Chapter 3 - Phaco Machine Settings Primer

Four main components and software to tie them together

• Pump - most important variable




• Parameters are dependant on tubing diameter and compliance


• Parameters are dependant on phaco needle diameter


• Allows removal of the emulsified lens material


• Set low during sculpting and higher during quadrant removal and chopping




• Irrigation System




• Typically is just an adjustable bottle held high to allow infusion of fluid


• Machine can adjust bottle height


• Machine can turn fluid on and off




• Ultrasound (U/S) hand piece




• Vibrates needle at a set rate in the 20,000 to 40,000 HZ range


• Increasing the ultrasound power increases the excursion of the needle


• With increasing load the frequency and excursion lessens


• Modern multiple crystal hand pieces can better handle load




• Footswitch




• Typically controlled with dominant foot (without shoes)


• Accelerator like pedal is common across all brands


• Position 0 - everything is off


• Position 1 - irrigation is on, no pump, no ultrasound


• Position 2 - irrigation is on, pump is on, no ultrasound


• Position 3 - irrigation is on, pump is on, ultrasound is on

Phaco Pumps

• Please read the classic definitive text for more details: Barry S. Seibel, Phacodynamics, Slack


• Flow rate: amount of fluid passing through the tubing (cc/min) also aspiration flow rate


• Vacuum: difference in fluid pressure among two points, e.g. tip of needle and AC (mm Hg)
  

1. Vacuum based Pumps – e.g. Venturi pump ( Millennium, Accurus ), diaphragm




• Increasing pump power increases vacuum directly and flow rate indirectly


• Venturi pump requires external source of compressed air




• This has limited acceptance of this pump (make sure your ASC has the proper air lines)


• Compressed gas flows over open top of rigid cassette attached to tubing


• Flow of gas creates vacuum much as flow over wing creates lift




• Flow rate is dependant on resistance of flow


• Roughly analogous to electric current voltage relationship (Ohm's law)




• i=e/r where e = voltage (analogous to vacuum)




• i = current (analogous to flow rate)


• r = resistance (analogous to tubing and occlusion)




• more flow rate with less resistance (fixed vacuum)


• more flow rate with more vacuum (fixed resistance)




• Pump settings -- No settings for flow rate only vacuum




• Fixed: no matter how deep the into position 2 or 3 vacuum is fixed




• Great for chopping and quadrant removal




• Variable: vacuum increases from 0 to max when deeper into pos 2 or 3




• Great for I/A can slowly increase vacuum to just what you need








2. Flow based pumps – e.g. peristaltic pump ( Infinity, Sovereign, and Legacy )




• Increasing pump power increases flow rate directly and vacuum indirectly


• Vacuum is dependant on resistance of flow




• Roughly analogous to electric current voltage relationship (Ohm's law)




• e=ir where e = voltage (analogous to vacuum)




• i = current (analogous to flow rate)


• r = resistance (analogous to tubing and occlusion)






• more vacuum with more resistance (fixed vacuum)


• more vacuum with more flow rate (fixed resistance)




• Pump Settings




• Set vacuum cutoff and flow rate




• Vacuum cut off




• Seems like you are setting the vacuum


• Really setting the vacuum at which the pump stops


• Increasing the vacuum does not increase pump speed


• Flow rate or Aspiration FR rate (AFR) sets pump speed (cc/min)






• with modern peristaltic pumps (eg. Infiniti ) for each foot position you can have:




• Fixed or variable flow


• Fixed or variable vacuum cut off
  

Variables affecting Phacoemulsification

Flow rate	Vacuum Cut off	Comment/Application
Fixed	Fixed	Independent of depth in foot position Low numbers good for sculpting
Fixed	Variable	More depth higher vacuum cut off Limited control Typical I/A setting on Alcon 20,000
Variable	Fixed	More depth faster pump More control pump speed changes Bimodal setting on Alcon 20,000
Variable	Variable	Both change with depth in foot position Feels like a venturi pump

Phaco Pump Comparison

Pump	Pros	Cons
Vacuum e.g. Venturi	Less posterior occlusion surge Better for vitreous removal Material comes to tip easily	Need source of compressed gas Need rigid cassette
Flow e.g. Peristaltic	Better for sculpting No need for compressed air	Post occlusion surge Need occlusion for vacuum to build

Ultrasound Control

• Four ultrasound modes: continuous, pulse, burst, and hyperpulse
• Continuous


• Phaco is on in position three
• Usually increasing ultrasound power with depth into foot position


• Pulse


• Phaco pulses with duty cycle on and off
• Usually with equal on and off time or 50% duty cycle (time on/cycle time)
• Usually the rate (or inverse of duty cycle) is fixed (Hz)
• Usually increasing ultrasound power with depth into foot position


• Burst
• Bursts of power come with off time that decreases with depth into foot position
• Usually when floored in position 3 -- ultrasound power becomes continuous
• ultrasound power is fixed


• Hyperpulse
• Uses short on time pulses e.g. 25% on; 75% off
• Fixed duty cycle; fixed pulse rate
• Usually increasing ultrasound power with depth into foot position

Advantages & Disadvantages of Various Modes

Mode	Advantages	Disadvantages	Applications
Continuous	Simple	Repels nuclear material Hot	Sculpting
Pulse	Less hot	Can repel nuclear material	Choo choo chop Segment removal
Burst	Less hot Holds material well		Chopping
Hyperpulse	Followability with Long off cycle Cool with long off cycle		Sculpting Bimanual small incision

My Typical Settings

[click on table for larger view]

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