Surgical Experiences with the CONSTELLATION® Vision System
Surgical observations of the new vitrectomy system.
FIRAS M. RAHHAL, MD
The ACCURUS® vitrectomy system (Alcon, Fort Worth, TX) has been in use for more than 10 years and has been a highly successful and versatile unit. It has been an important component in a decade that has seen sweeping advances and innovations in vitreoretinal surgery. Surgical cases that were considered extremely difficult only 5 or 10 years ago have become technically less challenging due to profound improvements in surgical instrumentation and other new technologies. Over the last decade, we have seen the development of "high-speed" vitreous cutters, 25- and 23-gauge surgery, and extremely powerful endo-illumination, all of which have greatly improved surgical outcomes and surgeon gratification. Combined with other advances, including wide-field viewing systems, PERFLUORON® perfluorocarbon liquid and the introduction of anti-VEGF and triamcinolone drug therapy, these changes continue to expand our ability to consistently and efficiently improve patients' health and quality of life. The recent introduction of the CONSTELLATION® Vision System (Alcon, Fort Worth, Texas) represents another important innovative technological advance in the field of vitreoretinal surgery. This article will review several important advancements on the CONSTELLATION® Vision System and my observations of the benefits associated with these technical improvements.
|Firas M. Rahhal, MD, is a partner with Retina-Vitreous Associates Medical Group and Assistant Clinical Professor of Ophthalmology at the UCLA School of Medicine, both in Los Angeles, CA. Dr. Rahhal is a consultant for Alcon Laboratories, Inc., Fort Worth, Texas.|
IS FASTER BETTER?
The CONSTELLATION® system utilizes the new ULTRAVIT® probe, which can achieve cut rates up to 5000 cuts per minute (cpm). This is substantially faster than the current ACCURUS® system and most other commercially available vitrectomy machines. Over the last decade, cutting speeds have progressively increased from 600 cpm to 2500 cpm. As these increases were introduced, many surgeons, the author included, questioned the need for these changes, and in fact wondered whether faster is always better. Some physicians questioned whether the continued striving for faster cutters was simply a matter of commercial gimmick rather than an advance of true clinical importance. Now, however, the vast majority of vitreoretinal surgeons have found that high-speed cutting indeed offers many advantages, particularly for complicated vitrectomy. With each increase in cut rate, surgeons have improved their ability to dissect membranes and preretinal tissues, as well as to shave vitreous over detached mobile retina, especially in the important area of the vitreous base.
We are enjoying these innovations in cutter speed even though in the early stages of their development we did not recognize the practical surgical applications for which they would be most helpful. There is every reason to believe that utilizing higher cut speeds up to 5000 cpm will further improve my ability to efficiently perform preretinal tissue dissection and removal of vitreous overlying mobile retina.
In addition to higher cutting speed, the ULTRAVIT® probe possesses other attributes that add to its clinical utility. First, the cutter port location has been improved (port optimization) over previous handpieces by bringing the port closer to the tip. The probe is available in 20-, 23- and 25-gauge. The probe has configuration options for the handle: a longer handle, similar to the INNOVIT® (Alcon) hand piece; and a shorter one that is very similar to the current ACCURUS® handpiece. The configurations are inter-changeable "on the fly," as the same probe easily converts from one to the other. Choice of hand piece is essentially a matter of surgeon preference, as neither should offer any practical advantage or disadvantage compared to the other.
The higher cutting speeds of the CONSTELLATION® system offer advantages for complicated vitrectomy cases.
A NEW CONCEPT: DUTY CYCLE
Looking beyond the probe to broader functionality, the CONSTELLATION® Vision System introduces an important new concept into clinical vitrectomy, namely, duty cycle. The concept itself is not new, but the incorporation of choices in duty cycle into a commercially available vitrectomy machine, and the utilization of alternative duty cycles for improvements in vitrectomy maneuvers, is indeed novel. Duty cycle refers to the ratio of time that the cutter port is open relative to the total time of one cut cycle. In the past, this was a fixed or non-adjustable ratio with any given vitrectomy system; in general only vacuum and cutter speed could be altered to suit various intraocular maneuvers during vitrectomy. The CONSTELLATION® system offers the surgeon 3 choices for duty cycle:
• CORE — representing when the port is open longer than it is closed
• 50/50 — representing when the port is open and closed for equal amounts of time
• SHAVE — representing when the port is closed longer than it is open.
The naming makes sense because duty cycle, as well as vacuum and cutter speed, relates directly to flow velocity into and up the cutter hand piece.
At any arbitrary fixed cutter speed and vacuum, the surgeon can now operate at any of 3 different duty cycles, thus improving the ability to perform high-flow and low-flow activities. At a given cutter speed and vacuum, I could choose the lower-flow "shave" duty cycle to possibly exert less traction on the retina while removing preretinal tissue or vitreous. This feature combined with much higher cut rates up to 5000 cpm offers the surgeon more variables to control flow than previously.
This is extremely important to me while working on the surface of the retina. One exciting application in this regard is complex diabetic traction retinal detachment with extensive preretinal membrane. During several such procedures using the CONSTELLATION® system, the author found that it was possible to use the 23-gauge cutter alone for dissection and removal of membranes overlying attached and detached retina, with intermittent forceps work to create planes of separation. Using the high cut rates and shave duty cycle, little or no retinal movement was observed, which was very reassuring when the planes of separation were narrow or nonexistent. When greater suction was necessary, such as in the presence of thick membranes or clotted vitreous hemorrhage, we easily switched to lower cut rates and a higher flow duty cycle (core or 50/50), which helped speed the rate of the procedure. These higher suction settings were employed in several cases of macular pucker and macular hole. The vitreous was removed rapidly and, in the case of macular hole, separation of the posterior hyaloid was performed quite easily using suction on the cutter alone.
The CONSTELLATION® Vision System has a number of other unique features that should provide clinically relevant advantages over my current system. Improvements in fluidics, most notably, a sensor that measures infusion fluid flow through the cassette and upon delivery to the patient, have produced improvements in direct control of intraocular pressure. Automated safe-guards built into the system could possibly reduce the occurrence of soft eye during surgery, essentially by preventing excessive flow rates during cutting and extrusion. Conversely, excessive infusion flow can be limited automatically by utilizing the infusion flow limit feature, thus decreasing the excessive flow of fluid through open 23-gauge cannula.
Furthermore, and perhaps most important surgically, the flow rate through the cutter port can be "capped" at a maximum level by the console by using the aspiration flow limit feature, assisting the surgeon when reacting to a sudden fluctuation or surge in flow. Ordinarily, the surgeon needs to carefully and quickly react to sudden changes in flow into the cutter port by changing the treadle position with a rapid change in foot position. This is important when the surgeon is aspirating thick fluid or tissue into the port and the material suddenly clears the port (for example, retina coming up into cutter), massively increasing flow at the fixed vacuum set by the foot-treadle position. The CONSTELLATION® system automatically reduces the vacuum instantly to lower the flow rate to a level below the surgeons set limit value on the console. The operator regains control of vacuum by simply reducing the vacuum using the footswitch, an action the surgeon presumably is performing already upon seeing the sudden change in flow.
Finally, modifications to fluidics have increased the maximum vacuum from 600mmHg to 650mmHg.
Other modifications to the CONSTELLATION® system are less dramatic but are of significant practical importance for easing the burden on operating room staff. The CONSTELLATION® has a 2-chamber infusion system, allowing the infusion bottle to be changed without interruption of the surgery. In addition, the connectors are color-coded and "keyed" so that they will fit and lock only into the correct location on the console. The connectors are constructed in a way to allow the scrub tech to connect everything directly, without assistance from a circulator, while still maintaining sterility.
These modifications are designed to improve efficiency and enhance cost containment for all surgical facilities, and they may be particularly beneficial for surgeons who visit operating rooms where the staff is not very familiar with vitrectomy instruments. In a User Acceptance Evaluation completed in July at this facility, the author's highly experienced and knowledgeable staff reported complete satisfaction with the use of the color-coded tubing system, and experienced no problems in running the entire system during all cases sampled. The OR team was confident that this very low learning curve should allow less experienced staff to easily learn to operate the CONSTELLATION® Vision System.
Changes to the foot pedal offer additional practical advantages. The foot pedal can be used to control internal cautery power as well as air-fluid exchange; that is, the surgeon can "switch to air" without assistance from the scrub tech. The author used both of these features comfortably during several cases. Especially for cases with inexperienced staff, this latter modification can diminish the surgeon's frustration and reduce intraoperative delays.
To date, the author has performed several dozen cases using the CONSTELLATION® Vision System and has found that the technical improvements did manifest themselves surgically. Using the 23-gauge cutter with various high cut rates, and at different duty cycles, complex cases such as proliferative diabetic retinopathy with traction detachment or rhegmatogenous retinal detachment with proliferative vitreoretinopathy were managed efficiently and successfully, with minimal added time or use of additional instrumentation. "One-handed" surgery continues to advance due to enhancements in vitrectomy cutters and, through the use of high cutter speed and the shave duty cycle, the CONSTELLATION® system further improves these techniques. The combination of settings, at various levels, also was very impressive in peripheral vitreous removal overlying detached mobile retina in cases of primary rhegmatogenous retinal detachment, where vitreous could be shaved close to the retinal surface with minimal retinal movement and traction. Although the author has not yet used the 25-gauge ULTRAVIT® probe, it is likely that, with the modifications found in the CONSTELLATION® system, vitreous removal and flow will be more efficient. This would address some of the concerns of many vitreoretinal surgeons when comparing 25-gauge to 23- or 20-gauge surgery.
In summary, the CONSTELLATION® system offers many new and innovative changes to current vitrectomy techniques, most notably, higher cut speed, the introduction of duty cycle control, and improved fluidics. It gives me the ability to improve my surgical performance and evolve my techniques related directly to these major changes. Furthermore, other practical modifications enhance ease of use for surgeons and operating room staff, not necessarily to improve surgical techniques but to improve efficiency and reduce frustration. Over time, it is likely that we will discover many new ways to take advantage of these improvements. Years from now, as in the recent past, we may find that we are performing cases in ways that make us wonder "how we ever did it before." RP