DEVICE FOR DETECTING LUNG VENTILATION

Description

[0001] In respiratory failure, reduced lung ventilation leads to reduced oxygen uptake and, in some cases, to increased carbon dioxide levels in the tissues. This leads to altered blood gas values. A fundamental distinction must be made between oxygenation disorders and ventilation disorders. In oxygenation disorders, the partial pressure of oxygen in the blood can drop, while the body can still compensate for the partial pressure of carbon dioxide. In ventilation disorders, both the partial pressure of oxygen and the partial pressure of carbon dioxide can be altered.

[0002] One method for determining lung ventilation is electrical impedance tomography (EIT). In electrical impedance tomography (EIT), weak alternating currents flow through the body along paths of least resistance, generating electrical voltages on the surface. The measured surface voltages depend on the impedance (resistance) distribution within the thorax. The measured resistance is largely determined by the intrapulmonary air content. Due to its high temporal resolution, the method offers the possibility of detecting rapid physiological changes. For example, the elisa 800 VIT ventilator (SALVIA medical GmbH & Co. KG, Niederhöchstadt Str. 62, 61476 Kronberg, Germany) uses EIT technology.

[0003] Using EIT technology, poorly ventilated lung areas can be identified.

[0004] According to the state of the art, EIT data can be used by the physician to assess lung ventilation.

[0005] However, the effects of changes in artificial ventilation on oxygen supply and carbon dioxide levels, particularly oxygen partial pressure and carbon dioxide partial pressure, are not adequately taken into account clinically when adjusting ventilation.

[0006] US 2008 / 0295839 A1 shows a ventilation system with a sensor array for monitoring a patient's carbon dioxide and oxygen levels. The recorded values ​​are used to control the ventilator, in particular to adjust the PEEP.

[0007] DE 197 16 166 A1 describes a device for assisting breathing. This device is equipped, among other things, with EIT sensors that monitor cardiac function depending on ventilation.

[0008] DE 10 2016 107 603 A1 proposes a system for displaying various patient data on a user interface. In particular, various display options for EIT measurements are discussed.

[0009] DE 103 01 202 B3 shows a combination of a ventilator and an EIT measurement system. Both devices, the ventilator and the EIT measurement system, are designed to enable bidirectional data exchange.

[0010] DE 10 2013 203 177 A1 describes a ventilator that can be automatically controlled based on EIT measurements. In particular, the analysis of EIT pixels is discussed.

[0011] The object of the invention is therefore to provide a ventilation device in which information about the ventilation of the lungs and information about the oxygen supply and the carbon dioxide content are used for, for example, automatic, control or regulation of the ventilation.

[0012] The object is achieved by a: ventilation device, comprising at least one ventilator with at least one controllable respiratory gas source and a programmable control device and at least one sensor device for determining pressure and / or flow of the respiratory gas, wherein the control device controls the respiratory gas source to specify a first ventilation pattern (with regard to pressure, flow, volume, frequency), wherein the ventilation device has three further sensor devices, wherein one sensor device has a plurality of individual sensors which are designed to generate and / or measure electrical potentials and are designed to non-invasively determine the electrical impedance (EI) of the lungs of a patient, wherein the second sensor device is designed to non-invasively determine the carbon dioxide supply,wherein the third sensor device is designed for the non-invasive determination of the oxygen supply of the patient, characterized in that the control device evaluates the sensor measured values ​​of the EI sensor device to determine the current ventilation of the lung during ventilation with the first ventilation pattern, wherein the control device evaluates the sensor measured values ​​of the second sensor device to determine the current carbon dioxide supply and wherein the control device evaluates the sensor measured values ​​of the third sensor device to determine the current oxygen supply and wherein the control device controls the respiratory gas source to specify a second ventilation pattern if the sensor device has an increased EIT sum signal and / or a reduced EIT change frequency, in comparison to the first ventilation pattern, and a reduced measure for the oxygen supply, wherein the second ventilation pattern has a,compared to the first ventilation pattern, may have an increased frequency and / or an at least short-term increase in the inspiration time and / or an adjustment of the PEEP.

[0013] The ventilation device is also characterized in that the control device controls the respiratory gas source to specify a first ventilation pattern and stores the resulting first sensor (measurement) values ​​of at least one sensor device, wherein the control device then controls the respiratory gas source to specify a second ventilation pattern and stores the resulting second sensor (measurement) values ​​of at least one sensor device and compares the first sensor (measurement) values ​​with the second sensor measurement values.

[0014] The ventilation device is also characterized in that the ventilation device has at least one storage unit communicating with the control device, in which at least standard values ​​and / or limit values ​​for the carbon dioxide supply and for the oxygen supply are stored.

[0015] The ventilation device is also characterized in that the control device controls the respiratory gas source to specify a second ventilation pattern which differs from the first ventilation pattern with regard to pressure and / or flow and / or volume and / or frequency when the sensor measured values ​​of the current carbon dioxide supply and / or the sensor measured values ​​of the current oxygen supply deviate from the standard values ​​and / or limit values ​​are at least reached.

[0016] The ventilation device is also characterized in that standard values ​​and limit values ​​are stored in the memory for the ventilation of the lungs and the control device controls the respiratory gas source to specify a second ventilation pattern which differs from the first ventilation pattern in terms of pressure and / or flow and / or volume and / or frequency when the current ventilation deviates from the standard values ​​and limit values ​​are at least reached.

[0017] The ventilation device is also characterized in that the control device evaluates the sensor measured values ​​of the EI sensor device to determine the resulting ventilation of the lungs during ventilation with the second ventilation pattern, wherein the control device evaluates the sensor measured values ​​of the second sensor device to determine the resulting carbon dioxide supply during ventilation with the second ventilation pattern, wherein the control device evaluates the sensor measured values ​​of the third sensor device to determine the resulting oxygen supply during ventilation with the second ventilation pattern and wherein the control device compares the current ventilation with the resulting ventilation.

[0018] The ventilation device is also characterized in that the control device controls the respiratory gas source to specify a second ventilation pattern such that the resulting ventilation of the lungs is improved compared to the current ventilation.

[0019] The ventilation device is also characterized in that the control device controls the respiratory gas source to specify a second ventilation pattern which differs from the first ventilation pattern in terms of pressure and / or flow and / or volume and / or frequency, so that the sensor measured values ​​of the resulting carbon dioxide or oxygen supply at least approach target values.

[0020] The ventilation device is also characterized in that the control device controls the respiratory gas source to specify a second ventilation pattern which differs from the first ventilation pattern in terms of pressure and / or flow and / or volume and / or frequency when the sensor measured values ​​of the current ventilation and / or the sensor measured values ​​of the current oxygen partial pressure deviate from the standard values ​​and limit values ​​are at least reached.

[0021] The ventilation device is also characterized in that the control device controls the respiratory gas source to specify a second ventilation pattern which differs from the first ventilation pattern in terms of pressure and / or flow and / or volume and / or frequency when the sensor device identifies an unchanged EIT sum signal and a high or increased EIT change frequency, wherein the second ventilation pattern has an increased mandatory frequency compared to the first ventilation pattern.

[0022] The ventilation device is also characterized in that the control device controls the respiratory gas source to specify a second ventilation pattern which differs from the first ventilation pattern in terms of pressure and / or flow and / or volume and / or frequency when the sensor device has an unchanged EIT sum signal, compared to the first ventilation pattern, and a reduced level for the carbon dioxide supply, wherein the second ventilation pattern has an increased mandatory frequency compared to the first ventilation pattern.

[0023] The ventilation device is also characterized in that the control device controls the respiratory gas source to specify a second ventilation pattern which differs from the first ventilation pattern in terms of pressure and / or flow and / or volume and / or frequency when the sensor device has a reduced EIT sum signal, compared to the first ventilation pattern, and a reduced measure for the carbon dioxide supply, wherein the second ventilation pattern has an increased mandatory frequency and / or an increased tidal volume and / or an increased pressure support, compared to the first ventilation pattern.

[0024] The ventilation device is also characterized in that the control device controls the respiratory gas source to specify a second ventilation pattern which differs from the first ventilation pattern in terms of pressure and / or flow and / or volume and / or frequency when the sensor device has an unchanged EIT sum signal and an increased measure for the carbon dioxide supply, wherein the second ventilation pattern has a changed EPAP pressure or curve compared to the first ventilation pattern.

[0025] The ventilation device is also characterized in that the control device controls the respiratory gas source to specify a second ventilation pattern which is different from the first ventilation pattern in terms of pressure and / or flow and / or volume and / or frequency when the sensor device has an unchanged EIT sum signal, in comparison to the first ventilation pattern, and an increased level for the carbon dioxide supply, wherein the second ventilation pattern can have an increased mandatory frequency compared to the first ventilation pattern if the EIT change frequency is reduced.

[0026] The ventilation device is also characterized in that the control device controls the respiratory gas source to specify a second ventilation pattern which is different from the first ventilation pattern in terms of pressure and / or flow and / or volume and / or frequency when the sensor device has a reduced EIT sum signal, compared to the first ventilation pattern, and a reduced EIT change frequency and an increased measure for the carbon dioxide supply, wherein the second ventilation pattern has an increased mandatory frequency and / or an increased tidal volume and / or an increased pressure support, compared to the first ventilation pattern.

[0027] The ventilation device is also characterized in that the control device controls the respiratory gas source to specify a first PEEP and stores the resulting first sensor (measurement) values ​​of at least one sensor device, wherein the control device then controls the respiratory gas source to specify a second PEEP and stores the resulting second sensor (measurement) values ​​of at least one sensor device, wherein the control device then compares the first sensor (measurement) values ​​with the second sensor measurement values.

[0028] The ventilation device is also characterized in that the control device controls the respiratory gas source to specify a first ventilation pattern in which the EPAP pressure has a first value or a first profile, wherein the sensor device for non-invasively determining the electrical impedance (EI) determines the resulting ventilation of the lungs and wherein the second sensor device determines the carbon dioxide supply and / or wherein the third sensor device determines the oxygen supply of the patient, wherein the control device stores the sensor measured values ​​that occur during ventilation with the first pattern, wherein the control device controls the respiratory gas source to specify a second ventilation pattern in which the EPAP pressure has a second value or a second profile,wherein the sensor device for non-invasively determining the electrical impedance (EI) determines the resulting ventilation of the lungs, and wherein the second sensor device determines the carbon dioxide supply and / or wherein the third sensor device determines the oxygen supply of the patient, wherein the control device stores the sensor measured values ​​that occur during ventilation with the second pattern, and wherein the control device compares the sensor measured values ​​that occur after application of the first ventilation pattern with the sensor measured values ​​that occur after application of the second ventilation pattern and / or displays them in a comparative manner on the display.

[0029] The ventilation device is also characterized in that the control device monitors at least one sensor signal for errors by comparing it with another current sensor signal when limit values ​​of a current sensor signal are reached in order to detect an error.

[0030] The ventilation device is also characterized in that the control device monitors an EIT sensor signal for errors by at least temporarily comparing the EIT sensor signal with the sensor signal of a sensor device for determining pressure and / or flow of the respiratory gas.

[0031] The ventilator is also characterized in that the control device monitors an EIT sensor signal for errors by comparing the EIT sensor signal with a modeled sensor signal.

[0032] The ventilator device is also characterized in that the modeled sensor signal is learned essentially continuously.

[0033] Sensor device for use with a ventilator according to at least one of the preceding claims.

[0034] The device according to the invention helps to detect and prevent ventilation complications early, thus preventing subsequent costs.

[0035] Costly and complicated intra-hospital transports of intensive care patients requiring ventilation are reduced.

[0036] At any time, a differentiated statement about the ventilation of the lungs and the supply of oxygen and / or carbon dioxide is possible.

[0037] A detailed assessment of ventilation was previously only possible as a snapshot using imaging techniques (e.g., chest CT). With this new technology, ventilation can be continuously analyzed and monitored. By overlaying the patient's lung contours, spatial ventilation distributions can be mapped and therapeutically evaluated. The visualization is non-invasive, high-resolution, and in real time.

[0038] With the device according to the invention, the lung condition can be assessed in real time and the effects of adjusting ventilation settings can be continuously evaluated. Respiratory cycle collapse areas and areas of overexpansion can be identified and assessed.

[0039] Further advantages and features of the present invention will become apparent from the description of the embodiments which are explained below with reference to the accompanying figure.

[0040] In theFigure 1 A ventilator 10 according to the invention is shown, which is designed here as a home ventilator, sleep therapy device, or clinical ventilator. The ventilator 1 and the ventilator 10 are designed to carry out the method according to the invention.

[0041] The ventilation device (10) comprises at least one ventilator (1) with at least one controllable respiratory gas source (100) and a programmable control device (21), and at least one sensor device (2) for determining the pressure and / or flow of the respiratory gas. The control device (21) controls the respiratory gas source to specify a first predetermined ventilation pattern (45) (with regard to pressure, flow, volume, frequency). The ventilation device (10) also comprises at least two further sensor devices (3, 30, 40) spatially separated from the ventilator (1) and communicating with the control device (21) of the ventilation device (10). A sensor (3) has a plurality of individual sensor devices (3, 3', 3" ...), and each sensor device is designed to generate electrical potentials and / or to noninvasively determine the electrical impedance (EI) of a body section and to determine and transmit the sensor measured values ​​to the control unit. The programmable control device (21) evaluates the sensor measured values ​​of the EI sensor device (3) to determine the current ventilation (44) of the lung during ventilation with the first ventilation pattern (45).The control device (21) also controls the respiratory gas source, for example, to specify a second ventilation pattern (55) that differs from the first ventilation pattern (45) in terms of pressure and / or flow and / or volume and / or frequency. The control device (21) evaluates the sensor measurement values ​​of the EI sensor device (3) to determine the resulting ventilation (54) of the lung during ventilation with the second ventilation pattern (55). The control device (21) compares the current ventilation (44) with the resulting ventilation (54) to determine the more suitable ventilation pattern. A user can make specifications to specify target values ​​that must be achieved to achieve a "more suitable ventilation pattern."Alternatively or additionally, changes in carbon dioxide and / or oxygen measurements are an important criterion that is relevant for the decision-making process when selecting or continuing ventilation patterns.

[0042] The ventilator 1 comprises a respiratory gas source 100 with, for example, a blower device and / or a valve device 101 for generating an air flow for ventilation. A control device 21 is provided here to control the respiratory gas source 100 and to acquire and process sensor data. The ventilator 1 is operated and configured via a user interface 61 with control elements and a display device 11 (display).

[0043] The ventilator 1 has a breathing interface 102 for supplying the airflow to a patient for ventilation. The breathing interface 102 shown here is a breathing mask 105, exemplified as a nasal mask. A headgear 106, for example, is provided for securing the breathing mask 105. The breathing interface 102 can also be configured, for example, as a full-face mask, a nasal cannula, a tube, or a laryngeal mask.

[0044] To connect the respiratory interface 102 to the respiratory gas source 100, at least one connecting tube 109 is provided, which is connected to the respiratory gas source 100 in an air-conducting manner via a coupling device 112. The connecting tube 109 is connected to the respiratory interface 102 via a coupling element 107. An exhalation element 108, which comprises or is designed as a valve, is arranged between the connecting tube 109 and the coupling element 107. The exhalation element 108 is provided, for example, to prevent rebreathing into the ventilator 1 during the user's exhalation.

[0045] The control device 21 is connected to a sensor device (2, 3, 30, 40) not shown in detail, which has one or more sensors for detecting device parameters and / or patient parameters and / or other variables characteristic of ventilation. The control device 21 can be designed as a central control device, for example in the ventilator, which processes all sensor values. The control device 21 can be designed in the form of several decentralized control devices, for example one in the ventilator and one each assigned to one (or the) sensor(s).

[0046] For example, the control device 21 comprises a pressure sensor (2) (not shown in detail here), which determines the pressure conditions of the respiratory gas. For this purpose, the pressure sensor is operatively connected to the respiratory gas, for example, via a pressure measuring hose 110 to the respiratory interface 102. The pressure measuring hose 110 is connected to the control device 21 via an inlet connection 111. For example, the control device 21 also comprises a flow sensor (2) (not shown in detail here), which determines the flow conditions of the respiratory gas.

[0047] Furthermore, the control device 21 serves to control the blower device and / or the valve device 101. The control device 21 provides a necessary minimum pressure and compensates for pressure fluctuations caused by the user's breathing activity. For example, the control device 21 also detects the current pressure in the breathing mask 105 (or the patient interface) and adjusts the output of the breathing gas source accordingly until a desired ventilation pressure is reached. The device parameters required to adjust the breathing gas source 100, as well as the device configuration and / or device software, are stored in a memory device 31. The control device 21 can also regulate the oxygen content in the breathing gas by appropriately controlling the blower device and / or the valve device 101, wherein the valve device comprises or connects to at least one oxygen source (compressed gas cylinder or hospital line).The oxygen is added to the breathing gas stream, for example, downstream or upstream of the blower device. In this case, the valve device is an oxygen mixing valve. The oxygen is added to the breathing gas stream, for example, by a valve unit that guides and regulates the breathing gas and oxygen flows.

[0048] The control device 21 can also be configured to detect sensor-detected patient parameters. For this purpose, the control device 21 can be equipped with sensors for measuring respiratory excursion, for measuring oxygen supply and / or carbon dioxide supply, and / or for measuring EEG, EMG, EOG, or ECG activity.

[0049] The ventilation device has, in particular, at least two sensor devices (3, 30, 40) which are spatially separated from the ventilator (1) and communicate with the control unit (21), wherein a sensor (3) has a plurality of individual sensor devices (3, 3', 3" ...) and each sensor device is designed to generate electrical potentials (13) for the non-invasive determination of the electrical impedance (EI) of a body section. The sensor devices (3) are designed, for example, as adhesive plasters, with an outer layer facing away from the skin and an adhesive layer facing the skin, or combined as a belt which holds the sensor devices.

[0050] The ventilation device (10) comprises at least one further sensor device (30) designed for the non-invasive determination of the CO2 (30). The sensor device (30) is designed, for example, as a clamp sensor or as an adhesive plaster with an outer layer facing away from the skin and an adhesive layer facing the skin. The ventilation device (10) comprises at least one further sensor device (40) designed for the non-invasive determination of the O2 (40). The sensor device (30) is designed, for example, as a clamp sensor or as an adhesive plaster with an outer layer facing away from the skin and an adhesive layer facing the skin.

[0051] The sensors (3, 30, 40) comprise, for example, energy and transmission means for determining and wirelessly transmitting the sensor measured values. Alternatively, the sensors (3, 30, 40) comprise, for example, communication means (35, 45) for transmitting the sensor measured values ​​to the controller (21).

[0052] Fig. 2 shows a schematic representation of the EIT measurement.

[0053] The sensor device (3) has a plurality of individual sensors (3, 3', 3" ...) which are designed to generate and / or measure electrical potentials and serve to non-invasively determine the electrical impedance (EI) of the lung (L) of a patient (P).

[0054] The sensor device comprises, for example, 32 high-resolution sensors (3, 3'...) in a textile belt (not shown). An integrated position sensor (not shown) determines the patient's position. The sensors are interconnected (4) by communication or wiring means (4) and arranged such that they can receive signals sequentially from all directions. The control unit (21) can therefore spatially assign the sensor measured values ​​to the EIT measurement (3). This allows the local tissue resistances to be determined from different directions and then converted into moving images. The control unit (21) processes the sensor measured values ​​of the EIT measurement (3) such that a specific electrical impedance (EI) is determined for individual lung sections (LA1, LA2). The sensor device (3) is connected to the control unit (21) via wired or wireless communication means (35).The control unit (21) stores (11) and processes the sensor measurements for use in the ventilator. The storage device (31) can be a component of the control unit (21) or a separate component.

[0055] Fig. 2also shows a schematic representation of the results of the EIT measurement on the display of the ventilator. The control unit (21) processes the sensor measured values ​​for use in the ventilator in such a way that a visualization of the patient's thorax (P) with the two lungs (L) is shown on the display of the ventilator (10). The control unit (21) processes the sensor measured values ​​of the EIT measurement (3) in such a way that a specific electrical impedance (EI) of the lung (L) is determined for individual lung sections (LA1, LA2). The specific electrical impedance (EI) of the lung sections (LA) is processed for representation on the display in such a way that lung sections with a high electrical impedance (L2) are graphically represented differently than those lung sections with a low electrical impedance (L1).The control unit (21) processes the sensor measured values ​​of the EIT measurement (3) in such a way that a specific electrical impedance (EI) of the lung (L) is determined breath by breath for individual lung sections (LA1, LA2) and is prepared for representation on the display.

[0056] The sensor device (3) is also configured and designed (together with the controller and the memory) to form an EIT sum signal (44'), which is a measure of the ventilation of the lung or lung sections. The sensor device (3) is also configured and designed (together with the controller and the memory) to determine a frequency of the EIT change frequency (44"). The sensor device (3) can thus determine the current ventilation (44) in summary.

[0057] In the sense of the invention, the EIT sum signal (44') is understood to mean that the impedance or impedance change distribution in the sectional plane determined by the sensors or the volume spanned by the sensors does not necessarily have to be represented graphically, for example on a display, for the implementation of the method according to the invention, but at least the calculated result values ​​of the impedance distribution or impedance change distribution (for the implementation of the method) are present in the device according to the invention.

[0058] When all impedance values ​​from the sensors are summed, the resulting total signal during inspiration differs from the total signal during expiration. This total value therefore represents an adequate measure for determining lung ventilation.

[0059] The EIT change frequency (44") can be determined from the respiratory phase-dependent change in the impedance values ​​of the sensors. The impedance values ​​of the sensors fluctuate with inspiration and expiration depending on the respiratory phase. The EIT change frequency (44") therefore represents an alternative or supplementary measure for determining the (frequency of) ventilation of the lungs.

[0060] For example, the sensors are integrated into a textile, breathable, and stretchable electrode belt, along with a position sensor. The sensor (3) and the control unit are configured to generate a frame rate of, for example, up to 50 frames per second. This visualizes lung regions (LA). According to the invention, patient-specific inputs such as height, weight, gender, and chest circumference are possible.

[0061] The EIT data thus acquired and processed enable a temporally and spatially resolved differentiated analysis and representation of the electrical impedance (EI) of the lung.

[0062] According to the invention, the measurement and control technology of the ventilator is networked with electrical impedance tomography (EIT). This allows for continuous imaging of lung function. The measured values ​​from the ventilator are combined with the results of the electrical impedance tomography. This technology thus makes it possible to evaluate a wide variety of clinical issues and tailor therapy accordingly.

[0063] The gases carbon dioxide (CO2) and oxygen (O2) can easily diffuse through body tissue, including the skin. Non-invasive sensors placed on the skin can measure O2 and CO2 when the skin adjacent to the sensor is warmed to a temperature above body temperature. The heat, typically 42° to 45°C, increases local capillary blood flow and enhances gas diffusion. This allows for a fairly precise determination of CO2 / O2 readings at the skin surface.

[0064] Fig. 3shows a schematic representation of transcutaneous blood gas analysis of tpCO2. Using transcutaneous carbon dioxide measurement, the skin's carbon dioxide tension (tpCO2) can be determined non-invasively. Measurement accuracy depends less on blood flow than on tpO2. At 44°C, the pCO2 at the skin surface is approximately 1.37 times higher than the arterial pCO2. The sensor used according to the invention takes this relationship into account using a correction factor. The pCO2 sensor typically warms the skin to 42° to 45°C and uses a pH glass electrode in a thin electrolyte layer beneath a hydrophobic, CO2- and O2-permeable membrane. An evaluation unit converts the signals from the interaction at the electrode into an electrical signal and sends this to the control unit.

[0065] Transcutaneous blood gas measurement allows the measurement of tpCO2 through a patient's skin. The basic functionality of the sensor is described in Figure 3shown. The carbon dioxide diffuses from the patient's skin (P) into the sensor (32, 34). The sensor has at least one sensor element (32, 34) which is sensitive to carbon dioxide; two or more sensor elements (32, 34) can also be used. A heat source (33) ensures that the patient's skin (P) adjacent to the sensor is heated (42-45 °C). The increased temperature leads to increased blood flow to the skin and the capillary bed. This results in an increased release of carbon dioxide. The sensor has a response time in the range of seconds to minutes. The sensor enables stable operation of at least 5 hours without signal drift. The sensor (30) is connected to the control unit (21) via wired or wireless communication means (35). The control unit (21) stores (11) and processes the sensor measured values ​​for use in the ventilator.The memory (31) can be part of the control unit (21) or a separate component.

[0066] The sensor device (30) is (together with the control unit (21) and the memory) arranged and designed to form an instantaneous measure (46) for the carbon dioxide supply, for example the carbon dioxide partial pressure.

[0067] Fig. 4shows a schematic representation of transcutaneous blood gas analysis of pO2. Transcutaneous oxygen measurement allows the non-invasive determination of skin oxygen tension (tpO2). The measurement accuracy depends on blood flow. If measured in the same arterial supply area, there is a close correlation between tpO2 and arterial oxygen pO2. An example sensor contains fluorescent dyes in the sensor surface. The oxygen molecules interact with the fluorescent dyes. An evaluation unit converts the interaction signals into an electrical signal and sends it to the control unit.

[0068] Transcutaneous blood gas measurement allows the measurement of pO2 through a patient's skin. The basic functionality of the sensor is described in Fig. 4shown. Oxygen diffuses from the patient's (P) skin into the sensor (42, 44). The sensor has at least one sensor element (42, 44) which is sensitive to oxygen; two or more sensor elements can also be used. A heat source (43) ensures that the patient's (P) skin adjacent to the sensor is heated (42-45°C). The increased temperature leads to increased blood flow to the skin and the capillary bed. This results in increased O2 release. The sensor has a response time in the range of seconds to minutes. The sensor enables stable operation of at least 5 hours without signal drift. The sensor (40) is connected to the control unit (21) via wired or wireless communication means (45). The control unit (21) stores (11) and processes the sensor measured values ​​for use in the ventilator. The memory (31) can be part of the control unit (21) or a separate component.Pulse oximetry is another non-invasive method for measuring arterial oxygen saturation. Established systems use two wavelengths to differentiate between oxygenated and deoxygenated blood. The signals are recorded by passing red and infrared light through a capillary bed (finger or earlobe) and measuring the changes in light absorption during the pulse cycle. The sensor uses red and infrared light-emitting diodes (LEDs) that transmit light through the capillary bed to a photodiode. The photodiode receives the light, converts it into an electrical signal, and sends this to the evaluation unit or control unit for calculation. The sensor device (40) is (together with the control unit (21) and the memory) configured and designed to generate an instantaneous measure (47) of the oxygen supply, for example, the oxygen partial pressure.

[0069] Tables 1 and 2 show how the control device (21) controls the respiratory gas source to specify a ventilation pattern (45, 55), and how the control device (21) also takes into account sensor measured values ​​of the current carbon dioxide supply (46) and / or the sensor measured values ​​of the current (47) oxygen supply to specify a ventilation pattern (45, 55). The specification of a ventilation pattern (45, 55) can occur directly, for example in the form of control commands for the respiratory gas source. The specification of a ventilation pattern (45, 55) can occur indirectly, for example in the form of a ventilation pattern (45, 55) that is suggested to the caregiver or operator of the ventilation device (for example on the display).

[0070] Tables 1 and 2 show how the control device (21) controls the respiratory gas source to specify a second ventilation pattern (55) which differs from the first ventilation pattern (45) in terms of pressure and / or flow and / or volume and / or frequency when the sensor measured values ​​of the current carbon dioxide supply (46) and / or the sensor measured values ​​of the current (47) oxygen supply deviate from the standard values ​​(62). Table 1 EIT sum signal (44') relative signals impedance 32 electrodes monitor themselves, up to 7 electrodes can be missing Frequency of EIT change frequency (=respiratory rate) (44") current measure (46) Carbon dioxide partial pressure Normal value Partial pressure 35 - 45 mmHg Limit below 35 or above 50 Specification (55) Control unit (21) to ventilator (1) unchanged High Low Increasing the mandatory frequency low Normal Low Increase tidal volume, Delta-P or pressure support Increase mandatory rate Unchanged Low High Increasing the mandatory frequency Low Low high Increase tidal volume, Delta-P or pressure support Increase mandatory rate High Unchanged High Reduction of tidal volume or Delta-P Automatic maneuvers to assess end-inspiratory overdistension Unchanged Unchanged High Continue ventilation, search for the cause (extrapulmonary cause)

[0071] Tables 1 and 2 also show how the control device (21) controls the respiratory gas source to specify a second ventilation pattern (55) which differs from the first ventilation pattern (45) in terms of pressure and / or flow and / or volume and / or frequency when the sensor measured values ​​of the current ventilation (44) and / or the sensor measured values ​​of the current carbon dioxide partial pressure (46) deviate from the standard values ​​and limit values ​​are at least reached. Table 2 EIT sum signal (44') Frequency of EIT change frequency (=respiratory rate) (44") current measure (47) partial pressure of oxygen normal value partial pressure 75 - 100 mmHg limit below 70 or above 105 Specification control unit (21) to ventilator (1) low Low low Short-term increase in o2 If necessary, reduce o2 again in the course of time Increase tidal volume, Delta-P or pressure support Increase mandatory rate Change of ventilation pattern Unchanged Unchanged low Short-term increase in o2 PEEP adjustments High Low low Increase frequency Increase in inspiration time Change of ventilation pattern

[0072] Tables 1 and 2 also show how the control device (21) controls the respiratory gas source to specify a second ventilation pattern (55) which differs from the first ventilation pattern (45) in terms of pressure and / or flow and / or volume and / or frequency when the sensor measured values ​​of the current ventilation (44) and / or the sensor measured values ​​of the current (47) oxygen partial pressure deviate from the standard values ​​(62) and limit values ​​(63) are at least reached.

[0073] Table 3 shows how the control device (21) controls the respiratory gas source to specify a second ventilation pattern (55) which differs from the first ventilation pattern (45) in terms of pressure and / or flow and / or volume and / or frequency so that the sensor measurements of the resulting carbon dioxide partial pressure or oxygen partial pressure reach target values.

[0074] The control device (21) controls the respiratory gas source to specify a second ventilation pattern (55) (with regard to pressure, flow, volume, frequency) when the sensor device (3) detects an unchanged EIT sum signal (44') and a high or increased EIT change frequency (44"), wherein the second ventilation pattern (55) can have an increased mandatory frequency compared to the first ventilation pattern (45).

[0075] The control device (21) controls the respiratory gas source to specify a second ventilation pattern (55) (with regard to pressure, flow, volume, frequency) when the sensor device (3) has an unchanged EIT sum signal (44') compared to the first ventilation pattern (45) and a reduced level for the carbon dioxide supply, wherein the second ventilation pattern (55) can have an increased mandatory frequency compared to the first ventilation pattern (45).

[0076] The control device (21) controls the respiratory gas source to specify a second ventilation pattern (55) when the sensor device (3) has a reduced EIT sum signal (44') compared to the first ventilation pattern (45) and a reduced level of carbon dioxide supply, wherein the second ventilation pattern (55) can have an increased mandatory frequency and / or an increased tidal volume and / or an increased pressure support compared to the first ventilation pattern (45).

[0077] The control device (21) controls the respiratory gas source to specify a second ventilation pattern (55) (in terms of pressure, flow, volume, frequency) if the sensor device (3) has an unchanged EIT sum signal (44') and an increased level of carbon dioxide supply, wherein the second ventilation pattern (55) has a modified EPAP pressure or profile compared to the first ventilation pattern (45). In this sense, the EPAP pressure can also have a first profile that is changed automatically or upon user selection in subsequent ventilation cycles.

[0078] For example, EPAP may rise at the beginning of exhalation and then fall, or reach a maximum or minimum value mid-exhalation. Alternatively, EPAP may also reach a maximum value at the end of exhalation. EPAP may also assume different pressure levels during exhalation. EPAP can also be applied over a longer period of time.

[0079] The control device (21) controls the respiratory gas source to specify a second ventilation pattern (55) (with regard to pressure, flow, volume, frequency) when the sensor device (3) has an unchanged EIT sum signal (44') compared to the first ventilation pattern (45) and an increased level of carbon dioxide supply, wherein the second ventilation pattern (55) can have an increased mandatory frequency compared to the first ventilation pattern (45) when the EIT change frequency (44") is reduced.

[0080] The control device (21) controls the respiratory gas source to specify a second ventilation pattern (55) when the sensor device (3) has a reduced EIT sum signal (44') compared to the first ventilation pattern (45), a reduced EIT change frequency (44") and an increased level of carbon dioxide supply, wherein the second ventilation pattern (55) can have an increased mandatory frequency and / or an increased tidal volume and / or an increased pressure support compared to the first ventilation pattern (45).

[0081] The control device (21) controls the respiratory gas source to specify a second ventilation pattern (55) when the sensor device (3) has an increased EIT sum signal (44') compared to the first ventilation pattern (45), an unchanged EIT change frequency (44") and an increased level of carbon dioxide supply, wherein the second ventilation pattern (55) can have a reduced tidal volume compared to the first ventilation pattern (45) and / or an automatic maneuver for assessing end-inspiratory over-expansion.

[0082] The control device (21) controls the respiratory gas source to specify a second ventilation pattern (55) (with regard to pressure, flow, volume, frequency) if the sensor device (3) has a reduced EIT sum signal (44') and / or a reduced EIT change frequency, compared to the first ventilation pattern (45), and a reduced measure for the oxygen supply, wherein the second ventilation pattern (55) can have an increased mandatory frequency compared to the first ventilation pattern (45) and / or an at least short-term increase in the oxygen admixture to the respiratory gas and / or an increase in tidal volume, delta-P or pressure support and / or a change in the ventilation pattern.

[0083] The control device (21) controls the respiratory gas source to specify a second ventilation pattern (55) (with regard to pressure, flow, volume, frequency) if the sensor device (3) has an unchanged EIT sum signal (44') and / or an unchanged EIT change frequency, compared to the first ventilation pattern (45), and a reduced level for the oxygen supply, wherein the second ventilation pattern (55) can have an increased mandatory frequency compared to the first ventilation pattern (45) and / or an at least short-term increase in the oxygen admixture to the respiratory gas and / or an adjustment of the PEEP.

[0084] The control device (21) controls the respiratory gas source to specify a second ventilation pattern (55) (with regard to pressure, flow, volume, frequency) when the sensor device (3) has an increased EIT sum signal (44') and / or a reduced EIT change frequency, compared to the first ventilation pattern (45), and a reduced measure of the oxygen supply, wherein the second ventilation pattern (55) can have an increased frequency, compared to the first ventilation pattern (45), and / or an at least brief increase in the inspiration time and / or an adjustment of the PEEP and / or a change in the ventilation pattern. Table 3 Ventilator controlled Sensory monitoring of resulting carbon dioxide and / or oxygen and / or EIT (Step-by-step) adjustment of the PEEPS (to test the individually required PEEPS) Until oxygen increases or remains stable without carbon dioxide increasing (gradual) lowering of inspiratory oxygen concentration Until oxygen reaches the desired target corridor (Step-by-step) adjustment of IPAP and / or EPAP Until oxygen increases or remains stable without carbon dioxide increasing and / or EIT sum signal unchanged (stepwise) adjusting the frequency Until oxygen increases or remains stable without carbon dioxide increasing and / or EIT sum signal unchanged

[0085] Table 3 is to be understood according to the invention as follows: The control device (21) controls the respiratory gas source to specify a first PEEP (45) and stores the resulting first sensor (measured) values ​​of at least one sensor device (2, 3, 30, 40). The control device (21) controls the respiratory gas source to specify a second PEEP (55) and stores the resulting second sensor (measured) values ​​of at least one sensor device (2, 3, 30, 40). The control device (21) then compares the first sensor (measured) values ​​with the second sensor (measured) values ​​to determine the more suitable PEEP pressure.

[0086] This procedure can be performed for n different PEEP pressures to determine the ideal PEEP pressure.

[0087] According to the invention, Table 3 is generally to be understood as follows: The control device (21) controls the respiratory gas source to specify a first ventilation pattern (45) and stores the resulting first sensor (measurement) values ​​of at least one sensor device (2, 3, 30, 40). The control device (21) controls the respiratory gas source to specify a second ventilation pattern (55) and stores the resulting second sensor (measurement) values ​​of at least one sensor device (2, 3, 30, 40).

[0088] The control device (21) then compares the first sensor (measured) values ​​with the second sensor measured values ​​to determine the more suitable ventilation pattern.

[0089] This procedure can be performed for n different ventilation patterns to determine the ideal ventilation pattern (45,55 ...).

[0090] The decision as to which ventilation pattern is more suitable or optimal is made based on stored or storable standard values ​​and limit values ​​for at least one, preferably at least two, of the sensor measurements, for example as a suggestion for the physician or user on the device's display or via remote transmission to a display. The user can then select the more suitable ventilation pattern and have it executed, or modify the ventilation pattern further and then have it executed. Alternatively, the device itself can determine which ventilation pattern is more suitable based on stored or storable standard values ​​and limit values ​​for at least one, preferably at least two, of the sensor measurements and execute it.

[0091] For example, the control device 21 regulates the ventilator's target device parameters, which have previously been individually calculated and determined based on the patient's characteristic breathing pattern, which was determined by sensors (2, 3, 30, 40). It is also possible for the respiratory gas source 100 to be adjusted dynamically, in particular depending on the patient's breathing phase. For example, the control device 21 can detect a change in breathing phase, so that a higher or lower pressure can be provided depending on the breathing phase. For example, the ventilator reacts to certain breathing events, such as snoring, shallow breathing, and / or obstructive pressure peaks, by adjusting the device parameters accordingly.

[0092] The pressure conditions recorded by the control device 21 are stored together with other device parameters in a memory device 31. Furthermore, the pressure conditions set by the control device 21 or the pressure adjustments made are also stored as device parameters in the memory device 31. The recorded patient parameters can also be stored in the memory device 31. The sensor values ​​of the sensors (2, 3, 30, 40) are also at least partially stored in the memory device 31.

[0093] For example, a starting therapy pressure, a maximum therapy pressure, a minimum therapy pressure, and / or a target volume and / or other device parameters suitable for adjusting the respiratory gas source 100 can be stored as device parameters. These device parameters are retrieved from the storage device 31 by the control device 21 for adjusting the respiratory gas source 100.

[0094] Furthermore, the pressure conditions and / or other device parameters and / or patient parameters recorded over the therapy period are stored in the storage device 31 as therapy courses. For example, a flow course, a pressure course, and / or an event course can be recorded as therapy courses. The therapy courses are provided to the storage device 31 by the control device 21, which records this data during the therapy.

[0095] The therapy data can also be read out via a display 11 located in the device 1 and / or connected to the device 1 or a user interface 61.

[0096] In some cases (ventilation insufficiency, formerly global respiratory insufficiency) with elevated pCO 2 values, the supply of oxygen and the exhalation of carbon dioxide is only possible with simultaneous ventilation.

[0097] For example, the control device (21) controls the respiratory gas source to specify a first ventilation pattern (45) in which the EPAP pressure has a first value or a first profile, wherein the sensor device (3) for noninvasively determining the electrical impedance (EI) determines the resulting ventilation of the lungs, and wherein the second sensor device (30) determines the carbon dioxide supply and / or wherein the third sensor device (40) determines the oxygen supply to the patient. The control device (21) stores the sensor measured values ​​that occur during ventilation with the first pattern.

[0098] The EPAP pressure may have an initial value that is changed automatically or by user selection in subsequent ventilation cycles. The change may be an increase or a decrease. The goal of the change is to find the EPAP pressure at which the sensor readings (3, 30, 40) can be interpreted as an improvement in ventilation and / or oxygenation.

[0099] In this sense, the EPAP pressure can also have an initial curve that is changed automatically in subsequent ventilation cycles or at the user's discretion.

[0100] For example, EPAP may rise at the beginning of exhalation and then fall, or reach a maximum or minimum value mid-exhalation. Alternatively, EPAP may also reach a maximum value at the end of exhalation. EPAP may also assume different pressure levels during exhalation.

[0101] Such titration can also be performed for IPAP (either separately from EPAP or in synchronized change with EPAP). In this sense, IPAP pressure can also have an initial curve that is changed automatically or at the user's discretion in subsequent ventilation cycles.

[0102] For example, IPAP may rise at the beginning of inspiration and then fall, or reach a maximum or minimum value mid-inspiration. Alternatively, IPAP may also reach a maximum value at the end of inspiration.

Claims

1. A ventilation device (10), comprising at least one ventilator (1) with at least one controllable respiratory gas source (100) and a programmable control apparatus (21) and at least one sensor apparatus (2) for determining pressure and / or flow of the respiratory gas, wherein the control apparatus (21) controls the respiratory gas source to specify a first ventilation pattern (45) (regarding pressure, flow, volume, frequency), wherein in the ventilation device has three further sensor apparatuses (3, 30, 40), wherein one sensor apparatus (3) has a plurality of individual sensors (3, 3', 3"...), which are designed to generate and / or measure electrical potentials and are designed to non-invasively determine the electrical impedance (EI) of the lung of a patient, wherein the second sensor apparatus (30) is designed to non-invasively determine the carbon dioxide provision, wherein the third sensor apparatus (40) is designed to non-invasively determine the oxygen provision of the patient, wherein the control apparatus (21) analyzes the sensor measured values of the El sensor apparatus (3) to determine the instantaneous ventilation (44) of the lung during ventilation with the first ventilation pattern (45), wherein the control apparatus (21) analyzes the sensor measured values of the second sensor apparatus (30) to determine the instantaneous carbon dioxide provision (46), and wherein the control apparatus (21) analyzes the sensor measured values of the third sensor apparatus (40) to determine the instantaneous (47) oxygen provision, characterized in that the control apparatus (21) controls the respiratory gas source to specify a second ventilation pattern (55) when the sensor apparatus (3) has an increased EIT sum signal (44') and / or a reduced EIT change frequency, compared to the first ventilation pattern (45), and a reduced measure of the oxygen provision, wherein the second ventilation pattern (55) has an increased frequency, compared to the first ventilation pattern (45), and / or an at least temporary increase in the inspiration time and / or an adjustment of the PEEP.

2. The ventilation device according to claim 1, characterized in that the control apparatus (21) controls the respiratory gas source to specify a first ventilation pattern (45) and stores the resulting first sensor (measured) values of at least one sensor apparatus (2, 3, 30, 40), wherein the control apparatus (21) then controls the respiratory gas source to specify a second ventilation pattern (55) and stores the resulting second sensor (measured) values of at least one sensor apparatus (2, 3, 30, 40) and compares the first sensor (measured) values with the second sensor measured values.

3. The ventilation device according to claim 1 or 2, characterized in that the ventilation device (10) has at least one memory unit (31) that communicates with the control apparatus and in which at least standard values (62) and / or limit values (63) for the carbon dioxide provision and for the oxygen provision are saved.

4. The ventilation device according to claim 1, 2, or 3, characterized in that the control apparatus (21) controls the respiratory gas source to specify a second ventilation pattern (55), which is different from the first ventilation pattern (45) with regard to pressure and / or flow and / or volume and / or frequency, when the sensor measured values of the instantaneous carbon dioxide provision (46) and / or the sensor measured values of the instantaneous (47) oxygen provision deviate from the standard values (62) and / or limit values (63) are at least reached.

5. The ventilation device according to at least one of the preceding claims, characterized in that standard values (72) and limit values (73) for the ventilation (44) of the lung are saved in the memory (31) and the control apparatus (21) controls the respiratory gas source to specify a second ventilation pattern (55), which is different from the first ventilation pattern (45) with regard to pressure and / or flow and / or volume and / or frequency, when the instantaneous ventilation (44) deviates from the standard values (72) and limit values (73) are at least reached.

6. The ventilation device according to at least one of the preceding claims, characterized in that the control apparatus (21) analyzes the sensor measured values of the El sensor apparatus (3) to determine the resulting ventilation (54) of the lung during the ventilation with the second ventilation pattern (55), wherein the control apparatus (21) analyzes the sensor measured values of the second sensor apparatus (30) to determine the resulting carbon dioxide provision (56) during the ventilation with the second ventilation pattern (55), wherein the control apparatus (21) analyzes the sensor measured values of the third sensor apparatus (40) to determine the resulting oxygen provision (57) during the ventilation with the second ventilation pattern (55), and wherein the control apparatus (21) compares the instantaneous ventilation (44) with the resulting ventilation (54).

7. The ventilation device according to at least one of the preceding claims, characterized in that the control apparatus (21) controls the respiratory gas source to specify a second ventilation pattern (55), which is different from the first ventilation pattern (45) with regard to pressure and / or flow and / or volume and / or frequency, so that the sensor measured values of the resulting carbon dioxide or oxygen provision at least approximate target values.

8. The ventilation device according to at least one of the preceding claims, characterized in that the control apparatus (21) controls the respiratory gas source to specify a second ventilation pattern (55), which is different from the first ventilation pattern (45) with regard to pressure and / or flow and / or volume and / or frequency, when the sensor measured values of the instantaneous ventilation (44) and / or the sensor measured values of the instantaneous (47) oxygen partial pressure deviate from the standard values (62) and limit values (63) are at least reached.

9. The ventilation device according to at least one of the preceding claims, characterized in that the control apparatus (21) controls the respiratory gas source to specify a second ventilation pattern (55), which is different from the first ventilation pattern (45) with regard to pressure and / or flow and / or volume and / or frequency, when the sensor apparatus (3) identifies an unchanged EIT sum signal (44') and a high or increased EIT change frequency (44"), wherein the second ventilation pattern (55) has an increased mandatory frequency compared to the first ventilation pattern (45).

10. The ventilation device according to at least one of the preceding claims, characterized in that the control apparatus (21) controls the respiratory gas source to specify a second ventilation pattern (55), which is different from the first ventilation pattern (45) with regard to pressure and / or flow and / or volume and / or frequency, when the sensor apparatus (3) has an unchanged EIT sum signal (44'), compared to the first ventilation pattern (45), and a reduced measure of the carbon dioxide provision, wherein the second ventilation pattern (55) has an increased mandatory frequency compared to the first ventilation pattern (45).

11. The ventilation device according to at least one of the preceding claims, characterized in that the control apparatus (21) controls the respiratory gas source to specify a second ventilation pattern (55), which is different from the first ventilation pattern (45) with regard to pressure and / or flow and / or volume and / or frequency, when the sensor apparatus (3) has a reduced EIT sum signal (44'), compared to the first ventilation pattern (45), and a reduced measure of the carbon dioxide provision, wherein the second ventilation pattern (55) has an increased mandatory frequency, compared to the second ventilation pattern (45), and / or an increased tidal volume and / or an increased pressure support.

12. The ventilation device according to at least one of the preceding claims, characterized in that the control apparatus (21) controls the respiratory gas source to specify a second ventilation pattern (55), which is different from the first ventilation pattern (45) with regard to pressure and / or flow and / or volume and / or frequency, when the sensor apparatus (3) has an unchanged EIT sum signal (44') and an increased measure of the carbon dioxide provision, wherein the second ventilation pattern (55) has a changed EPAP pressure or curve compared to the first ventilation pattern (45).

13. The ventilation device according to at least one of the preceding claims, characterized in that the control apparatus (21) controls the respiratory gas source to specify a second ventilation pattern (55), which is different from the first ventilation pattern (45) with regard to pressure and / or flow and / or volume and / or frequency, when the sensor apparatus (3) has an unchanged EIT sum signal (44'), compared to the first ventilation pattern (45), and an increased measure of the carbon dioxide provision, wherein the second ventilation pattern (55) can have an increased mandatory frequency compared to the first ventilation pattern (45) when the EIT change frequency (44") is reduced.

14. The ventilation device according to at least one of the preceding claims, characterized in that the control apparatus (21) controls the respiratory gas source to specify a first PEEP (45) and stores the resulting first sensor (measured) values of at least one sensor apparatus (2, 3, 30, 40), wherein the control apparatus (21) then controls the respiratory gas source to specify a second PEEP (55) and stores the resulting second sensor (measured) values of at least one sensor apparatus (2, 3, 30, 40), wherein the sensor apparatus (21) then compares the first sensor (measured) values with the second sensor measured values.

15. The ventilation device according to at least one of the preceding claims, characterized in that the control apparatus (21) controls the respiratory gas source to specify a first ventilation pattern (45), in which the EPAP pressure has a first value or a first curve, wherein the sensor apparatus (3) determines the resulting ventilation of the lung to non-invasively determine the electrical impedance (EI) and wherein the second sensor apparatus (30) determines the carbon dioxide provision and / or wherein the third sensor apparatus (40) determines the oxygen provision of the patient, wherein the control apparatus (21) stores the sensor measured values that occur during the ventilation with the first pattern, wherein the control apparatus (21) controls the respiratory gas source to specify a second ventilation pattern (55), in which the EPAP pressure has a second value or a second curve, wherein the sensor apparatus (3) determines the resulting ventilation of the lung to non-invasively determine the electrical impedance (EI) and wherein the second sensor apparatus (30) determines the carbon dioxide provision and / or wherein the third sensor apparatus (40) determines the oxygen provision of the patient, wherein the control apparatus (21) stores the sensor measured values that occur during the ventilation with the second pattern, and wherein the control apparatus (21) compares the sensor measured values that occur after application of the first ventilation pattern with the sensor measured values that occur after application of the second ventilation pattern and / or displays them as a comparison on the display.

16. The ventilation device according to at least one of the preceding claims, characterized in that the control apparatus (21) monitors at least one sensor signal (2, 3, 30, 40) for errors in that, when limit values of an instantaneous sensor signal (2, 3, 30, 40) are reached, said sensor signal is compared with another instantaneous sensor signal (2, 3, 30, 40) to detect if there is an error.