Abstract:
The present invention relates, in general, to prevention of false, annoying, or oversensitive alarms, providing early detection by a sensitive test, generating silent, semi-overt, or overt alarm conditions and/or initiating early passive or active interventions to untoward events. The invention buys time by providing an early intervention in the event that a highly sensitive early detection is later confirmed by a specific test. A particular embodiment of the invention is directed to the early detection of hypoventilation, including apnea and airway obstruction, and the pausing or interrupting of an action such as drug delivery during medical procedures.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 60/379,388, “System and Method for Transparent Early Detection, Warning, and Intervention During a Medical Procedure,” filed May 13, 2002, which is hereby incorporated by reference. 
     
    
     
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not Applicable  
         REFERENCE TO A “MICROFICHE APPENDIX” 
         [0003]    Not Applicable  
         BACKGROUND OF THE INVENTION  
         [0004]    1. Field of the Invention  
           [0005]    The present invention relates to prevention of false, annoying, or oversensitive alarms during medical procedures, providing early detection by a sensitive test, generating silent, semi-overt, or overt alarm conditions and/or initiating early passive or active interventions to untoward events.  
           [0006]    2. Description of Related Art  
           [0007]    In certain clinical incidents or emergencies, timely intervention may be critical to outcome. Earlier detection of a developing untoward clinical event facilitates timelier diagnosis and intervention and enhances the probability of a safe and minimally disruptive recovery. Sensitive tests and alarms, in general, assist in earlier detection. However, sensitive tests and alarms are also more prone to annoying, distracting and potentially disruptive false positive alarms. Thus, a medical device designer (or clinician in the case of user-adjustable alarms) generally compromises in setting alarm thresholds so that false positive alarms are minimized and true alarm conditions are detected. Much valuable time may be lost due to this compromise.  
           [0008]    Correct assessment of gas exchange during procedures involving sedation and analgesia is important because respiratory depressants are often administered to patients undergoing painful medical procedures. Respiratory depressants, such as sedation and analgesia agents, can relax the soft tissue of the throat causing partial or complete airway obstruction in some patients, or blunt the respiratory drive, i.e., the urge to breathe when the blood level of carbon dioxide rises. If not diagnosed promptly, such conditions can quickly develop into a life-threatening situation. If a patient does not move a sufficient volume of gas containing oxygen into and out of the lungs then the patient will develop a deficiency in the oxygen supply to body tissue (hypoxia) which, if severe and progressive, is a lethal condition.  
           [0009]    In many health care settings, clinicians assess respiratory gas exchange by using an elevated arterial partial pressure of carbon dioxide (P a CO 2 ) as an indicator of incipient respiratory failure or prolonged airway obstruction. In this regard, the determination of P a CO 2  is useful in optimizing the settings on ventilators, detecting life-threatening blood gas changes, and detecting the presence of airway obstruction in an anesthetized or sedated patient undergoing a medical procedure. The traditional method of obtaining arterial blood gas values is to extract a sample of arterial blood and measure P a CO 2  using a blood gas analyzer. Arterial puncture with a needle to extract the arterial blood sample has inherent limitations: 1) arterial puncture carries a degree of patient discomfort and risk, 2) handling of the blood is a potential health hazard to health care providers, 3) significant delays are often encountered before results are obtained and, 4) measurements can only be made intermittently. Furthermore, blood CO 2  measurements do not immediately reflect changes in patient ventilation, so they may not detect airway obstruction in its early stages when it may still be corrected prior to the onset of adverse physiological consequences. Therefore, clinically, early or timely detection of hypoventilation via blood gas analysis is not practical and this approach might even be considered unsafe and ineffective.  
           [0010]    Hypoventilation results from low or no minute ventilation (MV). Minute ventilation is the product of respiratory rate (RR) and tidal volume (V T ). Low MV may be caused by bradypnea (low RR) or apnea (no breathing; RR=0) or inadequate tidal volumes (resulting from, among others, airway obstruction, shallow breathing, insufficient V T , V T  less than dead space) or a combination of low V T  and low RR. A fast RR does not exclude hypoventilation if V T  is too small for effective ventilation of the lungs or less than the deadspace. Similarly, a large V T  does not exclude hypoventilation if RR is too low for adequate minute ventilation.  
           [0011]    Continuous invasive monitoring requires in-dwelling arterial lines that entail inherent problems such as, for example, sepsis or thrombosis. The nature and expense of this monitoring system excludes its application under routine care, restricting its use to intensive care units within a hospital facility. In-dwelling arterial lines providing real-time P a CO 2  analysis are not able to tell the immediate status of a patient&#39;s ventilation, because there is a time delay between the onset of ventilatory insufficiency or hypoventilation and a subsequent rise in arterial carbon dioxide levels.  
           [0012]    In current clinical practice, P a CO 2  levels are indirectly inferred via capnometry, the measurement of CO 2  levels in the gas mixture breathed by a patient. If the CO 2  levels, in addition to being measured, are also graphically displayed as a CO 2  level vs. time plot, the technique is called capnography and the resulting plot is called a capnogram. A typical capnogram comprises three distinct phases during exhalation. Phase I reflects the clearing of CO 2 -free gas from conducting airways which do not normally participate in gas exchange (i.e., airway dead space). Phase II is generated by exhalation of CO 2 -free gas from conducting airways mixed with alveolar gas containing CO 2  because the alveolar gas has undergone gas exchange with arterial blood containing CO 2  at the alveolar membrane. Phase III reflects the exhalation of alveolar gas which has had time, through the process of diffusion, to equilibrate its partial pressure of CO 2  with the partial pressure of CO 2  in arterial blood.  
           [0013]    Because the lung&#39;s airways are a dead-ended conduit, gas flow in the lungs follows a first in, last out principle. Thus the last amount of alveolar gas exiting the lungs during exhalation was the first in and has had the most time to equilibrate its partial pressure with the partial pressure of the equivalent substance in arterial blood, such as, among others, CO 2 , O 2 , volatile anesthetic, intravenous anesthetic, alcohol, medication and inert gas anesthetic. Thus, in healthy patients, alveolar gas exhaled during phase III is representative of the partial pressures of different substances dissolved in arterial blood. Further, the CO 2  component of alveolar gas exhaled during Phase III is generally a good indicator of the ventilatory status of a healthy patient.  
           [0014]    When using capnometry or capnography, clinicians generally utilize the peak or end-tidal CO 2  (P et CO 2 ) value as an estimate Of P a CO 2 . P et CO 2  is indicative of the mean alveolar partial pressure of carbon dioxide from all functional gas exchange units of the lung, which, in turn, approximates P a CO 2  in normal lungs. Because CO 2  readily diffuses from arterial blood into alveolar gas across the alveolar membrane, P et CO 2  closely approximates P a CO 2  when the lung has normal ventilation and perfusion. In addition to the information provided by the P et CO 2 , the shape of the capnogram also provides valuable diagnostic information regarding the respiratory ventilation.  
           [0015]    Other techniques have been utilized for assessing patient blood gas levels with mixed results. Transcutaneous CO 2  sensors measure the partial pressure of CO 2  in tissue. The sensors are placed onto the skin of the patient and measure CO 2  diffusing through heated skin but have practical and theoretical limitations. Pulse oximetry is a widely used, noninvasive method for estimating the arterial oxygen carried in hemoglobin. Neither transcutaneous measurements of CO 2  nor pulse oximetry directly measures and reports the status of respiratory ventilation. Thus, transcutaneous CO 2  measurement and pulse oximetry may be late to diagnose an impending problem. In the case of pulse oximetry, once the condition of low oxygen is detected, the problem already exists, and once the transcutaneous CO 2  measurement is elevated, it indicates that hypoventilation has already existed for a period of time sufficient for a rise in the partial pressure of tissue CO 2 .  
           [0016]    Capnometers have been used with some success as a means for detecting and avoiding the severe complications associated with hypoventilation, partial or complete airway obstruction, bradypnea and apnea. Systems assessing proper gas exchange based on predetermined or user-adjusted carbon dioxide thresholds detect instances of hypoventilation or airway obstruction. In general, the CO 2  level must exceed a lower threshold (indicating sufficient gas exchange and ruling out apnea) and stay below a higher threshold (indicating adequate ventilation and ruling out high end-tidal CO 2  concentrations due to, for example, hypoventilation). However, capnometers are often prone to false positive alarms.  
           [0017]    A false positive alarm occurs when a system indicates that a potentially dangerous situation has arisen, when in fact, it has not. False positive alarms may occur in situations where a change in CO 2  levels is unrelated to respiratory gas exchange. Such misleading alarms may result from a patient talking, breathing through an unmonitored orifice, or dilution of the exhaled gases at the sampling source. False positive alarms may occur in systems where a predetermined carbon dioxide threshold may be set at an arbitrary point that may not be representative of inadequate gas exchange. Systems prone to false positive alarms are often deactivated by clinicians or simply ignored, putting a patient at risk if a truly life threatening situation occurs.  
           [0018]    During inhalation, a patient breathing ambient air will inhale room air containing a negligible amount of carbon dioxide (0.03% v/v) that will not register on clinical capnometers. The beginning of an exhalation may be nearly indistinguishable from the inhalation phase due to a patient breathing out dead space gas that has not mixed with alveolar CO 2  found deeper in the lungs. As a patient continues to exhale, alveolar CO 2  will be expelled from the lungs and the CO 2  level will cross a lower threshold as he/she continues to exhale, eventually reaching a plateau or peak referred to as “end-tidal” CO 2 . As a patient begins to inhale, carbon dioxide levels will drop below the lower threshold level due to a negligible amount of CO 2  in room air. The period between a crossing of a threshold on an exhalation upstroke and a crossing of the same threshold on a subsequent exhalation upstroke is usually considered as a full breath or respiratory cycle.  
           [0019]    When hypoventilation is due to adequate V T  but low RR, the CO 2  level will cross a lower CO 2  threshold and eventually the P et CO 2  will exceed a higher CO 2  threshold as alveolar CO 2  concentration rises because CO 2  is accumulating in the alveoli as a result of inadequate minute ventilation. When hypoventilation is due to adequate RR or fast RR but low V T  (shallow breathing or panting), the CO 2  level may never cross the lower CO 2  threshold because the exhaled gas is comprised mainly of dead space gas devoid of CO 2  and is at most mixed with a minimal amount of alveolar CO 2 .  
           [0020]    Many CO 2  monitoring systems are programmed to initiate an alarm in the event that a patient does not complete a sufficient number of respiratory cycles (breaths) within a predetermined time window. False negative alarm conditions may result from such systems, where inadequate gas exchange is occurring in a patient but a system fails to recognize a potentially life threatening event. The fact that the exhaled CO 2  level crosses a lower CO 2  threshold within a predetermined time window is not sufficient to assure that a patient is experiencing adequate gas exchange. For example, a patient with a significant partial airway obstruction may break through a blockage in order to take a short (physiologically insignificant) breath, registering with a capnometer system that a patient is breathing at a normal rate within a predetermined time window such that an airway obstruction may remain undetected. Breaths taken by a patient, though of normal frequency, may not be of adequate volume to provide sufficient oxygen supply and carbon dioxide elimination to maintain a healthy state.  
           [0021]    An untoward event will usually generate an alarm to alert a clinician. Generally, a clinician will respond to an alarm by taking an appropriate corrective action. Thus, an untoward event generates two distinct actions: an alarm (usually automated) and a response (usually manual but it may also be automated). The terms “response” and “alarm” will be used consistently herein according to the definitions above. The response of a clinician usually also involves turning off the alarm because of its annoying nature, requiring a superfluous action that does not directly contribute to patient care. In the event of a false positive alarm, even more time and motion are wasted in activities that do not directly contribute to, and may detract from, patient care. False alarms may also devalue the benefit and credibility of alarms (the “cry wolf” syndrome).  
           [0022]    With some systems featuring automated responses (such as interruption of drug delivery) to alarms, an audible or visual alarm generally accompanies an automated response. A design rationale for having an overt alarm (a potential annoyance) generally accompany an automated response (a potential benefit to a busy, multi-tasked clinician) is that an untoward condition should not be masked from a clinician, even if the system has initiated an automated corrective response. Therefore, a tightly set automated response that is designed to intervene early and/or frequently to provide better control of a given parameter will, in general, also generate more frequent and potentially disruptive alarms.  
           [0023]    In the past, increasing the sensitivity of monitoring systems created a greater probability of detecting untoward events but also increased the probability of false alarms triggered by patient conditions that do not warrant the attention of a busy, multi-tasked clinician. Decreasing the sensitivity of monitoring systems diminishes the incidence of false alarms but increases the probability that critical untoward events may be missed.  
           [0024]    False positive alarms may be caused by an over-sensitive alarm algorithm that is vulnerable to spurious data or a data artifact. Over-sensitivity may be due to a short averaging period, or no averaging, of carbon dioxide. False negative alarms are generally attributable to low specificity, where specificity relates to determining the actual significance of information received via patient monitoring. High specificity may reduce alarms associated with spurious data or over-sensitivity, yet may also hide those patient episodes that constitute truly life-threatening situations.  
           [0025]    A further example of potential false negative alarm episodes occurs when a patient experiences ineffective hyperventilation, characterized by high respiratory rates with very low tidal volumes. Breathing at very low tidal volumes expels mainly dead space gas from the upper airway that has not, or minimally, mixed with alveolar CO 2 . The next inhalation of a small tidal volume is sequestered in the dead space formed by the upper airway and never or barely reaches the alveoli where gas exchange occurs. During hyperventilation, a carbon dioxide threshold may be just reached, indicating a breath to the CO 2  monitor. However, a patient may not be inhaling sufficient oxygen or eliminating sufficient carbon dioxide for adequate gas exchange.  
           [0026]    Because even short acting drugs exhibit a finite half-life, it is desirable to reduce or shut off drug delivery as early as possible in the event of an untoward patient state, providing in effect an “early response” system so that an untoward condition can be promptly reversed. In the context of systems integrating ventilatory monitoring and sedative and/or analgesic drug delivery, deactivation of drug delivery early in the development of a life-threatening condition is desirable.  
           [0027]    It would therefore be advantageous to provide a respiratory gas exchange monitoring system for detecting partial or complete airway obstruction or depressed respiratory drive to breathe comprising high sensitivity and high specificity, thus diminishing the incidence of false positive and false negative alarms. It would be even further advantageous to provide a respiratory gas exchange monitoring system integrated with a sedative and/or analgesic drug delivery system that deactivates drug delivery at the onset of a potentially dangerous patient episode.  
           [0028]    It would be further advantageous to provide a respiratory gas exchange monitoring system that accurately measures and indicates carbon dioxide elimination during every breath. It would be further advantageous to provide a respiratory gas exchange monitoring system that is capable of estimating overall carbon dioxide elimination during a procedure in such a way as to determine whether exhaled carbon dioxide levels are relatively constant. It would be further advantageous to provide a respiratory gas exchange monitoring system integrated with a drug delivery system designed for operation by non-anesthetists that provides additional patient safety features.  
         BRIEF SUMMARY OF THE INVENTION  
         [0029]    The present invention provides an anthropomorphic automated alarm and response paradigm that allows clinicians to enjoy the benefits of automated responses to adverse events concerning their patients that is not prone to false alarms and improper responses. More particularly, the present invention comprises a system for use during the performance of a medical procedure on a patient that monitors the ventilatory conditions of a patient and provides automated responses to certain of those conditions in a manner that is both highly sensitive in detecting adverse events and that reduces false positive and false negative alarms in a manner that is transparent, or nearly so, to the user. In particular embodiments of the present invention, the conditions that the system monitors are related to the gas exchange of the patient where certain suspect values of the gas exchange trigger the system&#39;s automated responses. Once triggered by the existence of those suspect ventilatory conditions should they occur, the system of the present invention initiates an automated response and then enters into a hypervigilant state during which it continues to acquire and evaluate data regarding the patient&#39;s conditions. During the hypervigilant state, the system may perform additional tests of high specificity to confirm whether an adverse condition truly exists with the patient. Such adverse conditions suspected by the system may include partial or complete airway obstruction, bradypnea, apnea, and hypoventilation. These additional tests may be related to the same data, such as gas exchange or capnometry data, that is collected by the system throughout the procedure or they may be related to different data the acquisition of which begins when the system enters the hypervigilant state.  
           [0030]    The automated responses initiated by the system of the present invention may be passive or active interventions in the continuance of the medical procedure or part of that procedure. Should an adverse condition truly exist, the system may continue the intervention and may initiate further interventions or it may even halt the entire medical procedure or parts of that procedure. For example, in particular embodiments of the present invention, the system operates in conjunction with a drug delivery system for providing sedation or analgesia to the patient during a medical procedure and acts to pause the delivery of drugs to the patient upon the detection of the suspect conditions. In these embodiments, the system may shut down the drug delivery altogether upon the determination during the hypervigilant state that a true alarm condition exists with the patient. In this manner the invention deactivates drug delivery in situations in which the continuance of drug delivery may be life-threatening to the patient, because the drug delivery itself may be causing the true alarm conditions to exist with the patient. A further example of a passive intervention in a medical procedure is where the system of the present invention pauses the delivery of shock waves to kidney stones during extra-corporeal shock wave lithotripsy when adverse effects on cardiac function are suspected. Examples of active interventions that may be employed by the system of the present invention include initiating sodium nitroprusside infusion and continuous positive airway pressure (CPAP) administration.  
           [0031]    The system may determine during the hypervigilant state that an adverse condition does not truly exist, i.e. the initial suspect conditions were merely a false alarm. In such situations, the system of the present invention may then end the interventions in the continuance of the medical procedure and may return the procedure to its state just prior to the interventions or to where it would have been had no interventions taken place. The invention thus provides early triggering of corrective interventions based on patient conditions that may be indicative of truly adverse events without waiting the few seconds it may take the system or the user to determine that a truly adverse event indeed exists. In this manner, the invention supplies added safety to a medical procedure while ensuring a highly sensitive analysis of patient data is completed before a permanent intervention in the procedure is automated. This invention is applicable where the costs of unnecessary interventions that it performs in a medical procedure (those during false alarms) are low, i.e., where no harm is done to the patient or the procedure by the temporary intervention.  
           [0032]    The initial interventions before the hypervigilant state is entered by the system may be accompanied by silent or semi-overt alarms or may be otherwise transparent to the user. Upon a true positive alarm, the user may be notified by the system of the adverse conditions of the patient and of the continued and/or further automated responses. If the system determines during the hypervigilant state that the suspect conditions that triggered the initial alarm response were not indicative of a truly adverse event, then no overt or annoying alarms are put in front to the user. In this manner, only true positive alarms and not false or disruptive alarms are portrayed to the user.  
           [0033]    The anthropomorphic alarm and response paradigm of the present invention is analogous to a anesthesia provider&#39;s reaction during a surgical procedure whereby he may lean forward to look closely at a given parameter that seems to be out of the norm (i.e., be hypervigilant) and then may reduce the dose of volatile anesthetic given to the patient (i.e., initiate an early intervention) all the while not raising an alarm to the surgeon until he has better assessed the parameter to see if it truly represents a serious condition. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0034]    [0034]FIG. 1 depicts a general embodiment of a method performed by the system of the present invention;  
         [0035]    [0035]FIG. 2 illustrates a block diagram depicting one embodiment of a gas analyzer integrated with a drug delivery system in accordance with the present invention;  
         [0036]    [0036]FIG. 3 illustrates one embodiment of a capnogram feature extraction algorithm in accordance with the present invention;  
         [0037]    [0037]FIG. 4 illustrates one embodiment of a method of gas analysis, display and interpretation in accordance with the present invention;  
         [0038]    [0038]FIG. 5 a  illustrates a flow chart depicting one embodiment of a method of generating hypervigilant conditions, alarm conditions and predetermined responses based on gas analysis in accordance with the present invention;  
         [0039]    [0039]FIG. 5 b  illustrates a flow chart depicting an alternative embodiment of a method of generating hypervigilant conditions, alarm conditions and predetermined responses, including a drug pause, based on gas analysis in accordance with the present invention;  
         [0040]    [0040]FIG. 5 c  illustrates a flow chart depicting an alternative embodiment of a method of generating hypervigilant conditions, alarm conditions and predetermined responses based on gas analysis in accordance with the present invention;  
         [0041]    [0041]FIG. 5 d  illustrates a flow chart depicting an alternative embodiment of a method of generating hypervigilant conditions, alarm conditions and predetermined responses, including a drug pause, based on gas analysis in accordance with the present invention; and  
         [0042]    [0042]FIG. 6 illustrates a flow chart depicting an alternate embodiment of a method of generating hypervigilant conditions, alarm conditions and predetermined responses based on gas analysis, including averaging over multiple predetermined time periods, in accordance with the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0043]    [0043]FIG. 1 represents a general embodiment of a method performed by the system of the present invention. After a start  1 , method  10  comprises measurement  1   a  of a variable or parameter X that is indicative of a parameter or property Y that a clinician desires to monitor and/or control. In certain situations (with blood pressure for example), it may be possible to measure Y directly so that X is the same as Y. In other cases, it may not be clinically practical to measure a parameter Y directly and therefore a variable or parameter X is measured that is an indirect estimate of a status and/or trend of parameter Y. For example, CO 2  and S p O 2  measurements may be taken to serve as indicators of ventilation and oxygenation respectively. For the sake of simplicity, FIG. 1 only shows one variable X being measured, however the concept of the present invention fully contemplates measurement of multiple variables X that are direct or indirect measurements of a plurality of parameters Y being simultaneously monitored and/or controlled. The frequency at which measurement  1   a  is performed can be 50-100 Hz, but could also be slower or faster depending on the characteristics of the parameter X being measured.  
         [0044]    Processes or sets of processes  2  and  3  are subsequently performed on a measured value of X. Sensitive process or sets of processes A  2  use the measured value of X to generate derived values of X that are sensitive indicators of the status and/or trend of Y that are also relatively immune from artifactual or spurious data. An example of sensitive process  2  may be averaging the value of X over moving time windows of the most recent 6, 12, 20, 30 and n seconds. Specific process or sets of processes B  3  use the measured value of X to generate derived values of X that are specific indicators of the status and/or trend of Y that are also relatively immune from artifactual or spurious data. An example of specific process  3  may be the cumulative addition of the value of X over a plurality of time periods starting at different start times. The invention also contemplates placing specific process or sets of processes  3  between sensitive test(s)  4  and specific test(s)  5  such that specific process or sets of processes  3  are only executed upon failure of sensitive test(s)  4 .  
         [0045]    Derived values of X generated by sensitive process or sets of processes  2  are used to perform sensitive test(s)  4 . For purposes of example, step  4  may comprise comparing derived values of X obtained from step  2  to a predetermined threshold. If test(s)  4  are passed, method  10  checks if any actions were paused and resumes them, if they were paused. Method  10  leaves the actions unaltered if no actions were previously paused; any silent or semi-overt alarms are deactivated. Method  10  then proceeds to check if an end of case or user interruption  7   a  is present. If an end of case or user interruption  7   a  is present, method  10  transitions to finish  7  and is concluded. If an end of case or user interruption  7   a  is not present, method  10  loops back to measurement of X  1   a , completing a normal, uneventful (i.e., no failed sensitive test) path.  
         [0046]    If one or more of sensitive tests  4  fails, method  10  transitions into a hypervigilant condition  9   c  that may include silent and/or semi-overt alarms. A semi-overt alarm is a low-key alarm that does not attempt to grab the attention of a user because an alarm condition has not yet been confirmed and still has a probability of being a false alarm. An experienced user may direct his or her attention to a location of a semi-overt alarm to obtain data regarding the status and operation of a system. An example of a semi-overt alarm may be a non-flashing visual indicator such as an LED of a white or neutral color. An example of a silent alarm is an alarm response accompanied by no visual or audible indication or other attention-getting feature of failure of tests  4 .  
         [0047]    A pause  9   a  of any actions that may adversely affect parameter(s) Y is initiated upon failure of sensitive test(s)  4 . An early intervention in the form of a pause or initiation of an action is especially beneficial in the case of conditions that exhibit an inertial component and take discrete and clinically significant amounts of time to identify and/or reverse. Examples of actions that may be paused are infusion of respiratory depressant drugs (such as propofol) if Y is ventilation; infusion of sedatives if Y is monitored patient responsiveness; infusion of blood pressure altering drugs if Y is blood pressure or intracranial pressure; initiation of CPAP in response to diagnosed airway obstruction; initiation of supplemental O2 delivery in response to ventilatory insufficiency and/or oxygen desaturation and a titrator for control of blood pressure that silently pauses or initiates sodium nitroprusside infusion in the event of a spike of BP downward or upward respectively. The invention is also applicable to similar systems for treatment of hypotension using levophed, neosynephrine, dopamine, or other inotropic/vasoconstrictive compounds where the infusion rate is increased in the event of a spike downward of blood pressure or decreased if the blood pressure spiked upward and then reassessed with further data. In the event of an early detection of a possible arrhythmia, the invention could be applied to charge the capacitor plates (a time-consuming process) of an internal or external defibrillator and then either give defibrillation/cardioversion joules if the event turns out (with more data) to be a true positive or drain the capacitor charge if the event turned out to be false positive.  
         [0048]    Confirmation test  5  uses derived values of X obtained from specific process or sets of processes  3  to confirm whether adverse conditions really exist. Confirmation test  5  could comprise, for example, comparing cumulative sums of X over set periods of time starting from a time of failure of sensitive test  4  to preset thresholds. If adverse conditions are not confirmed by confirmation test  5 , method  10  loops back to measurement of X  1   a , disabling  6   a  any active overt alarms along the way. As long as failure of sensitive test(s)  4  occurs, a pause of actions  9   a  is active; X is continuously measured and derived sensitive and specific values of X are updated to determine the status and/or trend of parameter(s) Y. If after actions have been paused, failure of sensitive test(s)  4  goes away, paused actions are resumed  9   b.    
         [0049]    If adverse conditions are confirmed by confirmation test  5 , overt alarms are generated  6  and actions are stopped  8 . Method  10  loops back to measurement of X to update the status and trend of X and the derived sensitive and specific values of X as indicators of the status and/or trend of parameter(s) Y. Subsequently, depending on the results of tests  4  and  5 , normal, hypervigilant or overt alarm conditions may be generated. If sensitive tests  4  pass, normal conditions prevail; paused actions are resumed or initiated actions are canceled, silent or semi-overt alarms are turned off and there is a general “stand down”. If sensitive tests  4  fail but specific tests  5  pass, then hypervigilant conditions that may include paused or initiated actions and silent or semi-overt alarms are in effect. If both sensitive tests  4  and specific tests  5  fail, overt alarm conditions and stoppage of actions remain enforced. The embodiment previously described comprises three preparedness conditions: normal, hypervigilant and overt alarm. The invention contemplates more than three levels of preparedness such as, for example, a plurality of gradations of hypervigilant conditions, interposed between normal and overt alarm conditions.  
         [0050]    [0050]FIG. 2 illustrates one embodiment of an integrated gas analysis and drug delivery system  26  comprising user interface  21 , controller  22 , gas analyzer  23 , patient interface  24 , and drug delivery system  19 . Drug delivery system  19  comprises delivering one or a plurality of drugs by one or a plurality of drug delivery devices, such as, for example, pumps. User  20  operates integrated gas analysis and drug delivery system  26  in order to monitor gas exchange occurring in patient  25 . In a further embodiment of the present invention, integrated gas analysis and drug delivery system  26  provides an early response that deactivates all or part of drug delivery system  19  when hypoventilation is detected. Examples of drug delivery system  19 , user interface  21 , patient interface  24 , and controller  22 , which may be used with the present invention, are disclosed in U.S. patent application Ser. No. 09/324,759, filed Jun. 3, 1999 which is herein incorporated by reference in its entirety.  
         [0051]    The present invention further comprises a plurality of means for monitoring and/or maintaining sufficient gas exchange, including, but not limited to, systems for use with intubated patients, full mask monitoring systems, systems introducing oxygen orally and/or nasally, and systems that selectively monitor a preferred airway path of patient  25 .  
         [0052]    User  20  may be an anesthesiologist, a certified registered nurse anesthetist (CRNA) or, in the case of a sedation and analgesia system, a trained non-anesthetist practitioner. One embodiment of the present invention comprises use of integrated gas analysis and drug delivery system  26  to deliver anesthesia, monitored anesthesia care, sedation, and/or analgesia with an associated pause in delivery of selected drugs that have a potential to cause respiratory depression upon detection of hypoventilation. However, other means of monitoring respiration are contemplated for use with the present invention for the detection of hypoventilation. Examples of such means are monitors of airway pressure, sound, temperature, humidity, intermittent water condensation on a polished end of an optical fiber leading to changes in refraction, chest movement, spirometry and transthoracic impedance plethysmography, among others. Monitoring respiration via airway pressure has advantages in decreasing response time of the system over some embodiments employing capnometers because of the relative time delay associated with the transport delay in sidestream capnometers. Further, it is contemplated that trained individuals may use the system and method of the present invention in a plurality of procedures, such as, for example, cardiac catheterization, colonoscopy and endoscopy where the benefits of reliable and early detection of hypoventilation are desirable. User  20  interacts with gas analysis and drug delivery system  26  via user interface  21 . User interface  21  comprises data displayed in the form of “real-time” graphical data, numeric data, and/or a printed hard copy relating to ventilation. An example of such a user interface is disclosed in U.S. patent application Ser. No. 10/285,689 filed Nov. 1, 2002, and incorporated herein by reference in its entirety.  
         [0053]    Controller  22  may be a CPU, or any other suitable data processing system. The software executed by controller  22  is coded in a language such as, for example, C or C++ under an operating system such as, for example, QNX. However other operating systems such as, for example, LINUX, VX Works, or Windows Embedded NT are consistent with the present invention. Certain embodiments operate in a real time operating system such as, for example, QNX, where programs relating to specific patient interfaces, user interfaces, capnometry, and other features of integrated gas analysis and delivery system  26  are compartmentalized into separate program modules (not shown). As will be disclosed herein, controller  22  further comprises programming related to gas analysis, activation and deactivation of all or part of drug delivery system  19 , and oxygen delivery.  
         [0054]    In one embodiment of the present invention gas analyzer  23  is a capnometer that is integrated with integrated gas analysis and drug delivery system  26 . Embodiments of capnometer  23  comprise nasal carbon dioxide monitors, oral carbon dioxide monitors, sidestream aspirating capnometers, mainstream capnometers, or other suitable capnometers such as, for example, infrared, Raman scattering and mass spectrometer.  
         [0055]    [0055]FIG. 3 illustrates one embodiment of a capnogram feature extraction algorithm  30  in accordance with the present invention comprising carbon dioxide level measured by a capnometer on y-axis  38 , time on x-axis  39 , carbon dioxide waveform (capnogram)  40 , and carbon dioxide threshold  37 , where capnogram feature extraction algorithm  30  is used to determine respiratory rate. An exhalation component of capnogram  40  comprises three phases: phase I  31 , phase II  32  and phase III  33 . The peak CO 2  values in phase III are end-tidal CO 2  concentrations  35  and  36  that are generally interpreted as representative of P a CO 2 .  
         [0056]    In one embodiment of the present invention, carbon dioxide threshold  37  is established, where respiratory cycle time  34  is measured from point  41  where exhaled CO 2  first crosses carbon dioxide threshold  37  on an upstroke, to point  42  where exhaled CO 2  again crosses carbon dioxide threshold  37  on an upstroke. Other CO 2  thresholds (not shown) may also be used with the present invention for other functions, for example, to set low and high alarm limits for P et CO 2 . The present invention further comprises respiratory cycle time  34  calculated from a time interval between peak CO 2  value  35  in phase III of one breath and peak CO 2  value  36  in a following breath, a first inhalation until a second inhalation, a time interval between similar distinctive and unique landmarks in consecutive capnograms or by any other suitable means of calculating a respiratory cycle time. If a patient does not exhale a sufficient amount of carbon dioxide in a predetermined period of time, capnometer  23  may signal controller  22  of the possibility of hypoventilation. In one embodiment of the present invention, capnogram feature extraction algorithm  30  is used in cooperation with a method for detecting hypoventilation and apnea monitoring  50  (FIGS. 5, 5B,  5 C,  5 D), as will be illustrated herein, while diminishing the incidence of annoying false positive and/or potentially life-threatening false negative alarms.  
         [0057]    [0057]FIG. 4 illustrates one embodiment of displaying and analyzing capnogram  60  in accordance with the present invention comprising partial pressure of CO 2  (pCO 2 ) in mm Hg on left y-axis  61 , time in minutes on x-axis  62 , waveform  67  of pCO 2  averaged over a moving time window of the most recent, for example, 12 seconds, waveform  63  of instantaneous pCO 2 , waveform  64  representing a cumulative sum of pCO 2  starting at time t=0 minutes, and cumulative pCO 2  in units of mm Hg on right y-axis  70 . Respiratory waveform  63  illustrates a plurality of respiratory cycles  34  measured in terms of partial pressure of CO 2  in mm Hg. However measuring carbon dioxide concentration as a fraction of overall gas concentration such as, for example, volume/volume, weight/weight, weight/volume, volume/weight, or by other suitable means, is consistent with the present invention. Averaged pCO 2  waveform  67  comprises, in the illustrated example, an average of pCO 2  over the previous or most recent 12 seconds. However averaging time periods other than 12 s, such as, for example, 20, 30 and 40 seconds, are consistent with the present invention. Cumulative pCO 2  waveform  64 , measured relative to cumulative pCO 2  right y-axis  70 , comprises a sum of all sampled pCO 2  values over the course of an entire procedure or over a specific time period. The present invention further comprises an addition of a plurality of averaged waveforms relating to method  100  (FIG. 6), numeric data, or other suitable means of illustrating data.  
         [0058]    [0058]FIG. 5A illustrates one embodiment of a method  50  for providing hypoventilation detection and apnea monitoring comprising the steps of: start  51  of the procedure, averaging  52  of partial pressure of carbon dioxide over a predetermined period of time to obtain average pCO 2  plot  67  and computing  53  a cumulative sum of pCO 2  that is used for plot  64 . Method  50  further comprises a standing query  54  whether average pCO 2    67  is below a predetermined threshold, which may stand through to the finish  57  of a procedure. A “yes” answer to query  54  prompts an assessment  55  whether, from a time of that “yes” response to query  54  forward, a cumulative sum of pCO 2  changes significantly over a predetermined period of time, representing for example, two good breaths with full exhalations in 20 seconds. In one embodiment of the present invention, after a “yes” to query  54 , a step of a procedure for which method  50  is provided may be automatically paused while query  55  is issued. For instance, as FIGS. 5B and 5D show, an administration of one or more drugs that have the potential to cause hypoventilation may be paused (“drug pause”) while query  55  proceeds. A “no” answer to query  55  prompts overt alarm condition  56 , which may lead to halting  58  of an aspect of a procedure, such as, for example, stopping one or more drugs. Following steps  56  and  58 , method  50  loops back to step  51  a of measuring pCO 2  and executes once more query  54  to determine if average pCO 2  is below a predetermined threshold.  
         [0059]    A “yes” answer to query  55  results in step  56   a  (FIGS. 5A, 5B,  5 C,  5 D) that removes overt alarm condition  56  and interruption  58  of an aspect of a procedure; method  50  loops back to measurement of CO 2    51   a  and remains in a hypervigilant mode with drug pause and/or silent or semi-overt alarms remaining in effect as long as query  54  indicates that a sensitive test for hypoventilation is positive. For example, in one embodiment of method  50 , if a predetermined threshold for average pCO 2  requires an average pCO 2  of 1 mm Hg over a ten second period, and a patient does not meet this threshold, drug delivery may be paused momentarily without an alarm necessarily sounding, thus acting as a silent response to a developing condition that could be harmful to the patient. A cumulative sum of pCO 2  may then be required to add to a sum total of, for example, 4,000 mm Hg (equivalent to two good breaths with full expirations) over, for example, a twenty second period at a given sampling rate, such as, for example, 50 Hz, in order to obviate an overt alarm and/or an interruption of drug delivery. It is to be noted that the actual value of a threshold for predetermined change in cumulative pCO 2  over a given time period is dependent on the sampling frequency of CO 2  measurement. Other suitable average and cumulative pCO 2  thresholds are consistent with the present invention, especially at different sampling frequencies of CO 2  measurement.  
         [0060]    If part or all of drug delivery system  19  has been paused due to a “yes” answer to query  54 , a subsequent “no” answer to query  54  causes part or all of drug delivery system  19  to resume suspended operations (FIGS.  5 B,  5 D); silent or semi-overt alarms are also cancelled (FIGS. 5A, 5B,  5 C,  5 D). Method  50  subsequently executes query  57   a  to verify if controller  22  or user  20  has requested an end of case or interruption. If an answer to query  57   a  is “no”, method  50  loops back to measurement of CO 2    51   a . If an answer to query  57   a  is “yes”, method  50  transitions to finishing step  57  which comprises deactivation of integrated gas analysis and drug delivery system  26 .  
         [0061]    Averaging of pCO 2    52  comprises measuring the pCO 2  associated with patient  25  via patient interface  24 . Data relating to pCO 2  levels associated with patient  25  is then transmitted to controller  22 , where controller  22  is programmed to calculate average levels of pCO 2 , for a predetermined time period. For example, controller  22  may be programmed to calculate an average pCO 2  level over a previous or most recent twelve-second period or moving time window. Averaging data over a moving time window of predetermined duration diminishes the effects of artifacts (spurious or invalid data) and presents user  20  and controller  22  with a more accurate reflection of an actual ventilatory status of patient  25  over the moving time window. The moving time window for averaging pCO 2  may be any length of time suitable to ensure patient safety, exhibiting a compromise between artifact filtering (generally improved by longer time windows) and response time (generally improved by shorter time windows). Weighted averages are also possible, where weights are used to emphasize or reduce an effect of pCO 2  values from a selected portion of a moving time window. For example, to emphasize pCO 2  values for the most recent 2 seconds within a 12 s moving average, all pCO 2  values from the most recent 2 seconds may be multiplied by a weight n, where n is greater than 1, before being included in the averaging process. An amount by which a weight n is greater than 1 will determine how much emphasis is provided to a desired time segment within a moving time window. A weighted time segment could be at any desired point in a moving time window. A time segment of the most recent 2 seconds was only used by way of an example and should not be considered limiting.  
         [0062]    Step  53  comprises computing a cumulative sum of pCO 2 , that is, adding a sum of all sampled pCO 2  values throughout a procedure or during a specified time period. In one embodiment of the present invention, controller  22  may be programmed to compute and/or display average pCO 2    67  and cumulative pCO 2    64  simultaneously.  
         [0063]    Query  54  comprises setting a predetermined threshold and determining whether an average pCO 2  measured over a predetermined time period and obtained from averaging step  52 , is above or below a predetermined threshold. Levels of carbon dioxide may be measured in partial pressure, as a fraction of expired or inspired gas, or by any other suitable means. A predetermined threshold consistent with query  54  may be expressed as a partial pressure, as a fraction of expired and inspired gas, or as any other suitable benchmark. In one embodiment of the present invention, a predetermined threshold is established such that average pCO 2  levels below it are indicative of a potentially life threatening situation. In particular, if gas levels exhaled by patient  25  are associated with average pCO 2  levels below a threshold, patient  25  may be experiencing a correspondingly low amount of gas exchange, resulting in a potentially dangerous situation. By averaging data for carbon dioxide levels over a predetermined moving time window, the present invention provides an accurate indicator as to whether a patient is indeed experiencing a low level of gas exchange when average pCO 2  drops below a predetermined threshold.  
         [0064]    If an answer to query  54  is “no”, method  50  proceeds to measurement of CO 2    51   a  if there is no end of case or user interruption and continues to average pCO 2  levels and to cumulatively sum pCO 2  (FIGS. 5A, 5C). If the answer is “yes” to query  54 , integrated gas analysis and drug delivery system  26  executes query  55  to determine if a cumulative sum of carbon dioxide, starting at a time when execution of step  55  is begun, changes significantly over a predetermined time (FIG. 5A). Query  55  comprises controller  22  computing a change in a cumulative sum of carbon dioxide according to step  53  for a period of time after an average pCO 2  falls below a predetermined threshold. In effect, query  55  functions to look ahead, prospectively anticipating future events, whereas query  54  looks back to determine retrospectively whether a past average pCO 2  is above or below a predetermined threshold. Unlike an average pCO 2  value, a change in a cumulative sum starting at a time of failure of a sensitive test is not weighted down by past history of the pCO 2  level, thus jettisoning past history of pCO 2  to provide faster response while still remaining fairly immune to artifacts. In one embodiment of the present invention, following a drop in average pCO 2  below a threshold, integrated gas analysis and drug delivery system  26  looks to the overall change in a cumulative sum of pCO 2  for a period of time to determine whether the change in the cumulative sum of pCO 2  rises enough to indicate that sufficient gas exchange is occurring. Like a predetermined threshold, an amount of increase in a cumulative sum of pCO 2  needed to indicate sufficient gas exchange, and a time period over which an increase in cumulative PCO 2  is anticipated, may be established by user  20 , by programming associated with controller  22 , or by other suitable means of establishing the aforementioned parameters.  
         [0065]    Further embodiments of the present invention comprise calculating a cumulative sum of pCO 2  only after query  54  has been answered “yes”, and discontinuing calculation of the cumulative sum of pCO 2  when a “no” response is given to query  54  as illustrated in FIGS. 5C and 5D.  
         [0066]    If there is a significant increase in cumulative pCO 2  after dropping below a predetermined threshold for pCO 2  average, method  50  will proceed through a hypervigilant path which incorporates step  51   a  of measuring CO 2  and query  54  as to whether an average pCO 2  is below a threshold. If an answer to query  54  is “no”, method  50  proceeds through a normal and uneventful path. If there is no significant increase in a cumulative sum of pCO 2  during a predetermined time period, query  55  will transition to alarm condition  56 . Query  54  and query  55  provide integrated gas analysis and drug delivery system  26  with a dual means of detecting inadequate gas exchange. The prospective nature of one detection means (such as, for example, cumulative sum) complements the retrospective nature of another detection means (such as, for example, time averaging). Similarly, the sensitivity of test  54  complements the specificity of test  55 . The present invention diminishes the incidence of false positive and false negative alarms by providing a rigorous querying process. A significant increase of a cumulative sum of pCO 2  required to obviate alarm condition  56  may be a required percentage increase from a point in time when query  55  begins, a specific numerical increase from a point in time when query  55  begins, or any other suitable means of indicating a patient is experiencing sufficient alveolar gas exchange.  
         [0067]    In one embodiment of the present invention, alarm condition  56  comprises an alarm signaling user  20  and a response of deactivating drug delivery system  19  (FIGS. 5B, 5D). It should be noted that drug delivery system  19  will already be paused when query  55  is executed as a result of a “no” answer to query  54  (FIGS. 5B and 5D). Deactivation of drug delivery system  19 , as a result of alarm condition  56 , is an extension of a “drug pause” in drug delivery system  19 . Signaling user  20  comprises audio alarms, visual alarms, or other suitable signaling means. Deactivation of drug delivery system  19  includes, but is not limited to, partial or total deactivation of intravenous drug delivery, partial or total deactivation of systemic drug delivery, and/or partial or total deactivation of inhalation drug delivery. Halting drug delivery may alleviate complete or partial airway obstruction due to overmedication. Following partial or total deactivation of drug delivery system  19 , integrated gas analysis and drug delivery system  26  will, in one embodiment of the present invention, loop back to CO 2  measurement  51  a and continue on to query  54 . If the answer to query  54  is still “yes”, query  55  is executed. Then, following a “yes” response to query  55 , integrated gas analysis and drug delivery system  26  will move out of alarm condition  56  and re-activate an aspect of a procedure that was halted. A further embodiment of the present invention comprises deactivating integrated gas analysis and drug delivery system  26  in the event of alarm condition  56 . Further embodiments of the present invention comprise gas analysis and drug delivery system  26  moving out of alarm condition  56  when average pCO 2  levels over a predetermined time period exceed a predetermined threshold, when a cumulative sum of pCO 2  increases at a predetermined rate, or beyond a predetermined percentage threshold over a given time period, and/or when combinations of average pCO 2  and cumulative sum of pCO 2  reach predetermined levels. Alarms may alert user  20  to a potential negative patient episode in a variety of means such as, for example, by way of the user interface disclosed in U.S. patent application Ser. No. 10/285,689.  
         [0068]    Method  50  for providing hypoventilation detection and apnea monitoring reduces the incidence of false positive alarms by evaluating average pCO 2  data in the context of cumulative pCO 2  data. A drop in expired pCO 2  related to patient phonation may be sufficient to set off alarms in existing capnometry systems. The present invention averages data over a time period to obviate false positive alarms due to artifact or data unrelated to patient ventilation. The present invention further provides a user with a dependable gas analysis and apnea monitoring system by relating averaged pCO 2  to cumulative sum of pCO 2 . By considering a cumulative sum of pCO 2 , the present invention diminishes the incidence of false positive alarms occurring in existing systems where exhalations do not exceed a predetermined threshold, yet are sufficient for adequate gas exchange.  
         [0069]    [0069]FIG. 6 illustrates one alternative embodiment of a method  100  for providing hypoventilation detection and apnea monitoring comprising the steps of: start  101 , CO 2  measurement step  101   a , computing step  102  for determining a first average of pCO 2  over a first predetermined period of time, computing step  103  for determining a second average of PCO 2  over a second predetermined period of time, step  104  for computing a cumulative sum of pCO 2 , step  105  for querying whether a first pCO 2  average is below a predetermined threshold, where a “no” answer prompts step  110   a  of checking for an end of case or interruption, and where a “yes” answer to query  105  prompts the first alarm condition in step  106 , step  107  for querying whether a second average of pCO 2  is below a predetermined threshold, where a “no” answer prompts step  110   a , and a “yes” answer prompts step  108  for querying if a cumulative sum of pCO 2  then changes significantly over a predetermined period of time, where a “yes” answer to query  108  prompts step  110   a  and a “no” answer prompts second alarm condition  109 . In one embodiment of the present invention, second alarm condition  109  returns to CO 2  measurement step  101   a . Finish  110  comprises deactivation of integrated gas analysis and drug delivery system  26  by user  20  or by controller  22 , deactivation during second alarm condition  109 , or deactivation at any desirable point of method  100 . A “no” response to query  110   a  indicates that there is no request for program interruption and method  50  loops back to CO 2  measurement  101   a . From step  101   a , method  100  may perform any or all of steps  102 ,  103  and/or  104 .  
         [0070]    Step  102  comprises establishing a predetermined period of time such as, for example, twelve seconds, for which an average pCO 2  is calculated. Step  102  comprises any suitable predetermined period of time for averaging pCO 2 .  
         [0071]    Step  103  comprises establishing a predetermined period of time such as, for example, forty seconds, for which an average pCO 2  is calculated. In one embodiment of the present invention, a predetermined time period of step  103  is longer than a predetermined time period established for step  102 .  
         [0072]    Step  104  comprises computing a cumulative sum of pCO 2  throughout a procedure or during a given time period. In one embodiment of the present invention, controller  22  may be programmed to calculate and/or display a first average of step  102 , a second average of step  103 , and a cumulative sum of pCO 2  of step  104  simultaneously.  
         [0073]    Query  105  comprises establishing an average pCO 2  threshold, where a measured average pCO 2  below the established threshold indicates potentially insufficient alveolar gas exchange. An established threshold may be any level indicative of a critical average CO 2  benchmark, and may be established as a partial pressure, a fraction of expired and inspired gas, or as any other suitable unit of measurement. If a response to query  105  is “no”, method  100  transitions to step  110   a . If the response to query  105  is “yes”, integrated gas analysis and drug delivery system  26  moves to first alarm condition  106 . One embodiment of the present invention comprises calculating and/or displaying averages and/or sums relating to steps  102 ,  103 , and/or  104  throughout the duration of method  100 .  
         [0074]    In one embodiment of the present invention, first alarm condition  106 , herein referred to as step  106 , comprises deactivating part or all of drug delivery  19 , an increased monitoring frequency of patient parameters with optionally tighter alarm bounds, and alerting user  20  of an alarm condition. In one embodiment of the present invention, step  106  comprises deactivating part or all of drug delivery  19 , but user  20  is not informed of a transition to first alarm condition  106 , minimizing user distraction.  
         [0075]    The present invention comprises utilizing a first average (step  102 ) measured over a relatively short predetermined time period such as, for example, twelve seconds, where a drop in average pCO 2  will be detected quickly. As a predetermined time period for averaging pCO 2  becomes shorter, the likelihood of a false positive alarm becomes higher due to an increase in sensitivity to artifact or spurious data. In one embodiment of the present invention, method  100  comprises exploiting the benefits of highly sensitive measurement, such as, for example, a diminished incidence of false negative alarms, in conjunction with an increased specificity gained by using longer time averages (step  103 ) of pCO 2 . To this effect, first alarm condition  106  is triggered upon first average pCO 2  (step  102 ) dropping below a predetermined threshold. First alarm condition step  106 , in one embodiment of the present invention, deactivates part or all of drug delivery  19  but does not inform user  20  that method  100  has entered first alarm condition  106 . In doing so, delivery of drugs that may have adverse effects on ventilation is discontinued without initiating an overt visual or audio alarm. A pause of part or all of drug delivery system  19  may be a response to a false positive alarm, resulting from a high sensitivity of a first average pCO 2  (step  102 ). Method  100  may reactivate part or all of drug delivery system  19  and deactivate first alarm condition  106  if it was previously enabled, upon receipt of a “no” response to query  105 . Pausing of part or all of drug delivery system  19  as a response to a false positive alarm for a brief interval while awaiting further diagnostic information to more fully define ventilatory status has no harmful effect, yet provides greater patient safety due to an “early response” intervention in the form of a drug pause in the event that a first alarm condition develops into a bona-fide emergency. This is especially so with drugs whose effects are not immediately discontinued as soon as drug administration is turned off and benefits accrue from early intervention so that a patient can thus recover earlier from a hypoventilation or apneic episode, possibly without a user even being aware of an early intervention. To minimize the risk of silent or semi-overt interventions being masked by methods  100  or  50 , these interventions may be logged by integrated gas analysis and drug delivery system  26  and may be available for review and quality assurance purposes. Method  100  continues to query more specific averages (query  107 ), as opposed to more sensitive averages, in determining whether a potentially life-threatening situation truly exists. If, for example, query  105  detects sufficient gas exchange upon a first average (step  102 ) exceeding a predetermined threshold, part or all of drug delivery system  19  may be reactivated with no negative patient effect caused by a partial or total pause in drug administration. A further embodiment of the present invention comprises second alarm condition  109  returning to query  108 , where if the answer is “yes”, step  106   a  of deactivating the second alarm condition is executed.  
         [0076]    Query  107  comprises setting a predetermined threshold and determining whether a second average of pCO 2  (step  103 ), measured over a predetermined time period, is above or below a predetermined threshold. Levels of carbon dioxide may be measured in partial pressure, as a fraction of expired or inspired gas, or by any other suitable means. A predetermined threshold may be established as a partial pressure, as a fraction of expired or inspired gas, or as any other suitable benchmark. In one embodiment of the present invention, a predetermined threshold is established at a level such that average pCO 2  values below the threshold are indicative of a potentially life threatening situation. In one embodiment of the present invention, a predetermined time period of a second average (step  103 ) is longer than a predetermined time period of a first average (step  102 ) in order to provide increased specificity. By providing a relatively long predetermined time period for a second average (step  103 ), method  100  diminishes the incidence of false positive alarms due to data artifact.  
         [0077]    If the answer to query  107  is “no”, integrated gas analysis and drug delivery system  26  remains in first alarm condition  106 . If the answer to query  107  is “yes”, integrated gas analysis and drug delivery system  26  executes query  108  to determine if a cumulative sum of pCO 2  changes significantly over a predetermined time. Query  108  comprises controller  22  evaluating data computed in step  104  for a period of time after first or second average pCO 2  falls below a predetermined threshold. In effect, query  108  functions to look ahead, anticipating future events, whereas query  107  looks back to determine whether a second average (step  103 ) of pCO 2  is above or below a predetermined threshold. In one embodiment of the present invention, following a drop in a second average (step  103 ) of pCO 2  below a threshold, integrated gas analysis and drug delivery system  26  looks to a cumulative sum of pCO 2  for a period of time to ascertain whether the cumulative sum rises enough to indicate sufficient gas exchange. As with a predetermined threshold, an amount of increase in a cumulative sum of pCO 2  needed to indicate sufficient gas exchange, and a time period over which the increase is anticipated, may be established by user  20 , by programming associated with controller  22 , or by other suitable means of establishing the aforementioned parameters.  
         [0078]    A further embodiment of the present invention comprises calculating a cumulative sum of pCO 2  only after query  107  has been answered “yes”, and discontinuing calculation of a cumulative sum of pCO 2  when a “no” response is given to query  107 . This further embodiment would move the cumulative summing step  104  such that it is located between queries  107  and  108 .  
         [0079]    If there is a significant increase of cumulative pCO 2  after dropping below a predetermined threshold associated with query  107 , method  100  loops back to CO 2  measurement step  101   a . If there is not a significant increase in a cumulative sum of pCO 2  during a predetermined time period, query  108  responds with second alarm condition  109 . Query  105 , query  107 , and query  108  provide integrated gas analysis and drug delivery system  26  with redundant means of detecting inadequate gas exchange while diminishing the incidence of annoying false positive and potentially life-threatening false negative alarms. The present invention diminishes the incidence of false positive and false negative alarms by providing a rigorous querying process. A significant increase of a cumulative sum of pCO 2  required to obviate second alarm condition  109  may be a required percentage increase from a point in time when query  108  begins, a specific numerical increase from a point in time when query  108  begins, or any other suitable means of assuring a patient is experiencing sufficient gas exchange. Query  107  and query  108  provide the present invention with increased specificity in determining whether patient  25  is experiencing a truly life-threatening episode. Pausing of part or all of drug delivery system  19 , associated with first alarm condition  106 , places patient  25  into a safe state while query  107  and  108  determine true ventilatory status. By placing patient  25  into a drug deactivated or paused safe state, integrated gas analysis and drug delivery system  26  combines the benefits of high-sensitivity and high-specificity in determining the true seriousness of an alarm condition, while diminishing a probability of overdose and/or apnea due to over-medication and minimizing disruptions.  
         [0080]    In one embodiment of the present invention, second alarm condition  109  comprises signaling user  20  and deactivating all or part of drug delivery system  19 . Signaling user  20  comprises overt audio alarms, visual alarms, or other suitable signaling means. Deactivation of part or all of drug delivery system  19  includes, but is not limited to, deactivation of intravenous drug delivery, deactivation of systemic drug delivery, and/or deactivation of inhalation drug delivery. Halting delivery of drugs that may cause hypoventilation may alleviate complete or partial airway obstruction caused by over-medication. Following deactivation of part or all of drug delivery system  19  in step  109 , integrated gas analysis and drug delivery system  26  will, in one embodiment of the present invention, continue to CO 2  measurement  101   a . In one embodiment of the present invention, following a “yes” response to query  108 , integrated gas analysis and drug delivery system  26  will, in step  109   a , disable second alarm condition  109 . A further embodiment of the present invention comprises deactivating integrated gas analysis and drug delivery system  26  in the event of second alarm condition  109 . Further embodiments of the present invention comprise integrated gas analysis and drug delivery system  26  moving out of alarm condition  109  when a first average of PCO 2  over a predetermined time period (step  102 ) exceeds a predetermined threshold, when a cumulative sum of pCO 2  increases at a predetermined rate or beyond a predetermined percentage threshold, or when a combination of average pCO 2  and cumulative sum of pCO 2  reaches a predetermined level.  
         [0081]    Method  100  provides increased specificity, increased sensitivity, and early deactivation of part or all of drug delivery system  19  in the event of a potentially dangerous patient episode, while diminishing the probability of false negative and false positive alarms. Method  100  further comprises integrating gas analyzer  23  with drug delivery system  19 , where resulting integrated gas analysis and drug delivery system  26  may be operated by a non-anesthetist practitioner. Operability of system  26  by a non-anesthetist practitioner is facilitated by the partially-automated, safety-biased nature of ventilatory monitoring and drug delivery associated with method  100 .  
         [0082]    While exemplary embodiments of the invention have been shown and described herein, it will be obvious to those skilled in the art such embodiments are provided by way of example only. Numerous insubstantial variations, changes, and substitutions will now be apparent to those skilled in the art without departing from the scope of the invention disclosed herein by the Applicants. Accordingly, it is intended that the invention be limited only by the spirit and scope by the claims as they will be allowed.