Patent Description:
Anesthetic agents induce a hypnotic state in a patient by the administration of such a drug, such as via inhalation of the drug through the patient's breathing circuit. Typical inhaled anesthetic agents include Sevoflurane, Isoflurane, Desflurane, and Enflurane, among others. These inhalation anesthetic agents are generally stored as a liquid and then vaporized in a vaporizer system. The vaporized anesthetic agent is mixed into the fresh gas and other ventilation gases delivered to the patient. Various types of anesthetic vaporizers are well known in the relevant art, including plenum vaporizers, drawover vaporizers, and dual-circuit gas-vapor blenders.

The anesthetic agent acts on the brain to produce a lessening or loss of consciousness in the patient. The extent to which the patient is anesthetized is often termed the "depth of anesthesia" or "hypnotic level. " Various patient monitoring devices are available for measuring a patient's depth of anesthesia, such as a bispectral index (BIS) monitor which analyzes the complexity of electroencephalographic (EEG) data obtained from the patient as a sensed indication of the hypnotic level of the patient. Other depth of anesthesia monitoring methods and systems are known, including train-of-four monitors, facial twitch monitors, and others.

In one embodiment, an electronic vaporizer system includes an anesthetic sump containing anesthetic agent, a vaporizer unit that vaporizes the anesthetic agent from the sump and delivers the vaporized agent to a patient breathing circuit, and a gas sensor configured to measure end tidal concentration of the anesthetic agent and exhalation gasses from the patient. A control system is configured to receive the measured end tidal concentration of anesthetic agent and compare the measured end tidal concentration to a desired end tidal concentration to be maintained for the patient. The vaporizer unit then automatically controls the delivery of a controlled amount of vaporized agent to the patient based on the comparison.

In one embodiment, a method of controlling a vaporizer system configured to vaporize an anesthetic agent and deliver the vaporized agent to a patient breathing circuit includes measuring end tidal concentration of the anesthetic agent in exhalation gasses from the patient and comparing the measured end tidal concentration to a desired end tidal concentration to be maintained for the patient. The vaporizer unit is then automatically controlled to deliver an amount of vaporized agent to the patient breathing circuit based on the comparison so as to maintain the measured end tidal concentration within a predetermined range of the desired end tidal concentration.

<CIT> describes a vaporizer for the delivery of anesthesics using end tidal CO2.

As described above, vaporizers take liquid anesthetic agent, such as Sevoflurane or Desflurane, and convert it to a vapor that gets titrated out to the patient. The patient inhales the anesthetic vapor with the breathing gasses delivered by the ventilator. Mechanically controlled vaporizer systems are a very common type of vaporizer system worldwide. Mechanical vaporizers are open-loop-control systems where a clinician sets a delivery amount for the vaporizer, such as by controlling a dial on the housing of the vaporizer system. Depending on the needs of the patient and the needed depth of anesthesia, or hypnotic level, based on the medical care being provided to the patient, the clinician manually adjusts the delivery amount of agent provided by the manual vaporizer.

The present inventors have recognized problems with manual vaporizers, which require significant attention and resources by the clinician to properly operate them to deliver optimal anesthetic amounts to the patient. Further, open-loop-controlled systems are subject to human error, where busy clinicians with divided attention may not provide optimal ventilator control settings and timing, and thus a patient may receive too little or too much anesthesia at any given point in a medical procedure. Yet, the inventors have also recognized that many care facilities may be unable to purchase entirely new anesthesia delivery and ventilator systems providing closed-loop-control.

Further, the inventors have recognized that controlling anesthesia delivery based on end tidal concentration of the anesthetic agent in the exhalation gasses from the patient would provide an effective close-loop-control means, and that such closed-loop-control is desirable and overcomes issues relating to human capital and clinician error.

In view of the foregoing challenges in the relevant art recognized by the inventors, the inventors have developed the disclosed electronic vaporizer system which can be retrofitted into current ventilator systems providing anesthesia delivery capabilities, such as having a circle breathing system. The disclosed electronic vaporizer systems replace mechanical vaporizers in existing anesthesia systems, and thus are configured to connect into the breathing circuit of the patient in the same way as the prior mechanical vaporizers. Namely, mechanical vaporizers can be removed and replaced with the disclosed close-loop-controlled electronic systems. In certain embodiments, the electronic vaporizer system may be shaped and sized similarly as the mechanical system such that it can fit onto the housing of the anesthesia system at the same location and/or by the same connection means as the mechanical ventilator being replaced.

The electronic vaporizer system is configured to receive a measured end tidal concentration of the anesthetic agent being delivered by the vaporizer and compare the measured end tidal concentration to a desired end tidal concentration to be maintained for the patient. For example, desired end tidal concentration may be, for example, a minimum alveolar concentration (MAC) value and may also include end tidal CO<NUM> and/or O<NUM>. The desired end tidal concentration may be set by the clinician or may be automatically set and controlled by the electronic vaporizer system, such as according to a predetermined routine. The electronic vaporizer system automatically delivers an amount of vaporized agent to the patient based on the comparison of the measured end tidal concentration to the desired end tidal concentration. For example, the electronic vaporizers system may determine a change in the amount of vaporized agent to be delivered to the patient breathing circuit based on a difference between the measured end tidal concentration and a desired end tidal concentration, and to control the vaporizer to effectuate the change in order to maintain the measured end tidal concentration within a predetermined range of the desired end tidal concentration.

In certain embodiments, the electronic vaporizer system may include and/or be communicatively connected to a depth of anesthesia monitor, such as BIS monitor or a train-of-four monitor configured to measure a depth of anesthesia of the patient. The electronic vaporizer system may be configured to utilize the depth of anesthesia information to provide further closed-loop-control in order to maintain the patient at a desired depth of anesthesia. For example, the electronic vaporizer system may be configured to set a desired end tidal concentration, or determine a change in the desired end tidal concentration, in order to achieve or maintain the desired depth of anesthesia. The system then controls delivery of vaporized agent based on that set desired end tidal concentration, using the measured end tidal concentration as feedback.

The system may further be configured to receive and/or follow one or more concentration routines providing end tidal concentration values over time, and to automatically adjust the desired end tidal concentration over time according to the concentration routine. The system may further be configured to calculate a recommended anesthesia concentration based on patient demographic data, for example, and to advise the clinician of the recommendation and/or to automatically adjust the desired end tidal concentration based on the recommended concentration. Thereby, transition periods of anesthetic delivery, such as induction and emergence, can be automatically controlled to maintain the patient's end tidal concentration at predefined desired levels over time. The provides safe and precise control of anesthetic during critical periods and frees the clinician to focus on other areas of patient care.

<FIG> and <FIG> depict embodiments of an electronic vaporizer system <NUM> operably connected to a ventilator system <NUM> and configured to deliver vaporized anesthetic agent to a patient breathing circuit <NUM>. The electronic vaporizer system <NUM> includes an electronic vaporizer <NUM> and one or more sensors communicatively connected thereto, including a gas sensor <NUM> configured to measure end tidal concentration of the anesthetic agent in exhalation gasses from patient and one or more physiological sensors <NUM> configured to measure physiological signals related to, or indicating, a depth of anesthesia of the patient <NUM>. The electronic vaporizer <NUM> is configured to receive the measured end tidal concentration of the anesthetic agent and/or the depth of anesthesia of the patient determined based on the physiological signals and to radically control delivery of vaporized agent to the patient accordingly.

The electronic vaporizer <NUM> includes a sump <NUM>, or reservoir, containing anesthetic agent to be delivered to the patient, such as Sevoflurane, Desflurane, Enflurane, etc. The sump <NUM> is configured to be refillable, such as from a refill bottle, as is standard in the relevant art. Thus, the sump <NUM> has sufficient volume capacity such that it can receive at least the entire volume of a standard refill container. In one embodiment, the sump can accommodate up to about <NUM> of liquid agent. The electronic vaporizer <NUM> includes a vaporizer unit <NUM> that vaporizes liquid anesthetic agent housed in a sump <NUM> and delivers the vaporized agent to the patient breathing circuit <NUM>. For example, the breathing circuit <NUM> may include a circle breathings system <NUM>, and the vaporizer unit <NUM> may be configured to deliver vaporized agent such that inhalation gasses comprises anesthetic agent are injected into the circle breathing system <NUM> and delivered to the patient by the ventilator system <NUM>.

The electronic vaporizer <NUM> further includes a controller <NUM> configured to control the vaporizer unit to deliver an amount of vaporized agent to maintain a desired end tidal concentration for the patient <NUM>. The control system for the electronic vaporizer system includes the controller <NUM> for the vaporizer unit <NUM> and may also include other control devices communicatively connected to the controller <NUM>. For example, the controller <NUM> may act in concert with an anesthesia computation module <NUM> on a network <NUM> communicatively connected to the electronic vaporizer <NUM> and/or a controller associated with a depth of anesthesia monitor <NUM>, such as a BIS monitor 40a, and/or a controller <NUM> for the ventilator system <NUM>.

A gas sensor, which may be a set of sensors, is positioned to measure end tidal concentration of anesthetic agent and other gasses in exhalation gasses within the patient breathing circuit <NUM>. The patient breathing circuit <NUM> includes an inspiratory section 4a that carries inhalation gasses from the ventilator system to the patient interface <NUM>. The expiratory section is configured to carry exhalation gasses from the patient back to the ventilator <NUM>. The patient interface is commonly, for example, an endotracheal tube as illustrated in <FIG>. In other embodiments, the patient interface <NUM> may be a facial mask or some other device configured to create a sealed interface between the patient's airway and the breathing circuit <NUM>. In the depicted example, the gas sensor <NUM> is positioned between the patient interface <NUM> and the inspiratory and expiratory arms of the patient breathing circuit <NUM>. Humidity and moisture exchange filter <NUM> may be positioned between the patient interface <NUM> and the gas sensor <NUM> in order to remove moisture from the exhalation gasses prior to measurement.

The gas sensor is configured to measure concentration of the anesthetic agent in the exhalation gasses from the patient, and may also be configured to measure a concentration of nitrous oxide (N<NUM>O) and carbon dioxide (CO<NUM>) and oxygen (O<NUM>). Such concentration measurements are taken during the exhalation cycle where exhalation gasses exit the patient's lungs through the patient interface <NUM> through the filter <NUM> to the first connector end <NUM> of the unit containing the gas sensor <NUM> and out the second connector end <NUM>, which is connected to the connector end 4c of the patient breathing circuit hose. The gas sensor <NUM> may further be configured to measure flowrate, including inspiratory flow rate and expiratory flow rate, as well as other gas concentration measurements, which may be inspiratory or expiratory measurements.

The concentration and other measurements from the gas sensor <NUM> are communicated to the electronic vaporizer <NUM>, which may be by a physical data connection and/or by wireless means. In the example at <FIG>, the gas sensor <NUM> is connected by cable <NUM> to the receiver port <NUM> on the electronic vaporizer <NUM>. The gas sensor <NUM> also includes a wireless transmitter <NUM>, which may be a wireless transceiver 42a communication, which is configured to wirelessly broadcast the concentration and other measurements conducted by the gas sensor <NUM>. Such wireless communications may be received by the network <NUM> such as the computer network system for the operating ward and/or by the hospital or healthcare facility network. In certain embodiments, the concentration and/or other gas measurement may also be received at the depth of anesthesia monitor <NUM>. In certain embodiments, the physical connection between the gas sensor <NUM> and the electronic vaporizer <NUM> may be eliminated and the electronic vaporizer <NUM> may be configured to receive wireless transmission of the measurements from the gas sensor <NUM>.

An additional gas sensor <NUM> may be configured to measures input gas from the ventilator to the patient's breathing circuit and configured to measure the ventilation gas blend provided by the ventilator <NUM>. Such a gas sensor <NUM> may be positioned upstream of the delivery point from the vaporized agent and may be configured to measure flowrate and gas concentrations of the ventilator gas blend such as measurement of oxygen (O<NUM>) and N<NUM>O in the ventilator gas blend. This provides information regarding the input gasses and flow rates provided by the ventilator system. In certain embodiments, the gas sensor <NUM> may be incorporated in the ventilator system <NUM> and the gas measurements may be communicated by the ventilator system <NUM> to the electronic vaporizer <NUM>. In other embodiments, the gas sensor <NUM> may be a stand-alone sensor connected at a point in the breathing circuit and configured to communicate directly with the electronic vaporizer <NUM>, which may be by wired or wireless means as described above. The input gas concentration information may also be supplied by an electronic gas mixer built into the anesthesia machine, if so equipped. For example, the additional gas sensor <NUM> may be integrated into an electronic gas mixer that automatically blends and delivers mixed gas to the patient breathing circuit (N2O/O2, Air/O2, O2 or Air). In such an embodiment, the gas composition is obtained from the electronic gas mixer through communications with therewith, which can be wired or wireless communications as described herein.

The system <NUM> may further include a depth of anesthesia monitor <NUM> configured to measure a depth of anesthesia of the patient. Various depths of anesthesia monitors are well known in the relevant art, including bispectral index (BIS) monitors, train-of-four monitors, facial twitch monitors, and others. In the example at <FIG>, the depth of anesthesia monitor <NUM> is a BIS monitor 40a. The BIS monitor includes a physiological sensor <NUM> in the form of a strip of EEG electrodes 44a configured to be placed on the forehead of the patient <NUM> and to measure EEG activity from the patient. The BIS monitor 40a is configured to determine a depth of anesthesia, or a hypnotic level, of the patient.

In the example at <FIG>, the BIS monitor 40a is a stand-alone device having a housing <NUM> to which the EEG electrode patch 44a is connected by a cable 45a to a receiver port <NUM> on the housing <NUM>. The BIS monitor includes a user interface display <NUM> configured to display the depth of anesthesia and EEG information collected by the monitor. The system <NUM> is configured such that the depth of anesthesia information gathered by the BIS monitor 40a is communicated to the electronic vaporizer <NUM>. In certain embodiments, the BIS monitor 40a includes a wireless transmitter or transceiver <NUM> configured to wirelessly communicate the depth of anesthesia and/or EEG information. The wireless transmission may be received at the electronic vaporizer <NUM>.

For example, a wireless communication link <NUM> may be established between the electronic vaporizer <NUM> and the BIS monitor 40a, i.e., between the I/O communication transceiver <NUM> and the transceiver <NUM>, for communication of the depth of anesthesia information. Such communication may be by any wireless communication protocol, such as Bluetooth, Bluetooth Low Energy (BLE), ANT, and ZigBee. Alternatively, the wireless transceivers of the BIS 40a and the electronic vaporizer <NUM> may communicate with one another via a longer-range wireless system, such as on a network operating on the wireless medical telemetry service (WMTS) spectrum or on a WiFi-compliant wireless local area network (WLAN). In other embodiments, the BIS 40a and the electronic vaporizer <NUM> may be body area network (BAN) devices, such as medical body area network (MBAN) devices, that operate as a wireless network of wearable or portable computing devices.

Alternatively or additionally, the electronic vaporizer system <NUM> may be configured to communicate with and receive communications from a hospital computer network, which may be wireless or wired communication means. The network <NUM> may include an anesthesia computation module <NUM> executable to communicate with the electronic vaporizer <NUM> and to oversee the anesthetic delivery routines and instructions being executed by the system. The system <NUM> may be configured such that the depth of anesthesia information is also received at the hospital network <NUM> and may be communicated from the network <NUM> to the electronic vaporizer <NUM>. In the example at <FIG>, the electronic vaporizer <NUM> communicates with the network <NUM> via wireless link <NUM> and the BIS monitor communicates with the network <NUM> via wireless link <NUM>. For example, the network <NUM> may be a local area network for the hospital or for the operating area of the hospital or other medical facility.

In one arrangement, the electronic vaporizer <NUM> and/or the BIS 40a may be configured as edge devices operating in an edge computing system where a central computer system for the operating department of the healthcare facility, for example, collects and analyzes patient data and ventilation data in order to oversee and guide the end tidal delivery of anesthetic agent to the patient. For example, the electronic vaporizer <NUM>, depth of anesthesia monitor <NUM>, and gas sensor <NUM> may all be edge devices communicating information to and receiving information from one or more edge servers comprising part of the network <NUM>.

In other embodiments, the BIS monitor 40a or other depth of anesthesia monitor <NUM> may be incorporated within a housing <NUM> of the electronic vaporizer <NUM>. As shown in <FIG>, the depth of anesthesia monitor <NUM> may be integrated with controller <NUM>, or integrally housed with the vaporizer unit <NUM>, sump <NUM>, and other elements of the electronic vaporizer <NUM>. In such an embodiment, the physiological sensor <NUM>, such as the EEG patch 44a or a train-of-four sensor, is connected by communication link <NUM> to the housing <NUM> of the electronic vaporizer <NUM>. The communication link <NUM> may be by wired or wireless means, examples of which are described above. In such an embodiment, the depth of anesthesia monitor <NUM> may include a dedicated controller for calculating the depth of anesthesia values. In other embodiments, the controller <NUM> may be configured to calculate the depth of anesthesia values based on the physiological data gathered and filtered by the depth of anesthesia monitor electronics.

The housing <NUM> of the vaporizer system <NUM> may be configured to removably attach to the ventilator system <NUM>. For example, the housing <NUM> may be configured to connect to existing ventilator systems <NUM> in place of an existing manual vaporizer. Thus, the housing <NUM> may be shaped similar to the manual vaporizer systems that it is configured to replace, or at least a portion of the housing that connects to the ventilator system <NUM> may be shaped and configured similarly or identically to the existing manual vaporizer housing. Thereby, the disclosed electronic vaporizer system <NUM> can replace the existing manual vaporizers on a wide variety of installed ventilator systems <NUM>.

The housing <NUM> may include a refill port <NUM> configured to receive a refill container of anesthetic agent in order to refill the sump <NUM>. A dial <NUM> may also be provided on the housing <NUM>. The dial <NUM> may be configured to control a mode of the vaporizer system, where the dial <NUM> is movable between a position associated with a manual mode, where a clinician manually controls the amount of vaporized agent delivered to the patient breathing circuit, and an automatic mode, where the control system automatically controls vaporizer unit to deliver the amount of vaporized agent to maintain a certain end tidal concentration anesthetic agent for the patient. In the example depicted at <FIG>, the automatic mode position <NUM> is at a far end of the rotational range of the dial <NUM>. When the dial <NUM> is in that maximum rotational position, the automatic mode marker <NUM> is aligned with the selection marker <NUM> on the housing <NUM>. When the dial is rotated away from the automatic mode position <NUM>, a manual mode is engaged where the clinician can operate the dial to select an end tidal concentration. Various position indicators <NUM> are associated with respective concentration outputs and the vaporizer unit <NUM> is controlled accordingly, similarly to existing manual vaporizer controls on manual vaporizer systems. Thus, the depicted electronic vaporizer <NUM> is also configured to be operated as a manual vaporizer when the automatic mode, or end tidal concentration control mode, is not selected.

In other embodiments, the dial <NUM> may instead be replaced with another user interface device for engaging and disengaging the automatic mode, such as a switch or a button configured to turn on and off the automatic mode where the control system automatically controls the vaporizer unit to maintain an end tidal concentration of the patient. In still other embodiments, the automatic mode may be engaged through a user interface <NUM> associated with the electronic vaporizer <NUM>. The user interface <NUM> may be a standalone device, such as a touchscreen that is separately housed from the housing <NUM> of the electronic vaporizer, as illustrated in <FIG>. In other embodiments, such as that illustrated in <FIG>, the user interface 30a may be integrated into the housing <NUM> of the electronic vaporizer <NUM>. The integrated interface 30a may be a touchscreen, such as an LCD touchscreen on a front side of the housing <NUM> that faces the clinician.

The user interface <NUM>, 30a is configured to display information relating to anesthetic delivery and control, such as including an agent indicator <NUM> indicating the anesthetic agent being delivered by the electronic vaporizer <NUM>, a desired concentration indicator <NUM> displaying the desired end tidal concentration setting which is to be automatically maintained by the system <NUM>, and a measured concentration indicator <NUM> indicating the current measured end tidal concentration of the anesthetic agent for the patient <NUM>. In the depicted embodiment, the desired concentration indicator <NUM> presents the desired concentration setting as a minimum alveolar concentration (MAC) value, and the measured concentration indicator <NUM> presents the measured concentration as a percent by volume of agent in the patient's exhalation gasses. In other embodiments, the measured concentration indicator <NUM> may be presented as a MAC value and/or the desired concentration indicator may be presented as a percentage by volume value. The user interface may also display an N<NUM>O indicator indicating the end tidal concentration of N<NUM>O. Alternatively or additionally, the user interface may also display an inspiratory N<NUM>O concentration, such as measured in the ventilator gas blend by the gas sensor <NUM> or ventilator electronic gas mixer. The user interface may further include one or more patient demographic indicators <NUM> providing demographic information about the patient <NUM>, such as age, weight, gender, etc..

The user interface <NUM>, 30a may also be configured to display information, suggestions, and instructions to the clinician. For example, the display may be configured to provide a recommended concentration to the clinician based on patient demographic data and/or a suggestion or instruction to the clinician to adjust the desired end tidal concentration based on the recommended concentration. Alternatively or additionally, the user interface <NUM>, 30a may be configured to prompt a clinician to input and/or receive clinician inputs instructing a desired end tidal concentration and/or inputting one or more concentration routines to be executed by the vaporizer system <NUM> over time. For example, the clinician may instruct a series of desired end tidal concentrations over a period of time to be executed at a particular stage in a procedure, such as an induction routine for inducing a desired depth of anesthesia, or hypnotic state, of the patient and/or an emergence routine for reducing the patient's depth of anesthesia at a desired rate.

In certain embodiments, the anesthesia computation module <NUM> may further be configured to calculate recommended concentration values and/or recommended concentration routines for controlling the electronic vaporizer <NUM> based on patient demographic data and/or historical data for the patient and to provide such recommended concentration values or recommended concentration routines to the electronic vaporizer <NUM>. The anesthesia computation module <NUM> may be configured to utilize the most up to date anesthetic calculation algorithms and information, including published MAC charts, as well as patient demographic information, medical history, etc. obtained from the patient's medical record, in order to calculate and suggest appropriate end tidal concentration settings and/or routines to provide optimal anesthesia delivery for the patient. An exemplary MAC chart is illustrated at <FIG>, which provides a desired MAC setting based on expired oxygen, expired N<NUM>O, and patient age. In an edge computing system, such MAC charts and other information for computing recommended concentrations for desired end tidal settings can be easily updated implemented at the network level and take advantage of advances in Artificial Intelligence (AI).

<FIG> depict exemplary methods, or portions thereof, of controlling an electronic vaporizer system. In the flowchart at <FIG>, the method <NUM> of controlling an electronic vaporizer system includes receiving a desired end tidal concentration at step <NUM>. For example, the desired end tidal concentration may be inputted by a clinician, such as via the user interface <NUM>, or may be automatically determined by the system, such as at the hospital LAN network and instructed by the anesthesia computation module <NUM>. The end tidal concentration of anesthetic agent in exhaled gasses from the patient is measured at step <NUM>, such as by gas sensor <NUM>. The measured concentration is compared to the desired concentration at step <NUM>. The vaporizer unit <NUM> is then controlled to deliver vaporized agent at step <NUM> based on the difference between the measured end tidal concentration and the desired end tidal concentration.

<FIG> depicts a portion of a control method of a vaporizer system relating to calculation and implementation of recommended concentration values or recommended concentration routines. The recommendation calculations may be carried at the network level, as described above, or the controller <NUM> of the electronic vaporizer <NUM> may be configured to conduct the recommendation calculations. Information regarding the inhalation gas being delivered to the patient and the current settings for the electronic vaporizer are provided and utilized to calculate recommended concentrations or routines, which may then be provided as recommendations to a clinician, who may accept or reject the recommendations. Alternatively, such recommendations may automatically be implemented by the electronic vaporizer <NUM>.

In the example shown at <FIG>, N<NUM>O concentration is received at step <NUM>, which may include the inspiratory N<NUM>O concentration provided by the ventilator <NUM>, the ventilator gas blend and/or may include the end tidal N<NUM>O concentration measured by the gas sensor <NUM>. The current desired end tidal concentration set for the vaporizer, and/or the current concentration routine set for the vaporizer, is received at step <NUM>. A recommended concentration for the end tidal concentration or a recommended concentration routine is calculated at step <NUM> on the measured N<NUM>O value and patient demographics, such as patient age and weight. The current setting, including the end tidal concentration and/or the concentration routine is then compared to the recommended concentration or recommended concentration routine at step <NUM> to determine if there is a discrepancy between the current vaporizer settings and the recommended values. A recommendation alert is displayed at step <NUM> if the difference exceeds a threshold difference warranting a change in the vaporizer settings as to improve anesthesia administration to the patient. For example, the recommendation alert may be presented on the user interface <NUM>, 30a of the electronic vaporizer <NUM>.

User input is then received at step <NUM>, such as via the user interface <NUM>, 30a to accept or reject the recommended concentration or recommended concentration routine. The vaporizer settings are then maintained or adjusted according to the user input so as to control the desired end tidal concentration of anesthetic agent over time for the patient based on the user's acceptance or rejection of the recommendation.

<FIG> depicts another embodiment of a method <NUM> of controlling the electronic vaporizer system <NUM>. A depth of anesthesia of the patient is measured at step <NUM>, such as by a depth of anesthesia monitor <NUM>, 40a. The measured depth of anesthesia of the patient is compared to a desired depth of anesthesia of the patient at step <NUM>. At step <NUM>, the control system determines whether the difference between the desired depth of anesthesia and the measured depth of anesthesia exceeds a threshold.

The end tidal concentration of anesthetic agent is measured at step <NUM> and the measured end tidal concentration is compared to a desired end tidal concentration at step <NUM>. If the difference between the measured and desired end tidal concentration exceeds a threshold value at step <NUM>, then a change in amount of vaporized agent delivered to the patient is determined at step <NUM> based on the difference.

If, however, the measured and desired depth of anesthesia are within the predefined threshold of one another and the measured and desired end tidal concentration are within the predefined threshold of one another, then the current delivery amount of vaporized agent is maintained, as represented at step <NUM>. In other words, if both the patient's depth of anesthesia and the patient's end tidal concentration are within a predetermined range of the desired values set for the vaporizer, then the current delivery amount is maintained. Otherwise, changes to anesthetic delivery by the electronic vaporizer <NUM> are effectuated.

Changes in anesthetic delivery amount may be calculated variously based on differences between the measured and desired depth of anesthesia levels and the measured and desired end tidal concentration values. In the depicted example, if the measured end tidal concentration is not within the threshold range of the desired end tidal concentration, then the difference between the measured and desired depth of anesthesia measurements may be attributable to the discrepancy in the end tidal concentration, especially if the discrepancies between the depth of anesthesia values and the end tidal concentration values are consistent. This example assumes such consistency. If the difference between the measured and desired end tidal concentration is greater than the threshold value, then the system adjusts the vaporize agent delivered to the patient based on the difference at step <NUM> in order to bring the measured end tidal concentration in line with the desired end tidal concentration. In a further embodiment, if the system is unable to achieve the set target end tidal concentration, i.e., the measured end tidal concentration is lower than the desired end tidal concentration, then the system may generate an alarm that it is unable to achieve its programmed target, potentially signaling a failure of the system, leaks in the breathing system, etc..

This is also likely to decrease the difference between the measured depth of anesthesia value and the desired depth of anesthesia value. However, if the difference between the measured and desired end tidal concentration is less than the threshold at step <NUM>, meaning that the measured and desired end tidal concentrations are within a predefined threshold range of one another, then steps may be taken to adjust or recalculate the desired end tidal concentration in order to bring the depth of anesthesia for the patient to the desired depth.

A new desired end tidal concentration is determined at step <NUM> based on the difference between the measured and desired depth of anesthesia values. A change in the amount of vaporized agent is then determined at step <NUM> based on the new desired end tidal concentration. The vaporizer unit <NUM> is then controlled accordingly to deliver the amount of vaporized agent.

As used herein, the terms controller or module may refer to, be part of, or include an application-specific integrated circuit (ASIC), an electronic circuit, a combinational logic circuit, a field programmable gate array (FPGA), a processor (shared, dedicated, or group) that executes code, or other suitable components that provide the described functionality, or a combination of some or all of the above, such as in a system-on-chip. The terms controller or module may include memory (shared, dedicated, or group) that stores code executed by the processor. The term code, as used herein, may include software, firmware, and/or microcode, and may refer to programs, routines, functions, classes, and/or objects. The term shared, as used above, means that some or all code from multiple modules may be executed using a single (shared) processor. In addition, some or all code to be executed by multiple different processors may be stored by a single (shared) memory. The term group, as used above, means that some or all code comprising part of a single controller or module may be executed using a group of processors. Likewise, some or all code comprising a single controller or module may be stored using a group of memories.

Claim 1:
An electronic vaporizer (<NUM>) system comprising:
an anesthetic sump (<NUM>) containing anesthetic agent;
a vaporizer unit that vaporizes the anesthetic agent from the sump and delivers the vaporized agent to a patient breathing (<NUM>) circuit;
a gas sensor (<NUM>) configured to measure end tidal concentration of the anesthetic agent in exhalation gases from a patient;
a control system (<NUM>) configured to:
receive the measured end tidal concentration of the anesthetic agent;
compare the measured end tidal concentration to a desired end tidal concentration to be maintained for the patient; and
automatically control the vaporizer unit to deliver an amount of vaporized agent to the patient breathing circuit based on the comparison;
wherein the control system is further configured to:
receive one or more concentration routines providing end tidal concentration values over time; and
automatically adjust the desired end tidal concentration according to the concentration routine