Automated Bag Valve Mask

A patient ventilation system comprising a BVM that is operable in both a manual operating mode and an autonomous operating mode. In the manual operating mode the user operates the BVM manually. Sensors collect data from which performance metrics are calculated and displayed to the user. The displayed metrics (e.g., airway pressure, tidal volume delivered, ventilation rate, and gas concentrations) provide responders with performance feedback allowing them to correct inadequate ventilation. Once the user is satisfied with their performance, they can then enable automated ventilation to provide consistent ventilation to the patient. The controller recognizes the user's technique and with the press of a button, the control system of the DIVA mirrors the performance of the user without requiring separate manual entry of target breathing parameters.

TECHNICAL FIELD

The present disclosure relates generally to a bag valve mask (BVM) to deliver positive pressure ventilation to a patient having trouble breathing and, more particularly, to automate control of a BVM.

BACKGROUND

Artificial ventilation has been a medical practice for a long time, with some of the earliest reports in the mid-18th century. The earliest bag valve mask (BVM) was introduced in 1956 and nicknamed the “Ambu” (Artificial Manual Breathing Unit). A BVM is a medical device used to provide positive pressure ventilation to patients who are unable to breathe unassisted or need an influx of oxygen. The bag valve mask comprises a flexible air chamber or bag attached to a face mask via a shutter valve. When the BVM is properly applied to a patient's face and the bag is squeezed, air is forced through the valve and into the patient's lung. When the bag is released, air with depleted oxygen levels is drawn while also allowing the patient's lungs to deflate to the ambient environment, especially in single user scenarios.

Due to its popular usage in emergency settings, many innovations have been attempted and some have become a part of the BVM, such as antiviral filters and one-way exhalation valves. This has become increasingly prevalent with the arrival and subsequent effects of COVID-19. However, problems, complications, and shortcomings remain in traditional BVM designs that need to be addressed BVM users within emergency medical services (EMS) and clinical emergency medicine (EM) need a way to gauge tidal volume and internal lung pressure delivered in order to prevent patient injury. Additionally, BVM users within EMS and clinical EM need a way to reduce operator fatigue during extended operation.

SUMMARY

The present disclosure provides a patient ventilation system comprising a BVM that is operable in both a manual operating mode and an autonomous operating mode. In the manual operating mode the user operates the BVM manually. Sensors collect data from which performance metrics are calculated and displayed to the user. The displayed metrics (e.g., airway pressure, tidal volume delivered, ventilation rate, and gas concentrations) provide responders with performance feedback allowing them to correct inadequate ventilation. Once the user is satisfied with their performance, they can then enable automated ventilation to provide consistent ventilation to the patient. The controller recognizes the user's technique and with the press of a button, the control system of the DIVA mirrors the performance of the user.

Automated ventilation fulfills the role of one responder (squeezing the bag at an adequate respiratory rate) allowing a single provider to focus on ensuring leak-proof mask seal around the patient's nose and mouth. This, in combination with sensor feedback to ensure adequate ventilation, minimizes the physical and mental strain on responders and improves patient outcomes.

DETAILED DESCRIPTION

A common problem encountered by users of traditional BVMs is that traditional BVMs can often exceed the upper threshold of the appropriate volume of air delivery, which could easily put a patient in a critical condition by causing lung injuries or other related conditions. One reason why traditional BVMs fail to deliver an appropriate amount of air is because, although the simplicity of BVMs allows for rapid deployment and use, lack of tidal volume delivery measurements often forces the operator to rely on ambiguous metrics such as chest rise. Such metrics can be quite difficult to rely upon depending on the body mass index of the patient. Thus, one advantage of certain embodiments discussed herein is a BVM design that will protect patients from erroneous use of the BVM that may end up in critical injuries.

In traditional BVMs, mask seal around a patient's face is achieved using two hands gripping around the mask and pulling up the patient's chin. However, in an emergency setting, it is common for only one medical provider to operate a BVM. This can make achieving appropriate mask-seal difficult. Further, the operation of squeezing a BVM over long durations of time can cause operator physical and emotional strain. Thus, another advantage of one or more embodiments discussed herein is a BVM design that facilitates ease of operation, particularly over protracted periods of time.

In general, a BVM is used for 15-45 minutes in one setting until they can switch to another provider or connect to hospital-use ventilation systems. In such a scenario, the provider is not only using the BVM by squeezing the bag every 6 to 8 seconds while keeping a good airway and mask seal, but is also monitoring other vitals and maneuvering calls to hospitals and other tasks, possibly in a moving, noisy, and bumpy ambulance ride. The mental and physical task load of an Emergency Medical Technician (EMT) or Paramedic is greatly challenged, given that they may be the only hope to keep a patient alive. Thus, mask seal leakage, the inability to gauge tidal volume delivery, and user physical and emotional strain became a significant priority in the development of compatible solutions. Embodiments of the present disclosure address at least some of these problems while also mitigating the frequency and/or extent of lung injuries caused by misuse of BVM.

In particular, embodiments of the present disclosure include a BVM comprising a sensor-based patient feedback system to provide operators with performance metrics as well as semi- or fully automatic assistance in operating the BVM. One or more such embodiments advantageously solve the pain points described above by freeing at least one hand from constantly squeezing the bag of a traditional BVM. Consequently, a BVM user can use a freed hand to ensure better mask seal, and/or use other equipment to ensure safe delivery of oxygenated air.

FIG.1is a high level block diagram illustrating a patient ventilation system indicated generally by the numeral10. The patient ventilation system10comprises a BVM20, a mechanical actuator40, a control system60, and user interface (UI)80. The BVM20can be operated manually or automatically to provide positive pressure ventilation to a patient that is not breathing or that needs supplemental oxygen. The mechanical actuator40provides a mechanism for automating the compression and expansion of the BVM20as will be hereinafter described. The control system60serves two main functions: to give feedback to the user via the user interface80in a manual operating mode and to automate operation of the BVM20in an autonomous mode.

FIG.2schematically illustrates the BVM20and actuator40. The BVM20comprises a flexible self-inflating bag22, an air intake valve24, a patient valve26and face mask28. The flexible self-inflating bag22is made of a plastic material that re-expands after being manually collapsed. The self-inflating bag22may come in various sizes, e.g., 240 mL for infants, 500 mL for children, and 1600 mL for adults. The air intake valve24is disposed at one end of the self-inflating bag22and the patient valve25is disposed at the opposite end. The air intake valve24allows air or oxygen to enter the bag when the bag re-expands after being collapsed. The air intake valve24typically includes an oxygen inlet port (not shown) for connection to an oxygen source. The patient valve26is a one-way valve that directs the flow of air or oxygen from the self-inflating bag22to the face mask28when the flexible self-inflating bag22is collapsed while preventing exhaled gases from re-entering the flexible self-inflating bag22. The patient valve26includes an exhalation port, pressure limiting valve and adapter for connecting to the face mask28. The face mask28is designed to conform to the patient's face and provide a seal to prevent gases from escaping. During exhalation, gases are directed to the patient valve26and exit through the exhalation port in the patient valve26.

During use, the self-inflating bag22is manually or automatically collapsed to force air through the patient valve26and into the face mask28to provide positive pressure ventilation. When the pressure on the self-inflating bag22is released, the self-inflating bag22re-expands to draw air in through the air intake24. Gases exhaled by the patient exit through the exhalation port in the patient valve26.

Automation of the BVM20can be achieved by having a mechanism, referred to herein as an actuator40, to compress the self-inflating bag22of the BVM20. The actuator40can be independent of the self-inflating bag22, like an external air pump connected to the self-inflating bag22, or a mechanism that integrates with the self-inflating bag22. The actuator40can be driven by a servo motor and powered by an onboard rechargeable battery (not shown).

FIGS.2and3illustrate an exemplary actuator40for automating BVM operation. The actuator40comprises two main assemblies, an internal link mechanism42and a drive unit. The link mechanism42comprises a tube44that is inserted into the self-inflating bag22through the air intake valve24, two primary linkages46, two connecting linkages48, and a slide50. The two primary linkages46are pivotally attached at one end to the tube42and at the opposite end to the interior of the self-inflating bag22on diametrically opposed sides. The connecting linkages48are pivotally attached at one end to the slide50and at the opposite end to the primary linkages46. The slide50comprises a collar that slides axially along the length of the tube44. The slide50is connected by a drive rod52to the drive unit54. The drive unit54comprises a servomotor56and pinion gear58that reciprocates the drive rod52back and forth in the axial direction.

When the autonomous mode activated, the servomotor56turns in a first direction during an inhalation phase and reverses direction during an exhalation phase. In the inhalation phase, the servomotor56pulls the internal linkages46,48inward, collapsing the self-inflating bag22and forcing air out through the face mask28. In the exhalation phase, the servomotor56reverses direction allowing the self-inflating bag22to re-inflate. This process can be repeated, allowing for automated ventilation.

The actuator40fits within the dimensions of a typical BVM20, enabling complex automation and sensor feedback within a form factor that is both portable and familiar to users.

The control system60provides feedback to the user via the user interface80and automates operation of the BVM20in the autonomous mode. The control system60comprises a flow rate sensor62and a pressure sensor64providing feedback to a controller66, which generates control signals based on the feedback from the sensors62,64to control the servomotor58. The servomotor56and sensors62,64can be coupled to the controller66via a wired or wireless interface (e.g., BLUETOOTH)68. In some embodiments, the control system60may further include one or more gas concentration sensors located in the patient valve26to measure, for example, the oxygen concentration in the air provided to the patient and the carbon dioxide concentration in the exhaled air.

The flow rate sensor62and pressure sensor64are disposed in the air flow path between the self-inflating bag22and the face mask. For example, the flow rate sensor46and pressure sensor64can be disposed in the patient valve26. As air flow through the patient valve26from the self-inflating bag into the face mask28during the inhalation phase, the flow rate sensor62and pressure sensor64measure the flow rate and pressure respectively. Exhaled air passes through the same flow rate sensor62and pressure sensor64in the exhalation phase. The measurements made by the flow rate sensor62and pressure sensor64are input to the controller66and used to make adjustments to the drive signals for the actuator40.

The user interface80provides means to receive user input and to output information to the user for viewing. The user interface80can be coupled to the controller66via a wired or wireless interface (e.g., BLUETOOTH)70. The user interface80comprises one or more input devices82to set and/or adjust the operating parameters of the controller60, and a display84to display information for viewing by the user. The user interface could also provide audible or tactile feedback to the emergency responder in place of or in addition to visual feedback. The user interface80can be coupled to the controller66by a wired or wireless interface.

The user input devices82may comprise one or more push buttons, a keypad, pointing device (e.g., mouse or trackball), touch screen, voice control, or combination thereof. Display84may comprise an electronic display such as a light emitting diode (LED) display, liquid crystal display (LCD), or other common type of display. In some embodiments, the display may comprise a touch screen display that also serves as a user input device82. The main purpose of the display84is to display operating parameters or metrics (e.g., airway pressure, tidal volume delivered, and gas concentrations) to provide responders with performance feedback, allowing them to correct inadequate ventilation.

FIG.4illustrates the operating states, also referred to as operating modes, of the patient ventilation system10. The operating modes include a power off state, a manual operating state, and an autonomous state. When the patient ventilation system is powered on, the control system60enters either the manual operating mode or autonomous operating mode based on user selection of the operating mode.

In the manual operating mode, the user manually operates the BVM22and the sensors62,64provide feedback to the controller66to generate performance metrics that can be displayed on the display84. Based on the feedback, the user can make adjustments to achieve the desired ventilation for the patient. In one embodiment, the displayed information comprises the ventilation rate and tidal volume. The concentrations of oxygen in the inhaled air and the CO2 in the exhaled air could also be displayed. The control system60also performs one or more safety checks as hereinafter described and alerts the user if an unsafe condition is detected to prevent injury to the patient.

In the automated mode, the user may enter target ventilation parameters (e.g., ventilation rate and tidal volume) via the user interface80and the controller66generates drive signals to operate the BVM20based on the input parameters. Generally, the controller66determines the angular displacement of the servomotor56needed to achieve the target tidal volume. Once the target tidal volume is determined, the controller66determines the motor speed from the target ventilation rate and angular displacement. The controller then computes the drive signals based on the computed motor speed and angular displacement.

During the autonomous operating mode, the control system60monitors the flow rate and pressure from the sensors62and64and computes the actual ventilation rate and tidal volume from the measured flow rate and timing of the inhalation/exhalation phases of the ventilation cycle. The controller66compares the computed values of the ventilation rate and tidal volume to the target values input by the user and computes error values based on the comparison. The control system60adjusts the drive signals sent to the actuator40based on the error values. For example, if the ventilation rate is low, drive signals are generated to increase the motor speed of the servomotor56and shorten the duration of the ventilation cycle. If the ventilation rate is high, drive signals are generated to decrease the speed of the servomotor56and increase the duration of the ventilation cycle. As another example, if the tidal volume is low, the control system60may adjust the angular displacement of the motor to increase the stroke length of the link mechanism42, i.e., to increase the amount by which the self-inflating bag22is compressed. If the tidal volume is high, the control system60may adjust the angular displacement of the motor to decrease the stroke length of the link mechanism42, i.e., to decrease the amount by which the self-inflating bag22is compressed. Note that changing the stroke length of the link mechanism may also require adjustment of the motor speed if the ventilation rate is unchanged.

Automated ventilation fulfills the role of one responder (squeezing the bag at an adequate respiratory rate), allowing a single provider to focus on ensuring leak-proof mask seal around the patient's nose and mouth. This, in combination with sensor feedback to ensure adequate ventilation, minimizes the physical and mental strain on responders and improves patient outcomes.

As shown inFIG.4, the patient ventilation system may transition directly from the manual operating mode to the autonomous operating mode. In one embodiment, the user input devices82include a readily accessible button that is manually pressed by the user to switch from the manual operating mode to the autonomous operating mode. While the BVM20is manually operated, the ventilation parameters are displayed to the user on the display84so that the user can adjust their performance based on the feedback. During manual operation, the ventilation parameters are saved in memory and continuously updated. Once the user is satisfied with their performance, the user can enable automated ventilation with the press of a button to switch to the autonomous mode. When the user switches to the automated mode, the saved ventilation parameters are taken as the target ventilation parameters. As described above, the controller66computes the initial angular displacement and motor speed based on the target ventilation parameters to mimic the user's technique. In effect, the controller66“remembers” the user's technique and mirrors the performance of the user (squeeze rate, volume delivered) without the need for the user to manually enter the input parameters.

The patient ventilation system10may transition directly from the autonomous operating mode to the manual operating mode. As noted above, the controller66performs a series of safety checks in the autonomous mode to avoid injury to the patient. If the controller66detects an unsafe condition, the controller66alerts the user and switches automatically to the manual operating mode.

FIG.5schematically illustrates a method of controlling the BVM22. The controller66implements an inner loop control mechanism66abased on feedback from the BVM20and an outer loop control mechanism66bbased on input from biometric sensors monitoring the patient P. The biometric sensors90may, for example, monitor the patient's pulse rate, oxygen saturation levels, breath rate, etc. The inner loop control mechanism66agenerates drive signals for the motor56to operate the BVM20based on target ventilation parameters provided by the outer loop control66band feedback from the BVM20. As previously noted, the measured flow rate provided by the flow rate sensor62is used to calculate an estimated ventilation rate and tidal volume. The estimated ventilation rate and tidal volume are compared to the target values and the drive signals are adjusted based on the comparison. The outer loop control66breceives input parameters from the user via the user interface80or reads the input parameters from memory in the case where the user switches from manual mode to automatic mode. The input parameters are used as the initial target ventilation rate and tidal volume. During autonomous operation, biometric sensors90provide feedback indicative of the patient's condition. The feedback from the biometric sensors90is used to adjust the target ventilation rate and target tidal volume. These new target values will then be used by the inner loop control66ato control the motor56.

FIGS.6A-6Cillustrate an exemplary control procedure100implemented by the controller66.FIG.6Aillustrates the overall procedure at a high level.FIG.4Billustrates a manual control loop200for the manual mode andFIG.4Cillustrates an autonomous control loop300for autonomous mode.

Referring toFIG.6A, the procedure100begins when the device is powered on (block110). It is presumed that the face mask28has been affixed to the patient. The user selects the desired operating mode via the user interface80(block110). The controller66determines the operating mode based on the user's selection (block130). If the manual operating mode is selected, the control logic enters the manual control loop200(block140). If the autonomous operating mode is selected the control logic enters the autonomous control loop300(block160). While in the manual control loop200, the controller66checks for switch command from the user instructing the controller66to switch from manual control to autonomous control, e.g., by pressing a button (block150). If a switch command is detected, the controller66enters the autonomous control loop300(block160). Controller66stores the ventilation parameters detected during manual ventilation of the patient. When it switches to autonomous mode, controller66retrieves the stored ventilation parameters and mirrors the performance of the user. While in the autonomous operating mode, the controller66checks for an unsafe condition (block170). If an unsafe condition is detected, the controller66automatically switches to the manual operating mode. Also, a user may switch back to manual operating mode. Controller66checks for a command to switch back to manual mode (block180). If a command to switch is detected, controller switches back to manual mode. Otherwise, controller66remains in autonomous mode.

FIG.6Billustrates one example of the control logic for the manual operating mode. The manual operating mode may be initially selected by the user, or may be triggered by detection of an unsafe condition while in the autonomous operating mode. In either case, the controller66enters the manual operating mode and begins collecting data from the flow rate sensor and pressure sensor (blocks205,210). The controller66analyzes the collected data to detect the inhalation and exhalation phases of operation (block215). The controller computes moving averages of the phases, which is taken as the ventilation rate, i.e., number of ventilation cycles per minute (block220). The controller66estimates the tidal volume as the integral of the flow rate over time (block225). The computed ventilation parameters are saved in memory and output for display to the user along with other data, such as pressure, gas concentrations, etc. (block230).

After the ventilation parameters are computed, the controller66performs a series of checks in order to ensure patient safety. In the first check, the controller66compares the computed ventilation rate to a threshold (block235). Separate thresholds can be used to define a range. For example, an upper threshold and a lower threshold can be defined for the ventilation rate. If the moving average is outside the range defined by the thresholds, the controller alerts the user, e.g., by generating an alarm (block255). In the second check, the controller66compares the tidal volume to a threshold and alerts the user if the threshold is exceeded (blocks240,255). In the third check, the controller66compares the measured pressure to a threshold and alerts the user if the threshold is exceeded (blocks245,255). After these safety checks are performed, the controller66determines whether the user has commanded a switch to the autonomous operating mode, for example, by pressing a button (block250). If not the control loop200repeats until the autonomous mode is enabled or until the system is powered off. If the user switches to the autonomous mode, the manual control loop200terminates and control passes to the autonomous control loop300.

FIG.6Cillustrates one example of the control logic for the autonomous operating mode. The autonomous operating mode may be initially entered from the power off state or from the manual operating mode (block305). Upon entry into the autonomous operating mode, the controller gets the initial ventilation parameters (block310). When switching from the manual operating mode, the saved ventilation parameters stored in manual operating mode (if switching) may be taken as the initial ventilation parameters so there is no need for the user to enter the ventilation parameters. Otherwise, the controller66prompts the user to enter the initial ventilation parameters. In some embodiments, the user may override the stored ventilation parameters by manually entering new ventilation parameters. The controller66sets the target ventilation rate and target tidal volume based on the input ventilation parameters and calculates the expected flow rate (block315). The expected flow rate can be calculated from the input ventilation rate and tidal volume. More particularly, the duration of the ventilation cycle phases can be computed from the ventilation rate and multiplied by the tidal volume to get an estimate of the expected flow rate. The controller66estimates the angular displacement and motor speed for the servomotor56to achieve the desired ventilation rate and tidal volume (block325). As noted, the angular displacement can be estimated from the tidal volume and a reference table relating angular displacement to tidal volumes. Once the angular displacement is determined, the motor speed is computed based on the angular displacement and ventilation rate. The controller then generates and sends the drive signals to the servomotor56(block330). While the servomotor56reciprocates the linkage mechanism in the actuator40, it provides feedback to the controller66on the motor position (block335).

While in the autonomous operating mode, the controller66also performs a series of safety checks to prevent injury to the patient. First, the controller66checks the motor position to make sure that it is within expected bounds (block340). Second, the controller66checks the flow rate to make sure that it does not deviate from the expected flow rate by more than a predetermined threshold (block345). In other embodiments, controller66may check whether the flow rate exceeds a predetermined threshold that might injure the patient. Third, the controller66checks the pressure to make sure that the pressure does not deviate from the expected pressure by more than a threshold (block350). In other embodiments, controller66may check whether the pressure exceeds a predetermined threshold that might injure the patient. If any safety checks fails, the controller generates an alert and switches to the manual operating mode (block365). If the performance is as expected, the controller66checks for a command to switch to a manual mode (block355). If a command to switch is detected, controller66returns to autonomous mode. Otherwise, controller66pauses for an intercycle delay (block360) and control returns to block325.

Following each cycle, the controller66receives the flow rate and pressure from the sensors62and64and computes the actual ventilation rate and tidal volume from the measured flow rate and timing of the inhalation/exhalation phases of the ventilation cycle. The controller66compares the computed values of the ventilation rate and tidal volume to the target values input by the user and adjusts the drive signals sent to the actuator40based on the error values.

The patient ventilation system10allows a single emergency responder to operate the BVM22to provide respiratory aid to a patient. Displaying performance metrics enables the emergency responder to adjust their technique to provide adequate air flow to the patient while reducing the chance of patient injury and the emotional strain on the emergency responder. Once the user is satisfied with their performance, they can then enable automated ventilation to provide consistent ventilation to the patient. The controller recognizes the user's technique and with the press of a button, the control system of the DIVA mirrors the performance of the user. The autonomous mode fulfills the role of one responder (squeezing the bag at an adequate respiratory rate) allowing a single provider to focus operate the BVM20so that other responder can focus on other tasks.