Normally, dual chamber aspiration cassettes incur a fluid handling flaw.  What happens as the smaller chamber starts to fill?  In this case, nothing.  At least not at the tip of the instrument were it really counts.  Inside the smaller chamber a float valve controls the opening of an orifice connecting the two chambers.  Below a certain fluid level in the smaller chamber, the orifice is closed.  As the fluid level rises to the correct level, the float valve starts to work.  At this level virtually every drop of aspirant that enters the smaller chamber causes a corresponding drop to enter the larger chamber.  All this occurs with no affect on the vacuum delivered to the instrument.

The cassette has two prisms molded into one side.  One is used to reflect light toward the front of the cassette.  This allows the operator to visually monitor aspirant level, even in a dark operating room.  The second prism is used by the system to monitor the fluid level.  The system can tell in approximately 15 cc increments how much fluid the cassette has in it.  The Syntec VitMan can display an icon on its front panel display, graphically showing cassette fluid level.   Warnings will be given, both audible and on the front panel display, when the cassette is approaching full.  This allows the surgeon plenty of time to handle the situation gracefully.