Patent Application
20080314386
The invention relates to devices for providing emergency ventilation.
When a patient has little or no ability to breathe, such as during cardiac arrest, a rescuer will typically ventilate the patient by providing oxygen/air at regular intervals through the patient's mouth and airways. Ventilation of the patient is often combined with chest compressions to provide circulation of blood in the patient. Research has shown that the intervals and rates of ventilation are essential for the outcome of the resuscitation session.
Animal experiments have demonstrated the relationship between ventilation rates and brain tissue oxygenation. If ventilation rates are too high or low, tissue oxygenation is compromised, as shown by the data below from the Resuscitation Science Symposium. Circulation Vol 114; No 18, Oct. 31, 2006 (Abstracts from Resuscitation Science Symposium, November 2006).
The data of Table 1 from Idris et al (abstract 109) and Lurie et al (abstract 35) reflects brain tissue oxygen pressure measured using a Licox probe at different ventilation rates.
The data suggest that there is an optimal ventilation rate, which causes a favorable brain tissue oxygenation in these models of low blood flow. With too low ventilation rates, apparently too little oxygen is circulated and the brain is harmed. With too high ventilation rates, too much carbon dioxide is removed from the blood which causes contraction of cerebral arteries, increased cerebral vascular resistance, and consequential reduced cerebral blood flow and cerebral tissue oxygenation. Irreversible cell damage is likely when tissue oxygenation drops below 10 mmHg. Under conditions of normal flow and fixed rate of 12 breaths per minute (bpm), brain tissue oxygenation was found to be in the range of 20-40 mmHg. In the low blood flow model above, 6-8 breaths per minute appears to be optimal with respect to cerebral tissue oxygenation.
In clinical practice, for patients in cardiac arrest or trauma, hyperventilation with rates higher than 6-8 bpm is standard. Reports show that ventilation rates in the range of 20-40 bpm are quite common during cardiac arrest. Such high ventilation rates have two known adverse effects. One effect is the excessive removal of carbon dioxide as mentioned above. The other effect is reduced cardiac preload, because ventilations result in increased airway and thoracic pressures. With elevated thoracic pressure, right side preload is compromised. With elevated airway pressure, right side preload is also compromised. Compromised preload means that less blood flows into the heart, hence less flow can be delivered out from the heart, and the effect is even lower perfusion pressures.
In order to reduce the incidence of hyperventilation, several mitigations have been tried, but with limited effect. These include visual and audible feedback and training. Other possibilities of preventing hyperventilation in low blood flow states include the use of automatic ventilators. These are limited in their application because of cost and complexity as well as size and logistic challenges. Feedback to the user (e.g. flashing lights or voice prompts) can help, but has so far have only demonstrated some improvement.
In view of the foregoing, it would be an advancement in the art to provide a ventilation device for effectively reducing hyperventilation during emergency ventilation.
In one aspect of the invention there is provided a ventilation device comprising a self-inflating bag, which, when compressed, produces an outgoing flow. The bag includes an inlet allowing air to be drawn into the bag and an outlet permitting the outgoing flow. At least one valve is connected to the inlet and/or outlet to control air flow therethrough. The self-inflating bag may be any kind of bag which self inflates, for example, the type typically used in the art to ventilate patients. The valve connected to the inlet and/or the outlet may be a one-way valve, a two-way valve or a combination of such valves.
In another aspect of the invention, the valve is connected to the outlet and is a two-way valve. The two-way valve may also be embodied as a combination of two one-way valves of different flow directions. There may also be a second valve connected to the inlet, and in other embodiments there may be several valves connected to the outlet and/or inlet.
In another aspect of the invention, the valve or valves are disposed to control the time period between two succeeding bag compressions, i.e., the ventilation rate. The ventilation rate may be defined as the time between the maxima of a number of consecutive ventilations. There may also be set a minimum volume threshold for each ventilation. Accordingly the valve or valves may be controlled to meter the volume of air as well.
In one embodiment the ventilation device comprises a controller for controlling the valve(s). The ventilation device may include a sensor positioned to detect flow through the outlet 13. The sensor is connected to the controller and may be connected to an indicator. The sensor may be a CO2 sensor, a ventilation sensor or a combination of these. The ventilation sensor may be disposed to measure the rate of ventilation, and/or the volume of each ventilation
The invention will now be described in more detail by means of examples of possible embodiments and with reference to the accompanying Figures.
In
The outlet 13 is connected to a secured airway 14, such as a mask, tube, combitube, laryngeal mask, or other suitable means which enables transport of air in and out of the airways without leakage. An oxygen source 15 may be connected to the inlet 12 to supply oxygen to the ventilation device and the patient's airways.
The Figure illustrates four valves, where V1, V2, V3 are connected to the outlet and V4 is connected to the inlet. In other embodiments, there may be other numbers and combinations of valves. The valves may, for example, be a valve V1 for controlling release of expired air to ambient, valve V3 for letting expired air into the bag 11, and valve V2 for letting air from the bag 11 into the outlet 13 and to the patient's airways. In some embodiments, the ventilation device 10 only comprises valves V1, V2 and V4, with valve V3 being omitted.
In some embodiments, the valve (or valves) is disposed to control the time period between two consecutive bag compressions to control the ventilation rate. The allowable ventilation rate may depend on the ventilation volume. For example a higher ventilation rate may be permissible if the ventilation volume is low compared to if the ventilation volume is high. Clinically, it is the product of ventilation rate and volume which has an impact on intrathoracic pressures and on gas exchange.
In one embodiment, the valve V4 connected to the inlet 12 and restricts air flow into the bag 11 through the inlet 12. This will increase the time used to fully inflate the bag, thus increasing the time period between two consecutive bag compressions. The restriction of valve V4 may be constant or adjustable. In the case of an adjustable restriction, the adjustment of the flow can be performed manually or automatically. Because different bag types have different elasticities and volumes, the restrictor may advantageously be calibrated according to a time constant for self inflation. Bags made of silicone have been found to have good stability over time and temperature with respect to elastic properties.
As an alternative to dial control of self-inflation, or other manually adjustable self inflation, the ventilation device 10 may comprise a controller for controlling the operation of one or several of the valves. Or the controller can be programmed to adjust the degree of restriction of valve V4 embodied as a restrictor for inlet air.
In another embodiment, the valve V4 which is connected to the inlet is an on/off valve that is switched on or off by the controller. This enables control of the number of self inflations per unit time. The timing control of the on/off valve can be set to limit the maximum set number of self inflations per minute.
The ventilation device 10 may in one embodiment comprise a sensor connected to the controller and/or to an indicator and positioned to sense air flow to and from the outlet 13. The sensor may be a CO2 sensor, a ventilation sensor, a combination of these, or other sensors for providing information with respect to the ventilation of a patient.
In one embodiment, the ventilation sensor is positioned in an airway adapter positioned to sense flow through the outlet 13 or airway 14. In other embodiments, the ventilation sensor is integrated into a mask placed over a patient's face in fluid communication with the outlet 13.
In some embodiments, the sensor includes a restriction in the outlet 13 or airway 14, and a pressure sensor for measuring the pressure drop over this restriction. The pressure sensor(s) may in this case be placed in the ventilation device in or by an airway adapter, such as an adapter securing the airway 14 to the ventilation device. The flow rate can then be calculated as proportional to the square-root of the pressure drop. By integrating the flow the ventilation volume is found.
Alternative ventilation sensors may be constituted by means other than differential pressure monitoring, such as monitoring temperature fluctuations in the airways, which indicate whether the air is coming in or out of the person. Alternatively, a single pressure transducer, which measures the airway pressure inside the airway adapter may be used to enable detection of ventilation events and associated pressure profiles. In other embodiments, the motion of small turbines positioned in the airway may be used to sense ventilation. In still other embodiments, impedance measurements of the chest may be used to indicate the air volume in the lungs.
In one embodiment, the controller is programmed to control the opening/closing of the valve, such as one or more of the valve V1 to V4, when the time between two, or some other number, of operations of the ventilation device exceeds a pre-set rate threshold and opening the valve when the time between two, or some other number of operations, is lower than the pre-set rate threshold. The controller may also be programmed to control the opening/closing of the valve based on measurements of ventilation volume and rate.
The basis for controlling timing of compressions using the valve or valves may, for example, be provided by a sensor set to measure an actual rate of ventilation.
In one embodiment the valve V2 is an on/off valve connected to the outlet and controlling air flow from the outlet. Switching of the valve V2 is controlled by the controller. The timing of the on/off valve V2 may be controlled to achieve a maximum number of ventilations (compressions of the bag) per minute. The timing may be based on the measurement of the ventilation rate by a sensor coupled to a controller as described above. When the actual ventilation rate is less than the set maximum ventilation rate, the valve V2 is kept fully open by the controller. When the ventilation rate exceeds the set maximum value, the valve V2 will close, and open for ventilation after a delay that brings the ventilation rate within the desired range, i.e. below the set maximum value of the ventilation rate. The on/off valve V2 may be disposed as a fully mechanical solution, using energy from the operation of the bag or energy from the oxygen source 15 to operate and control the valve. The on/off valve may comprise a set function, where the user can set the maximum allowable rate of self inflation, for example between 6 and 16 ventilations per minute or some other value.
The on-off valve may also be battery operated, where energy in the battery is used to operate and control the valve, and where the on-off valve is further disposed with a selector to set the desired maximum number of self inflations per minute.
In concert with the battery operated on-off valve, the bag can be provided with an indicator. This can be a display, which indicates the actual rate of ventilation as a number, or colored lights, where the green light indicates that the actual ventilation rate is appropriate, a yellow light indicates that the actual rate is becoming too low or too high, and a red light indicates that the actual rate is too low or too high.
In some embodiments the controller is programmed to control one or more of the valves V1 to V4 based on the CO2-level of the air expired by the patient. This can, for example, be used to increase or decrease ventilation rate to get the CO2 level within a desired range. Some embodiments of the invention deliver gas from a source with a predetermined composition, or by taking advantage of the gas in the expired air of either the patient or the rescuer. Although maintaining proper ventilation rates and volumes is beneficial, it may be insufficient without also maintaining proper CO2 levels. For example, ventilation rates of up to 12 bpm seem to be safe with respect to preload, but may still be too high to maintain normocapnia. Accordingly, the amount of CO2 delivered to the patient may be increased in some embodiments of the invention.
Table 2 from International Volcanic Hazard Network (http://www.esc.cam.ac.uk/ivhhn/guidelines/gas/co2.html) indicates at which levels of concentration of CO2 becomes dangerous.
The composition of air before and after breathing is shown in Table 3 below. Gas composition, from http://www.pdh-odp.co.uk/GasLaws.htm.
Aufderheide (Circulation, Apr. 27, 2004) demonstrated that a CO2 level of 5% in the inspired air (rate 30 per minute) resulted in normocapnia both looking at blood gases and at ETCO2. In this experiment, 5% CO2 came from a dedicated gas source.
An oxygen source 25, 35 may be provided and disposed such that a continuous flow of oxygen is collected in an O2 reservoir 28, 38.
The ventilation device 20, 30 may comprise a controller 26, 36 as described in connection with
In some embodiments, the bag 11, 21, 31 is divided into two separate compartments or volumes. As shown in
In an alternative embodiment, the controller may be connected to a carbon dioxide sensor positioned in fluid communication with the airway 24 to sense the carbon dioxide of expired air. In such embodiments, the controller may control valves V2 and V3 such that the proportion of recycled air is chosen to achieve a desired set level of carbon dioxide in the exhaled air.
In
Sensing of hyperventilation may be performed by a pressure sensor, for example an electronic pressure sensor connected to the patient side of the self-inflating bag. A microcontroller may be provided with a connection to the pressure sensor and comprise algorithms to calculate an approximate ventilation rate. When the approximate ventilation rate exceeds a predefined value, the microcontroller may output a signal to a bi-stable solenoid 42, which releases a locking member 43 which releases the piston 46. The piston 46 is driven by a spring 44, which may be non-linear. In normal conditions, that is without hyperventilation, the piston 46 may be locked in open position by the locking member 43 of the solenoid 42. This situation is illustrated in
