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Accurus forced infusion good for MICS, surgeon says
The vented gas infusion tubing of the Accurus surgical system helps stabilize the anterior chamber during microincision cataract surgery.
Maintaining anterior chamber stability is one of the key challenges of microincision cataract surgery. A feature of Alcon’s Accurus Surgical System can help surgeons maintain anterior chamber control while performing this technique.
MICS
Microincision cataract surgery (MICS) is a minimally invasive technique that offers astigmatic neutrality, better wound stability and faster rehabilitation than standard techniques. The concept was initially developed for use with laser cataract photolysis, but advances in ultrasound energy delivery have made it possible to use the technique with phaco as well.
A variety of new ultrasound technologies, such as the WhiteStar from AMO, the Sonic Wave from STAAR Surgical and the NeoSonix feature on Alcon phaco units, have demonstrated compatibility with the phakonit technique described by Amar Agarwal, FRCS.
Jorge Alió, MD, recently called the Accurus Surgical System his tool of choice because of the small diameter of the sleeveless tip, the polymer coating surrounding the tip that prevents friction, the ABS system that improves chamber stability and the stability of the settings in comparison to other phaco machines (30% phaco power, 90 mm Hg pressure inside the eye and 250 mm Hg vacuum). (See the March 1 Ocular Surgery News article: "Microincision cataract surgery ready to go").
We have also found that the Accurus is the best system to perform ultrasound MICS, but we would like to add to Prof. Alió’s concepts the use of the anterior vented gas forced infusion (AVGFI) tubing of this surgical system to increase the pressure of fluid inside the eye, thus increasing the stability of the anterior chamber during phaco and bimanual irrigation and aspiration.
In Dr. Agarwal’s description of phakonit, destabilization of the anterior chamber was the main problem in the early days of MICS. His solution was to push more fluid into the eye, so he created an “anti-chamber collapse system” keeping IOP high intraoperatively, making the surgery safe even with the use of high vacuum levels. He reported that simple separation of infusion from the phaco probe is not enough to perform the technique, hence the need for an air pump system to maintain a “safe” chamber.
We report the use of an air pump system (the AVGFI) that actively pushes fluid into the eye, that is already integrated in a phaco machine, and that can be actively and digitally controlled during surgery, giving the surgeon all the advantages of high IOP during MICS while avoiding the creation of a mechanical infusion system. Further, it is integrated with a surgical system that has been described as one of the best to perform MICS.
Setting surgical parameters
Before beginning surgery, the surgeon must adjust the parameters of the phaco machine.
Ultrasound power: Low ultrasound power is the goal for this procedure. The surgeon must learn that the maneuvers to disassemble the nucleus must be mostly mechanical rather than ultrasonic. The ultrasound power must be low, decreasing endothelial damage as in traditional phaco but increasing the safety of the wound, taking into account that in MICS the ultrasonic power emanates from a sleeveless tip. I recommend 30% to 40% of ultrasound power as an initial setting; it is strong enough to phacoemulsify almost every nucleus, avoiding thermal burns of the cornea.
Vacuum: To decrease the ultrasonic energy released inside the eye, mechanical maneuvers must be done instead of ultrasonic. Chop techniques are better performed with high vacuum settings. With the Accurus surgical system, the surgeon has direct and digitally controlled venturi vacuum; the surgeon has also the safety of the ABS system that helps to create an anterior chamber with stability, even in high vacuum conditions. I recommend an initial setting of 200 mm Hg of vacuum for phaco and 400 mm Hg for cortical aspiration. If the surgeon has high IOP during the surgery, high vacuum levels are safe.
Irrigation pressure: High irrigation pressure is a key factor in performing MICS safely. The advantages are as follows:
- It creates a high IOP during the procedure, allowing the surgeon to freely manipulate the instruments and tissues inside the eye; it makes room to perform maneuvers in a sufficiently strong eye.
- It places the endothelial cells far away from the phaco tip.
- It pushes the posterior capsule far away during the procedure. This is important during phaco because it creates a tense zonule containing a firm capsular bag and facilitates the surgeon’s chop maneuvers. But it is also important during nuclear and epinuclear extraction, because at this point the sharp side of the irrigating chopper looks directly into the posterior capsule without nuclear protection, and the high irrigation increases the distance between the two structures and thus decreases the risk of posterior capsular damage.
- It irrigates continuously from inside to outside of the phaco incision, decreasing the temperature of the phaco tip and in turn the possibility of corneal thermal wounds.
- It creates a wide-open capsular bag and a tense and very deep posterior capsule that increases the facility and safety of the cortical aspiration and polishing maneuvers during irrigation and aspiration (I&A).
- It helps to increase the pupil diameter.
I recommend starting the surgery with 100 cm H2O of positive pressure adjusted in the AVGFI system. In this system the surgeon is free to preset the maximum amount of irrigation desired, and go directly to this pressure at any time during the surgery by simply touching the right button of the foot pedal. This is helpful to avoid a chamber collapse. I recommend presetting the emergency maximum pressure at 130 to 140 cm H2O. During the procedure the surgeon or the assistant can increase or decrease the fluid pressure via the panel of the Accurus. During phaco, with 190 to 200 mm Hg vacuum, 100 cm H2O of fluid pressure is enough. During bimanual I&A, with 400 mm Hg of vacuum, I recommend 80 to 90 cm H2O of fluid pressure because the aspiration cannula is smaller in diameter than the phaco tip.
Phacoemulsification
Topical anesthesia is applied, the first 1-mm incision is performed with a keratome or a diamond blade, viscoelastic is inserted in the anterior chamber, a second 1-mm incision is performed with fixation of the globe with the viscoelastic cannula in the first incision and capsulorrhexis and hydrodelamination are performed.
The irrigating chopper is introduced inside the eye with the foot pedal in the irrigation position and with 100 cm H2O of positive pressure. The phaco tip is introduced in the second incision and the chop maneuver is performed.
At this step I recommend linear phaco. If the surgeon does not feel comfortable with the amplitude of the anterior chamber, more irrigation pressure can be achieved with the AVGFI. I do not recommend decreasing the vacuum; increasing the fluid is sufficient to maintain stability in the anterior chamber.
If a sudden surge occurs, the right button of the foot pedal will increase the IOP to maximum; this ensures that the surgeon can always achieve a wide anterior chamber any time during the surgery.
The high irrigation pressure creates turbulence, so when the nuclear fragments are free, they easily “fly” in the anterior chamber. My suggestion is to perform pulsed phaco. It increases the control of nuclear fragments in the chamber and decreases the amount of heat generated by the phaco tip and thus the possibility of corneal thermal burns. It is also important to maintain a good anterior chamber because the sharp side of the chopper looks directly at the posterior capsule and there is no protection of the nucleus inside the capsular bag.
Aspiration of the epinuclear material is easy with this technique. Sometimes, if I do not feel comfortable with the irrigating chopper inside the eye during this step, it can be removed and irrigation can be performed with a straight 21-gauge cannula, keeping the phaco tip in the another hand. Almost all the cortical material can be easily and safety removed with these two instruments. The AVGFI pressure is kept the same during this step.
Bimanual I&A
I perform bimanual I&A with two straight cannulas: 21-gauge for irrigation and 22-gauge for aspiration. If cortical material cleaning becomes difficult, I change to a side-perforated aspiration cannula, but the irrigation cannula is always straight.
I recommend decreasing the irrigation force a little (80 to 90 cm H2O) to avoid turbulence during I&A. The aspiration cannula is smaller in diameter than the phaco tip, so the chamber becomes much more stable even with high vacuum settings (400 mm Hg). The irrigation force can be increased any time during I&A if needed.
During this step, I always hold the irrigation cannula directly to the capsular bag, so the force is far away from the endothelial cells, the filtration of fluid by the incision is reduced and the capsular bag remains open, allowing aspiration of the cortical material.
Phacoaspiration
This technique is useful for soft nuclei (congenital cataract, young cataract patients, refractive lensectomy, etc.). If during hydrodelamination the surgeon observes that a dividing technique is not going to be needed, the use of the irrigating chopper is not practical and can result in posterior capsule damage. I feel this is the indication to insert the straight 21-gauge cannula instead of the irrigating chopper with 110 cm H2O of irrigation force in the AVGFI system. In these cases the ultrasonic power is used minimally or not at all, and the nucleus can be emulsified without ultrasound. Nevertheless, I recommend linear phaco in the machine settings if sometime during the procedure a small amount of ultrasound is needed.
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Results
Using this technique and the parameters described, we have operated on 235 eyes: 217 have uncorrected visual acuity of 20/40 or better. The change in astigmatism by topography was less than 1 D the day after surgery, and no thermal burns in the cornea were found in this series. The main complications in this series included minor corneal edema that appeared in 17 patients and resolved without complications, two vitreous losses and one zonular detachment. The average phaco time was 45.7 seconds, and phaco power was 17%; the average fluid by case is 129 cc, including I&A.
All the patients were operated on under topical anesthesia and only oral sedation; 123 were cataract patients and 39 were refractive lensectomies.
Discussion
Microincision cataract surgery is going to take its place in anterior segment surgery in the near future. Many concepts are waiting to be discovered in this field.
At this time concepts like low ultrasound, protection of sleeveless tips and stability of anterior chamber are well-established as parameters needed to achieve a safe procedure.
Much is being said about anterior chamber maintenance; even now, some authors discuss the possibility of a third incision, just to irrigate and maintain a good anterior chamber.
The Accurus vented gas forced infusion system was designed by Alcon engineers to provide control of irrigation and a rapid increase in IOP for both anterior segment and retinal surgeons.
We are describing the use of this infusion system — already incorporated in the phaco system — that allows the surgeon to create another kind of infusion system to maintain anterior chamber stability during MICS.
The Accurus Surgical System is gaining popularity because of the advantages for MICS, like the venturi system, the size and cover of the phaco tips and the ABS system as Prof. Alió has reported.
The AVGFI system, I think, is one of the main advantages of this machine that offers safety to the surgeon and full control in the anterior chamber.
My results are similar to what surgeons elsewhere are obtaining with MICS, but the control I feel during surgery and the options I have in the different steps of the procedure and in the different types of nucleus are greater than in traditional phaco.
I strongly recommend the use of this phaco machine with these settings to perform MICS. I think it will also be a good option for surgeons learning this procedure and others.
New phaco machines are coming, such as Alcon’s Infiniti system. I believe the incorporation of this kind of infusion pump with these new surgical systems will increase the safety and efficacy of performing MICS.
For me, this has been an insurance in my conversion to MICS.
For Your Information:
- Arturo Pérez-Arteaga, MD, is medical director of the Centro Oftalmológico Tlalnepantla. He can be reached at Toltecas Ave. No. 77, San Javier, Tlalnepantla, Estado de México, Mexico, 54000; (52) 555-565-4422; fax: (52) 555-390-7109; e-mail: drarturo@prodigy.net.mx. Dr. Pérez-Arteaga has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.
- Alcon can be reached at 6201 South Freeway, Fort Worth, TX 76134; (817) 293-0450; fax: (817) 568-6142.
References:
- Agarwal A, Agarwal A et al. Phakonit: phacoemulsification through a 0.9 mm incision. J Cataract Refract Surg. 2001;27:1548-1552.
- Agarwal A, Agarwal S, et al. Phakonit: lens removal through a 0.9 mm incision. J Cataract Refract Surg. 2001;27:1531-1532.
- Tsunekoa H, Shiba T, Takahashi Y. Ultrasonic phacoemulsification using 1.4 mm incision: clinical results. J Cataract Refract Surg. 2002;28:81-86.
- Agarwal A. Bimanual 0.9 mm approach to phaco promises astigmatic neutral cataract surgery and faster rehabilitation. Eurotimes. Feb. 2003.