WO2009107012A1

WO2009107012A1 - Automatic physiologic fluid measuring device

Info

Publication number: WO2009107012A1
Application number: PCT/IB2009/050423
Authority: WO
Inventors: Larry Nielsen; Mohammed Saeed
Original assignee: Koninklijke Philips Electronics, N.V.
Priority date: 2008-02-29
Filing date: 2009-02-02
Publication date: 2009-09-03

Abstract

When monitoring fluid output from a patient, a bodily fluid container (BFC) (12) is coupled to the patient and suspended from a scale (16). The scale (16) takes periodic or continuous weight measurements and transmits them to a patient monitor or workstation (40). A preceding weight measurement value is subtracted from the current weight measurement value to determine a change in weight since the last measurement. If the weight change value is within expected physiological range, it is then automatically converted to a volume value using a known density for the monitored fluid. The volume value is compared to historical data, and, if it is outside of a predefined range of expected values, an alarm is triggered to alert a healthcare technician that the patient requires attention.

Description

AUTOMATIC PHYSIOLOGIC FLUID MEASURING DEVICE

DESCRIPTION The present innovation finds particular application in patient monitoring, particularly involving vital signs. However, it will be appreciated that the described technique may also find application in other medical scenarios or techniques.

Monitoring the patient's vital signs is one of the most important activities performed within a hospital environment. It is done several times a day on the lowest- acuity patents using indirect measurements, and continuously on the highest-acuity patients using modern patient monitors. Recent studies suggest that a complete clinical picture that includes laboratory tests in conjunction with vital signs, fluid input, urine output, and hemodynamic parameters is the best way to determine and monitor the status of trauma patients. The measurement of urine output is important because it provides an assessment of end-organ perfusion. If there is little or no urine being produced, it is assumed that the kidneys are not being perfused, and therefore, other major viscera are also probably not being adequately perfused. The measurement of fluid input is necessary to provide indication of adequate fluid balance. In spite of the importance of these measurements, they are measured infrequently and usually only when the patient is in trouble or is being discharged. The measurement is often estimated, or at best, crudely measured. Patient Inputs and Outputs (I/O) are rarely automatically measured.

Meticulous documentation of a patient's fluid I/O status is important in the ICU. In certain units, such as a neonatal or pediatric intensive care unit, this information is even more paramount than in a typical adult ICU. Unfortunately, without specialized interfaces, today's monitoring systems are not capable of automatically tracking fluid balance and I/O.

Certain hospitals utilize special interfacing technologies to automatically gather information from infusion pumps as well as urimeters. For example, Bard urimeters have a rigid plastic container (needs to be empted once/day), provides continuous volume measurement, and has an embedded thermister in the tip of the Foley catheter to provide continuous core temperature measurements. This system has proven to be cost-effective, labor-saving and has reduced the frequency of performing unclean procedures. The interface provides a continuous display of measured I/O variables and automates data entry for flow sheet documentation.

Although critical fluid output measuring devices are available, their use within hospitals is severely limited. An analysis of the hospitals using such a system shows that the need to use specially designed collection bags and/or containers on critical fluid output measuring devices is a key deterrent of employing such systems. Another is that it takes a very specialized and capable Bioengineering Support Staff within the hospital that is willing to handle the unique interfaces and attachments to patient monitoring systems. The relatively high cost of such systems is yet another deterrent.

The present application provides new and improved fluid measuring systems and methods, which overcome the above -referenced problems and others.

In accordance with one aspect, a fluid output monitoring system includes a bodily fluid container (BFC) that receives an output fluid from a patient and is supported by a scale or weighing means, a transceiver in a workstation that receives BFC weight measurement information from the scale, and a processor that determines a difference between a current weight measurement value and a preceding weight measurement, and converts the difference value into a volume value. The system further includes a vital signs database in which the volume value is stored if valid.

In accordance with another aspect, a method of measuring fluid output of a patient includes receiving a current BFC weight measurement from a scale that supports a BFC coupled to a patient, and determining a value for a difference between the BFC current weight measurement value and a preceding BFC weight measurement value. The method further includes converting the difference value into a volume value, validating the volume value, and storing the validated volume value.

In accordance with yet another aspect, a method of measuring fluid output of a patient includes coupling a BFC to a patient and to a scale, measuring a current weight of the BFC, and wirelessly transmitting a current weight measurement to a workstation. One advantage is that fluid I/O information is recorded automatically. Another advantage resides in time savings for nurses and healthcare technicians.

Another advantage resides in artifact reduction.

Another advantage resides in automatic invalidation of measured values that are inconsistent with historical fluid output trend data.

Still further advantages of the subject innovation will be appreciated by those of ordinary skill in the art upon reading and understanding the following detailed description.

The innovation may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating various aspects and are not to be construed as limiting the invention. FIGURE 1 illustrates a fluid output (FO) monitoring system that monitors fluid output in real time as a function of fluid weight.

FIGURE 2 illustrates another embodiment of the system, including components of the workstation.

FIGURE 3 illustrates a flow chart diagram of a method of automatically measuring and storing fluid output in a patient.

FIGURE 4 illustrates a method for monitoring fluid input to a patient, which may be performed in parallel with the method of Fig. 3 to perform fluid I/O calculations.

FIGURE 1 illustrates a fluid output (FO) monitoring system 10 that monitors fluid output in real time as a function of fluid weight. The system 10 compares a current FO weight and/or volume measurement to previous measurement values and assesses the current measurement as a function of time since the previous measurements were taken to evaluate FO trends. In this manner, a validation criterion is provided by which a current measurement value can be evaluate to determine whether it is consistent with historical FO trends or whether it is invalid for being inconsistent with historical FO trends. For instance, if a body fluid container (BFC) 12 that stores fluid output form a patient is bumped or otherwise displaced (e.g., due to patient movement or the like), then a weight measurement may spike upward or downward to a level that is improbable in view of historical FO data. The system 10 recognizes such a spike as being outside of a predetermined but variable range of expected measurement values, and marks the measurement as invalid. The measurement is then excluded from the historical FO data unless or until its invalidity is overridden after review by an operator or healthcare technician. After reviewing the invalid measurement, the operator can recalibrate (e.g., reset) the system, include the measurement, or disregard the measurement and permit the system to proceed as normal. In this manner, the system 10 mitigates noise and/or artifacts caused by invalid measurement readings caused by patient movement or the like by comparing a current measurement to historical trend data (e.g., a plurality of previous FO measurements taken over time), in contrast to conventional systems that use only an immediately preceding measurement value and/or do not assess measurement values as a function of time. The system 10 includes the BFC 12, which receives fluid output from a patient 13 via a catheter 14. The BFC is suspended from a weight scale 16, which is coupled to a support 18 having a wide base 20 for supporting the scale and BFC. The scale 16 registers the weight of the BFC, periodically or continuously, and wirelessly transmits weight measurement information via an antenna 22. Various scales are contemplated, such as a strain gauge instrumented beam, a spring or counter balance based scale, or other mechanical or electronically instrumented scales. The scale may use wireless technologies such as Bluetooth, Zigbee, RF, laser, etc., to transmit the weight measurement information. The scale transmits the updated weight of a fluid container in real-time or on an intermittent or periodic basis to a work station 40 (e.g., a patient monitor or clinical information system) via antennas 22, 42. In another embodiment, the weight measurement information is transmitted over a wired connection to a workstation 40.

The system optionally includes a radio frequency identification (RFID) reader 24 that reads an RFID signal from a tag on the BFC 12 to identify the type of BFC being supported by the scale 16. Once BFC identity is determined, the scale transmits the identity information to the workstation 40, where a table lookup is performed to identify other information related to the BFC, such as intended BFC contents, tare weight of the BFC, capacity, etc. When the patient identification is ID enabled, the reader can read the patient ID and communicate it along with the fluid output data.

The system 10 also includes a fluid input monitoring system that monitors fluid intake by the patient 13 as a function of time. The fluid input monitoring system includes a fluid input container 12a that is coupled to the patient by a fluid delivery means 14a (e.g., a tube or straw), and supported by a scale 16a. The scale can include a support 18a and base 20a, as well as an antenna 22a for wirelessly transmitting fluid container weight measurement information to the workstation 40. Additionally, the fluid input monitoring system includes a reader (e.g., RFID, barcode, etc.) that reads identification information (e.g., container contents, volume, tare weight, etc.) from the fluid container and transmits the identification information to the work station. The work station determines a difference between current weight and a previous weight measurement, converts the weight difference to a volume value, and calculates fluid I/O information from the fluid input container measurements and the BFC measurements. It will be appreciated that the fluid input monitoring portion of the system may similar or identical to the fluid output monitoring portion of the system.

Since the fluid balance status of patients is automated, Clinical Decision Support (CDS) applications can be used to combine vital signs data with fluid balance data to alert care providers about significant change in I/O before serious consequences arise. The system 10 facilitates automatically measuring fluid I/O and entering the measured I/O values as a function of time into a monitoring system and/or patient's medical record where CDS applications provide alerts and reduce medical errors. These alerts can warn of fluid overload in a patient (a frequent iatrogenic error encountered in the ICU). Fluid overload may also be detected as significantly decreased urine output relative to input fluid infusion. Physiologic fluid includes fluid produced by a patient or administered to a patient. Physiologic fluids produced and output by a patient include but are not limited to: urine, chest tube fluid, gastric fluid, peritoneal fluid, cerebrospinal fluid, amniotic fluid, and blood. Physiologic input fluid are fluids administered to a patient and include but are not limited to: water (with or without a combination of electrolytes), blood products (packed red blood cells, fresh frozen plasma, whole blood), and medications.

The weight scale 16 assesses the weight within a physiologic fluid container. For example, when the container suddenly becomes lighter, it can assume that the container was just emptied, wherein a previous heavy weight includes the fluid weight plus the container (tare), and the current light weight includes only the container (tare). The weight scale can either be powered by battery to help reduce cable clutter, or can employ a power cord. The weight scale can be coupled to the illustrated support 18 or can be coupled to another stand, such as an IV stand. The support can be adjustable in height to accommodate BFCs of different sizes so that the containers are free-hanging to avoid erroneous weight measurements.

The BFCs that can be hung from the weight scale include but are not limited to simple off-the-shelf containers for urine collection, intravenous fluid administration bags, as well as rigid containers. The fluid containers have a baseline or tare weight, and the weight scale measures changes in weight to reflect only fluid volume differences. The fluid container may also be labeled with a bar-code or RFID tag that identifies the contents of the container. In one embodiment, the label of the container is also input into a monitoring system using conventional bar-code or RFID reading technologies at the beginning of the monitoring session. The RFID or barcode reading device 24 may be incorporated into the scale 16 or the support 18.

The system 10 is capable of automatically measuring fluid I/O and entering the measured I/O values as a function of time into a monitoring system and/or patient's medical record, which represents a major advancement in CDS, which provides several advantages. For instance, automatic collection and entry of key I/O information is accurate and complete than manual collection and entry. Automatic I/O fluid balance and patient I/O information automatically becomes a part of the patient record and is not subject to loss or technician error. Consistency and quality of medical reports is improved. Care provider knowledge is increased and a complete clinical picture for determining and monitoring the status of the ICU patients is enhanced. Moreover, a need for hospital staff to perform unclean procedures is mitigated, and automatic urimetry data acquisition saves valuable nursing minutes. Patient urinary infection rates are reduced, as are iatrogenic errors encountered within the ICU. Additionally, combining vital signs data with fluid balance data allows for several key alerts. In another embodiment, a plurality of fluid output monitors including BFCs are coupled to the patient, each receiving output fluids from different patient sites (e.g., bladder, lungs, intestines, circulatory system, lymphatic system, etc.) by tubes (14) and supported by a plurality of separate scales 16 transmitting respective fluid outputs that, combined, are representative of total body fluid output.

FIGURE 2 illustrates an embodiment of the system 10, including components of the workstation 40. The workstation 40 includes the wireless communication antenna 42, and a transceiver 44 that receives information from the scale 16 and transmits information thereto. The transceiver 44 decodes received signal and is coupled to a processor 46 that processes and analyzes the decoded information. A memory 48 stores information that has been received, decoded, and/or analyzed, as well as protocols for execution by the processor and/or transceiver in carrying out the various communication and/or analysis protocols described herein.

The workstation 40 further includes a vital signs database 50 that stores fluid output (FO) weight measurement information. In one embodiment, the vital signs database stores other vital sign information received from other vital sign monitors, in addition to the FO weight measurement information. Additionally, the workstation includes a user interface (UI) 52 via which information is displayed to a user and into which a user enters input information. For instance, the UI can include a monitor for viewing information and input devices such as a keyboard, microphone, mouse, stylus, etc. The input devices can be used to enter manually measured fluid inputs or outputs.

The memory 48 stores, and the processor 46 executes, software to measure changes in FO weight and convert the change in weight to volumetric values. The software also includes a routine to remove or "skip" artifacts. Specifically, the routine compares weighted changes with historical data to identify weight changes that should not be recorded. For example, when a urology bag is emptied or removed and replaced with an empty bag, the software recognizes the sudden decrease in weight and replacement with a much smaller weight (e.g., an empty bag) as the result of a change in the urology bag and starts measuring change from the weight of the new bag. Similar artifact recognition routines are used for other artifacts and on the fluid input side. Additionally, data that reflects a rate of fluid loss by perspiration can be received, stored, and processed.

The software further generates output information showing fluid input and fluid output versus time, generate alerts when the input/output ratio moves beyond selected or predetermined thresholds, and the like. As a further refinement, the workstation 40 is integrated or interconnected with a blood pressure, heart rate, or other physiological monitors (not shown). The workstation can then generate more sophisticated alerts for other potentially dangerous conditions such as an increase in the input to output ratio combined with a decrease in blood pressure.

Received weight measurement information is transformed into a volume measurement by performing and/or extrapolating a weight-to- volume calculation based on a presumed density of the fluid. Most fluids administered or collected have an approximate density of 1 gram per milliliter. A different density can also be set for denser or lighter fluids.

The input of fluid into a patient can be assessed as a decrease in weight of a fluid container that is the source of input infusion into a patient (e.g., an intravenous bag). Additionally or alternatively, a cup or other beverage container from which the patient drinks may be placed on a second scale (not shown) and fluid input may be monitored as a function of fluid weight using the methods described herein. The output of fluid from a patient (such as urine) is assessed as an increase in weight of a fluid container that collects such a fluid. The system is thus capable of measuring fluid I/O using existing storage and collection bags and catheters, while providing an intuitive interface with a monitoring system. Furthermore, the system allows for distinctive labeling and tracking of specific input or output bodily fluids using radiofrequency identification technology (RFID) and/or barcodes. The memory 48 stores transmitted weights as well as an integrative function that is executed by the processor 46 to continuously measure the change in weight of the BFC 12. Thus, for a fluid that is being collected, the stored volume value in the vital signs database 50 is a function of changes to weight rather than absolute weight since the container has an offset (tare) weight. Furthermore, the processor 46 performs other related functions, including but not limited to: zeroing of volumes or adjusting for offsets (tare weights) to volumes, automated fluid density calculation or incorporation, and alarms for abrupt changes in flow rates. Flow rates can be calculated as change in volume divided by change in time, where time periods can be pre-specified (e.g., minute or hourly intervals, or some other predetermined interval). In one embodiment, the weight measurements are acquired by the monitoring system wirelessly through the already installed wireless hospital WLAN infrastructure (802.11 b/g/a) or through other wireless infrastructures and protocols (802.15.4, ZigBee), or through wired transmission.

In another embodiment, alerts can be set at the user interface 52 to identify conditions when volumes exceed maximal thresholds or are below minimal thresholds. Similarly, alerts can be set for flow rates instead of or in addition to volumes.

In a related embodiment, an FO measurement that is determined to be invalid by the system 10 for being inconsistent with historical FO trends can be reviewed by an operator. After review, the operator can validate the measurement for inclusion in the vital signs database, disregard the measurement, and/or recalibrate the system (e.g., manually or automatically).

The system 10 can be applied in the fields of patient monitoring and clinical information systems. Examples of products that relate to this innovation include the bedside patient monitors, telemetry-based nursing central stations, and clinical information systems. FIGURE 3 illustrates a flow chart diagram of a method of automatically measuring and storing fluid output in a patient. At 60, a fluid container is suspended from the scale. The fluid container optionally has an RFID or barcode identifier label on it, which may be read by a reader device when the bag is coupled to the scale. Bag identification information (e.g., size, weight, intended fluid, etc.) can be transmitted to a workstation or patient monitor, where it is employed to account for bag tare weight and other variables.

At 62, container weight is measured. Measurement may be made continuously or intermittently. Weight measurement information is transmitted to a patient monitor or workstation at 64. Transmission may be wired or wireless (e.g., using Bluetooth, Zigbee, 802.11a/b/g, etc.). At 66, a change in weight is determined by comparing the current measurement to one or more previous valid measurement(s) and determining the difference there between, and the delta value is converted into a fluid volume value using a known or predetermined density for the fluid. Conversion from weight values to volume values may be performed before or after delta value is determined.

At 68, a determination is made regarding whether the current measurement is valid and within an expected range of values by comparing the current measurement value to historical data. If the measurement is not within a predetermined range of values, then, at 70, the measurement may be discarded or stored for review by a technician, and an optional alarm may be triggered. For instance, if the measurement value is substantially less than a most recent valid measurement value rather than greater, as would be expected, then an inference may be made that the fluid bag has been changed. If another embodiment, if the current measurement value is less than the most recent valid measurement and is consistent with a known offset or tare weight for the fluid container, an inference may be made that the bag has been changed. In another embodiment, if the current measurement is much larger than a recent valid measurement or than an expected value based on historical trend data, then an alarm may be triggered to alert a nurse or operator that the patient requires attention for a condition (e.g., dehydration, low blood pressure, etc.) or that an invalid measurement value requires operator review and potential override, system recalibration, etc.

If the measurement is within the predetermined range of values, it is valid and, at 72, the fluid volume value for a current measurement is stored to a vital signs database for display to the operator. In one embodiment, the weight (or volume) information is displayed to the operator as a function of time to permit the operator to determine whether fluid I/O is consistent with historical and/or expected trends. A box labeled "A" is depicted to illustrate a tie-in point to a parallel fluid input monitoring method illustrated in Fig 4., in accordance with one embodiment.

FIGURE 4 illustrates a method for monitoring fluid input to a patient, which may be performed in parallel with the method of Fig. 3 to permit fluid I/O calculations. It will be appreciated, however, that the method of Fig. 3 may also be performed independently. According to the figure, at 80, a full fluid container is supported by a scale. The container may be an IV bag or the like suspended from the scale, a container from which the patient drinks fluid support by the scale, etc. At 82, container weight is measured. At 84, the weight measurement is transmitted to the patient monitor or workstation. At 86, a change in weight is determined by subtracting a previous weight measurement value from the current weight value, and the difference is converted to a volume value. The input fluid volume value is stored at 88.

At 90, a fluid I/O calculation is performed using the input fluid volume value or input fluid volume values from 88 and the output fluid volume value or output fluid volume values (Fig. 3). Fluid I/O data (e.g., current, historical, etc.) is displayed to a user at 92.

In one embodiment, an alert may be triggered when the patient monitor registers a fluid container weight approximately equal to a tare weight for the fluid container, to trigger an alarm and prompt a technician to refill or replace the empty container. In another embodiment, an alert is triggered when the I/O calculation yields a value indicative of hypovolemia, dehydration, or some other undesirable patient condition.

The innovation has been described with reference to several embodiments.

Modifications and alterations may occur to others upon reading and understanding the preceding detailed description. It is intended that the innovation be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims

1. A fluid output monitoring system (10), including: a bodily fluid container (BFC) (12) that receives an output fluid from a patient and is supported by a scale or weighing means (16); a transceiver (44) in a workstation (40) that receives BFC weight measurement information from the scale (16); a processor (46) that determines a difference between a current weight measurement value and a preceding weight measurement, and converts the difference value into a volume value; and a vital signs database (50) in which the volume value is stored if valid.

2. The system according to claim 1, wherein the vital signs database (50) receives and stores the volume value with a timestamp corresponding to the time at which the current weight measurement was made.

3. The system according to claim 1, wherein the processor (46) is programmed to validate the volume value by comparing it to historical or expected physiological volume values and determines whether the volume value is within a predetermined range of expected values.

4. The system according to claim 3, further comprising a user interface (52) into which a user inputs instructions for at least one of: overriding a validity assessment for the volume value to include the volume value in the vital signs database (50); accepting a validity assessment for the volume value and permitting the system (10) to continue operation; and recalibrating the system (10) after review of a validity assessment for the volume value.

5. The system according to claim 3, wherein the processor (46) is programmed to determine that the CFB is an empty replacement CFB when the current weight measurement value is less than the preceding weight measurement value, and/or when the current weight measurement value is substantially equal to a known or estimated tare weight of the CFB.

6. The system according to claim 3, wherein the processor (46) is programmed to trigger an alarm when the current weight measurement value is invalid for being greater than the preceding weight measurement value by a predetermined amount and therefore outside the predetermined range of expected values.

7. The system according to claim 1, further comprising a reader (24) that reads an identification from the BFC and transmits the BFC identification to the transceiver (44).

8. The system according to claim 7, wherein the BFC identity information includes at least one of BFC capacity, identity of an intended fluid to be stored in the BFC, and tare weight of the BFC.

9. The system according to claim 8, wherein the identification includes one of: an RFID tag, and the reader (24) includes an RFID reader that receives an RFID signal from the RFID tag while the BFC is supported by the scale (16), for transmission via the scale (16) to the transceiver (44); and a barcode, and the reader (24) includes a barcode reader that scans the barcode to retrieve the BFC identity information for transmission via the scale (16) to the transceiver (44).

10. The system according to claim 1, wherein the output fluid is urine and the CFB (12) is coupled to the patient by a catheter (14).

11. The system according to claim 1, further comprising a user interface (52) on which historical and current volume values are presented to an operator.

12. The system according to claim 1, further comprising more than one fluid output monitors including BFCs (12) each receiving output fluids from different patient sites (13) by tubes (14) and supported by separate scales (16) transmitting fluid outputs representative of total body fluid output.

13. The system according to claim 1, further comprising fluid input monitor(s) that include fluid input container(s) (12a) coupled to the patient (13) by a tube(s) (14a) and supported by separate scale(s) (16a) that transmits fluid input container weight measurement(s) to the workstation (40) that is representative off total body fluid input, wherein the workstation calculates a ratio of total body fluid input to fluid output.

14. A method of measuring fluid output of a patient using the system of claim 1, including: coupling the BFC (12) to the patient and to the scale (16); measuring a current weight of the BFC (12); transmitting the measured weight to the workstation (40); determining a difference between the current measured weight and a preceding measured weight; converting the difference in weight measurement values into a volume value; validating the volume value; and storing the volume value to the vital signs database (50) if the volume value is valid.

15. A method of measuring fluid output of a patient, including: receiving a current bodily fluid container (BFC) weight measurement from a scale (16) that supports a BFC (12) coupled to a patient (13); determining a value for a difference between the BFC current weight measurement value and a preceding BFC weight measurement value; converting the difference value into a volume value; validating the volume value; and storing the validated volume value.

16. A method of measuring fluid output of a patient, including: coupling a bodily fluid container (BFC) (12) to a patient (13) and to a scale (16); measuring a current weight of the BFC (12); and wirelessly transmitting a current weight measurement to a workstation (40).

17. The method according to claim 16, further including: determining a difference between the current weight measurement value and a preceding weight measurement value; converting the difference in weight measurement values into an output volume value using a known density of the fluid in the BFC (12); validating the output volume value; and storing the output volume value to a vital signs database (50) if the output volume value is valid.

18. The method according to claim 17, wherein validating the output volume value includes determining whether the output volume value is within a predefined range of expected values.

19. The method according to claim 17, further including storing the output volume value for operator review, and triggering an alarm, if the output volume value is greater than an upper bound on the predefined range of expected values.

20. The method according to claim 19, further including permitting the operator to execute one or more of the following actions after reviewing the output volume value: override the invalidity of the output volume value and store it to the vital signs database (50); accept the volume value and permit the system (10) to continue operation; and recalibrate the system (10).

21. The method according to claim 17, wherein the fluid is urine and the BFC is coupled to the patient by a catheter (14).

22. The method according to claim 17, further including reading an identification label on the BFC (12) and determining at least one of BFC capacity, fluid to be collected in the BFC (12), and tare weight of the BFC (12).

23. The method according to claim 17, further comprising more than one fluid output monitors including BFCs (12) each receiving output fluids from different patient sites (13) by tubes (14) and supported by separate scales (16) transmitting fluid outputs representative of total body fluid output.

24. The method according to claim 17, further including: receiving a current input fluid container weight measurement(s) from scale(s) (16a) that support input fluid container(s) (12a) coupled to the patient (13); determining value(s) for difference(s) between the current weight measurement(s) and a preceding input fluid container weight measurement(s); converting the input difference value(s) into an input volume value(s); storing the input volume value(s); and calculating fluid I/O information from all input volume value(s) and all output volume value(s) calculating a ratio of total body fluid input to fluid output.

25. A computer readable medium (48) or processor (46) carrying software to execute instructions for performing the method of claim 17.

26. An apparatus for monitoring fluid output by a patient using the method of claim 17, including: means (12) for receiving fluid output from the patient; means (16) for measuring a current weight of the means (12) for receiving fluid output; means (16, 22) for wirelessly transmitting a current weight measurement to a workstation (40); means (46) for performing the steps of claim 15; and means (50) for storing the output volume value if the volume value is valid.