Patent Publication Number: US-8116837-B2

Title: System for adjusting power employed by a medical device

Description:
CROSS-REFERENCED TO RELATED APPLICATIONS 
     This is a non-provisional application of U.S. Provisional Application Ser. No. 60/697,615 filed Jul. 8, 2005. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to power conservation in portable medical devices, and in particular to power conservation in portable medical devices which use light emitting devices. 
     BACKGROUND OF THE INVENTION 
     Recent trends in miniaturization of medical devices, in particular the design and implementation of patient monitors as portable units, have created the need to maximize power conservation in order to reduce the required size of the attached battery. Standalone pulse oximetry systems have generally not attempted to conserve power because either the continuous AC power is available or a sizable battery is attached. Present monitoring needs, however, demand smaller profile, higher computational capacity for advanced algorithmic processing, integration with monitoring capability for other medical parameters, and also portability. In general, therefore, it is desirable to minimize power consumption. Power conservation in the pulse oximetry system, in particular, can yield additional running time for other medical parameter monitors in a multi-parameter patient monitor running on batteries. 
     In a typical pulse oximetry system, as much as 50% of power is used for driving the light emitting diodes (LEDs). Therefore, minimizing the power consumption of the LEDs enhances the lifetime of a battery after a full charge. In addition, advances in accurate calculation of blood oxygen level and pulse rate by pulse oximetry systems are due to the development of sophisticated algorithms and the integration of high capacity data processors capable of performing these algorithms into pulse oximetry systems. Such high capacity processors can also consume a significant amount of power. Minimizing the power consumption of the data processor can also enhance the lifetime of a battery after a full charge. A system according to invention principles addresses these needs and associated problems. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with principles of the present invention, a system for adjusting power employed by a medical device incorporating light emitting devices and being used for measuring patient medical parameters, includes a plurality of light emitting devices. A power unit is coupled to the light emitting devices and powers the light emitting devices responsive to respective control signals which determine power to be applied to the light emitting devices. A control unit provides the control signals and is coupled to the power unit. The control signals intermittently turn off at least one of the plurality of light emitting devices in a power save mode in response to a determination that a patient medical parameter value measured by the medical device, using an active light emitting device of the plurality of light emitting devices, is at a safe level. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       In the drawing: 
         FIG. 1  is a block diagram of a system according to principles of the present invention; 
         FIG. 2  is a flow chart illustrating the process of entering and terminating a power save mode in the system of  FIG. 1  according to the present invention; and 
         FIG. 3  is a block diagram illustrating a portion of the processing which is performed in a data processor according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A processor, as used herein, operates under the control of an executable application to (a) receive information from an input information device, (b) process the information by manipulating, analyzing, modifying, converting and/or transmitting the information, and/or (c) route the information to an output information device. A processor may use, or comprise the capabilities of, a controller or microprocessor, for example. The processor may operate with a display processor or generator. A display processor or generator is a known element for generating signals representing display images or portions thereof. A processor and a display processor comprises any combination of, hardware, firmware, and/or software. 
     An executable application, as used herein, comprises code or machine readable instructions for conditioning the processor to implement predetermined functions, such as those of an operating system, medical device system or other information processing system, for example, in response to user command or input. An executable procedure is a segment of code or machine readable instruction, sub-routine, or other distinct section of code or portion of an executable application for performing one or more particular processes. These processes may include receiving input data and/or parameters, performing operations on received input data and/or performing functions in response to received input parameters, and providing resulting output data and/or parameters. 
       FIG. 1  illustrates a portion of a medical device, incorporating light emitting devices, used to measure patient medical parameters.  FIG. 1  is a block diagram of a system  1  employed by such a medical device for adjusting power employed by the medical device. In system  1 , a plurality  10  of light emitting devices  12 ,  14  produce respective light signals  15 . The light signals  15  are passed through, or reflected off of, biological tissue  20 . The resulting respective light signals  25 , modified by passing through or being reflected off of the biological tissue  20 , are received by a corresponding plurality  30  of light sensor devices  32 ,  34 . The plurality  30  of light sensor devices  32 ,  34  convert the received light signals  25  into corresponding electrical signals  35 . Respective output terminals of the plurality  30  of light sensor devices  32 ,  34  are coupled to corresponding input terminals of a data processor  40 . A signal output terminal of the data processor  40  generates a medical parameter, and data processor  40  provides a further signal coupled to an input terminal of a control unit  50 . A control output terminal of the data processor  40  is coupled to an input terminal of a parameter value store  42 . An output terminal of the parameter value store  42  is coupled to a second input terminal of the control unit  50 . Respective output terminals of the control unit  50  generates control signals, and are coupled to corresponding control input terminals of a power unit  60 . Respective output terminals of the power unit  60  are coupled to corresponding input terminals of the plurality  10  of light emitting devices  12 ,  14 . A control output terminal of the control unit  50  is coupled to a control input terminal of the data processor  40 . An input terminal  55  is coupled to a source (not shown) of a control signal. The input terminal  55  is coupled to a control input terminal of the control unit  50 . 
     In operation, the power unit  60  powers the plurality  10  of light emitting devices  12 ,  14 , responsive to the respective control signals. The control signals determine the power applied to the plurality  10  of light emitting devices  12 ,  14 . The control unit  50 , coupled to the power unit  60 , provides the control signals. The control signals condition the power unit  60  to intermittently turn off at least one of the plurality  10  of light emitting devices  12 ,  14  in a power save mode. The control unit  50  initiates the power save mode in response to a determination that a patient medical parameter value measured by the medical device using an active light emitting device of the plurality of light emitting devices, is at a safe level. 
     For example, the system  1  may be implemented in a pulse oximeter medical device. A pulse oximeter produces successive blood oxygen saturation (e.g. SpO 2 ) and/or pulse rate (e.g. PLS) readings as the patient medical parameter values. In a pulse oximeter, the light emitting devices  10  are typically light emitting diodes (LEDs). The first LED  12  emits red light and the second LED  14  emits infrared (IR) light. They are typically time multiplexed to produce light signals  15  one at a time to produce a single SpO 2  and/or pulse rate reading. Respective signals  35  from the red  12  and IR  14  light sensors  32 ,  34  are read by the data processor  40  when the corresponding LED is on. The data processor  40  then processes those signals to calculate an SpO 2  and/or the pulse rate reading. Intermediate components are also typically calculated. For example, ac and dc components of the respective red and IR LED signals  35  are calculated and stored, and those components used to calculate the SpO 2  and/or pulse rate medical parameter. 
     In a pulse oximeter medical device, the system  1  enters a power save mode (described in more detail below) when a patient medical parameter value is at a safe level. The patient medical parameter value may be one measured by the medical device itself. For example, the patient medical parameter value may be the blood oxygen saturation representative value. The control unit  50  determines that the patient medical parameter value (e.g. the blood oxygen saturation representative value) is at a safe level when it is above a predetermined threshold, for example. The patient medical parameter value may also be the pulse rate. The control unit  50  determines that the patient medical parameter value (e.g. the pulse rate) is at a safe level when it is within a predetermined range. 
     Similarly, the patient medical parameter value may indicate a change in the blood oxygen saturation representative value or a change in the pulse rate. The control unit  50  also determines that the patient medical parameter value (e.g. the change in blood oxygen saturation representative value or pulse rate) is at a safe level when it is less than a predetermined value. The patient medical parameter value may also be a rate-of-change of the blood oxygen saturation representative parameter or pulse rate. The control unit  50  further determines that the patient medical parameter value (e.g. rate-of-change of the blood oxygen saturation value or rate-of-change of the pulse rate) is at a safe level when it is within a predetermined range. 
     It is also possible for the patient medical parameter value which controls entry to the power save mode to be provided from an external source, such as a separate patient monitoring device measuring other patient medical parameters. The patient medical parameter value may also be entered manually. An output terminal of such an external patient monitoring device (not shown) and/or manual input device (also not shown) may be coupled to the control unit  50  via the external terminal  55 . The patient medical parameter value, in such a case, may be at least one of: patient temperature; arterial blood pressure; a hematocrit level; and/or a cardiac index. One or more of the patient medical parameter values described above, and/or any other similar patient medical parameter value, may be used by the control unit  50  to determine if the patient medical parameter value is at a safe level. 
     In the illustrated pulse oximeter embodiment, the patient medical parameter value is determined to be at a safe level when the SpO 2  and pulse rate parameters are stable and within a predetermined range of acceptable values. This is illustrated in  FIG. 2  which illustrates the process of entering and terminating the power save mode in the system illustrated in  FIG. 1 . For example, in an adult, the SpO 2  reading should be between 90% and 100% and the pulse rate should be between 50 and 100 beats per minute (bpm). Stability is determined by the change and the rate-of-change in the SpO 2  and pulse rate values being less than a relatively low threshold. The acceptable range of SpO 2  and pulse rate values, and threshold levels for the change in these values may be adjusted by a user. The control unit  50  receives the SpO 2  and pulse rate values from the data processor  40 , and calculates the change in those values and the rate-of-change of those values. 
     More specifically, in the illustrated embodiment, both LEDs  12  and  14  are enabled in step  202 . In step  204  values for SpO 2  and pulse rate (PLS) medical parameters are calculated by the data processor  40  based on the signals  35  representing the received light from the LEDs  12 ,  14 . In block  205 , patient stability is determined. In step  206  the pulse rate value PLS is compared to low and high thresholds P L  and P H , respectively, and the SpO 2  value is compared to low and high thresholds, S L  and S H , respectively. If the PLS value is between P L  and P H  and the SpO 2  value is between S L  and S H , then step  208  is performed, otherwise, the medical device remains in normal mode and operation returns to step  202 . In step  208  the change in the PLS value (ΔPLS) is compared to a thresholds ΔP, and the change in the SpO 2  value (ΔSpO 2 ) is compared to a threshold ΔS. If the ΔPLS value is less than the ΔP threshold, and the ΔSpO 2  value is less than the ΔS threshold, then step  210  is performed, otherwise, the medical device remains in normal mode and operation returns to step  202 . In step  210  the rate-of-change of the PLS value (ROC PLS) is compared to a thresholds  min P ROC , and the rate-of-change in the SpO 2  value (ROC SpO 2 ) is compared to a threshold  min S ROC . If the ROC SpO 2  value is less than the  min S ROC  threshold, and the ROC PLS value is less than the  min P ROC  threshold, then step  210  is performed, otherwise, the medical device remains in normal mode and operation returns to step  202 . 
     In addition to checking the medical parameter to determine if the patient is safe and stable, it is also possible to check other signal parameters to determine whether the patient and the system are in condition to operate in a power save mode. In  FIG. 2 , a check is made on the consistency of the signals  35 , representing the light received from the plurality  10  of LEDs  12  and  14 . Signal consistency may be represented by the signal-to-noise ratio of the received signal, by drift of signal components, such as an ac and/or dc component, or any other similar measure of signal consistency. 
     In block  211 , signal consistency is determined. In step  212  the signal consistency of the signal  35  (SC RED ) representing the light received from the red LED  12  is compared to a threshold  min SC RED . If the signal consistency of the red signal SC RED  is greater than the threshold  min SC RED , then step  214  is performed, otherwise, the medical device remains in normal mode and operation returns to step  202 . Similarly, in step  212  the signal consistency of the signal  35  (SC IR ) representing the light received from the IR LED  14  is compared to a threshold  min SC IR . If the signal consistency of the IR signal SC IR  is greater than the threshold  min SC IR , then the patient is considered to be stable and the signals consistent. In this case, the system  1  ( FIG. 1 ) enters the power save mode and step  222  is performed, otherwise, the medical device remains in normal mode and operation returns to step  202 . 
     In one embodiment, the control unit  50  ( FIG. 1 ) provides control signals to the power unit  60  conditioning it to intermittently turn off at least first and second different LEDs  12 ,  14  of the plurality  10  of LEDs  12 ,  14  in the power save mode. Referring again to  FIG. 2 , in step  222 , one of the plurality  10  of LEDs is turned off. In this mode, when one LED (e.g.  12 ) is turned off, the other LED (e.g.  14 ) remains active. Prior to turning off an LED (e.g.  12 ), parameter values obtained using the active LED are stored in the parameter value store  42 . In step  224 , the parameter values for the LED to be turned off are stored, and a reading is taken using the other, active, LED. 
     More specifically, in the illustrated embodiment, parameter values resulting from e.g. intermediate calculations made by the data processor  40  ( FIG. 1 ) related to the IR LED (e.g.  14 ) are stored in the parameter value store  42 . When that LED (e.g.  14 ) is turned off, the stored parameter values are retrieved from the parameter value store  42  and used together with the parameter values obtained using the active LED (e.g. the IR LED  14 ) to calculate the medical parameter, e.g. SpO 2  and/or pulse rate. The calculation of the medical parameter, i.e. SpO 2  and/or pulse rate, are performed in step  224 . In addition, the control unit  50  retrieves the stored parameter value from the parameter value store  42 , and uses the stored parameter values obtained using the previously active LED (e.g.  14 ) together with a parameter values obtained using the active LED (e.g.  12 ) to determine that the patient medical parameter value measured by the medical device is remaining at a safe level while in the power save mode. 
     As described above, in the illustrated embodiment, the patient medical parameter value is considered at a safe level if the patient remains stable and the signal remains consistent. Block  225  checks signal consistency. In step  226  the change in the dc level ΔDC of the active LED (e.g.  14 ) signal  35  is compared to a threshold ΔDC min . If ΔDC is less than the threshold ΔDC min  then step  228  is activated. Otherwise, it is determined that the signal is not consistent and the power save mode is terminated by returning to step  202  where both LEDs are activated. In step  228  the change in the ac level ΔAC of the active LED (e.g.  14 ) signal  35  is compared to a threshold ΔAC min . If ΔAC is less than the threshold ΔAC min  then step  230  is activated. Otherwise, it is determined that the signal is not consistent and the power save mode is terminated by returning to step  202  where both LEDs are activated. 
     In block  235 , patient stability is checked. In step  230 , the change in the SpO 2  parameter ΔSpO 2  is compared to a threshold. In the illustrated embodiment, the threshold is 1%. If the change in the SpO 2  parameter ΔSpO 2  is less than 1%, then step  232  is activated. Otherwise, it is determined that the patient is not stable and the power save mode is terminated by returning to step  202  where both LEDs are activated. In step  232 , the change in the pulse rate parameter ΔPLS is compared to a threshold. In the illustrated embodiment, the threshold is also 1%. If the change in the PLS parameter APLS is less than 1%, then it is determined that the patient remains stable and the signal remains consistent. In this case, the system remains in the power save mode by returning to step  222 . Otherwise, it is determined that the patient is not stable and the power save mode is terminated by returning to step  202  where both LEDs are activated. 
     One skilled in the art understands that turning off one LED (e.g.  14 ) and using stored parameters representing the signals received when that LED was last active to calculate the medical parameter, i.e. SpO 2  and/or pulse rate, some inaccuracy may enter into the medical parameter value. However, because the power save mode is entered when the patient is stable, meaning that the medical parameter SpO 2  and/or pulse rate is relatively unchanging, the inaccuracy is relatively small, and is a reasonable trade off compared to the power savings entailed by turning off one LED. 
     In the embodiment illustrated in  FIG. 2 , the system remains in the power save mode for as long as the patient remains stable and the signals remain consistent. Alternatively, at some point in time, which may be a predetermined time duration, a predetermined number of heart beats, a predetermined number of readings of the medical parameter measured by the medical device, or a time period determined in any other similar manner, the system automatically terminates the power save mode, and returns to the normal mode. This may be done to reset the stored parameters for the LED which was turned off. The predetermined time duration may be user configurable 
     Also as described above, an external patient monitor may supply patient medical parameters to the control unit  50  via the external terminal  55 . The control unit  50  monitors the patient medical parameters from the external patient monitor, i.e. the medical parameters that are measured without using at least one of the plurality  10  of light emitting devices  12 ,  14 . In response to a determination that the externally monitored patient medical parameter value is outside a predetermined range, the control unit  50  terminates the power save mode and turns on the light emitting device (e.g.  14 ) of the plurality of light emitting devices which was previously turned off. 
     As described above, power is also employed by the data processor  40  ( FIG. 1 ) in performing the processing necessary to derive the patient medical parameter, e.g. SpO 2  and/or pulse rate, from the signals  35  representing the received light signals  25 .  FIG. 3  is a block diagram illustrating a portion of the processing which is performed in the data processor  40  according to the present invention. In  FIG. 3 , the light representative signals  35  are coupled to respective signal input terminals of time domain processes  302  and to a signal input terminal of an FFT process  304 . An output terminal of the FFT process  304  is coupled to respective signal input terminals of frequency domain processes  306 . 
     More specifically, in the illustrated embodiment, a plurality of N time domain processes, TD PROC  1 , TD PROC  2 , . . . TD PROC N, are illustrated. The light representative signals  35  are coupled to respective signal input terminals of the plurality  302  of time domain processes, TD PROC  1 , TD PROC  2 , . . . TD PROC N. Similarly, a plurality of N frequency domain processes, FD PROC  1 , FD PROC  2 , . . . FD PROC N, are illustrated. The output terminal of the FFT process  304  is coupled to respective signal input terminals of the plurality  306  of frequency domain processes  306 , FD PROC  1 , FD PROC  2 , . . . FD PROC N. 
     The control signal from the control unit  50  ( FIG. 1 ) to the data processor  40  is coupled to an input terminal of a control process  310 . Respective output terminals of the control process  310  are coupled to corresponding control input terminals of the plurality  302  of time domain processes, TD PROC  1 , TD PROC  2 , . . . TD PROC N, and the plurality  306  of frequency domain processes, FD PROC  1 , FD PROC  2 , . . . FD PROC N. Respective control output terminals of the controller  310  are also coupled to corresponding control input terminals of the FFT process  304  and the sensitivity selector  308 . 
     In operation, the data processor  40  employs a plurality of different processing functions (TD PROC  1 , TD PROC  2 , . . . TD PROC N; FD PROC  1 , FD PROC  2 , . . . FD PROC N) for processing the data in the signals  35  ( FIG. 1 ) derived using the plurality  10  of light emitting devices  12 ,  14  in determining the patient medical parameter value, e.g. SpO 2 , pulse rate, measured by the medical device. A subset  302  of the plurality of processing functions operate in the time domain. Another subset  304  of the plurality of processing functions operate in the frequency domain. The control unit  50  provides a control signal to the control process  310  in the data processor  40  for turning off at least one processing function of the plurality of processing functions (TD PROC  1 , TD PROC  2 , . . . TD PROC N; FD PROC  1 , FD PROC  2 , . . . FD PROC N) in the power save mode in response to a predetermined function disablement procedure, described in more detail below. As described above, the power save mode may be initiated in response to a determination that the patient medical parameter (e.g. SpO 2 , pulse rate), measured by the medical device using the active light emitting device (e.g.  14 ) of the plurality  10  of light emitting devices  12 ,  14 , is at a safe level. More specifically, in the illustrated embodiment, the power save mode is initiated in step  222  of  FIG. 2 . 
     In the illustrated embodiment, the predetermined function disablement procedure turns off at least one processing function (TD PROC  1 , TD PROC  2 , . . . TD PROC N; FD PROC  1 , FD PROC  2 , . . . FD PROC N) in response to a sensitivity determination. The sensitivity determination is used to turn off the function (TD PROC  1 , TD PROC  2 , . . . TD PROC N; FD PROC  1 , FD PROC  2 , . . . FD PROC N) having least effect in the determination of the patient medical parameter value (e.g. SpO 2 , pulse rate) measured by the medical device. In an alternative embodiment, the control unit  50  provides control signals  40  to the control process  310  for progressively turning off processing functions of the plurality of processing functions (TD PROC  1 , TD PROC  2 , . . . TD PROC N; FD PROC  1 , FD PROC  2 , . . . FD PROC N) in the power save mode in response to the sensitivity determinations. 
     In the illustrated embodiment, the sensitivity selector  310  operates as probability-based classifier. Such a selector  310  classifies the results from the plurality of processing functions (TD PROC  1 , TD PROC  2 , . . . TD PROC N; FD PROC  1 , FD PROC  2 , . . . FD PROC N), termed features, based on the calculated probability, termed sensitivity, of their being accurate estimates of the patient medical parameter, e.g. SpO 2 , pulse rate. With such a selector, the number of features (TD PROC  1 , TD PROC  2 , . . . TD PROC N; FD PROC  1 , FD PROC  2 , . . . FD PROC N) used for the classifier computation may be reduced without compromising performance. The decision to select a particular feature (TD PROC  1 , TD PROC  2 , . . . TD PROC N; FD PROC  1 , FD PROC  2 , . . . FD PROC N) to turn off is based on the sensitivity of that feature. During a typical computing iteration, multiple possible outcomes (e.g. SpO 2  readings and/or pulse rate frequencies) are considered concurrently by the feature processes (TD PROC  1 , TD PROC  2 , . . . TD PROC N; FD PROC  1 , FD PROC  2 , . . . FD PROC N). A feature process (TD PROC  1 , TD PROC  2 , . . . TD PROC N; FD PROC  1 , FD PROC  2 , . . . FD PROC N) assigns a probability value to the possible outcomes. The power of classification is computed for an individual feature process (TD PROC  1 , TD PROC  2 , . . . TD PROC N; FD PROC  1 , FD PROC  2 , . . . FD PROC N) to assess its sensitivity level S. For example, for a feature process (TD PROC  1 , TD PROC  2 , . . . TD PROC N; FD PROC  1 , FD PROC  2 , . . . FD PROC N) with n possible outcomes, the sensitivity S is computed by comparing the respective probabilities P n  of an outcome to the probability of the last reported outcome P′ where: 
     
       
         
           
             
               
                 
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     The process (TD PROC  1 , TD PROC  2 , . . . TD PROC N; FD PROC  1 , FD PROC  2 , . . . FD PROC N) with the lowest sensitivity level S is turned off and consequently not processed by the sensitivity selector  308 . In an alternate embodiment, processes (TD PROC  1 , TD PROC  2 , . . . TD PROC N; FD PROC  1 , FD PROC  2 , . . . FD PROC N) having the lowest sensitivity level S are progressively turned off. With fewer processes operating, power consumption by the data processor  40  is reduced. 
     It is further possible to control the FFT process  304  to reduce the processing required, and therefore, the power consumption. One skilled in the art understands that an FFT process transforms a set of time domain input samples, representing the respective signals  35  from the plurality  10  of light emitting devices  12 ,  14 , into a corresponding set of frequency domain output samples. The control unit  50  ( FIG. 1 ) provides a control signal to the control process  310  in the data processor  40  which conditions the FFT process  304  to reduce the processing required to produce the frequency domain samples in the power save mode. Specifically, the number of samples in the input and output sample set, and the rate at which conversion cycles are made may be controlled. In the power save mode, the number of samples in the set of time domain samples (and corresponding frequency domain output samples) is reduced and/or the rate at which successive sets of time domain input samples are transformed into corresponding sets of frequency domain samples is reduced. Less power is consumed when fewer samples are transformed, and when the rate of conversion cycles is reduced. 
     In the illustrated embodiment, the processing blocks in  FIG. 3  (e.g. TD PROC  1 , TD PROC  2 , . . . TD PROC N; FD PROC  1 , FD PROC  2 , . . . FD PROC N,  304 ,  308 ,  310 ) represent executable procedures which may be executed by the data processor  40 . One skilled in the art understands that these processing blocks may be implemented in hardware, firmware, software or any combination of the three. 
     It is also possible that a medical device, such as a pulse oximeter medical device, may be one component in a multifunction patient monitor device. For example, a multifunction patient monitor device may include an ECG monitor, blood pressure monitor, temperature monitor, ventilation monitor, etc. in addition to the pulse oximeter monitor providing SpO 2  and pulse rate medical parameters. In such a multifunction medical device, it is possible to provide further power savings by turning off operation of the pulse oximeter functions completely. More specifically, in the illustrated embodiment, the pulse oximeter system uses the plurality  10  ( FIG. 1 ) of light emitting devices  12 ,  14  to derive the SpO 2  and pulse rate patient medical parameters. However, the other medical devices in the multifunction monitor derive patient medical parameters (i.e. ECG lead signals, blood pressure, temperature, ventilation parameters, etc.) without using the plurality  10  of light emitting devices  12 ,  14 . 
     In such a monitor, the control unit  50  ( FIG. 1 ) may provide a control signal coupled to the power unit  60  for turning off the light emitting device in a power save mode for a predetermined time duration. The control unit  50  may further provide a control signal for turning off processing of data occurring in deriving the patient medical parameter (e.g. SpO 2 , pulse rate) using the light emitting device. The control unit  50  ( FIG. 1 ) may instead provide a control signal turning off operation of the medical device functions which are unused in deriving the patient medical parameter (e.g. SpO 2 , pulse rate) that is measured without using the light emitting devices  12 ,  14  in response to a determination that the patient medical parameter value measured by the medical device using an active light emitting device (e.g.  14 ) of the plurality  10  of light emitting devices  12 ,  14  (e.g. SpO 2 , pulse rate), is at a safe level. The control unit  50  then monitors a patient medical parameter that is measured without using the light emitting devices  12 ,  14  (e.g. EKG, temperature, ventilation parameters, etc.) and in response to a determination that the monitored patient medical parameter value is outside of a predetermined range, terminates the power save mode and turns on the light emitting devices  12 ,  14  and the processing of data. In this manner, the power consumed by the pulse oximeter monitor may be eliminated or substantially reduced.