Choosing a Gauge for Vitrectomy: Why Go Smaller?
ADVANCEMENTS IN SURGICAL TECHNOLOGY AND EFFICIENCY
Choosing a Gauge for Vitrectomy: Why Go Smaller?
BY PRAVIN U. DUGEL, MD
Why do I prefer smaller gauge instrumentation for my vitrectomies? Most people would say the answer relates to wound construction, but I think we now understand how to create good wounds, regardless of gauge. The reason I prefer a smaller gauge is not related to what we do outside the eye. The reason is the advantage inside the eye.
I was a 23-gauge surgeon, and I thought there was no reason whatsoever to switch. Recently, however, I learned I can do things inside the eye with 25+ that I cannot do or cannot do easily with 23-gauge, and certainly not with 20-gauge.
TWO COMPONENTS FOR SUCCESS
Two components necessary for successful surgery are fluidic stability and tissue separation. Fluidic stability means what I remove from the eye must exactly match what enters the eye. When that match is equal, there is less tissue movement and more stability inside the eye. It is safer for me to remove material when the tissue is not moving or incarcerated. In other words, the less flow there is, the safer my surgery will be.
That statement may surprise you because, in the past, we always heard we should want more flow. That is exactly wrong. We want sufficient instantaneous flow, but the overall flow should be the least possible to do the job.
What do I mean by tissue separation? In everything we do with any gauge — whether we use viscoelastic or bimanual techniques, horizontal or vertical scissors or picks — we are trying to create tissue separation. If we can separate bad tissue from good tissue, then surgery becomes easy. When they are intertwined, surgery is difficult.
Although creating tissue separation and maintaining fluidic stability is possible with 20-gauge and 23-gauge, I have found doing so is more difficult with these larger systems than it is with 25+. The 25+ system allows me sufficient instantaneous flow, decreased overall flow and the ability to create tissue separation because of the smaller gauge, larger internal lumen, larger port opening and more distal location of the port toward the tip of the probe.
When discussing fluidic stability, the following formula comes into play: Length of pull (of collagen fibers) = flow rate/lumen area/cut rate.
Using this formula, if we increase the flow rate, we increase the length of pull of collagen fibers and the amount of vitreous traction, making the surgery less safe. On the other hand, the faster the cut rate, the less the length of pull of collagen fibers, the less the vitreous traction and the safer the surgery.
So, where does the 25+ system fit into this formula? There are several important differences between the new ULTRAVIT® 25+ cutter and the old 25 gauge (Figure 1). The 25+ port and internal lumen are larger, and the port is closer to the tip of the cutter. These features are beneficial for tissue separation.
Figure 1. Compared with the 25-gauge cutter, the internal lumen and the port of the 25+ cutter are larger, and the port is closer to the tip.
Another important point for comparison is instantaneous flow rate. With the old 25-gauge, I did not perform lensectomies because the surgery was inefficient, and lens material would get stuck. Recently, I performed a lensectomy with the 25+. Not only could I easily remove a large piece of lens material, but later in the surgery, I was able to remove calcified material entirely with the 25+.
So far, I have discussed outflow. What about inflow? Just as the cutter's lumen diameter is larger, so is the lumen diameter for the infusion cannula (Figure 2). This feature, coupled with IOP compensation, improves fluidic stability. (For an in-depth discussion of IOP compensation, see "True IOP Control and Infusion Cannula Fluidics With the CONSTELLATION® Vision System" of this supplement.)
Figure 2. Note the larger internal diameter of the 25+ cannula as compared with the 25-gauge cannula.
OTHER IMPORTANT FEATURES
Because the 25+ cutter port is optimized to be larger and closer to the tip, I can use the cutter as a multifunctional tool. In addition, thanks to this technology, viscodissection is once again an option for me. Recently, I discovered an exciting new advancement in the viscodissection technique using a parameter available only in the CONSTELLATION® Vision System: proportional reflux dissection.
I am most excited about proportional reflux, which is a derivative of pulse reflux in the ACCURUS® Surgical System. With proportional reflux, I can create tissue separation in a well-controlled manner using the foot pedal. With it, I can create a little bit of space, separating fibrous tissue from retina, so I can insert my small-gauge instrument and dissect. I think proportional reflux dissection is a valuable technique. It allows for tissue separation and dissection without the need for adjuvants or instrument exchanges. It is efficient and safe.
Another improvement with the 25+ cutter is that it is stiffer than the standard 25-gauge (Figure 3). That is critical for peripheral dissection. For a patient with thick adherent tissue, for example, I normally would do a horizontal scissors dissection, which is difficult in the far periphery of a detached retina. Instead, I can use proportional reflux to create a tissue separation and then use my small-gauge instrumentation to go behind the fibrous tissue and dissect. The tissue does not move, the retina does not move, and the retina does not incarcerate because I have superior fluidic stability.
Figure 3. The new ULTRAVIT® 25+ cutter is the stiffest on the market.
In a recent retinal detachment case, I used proportional reflux to create tissue separation so I could place my small-gauge instrument to dissect fibrous tissue. I used the same instrument to remove blood from above the retina. After I did the air-fluid exchange through one of the existing holes and asked for the laser, I realized I had done the entire case without taking my hand out of the eye. This experience underscored the efficiencies I can achieve with this multifunctional tool and the proportional reflux dissection technique.
Fluidic stability and tissue separation can be achieved with any gauge. For me, thanks to the latest advancements in vitrectomy technology, the easiest and most efficient way to achieve fluidic stability and tissue separation is by using the CONSTELLATION® 25+ system. I believe the 25+ system makes me a better surgeon.
Pravin U. Dugel, MD, is managing partner for Retinal Consultants of Arizona in Phoenix, Ariz., and founding partner of Spectra Eye Institute in Sun City, Ariz. He is an advisory board member and/or consultant for: Alcon, Arctic Dx, Genentech, MacuSight and NeoVista.
Retinal Physician, Issue: October 2010