Device and method for non-invasive determination of a wedge pressure in the lung of a patient

Abstract

The invention relates to a device and a method for the non-invasive determination of a variable which is representative of a wedge pressure, and to a system having a ventilator, to a computer program and to a computer program product. The device (10) comprises an input (13) for data of a respiration pressure of a ventilator (30) over at least one respiratory cycle, an input (12) for EIT data from an EIT apparatus (20) collected during the at least one respiratory cycle, and a computing unit (14). The computing unit is designed to determine, based on the data of the ventilator and the EIT apparatus, the first temporal derivation of EIT values depending on the respiration pressure over at least one respiratory cycle. The computing unit (14) is furthermore designed to determine at least one characteristic property of the curve which is representative of the wedge pressure, in particular a characteristic expiratory curve point, further in particular the deflection point, the inflection point and / or the minimum, of the first temporal derivation of the EIT values depending on the respiration pressure.

Description

[0001] Device and method for the non-invasive determination of a

[0002] Closing pressure in a patient's lungs

[0003] The invention relates to a device and a method for the non-invasive determination of a quantity which is representative of a closing pressure in the lung of a patient, as well as to a system with a ventilator, a computer program and a computer program product.

[0004] Each year, more than 230 million people receive intraoperative mechanical ventilation to support respiratory function. In addition, a large number of patients are ventilated in intensive care units, sometimes for extended periods.

[0005] Mechanical ventilation is viewed controversially because it can entail cardiovascular and pulmonary risks and complications, even though its goal should be the protection or treatment of those organ systems. With every indication for ventilation, there is a potential for lung damage to be triggered by mechanical ventilation, even in previously healthy lungs. High ventilation pressures, which can lead to increased transpulmonary pressure (TPP) and even barotrauma, have been shown to be particularly damaging.

[0006] Choosing a suitable form of ventilation and adjusting the ventilation parameters to achieve sufficient ventilation and oxygenation without damaging the lungs therefore always represents a challenge.

[0007] Transpulmonary pressure is the pressure difference between intrapulmonary and extrapulmonary pressure, or in other words, between alveolar pressure and pleural pressure. Transpulmonary pressure largely determines the available lumen of the peripheral lungs (bronchioles, pulmonary alveoli).

[0008] The transpulmonary pressure determines the expansion and volume of the alveoli. The respiratory change in the transpulmonary pressure causes the inflow and outflow of respiratory air.

[0009] Alveolar collapse can occur with negative transpulmonary pressure and alveolar overdistension can occur with excessive transpulmonary pressure, e.g., during invasive ventilation.

[0010] Overstretching or collapsing of alveoli can be prevented and at the same time the tension in the individual alveoli can be kept as low as possible by aiming for transpulmonary pressure values ​​of less than 25 mbar, depending on the ventilation settings.

[0011] Transpulmonary pressure allows us to determine the respective contributions of the thorax and lungs to the overall compliance of the pulmonary-thoracic system. It is lowest at the end of expiration and highest at the end of inspiration. Since a direct measurement of pleural pressure would only be possible via thoracentesis, esophageal pressure is usually measured using an esophageal probe.

[0012] However, this method also has disadvantages, since the absolute values ​​of the esophageal pressure depend on numerous factors.

[0013] These include, among other things, the respective respiratory mechanics, lung volume, the weight of the mediastinum and abdomen, the patient's posture, the responsiveness of the smooth muscles, and the mechanical properties and inflation status of the inserted balloon. Furthermore, catheter placement and subsequent interpretation of the measured values ​​require a high degree of expertise, given the strong dependence on position and measurement site, as well as the interference from cardiac artifacts. For example, insufficient balloon blockage leads to incorrect pressure transmission, so that the pressures are incorrectly measured as too high.

[0014] The basis of a lung-protective ventilation strategy is to expose the lungs to as little mechanical stress as possible and to prioritize this protection over optimal oxygenation and ventilation. Ventilation with a smaller tidal volume (VT) applied per breath causes less ventilation-associated lung injury and significantly improves the survival of patients suffering from acute respiratory distress syndrome (ARDS).

[0015] To protect the tissue, the level of positive end-expiratory pressure (PEEP) is selected to reduce the pressure amplitude during mechanical ventilation. PEEP refers to the pressure present in the lungs at the end of expiration. It represents the lowest pressure value in the respiratory cycle.

[0016] The individual optimal PEEP is set according to Talmor within the framework of transpulmonary pressure monitoring. This involves placing an esophageal catheter, which allows measurement of the regional esophageal pressure in the area around the catheter. By subtracting this pressure from the global airway pressure (P AW ) the transpulmonary pressure TPP can be calculated.

[0017] To avoid atelectasis, PEEP is selected to achieve a resulting end-expiratory TPP value between 0 and 10 mbar, which is as close as possible to 0 mbar, but does not reach negative values. On the other hand, to limit tension in the individual alveoli, the tidal volume VT applied per breath is adjusted so that end-inspiratory TPP values ​​are always less than 25 mbar.

[0018] Electrical impedance tomography (EIT) is a non-invasive imaging technique that relies on the application of current and the measurement of voltage through electrodes attached to a patient's body. EIT provides images of the distribution of electrical conductivity, admittance, impedance, or resistance, or changes in these. The measured values ​​are usually referred to as EIT values, impedance values, or impedance measurements. This distribution is also referred to as "electrical properties."

[0019] The image is called an EIT image. The image or image sequences show differences in the electrical properties of various body tissues, bones, skin, body fluids, and organs, especially the lungs, which are useful for monitoring the patient's condition.

[0020] A typical EIT arrangement is shown in WO 2015 / 048917 A1. A series of electrodes is arranged on a belt so that they are placed at a specific distance from each other around the patient's chest and are in electrical contact with the skin. An electrical current or voltage input signal is applied alternately between different or all possible electrode pairs. While the input signal is applied to one of the electrode pairs, the currents or voltages between the remaining electrodes can be measured. The measured electrical voltages of the body section can be reconstructed into electrical properties or changes in electrical properties using a reconstruction algorithm. These can be used by a data processor to obtain a representation of the distribution impedance values ​​across a cross-section of the patient around which the electrode belt ring is placed.The electrical properties are displayed on a screen.

[0021] In the EIT procedure, a series of impedance measurements is recorded at, for example, 16, 32, or more electrodes. From these impedance measurements, the EIT image reconstruction algorithm can then generate two-dimensional images with pixels representing lung properties. The image can consist of 32 x 32 pixels representing locations inside and outside the lung.

[0022] The information on electrical properties obtained by EIT can be projected into a cross-sectional image derived from an anatomical model in an anatomical context, showing, for example, contours representing the outer boundaries of the modeled organs within the electrode plane.

[0023] Contours of functional structures can be used to (automatically) cluster pixels within such structures to form so-called "regions of interest" (ROIs) that correspond to functionally significant anatomical structures such as the lungs. Signals from pixels falling within such ROIs can be identified using automatic signal processing tools and algorithms and analyzed separately for each of the ROIs.

[0024] Up to 100 or more tomographic EIT images can be reconstructed per second. These high-resolution images reflect the regional electrical properties in the lung tissue, which are influenced by respiratory and cardiac cycles. Unlike CT scans, EIT images do not reveal morphological but rather functional information, such as regional tidal ventilation, local lung recruitment, expiratory time constants, or the distribution of lung perfusion. The data measured by EIT correlate with the corresponding lung volumes at the regional or pixel level.

[0025] Scaramuzzo et al. (Scaramuzzo G, Spandaro S, Spinelli E, Saldmann AD, Bohm SH, Ottaviani I, Montanaro F, Gamberini L, Marangoni E, Amuri T and Volta CA (2021) Calculation of Transpulmonary Pressure From Regional Ventilation Displayed by Electrical Impedance Tomography in Acute Respiratory Distress Syndrome. Front Physiol. 12:693736. doi: 10.3389 / fphys .2021.693736) propose using the relationship between regional parameters measured with EIT to estimate the difference between end-inspiratory and end-expiratory transpulmonary pressure (DP L ) non-invasively.

[0026] Strodthoff et al. (Strodthoff N, Strodthoff C, Becher T, Weiler N, Frerichs I. arXiv: 2010.09622vl [eess.IV] 19 Oct 2020) use AI to derive certain physiological parameters from measured EIT data. Among other things, esophageal pressure is to be determined noninvasively from a combination of EIT data and absolute airway pressure. The values ​​determined using the methods of Scaramuz zo et al. and Strodthoff f et al. are generally too imprecise for differentiated ventilation settings for an individual patient.

[0027] Becher et al. (Ann. Intensive Care (2021) 11:89) developed a protocol to individualize PEEP and tidal volume based on EIT-based data. However, this protocol does not replace transpulmonary pressure monitoring using an esophageal tube.

[0028] The object is to provide a device, a system, a method and a computer program which overcome the disadvantages of the known methods, by means of which in particular a value which is representative of the transpulmonary pressure can be determined as accurately as possible without performing an invasive procedure on the patient, in particular without having to insert an esophageal probe.

[0029] The above object is achieved with a device, a system, a method as well as a computer program and a computer program product according to the independent claims.

[0030] The device is a device for the non-invasive determination of a parameter representative of the closure pressure. The closure pressure is the airway pressure at which the expiratory transpulmonary pressure becomes less than or equal to zero.

[0031] The device comprises an input for ventilation pressure data from a ventilator over at least one ventilation cycle. The ventilator generates a controlled profile with an increasing and subsequent decreasing pressure ramp over the ventilation cycle. The input is used to receive the pressure profile data.

[0032] The pressure profile can also be generated by another suitable device and the data from this device can be received at the input.

[0033] This could be a device that generates a flow of breathing gas, for example a flowmeter, which measures the prevailing pressure and then gradually increases the flow to achieve the desired pressure.

[0034] However, it could also be a specially developed device that connects a gas source to a pressure sensor and a controller that then controls or regulates this ramp.

[0035] The pressure profile can begin at a previously defined PEEP or at a ZEEP (zero end-expiratory pressure) and, in particular, increase linearly over time beyond the opening or recruitment pressures up to a maximum. After reaching the maximum, the pressure can be reduced in a ramp-like manner, in particular linearly over time, until it has reached the previous PEEP level or ZEEP.

[0036] The device further comprises an input for EIT data from an EIT device collected during at least one ventilation cycle. This data can be received from the device at the EIT data input.

[0037] The EIT device can provide data that, for example, contains information about local impedances or conductivities. EIT values ​​refer to the changes in the EIT data, particularly the measured impedances or conductivities, compared to a baseline or reference value.

[0038] EIT images can be displayed as impedance or conductivity images. The EIT values ​​can therefore generally represent impedance changes or conductivity changes.

[0039] The EIT values, which can be recorded pixel by pixel as regional EIT values, for example, correlate with the corresponding lung volumes.

[0040] The device also comprises a computing unit designed to determine a first time derivative of the EIT values ​​over at least one ventilation cycle on the basis of the data from the ventilator and the data from the EIT device and to relate them to the ventilation pressure.

[0041] The determination can be made pixel by pixel or across multiple pixels, in particular across a row or column or across all relevant pixels.

[0042] Pixels that represent volumes that contribute to lung ventilation can be considered as relevant pixels.

[0043] If the EIT values ​​are derived over time, the resulting values ​​indicate the change in the EIT values ​​over time. The latter correlate with the volume flow or the flow of respiratory gases. Particularly at the regional level, EIT can be used to determine the first time derivative of the EIT values, in particular the time derivative of the impedance of each pixel, as a surrogate parameter for the regional flow dV / dt in this lung region.

[0044] The computing unit is designed to determine at least one characteristic property of the curve of the first time derivative of the EIT values ​​versus the ventilation pressure. The curve shape and thus this characteristic property is representative of the closure pressure, i.e., the airway pressure at which the transpulmonary pressure becomes less than or equal to zero.

[0045] A characteristic property of a curve is understood to be a property that results from a curve discussion, such as the position of at least one extreme point, at least one inflection point and / or at least one curvature or the limit behavior.

[0046] For this purpose, the temporal behavior of the EIT values ​​of a specific preselected pixel or the EIT values ​​of several pixels are considered, whose EIT values, temporal profiles, or characteristic properties are subsequently averaged. The pixels to be averaged can be arranged in a specific preselected pixel area, in one or more specific preselected pixel rows, or in one or more specific preselected pixel columns, for example, a pixel row whose position corresponds to the height of the esophagus.

[0047] The computing unit may be configured to receive data characterizing the specific preselected pixel region, for example, the number of the pixel row or the pixel column. The device may comprise an input unit via which a user enters the corresponding data.

[0048] The computing unit can be designed to use additional image data, for example computer tomography images, X-ray images or ultrasound images, and to select the specific preselected pixel area, for example a specific pixel row, on the basis of the additional image data.

[0049] As the airway pressure increases, air flows into the lungs. The volume may initially rise roughly proportionally to the increase in pressure, so that the flow curve can run roughly parallel to the pressure axis. As soon as additional lung areas that were previously inaccessible are opened up (recruitment), the flow increases disproportionately. This opening can happen suddenly. As long as further lung areas are recruited, the flow remains high. If no further lung areas are opened up by the increasing pressure, the flow can again run parallel to the pressure axis. The lungs do not open up further. This flow can be increased compared to the initial flow, i.e. shifted parallel.

[0050] The exposed lung areas will only be further filled with additional pressure. Therefore, a further increase in pressure is no longer effective.

[0051] The pressure can therefore be reduced again. Gas flows out of the lungs. This generates a negative flow that is initially constant. The flow curve therefore runs parallel to the pressure axis again. If the pressure reaches values ​​that are no longer sufficient to stabilize the alveoli, the alveoli begin to collapse, which can happen suddenly. In this usually sudden lung collapse, a disproportionate amount of gas flows out of the lungs.

[0052] This is reflected in an increase in the negative flow.

[0053] If further lung tissue collapses with further pressure reduction, the flow remains high and only subsides again when the collapse process is complete.

[0054] The flow then runs parallel to the pressure axis again.

[0055] Since the first time derivative of the EIT values ​​corresponds to the temporal change in lung volume, the curve of the first time derivative of the EIT values ​​over the ventilation pressure is analogous to the flow.

[0056] According to a preferred embodiment of the invention, at least one characteristic curve point can be determined as a characteristic property of the curve of the first time derivative of the EIT values.

[0057] Expiratory curve points lie within a pressure range that begins when pressure is reduced and typically ends when PEEP is reached. The alveoli may collapse during expiration.

[0058] The characteristic expiratory curve points to be determined are characteristic of the collapse of the alveoli, especially the initial collapse, which typically occurs when the expiratory transpulmonary pressure becomes negative. Since the airway pressure is known from the ventilation ramp, the esophageal pressure at the time of alveolar collapse can be deduced.

[0059] In particular, the deflection point, the inflection point and / or the minimum of the first time derivative of the EIT values ​​as a function of the ventilation pressure can be determined.

[0060] For the entire lung, the characteristic expiratory curve point lies between the onset of collapse, i.e., the point at which the curve deviates from the parallel straight line (deflection point), and the negative flow maximum, at which flow and thus collapse are in full swing. The latter tends to be too late, while the former tends to be early.

[0061] These characteristic expiratory curve points can be determined by a further derivative of the flow curve with respect to time, i.e. by means of tangent formation.

[0062] The inflection point of the expiratory curve, where the gradient of the derivative is greatest, lies between the deflection point and the maximum. The pressure at this point may be closest to the desired pressure value.

[0063] The EIT values ​​can be time-dependent and plotted against the ventilation pressure. Extremes, inflection points, and limit violations can be identified on this curve using standard computer-assisted methods.

[0064] The EIT signals are generally superimposed by cardiogenic (heartbeat-related) oscillating signals. The computing unit can be configured to filter the cardiogenic signals from the EIT data of the EIT device to extract the ventilation-related signals.

[0065] The computing unit can be designed to pass the data through a filter adapted to the heart rate, for example a low-pass filter, a bandpass or a bandstop, in which frequencies of one to four times the heart rate are preferentially filtered out of the EIT signal, i.e. frequencies in the range of 0-0.2Hz.

[0066] The computing unit may be designed to determine a PEEP value based on the characteristic property of the curve, in particular based on the characteristic expiratory curve point.

[0067] Those pixels located in the esophageal region should collapse when the transpulmonary pressure falls below zero. The airway pressure prevailing in the esophagus at this time corresponds exactly to the PEEP required to compensate for this collapse.

[0068] The pressure at the characteristic points on the curve, in particular the pressure at which the first signs of collapse are observed, is the pressure at which the expiratory transpulmonary pressure becomes less than or equal to zero. This pressure then corresponds to the PEEP required to compensate for the collapse and can therefore be considered the appropriate PEEP value to set.

[0069] The computing unit can be designed to determine the temporal derivative of the EIT values ​​regionally, in particular in the preselected pixel area and / or over one or more selected individual pixels, further in particular over pixel rows, for example over a preselected pixel row.

[0070] In this way, the time derivatives of the EIT values, in particular the impedance changes, of all pixels of an EIT image can be calculated and their course across the gravitational vector can be interpreted either in individual pixels or for entire pixel rows together.

[0071] In a patient lying on their back, the gravity vector becomes noticeable as an increasing pressure gradient from front to back in the lying lung.

[0072] All pixels in the respective rows that are perpendicular to the gravity vector can be summed and analyzed.

[0073] Of particular interest is the flow pattern in the pixel line of the EIT image that runs horizontally through the esophagus, because its behavior should reflect the situation in the esophagus.

[0074] The number of the corresponding pixel row can be selected and / or entered by the user and received by the computing unit. The computing unit can also be configured to determine the corresponding pixel row based on additional image data representing the esophagus.

[0075] If the EIT value in these pixels drops abruptly upon pressure reduction, it can be concluded that the pressure in the corresponding alveoli is no longer sufficient to prevent collapse. This point can therefore be interpreted as a sign of the transition from open to collapsed alveoli, which corresponds to a situation in which the transpulmonary pressure measured with an esophageal probe reaches a value close to zero.

[0076] The computing unit can be designed to determine a ventilation ramp. A linear ventilation ramp is characterized by the starting pressure, the positive slope, the maximum pressure, and the final pressure.

[0077] The pressure ramp can typically start at 0 mbar and increase linearly by 1 mbar / s. After reaching the maximum, the pressure ramp can be reduced by another 1 mbar / s.

[0078] The maximum and final pressure can be determined absolutely beforehand or can be derived from the measured data during the process.

[0079] The device may include an output for transmitting data to the ventilator, in particular data for a ventilation ramp and / or data for a specific PEEP value. The device is then designed as a device for controlling a ventilator.

[0080] The computing unit can be designed to determine the characteristic property of the curve and in particular the PEEP value before ventilation and / or during ventilation, in particular regularly.

[0081] This allows a constantly adjusted PEEP value to be determined and set, even during prolonged ventilation. The device may have a display unit, such as a screen, for showing the curves and / or the set values. The device may also include an output unit, via which curve data and / or the set values ​​are transmitted to an external display unit.

[0082] This value can also be output directly to a ventilator so that the PEEP can be adjusted.

[0083] The object is also achieved by a system comprising an EIT device, a ventilator and a device as described above.

[0084] The device can be an integral part of the EIT device and / or the ventilator.

[0085] The problem is also solved by a method for determining variables that are representative of the closure pressure, i.e. the airway pressure at which the expiratory transpulmonary pressure becomes less than or equal to zero.

[0086] Ventilation pressure values ​​are received from a ventilator over at least one ventilation cycle. In addition, EIT data are received from an EIT device, which are collected during at least one ventilation cycle.

[0087] A first time derivative of EIT values ​​is determined as a function of ventilation pressure over at least one ventilation cycle based on the data from the ventilator and the EIT device. At least one characteristic property of the curve of the first time derivative of the EIT values ​​as a function of ventilation pressure is determined.

[0088] The characteristic property is representative of the closure pressure .

[0089] In particular, at least one characteristic expiratory curve point is determined as a characteristic property.

[0090] In particular, the deflection point, the inflection point and / or the minimum of the first time derivative of the EIT values ​​as a function of the ventilation pressure is determined.

[0091] The method is carried out in particular with a device as described above.

[0092] During the slow pressure changes, the airway volume and / or the volume flow or flow of gases in the airways (dV / dt) can be measured simultaneously and synchronously over time using a gas flow sensor.

[0093] This ensures that the course of the global respiratory gas flow curve and the global EIT value (which is composed of all pixels) are very similar.

[0094] With a linear ventilation ramp, both the airway volume and the EIT values ​​exhibit a bell-shaped pattern. This is followed by a steep increase in the signal at the beginning of the ramp, which then levels off slightly as it progresses toward the maximum. After the maximum has been reached, the signal initially decreases slightly and then decreases more and more sharply, ending at a higher level than at the beginning of the ramp.

[0095] The PEEP value can be set based on the characteristic expiratory curve point.

[0096] The PEEP value can be output to the ventilator as a control variable. Ventilation can be performed based on this PEEP value.

[0097] The procedure can be performed before ventilation and / or during ventilation, particularly regularly.

[0098] The procedure can be carried out, for example, at predetermined time intervals or after a predetermined number of breaths.

[0099] The object is further achieved by a computer program with program code for carrying out the steps of the method as described above when the program is executed on a computer.

[0100] The object is further achieved by a computer program product which can be loaded directly into an internal memory of a digital computer and which comprises software code sections which carry out the method steps as described above when the program is run on the digital computer.

[0101] The invention is explained below with reference to drawings.

[0102] Fig. 1 shows the schematic structure of a system comprising a device according to the invention, an EIT device and a ventilator;

[0103] Fig. 2 shows the time course of ventilation pressure and flow;

[0104] Fig. 3 shows the flow plotted against the ventilation pressure;

[0105] Fig. 4 shows the first time derivative of an EIT value as a function of ventilation pressure for a healthy lung;

[0106] Fig. 5 shows the first time derivative of an EIT value as a function of ventilation pressure for an impaired lung;

[0107] Fig. 6 a comparison of a CT image and an EIT image;

[0108] Fig . 7 the first time derivatives of the regional EIT values ​​as a function of the ventilation pressure for a right and a left lung .

[0109] Figure 1 shows a system 1 with an EIT device 20 and a ventilator 30 .

[0110] The EIT device 20 includes an electrode belt 21 that can be attached to a patient and with which data for an EIT image can be acquired.

[0111] The system 1 also comprises a device 10 for the non-invasive determination of a quantity which is representative of the closure pressure, that is to say of the airway pressure at which the expiratory transpulmonary pressure becomes less than or equal to zero.

[0112] The device 10 has an input 13 for receiving ventilation pressure data from the ventilator 30 over at least one ventilation cycle. The device 10 also has an input 12 for receiving EIT data from the EIT device 20 collected during the at least one ventilation cycle.

[0113] The device 10 also has a computing unit 14 which is designed to determine the first time derivative of EIT values ​​as a function of the ventilation pressure over at least one ventilation cycle on the basis of the data from the ventilator 30 and the EIT device 20.

[0114] The computing unit is also designed to determine at least one characteristic property of the curve of the first time derivative of the EIT values ​​as a function of the ventilation pressure. In particular, a characteristic expiratory curve point is determined.

[0115] The device 10 comprises a display 16 for displaying the curve and / or the determined values.

[0116] The device includes an output 15 for outputting data to the ventilator 30.

[0117] The airway pressure p AW is plotted in Figure 2 synchronously with the flow dV / dt over time t. During pressure increase, the flow curve dV / dt shows a characteristic convexity, indicating the opening of lung areas. During pressure decrease, a concavity is visible, indicating the collapse of lung units.

[0118] The airway pressure p AWis only reduced to a predetermined PEEP value. Figure 3 shows the flow dV / dt plotted against the ventilation pressure PAW. The curve has some characteristic points.

[0119] The flow can be measured with a gas flow sensor. This measurement is not part of the inventive method.

[0120] On the path of pressure increase (upper part of the curve), a positive flow maximum A is reached. As the pressure is reduced, first a deflection point B is reached, then an inflection point C, and finally a negative flow maximum D.

[0121] Figure 4 shows an unfiltered original curve during the implementation of the method according to the invention. It shows the first temporal derivative of EIT values, in this case a relative impedance change, as a function of ventilation pressure, measured on the lung of a healthy pig, in this case summed over all relevant pixels.

[0122] It can be seen that the curve shape corresponds in principle to the flow curves shown in Figures 2 and 3. A correlation can be assumed between the time derivative of the EIT values ​​across all relevant pixels and the global airway flow dV / dt.

[0123] The superimposed heartbeat-synchronous oscillations can be seen.

[0124] In this case, the lungs do not open, as this requires airway pressures above 25 mbar. However, the convexity mentioned in Figure 2 can be seen with decreasing pressure. This indicates a certain degree of lung collapse, which reaches its maximum at approximately 10 mbar.

[0125] Figure 5 shows the corresponding curve measured in a pig in which a two-hour ventilator-induced lung injury (VILI) was induced, so that the lung corresponds to a lung in an ARDS state.

[0126] To investigate the ARDS-like state of lung damage, a two-stage surfactant lavage model is used. Following the first phase of measurements in a healthy lung state, the animals' lungs are repeatedly lavaged via an endotracheal tube with 35 ml / kg body weight of body-temperature, isotonic 0.9% sodium chloride (NaCl) solution. The surfactant is thus washed out of the lungs until a visually clear and non-foaming lavage solution is obtained.

[0127] After confirmation of this necessary condition, 120 minutes of lung-damaging ventilation is performed with an inspiratory oxygen fraction of 1.0, a PEEP of 0 mbar and tidal volume of 15 ml / kg at a respiratory rate of 12 breaths per minute and an inspiration to expiration ratio of 1:2.

[0128] During the pressure increase, the first time derivative of the EIT values, which corresponds to the flow, remains lower than in the healthy pig. The flow only increases when the lung begins to open. The maximum convexity is at approximately 37 mbar. The opening of lung areas is clearly visible but remains incomplete because the maneuver was accidentally aborted at approximately 42 mbar in this specific measurement. The maximum alveolar collapse is at approximately 10 mbar. Figure 6 shows a comparison of a CT image and an EIT image. The EIT image is a tidal image and shows the EIT values, in this case impedance changes, for each pixel in the measurement plane shown in the CT image.

[0129] The regional pixel impedance signal is assumed to correlate with the regional volume within that pixel.

[0130] The EIT image can be evaluated pixel-by-pixel or row-by-row. In this case, pixel row 20 corresponds to the height of the esophagus.

[0131] Pixels of the EIT image that represent less than 10% of the maximum impedance amplitude of this lung region are excluded from the analysis of the regional curves. They represent the so-called "silent spaces."

[0132] Figure 7 shows the first time derivatives of the regional EIT values ​​as a function of the ventilation pressure for the rows of the right and left lung.

[0133] For each pixel row, the results for the respective pixels are shown. The maxima of the curves are also marked.

[0134] It has been shown that the negative maxima of pixel row 20, which can be described as closure pressure, correlate with the PEEP according to Talmor measured in parallel via an esophageal probe.

[0135] Based on the EIT measurement, a value that is characteristic of the closure pressure can be determined. The individually optimal DEEP is set according to Talmor as part of transpulmonary pressure monitoring. This involves placing an esophageal catheter, which allows measurement of the regional esophageal pressure in the area around the catheter. By subtracting this pressure from the global airway pressure, the transpulmonary pressure can be calculated.

[0136] To avoid atelectasis, the PEEP is selected in such a way that the resulting end-expiratory transpulmonary pressure is between 0 and 10 mbar and is as close as possible to 0 mbar, but does not reach negative values.

[0137] On the other hand, to limit tensions in the individual alveoli, the tidal volume is adjusted so that end-inspiratory TPP values ​​are always less than 25 mbar.

[0138] The regional closure pressures can be used as a noninvasive surrogate parameter for the transpulmonary pressure according to Talmor for PEEP setting.

Claims

Patent claims 1. Device (10) for the non-invasive determination of a quantity representative of the closure pressure, comprising - an input (13) for data of a ventilation pressure from a ventilator (30) over at least one ventilation cycle; - an input (12) for EIT data from an EIT device (20) collected during at least one ventilation cycle; - a computing unit (14) which is designed to determine, on the basis of the data from the ventilator and the EIT device, the first time derivative of EIT values ​​as a function of the ventilation pressure over at least one ventilation cycle, and which is designed to determine at least one characteristic property of the curve of the first time derivative of the EIT values ​​as a function of the ventilation pressure, which is representative of the closure pressure, in particular a characteristic expiratory curve point, further in particular a deflection point, an inflection point and / or a minimum.

2. Device according to claim 1, wherein the computing unit is designed to determine a PEEP value based on the characteristic property of the curve, in particular the characteristic expiratory curve point.

3. Device according to claim 1 or 2, wherein the computing unit (14) is designed to determine the first time derivative of the EIT values ​​regionally, in particular via a one or more selected individual pixels, further in particular over a pixel row.

4. Device according to one of the preceding claims, wherein the computing unit (14) is designed to determine a ventilation ramp.

5. Device according to one of the preceding claims for controlling a ventilator, wherein the device comprises an output (15) for outputting data, in particular data for a ventilation ramp and / or data for a specific PEEP value, to the ventilator (30).

6. Device according to one of the preceding claims, wherein the computing unit (14) is designed to determine the characteristic property of the curve and in particular the PEEP value before ventilation and / or during ventilation, in particular regularly.

7. System (1) comprising an EIT device (10), a ventilator (30) and a device (1) according to one of the preceding claims.

8. System according to claim 7, wherein the device is an integral part of the EIT device (20) and / or the ventilator (30).

9. A method for determining variables representative of the closure pressure, comprising the steps of -receiving data of a ventilation pressure from a ventilator over at least one ventilation cycle, -receiving EIT data from an EIT device collected during the at least one ventilation cycle; -Determination of a first time derivative of the EIT values ​​as a function of the ventilation pressure over at least one ventilation cycle on the basis of the data from the ventilator and the EIT device, -Determination of at least one characteristic property of the curve of the first time derivative of the EIT values ​​as a function of the ventilation pressure, which is representative of the closure pressure, in particular a characteristic expiratory curve point, further in particular the deflection point, the inflection point and / or the minimum.

10. Method according to claim 9, wherein a PEEP value is determined based on the characteristic expiratory curve point.

11. Method according to claim 10, wherein the PEEP value is output to the ventilator as a control variable.

12. Method according to claim 11 or 12, wherein the ventilation is carried out on the basis of the PEEP value.

13. Method according to one of claims 9-12, wherein the method is carried out before ventilation and / or during ventilation, in particular on a rotating basis.

14. Computer program with program code for carrying out the steps of the method according to one of claims 9 to 13 when the program is executed on a computer. 15 . Computer program product that can be loaded directly into an internal memory of a digital computer and that includes software code sections that perform the method steps of at least one of claims 9 to 13 when the program is running on the digital computer.

Images