Safer, Faster, Better: How Advanced Fluidics on DORC EVA NEXUS Leads to Better Surgeries

Before the introduction of the DORC EVA NEXUS surgical platform’s advanced fluidics, many retina surgeons operated at high pressure to mitigate intraoperative IOP fluctuations. Sure, the introduction of valved trocars in the past two decades proved effective at limiting egress of fluid during surgery, but pressure fluctuations during surgery persisted, and little innovation was seen vis-à-vis fluidics in retina surgery.

Each surgical platform varies in its sensitivity to changes in pressure, requiring surgeons to become fluent in the fluidics of various machines. Surgeons on such platforms must split their attention between surgical maneuvering and maintaining consistent pressure during surgery, requiring them to focus less on their technical expertise and more on mechanical logistics.

In my view, DORC EVA NEXUS’s ability to maintain safe intraoperative pressure in the eye via an advanced fluidics design, called SMART IOP, represents the platform’s most significant innovation in the fluidics space in recent memory. Three engineering adjustments underpin SMART IOP:

• Redesigned infusion cannulas. Retina surgeons with a passion for physics know about Poiseuille's Law, which states (in part) that flow rate equals the radius of the inflow tube raised to the fourth power; surgeons less interested in these concepts nevertheless grasp that the wider the inflow tube, the less force required for infusion. DORC EVA NEXUS uses high flow infusion setups, which overlay (ie, are flush with) the infusion line atop, rather than inside, the infusion cannula, thereby maximizing the radius on the infusion line and reducing the necessary flow force. This in turn, minimizes velocity and turbulence inside the eye, giving the surgeon more control.
• VTi pumps. The Valve Timing Intelligence (VTi) pump reacts to changes in pressure in the eye in real time. Rather than relying on passive release of injected fluid following an increase in pressure (which could result in unwanted pressure fluctuations or inconsistent flow), SMART IOP automatically detects when irrigation or infusion is needed, keeping IOP at a predictable and consistent level during surgery. This use of “target pressure” as programmed in Smart IOP counteracts Bernoiulle’s Principle, which states that in a closed system, flow increases create pressure decreases. Smart IOP manages IOP in one of two ways: by increasing infusion/irrigation or, conversely, by relying on the pump to work in retrograde to release volume and pressure while maintaining targeted IOP.
• NEXUS system software. The centralized software hub housed within DORC EVA NEXUS connects hardware innovations with the surgeon’s hands. Real-time statistics on flow rates and irrigation/infusion status are shown on the NEXUS’s digital display, keeping surgeons updated on the metrics specific to the case at hand.
  

These design enhancements were designed to allow surgeons to execute safer surgeries, to perform more precise procedures, and to build the confidence of surgical trainees.

• Safety. With the risk of pressure fluctuations and eye collapse significantly reduced, I find that when I’m operating with DORC EVA NEXUS I start surgery at a safe baseline. By mitigating the risk of collapse, surgeons reduce the risk of iatrogenic damage caused by instruments touching tissue it otherwise shouldn’t (and wouldn’t) do so under normal structural conditions. Further, I don’t need to divide my attention between instrument manipulation and pressure monitoring. Instead, I can trust SMART IOP to maintain pressure while I efficiently and safety perform a given procedure.
  
  DORC EVA NEXUS requires intraoperative IOP levels that reflect daily IOP levels—that is, surgery occurs in the context of 16 or 17 mm Hg rather than 35 mm Hg used during many surgeries. This may be particularly important for patients with concomitant conditions that may be exacerbated by high intraoperative IOP requirements (eg, glaucoma). Smart IOP also takes out guesswork in anticipated hypotony and/or nerve pulse due to the fact that target pressure runs “parallel” to expected vacuum or flow levels. It’s also worth noting that operating at close-to-daily IOP levels can minimize capillary damage over extended cases
• Precision. Switching between vacuum mode (used for efficient vitreous removal and drawing nucleus fragments toward the tip of a cutter) and flow mode (used for navigating near mobile retina and precise removal of nuclear fragments) occurs easily on DORC EVA NEXUS and requires no change in instrumentation. On flow mode, surgeons can select customized cut rates for when they need conventional shaves or super-shaves. (Personally, I have selected the 10-cc setting and the 2-cc setting for shave and super-shave modes, respectively.) With more precise surgery comes better outcomes, safer maneuvering, and more efficient OR times. The pump also lends itself to creating or minimizing tractional forces depending on the case needs. This is applied by understanding the cone of effect that is generated by the values programmed in the vacuum or flow setting.
• Training fellows. Attendings are tasked with both keeping patients safe during surgery and encouraging novice surgeons to operate with confidence. By creating conditions that mitigate the risk of structural collapse or unanticipated changes in IOP thanks to SMART IOP, attendings teaching students on DORC EVA NEXUS permit trainees to focus more acutely on refining instrument manipulation and intraocular surgical movements—all while keeping patients safe from errant surgical movements secondary to unpredictable fluidics or changing anatomy. Fellows who operate on multiple platforms during their training will compare the fluidics of conventional platforms and those of DORC EVA NEXUS, broadening their experience and preparing them for real-world surgical practice.
  

The physics of retina surgery remain top of mind in the OR. Smaller spheres of influence and reduced chatter (ie, the reverberation of tissue near the mouth of a cutter) mean more precise and efficient surgeries, as well as a theoretical reduction in iatrogenic damage.

DORC’s most recent cutter, TDC VELOCE, reaches cut speeds of up to 20,000 cuts per minute (cpm). A noticeable reduction in tractional forces due to the mouth on DORC TDC VELOCE never fully closing means that my approach to the retina is more elegant and less disruptive. Further, improved aspiration flow compared with previous iterations of DORC TDC cutters mean faster vitrectomy times; specifically, aspiration flow rates are 14% and 26% higher, respectively, for the 25-gauge and 27-gauge instruments.

Importantly, DORC TDC VELOCE enables SMART IOP on DORC EVA NEXUS. With SMART IOP technology, surgeons access Valve Timing Intelligence pumps, which monitor IOP changes during surgery and adjust irrigation/infusion as needed. Surgeons thus spend less time worrying about IOP fluctuations and more time focused on the task at hand.

There are other important benefits to this next-generation vitrector:

• Increased staff stiffness empowers me to reach the periphery with confidence and to shave the vitreous base easily.
• An ergonomic dimple on the instrument’s shaft quickly and accurately orients the direction of the cutter when it’s in my hands. (Think of it like the bump on the f and j keys on a keyboard, which let you know where your fingers are without looking.)
• Reducing speed still leads to reliable cutting with DORC TDC VELOCE. When removing a hard material (e.g., a lens fragment), dropping to speeds as low as 1,000 cpm don’t sacrifice precision.

Retina surgeons seeking to improve surgical safety and precision should weigh whether including DORC EVA NEXUS in their OR could elevate their surgical offerings. Those who already have the platform in their OR should consider which types of surgical cases are best suited to the advantages offered by the engineering changes underpinning SMART IOP.

Check out this page dedicated to surgeon education if you want to learn more about why some surgeons think DORC EVA NEXUS represents world-class surgical innovation.

^{The statements of the author reflect only his personal opinions and do not necessarily reflect the opinions of any institution with whom he is affiliated.
The author has a contractual or other financial relationship with Carl Zeiss Meditec, Inc. and has received financial support.}