EVERYTHING YOU EVER WANTED TO KNOW ABOUT PHACO FLUIDICS
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
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
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
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 email@example.com