There is an entire article with 7 figures and 1000 words of text on CataractCoach.com (will be posted on Wed April 10, 2019). If you are only watching the YouTube video, you are missing out on a lot of the content. The best way to learn this is to visit CataractCoach.com every Wednesday.
All phaco platforms share the same basic structure and concepts. The phaco machine aims to balance fluidics within the eye, while delivering ultrasonic energy and vacuum in order to emulsify and aspirate the cataract through a small incision.
The three main functions of the phaco machine are: (1) to provide irrigation into the eye, (2) to create vacuum/aspiration to remove the cataract, and (3) to deliver ultrasound energy in order to emulsify the nucleus. These three functions correspond to the three phaco foot-pedal positions.
The phaco foot pedal is the primary instrument used to control the phaco machine during cataract surgery. This foot pedal traditionally works by depressing it towards the floor with the dominant foot (the right foot for most surgeons). Each foot pedal position is additive to the previous positions, so that while the pedal is in position 2 (vacuum/aspiration) it is also providing the full function of position 1 (irrigation). Similarly, once the pedal is in foot position 3 (ultrasound energy), it is also providing the function of position 2 (vacuum/aspiration), as well as position 1 (irrigation).
Foot Position 1: Irrigation
It’s important to realize that during phacoemulsification, we are working in the very small space of the anterior and posterior chambers, compromising well under one cubic centimeter of space together. During the surgery, we must always maintain the stability and structure within the eye, particularly to prevent collapse of the anterior and posterior chambers which can lead to severe complications.
The irrigation function of the phaco machine is meant to provide a source of fluid infusion into the eye during the surgery. By depressing the foot pedal to position 1, the infusion is turned on. There is no linear control of the infusion – the infusion is either turned on or turned off.
The height of the infusion bottle determines the relative infusion pressure and flow rate during the surgery. To keep the eye inflated during surgery, we need to make sure that the fluid inflow rate is greater than the fluid outflow rate.
Foot Position 2: Vacuum / Aspiration of fluid
Phaco foot position 2 is the control of the relative aspiration and vacuum level of the fluid from the eye. There is a linear control of vacuum and flow, so that the top of foot position 2 provides less vacuum or flow than the middle or bottom range of the same foot position 2. This is similar to the gas pedal in a car, where the car’s throttle is opened more as the gas pedal is further depressed.
To create the vacuum and the aspiration flow of fluid, the phaco machine must have a fluid pump. The most common types of fluid pumps are peristaltic and venturi.
The vacuum and aspiration levels that are created draw the fluid out of the eye and into a waste fluid collection via the outflow tubing. The regulation of vacuum and aspiration is controlled by the foot pedal, with more depression of the pedal resulting in higher levels. There are two primary sources of fluid outflow during phacoemulsification: the outflow from the phaco probe created by the fluid pump, and the leakage of fluid from the incisions.
Foot Position 3: Ultrasound Energy
The bottom-most position of the foot pedal is position 3, which controls the delivery of ultrasound energy into the cataract. There is linear control of the ultrasound energy level so that further pedal depression results in more ultrasound energy, such as would be needed for a denser cataract.
Note that if the pedal is in position 3, we are already engaging the full function of both positions 1 and 2. The irrigation is on, and the vacuum and aspiration level is at its highest preset level. Ultrasound energy should only be applied once the tip of the phaco probe is in contact with part of the cataract.
When we look at the phaco probe closely, we see that there are three lines attached: (1) the infusion tubing carrying fluid into the eye, (2) the outflow tubing that removes the fluid via flow that is created by the phaco machine’s fluid pump, and (3) the line that carries the electrical signals to control the ultrasound energy at the tip of the phaco probe. These three lines correspond to the three phaco foot pedal positions.
Changing Pedal Functions for Anterior Vitrectomy
There are two distinct modes under the anterior vitrectomy setting of your phaco machine and they change the function of foot pedal position 2 and 3.
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