Apparatus for monitoring gas concentrations

[0002] The invention relates to a patient monitor used to monitor gas concentrations. In particular, the patient monitor includes a module that facilitates a conversion from mainstream gas concentration measurement to sidestream gas concentration measurement.

[0003] Patient monitors are used to monitor and display patient data, typically in a medical setting. Examples of measured parameters may include electrocardiogram data, non-invasive blood pressure, impedance respiration, SpO2, and temperature. Further, patient monitors may be used to monitor the carbon dioxide (CO2) in a patient's breath during a respiratory cycle. Such measurement of carbon dioxide concentration over time is referred to as capnography and is used to assess the adequacy of patient ventilation, patient cardiac function, and other related patient functions.

[0004] In general, capnography data is presented on a patient monitor via a wave form or numerical data that displays the carbon dioxide level in the patient's breath, measured in kPa, mmHg, percent, or equivalent dimension. One capnography parameter that is particularly useful is the amount of carbon dioxide at the end of each breath, known as end-tidal carbon dioxide (EtCO2). EtCO2 may be used to calculate an approximate value of carbon dioxide pressure in arterial blood, which provides information as to the patient's cardiovascular and respiratory system functionality.

[0005] There are several different ways that the concentration of exhaled carbon dioxide may be measured. Methodologies may include photoacoustic spectroscopy, mass spectrometry, Raman scattering measurement, and infrared absorption spectroscopy (IR spectroscopy). IR spectroscopy is a common method utilizing a light source to transmit a beam of light through a gaseous sample. The light beam has a wavelength that is preferentially absorbed by CO2. The transmitted radiation is measured by a photodetector. The amount of absorbed radiation indicates the concentration of CO2 in the sample volume. A commonly used wavelength for IR spectroscopy when used to measure carbon dioxide concentration is 4.3 microns.

[0006] Two types of gas analyzers may be used to measure gas concentrations, such as carbon dioxide. Mainstream gas analyzers are typically located at a patient's airway as part of an adapter directly coupled to the airway of an intubated patient. The adapter is typically proximate the endotracheal tube. As the respiratory gases travel through the patient's airway and the mainstream gas analyzer adapter, the desired gas, such as CO2 may be monitored. A sidestream gas analyzer diverts a portion of the patient's inspired and expired respiratory gases from a patient's airway to be transported to the sidestream gas analyzer for measurement. The analyzed gas sample may be either returned to the patient's circuit or discarded.

[0007] Mainstream gas analyzers are typically utilized on intubated patients, who must be fully sedated. A sidestream side analyzer permits the physician to attach a nasal cannula accessory to the patient, avoiding the need to intubate. Further, a sidestream gas analyzer typically has the ability to measure low flow rates, as may be the case with smaller patients. In other circumstances, a mainstream gas analyzer may be desired, such as when an immediate gas concentration reading is desired, as opposed to the delayed response associated with the sample travel time of sidestream gas analyzers.

[0008] In certain conventional patient monitors, a port or interface may be provided to accept input signals from a mainstream CO2 analyzer, but a separate module may be required in an auxiliary rack to permit the monitoring and display of data from a sidestream CO2 analyzer. A separate interface or port may be required on the patient monitor for sidestream CO2 analysis. Accordingly, it would be advantageous to have a patient monitor that is adapted to easily receive and display the signals from a mainstream gas analyzer and a sidestream gas analyzer. It would further be advantageous to have a conversion module adapted to permit the user of a patient monitor to easily convert from a mainstream gas analyzer to a sidestream gas analyzer without requiring additional equipment.

[0009] It would be desirable to provide a system and/or method that provides one or more of these or other advantageous features. Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments that fall within the scope of the appended claims, regardless of whether they accomplish one or more of the aforementioned needs.

[0010] One embodiment of the invention relates to a patient monitoring system. The patient monitoring system has a patient monitor with a screen and a mainstream gas input connector configured to receive a mainstream gas concentration signal from a mainstream gas analyzer. The patient monitoring system further includes a sidestream gas analyzer having an output connector, the sidestream gas analyzer configured to transmit a sidestream gas concentration signal via the output connector. The patient monitor receives the sidestream gas concentration signal via the mainstream gas input connector for display on the screen.

[0011] The invention is capable of other embodiments and of being practiced or being carried out in various ways. Alternative exemplary embodiments relate to other features and combinations of features as may be generally recited in the claims.

[0012] The invention will become more fully understood from the following detailed description, taken in conjunction with the accompanying drawings, wherein like reference numerals refer to like elements, in which:

[0013] FIG. 1 is a schematic of a mainstream gas analyzer system;

[0014] FIG. 2 is a schematic of a sidestream gas analyzer system;

[0015] FIG. 3 is a perspective view of a patient monitor,

[0016] FIG. 4 is a perspective view of a sidestream conversion module; and

[0017] FIG. 5 is a perspective view of a patient monitor having a sidestream conversion module attached.

[0018] Referring to FIG. 1, in a mainstream gas analyzer system, a patient monitor 10 may be used to display the concentration of a gas component in respiratory gas by utilizing a mainstream gas analyzer 12. The mainstream gas analyzer 12 provides gas concentration data to the patient monitor 10 via a sensor cable 14 that is connected to the patient monitor 10 at an interface, such as a port or connector 16. The mainstream gas analyzer 12 is coupled to the airway 18 of a patient 22 near the patient's end of an external respiratory system via an airway adapter 20. Typically, the patient 22 is on mechanical ventilation via endotracheal intubation when mainstream gas analysis is used.

[0019] In an exemplary embodiment, the mainstream gas analyzer 12 measures the concentration of exhaled carbon dioxide (CO2), in particular, end-tidal CO2 (EtCO2). The mainstream gas analyzer 12 may utilize IR spectroscopy to measure the amount of absorption of light by CO2 in the airway, thus determining the CO2 concentration at a particular point in time. The patient monitor 10 then processes the signal (e.g. analog or digital) from the mainstream gas analyzer 12, and displays a waveform and other data associated with the mainstream gas analyzer measurement on a visual display of the patient monitor 10.

[0020] Referring to FIG. 2, a sidestream gas analyzer 30 may be used to measure the concentration of gas components in a sample drawn from the air stream of a patient 32. The sample may be drawn from a patient's endotracheal tube if the patient is intubated, but may also be drawn from a cannula or mask proximate a patient's trachea, such as via a nasal cannula accessory. The gas sample is conveyed to the sidestream gas analyzer 30 by a sample tube 34, which may be a few meters in length and utilize a flow rate in the range of 50-150 ml/min. The sidestream gas analyzer 30 measures gas concentrations, such as the concentration of CO2, utilizing a known measurement method such as IR spectroscopy and provides a signal to the patient monitor 10 via sensor cable 36. The sensor cable 36 may be connected to the patient monitor 10 via a port or connector 38.

[0021] Referring to FIG. 3, in an exemplary embodiment, patient monitor 10 is a multi-parameter patient monitor available from GE Medical Systems Information Technologies, although the term “patient monitor” is not intended to be limited to any particular brand or type of patient monitor. The patient monitor 10 includes a visual display such as screen 40 and is designed to monitor a set of parameters, including CO2 concentration. A set of controls 42 provides a user interface and a number of input data connectors 44 are provided that serve as inputs for data relating to patient parameters. The CO2 connector 16 is one of the input data connectors 44. As is known in the art, the patient monitor 10 includes logic, such as software, firmware, hard wired circuits, application specific integrated circuits, or other computerized instructions necessary to provide visual output and perform other calculations on the signals provided via connectors 44. In particular, the patient monitor 10 may display capnography data based on CO2 sensor readings, including EtCO2 data. The patient monitor 10 may perform various calculations, calibrations, and compensation functions to provide the desired output. As shown in the system depicted in FIG. 1, in one embodiment a mainstream gas analyzer 12 provides capnography data to patient monitor 10.

[0022] Referring to FIG. 4, in a preferred embodiment, a module, shown as sidestream conversion module 50 may be connected to sample tube 34. The module 50 includes sidestream gas analyzer 30 used to measure gas concentrations. In one embodiment, sidestream gas analyzer 30 utilizes a photodetector to determine the CO2 concentration in a sample via IR absorption spectroscopy. Data output from the sidestream gas analyzer 30 is sent as a signal (e.g. digital or analog) via a connector such as output plug 52.

[0023] Referring to FIG. 2, in certain conventional systems, the signal from sidestream gas analyzer 30 may be sent via a sensor cable 36 to a connector 38 on patient monitor 10 (separate from mainstream input connector 16). In other conventional embodiments, the sensor cable 36 may connect to a separate logic card or module in an auxiliary card rack (not shown) that separately provides data to patient monitor 10. However, referring to FIG. 5 in a preferred embodiment, sidestream conversion module 50 connects directly to patient monitor 10. The connection may be accomplished by plugging output plug 52 into CO2 connector 16. Accordingly, sidestream conversion module 50 permits easy conversion from mainstream gas analysis to sidestream gas analysis using the same connector 16 on the patient monitor 10. Further, sidestream conversion module 50 is directly plugged into patient monitor 10 without the need for sensor cable 36 as shown in the system of FIG. 2.

[0024] In an exemplary embodiment, sidestream conversion module 50 is able to provide its data signal directly to the mainstream CO2 connector 16 by emulating the signal provided by mainstream gas analyzer 12. For example, in an analog carbon dioxide measurement device, the output voltage corresponding to various CO2 concentrations would be the same for the sidestream gas analyzer 30 as the mainstream gas analyzer 12. Accordingly, the patient monitor 10 need not differentiate between the input signals provided by either mainstream gas analyzer 12 or sidestream gas analyzer 30 and may receive either input for data analysis and display via a signal connector, in a preferred embodiment, the mainstream carbon dioxide connector 16.

[0025] In another exemplary embodiment, patient monitor 10 may include logic that analyzes the signal input via connector 16 and discerns the type of device sending the signal. The logic of patient monitor 10 may then analyze and display the input gas concentration data properly by using an appropriate set of instructions depending upon the type of device sending the signal. In this fashion, signals from mainstream gas analyzer 12 or sidestream gas analyzer 30 may be received via the same connector 16 even if the signal from sidestream gas analyzer 30 does not emulate the signal from mainstream gas analyzer 12.

[0026] Sidestream conversion module 50 may be used to effectuate the conversion from mainstream gas monitoring to sidestream gas monitoring depending on the preference of the user of patient monitor 10. Note that in each of the two examples indicating how sidestream conversion module 50 may be used to convert between sidestream monitoring and mainstream monitoring using a single connector on the patient monitor 10, the mainstream carbon dioxide connector 16 is shown as being the single connector used to receive either signal. However, another type of connector may be used to receive each of the signals within the scope of the present invention.

[0027] Further referring to FIGS. 4 and 5, sidestream conversion module 50 attaches directly to patient monitor 10, providing the conversion from mainstream CO2 monitoring to sidestream CO2 monitoring with no additional hardware required. In an exemplary embodiment, the module 50 is intended to function with a number of similarly configured patient monitors having a single CO2 connector. In a preferred embodiment, the patient monitor 10 requires no additional logic, such as software, firmware, or other instructions to monitor, perform calculations on, or display the data provided by sidestream conversion module 50. Instead, sidestream conversion module 50 provides an electronic data signature via output plug 52 that is configured for use by the mainstream gas analyzer 12 via the mainstream CO2 connector 16.

[0028] In circumstances in which it may be desirable to utilize sidestream gas analysis instead of mainstream gas analysis, such as when the patient is not intubated, a medical provider may easily convert from mainstream gas analysis, in particular mainstream CO2 gas concentration analysis to sidestream gas analysis, in particular sidestream CO2 concentration analysis, utilizing the same patient monitor hardware in addition to conversion module 50.

[0029] While the detailed drawings and specific examples given describe various exemplary embodiments, they serve the purpose of illustration only. It is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the preceding description or illustrated in the drawings. For example, the conversion module may measure CO2 concentration using various methods known in the art. Additionally, the same approach may be used for other gas concentration measurements that utilize mainstream or sidestream technology. Further, the module may be constructed in various shapes and sizes depending on the configuration of the patient monitor. Furthermore, other substitutions, modifications, changes, and omissions may be made in the design, operating conditions, and arrangements of the exemplary embodiments without departing from the scope of the invention as expressed in the appended claims.