Improvements in Fluidics

Steinert: What technological changes in the past 5 years have improved the safety of phaco fluidics in the average case?

Miller: With smaller incisions and tubing compliance changes, chambers are more stable now than in the past. The computer-driven flow rates and vacuum settings, which can change quickly, allow surgeons to use more aggressive settings. We do not have to worry as much about post-occlusion surge, posterior capsules rising or chambers flattening.

Raviv: In the past 5 years, fluidics settings have been reduced with the advent of non-longitudinal phaco. Now that lateral and transversal technologies are available, there is less repulsion. A 600 mm Hg vacuum setting is not required; there is just as much efficiency with a venturi pump when I reduce the vacuum to 150 mm Hg.

Crandall: With safety improvements, surgeons have been able to push their parameters. We are more efficient, and my surgical style is changing in response to changes in fluidics. I can rely more on the machine rather than actively moving my hands and the phaco tip.

Fishkind: The beauty of this generation of phaco machines is that they are flexible in all parameters allowing each surgeon to adjust the settings to maximize efficiency during both phaco and irrigation and aspiration (I&A). Additionally, the ability to fine-tune the settings for each phase of the procedure has dramatically increased the margin for safety.

Garg: The advancement of the computer controls has made a significant improvement in safety during phaco. The machine can now sense what is happening at the phaco tip more precisely than in the past, which allows the surgeon to adjust the fluidics, often without realizing it.

Steinert: Although fluidics have improved, challenges remain. I watched footage of six cases at a course focusing on secondary IOL issues associated with a broken capsule. Capsular breaks mostly occurred by biting the posterior capsule with the phaco tip toward the end of nucleus removal. I emphasize to residents that they must have their second instrument under the phaco tip toward the end of the nucleus removal, because nothing keeps the posterior capsule back at that point.

Miller: Most machines have a quadrant or nuclear segment removal mode and an epinucleus removal mode, and then go right into cortex mode. To drive home the critical point that the last quadrant requires special attention, it would be helpful to have a last-quadrant mode. In the last-quadrant mode, surgeons would dial down the vacuum limit and slightly dial down the flow.

Hamilton: I use the epinucleus setting for the last quadrant, but it is not labeled “last-quadrant” mode. Surgeons who do not change their settings will not think to choose epinucleus mode for the last quadrant. They may wait until they get to the epinucleus to use it.

Raviv: The problem with only having traditional vertical foot positions 1, 2 and 3 is that, at any phacoemulsification power level, the surgeon is at maximum vacuum. This is disadvantageous for the final quadrant. I agree that switching to epinucleus or last-quadrant mode with lower fluidics is a good idea for the last quadrant. However, with the dual-linear foot pedal on the WhiteStar Signature System (Abbott Medical Optics, Inc.), I have the ability to control vacuum independently from phaco with a yaw motion in venturi mode. For example, I usually set my vacuum to 100 mm Hg maximum (for the vertical foot positions), with a vacuum boost up to 250 mm Hg using the yaw. During the early parts of quadrant removal, my foot is slightly to the right, generating about 200 mm Hg. For the last quadrant, I bring my foot to the center where it is only 100 mm Hg, all while maintaining phaco, without needing to change submodes.

Steinert: Do you prefer to use a peristaltic pump or a venturi pump?

Yan: When comparing the venturi and peristaltic pumps, surgeons must look at what the pumps do rather than how they work. With a peristaltic pump, the surgeon controls the flow rate and the vacuum is passive, whereas with a venturi pump the surgeon controls the vacuum and the flow rate is passive. Surgeons must decide which pump to use based on whether they need to control flow or vacuum. In the end, my pump preference depends on what step of the nuclear dissection and removal I am performing.

Miller: Phaco surgeons do not have the dynamic ability to adjust resistance other than changing how the tip occludes. Instead, they command flow and vacuum. They can behave similarly based on how the variables are modified.

Steinert: Over the past decade, peristaltic pumps had become almost indistinguishable from venturi pumps, especially in terms of the attention to fluidics and the computer control instead of the dummy-setting control with the peristaltic pump. However, that has changed as we enter an era of breaking up the nucleus with the femtosecond laser. A year or two ago, I believed these techniques were interchangeable; however, there is a striking difference between the venturi and peristaltic pumps in terms of followability with the cubes the femtosecond laser creates. The fluidics behave differently in the anterior chamber.

Hamilton: We are moving toward phaco-assisted aspiration, commonly using femtosecond technology rather than strictly phaco. The small cubes can be aspirated down the bore of the phaco needle, even when the nucleus is very dense. Ideally, surgeons match the holdability to the density of the nucleus with the yaw move. The inertia of that piece is different depending on its density. Followability becomes more important as surgeons begin to treat less dense nuclei.

Raviv: I have found that femtosecond technology coupled with venturi fluidics is efficient. Since the lens has been broken up with the femtosecond laser, the attractability and followability of the venturi fluidics allow for efficient lens removal with minimal ultrasound. I use a “femtosecond flip,” where I employ a supracapsular technique to emulsify the femto-softened nucleus. Along with venturi, the pieces are gently and effortlessly aspirated to the phaco tip.

Miller: Femtosecond technology may improve high-flow procedures because it has the potential to create more reproducible incisions. When performing high-flow surgery, leakage must be minimized. Surgeons want the flow to exit through the phaco needle, and not around the silicone sleeve. Metal and diamond blades cause leakage when a surgeon “freehands” the incisions, making them too large.

Raviv: When removing soft nuclei, I noticed that the small cubes act differently because they are not solid. In the past, surgeons split the nucleus into four quadrants; now there are hundreds of little quadrants. The cubes break free when I try to impale, so now I use flow to attract the pieces.

With soft nuclei, we want to bring the pieces toward us and avoid the periphery, and the venturi pump can do that more effectively than the peristaltic pump.

Miller: With followability, the stream inside the eye comes down the outside of the needle, goes out the various ways, leaves the silicone sleeve and circles throughout the eye. Then, the pieces enter into the stream and into the bore of the needle.

Followability is an interesting concept, but it does not play out perfectly; usually surgeons must chase after the pieces and bring them in. Pieces sometimes stick to each other and do not enter into the stream, so holdability is needed to attract the pieces out.

Raviv: Followability is the ability to emulsify one piece that is rapidly followed by another piece. Holdability keeps the piece at the tip, so repulsion and chatter do not occur. The emulsified piece rearranges itself so the next piece is readily available without chasing it. Attractability is when the nucleus is divided into quadrants and, after engaging foot position 2, the proximal piece quivers and comes toward the tip. This is one of my favorite features of the venturi.

Fishkind: Fragments of nucleus, whether created by the femtosecond laser or by chopping, are drawn into the passage of fluid through the phaco tip. This should be the prevalent fluid flow, much more significant than fluid leakage through the wound or side port. The venturi generates immediate vacuum with resulting fast flow, thus enhancing followability.

Yan: Holdability refers to the ability of the phaco tip to grab onto the lens and keep it stationary. This is important during chopping the lens because two points of fixation are required. Followability refers to the ability of the phaco pump to draw pieces of the lens to the phaco tip by creating a fluid stream. The lens pieces get pulled along in the fluid stream much like a raft is dragged downstream in a rushing river. In engineering, the term for this type of movement is entrainment. I do not like the term attractability as much, as that implies there is a direct force, like magnetism or gravity, between the phaco tip and the lens fragment. It is really an indirect force applied to the lens fragments by the phaco pump caused by the generation of fluid movement. The advantage of good followability is that the fluid stream can pull lens fragments out of the capsular bag without the surgeon having to bring the phaco tip into the bag to go after them with holdability.

Garg: The term holdability refers to the ability of the phaco tip to “hold” the nuclear fragment to allow the surgeon to either draw it in from the periphery or stabilize it to execute a chop. Followability refers to the ability of the phaco machine to keep things moving passively without the surgeon having to manipulate the fragments or “go fishing.”

Steinert: Even in conventional phaco, difficulties arise when most of the nucleus has been removed and a small fragment is next to the side port or main incision. This scenario occurs more often with the femtosecond laser because it creates several fragments rather than one or two. With the venturi pump, those fragments spontaneously go to the tip more easily than with the peristaltic pump, which means the venturi creates a current that is more dominant than in the peristaltic.

Miller: Higher flow means increased followability. Surgeons can achieve followability using a peristaltic pump; however, there is much higher flow with venturi systems, where surgeons command a certain level of vacuum in the cassette with low resistance. Because the tip is unoccluded, the pieces circulate inside the eye. As flow increases, there is more turbulence inside the eye. Turbulent flow is more damaging to the endothelium than heat production since heat is no longer as much of an issue with new phaco systems.2–4

Yan: Venturi systems inherently have much better followability despite the improvements made in peristaltic pumps in recent years. The venturi system’s flow rate depends on needle size and, for a 20-gauge needle size, a relatively safe and stable vacuum setting of 150 mm Hg will generate 55 cc to 60 cc per minute of flow rate. Peristaltic systems typically run at much lower flow rates, usually between 30 cc to 40 cc per minute with around 400 mm Hg to 450 mm Hg of maximum vacuum. Above these settings, chamber instability and post-occlusion surge can become significant problems in peristaltic systems. Venturi systems can safely produce nearly twice the maximum flow rate of peristaltic systems, all the while generating much lower vacuum levels in the fluid lines. The operating characteristics of the two pumps on the vacuum-flow rate plot (Figure 1) show that venturi systems operate in a high flow rate/low vacuum zone, whereas peristaltic systems operate in a high vacuum/low flow rate zone. I prefer a peristaltic machine when chopping for its high vacuum/low flow holdability, but for segment removal, the followability of a high flow/low vacuum venturi pump is superior.

Click here for larger version of Figure 1.

Steinert: The Signature system has both the venturi and peristaltic pumps. Do you feel that is an important feature?

Yan: The incorporation of both the venturi and peristaltic pumps in a single system is another example of how improved phaco technology has changed the way I perform and teach surgery. The ability to switch pumps on-the-fly defines two phases of the procedure, so residents learn there are two distinct phases to nuclear dissection and segment removal. In phase 1, the peristaltic pump holds the lens while the surgeon chops it. Its pressure transducer detects the vacuum rate so the surgeon knows when there is adequate occlusion and holdability and when to move the chopper into the lens. In phase 2, the surgeon switches to the venturi pump to remove the segments.

Raviv: Surgeons can test two fluidic pumps in the same case. I have a preset impale mode where the peristaltic pump holds the lens in place. The higher peristaltic vacuum (approximately 500 mm Hg) holds the lens for chopping. Once the quadrants are created, I switch to venturi mode (150 mm Hg).

The venturi is also great for I&A. With a peristaltic pump, occlusion of the tip (with the cortex) is needed for the vacuum to build up. However, since the cortex comes in wisps, it is easier and safer to clear with the venturi. Even in the “cap-vac” peristaltic setting, there will be less aspiration if that port is partially open, and the capsule frequently is engaged to create occlusion. On a venturi pump, the cortical strands will be drawn in without needing occlusion. The cap-vac setting is the best place to start with venturi, because a surgeon can go closely against the capsule, and the “shrink-wrap effect” occurs less often than with peristaltic.

Hamilton: The venturi intuitively makes the most sense for cortex removal. I am a stop-and-chop hybrid surgeon and, with increasingly softer nuclei, I perform hydrodelineation on most of my cases because I like to have separation between the nucleus and the epinucleus. After I create the groove and separate the epinuclei, I perform a stop-and-pull maneuver. I insert the Seibel nucleus chopper (Rhein Medical, Inc.) between the epinucleus and the nucleus and tilt it out to get the first heminucleus. If the nucleus is very dense, I perform a peristaltic chop. If the nucleus is soft, then the venturi is ideal because it will go right to the phaco tip without holding onto it.

Crandall: I have several pseudoexfoliation cases, which are variable in terms of zonular stability and wound size. I pre-chop if I can, or I ultra-chop if the nucleus is very hard. I switch between the venturi and peristaltic pumps depending on what I need each one to do. I often have devices in the eye, so I want the procedure to happen slowly. Therefore, I hydrodis-sect rather than hydrodelineate.

Hamilton: The hydrodelineation is less effective when the nuclei are dense because there is little epinucleus.

Miller: It is important to understand that, with the venturi, the vacuum at the tip is not the same as the vacuum at the cassette until occlusion occurs and the tubing collapses. When there is no flow, then the tip and in-cassette vacuums are the same, which is what happens in peristaltic systems.

Most of my patients have soft lenses, so I use the divide-and-conquer technique. For dense lenses, I use a vertical chop and, for the grade 3 to early grade 4 cataracts, I use a horizontal chop. I take out the first quadrant with the peristaltic pump because it provides more control. I use the venturi pump for the second, third and fourth quadrants because it holds the pieces and draws them to the tip. Initially, I use fairly high vacuum rates, but I dial down the vacuum toward the end of the procedure. Occlusion break surge still occurs with the venturi system but seems to occur more often with a peristaltic system. The peristaltic system’s vacuum limit is high and lacks vacuum control, making it difficult to dial down the vacuum.

Yan: Peristaltic pumps require at least 300 mm Hg of maximum vacuum to draw lens fragments to the tip, whereas 150 mm Hg is more than adequate with the venturi pump. Building up vacuum causes semi-rigid fluid lines to collapse. Breaking occlusion at the phaco tip will release this stored energy and cause post-occlusion surge. During segment removal, surgeons should avoid the build-up of vacuum in the lines for best chamber stability.

Additionally, the venturi and peristaltic pumps behave differently when the phaco tip is partly or fully occluded by lens material. The peristaltic pump must completely shut off when the tip is fully occluded to avoid generating vacuum past the maximum preset level. The pump cannot safely restart until vacuum has dropped sufficiently below the maximum vacuum. As the surgeon breaks occlusion with ultrasonic energy, the nuclear fragment starts to disengage from the phaco tip, and there is no flow rate to hold it in place. The venturi pump stays on because the cassette vacuum is not affected by breaking occlusion with ultrasound energy. When tip occlusion is broken in a venturi system, fluid flow will resume. The followability issues with the peristaltic pump arise from the delay in restarting the pump after the pressure transducer has detected a drop in vacuum.

Steinert: I use the venturi pump with the Signature system for I&A. It provides efficient control and generates ample suction for the cortex. When using the venturi for nucleus removal, the Signature’s ability to switch on-the-fly is important. I can adjust the foot pedal depending on how the anterior chamber reacts. The density of the nucleus is not always predictable, despite preoperative assessment.

Garg: Having dual-pump technology has been valuable for my cases and for teaching phaco. I learned phaco with peristaltic pumps, but the venturi pump’s instant vacuum is more efficient for experienced surgeons. It is also more efficient for viscoelastic removal, cortex removal and nuclear removal.

I use the peristaltic first and then quickly switch to the venturi for the remainder of the case. I like that I can switch on- the-fly with the Signature system, because the venturi pump can be too aggressive for certain cases. Having both pumps is advantageous because every case is unique. Two eyes, even on the same patient, can act differently, so flexibility is imperative.

The venturi pump’s followability is phenomenal. A second instrument can gently loosen fragments from the periphery so they come to the tip. The venturi is safer in that regard because surgeons do not have to move the phaco tip, which increases the chance of breaking the capsule in the periphery. The peristaltic pump’s holdability tends to hold the fragment more effectively because there is less movement at the tip. A surgeon can hold more effectively with the peristaltic pump and emulsify more effectively with the venturi pump (Figure 2).

Figure 2.

Steinert: What is different about the venturi today?

Miller: A disadvantage of the early version of the venturi pump was that surgeons had to haul in and set up a nitrogen tank. Now, the compressors are built into the machine, so it is more practical and the machine is quieter. Setup issues no longer impede the technology.

Fishkind: The venturi pump now is vastly different from the early pumps. A venturi chamber must be rigid so as not to collapse as vacuum is generated. The early chambers were large, so they would not need to be emptied. As the procedure progressed and fluid filled the container, there was a less open chamber. Therefore, the boost of the vacuum became more aggressive as the procedure progressed. In modern machines, the vacuum chamber is diminutive and is automatically emptied. Consequently, the vacuum generated is exceedingly more stable.

Steinert: The venturi pump requires a closed collection system where the vacuum is generated, so there is no floppy plastic bag like with the peristaltic pump.

Yan: The latest venturi systems feel dramatically more stable than previous generations. The main difference is in the size of the cassette. Older systems had a large cassette with approximately 230 cc of compressible air, whereas the new venturi cassette in the Signature only has 65 cc because it automatically vents the fluid as it fills up in a very small tank. The tank never fills because the venting pump senses the fluid level and automatically vents it to maintain a small cassette air volume. During the surgery when the cassette is partly filled, the venturi air volume of the Signature is 6 times smaller than the older systems, making the Signature system dramatically more stable.

In addition, the peristaltic pump can generate high-vacuum holdability for chopping. Surgeons are no longer forced to chop with the venturi in a single pump system, which requires a high vacuum rate. If I had to chop with the dual-pump system in venturi mode, I might have to increase the vacuum to 250 mm Hg to 300 mm Hg. Because flow is directly proportional to vacuum in venturi systems, high vacuum will generate too much flow rate, rendering the system unstable.

Hamilton: Surgeons now have ancillary devices that not only make phaco more efficient but also present new challenges, so the flexibility in having both pumps is critical. With femtosecond technology, the cubes move around and jam in areas that were never a concern. Now surgeons must adjust the direction of the flow to dislodge those cubes. These issues are going to drive innovations in the phaco part of the system.

Steinert: The connection of the foot pedal to the pump has improved as well, because the foot pedal settings are more programmable. These improvements give surgeons a better sense of control over the venturi.

Raviv: The new venturi pump is mechanically and digitally different than the old venturi pump. Surgeons have the ability to adjust the ramp-up time, a setting between 1 (slowest) to 5 (fastest) that controls the rise time to the maximum vacuum. Adjusting down the ramp time can make it a slower acting system, with more control. Surgeons can also use lower vacuum levels with the Signature venturi pump because the lateral movement of transversal phaco produces minimal repulsion compared to traditional longitudinal phaco.

Steinert: What would you recommend for a surgeon who has never used dual-pump technology?

Miller: The user interface is greatly improved in the new generation of phaco machines. Changing the settings of an earlier machine so the change would remain for the next operation was complicated. Now, once the change is made, it can be saved.

Garg: I recommend that, every time a new technology is available, try it. Surgeons usually dislike a new technique or device when they first try it. If they still dislike it after 30 or 40 cases, then it is not for them. We must keep our eyes and minds open, because there will be some great new improvements.

Fishkind: The machines we have in the United States are all amazing in their flexibility. They are also considerably complex. It is tricky for the surgeon or resident to make adjustments while performing the procedure. It is especially helpful to have a representative of the company present occasionally to help improve and fine-tune settings. If the surgeon can articulate the dilemma, then the representative should be able to attain the settings to meet the surgeon’s requirements.

Steinert: My impression is that if surgeons are struggling with a technology or device, then they are open to change. But if they are content, then they are reluctant to change or try anything new. What is the safest way to encourage surgeons to try something new?

Garg: I start with the easier steps, like viscoelastic removal, and allow residents to get a sense for what the pump does. Once I get the pieces loosened up, I work backwards by removing the fragments and then determining when I want to transition to the venturi.

Miller: That process works for a surgeon whose mainstay machine is the Signature system, but many surgeons have never used the Signature and do not want to adopt a new system. The differences between the venturi and peristaltic pumps are small compared to using a whole new system. Surgeons must constantly try new techniques and technologies, and instill that habit early on with residents.

Raviv: Teachers can introduce a new system gradually by pointing out specific features, such as safer fluidics, and convincing them that there will be improvement in safety and efficacy. Ultimately, the surgeon has to feel comfortable making the transition. The Signature allows peristaltic surgeons to try the venturi in just one part of the procedure, such as I&A, until they are comfortable using it in other parts of the procedure.

Garg: Residents often come in for surgery in rotations, and they learn a certain technique in the previous rotation. I switch them out of their comfort zone and change their routine. Surgeons should never be complacent; complacency prevents progress.

Miller: Manufacturers know that surgeons are set in their ways, so often times new machines are set up exactly like the previous machine and the settings can be changed gradually.

Yan: I first emphasize the safety and stability aspects of the new system. For example, I would use 150 mm Hg for segment removal because it is more stable yet still faster than the peristaltic. These settings will help surgeons feel more comfortable making the transition.

It is always more difficult to change a practicing surgeon’s technique as opposed to a resident learning surgery. The residents I teach embrace the dual-pump method, and most continue to use the technique in practice if the technology is available to them. When residents can adopt a new technique, then we know that it is something that all surgeons can adopt.

Originally Published on Healio