WO1997010856A1

WO1997010856A1 - Devices for monitoring fluids removed by suction

Info

Publication number: WO1997010856A1
Application number: PCT/US1996/014770
Authority: WO
Inventors: Richard A. Pollock; Mahmood Kassam (Michael), S.
Original assignee: Pollock Richard A
Priority date: 1995-09-18
Filing date: 1996-09-16
Publication date: 1997-03-27
Also published as: AU7238696A

Abstract

Devices (10) for monitoring fluids removed from patients, such as in surgery. A load cell (30) automatically senses the weight of fluid in a conventional or a non-conventional canister (14) supported by the load cell (30). The load cell (30) outputs or modifies signals corresponding to such loads, which are received by a controller (34). The controller (34) computes values corresponding to weight and volume of fluid in the canister (14) and supplies signals corresponding to such values, including, if desired, cumulative values, to output for display (58), storage, or use by external devices such as through a serial port. The controller (34) is adapted automatically to tare the weight of the canisters (14) and loads imposed by flexible tubing (15) connected to the canisters (14), and automatically to 'hold' values corresponding to a liner (16) that has been removed (should it become full) so that the monitoring process may be resumed when a new, empty canister (14) is supplied.

Description

DEVICES FOR MONITORING FLUIDS REMOVED BY SUCTION The present invention relates to devices for monitoring the weight and/or volume of fluids removed from patients, such as surgical patients, via suction.

BACKGROUND TO THE INVENTION

Blood, saline irrigant. and other fluids encountered in the body cavities and wounds of patients are conventionally removed directly from the surgical site via suction. Such fluids are scavenged using suction tips and tubing which are connected to canisters or disposable containers which are, in turn, connected to a vacuum source. Conventionally, a central vacuum source is accessed via a port on the wall of the surgical suite by connecting tubing to the canister or disposable container. Accordingly, blood not absorbed by surgical (cotton or synthetic) sponges used in surgery or absorbed by the surgical drapes can be removed with the aid of such tubing and vacuum-driven canisters or disposable containers.

The conventional canister is clear and is graduated to indicate the volume of fluid in an inner liner. The inner liner is disposable and has two or more ports. Each port may be independently capped or alternately connected to tubing. The tubing from the primary port is connected to the vacuum source, while the tubing from the second port is connected to an appropriate suction tip of conventional structure.

The rigid, graduated outer receptacle and the less rigid inner liner in such systems are both at least partially transmissive to light, so that the fluid in the liner may be seen. The graduations on the receptacle allow the volume of fluid in the liner to be estimated. Typically, the calibrations mark 100 ml (or cubic centimeter) increments so that estimations may be made of fluid and blood product losses and consequent infusion needs of the patient. These canisters comprising the receptacles and liners may be located on a conventional floor stand or engaged by a wall-mounted frame. In either case, the canisters are typically an appreciable distance from the surgical field, usually ten to twelve feet away. The calibrations on the receptacles are small, and, coupled with the usual distance, difficult to read.

Additionally, fluid suctioned from patients often froths or foams so that actual volume of fluid in the liner is difficult to estimate. This problem is magnified by the fact that the volume of the liner differs from the volume of the outer receptacle, because the liner does not Other objects, features and advantages ofthe present invention will become apparent in the remainder of this document.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a preferred embodiment of a device according to the present invention.

FIG. 2 is a view ofthe load cell and surrounding portions ofthe device of FIG. 1. FIG. 3 is a functional block diagram of certain circuit components ofthe device of FIG. 1. FIG. 4 is a flow diagram showing processes carried out by the device of FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 shows a preferred embodiment of a fluid monitoring device according to the present invention. Device 10 generally comprises a stand 12 which is adapted to support one or more canisters (receptacles with liners) 14 which are in turn adapted to contain fluids suctioned from patients. Stand 12 may be of conventional design and construction, such as those provided by The Baxter Hospital Supply Division of Baxter Healthcare. Altematively, stand 12 may be a conventional wall mounted frame for supporting canisters 14 so that they are supported by a wall bracket rather than the sort of stand shown in FIG. 1. Canisters 14 are also of conventional design in the preferred embodiment. In that embodiment, they comprise a disposable liner 16 mounted within a clear receptacle 18. As shown in FIG. 1. receptacles 18 feature graduated lines 20 which may be employed to estimate the volume of fluid contained in disposable liners 16. Disposable liners 16, receptacles 18, and other portions ofthe canisters 14 may be conventional products such as those supplied under the Medi-vac® line offered by Baxter Healthcare. The disposable liner

16, for instance, may be a semi-rigid, single-use thin walled container that fits into the reusable, hard-plastic, clear outer receptacle 18.

The liner 16 preferably includes a lid 22 with at least one vacuum port 24 which may be employed to connect the liner 16 to a wall vacuum source (not shown) of conventional nature, common to operating suites. The vacuum port 24 may include filtering as desired in order to trap aerosolized microorganisms and/or particulate matter such as bone chips.

4 The load cells in the devices according to the present invention are preferably structured to be of a monolithic block or segment of metallic or other deformable material. rather than conventional hinge-type load cells. One advantage ofthe monolithic load cell is that it contains fewer moving parts and is thus less susceptible to spilled fluids and other wear and tear, as canisters or liners are continually changed out and discarded.

The load cells according to the present invention serve as accurate and efficient sources of signals corresponding to the weight that they support. Those signals are applied to controller circuitry which receives, stores, and processes them to compute the values that correspond to the weight and volume of fluid contained in the canister. Those values may be applied to a display and. if desired, to memory capacity and/or output ports for coupling to extemal devices.

The controller circuitry ofthe present invention is adapted to tare the difference between the constant load placed on the load cell by the canister and the weight of fluid within. Additionally, the controller circuitry is adapted to sense when a disposable container has been removed from the device and then to store values corresponding to volume of fluid in the disposable container and containers previously mounted on the device. The device may thus continue the monitoring ofthe (weight and) volume of bodily fluid suctioned from the patient when and if a new disposable is placed on the monitor device.

It is accordingly an object ofthe present invention to provide a system for increasing the accuracy and efficiency with which loss of bodily fluids from patients may be monitored. It is an additional object ofthe present invention to provide a system for monitoring loss of bodily fluids in which ports in the lid of the liner are employed to connect central wall suction and to attach suction equipment in decontamination rooms that evacuate the fluid prior to "red bag" disposal ofthe canister or liner with other contaminated waste. It is an additional object of the present invention to calculate patient fluid loss automatically and efficiently in an automated, electronic fashion.

It is an additional object ofthe present invention to provide devices, monitors, disposables and processes for monitoring, storing, and providing data corresponding to patient fluid loss by suction, which data may be displayed in milliliters as an aid to appropriate calculation of patient fluid infusion needs. tension, and the area on the lower portion of segment 36 will be under compression, with substantially no bending moment.

A conductive element, such as a conventional resistive element or strain gauge 42. may be mounted at or near any ofthe areas 38 of carefully controlled cross section and connected to controller 34. Such element 42. being of conventional design, and mounted to such area 38. is adapted to modify an electrical signal applied to the element when its area 38 is under a tensile or compressive load. Conventionally, the impedance of element 42 changes, but capacitance or any other electrical property as desired may be the factor that changes as the stress on the area underlying the element 42 changes. The output of element 42 may be applied to a conventional bridge circuit in the controller 34 so that the modified electrical signals from element 42 may be read by controller 34 and converted in conventional fashion to values that correspond to the weight and volume ofthe fluid and other components imposing a load on the load cell 30.

FIG. 2 shows a functional block diagram of the circuits that create a display featured on display 32 using the modified signals 44 from the elements 42. A driver 46 of conventional design applies a drive signal 46 as desired to load cell 30 (element 42). Driver 48 generates drive signal 46 using reference signal 50 which may be. among other things, a standard voltage, direct current signal. Modified signals 44 from the load cell 30 are coupled to a desired conventional signal conditioning, amplifying and analog-to-digital conversion set of circuits so that they may be received and processed by microcontroller 54. Microcontroller 54, using such signals, computes, stores, outputs, and sends for display as desired, output signals 56 which are a function ofthe load placed on a particular load cell 30. Display 58 may be a conventional LED. LCD or other display which receives such signals and creates a display 58 showing a value which is a function of such load, such as fluid volume. One display 58 may correspond to a particular load cell 30 as shown in FIG. 1. or one display 58. microcontroller 54, and/or other components may receive signals from any number of load cells 30 corresponding to various containers of bodily fluids, in order to monitor and track fluids in a number of containers collectively or partially collectively. Such signals may also be sent to an input/output port 60. such as a standard RS232 port, for output. Microcontroller 54 contains computer programming which allows it to tare out the weight of disposable liners 16. receptacles 18, other portions of canisters 14. and loads

6 Disposable liner 16 may also contain a shut off valve which prevents overflow. Disposable liner 16 additionally includes an intake port 26 which may be connected to surgical tubing that is used for suctioning fluid from the patient. Thus, the vacuum source, such as accessible on the wall, induces a vacuum into disposable liner 16 via the tubing that connects to vacuum port 24. That vacuum also induces fluid in the patient to be suctioned or scavenged into the tubing that is connected to intake port 26. Undesired contaminants are prevented from entering the vacuum source preferably by the filtering contained in vacuum port 24. Nevertheless, dessicants. astringents, solidifiers. powders or other chemicals or compositions may be present within the liner 16. All ofthe foregoing structure is conventional. Canisters 14 are typically connected in removable fashion to a conventional stand 12 via dovetail fittings 28. a portion of which are connected to the stand 12 and a portion of which are connected to the canisters 14. In the present invention, however, and preferably for each canister 14. a load cell 30 is attached to each of these portions ofthe dovetail fitting 28 so as to be inteφosed between a particular canister 14 and the stand 12. The load cell 30 is electrically connected to a display 32 and a controller 34 (which may, but need not, as shown in FIG. 1. be a portion ofthe same physical unit). Load cell 30 supports all ofthe weight of its canister 14 and its contents, together with any positive or negative loads imposed upon the canister 14 via the tubing 15 connected to canister 14. The load cell 30 is adapted to output or modify an electrical signal as a function ofthe load placed upon load cell 30 by the weight of the canister 14, its contents, and forces imposed by the tubing 15.

Controller 34 receives such signals, stores them and outputs them to extemal devices as desired, and provides them to create a display on display 32 that corresponds to the volume and/or weight of fluid in the canister 14, as described below.

Load cell 30 is preferably formed of a monolithic segment or block of metallic or other suitable deformable material 36. In the preferred embodiment, segment 36 has three holes bored in it transverse to the direction in which canister 14 will impose a load on segment 36. The bores are performed in order to create three areas 38 of carefully controlled cross section in a plane substantially parallel to the vector of such load (substantially, a vertical plane). Segment 36 includes appurtenances 40 for mounting to the dovetail fittings 28 contained on canisters 14 and stand 12. Thus, when a canister which contains fluid is supported by segment 36, the two areas 38 on the upper portion of segment 36 will be under until the reset button is pressed or the power is re-cycled. During the time when actual values are calculated and displayed, a periodic check is made for any request via the serial communication port. If a request is detected, the current displayed value is also transmitted out over the serial link to the requesting device.

The foregoing is provided for purposes of disclosure of a preferred embodiment ofthe present invention. Modifications, changes, deletions and additions may be made without departing from the scope or spirit ofthe invention.

applied by tubing 15. These values may be preset into microcontroller 54 at point of manufacture or through serial port 60 as desired. The tare process may also be accomplished manually by zeroing out the value displayed on display 58 with an empty canister 14 loaded and connected as appropriate to tubing 15. Any additional fluid accretion will then start the monitoring, storing and display processes from ground zero.

Additionally, microcontroller 54 is adapted to allow canisters 14 or disposable liners 16 to be changed out without requiring the operator to remember the total and then add it to what is displayed when a new canister begins to be filled. Instead, microcontroller 54 "remembers" or "holds" automatically the current value corresponding to the cumulative weight ofthe fluid in the canister 14 when it is sensed to have been removed by load cell 30.

The monitoring process is resumed when the new canister 14 or disposable liner 16 with lid 22 is put in place.

Logic flow for a preferred embodiment of systems according to the present invention is shown in Fig. 4. As shown there, during power-on or closure of reset button, the microcontroller goes through an initialization sequence to configure its environment. The initialization routine configures the input/output digital data ports; the serial communication interface; the analog-to-digital (A/D) converter; the auto-calibration mode; the multiplexed display module; the intemal interrupts; the intemal timer; and other RAM variables. Upon completion ofthe initialization sequence, the display shows " " indicating to user that the microcontroller is continuously updating the current load cell value and awaiting actuation of the start button. While the start button is not pressed, the microcontroller fetches current load cell value about every 300 milliseconds; it then updates the current baseline value (tare weight) by keeping a running average of sixteen prior input samples. Upon detection of start button closure, the display will read "0000" indicating the actual incremental value of the weight. Any positive change in weight as a result of fluid build-up, over and above the tare weight, will be registered on the display on a continuous basis. Post closure of the start button, the following sequence is executed: the current load-cell value is fetched (every 300 milliseconds); running average of sixteen prior samples is maintained; the actual value is calculated by subtracting the baseline value from the averaged current value; the actual value is scaled to represent the displayed digits in decimal mode as cubic centimeter (cc) volume, with the leading zeros suppressed; and the display is updated. This sequence is maintained 6. A device according to claim 1 in which the microcontroller is adapted to tare the weight ofthe disposable liner and adapted to monitor cumulative volumes of fluids.

7. A device according to claim 6 in which the microcontroller is adapted to tare the weight ofthe disposable liner and loads imposed by the tubing.

8. A device according to claim 3 in which the microcontroller is adapted to sense when a liner which contains fluid has been removed from being supported by the load cell and to store data corresponding to the weight ofthe fluid in the removed liner, thus to permit replacement of disposable liners without interrupting monitoring of fluids removed from the patient.

9. A device according to claim 1 in which the load cell comprises a segment of material which contains at least one bore substantially transverse to a direction upon which a load is to be placed upon the segment, thereby to create at least one area of controlled cross section, the area to be placed under compression by the load, and a resistive element connected to one ofthe areas and adapted to modify electrical signals applied to the load cell by varying its impedance corresponding to the deformation ofthe area and therefore to the load placed on the segment.

10. A device for monitoring volumes of fluid suctioned by vacuum from a patient. comprising: a. at least one disposable liner containing a first port adapted for connection to tubing which in turn is adapted for suctioning fluids from the patient and a second port adapted for connection to a vacuum source; b. at least one load cell adapted for supporting the disposable liner, comprising a segment of deformable material which contains at least one hollow portion created to form at least two areas of controlled cross section, the first of said areas to be placed under tension when the disposable liner is supported by the load cell, and the second of said areas to be placed under compression when the disposable liner is supported by the load cell, and an element connected to one of the areas, at least one electrical property of which element varies corresponding to the weight ofthe fluid in the disposable liner;

10

Claims

What is claimed is: I . A device for monitoring fluids suctioned by vacuum from a patient. comprising: a. at least one container supported by a load cell, which load cell is adapted to modify electrical signals in a manner that corresponds to the weight of the fluids contained in the container; b. tubing connected to the container and to a tip adapted to aid in suctioning fluid from the patient; c. tubing connected to the container and to a vacuum source ; d. a stand adapted to support the load cell; e. a microcontroller connected to the load cell and adapted to apply electrical signals to the load cell, sense modified signals from the load cell, and therefrom to compute the volume of the fluids contained in the container and create signals corresponding to said volume; and f. a display adapted to receive signals from the microcontroller and create a display corresponding to the volume of fluids contained in the container.

2. A device according to claima 1 further comprising a valve which is adapted to allow redirection of the applied vacuum source to at least one or more of the containers, avoiding thereby the need to disconnect the tubing.

3. A device according to claim 1 in which the container comprises a canister that in turn comprises a receptacle and a disposable liner within the receptacle.

4. A device according to claim 3 in which the container is supported by the load cell via the receptacle being connected to the load cell and adapted to receive the disposable liner.

5. A device according to claim 1 comprising at least two load cells and at least two containers. 16. A device according to claim 10 in which the disposable liners are at least partially transmissive of light in order to allow the fluid in the liners to be seen.

17. A device according to claim 10 in which the disposable liners are off-the-shelf suction liners.

18. A device for monitoring fluids suctioned by vacuum from a patient. comprising: a. at least one disposable liner supported by a load cell, which load cell comprises a monolithic segment of deformable material which contains at least one hollow portion created to form at least two areas of controlled cross section, the first of said areas to be placed under tension when the disposable liner is supported by the load cell, and the second of said areas to be placed under compression when the disposable liner is supported by the load cell, and a resistive element connected to one ofthe areas, the impedance of which resistive element varies corresponding to the weight ofthe fluid in the disposable liner; b. tubing connected to the disposable liner and to a tip adapted to aid in suctioning fluid from the patient; c. tubing connected to the disposable liner and to a vacuum source; d. a stand adapted to support the load cell; e. a microcontroller connected to the load cell and adapted to apply electrical signals to the load cell, sense signals from the load cell which have been modified by the impedance of the resistive element in the load cell, and therefrom to compute the volume of the fluids contained in the disposable liner and create signals corresponding to said volume; and a display adapted to receive signals from the microcontroller and create a display corresponding to the volume of fluids contained in the disposable liner.

19. A device according to claim 18 in which the microcontroller is adapted to tare the weight of at least one disposable liner and any additional load that is placed on its corresponding load cell other than by the fluid contained in the disposable liner.

12 c. a stand for supporting the load cells; d. a microcontroller connected to at least one load cell for receiving signals from the load cell which are a function of said varying electrical property of the element in the load cell, and creating signals therefrom corresponding to the volume ofthe fluids in the disposable liner; and e. a display adapted to receive signals from the microcontroller corresponding to the weight of the fluids in the disposable liner and to create a display which corresponds to said weight.

1 1. A device according to claim 10 in which the microcontroller contains memory capacity for storing data corresponding to weight and volume of fluid contained in at least one disposable liner.

12. A device according to claim 10 in which the microcontroller is adapted to create signals corresponding to the weight and volume of fluids in the disposable liner.

13. A device according to claim 10 in which the microcontroller is adapted to sense when at least one disposable liner has been removed from the device, store data corresponding to the weight ofthe fluid contained in said disposable liner, and continue monitoring the weight of fluid removed from the patient when a new disposable liner is suspended from the load cell.

14. A device according to claim 10 in which the microcontroller is adapted to tare the weight of at least one disposable liner and any additional load placed on the corresponding load cell other than by the fluid contained in the disposable liner.

15. A device according to claim 10 in which at least one disposable liner is supported by a load cell via a receptacle which is connected to the load cell which receptacle is adapted to receive the disposable liner. 20. A device according to claim 18 in which the microcontroller contains memory capacity for storing data corresponding to weight and volume of fluid contained in at least one disposable liner.

21. A device according to claim 18 in which the microcontroller is adapted to create signals corresponding to the weight and volume of fluid contained in the disposable liner.

22. A device according to claim 18 in which the microcontroller is adapted to sense when at least one disposable liner has been removed from the device, store data corresponding to the weight ofthe fluid contained in said disposable liner, and continue monitoring the weight of fluid removed from the patient when a new disposable liner is suspended from the load cell.