2020–2021 BCSC Basic and Clinical Science Course™
11 Lens and Cataract
Chapter 8: Phacoemulsification for Cataract Extraction
Venturi (or Vacuum) Pumps
Vacuum pumps directly control only the level of vacuum in the aspiration tubing (indirectly controlling the aspiration flow rate). A Venturi pump (Fig 8-5) directly creates vacuum based on the Venturi effect: a flow of gas across a port creates vacuum proportional to the rate of flow of the gas. This direct control of the vacuum level in the pump cassette then indirectly produces flow (while the aspiration port is not occluded) by “pulling” on the fluid in the aspiration tubing. The actual aspiration flow rate that is produced depends on the resistance in the fluidic circuit. In the absence of significant occlusion, higher vacuum levels will produce a faster aspiration flow rate, attracting material to the aspiration port more quickly.
Figure 8-5 Illustration of the Venturi pump. The volume of gas flowing through the pump dictates the amount of air pulled from the rigid cassette, which in turn creates a vacuum that pulls fluid through the aspiration tubing.
(Illustration courtesy of Mark Miller.)
With occlusion, the surgeon can attenuate the inherently rapid rise time of a vacuum pump via a programmed time delay or by controlling the speed at which the foot pedal is depressed through position 2. That is, direct linear control of vacuum is achieved by varying the foot pedal’s excursion through position 2. During complete occlusion, the effect produced by a Venturi pump’s linear control of vacuum is clinically equivalent to that produced by a modern peristaltic pump’s linear control.
Excerpted from BCSC 2020-2021 series: Section 11 - Lens and Cataract. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.