This is the reason why most studies show a 15% to 30% reduction of phaco power. In my experience, if you are using a more efficient technique for removing the lens, you can decrease your phaco energy by 50% to 70% and eventually by more than 90%,” he said.
When the femtosecond laser was adopted in his practice in 2013, he and his colleagues were using peristaltic but speculated that there might be some theoretical benefit of venturi with femto-phaco. Because they had a dual pump phaco unit, they started transitioning to venturi only for irrigation and aspiration of cortical material and then gradually to removal of the lens.
“What we found was that transitioning from the occlusion-based vacuum of peristaltic to the continuous vacuum of venturi required a different and more immediate control by the surgeon. With peristaltic, when occlusion occurs at the aspiration port, the machine responds by building up vacuum, and when the tip occlusion is broken, it responds by decreasing the vacuum. With venturi, you don’t depend on the machine to decide. The vacuum is potentially always there, and it is up to you to decide when to build it up and release it. This can be a little intimidating at first, but when you realize how it works, you can use it to your advantage and do it in a safe way,” Scott said.
Comparing the two pumps
There are potential advantages of using venturi in femtosecond-assisted cataract surgery, according to Scott. Because the lens is broken up into thousands of tiny fragments, the constant vacuum pulls them to the tip and makes aspiration fast and efficient, without unnecessary delays.
In order to verify this potential advantage of venturi over peristaltic, in collaboration with Randall J. Olson, MD, Scott developed a study protocol to compare the energy requirement and phaco time with the two methods of vacuum.
“We also want to assess which method is gentler on the eye and reduces corneal swelling, and if the vision recovers faster with one method compared to the other,” Scott said.
In the 6 months before the study, Scott set up one operating room for peristaltic and another one for venturi.
“I did that so that I would do the same technique with the same setting and would become experienced with both systems,” he said.
Within the study, patients are now treated with venturi-based phacoemulsification in one eye and peristaltic-based phacoemulsification in the other eye. The aim is to include 250 subjects for a total of 500 eyes with bilateral cataract grade 1 to 3. Enrollment started in October 2019, and completion is expected by May 2021.
Reduced phaco energy
“It is still too early to draw even preliminary conclusions, but we hope that this study will provide useful parameters for both venturi and peristaltic users who are transitioning to femto, as well as a technique that will allow them to decrease their phaco energy by over 90% and do it safely. An efficient technique can reduce the power by more than 50%. With experience it should be consistently by 70%, but 90% is very doable,” Scott said.
There are other studies comparing peristaltic and venturi, but findings related to conventional phacoemulsification should not be applied to femto-phaco, which is an entirely different procedure.
“Our study is prospective, and the difference is only the two pumps. We are trying to get as objective as we can do in a prospective series using the two systems,” Scott said.
Since 2013, femto-phaco has become routine in his practice and is used in 100% of the patients who need cataract surgery. The laser is in the operating room because he sees lasers as a tool of surgery and not as a pretreatment.
“We don’t charge extra for doing the laser because this is our routine cataract surgery procedure. We are a high-volume center because of that. Since March 2013 we have performed 25,000 cases, and this has given me the option to get a lot of experience and better understand the differences between manual and femto,” Scott said.
- For more information:
- Alessandro Galan, MD, can be reached at Sant’Antonio Hospital, Via Jacopo Facciolati 71, 35127 Padua (PD), Italy; email: alessandro.galan@gmail.com.
- Wendell J. Scott, MD, can be reached at Mercy Eye Specialists, 1229 E. Seminole St., Suite 430, Springfield, MO 65804; email: wendell.scott@mercy.net.
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