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EVERYTHING YOU EVER WANTED TO KNOW ABOUT PHACO FLUIDICS

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Posted: Thursday, January 29, 2015

 

Fluidics play an important part in phacoemulsification and should be understood clearly by 

the beginner surgeon. Flow and vacuum both attract pieces towards the probe whereas 

phaco power repels pieces. 

FLUID INFLOW: Fluid enters the anterior chamber (AC) from the infusion bottle. This flow 

may be regulated by adjusting the bottle height when it is a purely gravity dependent

mechanism (approximately 11 mmHg above ambient atmospheric pressure for every 15 

cm bottle height above the patient's eye) or it may be in the form of pressurized infusion

(either as an air pump connected externally to the infusion bottle or as inbuilt gas forced 

infusion). 

FLUID OUTFLOW: Fluid exits the AC through the aspiration tubing as well as via leakage 

from incisions. This outflow is determined by the Aspiration flow rate (AFR), vacuum, 

incision size and geometry.

Aspiration flow rate: This refers to the amount of fluid that leaves the eye through the 

aspiration tubing per unit time. It is measured in cc/minute. A high AFR results in more 

rapid events. It can therefore result in more rapid removal of nuclear fragments but also 

result in less time for the surgeon to react, which may result in complications. Inflow needs 

to be increased when using high AFR to maintain a stable anterior chamber. This is better 

achieved using pressurized air infusion; the other option being to elevate bottle height. The 

AFR can act as a third hand within the AC by producing fluid currents that can be used to 

direct nuclear material into the aspiration port. These fluid currents flow from the irrigation 

ports in the sleeve towards the aspiration port. Faster AFR produces stronger currents. 

Some degree of turbulence occurs because of incisional leakage and other variables. The 

currents are stronger closer to the aspiration port and therefore, followability of material 

can be increased either by increasing AFR or by taking the aspiration port closer to the 

fragments

Vacuum: This is generated by the phaco machine pump and is the vacuum effective in 

the AC. It is measured in mmHg. Vacuum may be created by either peristaltic or venturi 

pumps. Vacuum is produced in Peristaltic pumps (flow based pump) on occlusion of the 

port. However, it may also be produced without occlusion at high flow rates and thus can 

emulate a Venturi pump at higher flow rate settings. Flow and vacuum may be adjusted 

independently. Vacuum is created even without phaco tip occlusion in Venturi pump 

(vacuum based pump), however vacuum and flow rate cannot be adjusted independently. 

Rapid flow rates and rapid rise times are seen with Venturi pumps. Alcon uses a peristaltic 

pump; the AMO pump can switch between peristaltic and venturi mechanisms in the same 

surgery whereas B&L has both peristaltic and venturi but these cannot be switched in the 

same surgery.

Pre-set or Maximum vacuum refers to the maximum vacuum level set by the surgeon. 

Actual vacuum depends on foot pedal position (with linear setting), maximum pre-set 

level, AFR, port size and degree of occlusion. Vacuum rise time is the speed with which 

the maximum pre-set vacuum is attained following complete occlusion. Low rise times 

make surgery more rapid but give lesser time to react. This is dependent on AFR, tubing 

compliance and venting mechanism. Higher the AFR, faster the rise time; lower the 

compliance of the tubings, faster the rise time. Fluid vented machines also have a faster rise 

time than air vented machines.

SURGE: Surge refers to a sudden shallowing or collapse of the anterior chamber in response 

to an excess of outflow as compared to inflow. It occurs when occlusion is broken. This 

can result in an anterior movement of the posterior capsule and a posterior movement 

of the cornea both of which can result in complications such as a posterior capsular rent 

or endothelial loss. Various phaco machines deal with surge by in-built mechanisms. This 

includes change in pump speed, vacuum rise time or AFR during occlusion; increased inflow 

on break of occlusion; low compliance tubings, venting etc. Alcon has the Intrepid Fluid 

Management System, AMO has Fusion Fluidics and B&L has EQ Fluidics.

GAS FORCED INFUSION (Air pump): Surge causes an unstable AC. A simple remedy 

suggested by Sunita Agarwal was the air pump. A simple fish tank aquarium is connected 

by a 20 G needle and tubing to a non-expandable infusion bottle. This gas forced into the 

infusion bottle causes a pressure rise that increases the amount of fluid entering the eye 

thus preventing surge even at higher vacuum levels. A millipore filter is used to prevent 

infection and to ensure particulate free air. The advantage with in-built gas forced infusion 

is the ability to actively and digitally control the parameters during surgery according to the 

conditions or the surgical steps of the individual case. This makes even difficult cases like 

mature white and hard brown cataracts, small pupils etc easier. It increases the fluid inflow 

thus resulting in a well formed, deep and stable AC. This decreases chances of damage 

to endothelium and capsule. As it allows for higher AFR, it makes surgery more rapid and 

brings nuclear material towards the probe. The fluid acts as a third hand. The air pump can 

make bimanual phaco easier and allows use of smaller bore instruments, making even sub-

1mm surgery possible. 

THERMAL BURNS: Overheating of the phaco tip can produce thermal burns at the clear 

corneal incision. Coaxial phaco depends on adequate needle cooling by fluid flow around 

the needle through the infusion sleeve whereas in biaxial phaco, needle is cooled by 

incisional leakage, smaller needle diameter and higher flow parameters. Most burns occur 

during tip occlusion. Tip heating can occur within 1-3 sec with inadequate irrigation and 

aspiration flow. Inadequate irrigation can occur from an unnoticed empty infusion bottle, 

inadequate bottle height, a crimped infusion sleeve, kinked tubings or a tight incision. 

AFR can be decreased by tip occlusion, low vacuum, crimped aspiration line or improperly 

loaded cassette/ tubings. 

~ Dr. Soosan Jacob is a Senior Consultant Ophthalmologist at Dr. Agarwal's Eye Hospital, Chennai, 

India and can be reached at dr_soosanj@hotmail.com