Phacodynamics Flashcards
Approximately how much does IOP increase with the pedal in position 1 for each 15cm (6 inch) rise in bottle height?
10-11mmHg
If the aspiration flow rate is increased while the bottle height is held steady, what will happen to IOP?
IOP will drop
What happens to IOP when the aspiration tip is occluded?
the IOP will rise to the hydrostatic level established by the bottle height
What is the relationship between rotational speed of a flow pump head and the rise time?
inversely proportional
What potential issue can result with highly compliant aspiration tubing?
Surge
What are the two major classifications of pumps used in phaco?
Flow-dependent (e.g., peristaltic pump) vs. Vacuum-dependent (e.g., Venturi)
How is vacuum defined in the context of phaco?
a pressure that is less than atmospheric pressure (i.e., negative pressure if atmospheric pressure is used as the origin)
What are the sources of vacuum (i.e. pressure less than atmospheric pressure) in a flow-pump system?
1) The small aspiration port
2) Occlusion of the aspiration port
3) The aspiration line tubing
These resistances become significant as aspiration flow rate rises.
Does a flow pump provide direct or indirect control over vacuum generated?
Indirect control
Can a flow pump actually reduce flow rate below the baseline expected due to bottle height?
Yes, flow pumps can act as “flow regulators”
With a flow pump, how does IOP change as aspiration port occlusion level increases (and therefore aspiration flow rate decreases)?
IOP rises
How is vacuum (i.e., negative pressure) buildup beyond a given preset avoided with a flow pump?
Through a venting mechanism or reduction in flow pump rotational speed
What is rise time?
The time required to achieve a given level of vacuum (i.e., negative pressure
How is compliance defined for an aspiration line?
change in volume in response to a change in pressure
How does high compliance of aspiration line tubing affect vacuum rise time?
High compliance of AL tubing increases potential rise time, as the pump must work to overcome the compliance (i.e., deform the tubing) prior to building vacuum against an occluding fragment at the aspiration port
How can patient positioning inadvertently alter the effects of your machine settings?
Height of the patient’s eye relative to the bottle affects the pressure generated with a given bottle height setting.
For a machine with linear control of vacuum, what is the maximum potential vacuum that can be generated when the foot pedal is pressed 1/2 way through position 2?
Half of the maximum preset vacuum
Is there open communication between the bottle, AC, and aspiration line in position 1?
Yes. However, remember that there is resistance to flow at the (small) aspiration port.
Is total tip occlusion necessary to build up holding pressure to the maximum preset vacuum with both flow and vacuum pumps?
Yes