HISTORY
The main problem encountered in bimanual phaco/phakonit was the destabilization of the anterior chamber during surgery. This was solved by us to a certain extent by using an 18-gauge irrigating chopper. Dr Sunita Agarwal suggested the use of an antichamber collapser, which injects air into the infusion bottle (Fig. 1.1). This pushes more fluid into the eye through the irrigating chopper and also prevents surge.1–11 Thus, we were able to use a 20 gauge or 21 gauge irrigating chopper as well as solve the problem of destabilization of the anterior chamber during surgery.
Fig. 1.1: Diagrammatic representation of the connection of the air pump to the infusion bottle
Abbreviation: BSS—Balanced salt solution
Now with microphakonit and gas forced infusion we are able to remove cataracts with a 0.7 mm irrigating chopper (22 gauge). Subsequently we used this system in all our co-axial phaco cases including microincisional co-axial phaco to prevent complications like posterior capsular ruptures and corneal damage.
INTRODUCTION
Since the introduction of phacoemulsification by Kelman,1 it has been undergoing revolutionary changes in an attempt to perfect the techniques of extracapsular cataract extraction surgery. Although advantageous in many aspects, this technique is not without its attending complications. A well-maintained anterior chamber without intraocular fluctuations is one of the prerequisites for safe phacoemulsification and phakonit.2
When an occluded fragment is held by high vacuum and then abruptly aspirated, fluid rushes into the phaco tip to equilibrate the built up vacuum in the aspiration line, causing surge.3 This leads to shallowing or collapse of the anterior chamber. Different machines employ a variety of methods to combat surge. These include usage of noncompliant tubing,4 small bore aspiration line tubing,4 microflow tips,4 aspiration bypass systems,4 dual linear foot pedal control4 and incorporation of sophisticated microprocessors4 to sense the anterior chamber pressure fluctuations.
The surgeon dependent variables to counteract surge include good wound construction with minimal leakage,5 and selection of appropriate machine parameters depending on the stage of the surgery.5 An anterior chamber maintainer has also been described in literature to prevent surge, but an extra side port makes it an inconvenient procedure.
We started a simple and effective method to prevent anterior chamber collapse during phacoemulsification and phakonit in 1999 by increasing the velocity of the fluid inflow into the anterior chamber. This is achieved by an automated air pump which pumps atmospheric air through an air filter into the infusion bottle thereby preventing surge. We stumbled upon this idea when we were operating cases with phakonit7 where we wanted more fluid entering the eye, but even now we use it in all our phacoemulsification cases.8
Air Pump
An automated air pump is used to push air into the infusion bottle thus increasing the pressure with which the fluid flows into the eye. This increases the steady-state pressure of the eye making the anterior chamber deep and well-maintained during the entire procedure. It makes phakonit and phacoemulsification a relatively safe procedure by reducing surge even at high vacuum levels.
TECHNIQUE
A locally manufactured automated device, used in fish tanks (aquariums) to supply oxygen, is utilized to forcefully pump air into the irrigation bottle. This pump is available in aquarium shops and has an electromagnetic motor which moves a lever attached to a collapsible rubber cap. There is an inlet with a valve, which sucks in atmospheric air as the cap expands. On collapsing, the valve closes and the air is pushed into an intravenous (IV) line connected to the infusion bottle (Fig. 1.1). The lever vibrates at a frequency of approximately 10 oscillations per second. The electromagnetic motor is weak enough to stop once the pressure in the closed system (i.e. the anterior chamber) reaches about 50 mm of Hg. The rubber cap ceases to expand at this pressure level. A millipore air filter is used between the air pump and the infusion bottle so that the air pumped into the bottle is clean of the particulate matter.
METHOD
- First of all, the balanced salt solution (BSS) bottle is taken and put on the IV stand.
- Now we take an air pump. This air pump is the kind which is used in fish tanks (aquariums) to infuse oxygen to the fishes. The air pump is plugged on to the electrical connection.
- An IV set now connects the air pump to the infusion bottle. The tubing passes from the air pump and the end of the tubing is passed into one of the infusion bottles.
- When the air pump is switched on, it pumps air into the infusion bottle. This air goes to the top of the bottle and because of the pressure; it pumps the fluid down with greater force. With this, the fluid now flows from the infusion bottle to reach the phaco handpiece or irrigating chopper. The amount of fluid now coming out of the handpiece is much more than what would normally come out and with more force.
- A millipore air filter is connected between the air pump and the infusion bottle so that the air which is being pumped into the bottle is sterile.
- This extra amount of fluid coming out compensates for the surge which would otherwise occur.
Continuous Infusion
Before we enter the eye, we fill the eye with viscoelastic. Then once the tip of the phaco handpiece in phaco or irrigating chopper in phakonit is inside the anterior chamber we shift to continuous irrigation. This is very helpful especially for surgeons who are in the learning curve of phacoemulsification or phakonit. This way, the surgeon never comes to position zero and the anterior chamber never collapses. Even for excellent surgeons this helps a lot.
Advantages
- With the air pump, the posterior capsule is pushed back and there is a deep anterior chamber.
- The phenomenon of surge is neutralized and this in turn prevents posterior capsular rupture.
- Striate keratitis postoperatively is reduced, as there is a deep anterior chamber.
- Hard cataracts can be operated quite comfortably, as striate keratitis does not occur postoperatively.
- The surgical time is shorter as one can emulsify the nuclear pieces much faster as surge does not occur.
- One can easily operate cases with the phakonit technique as quite a lot of fluid now passes into the eye. Thus, the cataract can be removed through a smaller opening.
- It is quite comfortable to do cases under topical or no-anesthesia.
Topical or No-Anesthesia Cataract Surgery
During phacoemulsification under topical or no-anesthesia, the main problem encountered is that sometimes the pressure is high especially if the patient squeezes the eye. In such cases, the posterior capsule comes up anteriorly and one can produce a posterior capsular rupture. To solve this problem, surgeons tend to work more anteriorly, performing supracapsular phacoemulsification/ phakonit. The disadvantage of this is that striate keratitis tends to occur.
With the air pump, this problem is solved totally as the posterior capsule is pushed back. In other words, there is a lot of space between the posterior capsule and the cornea, preventing striate keratitis and inadvertent posterior capsular rupture.
Internal Gas Forced Infusion
This was started by Arturo Pérez-Arteaga from Mexico. The anterior vented gas forced infusion system (AVGFI) of the Accurus surgical system is used.
This is a system incorporated in the Accurus machine that creates a positive infusion pressure inside the eye; it was designed by the Alcon engineers to control the intraocular pressure (IOP) during posterior segment surgery. It consist of an air pump and a regulator which are inside the machine; then the air is pushed inside the bottle of intraocular solution, and so the fluid is actively pushed inside the eye without raising or lowering the bottle. The control of the air pump is digitally integrated in the Accurus panel; it also can be controlled via the remote. Also the footswitch can be preset with the minimal and maximum of desired fluid inside the eye and go directly to this value with the simple touch of the footswitch. Arturo Pérez-Arteaga recommends to preset the infusion pump at 100 mm of Hg; it is enough strong irrigation force to perform a microincision phaco. This parameter is preset in the panel and also as the minimal irrigation force in the footswitch; then he recommends to preset the maximum irrigation force at 130 to 140 mm of Hg in the foot pedal, so if a surge exist during the procedure the surgeon can increase the irrigation force by the simple touch of the footswitch to the right.
Fig. 1.2: Millipore filter to connect the air pump to the tubing.
Air pump in the Stellaris (Bausch and Lomb) machine
With the AVGFI the surgeon has the capability to increase even more these values. A millipore filter is used again between the tubing and the air pump (Fig. 1.2).
Stellaris Pressurized Infusion System
Bausch and Lomb have installed air pump in their Stellaris machine in 2009. The advantage of this is that one has an internal gas forced infusion now as the air pump which was an external gas forced infusion system is now inside the machine (Fig. 1.3). Another advantage is there is a monitor in the panel of the machine and one can lower or raise the pressure of the air pump.
Centurion active fluidics by Alcon: Active fluidics allows the surgeon to set and maintain the appropriate intraocular pressure (IOP). The system has dual pressure laser sensors to detect irrigation pressure and aspiration vacuum to maintain the target IOP. It also has rotatory valves and dual segment pump designed for smooth flow.
DISCUSSION
Surge is defined as the volume of the fluid forced out of the eye into the aspiration line at the instant of occlusion break. When the phacoemulsification handpiece tip is occluded, flow is interrupted and vacuum builds up to its preset values.
Fig. 1.3: Stellaris (Bausch and Lomb) pressurized infusion system. Note in the upper right corner IV pole height in cm and next to it shows the air pump (gas forced infusion pressure) in mm of Hg
Additionally, the aspiration tubing may collapse in the presence of high vacuum levels. Emulsification of the occluding fragment clears the block and the fluid rushes into the aspiration line to neutralize the pressure difference created between the positive pressure in the anterior chamber and the negative pressure in the aspiration tubing. In addition, if the aspiration line tubing is not reinforced to prevent collapse (tubing compliance), the tubing, constricted during occlusion, then expands on occlusion break. These factors cause a rush of fluid from the anterior chamber into the phaco probe. The fluid in the anterior chamber is not replaced rapidly enough to prevent shallowing of the anterior chamber.
The maintenance of intraocular pressure (steady–state IOP)2 during the entire procedure depends on the equilibrium between the fluid inflow and outflow. The steady state pressure level is the mean pressure equilibrium between inflow and outflow volumes. In most phacoemulsification machines, fluid inflow is provided by gravitational flow of the fluid from the balanced salt solution (BSS) bottle through the tubing to the anterior chamber. This is determined by the bottle height relative to the patient's eye, the diameter of the tubing and most importantly by the outflow of fluid from the eye through the aspiration tube and leakage from the wounds.2
The inflow volume can be increased by either increasing the bottle height or by enlarging the diameter of the inflow tube. The intraocular pressure increases by 10 mm Hg for every 15 centimeters increase in bottle height above the eye.5
High steady-state IOPs increase phaco safety by raising the mean IOP level up and away from zero, i.e. by delaying surge related anterior chamber collapse.2
Air pump increases the amount of fluid inflow thus making the steady-state IOP high. This deepens the anterior chamber, increasing the surgical space available for maneuvering and thus prevents complications like posterior capsular tears and corneal endothelial damage. The phenomenon of surge is neutralized by rapid inflow of fluid at the time of occlusion break. The recovery to steady-state IOP is so prompt that no surge occurs and this enables the surgeon to remain in foot position 3 through the occlusion break. High vacuum phacoemulsification/ phakonit can be safely performed in hard brown cataracts using an air pump. Phacoemulsification or phakonit under topical or no-anesthesia6, 7 can be safely done neutralizing the positive vitreous pressure occurring due to squeezing of the eyelids.
SUMMARY
The air pump is a new device, which helps to prevent surge. This prevents posterior capsular rupture, helps deepen the anterior chamber and makes phacoemulsification and phakonit a safe procedure even in hard cataracts.
REFERENCES
- Kelman CD. Phacoemulsification and aspiration; a new technique of cataract removal; a preliminary report. Am J Ophthalmol. 1967;64:23–5.
- Wilbrandt RH. Comparative analysis of the fluidics of the AMO Prestige, Alcon Legacy, and Storz Premiere phacoemulsification systems. J Cataract Refract Surg. 1997;23:766–80.
- Seibel SB. Phacodynamics. Thorofare, NJ, Slack Inc. 1995;54.
- Fishkind WJ. The Phaco Machine: How and why it acts and reacts? In: Agarwal's four volume textbook of Ophthalmology. Jaypee Brothers Medical Publishers (P) Ltd. New Delhi. 2000. (In print).
- Seibel SB. The fluidics and physics of phaco. In: Agarwal's et al. Phacoemulsification, Laser cataract surgery and foldable IOLs, 2nd edn. Jaypee Brothers Medical Publishers (P) Ltd. New Delhi. 2000. pp. 45–54.
- Agarwal, et al. No-anesthesia cataract surgery with karate chop. In: Agarwal's Phacoemulsification, Laser cataract surgery and foldable IOLs, 2nd edn. Jaypee Brothers Medical Publishers (P) Ltd. New Delhi. 2000. pp. 217–26.
- Agarwal, et al. Phakonit and laser phakonit. In: Agarwal's Phacoemulsification, Laser cataract surgery and foldable IOLs, 2nd edn. Jaypee Brothers Medical Publishers (P) Ltd. New Delhi. 2000. pp. 204–16.
- Agarwal A. Agarwal S. Agarwal A. Antichamber collapser. J Cataract Refract Surg. 2002;28:1085.
- Agarwal A, Agarwal S, Agarwal A. Phakonit: phacoemulsification through a 0.9 mm incision. J Cataract Refract Surg. 2001;27:1548–52.
- Agarwal A, Trivedi RH, Jacob S, et al. Microphakonit: 700 micron cataract surgery. Clin ophthal. 2007;1(3):323–5.
- Agarwal A, Kumar DA, Jacob S, Agarwal A. In vivo analysis of wound architecture in 700 micron microphakonit surgery. J Cataract Refract Surg. 2008;34(9):1554–60.