Abstract:
A process and a device for oxygen regulation of a patient having at least two SPO 2  monitors and a control for automatic recognition of which measurements are more reliable. The measurement from one or more of the two SPO 2  is used to control the oxygen concentration delivered to a patient based on a comparison of the measurements from the at least two SPO 2  monitors.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to oxygen regulation with at least two saturation of peripheral oxygen (SPO 2 ) monitors with an automatic selection or recognition of a signal from one of at least two SPO 2  monitors. 
       BACKGROUND OF THE INVENTION 
       [0002]    An SPO 2  monitor is required for the regulation of the oxygen saturation in a patient. Physiological closed loop systems must pass over into a fallback mode in care of any error that generates an unacceptable risk. The recognition of incorrect measured SPO 2  values may take place by checking the signal in the SPO 2  itself. The manufacturer Masimo provides an index of the signal quality of an SPO 2  monitor. If the signal quality drops below a threshold value or the time integral of the signal quality drops below a threshold value, the control system recognizes the need for the fall back mode. However, such SPO 2  control systems only send a warning or alarm during phases of unacceptable signal quality such that the oxygenation of the patient can be set manually. Such SPO 2  control systems do not provide for the oxygenation of the patient to be set automatically. 
         [0003]    US 20100139659 A1 relates to a device and a process for controlling a respirator with inclusion of an oxygen saturation value for compensating a device-dependent time response, a physiological time response and a measuring method-dependent time response. The device-dependent time response, the physiological time response and the measuring method-dependent time response are determined in a continuous sequence and a run time of a change in the oxygen concentration from the metering means in the respirator to the patient is determined and taken into account in regulating the oxygen concentration. The device and process would benefit greatly from increased reliability of measured SPO 2  values. 
       SUMMARY OF THE INVENTION 
       [0004]    An object of the present invention is to increase the reliability of an SPO 2  control system by providing a higher correlation between the measured value essential for the control and actual oxygenation of the blood during phases of acceptable signal quality. The deviation between the actual oxygenation and the target oxygenation is reduced so that the average quality of the control is improved over long periods of time. 
         [0005]    The present invention allows for setting the saturation of a patient&#39;s blood during phases of poor signal quality. This provides a real improvement of patient therapy as it is not always ensured that a nursing staff is immediately available in clinical practice. 
         [0006]    Another object of the present invention is to make possible an emergency operation during phases of unacceptable signal quality to reduce the deviation between the actual oxygenation of the blood and the target oxygenation. 
         [0007]    Yet another object of the present invention is to increase the reliability of the closed loop of the SPO 2  monitor. The present invention reduces the percentage of time represented by phases of unacceptable signal quality. 
         [0008]    The control system contains at least two independent SPO 2  monitors. The SPO 2  monitors may be placed at different points or locations on a patient&#39;s body. The SPO 2  monitors may preferably be provided on different extremities of the patient. The system optionally has a measured value of the pulse rate or heart rate by means of an electrocardiography (ECG). Both SPO 2  monitors send measured values on the pulse rate or heart rate, perfusion and signal quality as well as the oxygen saturation of the patient&#39;s blood. 
         [0009]    The trustworthiness or reliability of the measurement values is rated by automatic comparison of the measured values of the first SPO 2  monitor with the measurement values of the second SPO 2  monitor. The pulse rates or heart rates of the monitors are optionally compared with the ECG-based pulse rate. The SPO 2  value that is used for the next control procedure is identified from the results of the comparison. The measured SPO 2  signal with the higher trustworthiness or reliability is used for the control. A mean value from the two measured SPO 2  values is sent to the control unit in case of comparable trustworthiness or reliability of the two measured values. 
         [0010]    In addition to the features provided in US 20100139659 A1 (the entire contents of US 20100139659 A1 are incorporated herein by reference), the system of the present invention has another SPO 2  monitor and an ECG. A decision unit processes a measured value, which is sent to the control unit based on the criterion discussed below. 
         [0011]    The first criteria is the oxygen saturation level. Above or equal to 80% oxygen saturation, SPO 2  monitors usually indicate less than the actual saturation when poor signal quality exists. However, the probability of excessively high measured values is low. The decision unit therefore rates the higher measured value as being more trustworthy or reliable. 
         [0012]    The second criteria is the agreement of the heart rates measured by each SPO 2  monitor with another reference heart rate measurement. The ECG provides a reference measurement. The SPO 2  monitor that has a heart rate that shows better agreement with the reference measurement is rated as being more trustworthy. 
         [0013]    The measured values of the SPO 2  monitor that has proved to be better, on average, is used for controlling the oxygen concentration delivered to the patient. The mean value of the two measured values is used in case of equal values. 
         [0014]    According to the present invention, a process for controlling a respirator is provided. A first oxygen saturation monitor is provided. A second oxygen saturation monitor is provided. A first measurement signal is detected with the first oxygen saturation monitor. The first measurement signal comprises a first patient blood oxygen saturation measurement. A second measurement signal is detected with the second oxygen saturation monitor. The second measurement signal comprises a second patient blood oxygen saturation measurement. A measuring reliability rating is determined for each of the first measurement signal and the second measurement signal when the first patient blood oxygen saturation measurement and the second patient blood oxygen saturation measurement are greater than or equal to a predetermined oxygen saturation threshold. At least one of the first measurement signal associated with the first oxygen saturation monitor and the second measurement signal associated with said second oxygen saturation monitor is selected based on the measuring reliability rating associated with each of the first measurement signal and the second measurement signal to define at least one selected measurement signal. An oxygen concentration delivered to the patient is controlled based on the at least one selected oxygen saturation measurement. 
         [0015]    The measuring reliability rating may be determined based on at least a comparison of the first patient blood oxygen saturation measurement and the second blood oxygen saturation measurement. 
         [0016]    The measuring reliability rating associated with one of the first measurement and the second measurement may be increased when the one of the first patient blood oxygen saturation measurement and the second patient blood oxygen saturation measurement is greater than another one of the first patient blood oxygen saturation measurement and the second patient blood oxygen saturation measurement. 
         [0017]    The predetermined oxygen saturation threshold may be eighty percent. 
         [0018]    An alarm element may be provided. The alarm element may be activated when the first patient blood oxygen saturation measurement and the second patient blood oxygen saturation measurement are less than the predetermined oxygen saturation threshold. 
         [0019]    An electrocardiography device may be provided. A patient may be measured with the electrocardiography device to provide a reference heart rate. A first patient heart rate signal may be detected with the first oxygen saturation monitor. The first patient heart rate signal may comprise a first patient heart rate measurement. A second patient heart rate signal may be detected with the second oxygen saturation monitor. The second patient heart rate signal may comprise a second patient heart rate measurement. The first patient heart rate measurement may be compared with the reference heart rate measurement. The second patient heart rate measurement may be compared with the reference heart rate. The measuring reliability rating may be determined based on the comparison of the first patient heart rate measurement with the reference heart rate and the comparison of the second patient heart rate measurement with the reference heart rate. 
         [0020]    The measuring reliability rating associated with one of the first measurement signal and the second measurement signal may be increased when a difference between the reference heart rate and at least one of the first patient heart rate measurement and the second patient heart rate measurement is less than a difference between the reference heart rate and another one of the first patient heart measurement and the second patient heart rate measurement. 
         [0021]    The measuring reliability rating associated with the first measurement signal may be compared with the measuring reliability rating associated with the second measurement signal. The measuring reliability rating associated with the one of the first measurement signal and the second measurement signal may be greater than the measuring reliability rating associated with the another one of the first measurement signal and the second measurement signal. The at least one selected measurement signal may correspond to the one of the first measurement signal and the second measurement signal with the greater measuring reliability rating. 
         [0022]    The measuring reliability rating associated with the first measurement signal may be compared with the measuring reliability rating associated with the second measurement signal. The at least one selected measurement signal may comprise an average of the first patient blood oxygen saturation measurement and the second patient blood oxygen saturation measurement. 
         [0023]    An oxygen saturation bedside monitor may be provided. The oxygen saturation beside monitor may provide the second patient blood oxygen saturation measurement as output. The second patient blood oxygen saturation measurement signal may be transferred to the second oxygen saturation monitor via a network. 
         [0024]    According to the present invention, a device for controlling a respirator is provided. The device comprises a first oxygen saturation monitor detecting a first measurement signal. The first measurement signal comprises a first patient blood oxygen saturation measurement. A second oxygen saturation monitor detects a second measurement signal. The second measurement signal comprises a second patient blood oxygen saturation measurement. A measurement selection means is provided for determining a reliability rating for each of the first measurement signal and the second measurement signal and for selecting at least one of the first measurement signal and the second measurement signal based on the measuring reliability rating associated with each of the first measurement signal and the second measurement signal when the first patient blood oxygen saturation measurement and the second patient blood oxygen saturation measurement is greater than a predetermined oxygen saturation threshold to define at least one selected measurement signal. A means is provided for controlling an oxygen concentration delivered to a patient based on said at least one selected measurement signal. 
         [0025]    The measuring reliability rating may be determined via the measurement selection means based on at least a comparison of the first patient blood oxygen saturation measurement and the second blood oxygen saturation measurement. 
         [0026]    The measurement selection means may increase the reliability rating associated with one of the first measurement signal and the second measurement signal when one of the first patient blood oxygen saturation measurement and the second patient blood oxygen saturation measurement is greater than another one of the first patient blood oxygen saturation measurement and the second patient blood oxygen saturation measurement. 
         [0027]    The device may comprise an alarm device. The predetermined oxygen saturation threshold may be eighty percent. The alarm device may generate an alarm signal as output when the first oxygen saturation measurement and the second oxygen saturation measurement is less than the predetermined oxygen saturation threshold. 
         [0028]    The device may further comprise an electrocardiography device. The electrocardiography device may provide a patient reference heart rate. The first oxygen saturation monitor may provide a first patient heart rate as output. The second oxygen saturation monitor may provide a second patient heart rate as output. The measurement selection means may receive the patient reference heart rate, the first patient heart rate and the second patient heart rate as input. The measurement selection means may determine the measuring reliability rating based on a comparison of the first patient heart rate measurement with the reference heart rate and a comparison of the second patient heart rate measurement with the reference heart rate. 
         [0029]    The measurement selection means may increase the measuring reliability rating associated with one of the first measurement signal and the second measurement signal when a difference between the reference heart rate and at least one of the first patient heart rate measurement and the second patient heart rate measurement is less than a difference between the reference heart rate and another one of the first patient heart measurement and the second patient heart rate measurement. 
         [0030]    The measurement selection means may select the at least one of the first measurement signal and the second measurement signal based on a comparison of the measuring reliability rating associated with the first measurement signal with the measuring reliability rating associated with the second measurement signal. The measuring reliability rating associated with the one of the first measurement signal and the second measurement signal may be greater than the measuring reliability rating associated with the another one of the first measurement signal and the second measurement signal. The at least one selected measurement signal may correspond to the one of the first measurement signal and the second measurement signal with the greater measuring reliability rating. 
         [0031]    The measurement selection means may select the at least one of the first measurement signal and the second measurement signal based on a comparison of the measuring reliability rating associated with the first measurement signal with the measuring reliability rating associated the second measurement signal. The at least one selected measurement signal may comprise an average of the first patient blood oxygen saturation measurement and the second patient blood oxygen saturation measurement. 
         [0032]    The device may comprise an oxygen saturation bedside monitor that provides the second patient blood oxygen saturation measurement as output. The second patient blood oxygen saturation measurement signal may be transferred to the second oxygen saturation monitor via a network. 
         [0033]    According to the present invention, a process is provided for controlling a respirator. The process comprises providing a first measuring device. The first measuring device provides a first measurement signal as output. The first measurement signal comprises a first patient oxygen saturation measurement. A first oxygen saturation monitor is provided and the first oxygen saturation monitor receives the first measurement signal. A second measuring device is provided. The second measuring device provides a second measurement signal as output. The second measurement signal comprises a second patient oxygen saturation measurement. A second oxygen saturation monitor receives the second measurement signal. The first patient oxygen saturation measurement and the second patient oxygen saturation measurement are compared with a predetermined saturation threshold. At least one measuring reliability rating criteria is provided. The at least one measuring reliability rating criteria comprises at least a comparison of the first patient oxygen saturation measurement with the second patient oxygen saturation measurement. At least one of the first measurement signal and the second measurement signal is selected based on the at least one measuring reliability rating criteria when the first patient oxygen saturation measurement and the second patient oxygen saturation measurement are greater than or equal to the predetermined saturation threshold to define at least one selected measurement signal. An oxygen concentration delivered to the patient is controlled based on the selected one of the first measurement signal and the second measurement signal. The selected one of the first measurement signal and the second measurement signal comprises one of the first patient oxygen saturation measurement, the second patient oxygen saturation measurement and an average of the first patient oxygen saturation measurement and the second patient oxygen saturation measurement. 
         [0034]    The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0035]    In the drawings: 
           [0036]      FIG. 1  is schematic view of a closed control loop; 
           [0037]      FIG. 2  is a diagram of the steps taken to determine which measurement from one or more of the SPO 2  monitors should be used to control the concentration of oxygen supplied to a patient; 
           [0038]      FIG. 3  is a view showing an algorithm used to determine which measurement from one or more of the SPO 2  monitors should be used to control the concentration of oxygen supplied to a patient; and 
           [0039]      FIG. 4  is a schematic view of another embodiment of the closed control loop. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0040]    Referring to the drawings in particular,  FIG. 1  is a schematic view of a closed control loop with a first oxygen saturation-measuring means  25 , a second oxygen saturation-measuring means  27 , a patient  4 , an ECG unit  28 , a decision unit  170 , a pneumatic patient connection to the respirator and time function elements formed by models. 
         [0041]    The closed control loop  70  comprises a controller element  101 , a controlled system  102 , a time modeling component  122  and measuring components  25 ,  27 ,  28 . Furthermore, a first summation point  104  and a first branching point  106  are arranged in series with controller  40 . The control loop  70  is preferably designed as a part of the control and regulating unit  7 , and controller  40  is designed in the digital form in another preferred manner. 
         [0042]    An input data set  55  transmitted by an input unit with a set point  37  of the oxygen saturation is sent as a command variable to the controller  40  via the control and regulating unit  7 . Device parameters of the respirator, of a gas path  6  and of the humidifier  23  are made available by the control and regulating unit  7  by means of a data connection  116 . In addition, measured parameters of the measuring arrangement comprising the SPO 2  monitor  25  and SPO 2  monitor  27  are made available to decision unit  170 . The humidifying unit  23  is in connection with the control unit  7  via the data connection  116 . A state of the liquid feed to the humidifying unit  23  or of a filling level of the liquid reservoir of the humidifying unit  23  can be transmitted to the control unit  7  via the data connection  116 . Control unit  7  can thereupon correspondingly adjust the device parameters and make them available to the modeling component  122  by means of the data connection  115 . 
         [0043]    The controlled system  102  comprises a patient  4 , the humidifying unit  23 , a gas-metering unit  9 , a gas-mixing unit  8 , an inspiration valve  2 , a breathing tube system as the gas path  6  and a Y-piece  22  for connecting the breathing tube system  6  to the patient  4 . 
         [0044]    The first SPO 2  monitor  25  provides a first SPO 2  measurement  103   a  as output. The second SPO 2  monitor  27  provides a second SPO 2  measurement  103   b  as output. The first SPO 2  monitor  25  may detect the first SPO 2  measurement  103   a  via an SPO 2  sensor  24  at one location, such as the finger  44  of patient  4 , with a sensor line  26 . The second SPO 2    27  may detect the second SPO 2  measurement  103   b  via an SPO 2  sensor at another location of the patient  4 . Alternatively, a signal comprising the SPO 2  measurement may be also be transferred to at least one of the SPO 2  monitors from a bedside monitor  180  via a network  182 , which may be wirelessly connected to at least one of the SPO 2  monitors as shown in  FIG. 4 . A reference patient heart rate  103   c  is provided as output by ECG unit  27 . The first SPO 2  measurement  103   a , the second SPO 2  measurement  103   b  and the patient heart rate  103   c  are provided as input to the decision unit  170 . The decision unit  170  determines whether the first SPO 2  measurement  103   a , the second SPO 2  measurement  103   b  or an average of the first SPO 2  measurement  103   a  and the second SPO 2  measurement  103   b  should be provided as an output signal based on criterion disclosed in the diagram or flow chart as shown in  FIG. 2 . The output signal of the decision unit  170  is sent as a controlled variable as a set of measured values of the oxygen saturation  34  to the controller input  41  of controller  40  in the controller element  101 . Controller element  101  comprises a controller  40 , a controller input  41 , which is designed to form a difference value of the oxygen saturation  36  from the set point  37  and actual oxygen saturation value  34 , and the controller output  43 , which receives the difference value  36  and at which the response of the controller  40  is present corresponding to the control characteristic. One or more values of oxygen saturation  34  are also provided as input to the modeling component  122  via the decision unit  170 . The modeling component  122  includes a time lag element  19 . The time lag element  19  includes a first-order time function element  191  and a dead time component  192 . The controller output signal  43  and feedback signal  108  of the modeling component  122  are sent to the first summation point  104 . The feedback signal  108  of the modeling component  122  is likewise sent to the first summation point  104 . A first branching point  106  from which the summation signal  110  is sent to the gas-metering unit  9 , on the one hand, and additionally to the modeling component  122  as an input variable, is arranged in series with the first summation point  104 . The set value of the oxygen concentration  30  is corrected in the gas-metering unit  9  on the basis of the summation signal  110 . 
         [0045]      FIG. 2  shows a flow chart of the steps taken by the decision unit  170  to determine the reliability rating of one or more measurements  103   a  associated with the first SPO 2  monitor  25  and the reliability rating of one or more measurements  103   b  associated with the second SPO 2  monitor  27 . The decision unit  170  is initiated in step  200 . The reliability ratings are set to zero in step  202 . The decision unit  170  acquires at least one oxygen saturation measurement associated with the first SPO 2  monitor  25  and at least one oxygen saturation measurement associated with the second SPO 2  monitor  27  in step  204 . The decision unit  170  determines whether the at least one oxygen saturation measurement associated with the first SPO 2  monitor  25  and the at least one oxygen saturation measurement associated with the second SPO 2  monitor  27  are greater than or equal to an oxygen concentration of 80%. If the oxygen saturation measurement associated with the first SPO 2  monitor  25  and the oxygen saturation measurement associated with the second SPO 2  monitor  27  are not greater than or equal to 80%, an alarm  208  is generated. The alarm  208  is of a therapeutical nature and alerts medical staff as to a dangerous level of patient oxygen saturation. 
         [0046]    The decision unit  170  compares the oxygen saturation measurement associated with the first SPO 2  monitor  25  with the oxygen saturation measurement associated with the second SPO 2  monitor  27 . The SPO 2  monitor with the greater oxygen saturation measurement is determined by the decision unit  170  to correspond to a more reliable measurement reading. If the oxygen saturation measurement associated with the first SPO 2  monitor  25  and the oxygen saturation measurement associated with the second SPO 2  monitor  27  are greater than or equal to 80%, the oxygen saturation measurement associated with the first SPO 2  monitor  25  is compared with the oxygen saturation measurement associated with the second SPO 2  monitor  27  to determine which of the oxygen saturation measurements is greater in step  210 . If the oxygen saturation measurement associated with the first SPO 2  monitor  25  is greater than the oxygen saturation measurement associated with the SPO 2  monitor  27 , the measuring reliability rating associated with the oxygen saturation measurement associated with the first SPO 2  monitor  25  is increased in step  212 . If the oxygen saturation measurement associated with the first SPO 2  monitor  25  is not greater than the oxygen saturation measurement associated with the second SPO 2  monitor  27 , the decision unit  170  checks to determine if the oxygen saturation measurement associated with the second SPO 2  monitor  27  is greater than the oxygen saturation measurement associated with the first SPO 2  monitor  25  in step  214 . The measuring reliability rating associated with the oxygen saturation measurement associated with the second SPO 2  monitor  27  is increased in step  216  if the oxygen saturation measurement associated with the second SPO 2  monitor  27  is greater than the oxygen saturation measurement associated with the first SPO 2  monitor  25 . 
         [0047]    After comparing the oxygen saturation measurements to determine which oxygen saturation measurement is greater and providing the higher reliability rating to the greater of the two oxygen saturation measurements or determining that one SPO 2  measurement is not greater than the other SPO 2  measurement, the decision unit  170  compares the pulse rate or heart rate associated with each SPO 2  monitor with a reference heart rate or pulse rate, which is measured by ECG unit  28 , in step  218 . If the heart rate or pulse rate measurement associated with the first SPO 2  monitor  25  is closer to the reference heart rate or pulse rate measurement than the heart rate or pulse rate measurement associated with the second SPO 2  monitor  27 , then reliability rating associated with the at least one measurement associated with the first SPO 2  monitor  25  is increased in step  220 . If the heart rate or pulse rate measurement associated with the first SPO 2  monitor  25  is not in agreement with the reference heart rate or pulse rate or closer to the reference heart rate or pulse rate measurement in step  218  than the heart rate or pulse rate associated with the second SPO 2  monitor, the decision unit  170  determines whether the heart rate or pulse rate measurement associated with the second SPO 2  monitor  27  is closer or more in agreement with the reference heart rate or pulse rate measurement than the heart rate or pulse rate measurement associated with the first SPO 2  monitor  25  in step  222 . If the heart rate or pulse rate measurement of the second SPO 2  monitor  27  is closer or more in agreement with the reference heart rate or pulse rate measurement than the heart rate or pulse rate measurement associated with the first SPO 2  monitor  25 , the measuring reliability rating associated with the at least one measurement associated with the second SPO 2  monitor  27  is increased in step  224 . 
         [0048]    The decision unit  170  determines whether one or more of the at least one measurement associated with the first SPO 2  monitor  25  and the at least one measurement associated with the second SPO 2  monitor  27  should be selected based on one or more of the reliability ratings determined in steps  212 ,  216 ,  220  and  224 . Steps  212  and  216  determine that the higher oxygen saturation measurement is the more reliable measurement and steps  220  and  224  qualify the SPO 2  sensor providing a heart rate or pulse rate as output that is closer to the reference heart rate or pulse as the more reliable SPO 2  sensor. If one SPO 2  monitor and the measurements provided as output from the respective SPO 2  monitor receive more votings or weight based on the ratings  212 ,  216 ,  220  and  224 , the sensor signal associated with the SPO 2  monitor with the most votings or weight is used as a controlled variable that is provided as input to the controller input  41  of the controller element  101  and to the time modeling component  122 . Examples of an SPO 2  monitor receiving a greater amount of reliability ratings than another SPO 2  monitor occurs when an oxygen saturation measurement associated with a first SPO 2  is greater than the oxygen saturation measurement associated with a second SPO 2  monitor and a heart rate or pulse rate associated with the first SPO 2  monitor is closer to the reference heart rate or pulse rate than the pulse rate or heart rate associated with the second SPO 2  monitor. If both sensors have the same amount of reliability ratings, an average of the at least one oxygen saturation measurement associated with the first SPO 2  monitor  25  and the second SPO 2  monitor  27  is used as a controlled variable as input to the controller input  41  of the controller element  101  and to the time modeling component  122 . An example in which the amount of the reliability ratings of each SPO 2  monitor are the same is in a case in which the oxygen saturation measurement associated with each SPO 2  monitor is not greater than the other and the pulse rate or heart rate associated with each SPO 2  monitor is equally close to the reference pulse rate or heart rate. Another example of when the average of the at least one oxygen saturation measurement associated with the first SPO 2  monitor  25  and the second SPO 2  monitor  27  would be used is in a case in which the saturation oxygen measurement associated with one of the SPO 2  monitors is greater than the saturation oxygen measurement associated with the other one of the SPO 2  monitors and the heart rate or pulse rate associated with the other one of the SPO 2  monitors is closer to the reference heart rate or pulse rate than the heart rate or pulse rate associated with the one of the SPO 2  monitors. 
         [0049]    The decision unit  170  determines in step  226  whether the reliability rating associated with the first SPO 2  monitor  25  is greater than the reliability rating associated with the second SPO 2  monitor  27 . The at least one measurement associated with the first SPO 2  monitor  25  is selected in step  228  if the reliability rating associated with the first SPO 2  monitor  25  is greater than the reliability rating associated with the second SPO 2  monitor  27  such that the at least one measurement associated with the first SPO 2  monitor  25  is sent as a controlled variable to the controller input  41  of controller  40  in the controller element  101  and to the time modeling component  122 . 
         [0050]    If the reliability rating associated with the first SPO 2  monitor  25  is not greater than the reliability rating associated with the second SPO 2  monitor  27  in step  226 , the decision unit  170  determines whether the reliability rating associated with the second SPO 2  monitor  27  is greater than the reliability rating associated with the first SPO 2  monitor  25  in step  230 . The at least one measurement associated with the second SPO 2  monitor  27  is selected in step  232  if the reliability rating associated with the second SPO 2  monitor  27  is greater than the reliability rating associated with the first SPO 2  monitor  25  such that the at least one oxygen saturation measurement associated with the second SPO 2  monitor  27  is sent as a controlled variable to the controller input  41  of controller  40  in the controller element  101  and to the time modeling component  122 . 
         [0051]    An average of the at least one measurement associated with the first SPO 2  monitor  25  and the at least one measurement associated with the second SPO 2  monitor  27  is selected in step  234  if the reliability rating associated with the first SPO 2  monitor  25  is comparable or substantially equal to the reliability rating associated with the second SPO 2  monitor  27 . The average of the at least one measurement associated with the first SPO 2  monitor  25  and the at least one measurement associated with the second SPO 2  monitor  27  is sent as a controlled variable to the controller input  41  of controller  40  in the controller element  101  and to the time modeling component  122 . The measurements associated with the first SPO 2  monitor  25  and the second SPO 2  monitor  27  are continuously compared to each other and each respective pulse rate or heart rate associated with one of the SPO 2  monitors  25 ,  27  is continuously compared to the reference heart rate or pulse rate to determine which of the oxygen saturation measurements are more reliable. In one embodiment, the decision about which SPO 2  sensor is more reliable may be done in a specific period of time, such as every second. 
         [0052]      FIG. 3  is a view showing an algorithm used to determine which oxygen saturation measurement from one or more of the SPO 2  monitors should be used to control the concentration of oxygen supplied to a patient. The algorithm shows the steps taken when the oxygen saturation measurement associated with the first SPO 2  monitor and the oxygen saturation measurement associated with the second SPO 2  monitor are greater than or equal to 80%, which are essentially the same as the steps shown in  FIG. 2 . 
         [0053]      FIG. 4  is a schematic view of another embodiment of the closed control loop. The closed control loop is identical to the closed control loop shown in  FIG. 1 , except that one or more of the signals comprising the SPO 2  measurement is transferred to one or more of the SPO 2  monitors from a bedside monitor  180  via a network  182 . The network  182  may be wirelessly connected to one or more of the SPO 2  monitors. 
         [0054]    While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.