Just as hybrid automobiles are more efficient, phaco machine makers would like surgeons to believe that machines that offer hybrids of both peristaltic and venturi pumps will make their surgeries more efficient, as well. They say that the machines offer surgeons greater flexibility during their cases, allowing them to handle situations that lend themselves to fast, responsive venturi pumps as well as those that might require a slower, possibly safer, peristaltic system. Here's a look at how the new systems work and the situations in which surgeons say their advanced fluidics might be useful.

 

The New Approaches to Fluidics

The new AMO WhiteStar Signature system features the option of Fusion Fluidics with a dual-pump pack, meaning there are two pumps, a peristaltic and a venturi, on one cassette (surgeons can also order a strictly venturi system, however, if they so desire).

William Fishkind, MD, a consultant for AMO, describes how the cassette works. "At the base of the cartridge there's a sump, a small, solid, rigid vacuum area where it builds vacuum," he says. "There's also a secondary pump in the machine that drains the cassette so it can't overflow, otherwise it wouldn't be able to work."

In the Bausch & Lomb Stellaris system, the surgeon can choose either a vacuum-based venturi machine or a flow-based peristaltic one. However, the company says if the latter system, called the Advanced Flow System, is chosen, it comes with emulation technology that allows it to operate like a venturi system when the surgeon needs it to.

"These machines have been designed from the ground up to incorporate the best of flow and vacuum [venturi]-based fluidics," says Uday Devgan, who consults for both AMO and Bausch & Lomb. "What this means is, in the old days, we always thought of a peristaltic pump as only flow-based. So, with that, you set up the machine and said, 'This is how much flow I want,' and the flow would then be controlled by the machine. You'd only achieve vacuum when you occluded the tip. The other school of thought was venturi, where you'd set the amount of vacuum you wanted to deliver, but the flow would vary based on the conditions in the eye. Both of these new machines have a pump that emulates either peristaltic or venturi, to give the surgeon either flow-based or vacuum-based control, depending on what step of the cataract procedure he or she is in."

Dr. Fishkind says the venturi modes in both the WhiteStar Signature and the Stellaris are also more conveniently handled than in past devices. "The beauty of the pumps in both machines is that you don't have to have nitrogen running through the machine," he says. "They pump enough air through to create a venturi effect that will bring about the vacuum without the need for nitrogen, which is expensive and can be difficult to handle."

"There are some people in cataract surgery who like the efficiency of venturi and use it all the time," says AMO consultant Randall Olson, MD, of the Moran Eye Center at the University of Utah. "But, they admit, safety-wise, that there are times when they would just as soon not have that active vacuum, particularly if they need to work near the capsule or iris, for instance. So, to be able to use it for efficiency in an area where you know there's little risk, then switch to peristaltic when you're going to a safer mode near the capsule or elsewhere, could give you some of your cake and the ability to eat it, too."

The Alcon Infiniti system, while not new, is a flow-based machine that has some elements, namely low-compliance membrane and tubing, that attempt to mimic the responsiveness of a venturi-based unit. "Using the software, the surgeon can alter flow based on the desired vacuum if that's his preference," says Nacogdoches, Texas, surgeon Robert Lehmann, an Infiniti user who also consults for Alcon. "What it allows is a very quick surgical response with the ability to control both flow and vacuum if needed."

Switching on the Fly

Surgeons say there are specific junctures of the typical cataract case in which a peristaltic or venturi pump might be ideal.

"Look at the classic divide-and-conquer technique, which is not a technique I normally use," says Dr. Devgan. "When you start it, you're sculpting grooves in the nucleus. Your goal is to aspirate out whatever cataract material you displace as you make the grooves. And so you use a flow-based system to provide a constant flow of fluid that keeps removing the material from the groove. Then, you go to the next step. After you've broken the nucleus into quadrants, you have to grab a quadrant and bring it out of the capsular bag. That's where you want the vacuum, because that's what holds the material and brings it up out of the capsular bag. So, in this situation, you want vacuum control, so you want a vacuum-based mode. In that mode, as soon as you step on the pedal, you achieve a very high vacuum. You can, therefore, aim your vacuum at a particular piece, and it will come toward you.

"Then, say you want control in removing epinucleus," Dr. Devgan continues. "In this situation, you want to keep the flow slower, you want a low amount of vacuum and a low flow, so you should go back to flow mode and set the flow directly to, say, 15 cc per minute. Then, when you go back for cortex removal, you want to make sure you grab onto the cortex very strongly, so you'll want to go back to vacuum mode."

Dr. Fishkind agrees that vacuum would help in moving fragments. "If you look specifically at phaco for a hard nucleus, venturi pumps generate vacuum quickly and things tend to happen a little faster with them, so they work very well in mobilizing fragments," he says. "So, if you use a venturi to allow the phaco tip to get into the nucleus and hold it for chopping, it will be a little more solid hold than a peristaltic mode. It's going to happen faster, which means you tend not to push material in front of the phaco tip, which is one of the problems with a hard nucleus—you don't want to push against the zonules and cause zonular problems. Once the chopping is done, a venturi system is nice because it can grab the fragments quickly and firmly; you don't have to sit there and wait to build vacuum. So, you can grab a fragment quickly with the venturi, bring it up to the plane of the iris for emulsification, then, with a side movement of the foot pedal, switch to peristaltic to emulsify the fragment to minimize surge.

"The other thing that venturi does really well is allow for the separation of vacuum and phaco, because you have definitive levels of vacuum with a venturi pump," Dr Fishkind adds. "So, you can use the dual-linear footpedal on the Bausch & Lomb unit, and now with the WhiteStar Signature unit as well, and it works really well because you can hold vacuum wherever you want and then kick in phaco power by yawing to the other side. You can't do that as well in peristaltic, it just works better in venturi."

Dr. Devgan uses chopping for most of his cases, and agrees that dividing up the phases using different modes makes sense. "I'd stay in vacuum mode for removing most of the cataract," he says. "I'd only go back to the flow mode to remove the epinuclear shell, mainly because I want to be a little more careful and have direct control over the amount of fluid flow into the eye. I'd go back to vacuum mode for cortex removal, and then, at the very end, back into flow mode for the removal of viscoelastic. What's neat is that it adjusts to the surgeon, who doesn't have to change his operating technique. Let the machine tailor itself to you."

Rosa Braga-Mele, MD, associate professor of ophthalmology at the University of Toronto and consultant for AMO, Bausch & Lomb and Alcon, says switching between pump modes can be useful in a couple instances. "If the nucleus is very soft and very difficult to manipulate, you may want to use more flow than vacuum to just sculpt and take it easy with the case," she says. "When you're removing segments, specifically with denser nuclei, I think vacuum has a large advantage as it lets you minimize the amount of total phaco power you're going to use and thereby limit the amount of trauma to the eye, maximizing the outcome. Also, I really like vacuum for cortex removal. It's smoother and a little more efficient."

Though the Alcon Infiniti doesn't have the dual-pump system, Dr. Lehmann says the system's linear control of flow and vacuum can be manipulated in certain situations to make things easier. "It delivers surgical control of both fluidic parameters and adjusts the pump to enable control of acquisition and holding force of lens material as the surgeon desires or the situation dictates," he says. "The benefit is I can now adjust the response of the fluidics depending on the surgical task that I need to accomplish. For example, during irrigation/aspiration, when you need high flow and vacuum for thick cortex, I can get that by pressing the foot controller down to max limits. But when I want to be delicate and polish the capsule or tease out residual cortex attached to the posterior capsule, I can lift my foot and get very low flow and vacuum levels that are safe for this situation. All of this is done without the need to change the machine parameters or surgical steps."

And one situation that users agree is helped by the WhiteStar Signature and Stellaris systems is the multi-surgeon environment. "It's advantageous in an ASC where you have multiple surgeons with different techniques and surgical capabilities, where some like flow and some may like vacuum," says Dr. Braga-Mele. "The ability to have both allows everyone in that surgery center to choose what they want to use. The ASC environment doesn't dictate the procedure by imposing on surgeons and saying: 'Everyone has to learn vacuum or everyone has to learn flow, and just be happy with it.' "

Avoiding Post-Occlusion Surge

Part and parcel with fluidics performance is how well a machine helps the surgeon avoid post-occlusion surge, or simply "surge," which can occur whenever the outflow of the system is greater than the inflow. The most likely time for this to happen, as surgeons know, is right after an occlusion breaks when material clears from the tip.

"Surge is what concerns surgeons the most," says Dr. Devgan. "It can cause the posterior capsule to flap around like a flag in the wind until, boom, it breaks."

In the Stellaris, there is a built-in system of fail-safes called EQ Fluidics, which basically encompasses the entire machine. "The pump is designed to be a fast-reacting pump," explains Dr. Devgan. "It's many times more responsive than the old Bausch & Lomb Millennium and has far less surge. New tubing also plays a role. The inflow tubing is a larger diameter and the outflow is smaller, which stacks the odds in your favor, helping to make sure that, at all times, the fluid inflow is always higher than the outflow."

Dr. Braga-Mele says EQ Fluidics will also be more proactive. "The system can anticipate an occlusion break a certain number of milliseconds after the tip's occluded," she says, "and it will drop down to a lower preset vacuum so that when occlusion does break, there isn't as much vacuum present and surge is minimized. This minimizes the bounce of the anterior chamber and movement of the posterior capsule, helping reduce complications."

On the WhiteStar Signature, a system called Chamber Stabilization Environment (CASE) attempts to minimize surge. "CASE actually lets you set a time at which vacuum will change after an occlusion occurs," says Dr. Olson. "This can be 100 ms, 200 ms, et cetera. So, you get that kick of the big vacuum early on to move things or manipulate them, but then the vacuum drops down to a safer level. The assumption is that you're not going to have an occlusion break before it drops to the lower level of vacuum. And, if you set it at the appropriate parameters, your odds of having an occlusion break before you drop to the lower level are going to be extremely low.

"Also, the system continuously monitors what the actual vacuum is and adjusts its parameters accordingly," Dr. Olson continues. "In post-occlusion surge, for example, it pushes fluid back into the chamber to overcome the surge. All of this happens in a matter of milliseconds, independent of the CASE system."

Is it Time to Switch Systems?

Though the latest systems with dual-pump action offer a unique way to approach various types of cataract cases, a surgeon may wonder if they're worth abandoning his current system.

"When it comes to switching technologies, it's always worth experimenting to see if something's better than what you're doing currently, as long as it's done safely," says Dr. Fishkind. "But I wouldn't change a machine just to be able to get peristaltic and venturi on the fly. I do think it adds flexibility, though, for situations with multiple users, so everyone can find what he or she likes."

"Clearly, if you're doing complicated surgery in which you know you're going to deal with vitreous, I think having both pump modes available is going to be a relatively strong draw  [since the vacuum-mode will be useful in these sorts of situations]," says Dr. Olson. "For the average surgeon who's happy with what he's got, will that be enough of a draw? It will be interesting to see how that evolves."

"We're very early in the learning curve with these new systems," says Dr. Fishkind. "This ability to change on the fly between venturi and peristaltic offers a surgeon certain theoretical advantages, but we have to start using it to determine what's theoretical and what is real. You frequently find things you didn't expect to be better actually are, and you get surprised as a result. You can theorize all you want, but in real time and real life situations, it's sometimes different."