Abstract:
The invention provides a fail-safe module (FSM) integral with a sedation and analgesia system that meets the high-reliability needs of sedation and/or analgesia delivered by non-anesthetist practitioners. The FSM may operate in “real-time” in order to ensure optimal patient safety. The FSM may deactivate specific patient interfaces, user interfaces, and/or sedation and analgesia delivery in order to ensure patient safety and has redundant safety systems in order to provide the fail-safe module with an accurate assessment of controller functionality.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119(e) from U.S. Provisional Patent Application No. 60/358,733, filed Feb. 25, 2002 and incorporated herein by reference. This application is also a divisional application of U.S. application Ser. No. 10/372,654, filed Feb. 25, 2003, now U.S. Pat. No. 7,527,052 issued May 5, 2009 and it also claims priority under the provisions of 35 U.S.C. 121 from the &#39;654 application. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates, in general, to fail-safe modules and, more particularly, to fail-safe modules integral with sedation and analgesia systems. 
     BACKGROUND OF THE INVENTION 
     In response to, among other things, market conditions and popularity amongst cost-conscious patients, out-of-hospital procedures continue to experience rapid growth. For various reasons, clinicians such as, for example, in office, ambulatory center, dental, non-hospital and hospital settings sometimes administer or supervise the delivery of sedation and analgesia without the services of trained anesthesia providers. This development has led the American Society of Anesthesiologists to issue guidelines for the delivery of sedation and analgesia by non-anesthesiologists. Because the non-hospital setting is in general not as well equipped and staffed as hospitals, malfunctions and complications (such as unintended over-medication leading to loss of consciousness and airway reflexes) may lead to severe outcomes. 
     A sedation and analgesia system is described in commonly assigned and U.S. patent application Ser. No. 09/324,759, filed Jun. 3, 1999, now U.S. Pat. No. 6,807,965. This system safely provides patients undergoing painful, uncomfortable or otherwise frightening (anxiety inspiring) medical or surgical procedures with sedative, analgesic, and/or amnestic drugs in a way that reduces the risk of overmedication, in both non-hospital and hospital settings. As this system may be used in settings where users may not be trained anesthesia providers skilled in resuscitation and airway management and where complications or malfunctions may have more severe repercussions, the number of potential failure modes was systematically reduced by elimination and/or mitigation. Mitigation was partly accomplished by careful design of the fail safe module for the sedation and analgesia system. Thus, the sedation and analgesia system may be safer than anesthesia machines for use in both non-hospital and hospital environments and may be safely operated by individuals other than trained anesthesia providers such as, for example, trained physicians, or other licensed clinicians and operators. 
     Anesthesia machines are mainly designed for inhalational anesthesia. In general, as a legacy from earlier anesthesia machine designs that were entirely pneumatic and did not require electrical power to operate. loss of electrical power in current anesthesia machines will not interrupt delivery of anesthetic gases and vapors. In contrast, one embodiment of the sedation and analgesia system described in the &#39;759 application, now U.S. Pat. No. 6,807,965, uses only intravenous anesthetics and no inhalational anesthetics and requires electrical power to operate. During sedation and or analgesia, continued safety in the absence of an anesthesia provider is paramount. These safety systems often employ a set of complicated features to prevent anesthesia machines from being switched off during an anesthetic. 
     Existing fail-safe systems used on anesthesia machines have the ability to fall back on an all-pneumatic operation mode of operation and may not be applicable to the needs of a sedation and analgesia or total intravenous anesthesia system requiring electrical power to operate. Furthermore, because the sedation and analgesia system is also designed for use by non-anesthesia providers, the consequences of equipment failure may be more severe and thus fail safe systems with a higher reliability that those used on anesthesia machines designed for use by anesthesia providers are required. 
     Due to the importance of patient safety, test modes for drug delivery devices have long been accepted as an important feature. However, existing fail-safe systems may not take into account the specific requirements that the fail-safe system itself may need to be tested to attain a high-reliability sedation and analgesia system. Simulating a failure to test the fail-safe system for a sedation and analgesia system may be disruptive and cause the system to power down upon detection of the simulated failure. Upon termination of the simulated failure, if the system was powered down, the system will power up and cause further disruption, especially if the power-up, including power-up on self test (POST) routines, takes a long time to complete. Therefore, a need has arisen for a fail-safe module that may be tested without untoward system disruption, in order to confirm proper function of the fail-safe system in a high-reliability sedation and analgesia system. 
     Further fail-safe systems implement methods of incorporating redundant constituent elements (modules) into the systems. A further need has arisen for a watchdog system integral with a sedation and analgesia system that powers down the sedation and analgesia system in the event of a detected malfunction. 
     SUMMARY OF THE INVENTION 
     The present invention provides a fail-safe module (FSM) integral with a sedation and analgesia system that meets the high-reliability needs of sedation and/or analgesia delivered by non-anesthetists. The FSM may operate in “real-time” in order to ensure optimal patient safety. The FSM may deactivate specific patient interfaces, user interfaces, and/or sedation and analgesia delivery in order to ensure patient safety and has redundant safety systems in order to provide the fail-safe module with an accurate assessment of controller functionality. 
     The present invention further includes a FSM measuring the functionality of software and/or hardware associated with critical patient interfaces and/or the sedation and drug delivery system. The FSM may reactivate patient interfaces, user interfaces, and/or sedation and analgesia delivery upon receipt of acceptable data indicating an operable controller. The FSM also may retain in memory a failure event in order to alert the next user that the machine has experienced a failure. The FSM may be included with a test mode capability that simulates a failure. During the simulated failure to test the FSM, automatic system power-down may be bypassed to create minimum system disruption. The simulated failure may be programmed to occur only on power-up or during normal operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an overall conceptual schematic block diagram of a system in accordance with the present invention; 
         FIG. 2  is an overall schematic block diagram of a fail-safe module system in accordance with the present invention; 
         FIG. 3  is a more detailed schematic block diagram of a fail-safe module illustrating associated inputs and outputs in accordance with the present invention; 
         FIG. 4  is a flow chart illustrating operation of a fail-safe module system in accordance with the present invention; and 
         FIG. 5  is a flow chart illustrating a method of operating a fail-safe test mode in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a block diagram depicting one embodiment of the present invention comprising sedation and analgesia system  22  having fail-safe module  23 , user interface  12 , controller  14 , peripherals  15  (which may include a memory device), power supply  16 , external communications  10 , patient interfaces  17 , and drug delivery  19 , where sedation and analgesia system  22  is operated by user  13  in order to provide sedation and/or drugs to patient  18 . An example of sedation and analgesia system  22  is described in and commonly assigned U.S. patent application Ser. No. 09/324,759, filed Jun. 3, 1999, now U.S. Pat. No. 6,807,965, and incorporated herein by reference. Patient interfaces  17  may comprise one or more physiological monitors, such as Sp02, ECG, C02 and NIBP among others. 
     The sedation and analgesia system of application Ser. No. 09/324,759, now U.S. Pat. No. 6,807,965, includes a patient health monitor device (such as patient interfaces  17 ) adapted so as to be coupled to a patient and generate a signal reflecting at least one physiological condition of the patient, a drug delivery controller supplying one or more drugs to the patient, a memory device storing a safety data set reflecting safe and undesirable parameters of at least one monitored patient physiological condition, and an electronic controller interconnected between the patient health monitor, the drug delivery controller, and the memory device storing the safety data set; wherein said electronic controller receives said signals and in response manages the application of the drugs in accord with the safety data set. 
       FIG. 2  illustrates a block diagram depicting fail-safe module system  60  having controller  14 , fail-safe module  23 , power supply  24 , controller input  25 , controller output  26 , drug delivery  19 , and patient interface  17 , where drug delivery  19  and patient interface  17  interact with patient  18 . Controller  14  receives input from patient interface  17 , drug delivery  19 , fail-safe module  23 , and other peripherals associated with sedation and analgesia system  22 . Data is inputted into controller  14  which executes a program designed in a language, such as, for example, C or C++, and functions within an operating system such as, for example, QNX. However other operating systems such as, for example, LINUX, VX Works, or Windows NT are contemplated. Preferred embodiments of the software operate in a “real time” operating system such as, for example, QNX, where programs relating to specific patient interfaces, user interfaces, and other features of sedation and analgesia system  22  are compartmentalized into separate program modules (not shown). 
     Controller  14  may be a CPU, or any other data processing system commonly known in the art. Controller  14  may further comprise, in one embodiment of the present invention, a health-check system (not shown) based, for example, on functionalities provided by the QNX operating system. where the health-check system sends a health check-request (not shown) to a program module (not shown) associated with a feature such as, for example, a system for the automated assessment of consciousness or responsiveness. Such an automated assessment system is described in the U.S. patent application Ser. No. 09/324,759 filed Dec. 28, 2002, now U.S. Pat. No. 6,807,965. Upon receipt of a health-check request, the program module is programmed to respond with a health check response. A malfunction of a program module will result in the failure of the module to deliver a health-check response to the health check system integral with controller  14 . The health-check request and health-check response may be in the form of a single byte, a plurality of bytes, a pulse, a TTL or logic signal, or other forms of data transfer suitable for use with the present invention. If the health check system fails to receive a health check response from a program module within a given time window, controller  14  will alert fail-safe module  23  that a failure has occurred resulting in fail-safe module  23  transferring sedation and analgesia system  22  into safe state mode  107  ( FIG. 4 ) as will be further discussed herein. The health check system is software based and exploits the inherent features of operating systems such as QNX, specifically the allocation of individual reserved memory space for each compartmentalized software program module. 
     In one embodiment of the present invention, data and/or commands may be outputted from controller  14  in the form of output  26  to peripherals associated with sedation and analgesia system  22 , fail-safe module  23 , and patient interface  17 . Depending on the functionality of controller  14  and program modules associated with controller  14 , controller  14  may be functioning properly, or may be outputting aberrant commands. In the event that controller  14  has malfunctioned and is outputting spurious commands and/or data, such as, for example, excessive drug delivery, fail-safe module  23  may detect improper operation in controller  14  associated with the failure and transfer sedation and analgesia system  22  into safe state mode  107  ( FIG. 4 ). 
     In one embodiment of the present invention, controller  14  is programmed to deliver, or initiate delivery of a strobe (as shown in  FIG. 4  at  103  and  104 ) to fail-safe system  23  within a predetermined window such as, for example, from between 900 and 1100 milliseconds. The strobe may be in the form of a byte, a plurality of bytes, a pulse, a TTL or logic signal or other forms of data transfer suitable for used with the present invention. Fail-safe module  23 , in one embodiment of the present invention, must receive the strobe initiated by controller  14  within the predetermined time window in order to maintain sedation and analgesia system  22  in an operational state mode ( FIG. 4 ). The failure of controller  14  to initiate and deliver the strobe within the specified window indicates to fail-safe module  23  that an anomaly has occurred in the health check system or in the program modules associated with sedation and analgesia systems  22 , resulting in fail-safe module  123  transferring sedation and analgesia system  22  into safe state mode  107 . A further embodiment of the present invention comprises providing a direct communication (not shown) between the program modules associated with sedation and analgesia system  22  and fail-safe module  23  in order to provide redundancy in verifying the program modules are functioning properly.  FIG. 2  further illustrates one embodiment of the present invention, where power supply  24  is connected to and powers fail-safe module  23 . In one embodiment of the present invention, power supply  24  delivers 0.5-200 volts DC and preferably 4.75-5.25 volts DC, and is capable of sourcing 0.5-200 amps and preferably 12 amps, and may be referenced to a system ground. The present invention further contemplates the use of alternating current. 
       FIG. 3  illustrates a block diagram depicting one embodiment of the present invention comprising fail-safe module  23 , inputs  30 ,  32 ,  34  associated with fail-safe module  23 , outputs  31 ,  33 ,  35  associated with fail-safe module  23 , and power supply  24 . Fail-safe module  23  comprises memory  27 , state machine  28 , and communications (comm) switching  29 . Fail-safe module  23  may be a central processing unit, a complex programmable logic device (CPLD), or any other suitable data processing device. In one embodiment of the present invention, state machine  28  receives state machine input  32 , where state machine input  32  comprises a fail-safe strobe, information relevant to controlling oxygen and drug delivery, information relevant to oxygen and drug enablement, information relevant to oxygen and drug disablement, and/or other suitable state machine input. Memory  27  receives memory input  30 , where memory input  30  includes, but is not limited to, information relevant to clearing fail-safe module  23  of a system fault event. Comm switching  29  receives input from comm switching input  34 , where comm switching input  34  includes, but is not limited to, commands to the drug delivery module, such as among others an IV pump, from the controller  14 , and commands to the non-invasive blood pressure module from controller  14 . In one embodiment of the present invention, comm switching  29  functions to convert RS-232 signals to transistor logic (TTL). 
     Memory  27  outputs memory output  31 , where memory output  31  includes, but is not limited to, information related to a failure event occurring after the last clearing of the memory  27  via memory input  30 . State machine  28  outputs state machine output  33 , where state machine output  33  includes, but is not limited to, an indication of an unknown system fault, output related to fail-safe module  23  control of the flowrate of oxygen and drug, and output relating to fail-safe module  23  control of enabling or disabling oxygen and drug delivery. Comm switching  29  outputs comm switching output  35 , where comm switching output  35  includes, but is not limited to, information from controller  14  dictating function of the pump (not shown) associated with drug delivery  19 , where the fail-safe module disables, for example, grounds, the signal if a problem is detected, and information from controller  14  dictating function of the blood pressure cuff, where the fail-safe module disables the signal if a problem is detected so that the blood pressure cuff is not left in an inflated position where it may cut off blood circulation. Routing control of oxygen delivery, the non-invasive blood pressure module (not shown), and drug delivery  19  through fail-safe module  23 , allows failsafe module  23  to disable the non-invasive blood pressure module and drug delivery  19  in order to prevent potential harm to a patient due to error. Oxygen delivery may be maintained, at a predetermined flow-rate and for a predetermined period of time, by fail-safe module  23 , if oxygen was being administered at the time of the failure. A plurality of other inputs and outputs, such as those described in U.S. patent application Ser. No. 09/324,759, now U.S. Pat. No. 6,807,965, are consistent with the present invention, as well as a plurality of patient interfaces such as, for example, capnometry monitoring, that may be routed through the fail-safe module  23  in order to provide desired safe state mode  107 . 
     In one embodiment of the present invention, memory  27  functions to maintain a record of failure events occurring within controller  14  or in the program modules associated with controller  14 . Information related to a failure is transmitted to memory  27  via error output path  36 . Memory of the failure will be maintained within memory  27  until a command is entered acknowledging the failure and clearing the memory via memory input  30 . Memory  27  functions to alert a user, via memory output  31 , that sedation and analgesia system  22  has, in the previous case, experienced a failure. The recorded failure in memory  27  may be removed via memory input  30 . In one embodiment of the present invention, the user may not activate the sedation and analgesia system until the failure recorded in memory  27  is acknowledged and removed. Memory of a software failure may be held in memory  27  by encoding a simple memory bit, or by other suitable means of recording a failure. One embodiment of the present invention comprises a code retained in memory  27  indicating whether the failure occurred in the program modules associated with controller  14  or in the health-check system, if the health-check system is present. 
     State machine  28  is, in one embodiment of the present invention, programmed to anticipate a strobe from controller  14  within a specified time window. The time window may be any window desirable for use in detecting flaws within the sedation and analgesia system  22 . If the strobe is received by state machine  28  of fail-safe module  23  within the specified time window, fail-safe module  23  will maintain sedation and analgesia system  22  in operation state mode  105 . If the strobe is not received by state machine  28  within the specified time window, state machine  28  will output information related to the failure via state machine output  33  in the form of a visual alarm, an audio alarm, and/or other suitable means for alerting a user that a failure has occurred. In response to a failed strobe, state machine  28  will also send data indicating a failure to memory  427  via error output path  36  and transfer sedation and analgesia system  22  into safe state mode  107 . In one embodiment of the present invention, state machine  28  disables control of comm switching  29  by controller  14 , via disable output  37 , in order to transfer sedation and analgesia system  22  into safe state mode  107  independent of controller  14 . 
     A further embodiment of the present invention comprises controller  14  programmed to rapidly strobe state machine  28  in the event of a failure in the modules associated with controller  14 . State machine  28  is programmed, upon receipt of rapid strobing from controller  14 , to output an alarm signal indicator of a sedation and analgesia system  22  failure, record the failure in memory  27 , disable control of comm switching  29  by controller  14 , and transfer sedation and analgesia system  22  into safe state mode  107 . 
       FIG. 4  depicts a method illustrating one embodiment of the operation of fail-safe module  23  in this sedation and analgesia system  22 . Commencing from a fail-safe module system (FSM) inactive mode  100 , the sedation and analgesia system  22  only moves into initiation state mode  102  upon receipt of power (query  101 ) applied to fail-safe module  23 . For example, initiation state mode  102  will commence upon receipt of 5 volts of direct current from power supply  24 , however other voltages and means of delivering power to fail-safe module  23  are consistent with the present invention. Any time power is removed from fail-safe module  23 , sedation and analgesia system  22  will return to fail-safe module system inactive mode  100 . Following reception of power, sedation and analgesia system  22  will operate in an initiation state mode  102  comprising fail-safe module  23  outputting safe state output in anticipation of a strobe from controller  14 . In one embodiment, fail-safe module  23  outputs safe state data until a valid strobe is received from controller  14  due to the fact that the condition of sedation and analgesia system  22  cannot be determined until valid strobing begins. Maintaining safe state output during the initiation state mode  102  ensures the controller  14  cannot send commands to important peripherals, such as, for example, drug delivery  19  or patient interface  17 , until fail-safe module  23  receives a valid strobe indicating controller  14  is healthy. Initiation state mode  102  further comprises disallowing user  13  from removing the record of a failure event stored in memory  27  until a valid strobe is received from controller  14  indicating sedation and analgesia system  22  is functioning properly. In the absence of a valid strobe, sedation and analgesia system  22  will remain in initiation state mode  102 . One embodiment of the present invention comprises powering down sedation and analgesia system  22  in the event that a valid strobe is not received during a predetermined window of, for example, five minutes. 
     Upon reception of a valid strobe from controller  14  by fail-safe module  23  (query  104 ), sedation and analgesia system  22  will be transferred to operation state mode  105 . Operation state mode  105  is maintained contingent on valid strobing (query  106 ) from controller  14  to fail-safe module  23  that falls within the allowed predetermined window. Consistent valid strobing from controller  14  to fail-safe module  23  maintains sedation and analgesia system  22  in an operation state mode  105 . Operation state mode  105  comprises allowing input received by fail-safe module  23  from controller  14  to control output relating to critical patient interfaces such as, for example, blood pressure cuff pressure, oxygen delivery, and drug delivery  19 . Operation state mode  105  further comprises indication to user  13  that sedation and analgesia system  22  is functioning properly. Data will continue to be displayed on the user interface  12 , backlighting of user interface  12  will remain active, and alarm signals relating to sedation and analgesia system  22  failure will remain quiet. One embodiment of the present invention comprises allowing user  13  or fail-safe module  23  to clear the memory unit held in memory  27  that previously indicated a failure in sedation and analgesia system  22  in order for a subsequent failure to recode the memory unit (not shown). 
     Failure to strobe, or rapid strobing of fail-safe module  23  (query  106 ) by controller  14  results in fail-safe module  23  transferring sedation and analgesia system  22  into safe state mode  107 . Strobes falling outside the predetermined response window, or rapid strobing from controller  14  indicate to fail-safe module  23  that a failure has occurred in sedation and analgesia system  22 . In order to protect the patient, it is necessary to convert sedation and analgesia system  22  into a safe state mode  107  to reduce potential harm caused by drug delivery  19 , patient interface  17 , or other critical peripherals that may include malfunctioning hardware or software. Safe state mode  107  comprises, in one embodiment of the present invention, ceasing transmission of command data from controller  14  to drug delivery  19 , patient interface  17 , oxygen delivery, and/or other critical peripherals related to patient safety. Safe state mode  107  further comprises deactivating drug delivery  19  in order to prevent possible patient overdose, deactivating the blood pressure cuff in order to prevent possible necrosis that occurs if the blood pressure cuff is left inflated for extended periods of time, and maintaining the flow of oxygen, if oxygen was being given during the procedure, in order to maintain suitable oxygen saturation of the blood. Safe state mode  107  further comprises triggering the memory bit located in memory  27  to indicate a sedation and analgesia system  22  failure  109 , sounding an audio alarm, signaling a visual alarm, and/or blanking the display such as, for example, by deactivating the backlight on user interface  12 . The backlight on user interface  12  may be deactivated in order to prevent display of spurious data that may be erroneously used to evaluate a patient&#39;s condition. 
     Following the transfer of sedation and analgesia system  22  to safe state mode  107 , fail-safe module  23  will continue to anticipate valid strobing from the main logic board or controller  14  (query  108 ). Absent valid strobing, fail-safe module  23  will maintain safe state mode  107 . In one embodiment of the present invention, alarms associated with fail-safe module  23  may be manually deactivated by user  13 . Upon reception of a valid strobe, or a predetermined number of valid strobes from controller  14 , fail-safe module  23  may transfer sedation and analgesia system  22  from safe state mode  107  to operation state mode  105 . A further embodiment of the present invention comprises sedation and analgesia system  22  remaining in safe-state mode for the duration of the medical procedure, even in the event of a valid strobe from controller  14 . 
     Query  110  relates to user  13  response to safe state mode  107 . If sedation and analgesia system  22  is turned off, sedation and analgesia system  22  will be transferred to fail-safe module inactive mode  100 . If sedation and analgesia system  22  is not deactivated, fail-safe module  23  will maintain sedation and analgesia system  22  in safe state mode  107 . 
       FIG. 5  depicts a method illustrating one embodiment of a test mode  210  for sedation and analgesia system  22  comprising the steps of: initiating a valid test strobe  200 , transferring sedation and analgesia system to the operation state mode  201 , setting inputs to the FSM  202 , outputting a test signal from the controller  203 , evaluating proper outputs of FSM in operation state mode given current inputs  204 , initiating valid test strobe  205 , transferring the sedation and analgesia system to the safe state mode  206 , evaluating proper outputs of FSM in safe state mode given current inputs  207 , initiating valid strobing from the controller  208 , and transferring the fail-safe module to the operation state mode  209 . 
     In one embodiment of the present invention, initiating a valid test strobe step  200  comprises transmitting one or a plurality of strobes from controller  14  to fail-safe module  23  that fall into the predetermined time window programmed into fail-safe module  23 , indicating that controller  14  is functioning properly. In one embodiment of the present invention, initiating a valid test strobe step  200  occurs during initiation state mode  102  after power has been delivered to controller  14  and fail-safe module  23 . 
     Transferring sedation and analgesia system to the operation state mode step  201  comprises, fail-safe module  23  receiving the valid strobe or strobes from controller  14 , where the valid strobe or strobes indicate to fail-safe module  23  that controller  14  is functioning properly, then converting sedation and analgesia system  22  to operation state mode  105  based on the valid strobe or strobes indicating that sedation and analgesia system  22  is functioning properly. 
     Setting initial inputs to FSM step  202  comprises inputting information related to oxygen delivery, drug delivery  19 , patient interface  17 , or other critical parameters relating to a desired safe state mode  107 . In one embodiment of the present invention, setting initial inputs to FSM step  202  occurs during operation state mode  105 , where controller  14  maintains control of critical parameters. 
     Outputting a test signal from the controller (step  203 ) comprises, user  13  inputting a test command into controller  14 , where the inputted test command decouples the power down functionality from detected failure of sedation and analgesia system  22 . One embodiment of the present invention comprises an automated system of initiating a test command, where the test command is initiated by controller  14  at a predetermined time before the beginning of a medical procedure, for example as part of the power-up routine of a sedation and analgesia system. In one embodiment of the present invention, a test bit (not shown) is triggered in fail-safe module  23  upon receipt of the test command from controller  14 . The triggered test bit of fail-safe module  23  may function to disable the power down capability associated with a failure, in order to test the functionality of fail-safe module  23  without initiating a power down. Providing a FSM test mode, absent a power down, obviates the need to retest fail-safe module  23  following a subsequent power up of the system had the system been powered down as part of the simulated failure. 
     Evaluating proper outputs of the FSM in the operation state mode given current inputs (step  204 ) comprises determining whether fail-safe module  23  is outputting data consistent with inputted data. In evaluating proper outputs of the FSM in the operation state mode given current inputs (step  204 ), outputted data should be consistent with inputted data due to the retention of control of critical parameters associated with fail-safe module  23  by controller  14 . 
     Initiating invalid test strobe (step  205 ) comprises outputting an invalid strobe from controller  14  to fail-safe module  23 , simulating a failure of sedation and analgesia system  22 . The invalid test strobe may be rapid strobing of fail-safe module  23  by controller  14 , strobing outside the predetermined time window, or other suitable means of communicating a failure of sedation and analgesia system  22 . 
     Transferring the sedation and analgesia system to the safe state mode step  206  comprises transferring sedation and analgesia system  22  to safe state mode  107  following receipt by fail-safe module  23  of an invalid strobe. In order to prevent the need for repetitive retesting upon power up of sedation and analgesia system  22  were it to be powered down during the simulated failure, sedation and analgesia system  22  is not powered down during test mode  210 . 
     Evaluating proper outputs of the FSM in the safe state mode given current inputs (step  207 ) comprises determining whether fail-safe module  23  is functioning properly in converting sedation and analgesia system  22  to safe state mode  107 . Evaluating proper outputs of the FSM in the safe state mode given current inputs (step  207 ) allows controller  14  to determine if fail-safe module  23  will function properly, in the event of an actual failure, in converting sedation and analgesia system  22  to safe state mode  107 . 
     Initiating valid strobing from the controller step  208  comprises outputting a valid strobe or strobes from controller  14  to fail-safe module  23  following the transfer of sedation and analgesia system to safe state mode  107 . Upon receipt of valid strobing, that is, strobing falls within the predetermined response window, fail-safe module  23  will transfer sedation and analgesia system  22  to operation state mode  105 , reallocating control of drug delivery system  19 , patient interface  17 , and oxygen delivery to controller  14 . Transfer of sedation and analgesia system  22  from safe state mode  107  to operation state mode  105  following successful strobing is consistent with transferring the sedation and analgesia system to the operation state mode (step  209 ). 
     Test mode  210  provides user  13  with a simulation of a failure event or message, where the response of fail-safe module  23  may be tested, in the absence of a power down, to determine whether it functions properly in transferring sedation and analgesia system  22  to safe state mode  107  and operation state mode  105  at the appropriate times. The memory bit recorded in memory  27  of the fail-safe module  23  may be reset upon transfer of sedation and analgesia system  22  to operation state mode  105 . 
     In one embodiment of the invention, the health check system polls each compartmentalized software module and verifies that each one indicates that it is operating properly. Upon receipt from all compartmentalized software modules that all is well, the health check system strobes the FSM to indicate that all system modules are functioning properly. This health check system occurs at all times that the system is running. The health check system is software based and the FSM is implemented via hardware such as a complex programmable logic device (CPLD).