Early Clinical Experience With the CONSTELLATION® Vision System
Safety is always a top priority, but increased efficiency is a critical benefit for the ASC.
PRAVIN U. DUGEL, MD
The ultimate goal of a vitrectomy system is to allow for the safest and most efficient surgery possible. I equate safety with the ability to dissect vitreous with minimal retinal traction, avoiding tears and retinal incarceration. Efficiency incorporates the utmost safety with maximum time and cost savings.
Safety and efficiency — and they must be in that order — are not mutually exclusive. In fact, they are complementary goals. In my opinion, the new CONSTELLATION® Vision System (Alcon Laboratories, Inc., Fort Worth, TX) is a giant step closer to achieving this ultimate goal. I base this opinion on my experiences to date, which are summarized in this article.
For more than 2 decades, Steve Charles, MD, has taught us that a faster cut rate is the single most important factor for surgical safety. A simple mathematical formula describes this relationship:
length of collagen pull = flow rate/lumen diameter/cut rate
Collagen pull is a measure of vitreous traction and, thus, surgical safety. As cut rate is increased, the length of collagen pull decreases, resulting in a safer vitrectomy.
The keystone of the CONSTELLATION® system is a re-engineered, redesigned, revolutionary cutting probe, which I believe is the single-most important safety advancement in the system. Previous generations of ACCURUS® probes relied on a pneumatic pressure valve to close the cutter and a mechanical spring to open it. The spring has been one of the limiting factors in higher performance probe technology. The INNOVIT® probe, on the other hand, used a novel dual pneumatic actuation line, whereby a pneumatic pressure valve opened and closed the cutter. Unlike the more familiar axial guillotine cutting action in the ACCURUS® probe, however, the INNOVIT® probe had a radial reciprocating cutting action. The new ULTRAVIT® probe has combined the best of both, with a dual pneumatic drive axial cutter. Moreover, its maximum cut rate is twice that of the ACCURUS® probe: 5000 cuts per minute.
The dual pneumatic valve-driven ULTRAVIT® probe incorporates duty cycle control, an elegant mechanism that increases or decreases flow without changing the cut rate or vacuum parameters. This feature will be most useful in difficult cases where thick, fibrous tissue is encountered.
The definition of duty cycle is the ratio of time the port is open in a cut cycle to the overall duration of the cut cycle. It is expressed as a percentage. The CONSTELLATION® system has three settings: CORE (port biased open), SHAVE (port biased closed) and 50/50. The open biased setting renders the port mostly open in the cutting cycle, maximizing flow for the given cut rate and vacuum. This setting may be appropriate for a core vitrectomy. The closed biased setting renders the port mostly closed in the cutting cycle, minimizing flow for the given cut rate and vacuum. This setting may be appropriate for close shaving of the vitreous base or delicate maneuvers near the retina, particularly if the retina is detached and mobile.
Since the earliest days of vitrectomy, surgeons had only 2 parameters to control safety: cut rate and vacuum. Now, we have a third — duty cycle — which creates a triad of surgical safety parameters.
The ULTRAVIT® probe also features port optimization for all 3 gauges. Advances in manufacturing technology have enabled placement of the port 50% closer to the probe's distal end. The probe then can be maneuvered to place the port very close to the retina to dissect fibrous tissue. Previously, I would have used horizontal scissors for such dissection; now I can use the ULTRAVIT® probe alone without instrument exchanges. Port optimization provides safety and efficiency, and, for the first time, the vitrectomy probe is a truly multifunctional tool.
The ULTRAVIT® cutter and graphical user interface of the CONSTELLATION® Vision System.
The mechanical distillation of achieving the primary goal of vitrectomy surgery — safety — is achieving what I have described as "effective flow." Effective flow is the least amount of flow necessary to do the job. The CONSTELLATION® system allows the surgeon to control a triad of parameters independently for a particular surgical maneuver. The ultimate safety goal is to use the fastest cut rate, the lowest vacuum, and a closed-biased duty cycle to achieve effective flow.
|Pravin U. Dugel, MD, is managing partner of Retinal Consultants of Arizona in Phoenix and founding partner of Spectra Eye Institute in Sun City, AZ. He reports moderate financial interest in Alcon.|
In addition to safety considerations, the designers of the CONSTELLATION® Vision System addressed the need for efficiency in the modern surgical setting with the introduction of V-LOCITY® Efficiency Components. The value of the V-LOCITY® Efficiency Components is apparent throughout the surgical process.
The presurgical V-LOCITY® efficiency components include: bar code reader, ENGAUGE® radio frequency identification (RFID), video directions, articulating tray arm, integrated intraocular pressure control, and push-prime control. All of the V-LOCITY® Efficiency Components can be performed by the scrub tech alone before the patient enters the OR.
When the Alcon pak or device is scanned using the bar code scanner, the console recognizes the gauge that is being scanned, displays the proper gauge setup onscreen, and populates the consumables list window.
The ENGAUGE® RFID system allows the scrub tech to set up all of the tubing, which are protected with a sterile cover to avoid contamination. The ENGAUGE® RFID not only recognizes the gauge, but also gives feedback as to whether the connector has been placed properly (green light) or improperly (amber light). If additional tools, such as forceps, are to be used, the forceps button can be pressed on the console and the proper receptacle illumination ring will light (blue light). These features help minimize the potential for errors while allowing the scrub tech to set up the case without the help of the circulator nurse. Moreover, the ENGAUGE® RFID and bar code scanner system recognizes and repopulates the consumables being used in each case. This is a modification of the just-in-time inventory system that has been used very successfully in the retail industry.
The video direction system consists of 2 modes: video help and wizard help. Video help launches videos that educate the user on a selected topic. Wizard help plays the same video and provides text directions, stopping periodically to allow the user to perform the task.
The articulating tray arm locks, unlocks, and swivels over the patient. My scrub tech finds this very useful when configuring the case setup before the patient is brought to the OR.
The integrated IOP control uses pressurized infusion chambers without the need to calibrate the fluid level or spike the bottle with a separate disposable VGFI® Pak.
The push-prime feature is a major advance. Pressure from the aspiration chambers primes the lines with a simple push of a button. A status bar on the console uses colors to indicate the progress and completion of each segment of the priming process. The sequence automatically transitions to a surgical mode when it is completed.
Surgical V-LOCITY® Efficiency Components include: auto infusion valve, auto gas fill, embedded PUREPOINT® laser, proportional diathermy, proportional and micro reflux, and servo-controlled integrated pressurized infusion.
Using the auto infusion valve, the surgeon can toggle the foot pedal to switch between air and fluid without assistance from the scrub tech or circulator nurse. This eliminates any confusion in turning the stopcock. Using the auto gas fill feature, the scrub tech can fill a syringe with undiluted C3F8 or SF6 gas from a sterile field without assistance from the circulator nurse. In addition, this feature eliminates the possibility of gas loss through the atmosphere and minimizes the potential for errors.
|Case 1: Simple Case to Initiate System|
|My first case using the CONSTELLATION® Vision System was a relatively simple one. The patient had retained lens material with a well-positioned, sulcusfixated IOL and a watertight sutured cataract incision site.|
I used 3D vitrectomy with the following settings for the core vitrectomy:
Cut rate………4000 cpm
Duty cycle………Open biased
I then carefully dissected the vitreous adhering to the lens material, which rested on the retina, with the following settings:
Cut rate………5000 cpm
Duty cycle………Closed biased
After removing all the adherent vitreous, I was left with approximately 50% cortical material and 50% moderately sclerotic nucleus. Typically, at this point, I would have removed my 23-gauge ACCURUS® cutter, made a conjunctival flap, enlarged the sclerotomy site, and used a fragmentation handpiece to remove the retained lens material. Instead, I decreased the cut rate to 3000 cpm, kept my vacuum at 400 and switched to an open biased duty cycle. I felt very comfortable decreasing the cut rate, as all the vitreous had been dissected, and this "low" cut rate was still higher than the ACCURUS® 2500 cpm cutter that I normally use. I removed the cortical and nucleus material easily.
This was the first time I was able to confirm what I had seen in the laboratory a year earlier: Duty cycle can change (increase or decrease) flow in concert with cut rate and vacuum. Instead of having to make a conjunctival flap, enlarge the sclerotomy, use the 20-gauge fragmentation unit, suture the sclerotomy and suture the conjunctival flap, I was able to vary the triad of surgical parameters and use the ULTRAVIT® cutter as a multifunctional instrument.
|Case 2: Complex Case Tests New Features|
|A young, poorly compliant diabetic patient had a vitreous hemorrhage and a traction rhegmatogenous retinal detachment. Large tears were present in the ischemic retina, complicated by traction from fibrous tissue adhering to the detached retina. The tears were in the mid periphery, and the temporal half of the retina was detached, including the macula. Using the CONSTELLATION® system, I performed a 3D vitrectomy, using the following parameters:|
Cut rate………4000 cpm
Duty cycle………Open biased
After the initial core vitrectomy, I approached the detached mobile retina with the highest cut rate, 5000 cpm. I was pleased that I could approach the retina with a minimal amount of movement. I was able to remove the vitreous entirely, without any retinal incarceration. The fibrous tissue stalk extended posteriorly to the attached retina, however, and was very adherent and vascular.
I decreased the cut rate to 3000 cpm and changed the duty cycle to open biased. This allowed me to increase flow while maintaining a fairly high cut rate. With the optimized port placement, I was able to direct the flow specifically to the fibrous tissue. At the same time, I used the IOP control and reset the IOP to 60 mmHg to reduce intraocular hemorrhage. I was able to remove this adherent fibrovascular tissue without using horizontal scissors.
I encountered a modest amount of hemorrhage, which I managed easily with the proportionally controlled diathermy. Thereafter, I performed an air-fluid exchange using the auto-infusion valve. I performed laser photocoagulation under the air using the embedded PUREPOINT® 532 nm laser. After performing endolaser photocoagulation with an articulated endolaser photocoagulation probe, I performed indirect laser photocoagulation with the PUREPOINT® laser. The endolaser and the indirect laser photocoagulation settings can be easily switched with a single button without disconnecting or reconnecting cables.
With the CONSTELLATION® system, I can perform vitreoretinal surgery in the safest manner to date. During this difficult case, I was able to use its many features, including the multifunctional ULTRAVIT® probe, effectively. This case demonstrates the level of safety and efficiency already available in the CONSTELLATION® Vision System. I look forward to future enhancements that will make this system even more valuable.
The embedded PUREPOINT® laser can be activated and controlled from the console or from the laser multifunctional foot pedal. The scrub tech can set up the laser for the surgeon, and the surgeon can change the laser parameters with the foot pedal. The circulator nurse is not needed. The surgeon controls proportional diathermy with the foot pedal without having to ask the scrub tech to change the console parameters.
The frequency of the proportional diathermy is higher than in earlier vitrectomy systems, which may allow treatment with the CONSTELLATION® system to be confined to the necessary area, with less depth of penetration.
The CONSTELLATION® system has a micro-reflux feature, which provides a short duration of pressure to the suction port. A proportional reflux feature allows for blood to be washed off the retinal surface. Proportional pressure from 0 to 120 mmHg can be applied.
The integrated pressurized infusion will warn the scrub tech and the surgeon when the bottle is low or empty. The bottle can be changed without having to worry about air bubbles in the infusion line or prime the system again.
The CONSTELLATION® Vision System's postsurgical V-LOCITY® Efficiency Components are, I believe, most valuable and perhaps revolutionary. These include the end case screen, end case reports, and end case forms. The end case screen gives detailed listings of anterior and posterior segment exam metrics, such as total on time, total power, and total energy for all surgical components, such as the vitreous cutter, fragmentation handpiece, extrusion, scissors, and forceps. By transmitting this information to a wireless printer, a bill of materials, dictation report, and inventory profile can all be generated easily.
Two cases of tractional detachment with vitreous hemorrhage that underwent vitrectomy using the CONSTELLATION® Vision System. Both were quiet and comfortable at two weeks postop.
ADVANTAGES INSIDE AND OUTSIDE THE OR
As an owner and user of an ambulatory surgical center (ASC) for the last 15 years, I have been frustrated that newer-generation vitrectomy machines seem to concentrate on intraocular features without regard to the efficiency requirements of our business. For instance, according to my labor cost-flow calculations, we spend approximately $60,000 to $100,000 a year on inventory management and billing. I am pleased that the manufacturer of the CONSTELLATION® Vision System has paid attention to our efficiency requirements both inside and outside the OR. This is a necessary and revolutionary undertaking. In my opinion, the CONSTELLATION® Vision System with V-LOCITY® Efficiency Components will not only be cost efficient, it will also reduce errors and improve safety, creating a win-win situation. RP