AU688018B2 - Fluid management systems - Google Patents

Description

AUSTRALIA

PATENTS ACT' 1990 COMPLETE SPECIF~ICATION FOR A STANDARD PATENT (Original) I) c/i.

-Sm kLe wynitsjf- nc- Name of Applicant/Nominated Person: 9* 0 9 9

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4* 4 *4 .4 4 .4.4 4444 4 Actual Inventor(s): Address for Service: David G. BEISER Steven B. WOOLFSON Kenneth W. KRAUSE

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DAVIES COLLISON CAVE, Patent Attorneys, 1 Little Collins Street, Melbourne, 3000.

invention Title: Fluid management systems The following statement is a full description of this invention, including the best method of performing it known to us: -1 W5530,qr~opczWky flidD2ASOI1 P <OPERiPHIUf0431-9523 212l9 -1A- FLUID MANAGEMENT SYSTEMS The present invention relates to an improved cannula.

According to the present invention, there is provided a cannula comprising a body portion having an internal bore extending therethrough and opening to the exterior at a proximal end and at a distal end of the body portion, elastomeric sealing means disposed at the proximal end for sealing the respective opening when in a normally closed condition and being deformable to open the interior bore to the exterior at the proximal end, a further S' 10 opening from the interior bore to the exterior between the distal end of the body portion and the elastomeric sealing means, and a valve member int said further opening which is displaceable between a closed condition and an open condition, said valve member being adapted to permit fluid flow into and from the internal bore through said further opening in its open condition, In one embodiment, said sealing means may comprise a one-piece elastomeric molding having opposed elastomeric face portions and an integral elastomeric mounting member about the periphery of said face portions, said face portions each having a slit formed therein, the slit in one face portion being transverse to the slit in the other face portion.

In another embodiment, said sealing means comprises opposed, spaced apart, first and second substantially planar sealing members, said first sealing member having a substantially circular aperture therein and said second sealing member having sealing elements formed by a slit therethrough.

An embodiment of the present invention provides an operative cannula that can serve as the outflow cannula. The cannula is provided with a sealing means at its proximal end for ssl I P:OiPE'R1'1i1243IM95 238 2'1 I lBsealingly engaging tools passing through the sealing means proximally to distally and distally to proximally. Preferably, the operative cannula is provided with a tapered obturator tip at said distal end closing said internal bore, and aperture means in said body portion adjacent said obturator tip for permitting liquid flowing through said internal bore to exit the cannula.

The valve member is preferably a push valve member which is manually actuatable from opposite ends to provide the displacement between the open and closed conditions.

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*o o e I II L I_ -2- The present invention will now be described by way of example in terms ce' a preferred embodiment with reference to the accompanying drawings, in which: Fig. 1 is a schematic illustration of a liquid supplying apparatus; Fig. 2 is a block diagram of a control system; Fig. 3 is a curve showing the relationship between the pressure drop from the pressure sensing means to the inflow cannula and the inflow flow rate; Fig. 4 is a family of curves showing the relationship between the inflow pump pressure and the inflow flow rate at various pump speeds; Fig. 5 is a curve showing the relationship between the pressure drop from the inflos,, pump to the pressure sensing means and the inflow flow rate; Fig. 6 is a view in section of a cannula according to an embodiment of the invention; Fig. 6A is an enlarged detail view of the seal in the cannula; Fig. 7 is a view in section of an irrigation extender; Fig. 8 is a view in section showing the cannula and irrigation extender coupled together to form an inflow cannula assembly, with an endoscope inserted in the inflow cannula assembly; :11. Fig. 9 is a detail view in section of a pressure sensing means; Fig. 10 is a view in section of a blade of a surgical tool inserted in the operative 20 cannula; Fig. I11 is a top plan view of a pump cassette; :Fig. 12 is a view in section along lines 12-12 in Fig, 11; Fig. 13 is a top plan view of the impeller of the centrifugal pump; Fig. 14 is a view in section taken along lines 14-14 in Fig. 11 Fig. 15 is a top plan view of one of the motors used to drive the pumps; Fig. 16 i3 a block diagram of another control system used with an embodiment of the present invention; Fig. 17 is a plan view, from the rear, of another pump cassette;, Fig. 17A is a detail exploded view, in section, of a portion of the pump cassette shown in Fig. 17; Fig 18 is a view in section taken along lines 18-18 in Fig. 17; Figs. 19A and 19B are views in section taken along lines 19419 in Fig. 17; 950S304%opcOiky,fluid2.10.2 Fig. 20 is a plan view, partly in section, of an operative cannula Fig. 21 is a view in section taken along lines 21- 21 in Fig. Fig. 22 is a view in section of an adaptor; Fig. 23 is a detail view, partly in section, of a modified distal obturator tip for the operative cannula of Fig. 20; and Fig. 24 is a plan view, partly in section, of an 0 obturator cannula Referring to Fig. 1, the apparatus includes a fluid source 1, usually two bags of sterile saline, communicating via conduit 2 with the inlet of a centrifugal inflow pump 4 (Fig. 2) housed within a cassette 200 in fluid management unit 5. Centrifugal inflow pump 4 supplies liquid under pressure through its outlet to conduit 7 and then to the body cavity 10. As will be discussed in detail hereinafter, S inflow cannula assembly 9 is inserted into body cavity 10 and endoscope 8 ia placed within inflow cannula assembly 9 such 0 that liquid under pressure is delivered by centrifugal inflow pump 4 to body cavity 10 via the annulus between the endoscope 8 and the inflow cannula assembly 9.

Pressure transducer 11 is located upstream of the body cavity 10 and senses the liquid pressure in conduit 7 as will be described in detail hereinafter. In the embodiment of the invention shown in Figs.l and 2, pressure transducer 11 is at Y LI the connection between conduit 7 and endoscope 8. The output from pressure transducer 11 is sent via line 12 to a pressure signal processor 13 (Fig. 2) within fluid management unit for computing the pressure within body cavity 10. The desired pressure for the body cavity will be set by operating a selector 5a on fluid management unit 5 and display 5b will display the set pressure. Pressure controller 40 (Fig. 2) within fluid management unit 5 is responsive to the body cavity pressure signal generated by pressure signal processor 13 to adjust the speed of centrifugal inflow pump 4 to increase or decrease the outlet pressure of the liquid delivered by centrifugal inflow pump 4 and thereby maintain the body cavity pressure at the desired set value, as will be explained in detail hereinafter.

An outflow cannula 14 (described in detail hereinafter) is inserted into the body cavity 10. Tool 15 is inserted via outflow conduit 14 into the body cavity 10, and the surgeon will manipulate tool 15 while viewing the procedure via endoscope 8, as is conventional. Tool control unit 21 powers tool 15 ria power cord 22. Outflow conduit 16 connects the inlet of a suction pump 18 (Fig. 2) within unit 5 with the outlet of Stool 15, whereby liquid within body cavity 10 may be aspirated and sent to waste container 19 via conduit 20. Fluid exiting body cavity 10 is filtered by tissue trap 16a located upstream of suction pump 18.

9 b Y Endoscope 8 and tool 15 are reused after sterilization.

It is presently preferred that the pumps 4 and 18, the pressure transducer 11, and the conduits are disposable, as well as the blades for the tool During the preoperative stage, the surgeon will select a desired pressure for the body cavity for the given surgical procedure by operating a set-pressure selector 5a, thereby causing set pressure generator 30 (Fig. 2) to generate a set pressure signal 31, which is applied to an input of pressure controller 40. To the other input of pressure controller is applied signal 32a corresponding to the pressure in body cavity Body cavity pressure rignal 32a may be calculated by pressure signal processor 13 using a lumped parameter model as follows. By empirically determining the pressure vs. flow characteristics of each of the components in the path of fluid flow, (from fluid source 1 to distal end 92 (Fig. 1) of inflow 0** assembly one can determine body cavity pressure by calculating pressure drops across each component. One method takes 2p into account the individual pressure vs. flow characteristics of centrifugal inflow pump 4, conduit 7 and inflow cannula assembly 9. While this will require more demanding software calculations, it will allow easier theoretical modeling of the effects of changing the pressure vs. flow characteristics of any component. Another method lumps the pressure vs. flow characteristics of the inflow pump 4 and conduit 7 up to the I -II I r. I point of pressure measurement by transducer 11. This method simplifies the calculation of the body cavity pressure, but it is specific to the design of the inflow pump and conduit 7.

Either method may be used in the present invention.

For eithier method, the body cavity pressure, PC, is calculated by subtracting the pressure drop across the inflow cannula assembly 9 from the pressure, sensed by transducer 11. The pressure drop across inflow cannula assembly 9, (P, PCwas empirically determined for various flows, Oin by LO measuring the pressure at the outlet 92 of inflow cannula assembly 9 at a given flow, Qjn, and subtracting it from the sensed pressure, at that flow. A typical curve plotting (PS PC versus f low is schematically shown in Fig. 3, and was accurately fit using the function: Pis PC A 1 Q 2 2n where A, and A 2 are constants, which can be rewritten as: PC P11 AjQ 2 A 2 Qjn The values for constants A, and A 2 are determined and stored in memory for use by pressure signal processor 13.

A more generic method used to determine cavity pressure calculates the inflow, Qij, by solving two simultaneous nonlinear equations es follows. The relationship between inflow, Q~n, and pump pressure, can be determined empirically by ::.plotting PP VS. Qi for the inlet pump 4 for a range of pump )5000 speeds, (RPM). A family of curves was obtained for P. vs. j a over a range of pump speeds (RPM), and is schematically shown in Fig. 4. For a given RPM, and using a centrifugal inflow pump connected to fluid source 1 via conduit 2 of 0.25 inch ID and 90 inches long and made of PVC, the equation was determined to be: Pp B 0 81Q 2 B2Qin which can be rewritten as: Qn B JB 2 4Bi (B P) 2B 1 .0 using the assumption that Qin must always be positive.

In this equation, B 0 is the constant obtained at zero flow, which includes a component derived from the height of the fluiU source the bag of saline above the inflow pump 4.

As the speed of motor 4a is varied, the values for B n change, but the general function does not. By repeating this pressure vs. flow experiment for many different motor speeds, functions are determined for B n as functions of motor speed.

0 The speed of motor 4a (Fig. 2) can be determined by employing a feedback tachometer, but the actual motor speed is assumed S. to be a direct function of the pulse width modulation signal e 61 (Fig. 2) used to drive motor 4a to be described in detail hereinafter. The functions for each B n can be expressed as a function of RPM by: B f(RPM) S and RPM can be expressed as a function of the pulse width modulation signal, (PWM), by: r r i s -~rr RPM C.pWM Pressure transducer 11 senses the pressure of liquid in conduit 7 at a point between centrifugal pump 4 and the inflow cannula 9. The relationship between the inflow, Qin, and the pressure drop from the centrifugal inflow pump 4 to the transducer 11 can also be determined empirically by measuring PY (pump outlet pressure) and P. (sensed pressure) over a range of flow rates and fitting the resulting (Pp vs. Qjn data, such as schematically shown in Fig. 5, to an equation. Using a conduit 7 of 0.25 inch ID and ten feet long made of PVC, the function, was determined to be: Pp P= DjQn D 2

QL

which can be rewritten as: Qn =-D 2

JD

2 1 4D, (Ps -_PSI) 2D 1 on the assumption that Qin must always be positive.

Given the sensed pressure, and the pulse width modulation signal, (PWM), cavity pressure, Pct is calculated in the following manner: a) Given PWM, calculate RPM from equation b) Given RPM, calculate B. from equation c) Given B n and solve equations and for the two unknowns, Qjn and P.; d) Given P 3 An and Qin, calculate Pc from equation Pressure signal processor 13 may be provided with any suitable algorithm to solve equations and for unknowns Pp and Qin. Suitable algorithms are commercially available.

Equations and are solved using appropriate software routines of a conventional nature.

Pressure signal processor 13 then generates a signal corresponding to the body cavity pressure, Pc, which is sent via lines 32 and 32a to the input of pressure controller and via lines 32 and 32b to a pressure display 5b on the face of fluid management unit 5 (Fig. Processor 13 can gener- LO ate a signal representing the flow rate, Qj, of liquid into the body cavity, which can be sent via line 33 to a display on unit 5 showing the inflow flow rate. If desired, inflow, Qin, can be integrated over time to estimate the total volume of liquid infused and the result displayed on unit 5 (not shown), so that the physician can monitor liquid usage and avoid unexpected depletion of the liquid supply. Since the pressure is maintained within narrow limits, QL, can be accurately measured.

Pressure controller 40 compares the set pressure signal applied via line 31 and the calculated body cavity pressure signal applied via line 32a and generates a signal representing a pump speed necessary to raise or lower the calculated body cavity pressure to equal the set pressure. Pressure controller 40 thus sets the speed of motor 4a of centrifugal pump 4 and therefore the output from pressure controller 40 at Sany given time represents the actual speed of the pump 4 at that time. This pump speed output signal is supplied via lines 41 and 42 to an input of pressure signal processor 13 so that the processor 13 can select the constants B n of equation using equation That is, processor 13 can be provided with equation for constants Bn as a function of RPM.

Cavity pressure Pc can then be calculated using the method described above.

A different and presently preferred method used to calculate cavity pressure, Pc, eliminates the need to calculate Qin from Pp and the pressure drop caused by conduit 7. Instead, the pressure vs. flow characteristics of the inflow pump 4 and conduit 7 are lumped together and empirically determined as a single component; therefore, Qin can be determined directly from The pressure vs. flow characteristics of the inflow cannula assembly 9 are as described previously in equation Pc Ps A 1 Q A2Qn Since P, is measured, and An are predetermined empirically, Pc can be calculated, knowing Qin.

26 To calculate Qjn, the pressure vs. flow characteristics of inflow pump 4 in communication with conduits 2 and 7 from fluid source 1 to the point of pressure measurement by trans- S ducer 11 were determined empirically over a range of speeds of motor 4a. This empirical pressure vs. flow relationship was accurately fit with the following function: E EQn E 2 Q which can be rewritten as: Qjn =E 4E, (Ps 0 2E, As described above the functions for each Bn can be expressed as functions of RPM by: and RPM can be expressed as a function of the pulse width modulation signal, (PWM), by: (12) RPM C- PSM Although the value for C in equation (12) is the same as the value for C in equation f 6) the values for En derived frck equation' (11) are not the same as the Bn values derived from equation Given the sensed pressure, and the pulse width modulation signal, (PWM),I body cavity pressure, Pt,, is calculated in the following manner: a) Given PWH, calculate RPM from equation 7'2; b) Given RPM, calculate En from equation 3.1; c) Given En and P. calculate Qin from equation 10; and Given Pat An and Qin calculate Pc, from equation 2.

Equations and1 (12) can be solved using appropriate software routines of u convefrkional mature, AND gates 60a and 60b (Fig. 2) are software conditional statements, but could be implemented,. in hardware, if desired.

To the input of AND gate 60a is applied the pump speed signal via lines 41 and 43. Unless an override signal is provided via line 52 at the other input of AND gate 60a, the pump s~,eed PWN signal is sent via line 61 to a variable speed pump motor 4a to-. raise or lower the pump speed so that it equals thq pump speed represented by the pump speed signal.

A fault contltion controller 50 is provided to generate an override signal if any of a number of system faults is detected. To the inputs 50a of controller 50 are applied signals representing faults such as excessive body cavity LO pressure, excessive inflow, sensor failure, etc. Controller generates a fault signal in a conventional manner, which is sent via lines 51 and 52 to the AND gate 60a and via lines 51 and 53 to the AND gate 60b associated withi the suction pump 18. The presence of a fault signal at the input of gates and 60b provides a pump OFF signal as the output of gates and 60b that will shut down motors 4a and 18a of centrifugal inflow pump 4 and suction pump 18, respectively.

Gates 60a, 60b, processor 13 and controllers 40, 50 are preferably provided by a midcroprocessor.

z0.:~.Tool 15 and tool control unit 21 are preferably provided S by the PS 3500 motor drive and PS 3500 EP control unit, respectively, available from Smith Nephew Dyonics Inc., Andover, Massachusetts. Tool 15 will thus contain a motor, a coupler for accepting a desired surgical blade and an internal passageway for the flow of liquid from the surgical site through the blade an~d tool to the conduit 16 and thence to suction pump 18. Tool control unit 21 contains a power source and a controller for the tool motor. As is known, the DYONICS PS-3500 control unit stores the ranges of tool motor speeds suitable for each of the DYONICS surgical blades that can be used with the DYONICS PS-3500 motor drive, and automatically displays this range to the surgeon on displays 6b (Fig. 1) after the blade is inserted into the PS-3500 motor drive. The surgeon selects a blade speed within this range by operating selector 6a (Fig. See United State3 Patent 4,705,038, issued November 10, 1987.

Control unit 21 generates output signals representing the blade selected the speed of the tool motor, the signals being sent via line 23 to lines 23a and 23b (Fig. respectively, and thence to suction pump controller 70. This information is processed by the suction pump controller 70, which sends an output signal representing the desired suction pump motor speed via line 70a to AND gate 60b. If the tool motor is OFF, the suction pump motor may be OFF or run at a low speed, such as up to about 200 RPM. If the tool motor is ON, 2Q depending on the blade selected, the suction pump motor speed will be in the range of about 500 to about 4,000 RPM. The suction pump motor speed signal is sent by AND gate 60b to pump motor 18a via line 70b, unless a fault signal has been applied to the input of gate 60b by line 53.

No feedback loop is provided for motor 18a. The outflow rate of liquid is solely a function of the blade used in tool _ILI 1 and whether the motor (not shown) of tool 15 is running or idle.

A manual override selector 71 is provided to enable the surgeon to override controller 70 to select a low, medium or high speed for motor 18a for different outtlow scenarios.

Fault condition controller 50 will also override controller by sending a fault signal via line 53 to an input of AND gate which will shut down pump motor 18a, as described above.

Figs. 6 and 7 show an operative cannula 9a and irrigation extender 9b that snap together to form the inflow cannula assembly 9 illustrated in Fig 8. Operative cannula 9a has a needle portion 91 terminating in distal end 92. Bores 93a and 93b are-bealed by seal 94, which when opened by seal piercer 95 (Figs. 7 and 8) of extender 9b, allows fluid to flow through the cannula assembly 9 into body cavity Extender 9b is provided with bore 96 that receives the proximal end 97 of cannula 9a. Latch 104 snaps into groove 98 i of cannula 9a to hold the inflow cannula members 9a, 9b to- S: gether. Seal 94 (Fig. 6A) has opposed faces 94a, 94b formed of an elastomer with transverse slits 94c, 94d formed therein and an outer mounting ring 94e. Seal 94 may be formed using a S removable insert between the faces 94a, 94b. Seal piercer passes through slits 94c, 94d to open the seal; the seal 94 being resealed when extender 9b is uncoupled from cannula 91.

Extender 9b is provided with a rotatably mounted inlet 99 that communicates with the interior bore 99a via inlet bore I- 99b and apertures 99c. When endoscope 8 (Fig. 8) is inserted into the inflow cannula assembly 9, inflow liquid flows through bore 99b of inlet 99 and exits distal end 92 via apertures 99c and the annulus 99d between the tube 91 of cannula 9a and the endoscope 8.

Endoscope 8 may be secured to extender 9b by a bayonet lock (not shown) using post 99e to facilitate locking of the extender 9b to endoscope 8. Endoscope 8 is a conventional endosccpe having eyepiece 8b, light transmitting optics 8c and .0 light inlet 8d.

Referring to Fig. 9, a piezoresistive bridge pressure transducer 11 is carried by connector 100. Commercially available transducers can be used if modified to use bioccapatible materials. Connector 100 is formed of a front portion 101 and rear portion 102. Front portion 10 has an internal bore 103 for receiving the inflow inlet 99 of extender 9b, which is held in place by the spring-loaded latch 104 being inserted into groove 98 in inflow inlet 99. Insertion of inflow inlet 99 into bore 103 will also open spring- 0 loaded valve 101a in front unit 101. Rear unit 102 is provided with a stepped bore 104a, 104b connected by shoulder 104c. Transducer 11 is glued to the underside of unit 102 with bore 105 in unit 102 in liquid communication with bore lla in transducer 11 such that liquid flowing through conduit 7 will fill bores 105 and lla to come into direct contact with Ssensing diaphragm llb of transducer 31. Bores 105 and lla are

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of small diameter, such as about 0.04 inches, and diaphragm 11b is hence in contact with a small column of liquid that is at the same pressure as the inflow liquid. Transducer 11 transmits a voltage signal corresponding to the pressure, P., sensed by diaphragm 1lb to processor 13 via line 12.

Of course, pressure transducer 11 can be located anywhere between the pump 4 and body cavity 10, with the body cavity pressure being calculated as described above. If the transducer 11 is located at the pump 4, then only the pressure drop .0 between the pump 4 and cannula tip 92 need be taken into account.

Alternatively, A pressure sensing tube (not shown) may be used, communicating at one end with the body cavity 10 or witil conduits 7 or 16 immediately outward of body cavity 10 and utilizing air as the pressure transmission medium, as is known. See, DeSatnick et al. U.S. Patent 4,650,462.

Other pressure sensors may also be used.

In Fig. 10, outflow cannula 14 is shown assembled to blade 15a of a surgical tool 15. Outflow cannula 14 is pref- 0:6o erably identical to the operative cannula 9a and has a luer .i taper 14a in bore 14b and a double lead scrv 14c at its proximal and 14d. Blade 15a has a complementary luer taper 15b and double lead thread 15c so that blade 15a can be sealingly fastened to the cannula 14. Tubular portion 15d opens and passes through seal 94. Blade 15a is operatively connected by shank 15e to a tool 15 (Fig. Suction applied by suction pump 18 will aspirate fluid from body cavity through the tubular portion 15d into tool 15. Fluid exits tool 15 via outlet 15f (Fig. 1) into conduit 16.

Figs. 11-15 describe a disposable pump cassette 200 containing the centrifugal inflow pump 4 and a gear pump 18 serving to aspirate fluid from body cavity 10. Pumps 4 and 18 are housed in plastic housing 201 having recesses formed therein during the molding of housing 201 to provide a centrifugal pump chamber 202 (Fig. 12), and an inlet conduit 203 LO and an outlet conduit 204 connected between the centrifugal pump inlet 205 and outlet 206, respectively, and chamber 202.

Centrifugal pump impeller 207 is received in chamber 202 and is secured to plastic shaft 207a. Impeller 207 is made of plastic and is provided with curved vanes 208 formed during the molding of impeller 207. Impeller 207 is cemented to plastic spacer 209 and electroless nickel-plated low carbon steel cross-member 210 (Fig. 13). The widths of the arm 210a and hub 210b are empirically determined to maximize the torque i imparted to the impeller 207. Impeller assembly 207, 207a, 0 208, 209, 210 is spaced from the bottom 201a so that it may freely rotate.

Motor Aa is provided with plastic member 301, magnets 302 and iron cross-member 303 that are assembled together and are rotated by shaft 300. Motor 4a is secured to housing 305, which is contained within fluid management unit 5. Magnets 302 are magnetically coupled to the iron cross-member 210 such that impeller 207 will rotate at the same speed as plastic disc 301 when motor 4a is operated to rotate shaft 300 and disc 301.

Suction pump 18 is a displacement pump provided by gears 2111 212. Driving gear 211 is carried by a rotatable plastic rotor 211a (Fig. 14) cemented to plastic spacer 209 and assembled to iron cross-member 210 in -the same manner as described above. Driven gear 212 is rotatably mounted in housing 200 by providing a suitable recess for receiving the gearshaft of 11O gear 212.

Housing 201 has recesses therein formed during the molding thereof to provide a cavity 213 for receiving the rotor assembly 211a, 209, 210, a cavity 21!b for receiving gear 211 and an inlet conduit 214 and outlet conduit 215 connected between the suction pump inlet 216 and outlet 217, respectively,, and cavity 211a. Rotor assembly 211a, 209, 210 is spaced from bottom 201a so that it may freely rotate. Shaft S 300 of motor 18a, which is supported on member 305 within fluid management unit 5, carries the disc and magnet assembly 301, 302, 303, so that operation of motor 18a causes rotor 211a and gear 211 to rotate, thereby rotating the meshing gear **212. Fluid is pumped out of outlet 217 by the displacfiment too:% *0 pumping action of gears 211, 212.

*6 Housing 201 is closed by cover 200b, which is in liquidsealing engagement with 0-rings 221 and 222 (Fig 11). Bottom 201a sealingly engages 0-ring 223 (Fig. 12).

The apparatus of an embodiment of the present invention may be operated as follows. Inflow cannula assembly 9 and outflow cannula 14 are inserted into the body cavity 10, endoscope 8 is inserted into body cavity 10 via inflow cannula assembly 9 and conduit 7 is connected between fluid management unit 5 and the inlet 99 of extender 9b. If the surgeon intends to examine the site before inserting tool 15 into cavity 10, then outflow conduit 16 is preferably connected directly between fluid management unit 5 and outflow cannula 14. In such a case, the appropriate speed for pump 18 is determined by manual override 71.

Otherwise, outflow conduit 16 is connected between fluid management unit 5 and the outlet 15f of tool 15 as shown in Fig. 1. In either case, the desired pressure in body cavity 10 is maintained by the feedback loop described above, while the outflow flow rate is determined independently of the pressure in body cavity 10 by the nature of the blade in tool 15 and the speed of the motor in tool Set pressure generator 30 is then operated to select a pressure suitable for the surgical site. For example, the selected pressure may be within the ranges set forth below: Surical Site Pressure Rane (mmHg) Ankle 80-150 Knee 35-90 S"Shoulder 80-150 Wrist 30-80 User defined <150 Fig. 16 illustrates a presently preferred embodiment in which some of the elements shown in Figs. 1 and 2 have been eliminated and/or replaced. In particular, the suction pump 18 has been eliminated from the cassette 200, and the suction pump motor 18a and its associated controls have likewise been eliminated. Other modifications have been made to the system shown in Fig. 2, as will be discussed hereinafter. Those elements from Fig. 2 that have been retained are illustrated in Fig. 16 using the same reference numerals as used in Fig.

2.

Referring to Fig. 16, the outlet of tool 15 is connected 0 via tubing 16, 20 and waste containers 401, 402 to a source of suction 403, such as wall suction, whereby liquid may be aspirated from body cavity 10. Connected between the ends of tubing 16, 20 is a length of tubing 400 carried by cassette 250 (Fig. 17). A normally closed pinch valve 500 (Figs. 19A, 19B) restricts the flow of liquid flowing through tubing 16, 9 20 by the degree to which the tubing 400 is pinched or crimped. Pinch valve 500 may be set to provide no flow of liquid in its "closed" position or a nominal flow of liquid, as desired. Pinch valve controller 404 will process the 0 output signals in lines 23a, 23b representing the blade selected for tool 15 and the speed of the tool motor and will generate an output signal 405 representing the desired degree of opening of the pinch valve 500, which in turn permits the desired rate of flow of liquid through tubing 400 and tubing 16,20. Output signal 405 will be applied to pinch valve 500 by AND gate 60b via line 70b unless a fault signal has been applied to the input of gate 60b by line 53. Manual override selector 71 allows the surgeon to override the pinch valve controller 404 to select the desired degree of crimping of tubing 400 by pinch valve 500 to thus obtain low, medium or high outflow flow rates through tubing 400 and tubing 16,20.

Suction source 403 aspirates liquid from joint 10 into waste containers 401, 402 connected in series. A suitable number of containers 401, 402 is provided to accommodate the predicted volume of waste liquid. Suction source 403 may be 0 hospital or office wall suction or a stand alone wateraspirator or the like.

Fig. 16 shows that the pressure transducer 257 is upstream of the body cavity 10. As will be described hereinafter, pressure transducer 257 (Fig. 18) is located at the outlet of centrifugal inflow pump 4.

The speed of motor 4a is determined by tachometer 406 and this information is provided via lines 42a and 42b to motor speed controller 407, which also receives the pump speed signal via line 61. Motor speed controller 407 compares the 0 desired motor speed signal to the actual motor speed signal sent by the tachometer 406 and sends a signal to motor 4a via line 42c representing the pump speed necessary to raise or lower the calculated body cavity pressure to equal the set pressure. The motor speed signal is also fed back by tachometer 406 to an input of pressure signal processor 13 via lines 42a,42d.

i; The presently preferred embodiment of pressure signal processor 13 used in Fig. 16 employs a simplified version of the pressure signal processor described earlier. First, rather than estimating the pump speed using the P signal as described above, the pump speed is monitored directly from the tachometer 406 feedback signal, TAC, sent via line 42d.

Second, the need to calculate the flow rate, Qjn, from equations and or from equation (10) was eliminated, thius significantly reducing the time for processor 13 to L0 calculate the estimated body cavity pressure, PC* This was accompJJ~shed by using a direct relationship between the flow related pressure drop, P 1 upstream of the sensor 257 to the fiuid source .1 and the flow related pressure drop, P 2 to downstream of the sensor 257 to the cannula tip 92.

*Another simplification was made because it was to.

empirically determined that, for a given centrifugal pump design, the coefficient B 0 in equation 4 and K 0 in equation were strictly dependent on TAC and the height of the fluid supply 1 above the pump 4, but were not dependent on flow.

The remaining variables B 1 BV, Ej# and E 2 were actually constants that were dependent only on the design of the tubing 2,7 and cannula 9. Since the design of the tubing, cannula arnd pump are fixed, so will be the associated variables, B 1 1

B

2 1 Ej, and E 2 The variables B 0 and E 0 described previously are dependent on the height of fluid source I above pump 4, the pump speed, RPM, and the design of the centrifugal pump 4.

Therefore, since the pump design will be fixed and the pump speed is measurable, the height of bags 1 above pump 4 must be either fixed or a measurable variable. Since the presently preferred embodiment fixes the height of fluid supply bag 1 at two feet above pump 4 (45 mmHg), the processor 13 software contains the variable Po (bag offset) preset to a constant of mmHg, but the bag height offset may be used as a variable input with appropriate change in the processor software.

0 Given a fixed centrifugal pump design, the peak pressure that the centrifugal pump can generate with no flow through it is a function of tachometer speed, TAC, by: PZ f(TAC) Gi(TAC) 2

G

2

(TAC).

The peak sero flow pressure that the system can generate is also dependent on the fluid supply bag offset, Pg; therefore the total zero flow pressure, Pt, that the system can generate is defined by: Pt PZ Po.

The pressure drop upstream of the sensor, P 1 across the 0 tubing 2 and centrifugal pump 4, is related to the flow oo through them by, P. -PQ HQin 2

H

2

Q

where P, is the sensed pressure, and Pt is the total zero flow pressure described earlier. Equation C is the same relationship as equation 9 where PI=E0, Hi=El, and H 2

-E

2 The values for H i and H 2 are dependent on the placement of the d I pressure sensor 257 in the outflow path of the centrifugal pump, the geometry of the centrifugal pump, the geometry of tubing 2 and the size of the spikes (not shown). Because the entire inflow tube set 2 and pump 4 are manufactured under tight tolerancing, it has been found that the values for H, and H 2 do not change significantly from assembly to assembly.

Therefore the following pressure conversion algorithm can apply to any such pump and inflow tubeset assembly as long as the values for A 1 and A 2 in equation 1 and H, and H 2 in .0 equation C are not significantly changed from setup to setup.

The pressure drop, P 2 downstream of the sensor across the tubing 7 and cannula 9, is related to the flow through them by equation D, which is the same as equation 1:

P

2 Pe-Pc AlQin 2

A

2 Qin P. is the sensed pressure, and PC is the pressure at the distal end 92 of the cannula 9. The constants A, and A 2 are dependent on the size of the tubing 7 and the size and design of the arthroscope 8 and inflow cannula 9, and therefore care must be taken so that variations in design or manufacturing of 0 the different components do not significantly affect the overall pressure vs. flow relationship, equation D, over the desired ranges. If changes do occur, then processor 13 will be provided with software that will update the processor with the differont constants A, and A 2 Although this is not the presently preferred embodiment, If one were able to directly measure both the flow rate, Qtn, and pressure, then PC could be estimated from equation 2 directly, PC Pe AIQin 2

A

2 Qin" Alternatively, the total pressure drop through the syntex, (Pt-Pc) could be used, which equals P 1 .lus P 2 and can be represented as, Pt-Pc=(Al+Hj)QLn 2

(A

2

+H

2 )QLn in which case only the flow rate, Qi,, would be needed to estimate body cavity pressure, Pc, because P. is known as a function of TAC. This was not implemented due to the high cost of using both a pressure sensor and a flow sensor in the system, and because a means was found to estimate the flow, Qin, from the known characteristics of the centrifugal pump and tubing 2,7.

S The presently preferred embodiment effectively estimates the body cavity pressure, Pc, by calculating the pressure drop downstream of the pressure sensor, P 2 from the measured pressure drop upstream of the pressure sensor, P 1 This is possible because since the flow through the bag 1-tubing 2- 2q pump 4 and the flow through the tubing 7-cannula 9 are the So* same, there must be a direct relationship between the pressure drop across the bag 1- tubing 2- pump 4, PI, and the pressure *o Se drop across the tubing 7- cannula 9, P 2 Since P 2 is a function of flow, Qj., and P 1 is also a function of flow, Oin, then P 2 must be a function of P, by the relationship

P

2 -k(Pj) which can be predetermined and stored in the program memory for processor 13.

Pressure signal processor 13 receives a pressure signal, Ps, from pressure transducer 257 via line 12. Pressure signal processor 13 scales pressure signal P, to obtain a pressure value in units of mmHg pressure P,(mmHg)P,/16.

Pressure signal processor 13 also receives a tachometer signal, TAC, from tachcmeter 406 from line 42d. Pressure signal processor 13 calculates the zero flow pump pressure, Pz, using equation A, PZ f(TAC) GI(TAC) 2

G

2

(TAC)

and then calculates the total zero flow pump pressure, Pt, 0 using equation B, where P 0 is the known height of bag 1 above *.0 I pump 4: Pt PZ+P0 GI(TAC) 2

G

2

(TAC)+P

0 By definition Pi is the pressure drop upstream of the pressure sensor, as described by equation C, Pi" Pt-P,(mHg).

From equation D, P 2 -P-Pc, and from equation F, joint pressure *4.

Pc can be defined in terms of the calculatable pressure drop PI by, Pc-P,-k(P 1 which can then be sent via 32a to be represented in pressure display Pressure signal processor 13 also communicates with pressure controller 40 via lines 32 and 32b. Pressure controller 40 receives the values for P 1 fro pressure signal processor 13 and calculates the total pressure drop, Pd, through the pump, tubing and cannula by, Pd PI+P2 Pi+k(PI)" A running average of 16 calculations per second of Pd is maintained to filter out turbulent noise from the motor 4a.

From equation E and knowing the desired set pressure, P,,t, pressure controller 40 calculates the required peak pump pressure, P 1 z, to overcome the total pressure drop, Pd, through the system by, z= P.t Pd PO Because a centrifugal pump cannot produce negative pressures,

P

z is bounded to positive values. The TARGET tachometer speed is calculated by solving equation B for TAC, which can 0:99 be written as *oo.

.00.

TAC

1 TARGET G 1 1G 1 4G 1

P

1 2G 2 :Since Pl z is known from equation I, equation J can be solved for TARGET. The TARGET pump speed is then sent to the motor speed controller 407 via lines 41 and 61. If TARGET is more than 100, then pressure controller 40 produces a TARGET signal equal to 100, to maintain a maximum pump speed of 4000 RPM, since for the motor 4a used RPM-40 TAC.

It is presently preferred to solve equations A and I by means of a lookup table stored in memory listing values of Pz and their corresponding TAG values.

To summarize, processor 13 and pressure controller 40 calculate the TARGET speed of motor 406a and hence the speed of pump 4 using as inputs the motor speed, TAG, the sensed pressure, Ps, and the set pressure, based upon the pressure drops upstream of the sensor to the fluid supply and downstream of the sensor to the inflow cannula tip.

In the preferred embodiment described, motor 4a is a brushless, three-phase DC motor, obtained from BET KLMCO Magnetics Division, San Marcos, California, Part No. DIN? 23-20-BBNB, controlled by a microprocessor. While conventional microprocessor controls can be used, it is presently preferred to use the brushless motor control system described hereinafter.

Cassette 250 is shown in Fig. 17 in its vertical position as viewed from the rear. For clarity, the front and rear covers 262, 263 (Fig. 18) have been omitted from Fig. 17.

Cassette 250 is made of molded plastic and houses the centrifugal inflow pump 4 disposed vertically, rather than horizontally as in cassette 200 (Figs. 11-12).

Centrifugal inflow pump 4 in cassette 250 is identical to centrifugal inflow pump 4 in cassette 200.

to 0 00.

Within cassette 250 is pump chamber 202 and inlet and outlet conduits 203, 204 connected between pump inlet 205 and pump outlet 206, respectively, and chamber 202. Pump 4 is composed of elements 207-210 as described before and is driven by motor 4a and its elements 300-303 as described before, except that the motor 4a is mounted horizontally, (not shown) in motor support 280 (Fig. 18). Motor 4a drives pump 4 in the cassette 250 in the same manner as described above. Rear cover 263 of the cassette 250 (Fig. 18) has an aperture (not shown) to allow the horizontally mounted motor 4a to be closely adjacent the wall portion 250a (Fig. 17) and hence adjacent to pump 4.

Cassette 250 is provided with a thin, flexible diaphragm 251 suitably made of silicone rubber that closes the open end 252 (Fig. 17A) of chamber 253. Flexible diaphragm 251 is securely held in place by clamp 254 by locking the legs 255 into slots 256. Rear cover 263 (Fig. 18) has an aperture 263a exposing the clamp 254 and diaphragm 251. A best seen in Figs. 17 and 18, a tap hole or channel 204a in outlet conduit 204 permits liquid under pressure delivered by pump 4 to enter chamber 253, thereby exerting a pressure on diaphragm 251 equal to the output static pressure of pump 4, which is inversely related to flow through conduit 204.

Cassette 250 is mounted vertically on the outside of fluid management unit 5 by means of brackets 270, 271 (Figs.

18, 19A, 19B) such that the rear cover 263 of cassette 250

L,

rests flush against the unit 5f aligned by pins 264. Within unit 5 is a pressure transducer 257 (Fig. 18), whose pressuresensing element 258 is urged by spring 259 into contact with the diaphragm 251. The relatively small hole 204a and large chamber 253 filled with liquid and air tends to damp high frequency pressure variations of liquid delivered by pump 4 due to flow turbulence. The output of pressure transducer 257 is fed by wires 260 to the input of pressure signal processor 13.

Cassette 250 (Fig. 17) also includes a length of resilien~t silicone tubing 400 held between connectors 400a and 400b. Tubing 16 and 20, shown in phantom lines, connects tubing 400 to the tool 15 and the suction sourc~e 403 (via waste tanks 401, 402',, respectively.

Pinch valve 500 includes an arm 501 that is reciprocated between its normally closed position (Fig. 19A) and its fully open position (Fig. 19B) I by the linear actuator motor 502, which, in turn, is controlled by the pinch valve controller 404 and AND gate 60b, as described above. Thus, the normally a? :9 closed, fully open and intermediate positions of arm 501 are determined by the blade selected for tool 15 and the speed of the tool motor. Linear actuator notor 502 is located inside the fluid management unit 5 with arm 501 extending out of the side wall of unit 5 as shown. While Figs. 19A and 19B show tubing 400 fully closed anid fully open, as discussed above, the "closed" and "open" positions may be less than fully closed or fully open, as desired. Rear cover 263 is slotted to allow the arm to freely move between its open and closed positions.

Before power is initially supplied to the motor 502, arm 501 is fully extended (Fig. 19B) to allow the cassette 250 to be inserted in position on fluid management unit 5. As cassette 250 is lowered into place onto brackets 270,271, tubing 400 will fit behind the fin~ger 501a. A pair of alignment pins 264 on fluid management unit 5 are arranged to fit into recesses 265 in rear cover 263 when cassette 257 is in its proper position. (Figs. 19A, 19B). After the cassette 250 is snapped in place, the tubing 16, 20 is connected. Whlen power is supplied to the fluid management unit 5, motor 502 V0.moves arm 501 to its normally closed position.

havingFig. 20 shows a disposable operative cannula 600 too haingbody portion 601, opposed proximal and distal ends 602,603, and internal bore 604 extending from end to end. The ::body portion 601 is provided with spaced apart, external circumferential ribs 614. Sealing members 605,606 which are suitably made of silicone rubber, are securevd to proximal end 602 to seal the bore 604.* Member 605 has a circular aperture '~605a therein for sealingly engaging a tool, such as a powered shaver, inserted into cannula 600. Member 606 has sealing elements 606&t606b on either side of slit 606c. Slit 606c is shown as a straight slit, but Y-shaped slits ae. may be used.

Removal of a tool from cannula 600 or inserting a switching stick through cannula 600 from the distal end 603 to the proximal end 602 vill cause elements 606a,606b to flex toward member 605. Member 606 is therefore spaced distally of member 605 by a distance that prevents extrusion of elements 606a,606b through aperture 605a. Accordingly, since sealing elements 606a,606b are unsupported by member 605, they must be sufficiently thick to be stiff enough to withstand the back prassure of the liquid in cannula 600, suchias about 0.075 inches thick.

If desired, member 605 can-be provided with the slit and member 606 with the circular aperture (not shown). In such a case, the sealing elements 606a,606b must be spaced' Sfrom member 605 to prevent extrusion of elements 606a,606b i through aperture 605a when a tool is inserted into cannula 600.

Cannula 600 includes conduit 607 for aspirating liquid from cannula 600 or for supplying liquid to cannula 600. In either case, push valve member 608 will be pushed through fitting 609 from the closed position shown in Fig. 21 to its fully open position (not shown) in which transverse oo* bore 610 is aligned with bores 611,612 in conduit 607 and fitting 609, respectively. Cannula 600 is conveniently molded .*oooo from suitable plastics. Push valve 608 is suitably molded from silicon rubber, preferably with a hardness greater than Shore A 70. Push valve 608 is color coded such that the red r end 608a is showing when valve 608 is closed, and the green end 608b is showing when valve 608 is open.

Cannula 600 desirably includes a circular groove 613 formed in circular body portion 601 near the distal end 603.

If the surgeon desires a shorter cannula 600, the body portion can be cut through the groove 613 leaving a shorter cannula having a tapered tip.

Fig. 22 shows a diagnostic cannula 700 having a body 701 and a rotatably mounted inlet 702 that communicates wxtb the LO internal bore 703 via inlet bore 702a and apertures 702b.

Diagnostic inflow cannula 700 is different from inflow cannula assembly 9 -described earlier. Without extender-9b, cannula 700 permits the surgeon to reach deeper into the surgical site, whica is helpful specifically for shoulder arthroscopy.

Although different in application, cannula 700 and cannula assembly 9 have identical pressure vs. flow characteristics, as is required for pressure signal processor 13.

For portal interchangability, cannula 600 is available with an inner diameter suitable for inserting inflow cannula 700 through cannula 600. For example, an endoscope may be first inserted and locked into cannula 700 and remain assembled throughout the surgical procedure. If the surgeon has two operative cannulas 600 in place in the body, one can be used for a tool 15 ard the other for the inflow cannula 700. The inflow cannula 700 and endoscope assembly is inserted through sealing members 605,606 until the distal end Ir~l CI LI 703 of body 701 abuts the seal member 605. Push valve member 608 is moved to the closed position. Inflow liquid flows through bore 702a and exits tube 704 through apertures 702b and the annulus between the endoscope and the tube 705. The fluid and operative debris within the surgical site is removed either through the suction adapter on the surgical tool, or can be removed through conduit 607 of operative cannula 600 being used with the surgical tool, in which case push valve member 636 is moved to the open position.

.0 Fig. 23 shows a modified distal tip for the operative cannula of Fig. 20. Thus, the cannula 600 of Fig. 20 has a tapered distal end 603, with internal bore 604 extending through body 601 from the proximal end 605 to and through the distal end 603. In Fig. 23, however, cannula 600 terminates in the distal end 603a which has a tapered obturator tip 603b S closing the internal bore 604. Liquid exits internal bore 604 via apertures 603c spaced circumferentially about body 601 just upstream of obturator tip 603b. With this modified S distal end 603a, the cannula 600 acts as its own obturator and 0 can be directly advanced through the body without the use of a separate obturator.

Fig. 24 shows a further cannula 800 having a body portion 801 with external ribs 802. An internal bore 803 extends from S the proximal end 804 through the body portion 801, with tapered obturator tip 805 closing the bore 803. Liquid exits internal bore 803 via apertures 806. Cannula 800 is made of 35 suitable plastic and can also be advanced into the body without the need for a separate obturator, Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

4 4 4 .oo• 4 4 .4 4 4 44.4 9. 4 44* *4 S 4.4.

oo 4 4 .go4 *c r A* f 9SS~j~aka4i~fl.ISOM~

Claims (10)

1. A cannula comprising a body portion having an internal bore extending therethrough and opening to the exterior at a proximal end and at a distal end of the body portion, elastomeric sealing means disposed at the proximal end for sealing the respective opening when in a normally closed condition and being deformable to open the interior bore to the exterior at the proximal end, a further opening from the interior bore to the exterior between the distal end of the body portion and the elastomeric sealing means, and a valve member in said further opening which is displaceable between a closed condition and an open condition, 10 said valve member being adapted to permit fluid flow into and from the internal bore through said further opening in its open condition.

2. A cannula as claimed in claim I wherein said sealing means comprises opposed, spaced apart, first and second substantially planar sealing members, said first sealing member 15 having a substantialy circular aperture therein and said second sealing member having a slit therethrough.

3. A cannula as claimed in claim 2, wherein said second sealing member is spaced distally of said first sealing member by a distance that prevents extrusion of portions of said second sealing member through said aperture of said first sealing member when a tool is moved thiough said sealing members toward the proximal end of said cannula.

4. A cannula as clairi ed in claim 2, wherein said first sealing member is spaced distally of said second sealing member. A cannula as claimed in any one of the preceding claims, wherein a distal part of said body portion is circular in cross-section and has an external circular groove formed therein near said distal end.

6. A cannula according to any of the preceding claims, further comprising a tapered ^r o 1 (1i t 1111211411 '1 18 I -37- obturator tip at said distal end which axially closes said internal bore, and wherein aperture means are provided in said body portion adjacent said obturator tip for permitting fluid flow therethrough to and from said internal bore.

7. A cannula as claimed in claim 6, wherein said aperture means are circumferentially spaced openings in said body portion.

8. A cannula as claimed in any one of the preceding claims, wherein said body portion has a main body portion comprising said proximal end and a needle portion comprising said 10 distal end,

9. A cannula as claimed in any one of the preceding claims wherein the valve member is a push valve member which is manually actuatable from opposite ends to pro' the displacement between the open and closed conditions. A cannula as claimed in any one of the preceding claims wherein the valve member is moulded from silicon rubber.

11. A cannula substantially as hereinbefore described with reference to Figures 20, 21 and

23. DATED this 2nd day of December, 1997. SMITH NEPHEW DYONICS, INC. By its Patent Attorneys DAVIES COLLISON CAVE uj K .9 ~Vr Oy