Surgeon explains transition from peristaltic to venturi phaco

Vacuum-based venturi pump systems offer improved efficiency and comparable safety.

Pablo Arregui

With modern-day refractive cataract surgery, it is becoming more critical to deliver better results in a more consistent, safe and efficient manner. This is one of the reasons I have switched from using primarily peristaltic phacoemulsification to mostly using venturi phacoemulsification.

The theoretical advantages of venturi over peristaltic pump systems have always made sense to me, but my concerns about the safety of venturi systems made me shy away from them. However, with the improvements in fluidics in some of the more modern phacoemulsification systems, such as the Signature (Abbott Medical Optics) and Stellaris (Bausch + Lomb) systems, the safety of the venturi systems matches that of peristaltic systems. And with the increased efficiency I get from venturi, I feel that the advantage has swung in favor of these vacuum-based systems.

The basics of the two pump systems are compared in Table 1.

Safety concerns

One of the most critical safety concerns with phacoemulsification is the ability to control post-occlusion surge during surgery. In a typical case of this, vacuum is present in the tubing while the phacoemulsification tip is occluded with material. When the tip occlusion disappears or resolves, there is a surge as the fluid in the anterior chamber and the phacoemulsification machine tubing equalize the disparity of the pressure gradients. This in turn makes the anterior chamber more shallow and dramatically increases the likelihood of capsular rupture.

With venturi systems, flow is not controlled separately from vacuum; therefore, as vacuum increases, so does flow. In the past, this led to increased chamber instability with these systems. Advances in fluidics have improved the stability of the anterior chamber and minimized the risks of post-occlusion surge even at high vacuum and flow rates. I use AMO’s Signature machine with the CASE system, which allows high vacuum for a limited time and then steps down the vacuum level before tip occlusion disappears to prevent surge. Bausch + Lomb uses a mechanical flow restrictor and hypercruise technology to decouple vacuum and flow, which leads to lower flow at high vacuum and a decreased likelihood of surge. In addition, the Fusion Fluidics in the Signature machine are better able to monitor the pressure inside the aspiration line and respond more quickly than older machines to changes in pressure.

Peristaltic machines were thought to be safer partly because the vacuum builds gradually at the tip, and it was erroneously assumed that there was no vacuum until the tip was occluded. However, with the parameters that are most frequently used by cataract surgeons today, studies have shown that there is indeed vacuum at the tip of peristaltic machines even when the tip is not occluded. What we thought and were taught was a safer system is not really safer for most of today’s surgeons. If there is no longer a dramatic difference in safety between venturi and peristaltic systems, the increased efficiency of venturi systems gives them the advantage when it comes to overall phacoemulsification performance.

Surgical technique

My surgical technique has evolved as I have become more comfortable and more aware of the benefits of a venturi system. I began by using the venturi system to remove the ophthalmic viscoelastic device (OVD) at the end of my cataract procedures. It was remarkable how quickly this happened compared to using our older machine. In addition, the efficiency of this type of pump has meant that I do not need to go behind the IOL to get the OVD. I mostly use Healon (sodium hyaluronate, AMO), and I used to have to tiddlywink the IOL to remove all the OVD. I have found that I seldom have to do this anymore. This saves me a little time, but more importantly it allows me to keep the irrigation and aspiration tip centered in the pupil, and I do not have to go in search of the OVD in the peripheral parts of the anterior chamber. This diminishes the risk of accidentally grabbing unwanted ocular tissue and has been especially helpful in floppy iris cases. It has also led to fewer postoperative IOP spikes.

Shortly after I began using the venturi system, I added its use in quadrant removal. Because of the high vacuum and flow settings, it is extremely easy to grab nuclear fragments and hold them in place. The nuclear fragments seem to come to the tip more quickly, are easier to manipulate, and hold better. For the same reason, I am able to keep my phacoemulsification tip in the middle of the eye with a minimal amount of handpiece movement. I feel that this places less strain on the zonules and reduces the likelihood of accidentally grasping the iris.

My next step was to use the venturi system for performing phaco chop. I do both horizontal and vertical chopping. The improved holding power with venturi has allowed me to modify my horizontal chopping technique so that I do not have to go out to the lens equator to perform this maneuver. Instead, I am able to remain in an area inside the capsulorrhexis and do my usual horizontal chopping maneuver with ease in most moderate to hard cataracts. Eliminating the somewhat blind maneuver of going out to the lens equator makes my technique safer.

The last area I transitioned to venturi was for cortical cleanup I&A. This was an area in which I always wanted to have things happen more slowly to ensure a safer procedure. However, as I have become more comfortable with the Signature venturi system and the flexibility in programming it, I now use venturi for most of my cortical cleanups.

This transition from peristaltic to venturi systems made sense to me then, and I think it is a good way for most surgeons to transition to this improved technology. Depending on cataract surgical technique, some surgeons may want to use peristaltic for making grooves or for cortical cleanup. These can be pre-programmed prior to surgery with a combination of peristaltic and venturi settings. The great advantage of the Signature system is the ability to transition from peristaltic to venturi on the fly, depending on the surgical situation.

Better safety, efficiency

After reviewing several hundred cases, I have noticed that I am using less phacoemulsification energy, which leads to better protection of the corneal endothelium and the phacoemulsification incision. Whether performing intraocular surgery or treating medical conditions, having more options is always advantageous. The ability to use either venturi or peristaltic pumps, or a combination of both, has increased my surgical efficiency and safety. I am able to keep my surgical instrumentation centered in the eye with a minimal amount of movement, decreasing my likelihood of damaging other ocular structures.

With the improved fluidics, the prior risk of post-occlusion surge is no higher with venturi than it is with peristaltic systems. As no two cataract surgeries are identical, you should not limit your options. More choices and extra flexibility are always preferable during surgery.

• Pablo Arregui, MD, can be reached at Chico Eye Center, 605 W. East Avenue, Chico, CA 95926; 530-895-1727; email: parregui@chicoeye.com.
• Disclosure: Dr. Arregui has no relevant financial disclosures.