September 2009 Advertorial Return to Homepage

Integrated Infusion Pressure and IOP Control

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When performing vitrectomy, one of the challenges that surgeons have faced is controlling intraocular pressure (IOP) in relation to the pressure of the fluid that is infused through the cannula during surgery. Improvements in the CONSTELLATION Vision System (Alcon Laboratories, Inc., Fort Worth, TX) include a new integrated infusion pressure and IOP control system, which represents a significant advancement in safety for vitrectomy. This article will describe the features on the CONSTELLATION system that work to control fluidics during surgery.

IOP CONTROL
IOP control is a significant advancement in vitrectomy surgery. IOP control can assist with sudden bleeding in patients with diabetes due to pressure changes, and makes it easier for the surgeon to control bleeding during surgery. Additionally, this feature has allowed me to set a lower IOP during surgery because the lag time in adjustment is eliminated.

The ACCURUS Surgical System (Alcon Laboratories, Inc.) utilizes gravity as fluidics control with an automated IV pole or vented gas forced infusion (VGFI) to control IOP. In VGFI, gas is driven by pressurizing the bottle via low-pressure air pump. The stopcock is controlled manually, and the IOP must be offset artificially at 35 mm Hg to 45 mm Hg to ensure globe stability during aspiration. Pressure in static condition is consequently higher than needed. Conversely, the pressure might be set at 32 mm Hg for a static eye, but if there is a leak or aspiration along the tubing, the pressure drops unexpectedly.

The IOP control on the CONSTELLATION system automatically adjusts for the infusion tubing and pressure drop that occurs when fluid is flowing through the cannula by measuring and checking the infusion cannula and tubing resistance during priming. With the CONSTELLATION, the IOP is maintained to within ±2 mm Hg of the surgeon’s setpoint. Figure 1 shows the IOP compensation calculation that is used for the CONSTELLATION. If I want to maintain 32 mm Hg, I need more infusion coming out of the system. The compensation calculation that takes place at 20 cc/min with a 23-gauge cannula and a pressure tubing and cannula drop of 22 mm Hg uses the pressure set point plus the pressure drop to determine the infusion pressure.

AUTO INFUSION VALVE
Another useful feature that has been included on the CONSTELLATION fluidics system is the auto-infusion valve, which allows the surgeon to control an automated air:fluid exchange. The stopcock does not need to be manually switched; the surgeon activates using the footpedal or pushes a button on the display to initiate air:fluid exchange, reducing errors or delays.

BOTTLE MONITORING
New efficiency features on the CONSTELLATION system include the ability to change the balanced salt solution bottle during surgery with no need to stop, plug, and clamp. Additionally, the CONSTELLATION calculates fluid use, estimates how much fluid is in the bottle, and issues a warning when the fluid is low.

SUMMARY
The CONSTELLATION fluidics represent a significant advancement over previous technology. The more accurate and responsive IOP management enhances surgeon control and the automated features on the system save time and reduce errors that are inherent in manual procedures.

David S. Dyer, MD, is in private practice in Shawnee Mission, KS. Dr. Dyer states that he is a member of the Retina Advisory Council for Alcon Laboratories, Inc. He can be reached by e-mail at davidsdyer@aol.com.

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