(19)
(11)EP 2 677 929 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
17.01.2018 Bulletin 2018/03

(21)Application number: 12708401.0

(22)Date of filing:  22.02.2012
(51)Int. Cl.: 
A61B 5/083  (2006.01)
A61M 16/00  (2006.01)
(86)International application number:
PCT/IB2012/050807
(87)International publication number:
WO 2012/114286 (30.08.2012 Gazette  2012/35)

(54)

CAPNOGRAPHY SYSTEM FOR AUTOMATIC DIAGNOSIS OF PATIENT CONDITION

KAPNOGRAFIESYSTEM ZUR AUTOMATISCHEN DIAGNOSE EINES PATIENTENZUSTANDS

SYSTÈME DE CAPNOGRAPHIE POUR DIAGNOSTIC AUTOMATIQUE D'ÉTAT DE PATIENT


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 22.02.2011 US 201161445192 P
16.12.2011 US 201161576907 P

(43)Date of publication of application:
01.01.2014 Bulletin 2014/01

(73)Proprietor: Koninklijke Philips N.V.
5656 AE Eindhoven (NL)

(72)Inventors:
  • BABAEIZADEH, Saeed
    NL-5656 AE Eindhoven (NL)
  • HELFENBEIN, Eric
    NL-5656 AE Eindhoven (NL)
  • BUTLER, Dawn
    NL-5656 AE Eindhoven (NL)
  • ZHOU, Sophia, Huai
    NL-5656 AE Eindhoven (NL)

(74)Representative: Steffen, Thomas 
Philips Intellectual Property & Standards High Tech Campus 5
5656 AE Eindhoven
5656 AE Eindhoven (NL)


(56)References cited: : 
WO-A1-2010/052608
WO-A1-2011/154948
US-A1- 2011 040 713
WO-A1-2010/150239
US-A- 5 598 508
US-B1- 6 428 483
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description


    [0001] This invention prelates to an improved medical carbon dioxide (CO2) monitoring system and, in particular, to a CO2 monitoring systems that automatically determines the effectiveness of intubation or other advanced airway placement therapy or cardiopulmonary resuscitation (CPR) therapy, or respiration therapy has applied to the patient. Respiration therapy could include monitoring the response to a bronchodilator medication for obstructive airway disease, such as asthma. The effectiveness of such therapy can be seen in the changing shape of the CO2 waveform. The system also determines the occurrence of the return of spontaneous circulation (ROSC) during treatment.

    [0002] CO2 monitoring systems are presently employed in hospital surgical suites and intensive care units to monitor a patient's respiration. Generally these systems are sophisticated and sizeable ventilation systems which monitor the patient's oxygen intake and respiratory CO2. However, there are other scenarios where more advanced CO2 monitoring is desirable. One scenario is intubation or advanced airway placement, where air is being supplied to a patient by a respiration device the end of which is inserted into the patient's airway. Another is the application of CPR to a patient stricken by cardiac arrest. Another is when a person is in respiratory distress, such as from obstructive airway disease e.g., asthma, and respiratory therapy, such as a bronchodilator medication, is being applied while their expired CO2 is being monitored. A portable unit is desirable in such situations, such as the MRx defibrillator monitor produced by Koninklijke Philips North America {Andover, MA}, which may be used in a hospital but is portable and can be taken to the site of an accident or location of a stricken patient. It would be desirable for such a portable monitor to be capable of monitoring the CO2 expiration of a patient and interpreting the CO2 waveform in order to determine the effectiveness of the treatment applied in each of these situations.

    [0003] For example, intubation is a notoriously difficult procedure that if applied in error can be fatal to the patient. Unrecognized esophageal intubation, in which the tube is mistakenly routed into the digestive tract instead of to the lungs, is a great danger in pre-hospital airway management and can lead to the long-term sequelae of anoxic brain injury and death. In some instances, even if the patient has been initially intubated correctly in the field, the endotracheal tube (ETT) may migrate out of the trachea during transport to the emergency department. In one study, the overall misplaced airway rate for patients arriving at the emergency department was an alarming 25% of which 16.7% were esophageal. In addition, the observational methods to confirm correct placement of the ETT have been shown to be unreliable. The use of supraglottic advanced airways has reduced the prevalence of mis-intubations, but these devices may also be misplaced with subsequent disastrous consequences.

    [0004] Death by hyperventilation is another common and life-threatening airway management problem that arises during cardiopulmonary resuscitation. At least one study has shown that despite seemingly adequate training, professional rescuers consistently hyperventilate patients during out-of-hospital CPR. The study also indicated that excessive ventilation rates significantly decrease coronary perfusion pressures and survival rates. Unrecognized and inadvertent hyperventilation may be contributing to the currently dismal survival rates from cardiac arrest. In the presence of CPR, determination of ventilation rate can be performed more accurately using the CO2 waveform than the commonly used impedance method, and when combined with analysis of end-tidal CO2, this can be an effective method for detection of inadvertent hyperventilation. Hyperventilation in the presence of traumatic brain injury is also extremely detrimental, and may result in cerebral ischemia.

    [0005] Effective CPR is universally recognized as a critical treatment for cardiac arrest victims. Although CPR is commonly applied, its quality is often poor due to inadequate training or caregiver fatigue. What is needed is a real-time indication to the caregiver of whether or not the applied CPR is effective. If the CPR is not effective, the caregiver can be guided to improving the technique. The inventors have recognized that one indicator of CPR quality may lie in the patient's expired CO2 profile.

    [0006] Each of the above described treatments, if successful, will result in a return of spontaneous circulation (ROSC). It would also be desirable for a portable monitor that automatically recognizes the occurrence of ROSC and provides an indication of such to the rescuer. Similarly, loss of spontaneous circulation after ROSC may be initially detected as a sudden drop in the et CO2 values, and would be an indication to resume CPR.

    [0007] Patients in respiratory distress, such as from obstructive airway diseases such as emphysema, asthma, chronic bronchitis or cystic fibrosis, are often provided medication such as bronchodilators to open their airways. The shape of the CO2 waveform can be used to both diagnose obstructive airway, and to monitor the effectiveness of treatment.

    [0008] CO2 analyzing technology, or capnography, is currently used for determining a patient condition based on the trending of the patient's CO2 expiration. The prior art and co-assigned patent application, entitled "Carbon Dioxide Monitoring System" (WO2010/052608), describes a capnographic monitor which is implemented in a portable monitoring device to provide CO2 monitoring and interpretation during intubation, advanced airway placement, CPR treatment, or ventilation. The device incorporates an input setting to identify the particular treatment being applied to the patient, so that the monitor is sensitive to the respiratory condition which may be expected during that treatment.

    [0009] Documents US6428483B1, WO2011/154948A1 and WO2010/150239A1 also disclose similar CO2 analysing systems.

    [0010] From the above described problems, the inventors have realized that what is needed is an improved capnography system which provides feedback as to the effectiveness of cardiovascular therapies. The improvements in the system relate to the automatic detection of breaths, discrimination of true breaths from artifact, and therapy analysis which takes into account physiological trends in the patient's CO2 expiration during the therapy.

    [0011] It is in accordance with the principles of the present invention to describe a system for providing clinical decision support, and in particular by analyzing CO2 waveforms in order to aid clinicians with the decision making process during cardiac-and respiratory-related rescues. The system may be implemented in a software scalable algorithm that can operate at appropriate levels to match user needs with the processing hardware. An algorithm of the system analyzes the patient's CO2 waveform and produces parameters and events. The results of the analysis are either directly reported or may be used to report a relevant clinical statement.

    [0012] The software algorithm is preferably designed to be machine (host) independent and can, therefore be used in more than one operating environment. The common source code of the algorithm can be configured to achieve the appropriate level of functionality and to conform to the operating environment of the host device. The algorithm includes specified interfaces for CO2 signal input, controls, and output signals as well as operating environment specifications.

    [0013] It is thus an object of the present invention to provide a system in which a CO2 monitoring method is integrated into a portable monitoring device for use in the hospital or in ambulatory settings, where lifesaving cardiovascular rescue techniques are commonly employed. The method may optionally be implemented in a machine-independent software algorithm such that the method may be used by any computer processor and operating system hardware.

    [0014] Another object of the present invention is to provide a CO2 monitoring system which processes and analyzes the variation of CO2 during respiration to provide useful treatment information to a caregiver. The system uses a CO2 sensor that produces a signal which is a measure of the CO2 level of a patient's respiration. The CO2 signal is digitized and recorded by the CO2 monitor. The CO2 signal stream is optionally analyzed for noise content and the noise level reduced to produce a "clean" CO2 signal. Various characteristics of the waveform, such as corners and peaks, are detected and measured. The characteristics are applied to an artifact detector to determine and remove artifact from true breaths. The stream of true breaths is then analyzed to identify the likely treatment being provided and the treatment's effectiveness. If an adverse respiratory condition is found, the monitor may issue an audible or visible alarm and/or may issue a clinical advisory statement by means of a display or annunciator.

    [0015] Another object of the present invention to provide a system for determining the effectiveness of treatment during intubation, advanced airway placement, or CPR by means of the patient's expiration of CO2. The system comprises a novel use of end-tidal CO2 readings over a sequence of true breaths to determine if the patient is improving during the treatment, or if the endotracheal- tube or advanced airway has been properly placed.

    [0016] Another object of the invention is to provide a system for identifying the occurrence of the return of spontaneous circulation (ROSC), or the loss of spontaneous circulation. The method may be incorporated into a medical rescue device such as a defibrillator.

    [0017] The invention is defined by the annexed claims.

    [0018] In the Drawings :

    FIGURE 1 illustrates in block diagram form a CO2 monitoring system of the present invention that is operatively connected to a patient.

    FIGURE 2 illustrates the parameters of a typical breath candidate portion of a CO2 signal.

    FIGURE 3 illustrates a flow chart of the method of determining the condition of a patient from a capnography waveform.

    FIGURE 4 illustrates an artifact breath sequence of a CO2 signal for a patient undergoing CPR compressions.

    FIGURE 5 illustrates a typical breath sequence of a CO2 signal juxtaposed with a calculated end-tidal CO2 (etCO2) trend and respiration rate trend which may be produced from a patient who is being inadvertently hyperventilated.

    FIGURE 6 illustrates a typical breath sequence of a CO2 signal for an improperly intubated patient.

    FIGURE 7 illustrates a flow chart of the method of analyzing airway placement and providing user guidance in the case of an improper ETT or advanced airway placement.

    FIGURE 8 illustrates in graphical form a measured etCO2 signal and calculated respiration rate, used in a method for determining the effectiveness of CPR.

    FIGURE 9 illustrates in graphical form a measured etCO2 signal used in a method for determining ROSC.



    [0019] Referring first to FIGURE 1, a CO2 monitoring system 14 including a CO2 monitor 20 and a CO2 analyzer 22 is shown in block diagram form. A CO2 monitor is shown being used to monitor a subject patient 10. CO2 monitor 20 is capable of monitoring CO2, and may also be capable of monitoring other patient functions, such as blood pressure, blood oxygen, ECG and the like. CO2 monitor 20 may also comprise controls, display and indicator lights, and aural alarms and prompts.

    [0020] The patient's respiratory gases are provided to a CO2 sensor 12 within CO2 monitor 20. CO2 sensor 12 senses the CO2 gas concentration in the subject's expiration. The CO2 measurement signals from the sensor 12 are conveyed to a CO2 processor 22. The CO2 processor 22 is shown in FIGURE 1 as residing separate from the CO2 monitor 20. However, the invention is not so limited. CO2 processor 22 may reside within the monitor 20, may be a separate apparatus, or may alternatively be constructed as a software module.

    [0021] CO2 processor 22 comprises a pre-processor 24 which digitizes the CO2 signals into a stream of samples and stores the stream in a computer memory for later use. The digitized CO2 signal stream represents a continuous CO2 waveform. The waveform is preferably a variation with time of CO2 in mmHg. Exemplary CO2 signal streams are shown in FIGURES 2, 4, 5, 6, 8, and 9.

    [0022] The CO2 signal stream output from pre-processor 24 may optionally be processed to reduce noise content at a noise reduction filter 26. One technique for analyzing the noise content at filter 26 is to analyze the high frequency content of the CO2 signal stream. A clean CO2 waveform will exhibit relatively little high frequency content. Filter 26 may thus comprise a digital low pass filter which reduces the signal stream noise level.

    [0023] The digitized and filtered CO2 signal stream undergoes a first waveform detection at breath candidate detector 30. One technique for detecting a CO2 breath candidate is to detect the difference in successive CO2 samples, which effectively detects the slope of the CO2 waveform. Referring to the example breath candidate sequence 100 at FIGURE 2, a steeply rising slope 108 which passes from a background noise threshold level 104 is a characteristic of either the beginning of a patient exhalation, or may be indicative of an artifact event. A further indication of an exhalation or artifact event is a steeply falling slope 110 which passes below the background noise threshold level 104. The breath candidate detector 30 thus operates to identify a time sequence of breath candidates such as breath 1 and breath 2, separated by a period of inactivity.

    [0024] Still referring to FIGURE 1, the sequence of breath candidates is next processed by breath characterizer 32. Breath characterizer 32 determines a set of characteristics for each breath candidate. These characteristics may include the baseline of the waveform candidate, the amplitude of the waveform, the frequency of the waveform with regard to the previous candidate, the rhythm of the waveform, the corners of the waveform, the slopes of the waveform, and characteristics of the shape of the waveform.

    [0025] The breath candidate characteristics are classified at breath classifier 34 to assess whether each candidate waveform is a respiration waveform or artifact. In particular, artifact generated as a result of external CPR compressions has distinguishing characteristics from true breath waveform shapes. Breath classifier 34 analyzes the breath candidates accordingly, and segregates true breaths from artifact. A therapy input 64 may optionally communicate a treatment identifier to breath classifier 34 in order to improve the accuracy of the analysis. The method of distinguishing artifact from true breaths will be discussed in more detail below.

    [0026] Breath classifier 34 conveys a sequence of true breaths to therapy analyzer 36. Therapy analyzer 36 operates to determine the effectiveness of the underlying patient therapy based on the trending of at least two true breaths. Exemplary determinations are the effectiveness of CPR, the proper placement and/or continued proper placement of an endotracheal tube (ETT) or advanced airway, and the occurrence of a return of spontaneous circulation (ROSC) during the rescue therapy. In addition, the incidence of hyper- or hypo- ventilation during CPR can be determined by therapy analyzer 36.

    [0027] Therapy input 64 may optionally be provided to therapy analyzer 36 in order to improve the accuracy of the analysis. For example, a start time for intubation or airway placement, or of initiation of bronchodilator therapy may be conveyed by a user input, such as a therapy input switch. The start time is useful in the airway placement analysis, as described in more detail below,

    [0028] The effectiveness of the patient therapy as determined by therapy analyzer 36 may be communicated back to the user via an output generator 40 in several ways. Display 60 may provide an output instruction as generated by clinical guidance generator 42, or may display alarms or alerts as generated by alarm 44. An annunciator 62 may provide audible instructions from clinical guidance generator 42, or alarm signals from alarm 44. Although display 60 and annunciator 62 are shown in FIGURE 1 as residing in monitor 20, it is understood that either may be disposed in analyzer 22 or in a completely different location such as a networked central monitoring location. The clinical guidance instruction advises the user that a particular problem or difficulty should be investigated, or alternatively that the patient is improving. Output instructions such as "no respiration received" or "erratic CO2 waveform" may be generated to indicate a malfunction or erroneous use.

    [0029] When the CO2 monitoring system 20 is coupled to the patient, it should be set to identify the treatment being applied to the patient, such as intubation, CPR, or ventilation. This may be done by a manual switch or input to the monitoring system which set by the clinician. The setting may also be done automatically by the particular treatment device being used. For instance, when the air conduit of an intubation device is connected to the CO2 monitor 20, the monitor may sense the connection of the air conduit and thereby is informed that intubation is being monitored. For CPR a CPR pad which is placed on the chest of the patient and depressed during CPR may be connected to the monitor 20 and so inform the monitor that CPR is being performed. During ventilation the ventilator or its air conduit may be connected to the monitor 20 to inform the monitor that ventilation is being performed. The identification of the treatment regimen will condition the monitor 20 to be particularly sensitive to respiratory conditions which may be expected during the treatment regimen being applied. This automatic identification of treatment may be supplied in addition to or alternative to the therapy input 64.

    [0030] FIGURE 2 illustrates the standard parameters of a normal CO2 waveform 100. When the patient exhales and the expiration phase begins, the waveform will rise from a background noise level 104 which represents a baseline CO2 value with a steep slope 108 until a sustained plateau level 106 of CO2 content of the exhaled air is attained. The waveform 100 will exhibit a corner alpha 112 when the sustained level is reached. When the patient finishes exhaling the waveform will drop from a corner beta 114 along a downstroke falling slope 110 to the signal the start of the next inspiration phase. The waveform will then repeat in this manner at the frequency and periodicity of the patient's respiration.

    [0031] The shape of the CO2 breath waveforms in FIGURE 2 contains other identifiable and useful characteristics. Waveform corners 102a, 102b, 102c, 102d, 103a, 103b, 103c, and 103d define the major events of exhalation and inhalation. Maximum amplitude points 102e and 103e define the end-tidal CO2 (etCO2) values for each breath. The plateau shape 106, or portions of the plateau shape 106, may be an indicator of a true breath. These may also be used to determine the presence of acute airway obstruction. The above described parameters can easily be used to determine breath characteristics such as waveform baseline, waveform amplitude, waveform frequency, waveform slope, and waveform rhythm

    [0032] FIGURE 3 illustrates a method of using a capnography system for providing information to the user to guide clinical treatment decisions. The method is initiated when CO2 data is received in step 312 from a patient-worn CO2 sensor. The CO2 data is digitized and stored at step 314, and optionally filtered to reduce noise at step 326. The output of step 326 is a CO2 waveform which encompasses a sequence of breaths from the patient.

    [0033] Breath candidates are selected from the CO2 waveform at step 330. Referring back to FIGURE 2, step 330 may incorporate a technique for detecting a CO2 breath candidate by detecting the difference in successive CO2 samples, thus effectively detecting the slope of the CO2 waveform. Referring to the example breath candidate sequence 100 at FIGURE 2, a steeply rising slope 108 which passes from a background noise threshold level 104 is a characteristic of either the beginning of a patient exhalation, or may be indicative of an artifact event. A further indication of an exhalation or artifact event is a subsequent steeply falling slope 110 which passes below the background noise threshold level 104. The breath candidate detector 30 thus operates to identify a time sequence of breath candidates such as breath 1 and breath 2, separated by a period of inactivity. The resulting sequence of breath candidates is then provided to the annotate breath candidate step 332 for further processing.

    [0034] Parameters for the sequence of breath candidates are calculated at step 332. The corners 102a-d, peak value 102e, plateau 106 slope, upstroke 108 slope, downstroke 110 slope, baseline value 104, sequence frequency and stability of rhythm are determined. The parameters are then passed to the classify breath step 333.

    [0035] Breaths are classified as artifact or true breath at step 333. One source of artifact in the CO2 signal stream is introduced during CPR. CPR is performed by applying chest compressions at a rapid rate, generally about 100 compressions per minute. These rapid but firm compressions will cause the lungs to be compressed and recoil from compressions in short, high frequency increments, which causes some gases to be cycled through the lungs. CPR artifact may thus exhibit a shape similar to a typical breath, FIGURE 2, or may appear as "bumps" 470 as shown in FIGURE 4.

    [0036] Step 333 distinguishes artifact by the following algorithm. Accuracy of the algorithm may be increased by means of a user input 364, such as a button or CPR force sensor signal when CPR is being administered. In the case of a CO2 waveform having the general shape of FIGURE 2, CPR artifact is determined for breath 2 if

    AND

    where T1 is a fixed fraction of the average breath gap having a range from about 0.4 to 0.5, the average breath gap is a dynamic value updated with every true breath, and T2 is a fixed interval of duration for a reasonable breath having a value of about 600 milliseconds.

    [0037] In the case of a CO2 waveform breath candidate having the multiple bump shape 470 of FIGURE 4, CPR artifact is determined if the greatest bump interval 460a, 460b, or 460c is shorter than 550 milliseconds. The bump interval is measured where the CO2 waveform 470 crosses a threshold line 450 equal to 75% of the average of the peak-peak bump amplitudes.

    [0038] The breath candidates which are classified as artifact are segregated from the breath candidates classified as true breaths at step 334. Artifact breath candidates are normally not discarded. Further analysis of the artifact candidates may occur at step 370 to provide an output instruction that CPR is being administered, or to obtain end-tidal CO2 readings indicating whether CO2 is being exchanged in the lungs during CPR. Such readings are useful to determine the effectiveness of CPR.

    [0039] True breaths are passed from step 334 to the generate breath sequence step 335. In step 335, the true breaths are further processed to determine parameters such as an end-tidal CO2 trend curve 520 and a respiration rate trend curve 530. Referring now to FIGURE 5, curve 520 may be calculated by known methods such as by a running mean of true breath etCO2 values. Respiration rate trend curve 530 may be calculated by known methods such as by a running occurrence rate of true breaths, as shown by CO2 ventilation signal stream 510. The output of these values is communicated to the analyze therapy step 336.

    [0040] Analyze therapy step 336 determines whether the underlying therapy is effective or defective in some way. A first determination is for the hyperventilation case. FIGURE 5 shows that a respiration rate 530 greater than a threshold such as 15 breaths per minute in combination with a declining etCO2 value at 520 is an indicator of hyperventilation condition 540. In such a state, a hyperventilation signal is provided to the output guidance and alerts step 340 to alert the rescuer to reduce ventilations.

    [0041] Analyze therapy step 336 also detects an improper or dislodged placement of an endotracheal tube or advanced airway in the patient. FIGURE 6 shows an example of a CO2 waveform 600 resulting from an improper endotracheal intubation. A few normal-looking true breaths 620a and 620b seen right after intubation due to CO2 in the stomach may lead to the erroneous belief that the placement is proper. The inventive method, however, continuously analyzes the sequence of true breaths for a predetermined period 610, in this case about 20 seconds, and provides corrective output guidance if an improper airway placement is detected.

    [0042] The method of analyzing intubation therapy 636 is illustrated by FIGURE 7. A first true breath is received at step 710 in which the etCO2 value is assessed. If the etCO2 value is initially less than a lower threshold, such as 3 mmHg, then step 720 sends an indication to an output guidance step 640 to provide a first respiration alert at step 750. The first respiration alert comprises guidance that etCO2 is low.

    [0043] If, however, the first true breath etCO2 value is above the threshold, then a pause period is entered at step 730. After the pause period, such as 20 seconds, is concluded at step 730, a second true breath is received at step 740. The second true breath is then analyzed at step 720 in the same way as the first true breath. If the second etCO2 value has decayed over the time period to below the threshold, then a misplaced or dislodged endotracheal tube is indicated. Step 720 then provides an indication to output guidance step 640 such that an alert is generated at intubation alert step 760. If the second true breath continues to exceed the threshold value, then a third output guidance is generated at step 640 to indicate proper tube placement.

    [0044] An alternative method for analyzing intubation therapy involves skipping the first step 720 of FIGURE 7 altogether, and merely pausing for time T before analyzing a true breath. This alternative method is preferably begun by a signal from a user input 664 to analyze therapy step 636 which indicates the beginning of the intubation or airway placement period.

    [0045] Now referring to FIGURE 8, an analyzing therapy step 336 is described which analyzes the effectiveness of ongoing CPR. A true breath sequence and corresponding data is obtained in accordance with the foregoing method steps shown in FIGURE 3. However, the analyzing therapy step 336 further uses a calculated respiration rate trend 820 and a detected gradual change of the etCO2 trend curve 800 to evaluate the effectiveness of CPR. In the FIGURE 8 example, the respiration rate 820 lies below a high threshold limit of 15, while the etCO2 trend shows an increase over two minutes from 20 to 30 mmHg, or 50%. The respiration rate 820 with slowly increasing etCO2 indicates that the ongoing CPR is effective. In the effective case, a corresponding clinical guidance instruction is issued at the output step 340. On the other hand, if the respiration rate 820 and etCO2 trend parameters fail to indicate effective CPR, a corresponding clinical guidance instruction and/or an alert is issued at the output step 340.

    [0046] The accuracy of the CPR effectiveness determination is improved with an indication that CPR compressions are occurring. Either a user input 364, information from a CPR sensor, or a stream of CPR artifact breath candidates 370 from step 334 may be used in the analyze therapy step 336 to ascertain ongoing CPR. Information from the CPR sensor can also be used in conjunction with the etCO2 algorithm at the classify breath step 333. Thus, the method can avoid a false CPR effectiveness guidance.

    [0047] Now referring to FIGURE 9, an analyzing therapy step 336 is described which analyzes for the occurrence of the return of spontaneous circulation (ROSC). A true breath sequence and corresponding data is obtained in accordance with the foregoing method steps shown in FIGURE 3. However, the analyzing therapy step 336 further uses a calculated respiration rate trend 820 and a detected rapid change of the etCO2 trend curve 900 to ascertain the occurrence of ROSC.

    [0048] In the FIGURE 9 example, the etCO2 trend shows a rapid increase from one true breath to the next true breath from 25 to 60 mmHg, which is greater than 50%. The rapidly increasing etCO2 indicates that the patient has begun to exchange CO2 naturally and without assistance. If ROSC is detected, a corresponding clinical guidance instruction is issued at the output step 340. On the other hand, if the etCO2 trend parameters fail to indicate ROSC, a corresponding clinical guidance instruction and/or an alert is issued at the output step 340. Also if the etCO2 trend shows a rapid drop, such as from 60 to 10 mmHg, then the loss of spontaneous circulation is indicated, and an alert to resume CPR may be provided.


    Claims

    1. A carbon dioxide (CO2) monitoring system (14) for use with patients undergoing cardiopulmonary resuscitation (CPR), comprising:

    - a CO2 sensor (12) which receives respiratory gases from a patient and senses the CO2 content of the gases to produce CO2 measurement signals;

    - a pre-processor (24) which digitizes and stores the CO2 measurement signals as a CO2 signal stream;

    - a breath candidate detector (30) responsive to the CO2 signal stream which identifies a plurality of breath candidates;

    - a breath characterizer (32) which determines an end-tidal CO2 value for each breath candidate;

    - a breath classifier (34) which classifies each breath candidate as a true breath or an CPR artifact generated as a result of an external CPR compression based on the breath candidate end-tidal CO2 value, and which analyzes the breath candidates and segregates true breaths from CPR artifacts;

    - a therapy analyzer (36), responsive to a plurality of true breaths from the breath classifier, which determines the effectiveness of the patient therapy; and

    - an output generator (40) which provides an output instruction regarding the effectiveness of the patient therapy, wherein

    - the monitoring system is further configured to analyse the CPR artifacts to provide an instruction that CPR is being administered.


     
    2. The CO2 monitoring system of Claim 1, wherein the breath classifier (34) is configured to classify the breath candidate as the CPR artifact if a greatest bump interval (460a, 460b, 460c) of multiple bumps of a CO2 waveform (470) of the CO2 signal stream is shorter than 550 milliseconds, and crosses a threshold line (450) equal to 75% of the average of the peak-peak amplitudes of the bumps.
     
    3. The CO2 monitoring system of Claim 1, further comprising a filter which removes noise from the pre-processed CO2 signal stream.
     
    4. The CO2 monitoring system of Claim 1, wherein the breath characterizer further determines at least one of waveform baseline, waveform amplitude, waveform frequency, waveform slope, waveform rhythm, and waveform corners for each breath candidate, and further wherein the breath classifier classifies each breath candidate as a true breath or an artifact based on the at least one of waveform baseline, waveform amplitude, waveform frequency, waveform slope, waveform rhythm, and waveform corners for each breath candidate.
     
    5. The CO2 monitoring system of Claim 1, further comprising a therapy input to the therapy analyzer, wherein the therapy analyzer is further responsive to the therapy input to determine the effectiveness of the patient therapy.
     
    6. The CO2 monitoring system of Claim 5, wherein the therapy input comprises a switch which indicates an initiation of receiving respiratory gases at the CO2 sensor.
     
    7. The CO2 monitoring system of Claim 1, wherein the output instruction is responsive to an abnormal condition comprising one of no respiration received or erratic CO2 waveform.
     
    8. The CO2 monitoring system of Claim 1, wherein the output instruction comprises a visual or audio advisory to check the advanced airway.
     
    9. The CO2 monitoring system of Claim 1, wherein the output instruction is responsive to an abnormal condition comprising a decrease in the end-tidal CO2 values from the plurality of true breaths.
     
    10. The CO2 monitoring system of Claim 9, wherein the output instruction comprises a visual or audio advisory of the effectiveness of the CPR.
     
    11. The CO2 monitoring system of Claim 1, wherein the output instruction is responsive to an abnormal condition comprising one of airway obstruction, apnea, or undesirable rate of ventilation.
     
    12. The CO2 monitoring system of Claim 11, wherein the output instruction comprises one of check patient or adjust ventilator settings.
     


    Ansprüche

    1. Kohlendioxid- (CO2) Überwachungssystem (14) zur Verwendung bei Patienten, die einer Herz-Lungen-Wiederbelebung (HLW) unterzogen werden, umfassend:

    - einen CO2-Sensor (12), der Atemgase von einem Patienten empfängt und den CO2-Gehalt der Gase erfasst, um CO2-Messsignale zu erzeugen;

    - einen Vorprozessor (24), der die CO2-Messsignale digitalisiert und als einen CO2-Signalstrom speichert;

    - einen Atmungskandidatendetektor (30), der auf den CO2-Signalstrom reagiert und eine Vielzahl von Atmungskandidaten identifiziert;

    - eine Atmungscharakterisierungseinheit (32), die einen endtidalen CO2-Wert für jeden Atmungskandidaten ermittelt;

    - einen Atmungsklassifizierer (34), der basierend auf dem endtidalen CO2-Wert des Atmungskandidaten jeden Atmungskandidaten als echte Atmung oder als einen infolge einer externen HLW-Kompression erzeugen HLW-Artefakt klassifiziert und der die Atmungskandidaten analysiert und echte Atmungen von HLW-Artefakten trennt;

    - einen Therapieanalysator (36), der auf eine Vielzahl von echten Atmungen von dem Atmungsklassifizierer reagiert und die Wirksamkeit der Patiententherapie ermittelt; und

    - einen Ausgabegenerator (40), der eine Ausgabeanweisung in Bezug auf die Wirksamkeit der Patiententherapie bereitstellt, wobei

    - das Überwachungssystem weiterhin dafür konfiguriert ist, die HLW-Artefakte zu analysieren, um eine Anweisung bereitzustellen, dass HLW verabreicht wird.


     
    2. CO2-Überwachungssystem nach Anspruch 1, wobei der Atmungsklassifizierer (34) dafür konfiguriert ist, den Atmungskandidaten als den HLW-Artefakt zu klassifizieren, wenn ein größtes Buckelintervall (460a, 460b, 460c) von mehreren Buckeln einer CO2-Wellenform (470) des CO2-Signalstroms kürzer als 550 Millisekunden ist und eine Schwellenwertlinie (450) gleich 75 % des Mittelwerts der Spitze-Spitze-Amplituden der Buckel überquert.
     
    3. CO2-Überwachungssystem nach Anspruch 1, weiterhin umfassend einen Filter, der Rauschen aus dem vorverarbeiteten CO2-Signalstrom entfernt.
     
    4. CO2-Überwachungssystem nach Anspruch 1, wobei die Atmungscharakterisierungseinheit weiterhin mindestens eines von Wellenformbasislinie, Wellenformamplitude, Wellenformfrequenz, Wellenformsteigung, Wellenformrhythmus und Wellenformecken für jeden Atmungskandidaten ermittelt, und wobei weiterhin der Atmungsklassifizierer jeden Atmungskandidaten basierend auf mindestens einem von Wellenformbasislinie, Wellenformamplitude, Wellenformfrequenz, Wellenformsteigung, Wellenformrhythmus und Wellenformecken für jeden Atmungskandidaten als echte Atmung oder als Artefakt klassifiziert.
     
    5. CO2-Überwachungssystem nach Anspruch 1, weiterhin umfassend eine Therapieeingabe zum Therapieanalysator, wobei der Therapieanalysator weiterhin auf die Therapieeingabe reagiert, um die Wirksamkeit der Patiententherapie zu ermitteln.
     
    6. CO2-Überwachungssystem nach Anspruch 5, wobei die Therapieeingabe einen Schalter umfasst, der einen Beginn des Empfangens von Atemgasen am CO2-Sensor angibt.
     
    7. CO2-Überwachungssystem nach Anspruch 1, wobei die Ausgabeanweisung auf eine abnormale Bedingung umfassend den fehlenden Empfang von Atmung oder eine fehlerhafte CO2-Wellenform reagiert.
     
    8. CO2-Überwachungssystem nach Anspruch 1, wobei die Ausgabeanweisung eine visuelle oder akustische Empfehlung zur Überprüfung der fortgeschrittenen Atemwege umfasst.
     
    9. CO2-Überwachungssystem nach Anspruch 1, wobei die Ausgabeanweisung auf eine abnormale Bedingung umfassend eine Abnahme der endtidalen CO2-Werte aus der Vielzahl von echten Atmungen reagiert.
     
    10. CO2-Überwachungssystem nach Anspruch 9, wobei die Ausgabeanweisung eine visuelle oder akustische Empfehlung bezüglich der Wirksamkeit der HLW umfasst.
     
    11. CO2-Überwachungssystem nach Anspruch 1, wobei die Ausgabeanweisung auf eine abnormale Bedingung umfassend eine Atemweg-Obstruktion, Apnoe oder eine unerwünschte Beatmungsrate reagiert.
     
    12. CO2-Überwachungssystem nach Anspruch 11, wobei die Ausgabeanweisung das Überprüfen des Patienten oder das Anpassen der Einstellungen des Beatmungsgeräts umfasst.
     


    Revendications

    1. Système de surveillance de dioxyde de carbone (CO2) (14) destiné à être utilisé avec des patients subissant une réanimation cardiopulmonaire (RCP), comprenant :

    - un capteur de CO2 (12) qui reçoit des gaz respiratoires en provenance d'un patient et détecte la teneur en CO2 des gaz pour produire des signaux de mesure de CO2 ;

    - un préprocesseur (24) qui numérise et stocke les signaux de mesure de CO2 en tant que flux de signaux de CO2 ;

    - un détecteur de candidats de souffle (30) sensible au flux de signaux de CO2 qui identifie une pluralité de candidats de souffle ;

    - un dispositif de caractérisation de souffle (32) qui détermine une valeur de CO2 de fin d'expiration pour chaque candidat de souffle ;

    - un dispositif de classement de souffle (34) qui classe chaque candidat de souffle en tant que souffle véritable ou artéfact de RCP généré suite à une compression de RCP externe d'après la valeur de CO2 de fin d'expiration de candidat de souffle, et qui analyse les candidats de souffle et trie les souffles véritables des artéfacts de RCP ;

    - un dispositif d'analyse de thérapie (36), sensible à une pluralité de souffles véritables provenant du dispositif de classement de souffle, qui détermine l'efficacité de la thérapie du patient ; et

    - un générateur de sortie (40) qui fournit une instruction de sortie concernant l'efficacité de la thérapie du patient, dans lequel

    - le système de surveillance est en outre configuré pour analyser les artéfacts de RCP afin de fournir une instruction d'administration de RCP.


     
    2. Système de surveillance de CO2 selon la revendication 1, dans lequel le dispositif de classement de souffle (34) est configuré pour classer le candidat de souffle en tant qu'artéfact de RCP si un intervalle de bosse le plus grand (460a, 460b, 460c) de multiples bosses d'une forme d'onde de CO2 (470) du flux de signaux de CO2 est plus court que 550 millisecondes, et croise une ligne seuil (450) égale à 75 % de la moyenne des amplitudes de crête à crête des bosses.
     
    3. Système de surveillance de CO2 selon la revendication 1, comprenant en outre un filtre qui élimine le bruit du flux de signaux de CO2 prétraité.
     
    4. Système de surveillance de CO2 selon la revendication 1, dans lequel le dispositif de caractérisation de souffle détermine en outre au moins l'un d'une ligne de base de forme d'onde, d'une amplitude de forme d'onde, d'une fréquence de forme d'onde, d'une pente de forme d'onde, d'un rythme de forme d'onde, et de coins de forme d'onde pour chaque candidat de souffle, et en outre dans lequel le dispositif de classement de souffle classe chaque candidat de souffle en tant que souffle véritable ou artéfact d'après au moins l'un d'une ligne de base de forme d'onde, d'une amplitude de forme d'onde, d'une fréquence de forme d'onde, d'une pente de forme d'onde, d'un rythme de forme d'onde, et de coins de forme d'onde pour chaque candidat de souffle.
     
    5. Système de surveillance de CO2 selon la revendication 1, comprenant en outre une entrée de thérapie dans le dispositif d'analyse de thérapie, dans lequel le dispositif d'analyse de thérapie est en outre sensible à l'entrée de thérapie pour déterminer l'efficacité de la thérapie du patient.
     
    6. Système de surveillance de CO2 selon la revendication 5, dans lequel l'entrée de thérapie comprend un commutateur qui indique un début de réception de gaz respiratoires au niveau du capteur de CO2.
     
    7. Système de surveillance de CO2 selon la revendication 1, dans lequel l'instruction de sortie est sensible à une condition anormale comprenant l'une d'une absence de respiration reçue ou d'une forme d'onde de CO2 erratique.
     
    8. Système de surveillance de CO2 selon la revendication 1, dans lequel l'instruction de sortie comprend un visuel ou un audio renseignant qu'il faut vérifier les voies respiratoires avancées.
     
    9. Système de surveillance de CO2 selon la revendication 1, dans lequel l'instruction de sortie est sensible à une condition anormale comprenant une diminution des valeurs de CO2 de fin d'expiration parmi la pluralité de souffles véritables.
     
    10. Système de surveillance de CO2 selon la revendication 9, dans lequel l'instruction de sortie comprend un visuel ou un audio renseignant de l'efficacité de la RCP.
     
    11. Système de surveillance de CO2 selon la revendication 1, dans lequel l'instruction de sortie est sensible à une condition anormale comprenant l'un d'une obstruction des voies aériennes, d'une apnée, ou d'un taux de ventilation indésirable.
     
    12. Système de surveillance de CO2 selon la revendication 11, dans lequel l'instruction de sortie comprend l'un de paramétrages de vérification du patient ou de réglage du ventilateur.
     




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    REFERENCES CITED IN THE DESCRIPTION



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    Patent documents cited in the description