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Pressurized infusion techniques dominate innovations in phaco fluid management
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Ongoing advances in phacoemulsification technology are designed to ensure safe, rapid and thorough removal of cataracts with minimal trauma to the anterior chamber.
In phacoemulsification, ultrasound energy, vacuum and fluidics work in a delicate balance to break up and remove the diseased crystalline lens. Fluidics depends on the infusion of balanced saline solution to maintain IOP and anterior chamber depth.
“The key to a safe and efficient cataract surgery is achieving balance in the phaco fluidics,” Uday Devgan, MD, Healio.com/Ophthalmology Section Editor, said. “Our goal is to balance the inflow of fluid, which comes from the balanced salt solution bottle, with the outflow, which is from the aspiration at the phaco tip, as well as leakage from incisions.”
The importance of fluidics is growing as surgeons perform more phaco-assisted aspirations of softer cataracts, according to OSN Chief Medical Editor Richard L. Lindstrom, MD.
“Patients are now in their high 60s rather than middle 70s, and their lenses are softer,” Lindstrom said. “We now have femtosecond lasers that many of us are using to soften the nucleus even further. With use of ultrasound-assisted aspiration, the fluidics become even more important.”
Phaco platforms use two types of infusion: passive infusion, in which gravity pulls fluid from an elevated bottle, and active or forced infusion, which does not rely on gravity. Active infusion is driven by gas injected into the bottle or mechanical pumping.
One advantage of mechanical pumped infusion is that IOP is maintained without wide fluctuations, according to Richard B. Packard, MD, FRCS, FRCOphth.
Image: Packard RB
Devgan said the majority of phaco machines are gravity based. So for most surgeons, passive infusion is the gold standard. However, as incision size has decreased, surgeons have experienced a lack of fluid going into the eye, which can cause surge and lead to shallowing or collapse of the anterior chamber, resulting in complications such as endothelial cell loss and posterior capsular rupture.
To prevent surge, gas-forced infusion was developed in the late 1990s.
Amar Agarwal, MS, FRCS, FRCOphth, OSN APAO Edition Board Member, an early adopter of gas-forced infusion, said he and his colleagues use it in nearly every cataract case they handle.
Amar Agarwal
“I will use it in every case of mine, whether I’m doing coaxial or bimanual surgery,” Agarwal said. “I want [surgeons] to use this pressurized infusion for all their cases.”
The Centurion Vision System (Alcon), launched at the European Society of Cataract and Refractive Surgeons meeting in Amsterdam, Netherlands, in October, features active fluidics and operates on a different principle. Instead of air being forced into the infusion bottle, a bag of balanced saline solution is squeezed or relaxed by microprocessor-controlled paddles.
Gas-forced infusion is rendered obsolete with the advent of the Centurion, according to Richard B. Packard, MD, FRCS, FRCOphth, OSN Europe Edition Board Member.
“All [gas-forced infusion] does is push gas into the bottle to effectively increase the flow through the irrigating chopper,” Packard said. The original reason for developing gas-forced infusion was “because the size of the chopper was such that with normal gravity feed, there wasn’t enough flow going into the eye to keep the anterior chamber stable so that you could use normal vacuum and aspiration flow-rate settings to do the phaco,” he said. “With the Centurion, you just don’t need to worry about it.”
Lindstrom said there is no evidence that the Centurion’s active fluidics system is superior to gas-forced infusion. However, both are superior to passive infusion, he said.
“In the future, I anticipate that all phaco machine platforms will incorporate this [active infusion] technology,” Devgan said.
“By and large, all phaco machines will start having a built-in system for gas-forced infusion,” Agarwal said. “This is the bottom line.”
Microincisions and intraoperative surge
For fine vitreoretinal procedures, surgeons have switched from using gravity feed infusion to forced infusion so that IOP can be maintained without fluctuation during surgery, Lindstrom said.
Richard L. Lindstrom
“Vitreoretinal surgeons almost immediately realized that [gravity feed infusion] was inadequate for their purposes because there was poor maintenance of the vitreous cavity when doing vitrectomy and retinal peels,” he said. “If there was a sudden surge or shallowing, they could be cutting a hole in the retina. So, they very early on went to forced infusion. You can set the IOP, and the system holds at that IOP.”
Cataract surgeons, on the other hand, did not initially need forced infusion because they were working with large incisions, Lindstrom said. The drive to adopt forced infusion came when surgeons began undertaking microincision cataract surgery.
“With the smaller incisions, it was impossible to get adequate inflow with gravity feed, no matter how high you put the bottle,” he said. “Even with coaxial microincision cataract surgery, we’re starting to have trouble with maintaining chambers during phacoemulsification. Getting a bottle high is just not adequate.”
Surge can occur at different levels, Agarwal said.
“I can have a massive chamber collapse, or I can have a small fluttering of the iris. Even a small fluttering of the iris is not a good sign because that also indicates surge,” he said.
Packard said the size of the needle affects inflow in microincision cataract surgery.
“It depends on what size phaco needle you’re using and what size incision you’re using because with a smaller incision and a bigger needle there’s going to be less room for the fluid to get into the eye,” he said. “I personally use a 700-µm needle that is made for me by MST. Even in a 1.8-mm incision, there’s still enough room for the fluid to get in there.”
Gravity vs. forced infusion
Aside from anterior chamber shallowing and surge, another downside of passive infusion is that inflow and pressure can fluctuate, depending on the patient’s position, Devgan said.
“What if your patient can’t lie down and you have to sit your patient at a 45° angle?” he asked. “If you raise your patient’s head by 2 feet, you better raise your bottle by 2 feet. Only the difference between those two will help. … That’s obviously a very slow system.”
In 1998, Sunita Agarwal, MS, DO, Agarwal’s sister, improvised a gas-forced infusion system using an air pump from an aquarium. Today, some phacoemulsification machines, such as the Stellaris (Bausch + Lomb), feature gas-forced infusion based on similar principles.
In the Agarwal system, the air pump is connected to the infusion bottle with intravenous tubing that passes from the air pump into the infusion bottle. Air is pumped into the top of the bottle and pumps the fluid down and out of the bottle. Air is filtered with a standard Millipore filter.
“Air would go up into the infusion bottle, and because of pressure, it pushes more fluid into the eye,” Agarwal said.
After consulting with Agarwal, Bausch + Lomb added the DigiFlow Pressurized Infusion system to the Stellaris in 2009.
“In the Bausch + Lomb machine, it’s built into the machine so you don’t have to buy a separate air pump. You can monitor the pressure,” Agarwal said.
Forced infusion enables surgeons to instantaneously increase pressure, Devgan said.
“Now we are seeing this technology brought to cataract surgery in new phaco machine platforms. With a continuously monitored forced infusion, we can improve anterior chamber stability and use higher flow rates during surgery, which can improve efficiency. And this is done real time without the need to change bottle height during surgery,” he said.
Lindstrom said the surgeon has the ability to instantly increase inflow with mechanical pumping.
“The benefit is a stable chamber while you’re doing phaco with an absence of surge,” Lindstrom said. “So, when the occlusion breaks and the vacuum suddenly goes up, you can’t adjust the bottle height within an instantaneous second. But if you have either forced infusion via gas into the bottle or by squeezing the bottle, which is what Alcon’s Centurion does, then you can pretty much have an instantaneous increase in inflow to cover for the surge so you don’t get a [shallow chamber].”
The main intraoperative advantage of gas-forced infusion is deepening of the anterior chamber, which gives the surgeon more room to perform surgical maneuvers, Agarwal said.
“When I have gas-forced infusion working, my chamber becomes deep because now I have got a lot of fluid inside the eye,” he said. “So, obviously, the corneal endothelium goes up and the posterior capsule goes down. I have more space to play around with. Endothelial loss has come down, and the chances of posterior capsule rupture for a beginning surgeon will be much less because of these advantages.”
Gas-forced infusion is particularly advantageous in complex cases with shallow anterior chamber, Agarwal said.
“If I am operating on a patient who is hyperopic, his anterior chamber is shallow. I may be operating on a patient who has nanophthalmos, where the anterior chamber is very shallow. In all such cases, if I can get the chance to deepen the anterior chamber, even just a little bit, the chance of success for me is obviously better, and postoperative results will be much better,” he said.
Safety, speed and comfort
Gas-forced infusion increased the safety, ease and speed of coaxial phacoemulsification, according to a study that Agarwal and colleagues published in the Journal of Cataract and Refractive Surgery in 2010.
The prospective study included 90 patients; 45 patients underwent phacoemulsification with gas-forced infusion and 45 underwent surgery without infusion. Mean phaco time, total surgical time and effective phaco time were similar in the two groups. However, irrigation and aspiration time was significantly less in the infusion group than in the control group (P < .0001). Irrigating fluid volume was significantly higher in the infusion group (P = .003).
No surge was reported in the infusion group. Surge occurred three times in the control group; the between-group difference was significant (P < .0001).
Mean endothelial cell loss was significantly lower in the infusion group than in the control group (P = .045).
“The surgeon-graded ease of surgery was significantly higher when gas-forced infusion was used,” Agarwal said. “Although the benefit was perceived in all components of the surgery, irrigation-aspiration was particularly easier to perform because the surgeon had a better grip of the cortical matter and the posterior capsule was pushed back. This may be especially beneficial under more difficult conditions and to surgeons in the learning curve. The surgical time was generally less with the use of gas-forced infusion.”
Gas forced vs. mechanical pumping
Like the Constellation vitrectomy machine, the Centurion offers flexibility in managing complicated cases, Lindstrom said. The key issues are a stable chamber, more control and safety. He called the Centurion a responsive system, making for fewer anxious moments.
“Instead of raising the bottle, now we just change the pressure. If the chamber is not what you want it to be and you’ve got it at 55 mm Hg, you can go to 65 mm Hg. Or if the patient is a high myope and you have an overinflated chamber in a vitrectomized eye, you can drop down to 35 mm Hg or 40 mm Hg, whatever you need it to be to be comfortable during the surgery,” he said.
The phaco machine has a sensor that reports continuously and automatically, like a car’s cruise control, pumping more fluid when needed to keep the IOP steady, Devgan said.
Uday Devgan
Fluid management by mechanical pumping is better than gas-forced infusion because it does not elevate IOP to extreme levels, Packard said.
“The thing about using a system that does not require gas-forced infusion is that you can operate at much lower IOPs because you only actually get fluid going into the eye when you need it,” he said. “The system is monitoring what the pump is doing and what the pressure inside the cassette is. It only pushes fluid into the eye in order to maintain a level of IOP.”
In addition, mechanical pump fluid management does not result in wide fluctuations in IOP, Packard said.
“All that the gas-forced infusion is doing is effectively the same as having a bottle at about 200 cm,” he said, which provides enough fluid to overcome any possibility of post-occlusion surge.
Lindstrom said that it is up to the individual surgeon to decide whether gas-forced infusion or fluid management is appropriate for his or her skill level and surgical style.
“Individual surgeons will have to, in the clinical setting, experience both and make their own decision. I’m still using both. I find they are both superior to gravity feed,” Lindstrom said.
Devgan agreed, saying that there is no meaningful difference between gas-forced infusion and mechanical pumping.
“It doesn’t really matter what kind of pump it is,” Devgan said. “It doesn’t matter how you do it, other than that you have to actively pump fluid into the eye.” – by Matt Hasson
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For more information:
Can microincision cataract surgery be performed using gravity-based fluidics?
Forced infusion essential in MICS
You cannot reduce your incision size to less than 2 mm if you do not use pressurized infusion. Pressurized infusion is a basic element of modern phacoemulsification. It is the way in which all phacoemulsification machines will work in the future, reducing corneal incision size below the limit of 2 mm.
Jorge L. Alió
Intraoperative surge is a problem, and you need to use pressurized infusion in order to keep the volume stable in the anterior chamber. This is why it is important because this is just at the cutting edge of the progression of the phaco technology.
Gas-forced infusion and mechanical pumping are about the same in terms of increasing pressure in the bottle in order to get more fluid inside the eye in a much better, more pressurized way. Basically, what they do is the same. They create pressure to inject more fluid. This can be made by gas, which is the traditional way, or by any other means because pressure can be created by many forces.
Jorge L. Alió, MD, PhD, is an OSN Europe Edition Board Member. Disclosure: Alió has no relevant financial disclosures.
Forced infusion not necessary, if you have good control
Infusion of balanced saline solution in phaco surgery has the purpose of replacing the fluid in the eye removed by phaco or irrigation-aspiration. As such, if you have adequate control of the vacuum and power settings with phaco, it is generally not necessary to force the infusion. What forced infusion can do is cause more fluid to pass through the eye than is necessary to accomplish the surgery safely, which may be damaging to the endothelial cells of the cornea and have other untold damaging effects, all unnecessary for the surgeon who has good control.
John A. Hovanesian
So, what elements give good control? Personally, I use a phaco machine that has dual linear foot pedal control, so I can separately control vacuum and phaco, and one that has a venturi pump, which provides very responsive vacuum. These allow very fine-tuned control of what is happening in the eye. I simply do not find that forced infusion is necessary.
John A. Hovanesian, MD, FACS, is OSN Cataract Surgery Section Editor. Disclosure: Hovanesian is a consultant for Abbott Medical Optics and Bausch + Lomb.