Abstract:
A dual pump aspiration system having both a vacuum level control loop and a flow rate control loop. The system can be operated either as a vacuum priority system or a flow rate priority system.

Description:
This invention relates to surgical control consoles and more particularly to irrigation/aspiration systems used in surgical control consoles. 
     BACKGROUND OF THE INVENTION 
     During small incision surgery, and particularly during ophthalmic surgery, small probes are inserted into the operative site to cut, remove or otherwise manipulate tissue. During these surgical procedures, the surgical site typically is flushed with an irrigating solution and the irrigating solution and tissue is aspirated from the surgical site. The types of aspiration system used, prior to the present invention, where generally characterized as either flow controlled or vacuum controlled, depending upon the type of pump used in the system, and each type of system has certain advantages. 
     Vacuum controlled aspiration systems are operated by setting a desired vacuum level, which the system seeks to maintain. Flow rate information is not available directly. Vacuum controlled aspiration systems typically use a venturi or diaphragm pump. Vacuum controlled aspiration systems offer the advantages of quick response times, control of decreasing vacuum levels and good fluidic performance while aspirating air, such as during an air/fluid exchange procedure. 
     Disadvantages of such systems are the lack of flow information resulting in high flows during phacoemulsification/fragmentation coupled with a lack of occlusion detection. Vacuum controlled systems are difficult to operate in a flow controlled mode because of the problem of non-invasively measuring flow in real time. 
     Flow controlled aspiration systems are operated by setting a desired aspiration flow rate for the system to maintain. Flow controlled aspiration systems typically use a peristaltic, scroll or vane pump. Flow controlled aspiration systems offer the advantages of stable flow rates and automatically increasing vacuum levels under occlusion. Disadvantages of such systems are relatively slow response times, undesired occlusion break responses when large compliance components are used and vacuum can not be linearly decreased during tip occlusion. In addition, peristaltic pumps produce pulsations in the aspiration fluid flow. When such pumps are in fluid communication with a surgical site, these pump pulsations can be manifested at the surgical site. Flow controlled systems are difficult to operate in a vacuum controlled mode because time delays in measuring vacuum can cause instability in the control loop, reducing dynamic performance. 
     One surgical system currently commercially available, the Millennium from Storz Instrument Company, contains both a vacuum controlled aspiration system (using a venturi pump) and a flow controlled aspiration system (using a scroll pump). The two pumps can not be used simultaneously, and each pump requires separate aspiration tubing and cassette. 
     Another currently available system, the ACCURUS® system from Alcon Laboratories, Inc., contains both a venturi pump and a peristaltic pump that operate in series. The venturi pump aspirates material from the surgical site to a small collection chamber. The peristaltic pump pumps the aspirate from the small collection chamber to a larger collection bag. The peristaltic pump does not provide aspiration vacuum to the surgical site. Thus, the system operates as a vacuum controlled system. 
     Accordingly, a need continues to exist for a surgical system that operates in both vacuum controlled and flow controlled modes. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention improves upon prior art by providing a dual pump aspiration system having both a vacuum level control loop and a flow rate control loop. The system can be operated either as a vacuum priority system or a flow rate priority system. 
     Accordingly, an objective of the present invention to provide a dual pump aspiration system. 
     Another objective of the present invention to provide an aspiration system having both a vacuum level control loop and a flow rate control loop. 
     A further objective of the present invention to provide an aspiration control system and method that can be operated either as a vacuum priority system or a flow rate priority system. 
     Other objectives, features and advantages of the present invention will become apparent with reference to the drawings, and the following description of the drawings and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The FIGURE is a schematic diagram of the dual mode system of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As best seen in the FIGURE, system  10  of the present invention generally contains vacuum pump  12 , flow pump  14 , pressure transducer  16 , small collection chamber  18 , fluid level sensor  20 , drain bag  22 , control circuitry  24  and sensor  26 , such as a flow or pressure sensors. Vacuum pump  12  may be any suitable pump, such as a diaphragm pump, a vane pump, a scroll pump or a peristaltic pump, but a venturi pump is preferred. Pressure transducer  16  may be any suitable device for directly or indirectly measuring pressure or vacuum, such as a vacuum transducer or an absolute pressure transducer. One suitable system for controlling vacuum pump  12  is disclosed in U.S. Pat. No. 5,674,194, the entire contents of which being incorporated herein by reference. Flow pump  14  may be any suitable pump, such as a venturi pump, a diaphragm pump, a vane pump or a scroll pump, but a peristaltic pump is preferred. Fluid level sensor  20  may be any suitable device for measuring the fluid level in small collection chamber  18 , but an optical fluid or acoustic level sensor, such as the one described in U.S. Pat. No. 5,747,824, the entire contents of which being incorporated herein by reference, is preferred. Control circuitry  24  contains all of the necessary hardware and software to control system  10 , such hardware and software being well within the ordinary skill of those in the art. 
     In vacuum controlled, system  10  operates by vacuum pump  12  drawing a preselected vacuum in small chamber  18  through aspiration line  11 . This vacuum is transmitted to surgical site  28  through aspiration line  30 . As small chamber  18  begins to fill with fluid  32 , changes in the vacuum level are sensed by pressure transducer  16 , which sends a signal to control circuitry  24  through interface  33 . Control circuitry  24  communicates a control signal to vacuum pump  12  through interface  34  to adjust the vacuum supplied by vacuum pump  12  as required. When the level of fluid  32  in small chamber  18  reaches a preselected level, fluid level sensor  20  sends a signal to control circuitry  24  through interface  36 . Control circuitry  24  generates a flow pump control signal and communicates the signal to flow pump  14  through interface  38 , directing flow pump  14  to begin evacuating fluid  32  from small chamber  18  through line  40  and into drain bag  22 . The operation of system  10 , under the direction of control circuitry  24 , maintains a steady pressure level in aspiration line  30 . 
     In flow controlled mode, system  10  operates by vacuum pump  12  drawing a vacuum in small chamber  18  through aspiration line  11 . This vacuum is transmitted to surgical site  28  through aspiration line  30 . The vacuum at surgical site  28 , along with the pressurization of the infusion fluid cause by elevating or pressurizing irrigation fluid source  29  causes irrigation fluid  32  to flow to surgical site  28  through irrigation line  31 . The flow rate or pressure within irrigation line  31  can be measured by sensor  26 , and communicated to control circuitry  24  through interface  27 . Irrigation fluid  32  continues to flow to surgical site  28  and out of surgical site  28  to small chamber  18  through aspiration line  30 . As small chamber  18  begins to fill with fluid  32 , changes in the vacuum level are sensed by pressure transducer  16 , which sends a signal to control circuitry  24  through interface  33  and changes in the fluid level are detected by fluid level sensor  20 , which sends a signal to control circuitry  24  through interface  36 . With the information from fluid level sensor  20 , flow pump  14  and sensor  26 , control circuitry  24  can estimate aspiration fluid flow in aspiration line  30 . Control circuitry  24 , therefore, can control system  10  based on the calculated aspiration flow rather than aspiration pressure. One skilled in the art will understand that by varying the vacuum in collection chamber  18 , the flow through aspiration line  30  can be controlled. In addition, by comparing calculated aspiration fluid flow and measured irrigation fluid flow, control circuitry can detect a number of events, such as amount of wound leakage at surgical site  28 , obstructions in irrigation line  31  and obstructions or occlusions in aspiration line  30 . 
     One skilled in the art will recognize that hybrid control modes may also be used, wherein system  10  operates in flow control mode unless certain conditions are present in which case system  10  begins operating in vacuum control mode or visa versa. 
     While certain embodiments of the present invention have been described above, these descriptions are given for purposes of illustration and explanation. Variations, changes, modifications and departures from the systems and methods disclosed above may be adopted without departure from the scope or spirit of the present invention.