Patent Description:
During some medical procedures, such as surgical procedures, a patient may be placed under general anesthesia by administrating an anesthetic agent. In some examples, the anesthetic agent may be a volatile anesthetic agent that is administered to the patient via an anesthetic vaporizer. For example, the anesthetic vaporizer may induce and control vaporization of the volatile anesthetic agent from a liquid form. A carrier gas (e.g., a mixture of oxygen and fresh air) may flow into the vaporizer and blend (e.g., mix and converge) with the anesthetic agent vapors before flowing to the patient, where they may be introduced via inhalation, for example.

Conventional anesthetic vaporizers include a sump for storing the liquid anesthetic agent before it is vaporized and delivered to the patient for inhalation. An operator (e.g., an anesthesiologist or other clinician) may monitor a level of liquid anesthetic agent in the sump, both before use and during use, to ensure sufficient anesthetic agent is available for delivery to the patient during the medical procedure.

<CIT> is directed to a device for identifying anaesthetics in an anaesthetic system. The device identifies anaesthetics by determining a parameter related to a physical property, such as density, of liquid anaesthetics. A floating body can be immersed in the anaesthetic fluid. The floating body then sinks to a depth which depends on the fluid's density. The identity of the anaesthetic can then be read off a measurement stick arranged on the floating body.

In one embodiment, a system for a level sensor for an anesthetic vaporizer includes a measurement tube including a float positioned therein, a bottom portion of the measurement tube coupled to a cap having a central opening, a retaining bracket coupled to a top portion of the measurement tube, an optical sensor housed within the retaining bracket, the optical sensor including a light source positioned to emit light toward an interior of the measurement tube and a light detector positioned to receive light from the interior of the measurement tube, and an optical window housed within the retaining bracket and coupled between the optical sensor and the interior of the measurement tube. In this way, the level sensor may provide anesthetic agent level measurements with increased accuracy.

It should be understood that the brief description above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.

The present disclosure will be better understood from reading the following description of non-limiting embodiments, with reference to the attached drawings, wherein below:.

The following description relates to various embodiments for measuring and monitoring a level of liquid anesthetic agent in an anesthetic vaporizer, which may be included in an anesthesia machine. Currently available anesthetic agent level sensors, such as capacitive, acoustic/ultrasonic, and differential hydrostatic level sensors, may be affected by characteristics of the liquid anesthetic agent. For example, liquid anesthetic agents are halogenated solvents that may aggressively react with certain materials and/or deposit residues, such as a film composed of butylated hydroxytoluene (BHT), over time. As one example, changes to dielectric properties of the liquid anesthetic agent caused by BHT deposition over time may affect measurements made by capacitive level sensors. As another example, acoustic/ultrasonic level sensors may be impacted by changes in humidity and a temperature of the liquid anesthetic agent. As still another example, differential hydrostatic level sensors may be incompatible with the reactive anesthetic agents. As a result, the above-mentioned sensors may be unable to accurately measure anesthetic agent level, and therefore volume, across time and conditions.

Thus, according to embodiments disclosed herein, a level sensor is provided that is not affected by changes in in the characteristics of the liquid anesthetic agent. In the embodiments disclosed herein, the level sensor is coupled in a sump storing liquid anesthetic agent and includes a measurement tube and a float positioned therein. According to embodiments disclosed herein, the float vertically moves within the measurement tube and sits at a surface of the liquid anesthetic agent. In the embodiments disclosed herein, the level sensor includes an optical sensor including a light source positioned to emit light toward the float within the measurement tube and a light detector positioned to receive light reflected by the float. Further, the optical sensor may be coupled to an electronic controller, which may receive a signal output from the optical sensor corresponding to a distance between the float and the optical sensor, and the controller may use the signal output to determine a volume of liquid anesthetic agent remaining in the sump as well as a time-to-empty. In some embodiments, the controller may output a refill alert responsive to the time-to-empty decreasing below a threshold duration.

The embodiments disclosed herein may provide several advantages. For example, the optical sensor may measure a physical distance between the float and the sensor, which is not sensitive to physical characteristics of the liquid anesthetic agent, increasing an accuracy of the measurements made by the optical sensor. Further, the physical distance reproducibly relates to a calculable volume of the liquid anesthetic agent, enabling higher accuracy volume calculation. As another example, the embodiments disclosed herein provide a level sensor with a small form-factor that is agent compatible. Further, by determining the time-to-empty and outputting the refill alert, it may be ensured that sufficient anesthetic agent is available for delivery to a patient during a medical procedure without an operator of the anesthetic vaporizer having to closely monitor the liquid level, freeing the operator to focus on patient monitoring, for example.

<FIG> schematically shows an exemplary embodiment of an anesthesia machine. <FIG> shows an exemplary embodiment of an anesthetic vaporizer that may be included in the anesthesia machine of <FIG>. <FIG> shows a sectional view of an exemplary embodiment of a level sensor that may be coupled in a sump of the anesthetic vaporizer of <FIG>. The level sensor may include at least one light source and at least one light detector, as shown in <FIG>, and may measure a distance from the level sensor to a float on a surface of liquid anesthetic agent based on light reflections by the float, as diagrammed in <FIG>. <FIG> depicts an example graph of how the measured distance may change over time as the sump is emptied, and <FIG> shows an example graph of a relationship between the measured distance and a volume of liquid anesthetic agent in the sump. <FIG> shows an example timeline showing how a level of the float, and a corresponding distance measured by the level sensor, changes as the level (and volume) of liquid anesthetic agent in the sump changes. A controller may track the volume of liquid anesthetic agent in the sump during use and alert an operator to refill the sump when a remaining operational time is low, such as according to the example method of <FIG>. Likewise, depending on a current fresh gas flow rate and output agent concentration, the controller may calculate and display an instantaneous "time-to-empty".

<FIG> schematically shows an example anesthesia machine <NUM>. Anesthesia machine <NUM> includes a frame (or housing) <NUM>. In some embodiments, frame <NUM> may be supported by casters, where the movement of the casters may be controlled (e.g., stopped) by one or more locks. In some examples, the frame <NUM> may be formed of a plastic material (e.g., polypropylene). In other examples, the frame <NUM> may be formed of a different type of material (e.g., metal, such as steel).

Anesthesia machine <NUM> also includes an anesthesia display device <NUM>, a patient monitoring display device <NUM>, a respiratory gas module <NUM>, one or more patient monitoring modules, such as a patient monitoring module <NUM>, a ventilator <NUM> (explained in more detail below), an anesthetic vaporizer <NUM>, and an anesthetic agent storage bay <NUM>. Anesthesia machine <NUM> may further include a main power indicator <NUM>, a system activation switch <NUM> (which, in one example, permits gas flow when activated), an oxygen flush button <NUM>, and an oxygen control <NUM>. An example embodiment of anesthetic vaporizer <NUM> will be described below with respect to <FIG>. Anesthetic vaporizer <NUM> may vaporize the anesthetic agent and combine the vaporized anesthetic agent with one or more medical grade gases (e.g., oxygen, air, nitrous oxide, or combinations thereof), which may then be delivered to a patient.

Anesthesia machine <NUM> may additionally include an integrated suction, an auxiliary oxygen flow control, and various other components for providing and/or controlling a flow of the one or more medical grade gases to the patient. For example, anesthesia machine <NUM> includes one or more pipeline connections <NUM> to facilitate coupling of the anesthesia machine to pipeline gas sources. Additionally, anesthesia machine <NUM> includes a cylinder yoke <NUM>, via which one or more gas-holding cylinders <NUM> may be coupled to the anesthesia machine. Thus, through the pipeline connection and/or cylinder connections, gas may be provided to the anesthesia machine, where the gas may include (but is not limited to) medical air, oxygen, nitrogen, and nitrous oxide. The gas that enters the anesthesia machine may mix with the vaporized anesthetic agent at the anesthetic vaporizer <NUM>, as described above, before being supplied to a patient via the ventilator <NUM>. The anesthesia machine may also include a serial port, a collection bottle connection, a cylinder wrench storage area, and an anesthesia gas scavenging system.

The ventilator <NUM> may include an expiratory check valve at an expiratory port <NUM>, an expiratory flow sensor at the expiratory port <NUM>, an inspiratory check valve at an inspiratory port <NUM>, an inspiratory flow sensor at the inspiratory port <NUM>, an absorber canister, a manual bag port, a ventilator release, an adjustable pressure-limiting valve, a bag/vent switch, and a bellows assembly. When a patient breathing circuit is coupled to the ventilator <NUM>, breathing gases (e.g., air, oxygen, and/or nitrous oxide mixed with vaporized anesthetic agent) exit the anesthesia machine from the inspiratory port <NUM> and travel to the patient. Expiratory gases from the patient re-enter the anesthesia machine via the expiratory port <NUM>, where carbon dioxide may be removed from the expiratory gases via the absorber canister.

During operation of the anesthetic vaporizer <NUM>, an operator (e.g., an anesthesiologist) may adjust an amount of vaporized anesthetic agent that is supplied to the patient by adjusting a flow rate of gases from the gas source(s) (e.g., the pipeline gas supply) to the vaporizer. The flow rate of the gases from the gas source to the vaporizer may be adjusted by the operator via adjustment of one or more flow adjustment devices. For example, the flow adjustment devices may include analog and/or digital adjustment dials and/or other user input devices configured to actuate one or more flow control valves of anesthesia machine <NUM>. In some embodiments, a first flow control valve may be positioned between the gas source(s) and the anesthetic vaporizer <NUM> and may be actuatable via the flow adjustment devices to a fully opened position, a fully closed position, and a plurality of positions between the fully opened position and the fully closed position.

Anesthesia machine <NUM> may additionally include one or more valves configured to bypass gases from the gas source(s) around the anesthetic vaporizer <NUM>. The valves may enable a first portion of gases to flow directly from the gas source to the inspiratory port <NUM> and a second portion of gases to flow from the gas source through the anesthetic vaporizer <NUM> to mix with the vaporized anesthetic agents prior to flowing to the inspiratory port <NUM>. By adjusting a ratio of the first portion of gases relative to the second portion of gases, the operator may control a concentration of vaporized anesthetic agent administered to the patient via the inspiratory port <NUM>.

Further, the adjustments described above may be facilitated at least in part based on output from the respiratory gas module <NUM>. The respiratory gas module <NUM> may be configured to measure various parameters of the gases exiting the vaporizer and/or being provided to the patient. For example, the respiratory gas module <NUM> may measure the concentrations of carbon dioxide, nitrous oxide, and the anesthetic agent provided to the patient. Further, the respiratory gas module <NUM> may measure respiration rate, minimum alveolar concentration, patient oxygen, and/or other parameters. The output from the respiratory gas module <NUM> may be displayed via a graphical user interface on a display device (e.g., the anesthesia display device <NUM> and/or the patient monitoring display device <NUM>) and/or used by a controller to provide closed-loop feedback control of the amount of anesthesia provided to the patient.

The ventilator <NUM> may optionally be coupled to a breathing circuit (not shown) including a plurality of tubes (e.g., gas passages) <NUM>. The breathing circuit may be coupled between an airway of a patient (e.g., via a breathing mask positioned to enclose the mouth and/or nose of the patient or a tracheal intubation tube) and the inspiratory port <NUM>. Gases (e.g., the one or more medical gases, or a mixture of the one or more medical gases and vaporized anesthetic agent from the anesthetic vaporizer <NUM>) may flow from the inspiratory port <NUM>, through the breathing circuit, and into the airway of the patient, where the gases are absorbed by the lungs of the patient. By adjusting the concentration of vaporized anesthetic agent in the gases as described above, the operator may adjust a degree to which the patient is anesthetized.

During conditions in which the breathing circuit is coupled to the airway, the anesthetic agent and/or fresh gas (without the anesthetic agent) may flow into the airway of the patient (e.g., through inhalation) via the inspiratory port <NUM> and the inspiratory check valve. As an example, the inspiratory check valve may open automatically (e.g., without input or adjustment by the operator) in response to inhalation by the patient and may close automatically in response to exhalation by the patient. Similarly, the expiratory check valve may open automatically in response to exhalation by the patient and may close automatically in response to inhalation by the patient.

In some embodiments, the operator may additionally or alternatively control one or more operating parameters of the anesthesia machine <NUM> via an electronic controller <NUM> of the anesthesia machine <NUM>. Controller <NUM> includes a processor operatively connected to a memory. The memory may be a non-transitory computer-readable medium and may be configured to store computer executable code (e.g., instructions) to be processed by the processor in order to execute one or more routines, such as those described herein. The memory may also be configured to store data received by the processor. Controller <NUM> may be communicatively coupled (e.g., via wired or wireless connections) to one or more external or remote computing devices, such as a hospital computing system, and may be configured to send and receive various information, such as electronic medical record information, procedure information, and so forth. Controller <NUM> may also be electronically coupled to various other components of the anesthesia machine <NUM>, such as the anesthetic vaporizer <NUM>, the ventilator <NUM>, the respiratory gas module <NUM>, the anesthesia display device <NUM>, and the patient monitoring display device <NUM>.

The controller <NUM> receives signals from the various sensors of the anesthesia machine <NUM> and employs the various actuators of the anesthesia machine <NUM> to adjust operation of the anesthesia machine <NUM> based on the received signals and instructions stored on the memory of the controller. For example, the flow of gases to the inspiratory port <NUM> may be controlled via an input device (e.g., keyboard, touchscreen, etc.) coupled to the electronic controller of the anesthesia machine <NUM>. The controller <NUM> may display operating parameters of the anesthesia machine <NUM> via the anesthesia display device <NUM> and/or the patient monitoring display device <NUM>. The controller may receive signals (e.g., electrical signals) via the input device and may adjust operating parameters of the anesthesia machine <NUM> in response (e.g., responsive) to the received signals.

As one example, the operator may input a desired concentration of the anesthetic agent to be delivered to the patient. A corresponding valve position of one or more valves of the anesthesia machine (e.g., a position of one or more bypass valves, as described above) may be empirically determined and stored in a predetermined lookup table or function in a memory of the controller. For example, the controller may receive the desired concentration of the anesthetic agent via the input device and may determine an amount of opening of the one or more valves corresponding to the desired concentration of the anesthetic agent based on the lookup table, with the input being the concentration of the anesthetic agent and the output being the valve position of the one or more valves. The controller may transmit an electrical signal to an actuator of the one or more valves in order to adjust each of the one or more valves to the corresponding output valve position. In some examples, the controller may compare the desired flow rate of gases to a measured flow rate of gases, such as measured by the inspiratory flow sensor, for example.

Controller <NUM> is shown in <FIG> for illustrative purposes, and it is to be understood that controller <NUM> may be located in various locations within, around, and/or remote from anesthesia machine <NUM>. As an example, controller <NUM> may include multiple devices/modules that may be distributed throughout anesthesia machine <NUM>. As such, controller <NUM> may include a plurality of controllers at various locations within anesthesia machine <NUM>. As another example, additionally or alternatively, controller <NUM> may include one or more devices/modules that are external to anesthesia machine <NUM>, located proximate to (e.g., in a same room) or remote from (e.g., a remote server) anesthesia machine <NUM>. In each example, the multiple devices/modules may be communicatively coupled through wired and/or wireless connections.

Anesthetic vaporizers, such as anesthetic vaporizer <NUM> shown in <FIG>, may employ various methods to vaporize a liquid anesthetic agent. For example, the anesthetic vaporizer may use a flow-over method (in which a carrier gas flows over a top surface of a volatile liquid anesthetic agent), a bubble-through method (in which the carrier gas is bubbled up through the liquid anesthetic agent), or a gas/vapor blender (in which heat is used to vaporize the liquid anesthetic agent, and the vapors are injected into a fresh gas flow). Regardless of the vaporization method, in some embodiments, the anesthetic vaporizer <NUM> may include a sump for storing the liquid anesthetic agent before it is delivered to a vaporizing chamber.

<FIG> shows an exemplary embodiment of an anesthetic vaporizer <NUM>, which may be included in an anesthesia machine (e.g., anesthesia machine <NUM> shown in <FIG>). As one example, anesthetic vaporizer <NUM> may be anesthetic vaporizer <NUM> of <FIG>. In the embodiment shown in <FIG>, anesthetic vaporizer <NUM> is a bubble-through anesthetic vaporizer, including a vaporizing chamber <NUM> defined by a housing <NUM>. However, in other embodiments, anesthetic vaporizer <NUM> may be another type of anesthetic vaporizer (e.g., draw over, injector-based, wick-based, etc.) for use with a volatile liquid anesthetic agent that includes a controller and level sensing technology.

A lower portion of vaporizing chamber <NUM> is shown holding a liquid anesthetic agent <NUM> that is supplied from a sump <NUM> via a conduit <NUM> and a pump <NUM>. The liquid anesthetic agent <NUM> may be isoflurane, sevoflurane, or another liquid anesthetic agent of similar volatility, for example, that is stored in sump <NUM>. Pump <NUM> may be a positive displacement pump, such as a reciprocating positive displacement pump, for example. Pump <NUM> may be selectively operated to deliver liquid anesthetic agent <NUM> from sump <NUM> to vaporizing chamber <NUM> in response to a command signal from a controller <NUM>, as will be further described below. Controller <NUM> may be an electronic controller including a processor operatively connected to a memory <NUM>. Controller <NUM> may be included in (e.g., a part of) or communicatively coupled to controller <NUM> shown in <FIG>, for example.

Sump <NUM> may be refilled via a fill cap <NUM> and a filler port (e.g., neck) <NUM> having an inlet filler port valve <NUM> positioned therein. Together, fill cap <NUM>, filler port <NUM>, and inlet filler port valve <NUM> may be included in a fill assembly. For example, an operator of anesthetic vaporizer <NUM> may remove fill cap <NUM> to refill sump <NUM> with additional liquid anesthetic agent <NUM> (e.g., from a refill bottle) via filler port <NUM> and inlet filler port valve <NUM> and then replace fill cap <NUM> to seal sump <NUM>. Fill cap <NUM> may be a screw cap, for example. In some embodiments, inlet filler port valve <NUM> may be a mechanically actuated spring-loaded valve that opens when the refill bottle is attached to filler port <NUM> to enable liquid anesthetic agent <NUM> to flow from the refill bottle to the interior of sump <NUM> and closes when the refill bottle is not attached to filler port <NUM>. Additionally or alternatively, in some embodiments, inlet filler port valve <NUM> may be an electronically actuated valve that may be adjusted in response to a control signal received from controller <NUM>, as will be further described below. Thus, in some embodiments, inlet filler port valve <NUM> may be both mechanically and electronically actuated. Thus, sump <NUM> may be a sealed system when fill cap <NUM> is in place.

Conduit <NUM> may further include a shut-off valve <NUM> coupled between pump <NUM> and vaporizing chamber <NUM>. For example, shut-off valve <NUM> may be an on-off valve, wherein shut-off valve <NUM> is actuated to an open (e.g., fully open) position that allows liquid anesthetic agent <NUM> to flow between and pump <NUM> and vaporizing chamber <NUM> or a closed (e.g., fully closed) position that prevents (e.g., blocks) the flow of liquid anesthetic agent <NUM> between pump <NUM> and vaporizing chamber <NUM>. Shut-off valve <NUM> may be actuated between the open and closed positions in response to a command signal from controller <NUM>, for example. A liquid return line <NUM> may be coupled to conduit <NUM> between shut-off valve <NUM> and pump <NUM> to reduce pressure build up between shut-off valve <NUM> and pump <NUM>, such as when shut-off valve <NUM> is closed. For example, excess liquid anesthetic agent <NUM> provided by pump <NUM> may be returned to sump <NUM> via liquid return line <NUM>. Further, liquid return line <NUM> may include a restriction <NUM>, such as an orifice, to control flow through liquid return line <NUM> such that liquid anesthetic agent <NUM> preferentially flows through shut-off valve <NUM> instead of restriction <NUM> when shut-off valve <NUM> is open.

Controller <NUM> may selectively activate pump <NUM> to provide liquid anesthetic agent <NUM> from sump <NUM> to vaporizing chamber <NUM>. In one embodiment, controller <NUM> may adjust operation of pump <NUM> responsive to a measurement received from a level sensor <NUM>. For example, level sensor <NUM> may be any type of liquid level sensor, such as an optical, ultrasonic, capacitive, float, or pressure-based liquid level sensor positioned to measure a level of liquid anesthetic agent <NUM> in vaporizing chamber <NUM>. As one example, controller <NUM> may be configured to maintain the level of liquid anesthetic agent at a target level or within a target range in order to prevent both underfilling and overfilling of vaporizing chamber <NUM>.

In some embodiments, pump <NUM> may include a positive displacement stepper motor, where each positive displacement step of the pump is equivalent to a specified volume of liquid anesthetic agent <NUM>. In this manner, the pump can be used to precisely fill the vaporizing chamber <NUM> and prevent overfill by recording the number of pump steps delivered. This approach may also be used to record a volume of anesthetic agent delivered to vaporizing chamber <NUM>, which may be valuable for vaporizer run-time/maintenance analysis (service metrics), liquid leak detection, precise determination of an amount of liquid anesthetic remaining and available for delivery, vaporization efficiency calculations, etc..

Anesthetic vaporizer <NUM> includes an additional level sensor <NUM> positioned to measure a level of liquid anesthetic agent <NUM> in sump <NUM>. In the embodiment shown in <FIG>, level sensor <NUM> includes an optical time-of-flight (ToF) proximity sensor, components of which will be detailed below with respect to <FIG>. Level sensor <NUM> serves as a continuous liquid level sensor that is not affected by changes in operating conditions (e.g., temperature and humidity) or changes in liquid anesthetic agent <NUM> itself (e.g., dielectric constant). As will be further described below with particular respect to <FIG>, output from level sensor <NUM> may be used to determine a volume (e.g., amount) of liquid anesthetic agent <NUM> remaining in sump <NUM> as well as a duration of time remaining until refilling of sump <NUM> is indicated. As shown in the embodiment of <FIG>, level sensor <NUM> may be coupled to a top exterior surface of sump <NUM> and extend into an interior of sump <NUM>. For example, an elongated portion of level sensor <NUM> may extend through an opening in a housing of sump <NUM>, while the external portion of level sensor <NUM> may form a gas-tight seal with sump <NUM>. This configuration may enable level sensor <NUM> to perform top-down measurements through a vapor space above a surface of liquid anesthetic agent <NUM>, for example. Further, in the exemplary embodiment of anesthetic vaporizer <NUM>, level sensor <NUM> does not touch a bottom interior surface of sump <NUM>, although a distance between the bottom-most surface of level sensor <NUM> and the bottom interior surface of sump <NUM> may vary. As will be elaborated herein, the distance between the bottom-most surface of level sensor <NUM> and the bottom interior surface of sump <NUM> results in a volume of liquid anesthetic agent <NUM> that is not measured by level sensor <NUM> as an additional reserve to help prevent complete emptying of sump <NUM>. Further, controller <NUM> may track the level (or volume) of liquid anesthetic agent <NUM> in sump <NUM> during refilling via measurements received from level sensor <NUM>. In embodiments where inlet filler port valve <NUM> is electronically actuated, controller <NUM> may actuate inlet filler port valve <NUM> closed responsive to the measured level (or volume) reaching a maximum level (or volume) to prevent inadvertent overfilling/overflowing of sump <NUM>.

An upper portion of vaporizing chamber <NUM> (e.g., above a surface of liquid anesthetic agent <NUM>) holds vapor, which may be a mixture of vaporized anesthetic agent and a carrier gas from a fresh gas flow. The fresh gas flow, and thus the carrier gas, may include one or more medical grade gases, such as oxygen, air, nitrous oxide, and combinations thereof. The fresh gas flow may be provided via one or more gas pipelines (e.g., via pipeline connections <NUM> shown in <FIG>) and/or one or more gas-holding cylinders (e.g., gas-holding cylinder <NUM> of <FIG>). As shown in <FIG>, the fresh gas flow may enter anesthetic vaporizer <NUM> via a first gas passage <NUM>. A first mass flow sensor <NUM> may be coupled to first gas passage <NUM> to measure a flow rate of the fresh gas flow entering anesthetic vaporizer <NUM>. For example, first mass flow sensor <NUM> may be an ultrasonic flow meter or a calorimetric (thermal) mass flow meter.

In the exemplary embodiment of <FIG>, a second gas passage <NUM> branches off from first gas passage <NUM> downstream of first mass flow sensor <NUM> to provide carrier gas to vaporizing chamber <NUM>. As used herein, "carrier gas" refers to a portion of the fresh gas flow that flows to vaporizing chamber <NUM>, whereas "bypass gas" refers to a remaining portion of the fresh gas flow that does not flow through vaporizing chamber <NUM>, as will be elaborated below. For example, second gas passage <NUM> may pass through an opening in housing <NUM>, which may include a gas-tight seal, to flow the carrier gas through a bottom of vaporizing chamber <NUM>. However, in other embodiments, anesthetic vaporizer <NUM> may not include second gas passage <NUM>, and carrier gas may not be delivered to vaporizing chamber <NUM>. For example, carrier gas may not be delivered to vaporizing chamber <NUM> when the liquid anesthetic agent <NUM> has a relatively low boiling point (e.g., at or around room temperature), such as when liquid anesthetic agent <NUM> is desflurane or another liquid anesthetic agent of similar volatility. Additionally or alternatively, second gas passage <NUM> may not be included in embodiments where a different type of anesthetic vaporizer architecture is used (e.g., a flow over type or a gas/vapor blender). Thus, the embodiment shown in <FIG> is provided by way of example.

The carrier gas delivered to vaporizing chamber <NUM> via second gas passage <NUM> flows through liquid anesthetic agent <NUM> to form a plurality of gas bubbles <NUM>. The plurality of gas bubbles <NUM> pass through liquid anesthetic agent <NUM>, becoming saturated with vaporized anesthetic agent, as they rise to the surface of the liquid. In some examples, a heating element may be coupled to or within vaporizing chamber <NUM> to increase a temperature of liquid anesthetic agent <NUM> and provide energy for vaporization (e.g., latent heat of vaporization).

Vapor, such as the carrier gas that is saturated with vaporized anesthetic agent, may flow out of vaporizing chamber <NUM> via a third gas passage <NUM> (e.g., a vapor delivery passage). For example, third gas passage <NUM> may pass through an opening at or near a top of housing <NUM> and form a junction with first gas passage <NUM> to fluidically couple the upper portion of vaporizing chamber <NUM> with first gas passage <NUM>. Upstream of the junction with third gas passage <NUM> and downstream of the junction with second gas passage <NUM>, first gas passage <NUM> carries the bypass gas portion of the fresh gas flow. The bypass gas does not pass through vaporizing chamber <NUM>. The bypass gas, containing no vaporized anesthetic agent, and the vapor from vaporizing chamber <NUM>, containing the carrier gas saturated with the vaporized anesthetic agent, mix at and downstream of the junction between first gas passage <NUM> and third gas passage <NUM>. The mixed gas may then be delivered to the patient via an inspiratory limb of a breathing circuit (e.g., via inspiratory port <NUM> described with respect to <FIG>). A second mass flow sensor <NUM> may be coupled to first gas passage <NUM> downstream of the junction with third gas passage <NUM> to measure a flow rate of the mixed gas exiting anesthetic vaporizer <NUM>. For example, second mass flow sensor <NUM> may be an ultrasonic flow meter or a calorimetric mass flow meter. In the case of an ultrasonic flow metering architecture, the output anesthetic agent concentration may be calculated by the difference in the measured time-of-flight between upstream ultrasonic flow sensor <NUM> and downstream ultrasonic flow sensor <NUM>.

In some embodiments, an independent concentration sensor <NUM> may be coupled to first gas passage <NUM> downstream of the junction with third gas passage <NUM>. Concentration sensor <NUM> may be any suitable sensor that is configured to measure a concentration of the anesthetic agent in the mixed gas. As one example, concentration sensor <NUM> may be an optical sensor that transmits light of a suitable wavelength (e.g., infrared) through the mixed gas and determines a concentration of the anesthetic agent based on an absorption of the light by the mixed gas. In other examples, the concentration sensor may be a carbon dioxide or oxygen sensor that measures the concentration of the anesthetic agent based on a displacement of the carbon dioxide or oxygen relative to a supplied concentration of carbon dioxide or oxygen in the fresh gas flow. Concentration sensor <NUM> may output a signal to controller <NUM> indicative of the measured concentration of the anesthetic agent (e.g., the concentration of the anesthetic agent vapor) in the mixed gas.

In addition to receiving signals output by level sensor <NUM>, level sensor <NUM>, concentration sensor <NUM>, first mass flow sensor <NUM>, and second mass flow sensor <NUM>, controller <NUM> may receive additional signals, including signals from one or more pressure and temperature sensors coupled in various locations throughout anesthetic vaporizer <NUM>. Controller <NUM> receives the signals from the various sensors of <FIG>, processes the input data, and employs the various actuators of <FIG> to adjust operation of anesthetic vaporizer <NUM> based on the received signals and instructions stored on a memory of the controller. For example, controller <NUM> may receive a measurement from level sensor <NUM> and determine a volume of liquid anesthetic agent <NUM> remaining in sump <NUM> based on the received measurement, as will be described below with respect to <FIG>. Additionally, the controller may output an alert to the operator via a human-machine interface (HMI) <NUM> that is operationally connected to the controller (e.g., via wired or wireless communication) responsive to a refill indication. Further, data may be input to controller <NUM> by the operator of anesthetic vaporizer <NUM> via HMI <NUM>. Thus, HMI <NUM> may include both a user input device and an output device. The user input device may include one or more of a mouse, a keyboard, a voice input device, a touch input device for receiving a gesture from the operator, a motion input device for detecting non-touch gestures and other motions by the operator, and other comparable input devices, as well as associated processing elements capable of receiving user input from the operator. The output device may include one or more of a display (e.g., anesthesia display device <NUM> and/or patient monitoring display device <NUM> of <FIG>) for providing visual alerts or text-based messages and a speaker for providing audible alerts or messages.

Turning now to <FIG>, a top perspective sectional view of level sensor <NUM> introduced in <FIG> is shown. Specifically, <FIG> shows an example configuration of level sensor <NUM> with relative positioning of the various components. If shown directly contacting each other, or directly coupled, then such elements may be referred to as directly contacting or directly coupled, respectively, at least in one embodiment. Similarly, elements shown contiguous or adjacent to one another may be contiguous or adjacent to each other, respectively, at least in one embodiment. As an example, components laying in face-sharing contact with each other may be referred to as in face-sharing contact. As another example, elements positioned apart from each other with only a space there-between and no other components may be referred to as such, in at least one example. As yet another example, elements shown above/below one another, at opposite sides to one another, or to the left/right of one another may be referred to as such, relative to one another. Further, as shown in the figures, a top-most element or point of element may be referred to as a "top" of the component and a bottom-most element or point of the element may be referred to as a "bottom" of the component, in at least one example. As used herein, top/bottom, upper/lower, above/below, may be relative to a vertical axis of the figures and used to describe positioning of elements of the figures relative to one another. As such, elements shown above other elements are positioned vertically above the other elements, in one example. As yet another example, shapes of the elements depicted within the figures may be referred to as having those shapes (e.g., such as being circular, straight, planar, curved, rounded, chamfered, angled, or the like). Further, elements shown intersecting one another may be referred to as intersecting elements or intersecting one another, in at least one example. Further still, an element shown within another element or shown outside of another element may be referred as such, in one example. Additionally, reference axes <NUM> are provided to describe the relative arrangement of components. Reference axes <NUM> includes the z-axis as the vertical axis, with the z-axis increasing from bottom to top (e.g., in the direction of the z-axis arrow). The top-most point has the greatest z-axis value and is also the top-most point with respect to gravity.

Level sensor <NUM> includes a measurement tube <NUM> with a float <NUM> positioned therein. Measurement tube <NUM> is shaped as an elongated hollow cylinder (e.g., extending in the vertical direction) having an inner diameter and an outer diameter, the outer diameter and the inner diameter separated by a wall thickness of the measurement tube. Float <NUM> is shaped as a sphere having an outer diameter that is smaller than the inner diameter of measurement tube <NUM>. Because the outer diameter of float <NUM> is less than the inner diameter of measurement tube <NUM>, float <NUM> may move freely along a length of measurement tube <NUM> (e.g., in the vertical z-direction) between an upper bound and a lower bound, as will be elaborated below. Further, the difference between the outer diameter of float <NUM> and the inner diameter of measurement tube <NUM> may be small, such that float <NUM> does not appreciably translate within measurement tube <NUM> in the (horizontal) x- and y-directions.

Measurement tube <NUM> and float <NUM> may each be comprised of one or more anesthetic agent-compatible (e.g., non-reactive) materials. Further, measurement tube <NUM>, particularly an inner surface of measurement tube <NUM>, may be comprised of a smooth, anti-reflective material. In one exemplary embodiment, measurement tube <NUM> is comprised of aluminum and includes black nickel plating on the inner surface. In another exemplary embodiment, measurement tube <NUM> is comprised of black extruded polypropylene. In still another embodiment, measurement tube <NUM> is comprised of opaque high density polyethylene. Float <NUM> may be comprised of a reflective material that is less dense than the anesthetic agents to be measured using level sensor <NUM>, enabling float <NUM> to sit on or at a surface of the liquid anesthetic agent. As one exemplary embodiment, float <NUM> may be comprised of while nylon. As another exemplary embodiment, float <NUM> may be comprised of while polypropylene. Further still, in some embodiments, reflectors and/or focusing lenses may be positioned on float <NUM>, such as attached to a top-most surface of float <NUM>.

Level sensor <NUM> further includes a cap <NUM> coupled to a bottom portion of measurement tube <NUM> (with respect to the page and with respect to gravity). In the embodiment shown in <FIG>, cap <NUM> interlocks with the bottom-most surface of measurement tube <NUM>, such as by a lip of cap <NUM> fitting into a groove on measurement tube <NUM>. Furthermore, cap <NUM> includes a circular central opening, the inner diameter of which is less than the outer diameter of float <NUM>. When the measurement tube is positioned in a sump, as will be elaborated below, the circular central opening may fluidically couple the interior of measurement tube <NUM> to the interior of the sump. That is, liquid anesthetic agent stored in the sump may enter and exit the bottom of measurement tube <NUM> via the central opening of cap <NUM>, enabling the liquid anesthetic agent to flow between the interior of measurement tube <NUM> and the rest of the sump (e.g., exterior to measurement tube <NUM>). Further, the central opening of cap <NUM> forms a constriction that prevents float <NUM> from exiting measurement tube <NUM>. Thus, float <NUM> may sit on or at the surface of the liquid anesthetic agent within measurement tube <NUM>, and the central opening of cap <NUM> may define the lower bound for the vertical movement of float <NUM>.

Measurement tube <NUM> may further include one or more vent holes <NUM> at or near a top of the measurement tube. Vent holes <NUM> may enable gas transfer (and therefore pressure equalization) between the interior of measurement tube <NUM> and the exterior of measurement tube <NUM> (e.g., an interior of the sump), preventing pressure build up or vacuum formation within the interior of measurement tube <NUM>. For example, as will be illustrated in <FIG>, the vertical position of float <NUM> changes as the level of liquid anesthetic agent changes. As the level (e.g., height) increases, the vertical position of float <NUM> increases (e.g., with respect to the z-axis), forcing gas molecules out of measurement tube <NUM> above float <NUM> and through vent holes <NUM> to the exterior of measurement tube <NUM>. That is, the volume above float <NUM> decreases as float <NUM> rises within measurement tube <NUM>, and so gas flows out of the interior of measurement tube <NUM> via vent holes <NUM> in order to prevent a pressure increase above float <NUM> that may hinder the vertical movement of float <NUM>. As the level decreases, the vertical position of float <NUM> decreases, drawing in gas molecules from the exterior of measurement tube <NUM> via vent holes <NUM>. That is, the volume above float <NUM> increases and float <NUM> descends within measurement tube <NUM>, and so gas flows into the interior of measurement tube <NUM> via vent holes <NUM> in order to prevent vacuum formation above float <NUM> and maintain the pressure above float <NUM> relatively constant. Overall, the pressure equalization helps ensure that when measurement tube <NUM> is at least partially submerged in the liquid anesthetic agent, the level (e.g., height) of the liquid anesthetic agent within measurement tube <NUM> is substantially equal to the level of the liquid anesthetic agent exterior to measurement tube <NUM> within the sump.

Level sensor <NUM> further includes a retaining bracket <NUM> coupled to a top portion of measurement tube <NUM>, such as positioned on the top-most surface of measurement tube <NUM>. As shown, retaining bracket <NUM> may include prongs that extend into the interior of measurement tube <NUM>, each prong having a lip that is shaped to engage with a corresponding opening in measurement tube <NUM>. The engagement of the prongs of retaining bracket <NUM> with measurement tube <NUM> fastens (e.g., removably couples) retaining bracket <NUM> to measurement tube <NUM>. The distance between the prongs across measurement tube <NUM> is less than the outer diameter of float <NUM>, and thus, the prongs of retaining bracket <NUM> form a constriction that defines the upper bound for the vertical movement of float <NUM> within measurement tube <NUM>.

Further, retaining bracket <NUM> may couple level sensor <NUM> to a sump (e.g., sump <NUM> shown in <FIG>), such as via a plurality of attachment screws <NUM>, and may form a gas-tight seal with the sump via a seal <NUM> that is coupled within retaining bracket <NUM>. For example, seal <NUM> may be an elastomeric seal, such as an o-ring, comprised of polytetrafluoroethylene (PTFE), neoprene, polyurethane, or the like that forms a gas-tight barrier between the sump and retaining bracket <NUM>. When level sensor <NUM> is coupled to the sump, an upper portion of retaining bracket <NUM> (e.g., the portion of retaining bracket <NUM> vertically above measurement tube <NUM>) may be external to the sump, whereas a lower portion of retaining bracket <NUM> (e.g., the portion of retaining bracket <NUM> within the interior of measurement tube <NUM>) may be located within the interior of the sump. For example, a top wall of a housing of the sump may include an opening that is shaped to receive measurement tube <NUM> so that measurement tube <NUM> extends into the interior of the sump. The opening in the sump housing may have an inner diameter that is larger than an outer diameter of measurement tube <NUM> so that measurement tube <NUM> can be vertically lowered therein, but small enough that horizontal movement of measurement tube <NUM> is restricted. Further, the opening in the sump housing may be smaller than a width of the upper portion of retaining bracket <NUM>.

Retaining bracket <NUM> additionally houses an optical window <NUM> and an optical sensor <NUM>, which may communicate with a controller (e.g., controller <NUM> of <FIG>) via wires <NUM>. In one embodiment, optical sensor <NUM> is a proximity sensor including at least one light emitter and at least one light detector, as will be further described below with respect to <FIG>. In other embodiments, optical sensor <NUM> may be another type of optical sensor that may be used to determine a distance to a measurement target, such as a structured light sensor or a laser Doppler vibrometer.

Optical sensor <NUM> is positioned to emit light in a top-down manner, toward the interior of measurement tube <NUM> (e.g., via the at least one light emitter), and receive light from the interior of measurement tube <NUM> (e.g., via the at least one light emitter). Optical window <NUM> is shown positioned vertically below optical sensor <NUM>, between optical sensor <NUM> and the interior of measurement tube <NUM>, and may be comprised of a transparent polymer (e.g., polyphenylsulfone), a crystalline material (e.g., sapphire glass), or another suitable material having high optical transmission in the emission range of the light source and high anesthetic agent compatibility. In some embodiments, optical window <NUM> may also serve as a focusing lens. Although optical window <NUM> is shown as a flat window in the example embodiment of <FIG>, it may be understood that optical window <NUM> may have various geometries or be configured as various lens types, such as a half-ball lens, a spherical lens, or a Fresnel lens.

Continuing to <FIG>, a surface view of optical sensor <NUM> introduced in <FIG> is shown. Specifically, <FIG> shows an exemplary embodiment of a potential configuration of optical sensor <NUM>, although other configurations are also possible, and includes reference axes <NUM> introduced in <FIG> to show a relative orientation of the views shown in <FIG>. For example, the view of <FIG> is in the x-y plane, with the z-axis going into the page. In the embodiment shown in <FIG>, optical sensor <NUM> includes a light source <NUM>, an ambient light detector <NUM>, and a light detector <NUM> within a common housing <NUM>. For example, light source <NUM> may emit light through a first, light emission aperture in housing <NUM>; ambient light detector <NUM> may receive and detect light present outside of housing <NUM> via a second, ambient light sensor aperture in housing <NUM>; and light detector <NUM> may receive and detect light emitted by light source <NUM> that has been reflected outside of housing <NUM> via a third, position return aperture in housing <NUM>. For example, the first aperture may create an illumination cone of a defined geometry for desired illumination properties, and the second and third apertures may create field of view cones of differing defined geometries for desired light collection properties. However, in other embodiments, ambient light detector <NUM> may not be included. Further, in some such embodiments, light detector <NUM> may include a filter, such as a bandpass filter, to filter out ambient light that has not been emitted by light source <NUM>.

Light source <NUM> may emit light of a defined wavelength or wavelength range when commanded (e.g., energized). For example, light source <NUM> may receive a command signal from controller <NUM> shown in <FIG> via wires <NUM> shown in <FIG>. The command signal may include information concerning an intensity of light to emit as well as a duty cycle of activation, for example. In some embodiments, light source <NUM> may emit light in the near infrared (NIR) or infrared (IR) range. For example, the longer wavelength NIR and IR light may undergo less scattering (compared with shorter wavelength visible light), enabling optical sensor <NUM> to detect longer distances. In some embodiments, light source <NUM> may emit light of a defined wavelength within a range between <NUM> and <NUM> nanometers (nm). As one exemplary embodiment, light source <NUM> may be configured to emit <NUM> light. As another exemplary embodiment, light source <NUM> may be configured to emit <NUM> light. Light source <NUM> may be a light emitting diode (LED) or a laser, for example.

Ambient light detector <NUM> may be configured to detect light from a broad wavelength range across the visible spectrum, for example, whereas light detector <NUM> may be configured to detect light from a narrow wavelength range that includes the wavelength of the light emitted by light source <NUM>. Therefore, light detector <NUM> may be specifically configured to detect light emitted by light source <NUM>, at least in some embodiments. Further, due to the spacing between light source <NUM> and light detector <NUM> and a relatively narrow illumination cone of light source <NUM> and a relatively narrow field of view cone of light detector <NUM>, light detector <NUM> may not directly detect light emitted by light source <NUM>. Instead, light detector <NUM> may detect light emitted by light source <NUM> that has been reflected, as will be further described below with respect to <FIG>. One or both of ambient light detector <NUM> and light detector <NUM> may be a variable-wavelength detector or a diode array, for example, and may each output a signal (e.g., in volts or amps) based on characteristics of the light received. For example, as the intensity of light received increases, the voltage output of ambient light detector <NUM> or light detector <NUM> may increase. The signals output by ambient light detector <NUM> and light detector <NUM> may be received by the controller, which may perform various data processing actions, as further described herein.

Continuing to <FIG>, a diagram <NUM> illustrates light emission and light detection by optical sensor <NUM> of level sensor <NUM>. As such, components previously introduced in <FIG> are numbered the same and may not be reintroduced. <FIG> includes reference axes <NUM> to highlight the relative arrangement of components with respect to the views shown in <FIG>. For example, the view of <FIG> is in the x-z plane, with the y-axis going into the page. Further, a simplified view of level sensor <NUM> is shown, without all of the components included, although it may be understood that such components may be present (e.g., measurement tube <NUM>).

Diagram <NUM> shows a partial side view of level sensor <NUM>, including optical sensor <NUM> positioned directly above and in face-sharing contact with optical window <NUM>. Optical window <NUM> covers light source <NUM>, ambient light detector <NUM>, and light detector <NUM>, the positions of which are schematically illustrated by dashed lines. Float <NUM> is partially shown a distance below (and not in direct contact with) optical window <NUM>.

In general, optical sensor <NUM> may be used to determine a travel time of a photon of light from an emitter (e.g., light source <NUM>) to a detector (e.g., either ambient light detector <NUM> or light detector <NUM>), which directly relates to a travel distance of the photon of light. As will be elaborated below, light emitted by light source <NUM> may be at least partially reflected by a target (e.g., float <NUM>) and directed back toward optical sensor <NUM>. A time delay between light emission by light source <NUM> and light detection by light detector <NUM> may be determined as a travel time of the photon of light. Because the speed of light is a known constant, the travel time multiplied by the speed of light is equivalent to the distance which the photon of light has traveled. As a non-limiting illustrative example, <NUM> of distance between optical sensor <NUM> and a reflector may result in a <NUM> psec travel time. Furthermore, the travel time is not affected by target reflectance, although high reflectivity may increase an amount (or intensity) of light that is reflected.

Light emitted by light source <NUM> is directed downward toward optical window <NUM>. Because optical window <NUM> is transparent, at least a portion of the light emitted by light source <NUM> passes through optical window <NUM>, while a portion may be reflected by the optical window (e.g., at a window/gas interface). Light source <NUM> may be activated to emit light in pulses, each pulse having a predetermined duration and with a predetermined interval between each pulse. For example, controller <NUM> (not shown in <FIG>) may command light source <NUM> at a predetermined duty cycle of activation according to instructions stored in memory. As an illustrative example, diagram <NUM> shows light paths for three different photons of light emitted by light source <NUM>, including light path <NUM>, light path <NUM>, and light path <NUM>.

Light in light path <NUM> is reflected by optical window <NUM> and received by ambient light detector <NUM>, which may also receive any ambient light present. Although measurement tube <NUM> (not shown in <FIG>) and its position within sump <NUM> (also not shown in <FIG>) may reduce ambient light exposure, ambient light detector <NUM> enables compensation for optical crosstalk and high ambient light conditions as well as light distortions made by optical window <NUM>. For example, the controller may receive a signal output from ambient light detector <NUM>, which may correspond to an intensity of all light (including light in light path <NUM> in addition to any ambient light), and use the signal output from ambient light detector <NUM> to adjust distance calculations made using measurements received from light detector <NUM> according to instructions stored in memory. As one example, because light source <NUM> may emit light in pulses and ambient light may remain relatively constant, the controller may determine an intensity of ambient light present based on a relatively constant signal component received from ambient light sensor <NUM>. Further, the controller may subtract the determined intensity of the ambient light from a signal output by light detector <NUM>. In a further embodiment, an optically opaque feature can be disposed within the optical window and between light source <NUM> and light detector <NUM>, thereby forming individual windows (e.g., one window for the emitter, one for the detector) to prevent and/or reduce optical crosstalk.

Light in light path <NUM> is reflected by optical window <NUM> (e.g., at the window/gas interface) and is received by light detector <NUM>. However, because optical window <NUM> is a fixed, known distance from light detector <NUM>, the controller may identify signals output by light detector <NUM> that correspond to reflections by optical window <NUM>. In contrast, float <NUM> is a variable distance from light source <NUM> and light detector <NUM>. Light in light path <NUM> is reflected by float <NUM> and received by light detector <NUM>. An elapsed time between light source <NUM> emitting light and light detector <NUM> receiving light reflected by float <NUM> (e.g., in light path <NUM>) changes based on the distance between float <NUM> and optical sensor <NUM>. For example, as the distance between float <NUM> and optical sensor <NUM> increases, the elapsed time increases, and as the distance between float <NUM> and optical sensor <NUM> decreases, the elapsed time decreases. The controller may receive a signal output by light detector <NUM> (e.g., via wires <NUM> shown in <FIG>) that directly corresponds to the distance between float <NUM>, and thus the surface of liquid anesthetic agent within the measurement tube, and optical sensor <NUM>. For example, the controller may include a look-up table, graph, or function stored in memory that relates the signal output of light detector <NUM> to a distance between float <NUM> and optical sensor <NUM> and takes into account sensor calibrations (to account for distortions by optical window <NUM>, a height of float <NUM> above the liquid level, etc.). In an alternative embodiment, the signal output by light detector <NUM> may correspond to the elapsed time, and the controller may calculate the distance to the surface of liquid anesthetic agent within measurement tube <NUM> based on the elapsed time and the speed of light, as mentioned above, according to instructions stored in memory, which may also take into account sensor calibrations.

<FIG> illustrates an example graph <NUM> of a relationship between a measurement sample number made by a level sensor (e.g., level sensor <NUM> described with respect to <FIG>) and a liquid surface distance from the level sensor. The measurement sample number is shown on the horizontal axis, with the measurement sample number increasing from left to right and increasing with time. For example, each measurement sample may refer to a discrete measurement made by the level sensor, such as one light pulse emission by light source <NUM> and the corresponding detection by light detector <NUM>, each introduced in <FIG>. The vertical axis shows the liquid surface distance from the level sensor, with the liquid surface distance increasing along the vertical axis from bottom to top. In the example of graph <NUM>, the liquid surface is a surface of liquid anesthetic agent within a sump of an anesthetic vaporizer, such as according to the system shown in <FIG>.

Graph <NUM> includes a plot <NUM> showing how the liquid surface distance from the sensor changes as the sump is emptied over a measurement period lasting from the lowest measurement sample number to the highest measurement sample number. Graph <NUM> also includes a first bound <NUM>, corresponding to a smallest liquid surface distance from the sensor that the sensor can measure, and a second bound <NUM>, corresponding to a largest surface distance from the sensor that the sensor can measure. For example, the first bound <NUM> and the second bound <NUM> may be defined by physical constraints of the level sensor, such as the constrictions described above with respect to <FIG> that define bounds for vertical moment of a measurement target (e.g., float <NUM>) within a measurement tube (e.g., measurement tube <NUM>).

The sump is completely full at the beginning of the measurement period (e.g., the first measurement sample). As a result, the float is the closest it can get to the level sensor, and so the liquid surface distance from the sensor measured by the level sensor (plot <NUM>) is equal to the first bound <NUM>. As the sump is drained over the measurement period, the measured liquid surface distance from the sensor (plot <NUM>) increases, corresponding to a decrease in the level (and volume) of liquid anesthetic agent in the sump. The measured liquid surface distance from the sensor (plot <NUM>) approaches the second bound <NUM> near the end of the measurement period and reaches the second bound <NUM> at the last measurement sample. For example, the float is the furthest it can get from the level sensor, and thus, even if the liquid level were to continue to decrease, the level sensor may not detect these changes.

Further, a controller (e.g., controller <NUM> of <FIG>) may use the measured liquid surface distance from the sensor to determine a liquid volume in the sump according to a pre-calibrated relationship stored in memory. Continuing to <FIG>, an example graph <NUM> shows a plot <NUM> of an inverse linear relationship between the measured liquid surface distance from the sensor and the liquid volume in the sump. Graph <NUM> includes the measured liquid surface distance from the sensor as the horizontal axis, with the distance increasing along the horizontal axis from left to right, and the liquid volume in the sump as the vertical axis, with the liquid volume increasing up the vertical axis from bottom to top.

Plot <NUM> shows that as the measured liquid surface distance from the sensor increases, the volume of the liquid anesthetic agent in the sump decreases. Further, plot <NUM> is bounded by a lower bound <NUM>, corresponding to a lowest volume that the sensor can measure, and an upper bound <NUM>, corresponding to a highest volume that the sensor can measure. For example, lower bound <NUM> may correspond to second bound <NUM> of <FIG>, representing a first, lower volume of liquid anesthetic agent in the sump when the float reaches its lowest possible position in the measurement tube. Upper bound <NUM> may correspond to first bound <NUM> of <FIG>, representing a second, higher volume of liquid anesthetic agent in the sump when the float reaches its highest possible position in the measurement tube. Both lower bound <NUM> and upper bound <NUM> may be pre-calibrated values that may change based on a size (e.g., capacity) and geometry of the sump.

In one embodiment, the controller may reference graph <NUM> to determine the liquid volume in the sump, such as by determining a corresponding liquid volume for a received measured liquid surface distance from the sensor using plot <NUM>. In another embodiment, the controller may additionally or alternatively refer to a look-up table of values that define plot <NUM>. For example, the controller may input the measured liquid surface distance from the sensor into the look-up table, which may output the corresponding liquid volume in the sump. In still another embodiment, the controller may additionally or alternatively determine the liquid volume in the sump as a function of the measured surface distance from the sensor. For example, the controller may input the measured liquid surface distance from the sensor into an equation that defines the relationship shown in plot <NUM>, which may output the corresponding liquid volume in the sump.

Next, <FIG> schematically shows an example timeline <NUM> illustrating usage of an optical ToF proximity sensor for determining an anesthetic agent level in an anesthetic vaporizer. The anesthetic vaporizer may be anesthetic vaporizer <NUM> introduced in <FIG>, including level sensor <NUM> coupled in sump <NUM>. As such, components of <FIG> that function the same as components previously introduced in <FIG> and <FIG> are numbered the same and may not be reintroduced. Further, some components of anesthetic vaporizer <NUM> and level sensor <NUM> are not shown in the example of timeline <NUM> for simplicity, although it may be understood that such components are present. Controller <NUM> (not shown in <FIG>) may execute one or more methods to determine a volume of the liquid anesthetic agent <NUM> within sump <NUM> based on data received from level sensor <NUM>, such as the example method described below with respect to <FIG>.

Timeline <NUM> shows a plurality of "snapshots," each representing an instantaneous depiction of an amount (e.g., volume) of liquid anesthetic agent <NUM> within sump <NUM> at the corresponding time, including a first snapshot <NUM> at a first time t1, a second snapshot <NUM> at a second time t2, a third snapshot <NUM> at a third time t3, and a fourth snapshot <NUM> at a fourth time t4. The first time is the earliest time and the fourth time is the latest time, as shown by a direction of a time axis <NUM>. In particular, each snapshot shows how float <NUM> vertically moves with a changing level of liquid anesthetic agent <NUM> within sump <NUM> (and therefore within measurement tube <NUM>) and the resulting changes in the distance to float <NUM> measured by optical sensor <NUM>.

First snapshot <NUM> shows float <NUM> at a first distance d1 from optical sensor <NUM>. Further, float <NUM> is between a minimum level <NUM> (e.g., corresponding to a maximum possible distance between optical sensor <NUM> and float <NUM>, such as corresponding to second bound <NUM> of <FIG>) and a maximum level <NUM> (e.g., corresponding to a minimum possible distance between optical sensor <NUM> and float <NUM>, such as corresponding to first bound <NUM> of <FIG>). For example, a top-most surface of float <NUM> cannot drop below the minimum level <NUM> due to a restriction at the bottom of measurement tube <NUM>. Similarly, due to a restriction near the top of measurement tube <NUM>, the top-most surface of float <NUM> cannot rise above the maximum level <NUM>, creating a "dead space" at the top of the tube. Thus, only liquid levels between the minimum level <NUM> and the maximum level <NUM> (e.g., greater than the minimum level <NUM> and less than the maximum level <NUM>) result in accurate liquid level measurements by optical sensor <NUM>. Because the first distance d1 is between the minimum level <NUM> and the maximum level <NUM>, the controller accurately calculates the volume of liquid anesthetic agent <NUM> as a first volume V1 based on the first distance measurement received from optical sensor <NUM>, such as by inputting d1 into one or more pre-calibrated look-up tables, equations, or graphs, such as graph <NUM> described above with respect to <FIG>.

Between time t1 and time t2, the anesthetic vaporizer is operated to deliver anesthetic agent to a patient. As shown in second snapshot <NUM>, a vertical height of the float <NUM> decreases with the vertical height of liquid anesthetic agent <NUM> within measurement tube <NUM> and external to measurement tube <NUM>. Float <NUM> has a second distance d2 from optical sensor <NUM>, which is greater than first distance d1 at time t1. The second distance d2 remains between the minimum level <NUM> and the maximum level <NUM>, and so the controller accurately calculates the volume of liquid anesthetic agent <NUM> as a second volume V2, which is less than V1, based on the second distance measurement received from optical sensor <NUM>.

The anesthetic vaporizer continues to be operated between time t2 and time t3. Third snapshot <NUM> shows float <NUM> having a third distance d3 from optical sensor <NUM>, which is greater than each of first distance d1 and second distance d2. Further, the level of liquid anesthetic agent <NUM> in sump <NUM> has decreased below minimum level <NUM>, and measurement tube <NUM> is no longer at least partially submerged within liquid anesthetic agent <NUM>. Therefore, the controller is unable to accurately calculate a third volume V3 based on the third distance measurement received from optical sensor <NUM>, but may recognize that float <NUM> has reached the minimum level <NUM> based on the measured third distance d3. In some embodiments, the controller may take an action, such as outputting an alert to refill the sump, responsive to measuring third distance d3.

Sump <NUM> is refilled between time t3 and time t4. As shown in fourth snapshot <NUM>, a vertical height of the float <NUM> increases due to the refilled liquid anesthetic agent <NUM>. Float <NUM> has a fourth distance d4 from optical sensor <NUM>, which is the smallest distance shown in timeline <NUM> and remains between the minimum level <NUM> and the maximum level <NUM>. The controller accurately calculates the volume of liquid anesthetic agent <NUM> as a fourth volume V4, which is the greatest volume shown in timeline <NUM>, based on the fourth distance measurement received from optical sensor <NUM>. In some embodiments, the controller may provide real-time filling information via a display of a human-machine interface (e.g., HMI <NUM> of <FIG>) to indicate the level of filling based on the signal received from optical sensor <NUM> during refilling. This feature can be used to prevent an unintended potential overfill/overflow of the liquid anesthetic by alerting a user and/or closing a valve which fluidically couples an inlet filler port to the sump. For example, the controller may output the real-time volume (or level) of liquid anesthetic agent <NUM>, as determined via level sensor <NUM>, via the HMI and may further output an overfill alert and/or actuate the inlet filler port valve closed responsive to the volume (or level) surpassing a maximum volume (or level).

Turning now to <FIG>, a high-level flow chart of an example method <NUM> for determining a volume of liquid anesthetic agent in an anesthetic vaporizer sump using a level sensor is shown. Method <NUM> may be executed by a controller, such as controller <NUM> of <FIG>, according to instructions stored in a memory of the controller (e.g., memory <NUM> of <FIG>) and in conjunction with one or more inputs, such as inputs received from an operator via a human-machine interface (e.g., HMI <NUM> of <FIG>) and one or more sensors (e.g., level sensor <NUM> introduced in <FIG>). Further, the controller may output information to the operator of the anesthesia machine via the human-machine interface. Although method <NUM> will be described with respect to anesthetic vaporizer <NUM> shown in <FIG>, it may be understood that method <NUM> may be applied to any anesthetic vaporizer configuration that includes an electronic controller and a level sensor that uses time-of-flight sensing.

A distance to a measurement target is measured via an optical sensor at <NUM>. The optical sensor is the proximity sensing component of the level sensor (e.g., optical sensor <NUM> introduced in <FIG>), and the measurement target may be a reflective float (e.g., float <NUM> introduced in <FIG>) positioned within a non-reflective measurement tube (e.g., measurement tube <NUM> introduced in <FIG>). Measuring the distance to the measurement target via the optical sensor may include operating a light source of the optical sensor (e.g., light source <NUM> shown in <FIG>) to emit pulses of light at a predetermined duty cycle of operation and measuring an elapsed time between the emission of each pulse and light detection by a light detector (e.g., light detector <NUM> shown in <FIG>). The optical sensor may output a signal to the controller corresponding to the distance and/or corresponding to the elapsed time, as elaborated above with respect to <FIG>.

An anesthetic agent volume in the sump is determined based on the measured distance at <NUM>. The controller may store a pre-calibrated relationship between the measured distance and the anesthetic agent volume in memory, such as stored as a graph, look-up table, or equation. Therefore, the controller may input the measured distance into the graph, look-up table, or equation, which may output the corresponding anesthetic agent volume that produces the measured distance. As mentioned above with respect to <FIG>, the pre-calibrated relationship may be specific to each sump configuration (e.g., volume capacity and/or geometry). As one example, smaller volume changes may result in larger distance changes between the optical sensor and the measurement target when the sump is narrower and taller compared to when the sump is wider and shorter for a same volume capacity.

A fresh gas flow rate and an output anesthetic agent concentration are received at <NUM>. For example, the controller may receive a measurement of a concentration of anesthetic agent output by the anesthetic vaporizer from a concentration sensor (e.g., concentration sensor <NUM> of <FIG>) and a fresh gas flow rate measurement indicative of the flow rate of the fresh gas into the anesthetic vaporizer from a mass flow sensor (e.g., first mass flow sensor <NUM>). Alternatively, the controller may receive an output anesthetic agent concentration setpoint and a fresh gas flow rate setpoint from the operator via the human-machine interface. For example, the controller may use the setpoints when measured values are unavailable.

A time-to-empty is calculated based on the determined anesthetic agent volume (e.g., as determined at <NUM>), the fresh gas flow rate, and the output anesthetic agent concentration at <NUM>. The time-to-empty refers to a remaining time duration until the volume liquid anesthetic agent in the sump is depleted. Additionally or alternatively, the time-to-empty refers to a remaining operational time of the anesthetic vaporizer using the current operating conditions. In one embodiment, the time-to-empty may correspond to the remaining time duration until the volume of liquid anesthetic reaches zero (e.g., the sump is completely empty). In another embodiment, the time-to-empty may correspond to the remaining time duration until the volume of liquid anesthetic reaches a non-zero volume, such as a lowest measureable volume by the level sensor.

In one embodiment, the controller may calculate the time-to-empty based on a running average the fresh gas flow rate (e.g., over a predetermined duration of anesthetic agent usage, such as a duration in a range from <NUM> to <NUM> minutes), a running average of the output anesthetic agent concentration (e.g., over the duration), and the determined anesthetic agent volume in the sump into one or more look-up tables, graphs, or equations. As one example, the controller may calculate the time-to-empty using the following equations:
<MAT>
<MAT>.

Equation <NUM> results in the term Saturated_Gas_Volume (in milliliters, mL), which corresponds to an amount of vaporized anesthetic agent produced at a given temperature (T) of the anesthetic agent for the type of anesthetic agent being used. The term SW is the specific weight of the anesthetic agent in g/mL, which is selected based on the type of anesthetic agent being used (e.g., <NUM>/mL for isoflurane, <NUM>/mL for sevoflurane, or <NUM>/mL for desflurane). For example, the controller may input the type of anesthetic agent into a look-up table, which may output the specific weight of the given type of anesthetic agent. The term GC is Avogadro's gas constant, which is a universal constant for all gases (e.g., independent of the type of anesthetic agent being used) that defines that at standard conditions for temperature and pressure, dry (e.g., STPD, corresponding to a temperature of <NUM> and a pressure of <NUM> atmosphere, without water vapor), one mole of any gas contains <NUM> × <NUM><NUM> molecules, which occupy a volume of <NUM>,<NUM>. The term MW is the molecular weight of the anesthetic agent being used in g/mol, which is selected based on the type of anesthetic agent being used (e.g., <NUM>/mol for isoflurane, <NUM>/mol for sevoflurane, or <NUM>/mol for desflurane). For example, the controller may input the type of anesthetic agent into a separate look-up table, which may output the molecular weight of the given type of anesthetic agent.

The Saturated_Gas_Volume calculated via Equation <NUM> may be used in Equation <NUM> to determine Time_to_Empty (in minutes), which corresponds to the duration of time remaining before the sump is emptied at the current anesthetic agent usage rate. In Equation <NUM>, the term Ave_FGF is the average fresh gas flow rate (in mL/min), the term Ave_Agent_Conc is the average output anesthetic agent concentration (in % volume), and the term Volume_in_Sump is the anesthetic agent volume determined via the optical sensor (e.g., at <NUM>).

It is determined if the time-to-empty is less than a threshold duration at <NUM>. The threshold duration may be a non-zero time duration corresponding to a remaining time of anesthetic agent usage below which refilling the sump is indicated. For example, the threshold duration may provide a time buffer to account for an anticipated amount of time it may take the operator to refill the sump, thereby reducing instances of the sump becoming completely empty (or reaching a non-zero minimum volume).

If the time-to-empty is not less than the threshold duration, method <NUM> proceeds to <NUM>, and the determined anesthetic agent volume and the calculated time-to-empty are output. For example, the controller may output the determined anesthetic agent volume (e.g., determined at <NUM>) and the calculated time-to-empty (e.g., calculated at <NUM>) via the human-machine interface, such as via one or more of a visual and an audible message. Method <NUM> may then return so that the anesthetic agent volume and the time-to-empty may be updated as new measurements are made by the optical sensor.

If the time-to-empty is less than the threshold duration, method <NUM> proceeds to <NUM>, and the determined anesthetic agent volume, the calculated time-to-empty, and a refill alert are output. For example, in addition to outputting the determined anesthetic agent volume and the calculated time-to-empty, as described above at <NUM>, the controller may communicate the refill alert via the human-machine interface. In one embodiment, the refill alert may include an audible alarm or message. In another embodiment, the refill alert may additionally or alternatively include a visual message. Method <NUM> may then return.

Claim 1:
A system for a level sensor for an anesthetic vaporizer, comprising:
a measurement tube (<NUM>) including a float (<NUM>) positioned therein, a bottom portion of the measurement tube coupled to a cap (<NUM>) having a central opening;
a retaining bracket (<NUM>) coupled to a top portion surface of the measurement tube;
an optical sensor (<NUM>) housed within the retaining bracket, the optical sensor including a light source positioned to emit light toward an interior of the measurement tube and a light detector positioned to receive light from the interior of the measurement tube; and
an optical window (<NUM>) housed within the retaining bracket and coupled between the optical sensor and the interior of the measurement tube.