The document discusses the fluidics of phacoemulsification machines. It describes the infusion and aspiration systems, which work together to maintain stable anterior chamber pressure and volume. The infusion system uses bottle height to provide fluid inflow. The aspiration system uses either peristaltic or venturi pumps to generate vacuum for tissue removal. Key factors discussed include rise time, followability, and surge prevention through compliance tubing, venting, ABS tips, and partial occlusion techniques.

1. Jagdish Dukre

2. FLUIDICS
 The fluidics of the machine refers to the integrated functions
performed by infusion and aspiration systems by which a
stable AC is maintained.
 It consists of :
1. Infusion system
2. Aspiration System

3. Infusion System
 The infusion system consists of a
bottle, the height of which
provides the gradient for flow.
 The tubing from the bottle is run
through a pinch valve which is
controlled by the foot pedal.
 A bottle height of 3 ± 1 ft
maintains a safe IOP with
sufficient fluid entering the eye.

4.  In addition, when the machine flow rate is increased,
increased fluid evacuation from the anterior chamber requires
increased inflow to maintain the steady-state system.
 Therefore, when the machine flow rate is increased, the bottle
height should also be increased.
 Raising the bottle height too much can have undesirable
effects due to repeated iris prolapse, especially if the pupil is
small and wound is large.

5. Aspiration System
 The two functions of the aspiration system are lavage of the
anterior chamber and creation of a hold for emulsification or
crushing of the nucleus.
 Lavage is governed by the flow rate.
 The hold is a function of the vacuum generated by the system.

6.  Flow rate (FR) is the quantity of the fluid pulled from the eye
per minute.
 Flow rate therefore helps in bringing the material towards the
tip and is measured in cc/min.
 Vacuum level is the difference in pressure between
atmospheric pressure and the pressure inside the aspiration
tubing.
 This is a negative suction pressure that is created by the
pump.

7.  The aspiration systems consist of a pump that is either flow
based or vacuum based.
 The common type of flow pump is the Peristaltic pump.
 Venturi is the prototype of a vacuum-based machine.

8. Peristaltic System

9. Advantages of Peristaltic Pump
 In this system, vacuum will be built up only after the tip is
occluded.
 There is a large safety margin in this pump as it is slower in
building up vacuum.
 There is no inadvertent pull on the ocular structure since
vacuum builds up only on occlusion
 Flow rate and vacuum can be set independently in a
peristaltic system.

10. Disadvantages of Peristaltic Pump
 The vacuum build-up is in a stair-stepped pattern causing
more pulsations in the anterior chamber.
 The vacuum build-up is directly related to the density of
occlusion which in turn would depend upon the bevel angle
of the titanium tip.
 One has to mechanically approach the nuclear or cortical
matter to first achieve occlusion for vacuum to build up in
order to aspirate the tissue.

11. Venturi System

12. Advantages of Venturi Pump
 The vacuum build-up is linear.
 There is a consistent increase in the vacuum from zero to
the preset level on depressing the foot switch.
 Nuclear and cortical material can be attracted towards the
probe on depressing the foot pedal.

13. Disadvantages of Venturi Pump
 This pump has the least safety margin.
 The incidence of iris trauma and posterior capsular rents have
been reported to be much higher with this pump.
 In the venturi system only the level of vacuum can be
controlled and not the flow rate.
 The flow rate is a fixed fraction of the vacuum.
 However, the change in vacuum level doesn’t always lead to a
proportionate change in the flow rate since port size and
resistance in the passage also modify flow rate.

14. Rise Time (RT)
 The rise time is the time taken by a
machine to reach maximum preset
vacuum after occlusion has been
achieved.
 In a Venturi system, the RT is fast,
linear and dependent upon the
highest preset vacuum.
 In a peristaltic pump, RT depends
on the FR of the machine.
 The higher the FR, the lesser the
RT though the relationship is not
absolutely linear.

15. Followability
 Followability refers to the tendency of the nuclear
fragments/cortical matter to come into the tip.
 The positive pressure due to the infusion and the negative
pressure created by the aspiration pump are responsible for
the creation of a pressure gradient at the tip.
 This in turn leads to eddy currents from the infusion orifice to
the phaco tip.
 The area encompassed by these eddy currents is known as the
zone of followability.

16.  The area just in front of the tip is the
area of highest followability.
 There are some areas of no
followability.
 Here the positive pressure from the
infusion pushes the pieces out of the
eye.

17. Surge
 A principal limiting factor in the selection of high levels of
vacuum or flow is the development of surge.
 Sudden withdrawal of fluid from AC after occlusion breaks
is called surge.

18.  There are various methods of controlling the surge.
 Some are incorporated into the newer machines and there
are some measures that the surgeon can apply.

19. Surge prevention by the machine
 Property of the tubing to collapse (deform under pressure) is
the compliance of the tubing.
 This extent of collapse of the tubings will depend on the
thickness of the tube.
 The collapse is less if the walls are thicker (less compliant
tubing).
 In a peristaltic machine, these high vacuum tubings and
cassettes are used to decrease the compliance of the tubings
thus preventing surge.

20. Venting
 The machine has a sensor which detects occlusion break and
releases fluid into the system to fill the volume of the re-expanding
tubing.
 This prevents fluid being drawn out of the AC.

21. ABS tip
 The tip has a 0.175 mm hole drilled
in the shaft of the phaco needle.
 When occlusion occurs at the tip,
fluid flows into this hole.
 The amount of flow depends on the
vacuum and flow settings.
 Because some flow always exists, in
reality there is never complete
occlusion.
 This modification must be used with
the high vacuum tubing or it does
not function properly.

22. Partial-Occlusion Phacoemulsification
 In partial-occlusion phaco, micro-pulse phaco is used to avoid
total occlusion to prevent surge.
 The nuclear fragment is brought close to the phaco tip with a
4-millisecond period of aspiration until the fragment partially
occludes it.
 With the onset of a 4-millisecond burst of phaco energy, the
fragment is emulsified before it can totally occlude the phaco
tip.
 Therefore, flow never falls to zero and vacuum never builds
to maximum, thus preventing surge.

23. Surgeon’s Control of Surge
 Increasing the infusion by raising the bottle height may be
useful in some cases.
 The use of an ACM is useful for decreasing surge.
 Increased viscosity of the AC contents: The flow rate
settings are for clear fluids like BSS/Ringers.
 A thicker fluid increases the resistance and does not flow out
easily.

24.  The use of visco-elastic is particularly useful in hard
cataracts where the settings are usually high.
 This will maintain occlusion and prevent fluid from the AC
being aspirated.
 Good foot pedal control is importance in controlling surge
and utilizing it to surgeon’s own advantage.

25.  As soon as the occlusion is about to break (i.e. the piece is
about to be aspirated into the tip) is the surgeon lifts the FP to
IAo, the piece will go in on its own momentum and without
any of surge as the FR will decrease.
 Thus fluid withdrawn from the AC will be very little to
overcome the compliance of the system.
 However, if the FP is withdrawn too early and there is not
enough momentum then it will take more time to build up
vacuum again.