Apparatus and method for non-invasively determining the wedge pressure in a patient's lungs

Abstract

The present invention relates to an apparatus and method for non-invasively determining a quantity representative of wedge pressure, as well as a system, computer program, and computer program product comprising a ventilator. The device (10) comprises a data input unit (13) for ventilation pressure from a ventilator (30) over at least one ventilation cycle, an input unit (12) for EIT data from an EIT device (20) collected during at least one ventilation cycle, and a computing unit (14). It is designed to determine the first time derivative of the EIT value as a function of ventilation pressure over at least one ventilation cycle, based on data from the ventilator and the EIT device. The computing unit (14) is further designed to determine, with respect to the first time derivative of the EIT value as a function of ventilation pressure, at least one characteristic feature of the curve representing the wedge pressure, in particular a characteristic expiratory curve point, more specifically a deflection point, a turning point, and / or a minimum value.

Description

Technical Field

[0001] The present invention relates to an apparatus and method for non-invasively determining a quantity representative of a patient's pulmonary wedge pressure, and to a system, computer program, and computer program product comprising a ventilator.

Background Art

[0002] Each year, more than 230 million people are subjected to mechanical ventilation during surgery to assist lung function. Additionally, a large number of patients are ventilated in intensive care units, sometimes for extended periods.

[0003] Mechanical ventilation is debatable as it can carry risks and complications for the cardiovascular and lungs, despite the aim of protecting or treating these organ systems. In all cases where ventilation is required, mechanical ventilation can cause lung damage, even in previously healthy lungs. High ventilation pressures that lead to an increase in transpulmonary pressure (TPP) and can even cause barotrauma have been identified as particularly harmful.

[0004] Therefore, the selection of an appropriate ventilation mode and the adjustment of ventilation parameters to achieve appropriate ventilation and oxygen supply without damaging the lungs always pose challenges.

[0005] Therefore, it is always a challenge. Transpulmonary pressure is the pressure difference between the pressure inside the lungs and the pressure outside the lungs, i.e., the pressure difference between alveolar pressure and intrathoracic pressure. Transpulmonary pressure significantly determines the available lumen of peripheral lung segments (bronchioles, alveoli).

[0006] Transpulmonary pressure determines alveolar expansion and volume. Due to the respiratory changes in transpulmonary pressure, air enters and exits the lungs.

[0007] If transpulmonary pressure is negative, alveolar collapse may occur, and if transpulmonary pressure is too high, for example during invasive ventilation, alveolar hyperinflation may occur.

[0008] By aiming for transpulmonary pressure values ​​of less than 25 mbar, depending on the ventilation settings, it is possible to prevent alveolar hyperinflation or collapse while simultaneously minimizing the tension of individual alveoli.

[0009] Transpulmonary pressure allows us to determine the respective contributions of the thoracic cavity and lungs to the overall compliance of the lung-thoracic system. This is lowest at the end of exhalation and highest at the end of inspiration. Direct measurement of intrathoracic pressure is considered possible only by pleuropuncture, and esophageal pressure is usually measured as a substitute using an esophageal probe.

[0010] However, this method also has drawbacks because the absolute value of esophageal pressure depends on numerous factors.

[0011] These factors include respiratory mechanics, lung volume, mediastinal and abdominal weight, patient posture and position, smooth muscle responsiveness, and the mechanical properties and inflation state of the balloon used. Furthermore, catheter placement and subsequent interpretation of measurements require a high level of expertise due to the strong dependence on position and measurement location, as well as interference from cardiac artifacts. For example, insufficient balloon occlusion can lead to inaccurate pressure transmission, while excessively high pressure can result in mismeasurements.

[0012] The fundamental principle of lung-protective ventilation strategies is to minimize the mechanical stress on the lungs as much as possible, prioritizing this protection over optimal oxygen supply and ventilation. Low tidal volume (VT) ventilation causes less ventilation-related lung damage and significantly improves survival rates in patients who develop acute respiratory distress syndrome (ARDS).

[0013] To protect tissues, the level of positive end-expiratory pressure (PEEP) is selected for lung protection in a way that results in a reduction of pressure amplitude during mechanical ventilation. PEEP refers to the pressure present in the lungs at the end of exhalation. In the respiratory cycle, this represents the lowest pressure value.

[0014] According to Talmor, the optimal PEEP for an individual is set as part of transpulmonary pressure monitoring. This involves inserting an esophageal catheter, which is used to measure the local esophageal pressure in the area around the catheter. This pressure is called global airway pressure (PEEP). AW By subtracting from ), it becomes possible to calculate transpulmonary pressure TPP.

[0015] PEEP is selected to prevent atelectasis in such a way that the end-expiratory TPP value is achieved between 0 and 10 mbar, as close to 0 mbar as possible but never taking a negative value. On the other hand, to limit the tension of individual alveoli, the tidal volume (VT) applied per breath is set so that the end-spiratory TPP value is always less than 25 mbar.

[0016] Electrical impedance tomography (EIT) is a non-invasive imaging technique based on the application of electric current and measurement of voltage using electrodes attached to the patient's body. EIT provides images of conductivity, admittance, impedance, or resistance, or the distribution of changes in these parameters. The measured values ​​are commonly called EIT values, impedance values, or impedance measurements. This distribution is also called the "electrical properties."

[0017] The images are called EIT images. The images or image sequences show differences in the electrical properties of various body tissues, bones, skin, body fluids, and organs, particularly the lungs, which are useful for monitoring the patient's condition.

[0018] A typical EIT configuration is shown in International Publication No. 2015 / 048917. A series of electrodes are placed on a belt around the patient's chest at specific distances from each other, making electrical contact with the skin. Current or voltage input signals are alternately applied between different electrode pairs or all possible electrode pairs. While the input signal is applied to one of the electrode pairs, the current or voltage between the remaining electrodes can be measured. The voltages measured for the body parts can be reconstructed into electrical characteristics or changes in electrical characteristics using a reconstruction algorithm. These can be used by a data processor to obtain a representation of the distributed impedance values ​​in the cross-section of the patient where the electrode belt ring is placed. The electrical characteristics are displayed on a screen.

[0019] In the EIT method, a series of impedance measurements are recorded at, for example, 16, 32, or even more electrodes. From these impedance measurements, the EIT image reconstruction algorithm can generate a two-dimensional image with pixels representing the characteristics of the lung. The image can be composed of 32x32 pixels representing the internal and external positions of the lung.

[0020] Information regarding electrical properties obtained by EIT can be projected, for example, onto cross-sectional images derived from an anatomical model in an anatomical context that shows contours representing the outer boundaries of modeled organs within the electrode plane.

[0021] Using the contours of functional structures, pixels within such structures can be (automatically) clustered to form so-called "regions of interest" (ROIs) corresponding to functionally important anatomical structures such as the lungs. Signals from pixels contained within such ROIs can be identified by automated signal processing means and algorithms, and each ROI can be analyzed separately.

[0022] Up to 100 or more tomographic EIT images can be reconstructed per second. These high-temporal-resolution images reflect the local electrical properties of lung tissue, which are influenced by the respiratory and cardiac cycles. Unlike CT scans, EIT images do not show morphological information, but rather functional information such as local tidal volume, local lung recruitment, expiratory time constant, or pulmonary perfusion distribution. Data measured by EIT correlate with corresponding lung volume at the local or pixel level.

[0023] 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) used the relationship between local parameters measured by EIT to calculate the difference between end-spiratory transpulmonary pressure and end-expiratory transpulmonary pressure (DP). (L) It is proposed to determine this non-invasively.

[0024] Strodthoff et al. (Strodthoff N, Strodthoff C, Becher T, Weiler N, Frerichs I. arXiv:2010.09622v1[eess.IV]19 Oct 2020) used AI to derive specific physiological parameters from measured EIT data. In particular, esophageal pressure can be estimated non-invasively by using a combination of EIT data and absolute airway pressure.

[0025] The values determined using the methods of Scaramuzzo et al. and Strodthoff et al. are generally too inaccurate for the differential ventilation settings of individual patients.

[0026] Becher et al. (Ann. Intensive Care (2021) 11:89) have developed a protocol for individualizing PEEP values and tidal volume based on EIT-based data. However, this protocol does not replace transpulmonary pressure monitoring using an esophageal probe.

Summary of the Invention

Problems to be Solved by the Invention

[0027] [[ID=ID=14]]The problem is to overcome the drawbacks of the known art and, in particular, to provide an apparatus, system, method, and computer program that can determine as accurately as possible a variable representing transpulmonary pressure without performing invasive procedures on the patient, particularly without inserting an esophageal probe.

Means for Solving the Problems

[0028] The above problems are solved by the apparatus, system, method, computer program, and computer program product described in the independent claims.

[0029] The apparatus is for non-invasively determining a quantity representative of the wedge pressure. The wedge pressure is the airway pressure at which the transpulmonary pressure during exhalation becomes zero or less.

[0030] The apparatus comprises an input section for data on the ventilation pressure from a ventilator over at least one ventilation cycle. The ventilator generates a pressure profile controlled by a microcomputer over a ventilation cycle with a rising and subsequent falling pressure ramp. The input section is used to receive the data of the pressure profile.

[0031] The pressure profile can also be generated by another suitable device, and the data from this device can be received at the input unit.

[0032] This may be a device that generates a flow of breathing gas, such as a flow meter, which measures the current pressure and then gradually increases the flow rate to achieve a desired pressure.

[0033] However, this could be a specially developed device that connects a gas supply source to a pressure sensor and controller, and controls or adjusts this lamp with the controller.

[0034] The pressure profile can start at a predetermined PEEP or ZEEP ("zero end-expiratory pressure") and increase linearly over time, particularly beyond the release or recruitment pressure, up to a maximum value. After reaching the maximum value, the pressure can be decreased in a ramp-like manner, particularly linearly over time, until it returns to the previous PEEP or ZEEP level.

[0035] Furthermore, the device includes an input unit for EIT data collected from an EIT device during at least one ventilation cycle. This data can be received at the input unit for EIT data from the device.

[0036] The EIT device can provide data that includes, for example, information about local impedance or local conductivity.

[0037] The EIT value is the EIT data, specifically the measured change in impedance or conductivity, relative to a baseline or reference value.

[0038] EIT images can be displayed as impedance or conductivity images. Therefore, EIT values ​​can represent changes in impedance or conductivity.

[0039] For example, EIT values ​​that can be collected pixel by pixel as local EIT values ​​correlate with the corresponding lung volume.

[0040] Furthermore, the device includes a computing unit designed to determine the first time derivative of the EIT value over at least one ventilation cycle, based on data from the ventilator and data from the EIT device, and to correlate it with the ventilation pressure.

[0041] The decision can be made pixel by pixel, or across several pixels, and in particular across rows or columns, or across all relevant pixels.

[0042] Pixels representing the volume that contributes to lung ventilation can be considered as related pixels. When the EIT value is derived over time, this yields a value that shows the change in the aforementioned EIT value over time. The latter correlates with the volumetric flow rate or flow rate of the breathing gas.

[0043] Particularly at the local level, EIT can be used to determine the first time derivative of the EIT value, especially the time derivative of the impedance of each pixel, as a surrogate parameter for the local flow rate dV / dt in this lung region.

[0044] The computing unit is designed to determine at least one characteristic feature of the curve of the first time derivative of the EIT value with respect to ventilation pressure. The curve, and therefore this characteristic feature, represents the wedge pressure, i.e., the airway pressure at which transpulmonary pressure is zero or less.

[0045] The characteristic properties of a curve are understood to be properties derived from the analysis of the curve, such as the location of at least one pole, the location of at least one inflection point, and / or the location of at least one curvature or limit behavior.

[0046] For this purpose, the temporal behavior of the EIT values ​​of specific pre-selected pixels is examined, or the EIT values ​​of several pixels whose EIT values, time curves, or characteristic properties are averaged are examined. The pixels to be averaged may be located in a specific pre-selected pixel region, one or more specific pre-selected pixel rows, or one or more specific pre-selected pixel columns, for example, in a pixel row whose position corresponds to the height of the esophagus.

[0047] The computing unit may be designed to receive data characterizing a specific, pre-selected pixel region, such as the number of pixel rows or pixel columns.

[0048] The device may include an input unit into which the user inputs the corresponding data. The computing unit may be designed to read additional image data, such as computed tomography images, X-ray images, or ultrasound images, and to select specific pre-selected pixel regions, such as specific pixel rows, based on the additional image data.

[0049] As airway pressure increases, air flows into the lungs. Initially, the volume can increase almost proportionally to the increase in pressure, and as a result, the flow curve extends almost parallel to the pressure axis. As soon as additional lung areas that were previously inaccessible are opened up (recruited), the flow rate increases disproportionately. This opening can occur abruptly. The flow rate remains high as long as further areas of the lung are recruited. When the lung area is no longer opened up even with increasing pressure, the flow rate once again continues parallel to the pressure axis. No further opening of the lung occurs. Due to the increase in lung volume resulting from the previous recruitment, this flow rate can be greater than the initial flow rate, i.e., it can shift parallel to the pressure axis.

[0050] The recruited lung region is simply filled further with additional pressure. Therefore, further increases in pressure are no longer effective.

[0051] Therefore, the pressure can be lowered again. The gas flows out of the lungs. This creates a negative flow rate, which is initially constant. The flow rate curve then extends again parallel to the pressure axis.

[0052] When the pressure reaches a level that is no longer sufficient to stabilize the alveoli, the alveoli begin to collapse, and this can happen suddenly. Typically, during sudden lung collapse, a disproportionate amount of gas leaks out of the lungs.

[0053] This can be seen as a negative increase in flow rate. If further lung tissue collapses as the pressure continues to decrease, the flow rate remains high and only decreases after the collapse process is complete.

[0054] Next, the flow rate extends again parallel to the pressure axis. Since the first time derivative of the EIT value corresponds to the change in lung volume over time, the curve of the first time derivative of the EIT value with respect to ventilation pressure is similar to that of flow rate.

[0055] According to a preferred embodiment of the present invention, at least one characteristic curve point can be determined as a characteristic feature of the curve of the first time derivative of the EIT value.

[0056] The expiratory curve point is within a pressure range that begins when pressure decreases and typically ends when the PEEP value is reached. Alveoli can collapse during exhalation.

[0057] The characteristic expiratory curve point that is determined is typically characterized by alveolar collapse, especially at its inception, which occurs when the expiratory pulmonary pressure becomes negative.

[0058] Since the airway pressure is known from the ventilation lamp, the esophageal pressure during alveolar collapse can be estimated.

[0059] In particular, it is possible to determine the deflection point, turning point, and / or minimum value of the first time derivative of the EIT value as a function of ventilation pressure.

[0060] For the entire lung, the characteristic expiratory curve point lies between the onset of collapse, i.e., the point where the curve deviates from a parallel straight line (the point of deviation), and the maximum negative flow rate, where collapse is at full swing. The latter occurs quite late, while the former occurs quite early.

[0061] These characteristic exhalation curve points can be determined by further deriving the flow curve over time, i.e., by forming tangents.

[0062] The turning point of the exhalation curve, where the differential slope is maximum, lies between the point of deviation and the maximum value. The pressure at this point is likely to be closest to the desired pressure value.

[0063] The EIT value can be derived over time and plotted against ventilation pressure. Using standard computer-aided methods, extreme values, turning points, and threshold exceedances can be determined from this curve.

[0064] Generally, cardiogenic (heartbeat-related) oscillatory signals are superimposed on the EIT signal. A computing unit can be designed to remove cardiogenic signals from EIT data from an EIT device in order to extract ventilation-related signals.

[0065] The computing unit can be designed to pass the data through a heart rate-adjusted filter, such as a low-pass filter, band-pass filter, or band-stop filter, which preferably removes frequencies in the range of 0 to 0.2 Hz, i.e., frequencies 1 to 4 times the heart rate, from the EIT signal.

[0066] A computing unit can be designed to determine PEEP values ​​based on the characteristic properties of the curve, particularly based on characteristic exhalation curve points.

[0067] When transpulmonary pressure drops below zero, pixels in the esophageal region should collapse. At this point, the airway pressure present in the esophagus corresponds precisely to the PEEP required to compensate for this collapse.

[0068] The pressure at characteristic curve points, particularly the pressure at which the first signs of collapse are detected, is the pressure at which the expiratory pulmonary pressure falls below zero. This pressure corresponds to the PEEP required to compensate for collapse and can therefore be considered an appropriate PEEP value to set.

[0069] The computing unit can be designed to determine the time derivative of the EIT value locally, in particular over a pre-selected pixel region and / or over one or more individual pixels selected by "" (e.g., over a pre-selected pixel line).

[0070] In this way, the time derivative of the EIT value for every pixel in the EIT image, particularly the impedance change, can be calculated, and their courses across the gravity vector can be interpreted together for individual pixels or entire pixel lines.

[0071] In a patient lying supine, the gravity vector manifests as an increasing pressure gradient from the front to the back of the lungs.

[0072] The data can be analyzed by summing up all pixels within each line perpendicular to the gravity vector.

[0073] Here, the flow rate pattern of the pixel lines in the EIT image that pass horizontally through the esophagus is of particular interest because its behavior should reflect the conditions within the esophagus.

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

[0075] If the EIT values ​​of these pixels drop sharply when the pressure decreases, it can be concluded that the pressure present in the corresponding alveoli is no longer sufficient to prevent collapse. Therefore, this can be interpreted as a sign of the transition from open alveoli to collapsed alveoli, which corresponds to a situation where the transpulmonary pressure, determined by "" on the esophageal probe, reaches a value near 0.

[0076] A computing unit can be designed to determine a ventilation ramp. A linear ventilation ramp is characterized by its starting pressure, positive gradient, maximum pressure, and ending pressure.

[0077] A pressure ramp typically starts at 0 mbar and can show a linear increase of 1 mbar / s. Once the maximum value is reached, the pressure ramp can be decreased by 1 mbar / s.

[0078] The maximum and final pressures can be preset or derived from measurement data during the process.

[0079] The device may include an output unit that transmits data to the ventilator, particularly data regarding the ventilation lamp and / or data regarding specific PEEP values. Therefore, the device is designed as a device for controlling the ventilator.

[0080] The computing unit can be designed to determine the characteristic properties of the curve, particularly the PEEP value, before and / or during ventilation, especially at regular intervals.

[0081] This means that the PEEP value to be adjusted at any given time can always be determined and set, even during prolonged ventilation.

[0082] The device may have a display unit, such as a screen, on which curves and / or set values ​​are displayed. Furthermore, the device may include an output unit that transmits curve data and / or set values ​​to an external display unit.

[0083] This value can also be output directly to the ventilator so that PEEP can be readjusted.

[0084] The problem can also be solved by a system that includes an EIT device, a ventilator, and the devices described above.

[0085] The device may be part of an EIT device and / or a ventilator. The problem can also be solved by determining a method for identifying the wedge pressure, that is, a representative value of the airway pressure at which the expiratory lung pressure falls below zero.

[0086] In this method, ventilation pressure values ​​are received from the ventilator over at least one ventilation cycle. Furthermore, EIT data collected during at least one ventilation cycle is received from the EIT device.

[0087] The first-order time derivative of the EIT value is determined as a function of ventilatory pressure over at least one ventilation cycle, based on data from the ventilator and EIT device.

[0088] At least one characteristic feature of the curve of the first time derivative of the EIT value as a function of ventilation pressure is determined.

[0089] A distinctive feature is the wedge pressure. In particular, at least one characteristic exhalation curve point is determined as a characteristic feature.

[0090] In particular, the deflection points, turning points, and / or minimum values ​​of the first time derivative of the EIT value as a function of ventilation pressure are determined.

[0091] This method is particularly carried out using the apparatus described above. During slow pressure changes, airway volume and / or the volumetric flow rate or flow rate (dV / dt) of gas within the airway can be measured simultaneously and synchronously over time using a gas flow sensor.

[0092] This ensures that the overall respiratory gas flow curve and the overall EIT value (composed of all pixels) are remarkably similar over time.

[0093] On a linear ventilation ramp, both the airway volume and EIT values ​​show a bell-shaped pattern. Following this, the signal rises sharply at the start of the ramp, then flattens slightly as it approaches the maximum value. After exceeding the maximum value, the signal initially decreases slightly, then decreases further in a "" pattern until it ends at a level higher than the start of the ramp.

[0094] The PEEP value can be determined based on characteristic expiratory curve points. The PEEP value can be output to the ventilator as a control variable. Ventilation can then be controlled based on this PEEP value.

[0095] This procedure can be performed before and / or during ventilation, and especially periodically. This method can be performed, for example, at predetermined intervals, or after a predetermined number of breaths.

[0096] The problem can also be solved by a computer program that has program code to perform the steps of the method described above when the program is executed on a computer.

[0097] The problem can also be solved by a computer program product that can be directly loaded into the internal memory of a digital computer and which includes a software code portion that performs the steps of the method described above when the program is executed on the digital computer.

[0098] The present invention will be described below with reference to the drawings. drawing [Brief explanation of the drawing]

[0099] [Figure 1] This diagram shows the schematic structure of a system comprising the apparatus according to the present invention, an EIT device, and a ventilator. [Figure 2] Time course of ventilation pressure and flow rate. [Figure 3] This shows the flow rate plotted against the ventilation pressure. [Figure 4] The first time derivative of the EIT value as a function of ventilatory pressure for a healthy lung. [Figure 5] The first time derivative of the EIT value as a function of ventilatory pressure for an abnormal lung. [Figure 6] Comparison of CT images and EIT images. [Figure 7] The first-order time derivative of the local EIT value as a function of ventilation pressure for the left and right lungs. [Modes for carrying out the invention]

[0100] Figure 1 shows a system 1 having an EIT device 20 and a ventilator 30. The EIT device 20 includes an electrode belt 21 that can be attached to a patient and used to collect data for EIT imaging.

[0101] Furthermore, System 1 includes a device 10 for non-invasively determining a variable representing the wedge pressure, i.e., the airway pressure at which the expiratory lung pressure becomes zero or less.

[0102] The device 10 has an input unit 13 for receiving ventilation pressure data from the ventilator 30 over at least one ventilation cycle.

[0103] Furthermore, the device 10 has an input unit 12 for receiving EIT data from the EIT device 20 collected during at least one ventilation cycle.

[0104] Furthermore, the device 10 includes a computing unit 14 designed to determine the first time derivative of the EIT value as a function of ventilatory pressure over at least one ventilation cycle, based on data from the ventilator 30 and the EIT device 20.

[0105] Furthermore, the computing unit is designed to determine at least one characteristic feature of the curve of the first time derivative of the EIT value as a function of ventilation pressure. In particular, characteristic expiratory curve points are determined.

[0106] The device 10 includes a display 16 for displaying curves and / or determined values.

[0107] The device includes an output unit 15 for transmitting data to the ventilator 30. Airway pressure p AW However, the flow rate dV / dt is plotted in sync with time t in Figure 2. The flow rate curve dV / dt shows a characteristic convexity during the pressure increase, which indicates the opening of the lung region. When the pressure decreases, a concave shape can be observed, indicating the collapse of the lung unit.

[0108] Airway pressure p AW It will only decrease to a predetermined PEEP value. Figure 3 shows the ventilation pressure p AW The plotted flow rate dV / dt is shown. The curve has several characteristic points.

[0109] The flow rate can be measured using a gas flow sensor. This measurement is not part of the method according to the present invention.

[0110] As the pressure increases (upper part of the curve), the maximum positive flow rate A is reached. As the pressure decreases, the deflection point B is reached first, then the inflection point C, and finally the maximum negative flow rate D is reached.

[0111] Figure 4 shows the original, unfiltered curve during the implementation of the method according to the present invention. The EIT value as a function of ventilation pressure measured for the lungs of a healthy pig, here the first time derivative of the relative impedance change, is shown, in this case summed over all relevant pixels.

[0112] It can be seen that the curves roughly correspond to the flow curves shown in Figures 2 and 3. We can assume that there is a correlation between the time derivative of the EIT value across all relevant pixels and the total airway flow rate dV / dt.

[0113] We can observe the superposition of vibrations synchronized with the heartbeat. In this case, the lungs will not open because an airway pressure exceeding 25 mbar is required.

[0114] However, the convexity shown in Figure 2 can be observed when the pressure decreases. This indicates a certain degree of lung collapse, which reaches its maximum at approximately 10 mbar.

[0115] Figure 5 shows the corresponding curves measured in pigs that underwent 2 hours of "ventilator-induced lung injury" (VILI) corresponding to lungs in an ARDS state.

[0116] To investigate ARDS-like conditions in lung injury, a two-step surfactant washing model is used. Following the first step of measurements in a healthy lung state, the animal's lungs are repeatedly washed with a 0.9% isotonic sodium chloride (NaCl) solution at body temperature at a rate of 35 ml per kg of body weight via an endotracheal tube. This washes away the surfactant from the lungs until the washing solution is visually clear and no longer foamy.

[0117] After confirming that these requirements are met, perform lung injury ventilation for 120 minutes with an inspired oxygen fraction of 1.0, PEEP of 0 mbar, and a tidal volume of 15 ml / kg with a respiratory rate of 12 breaths per minute and an inspiration-to-expiration ratio of 1:2.

[0118] As pressure increases, the first time derivative of the EIT value corresponding to the flow rate remains lower than in healthy pigs. The flow rate increases only when the lungs begin to open. The maximum convexity is approximately 37 mbar. The opening of the lung region is clearly visible, but this measurement remains incomplete because the operation was accidentally interrupted at approximately 42 mbar. Maximum alveolar collapse is approximately 10 mbar.

[0119] Figure 6 shows a comparison between CT images and EIT images. The EIT image is a single-tidal ventilation image, and for each pixel in the measurement plane shown in the CT image, it shows the EIT value, in this case the impedance change.

[0120] The local pixel impedance signal is assumed to correlate with the local volume within that pixel.

[0121] The EIT image can be evaluated pixel by pixel or line by line. In this case, the pixel line 20 corresponds to the height of the esophagus.

[0122] Pixels in the EIT image that represent less than 10% of the maximum impedance amplitude in this lung region are excluded from the evaluation of the local curve. These represent so-called "silent spaces."

[0123] Figure 7 shows the first time derivative of the local EIT value as a function of ventilation pressure for the lines of the left and right lungs.

[0124] The result for each pixel is shown for each pixel row. The maximum value of the curve is also marked.

[0125] The negative maximum value of pixel line 20, which can be called wedge pressure, has been shown to correlate with PEEP measured in parallel via an esophageal probe by Talmor.

[0126] Therefore, based on EIT measurements, it is possible to determine values ​​that represent the characteristics of the wedge pressure. According to Talmor, the optimal PEEP for each individual is set as part of transpulmonary pressure monitoring. This involves inserting an esophageal catheter, which allows for the measurement of local esophageal pressure in the area around the catheter. By subtracting this pressure from the total airway pressure, it becomes possible to finally calculate the transpulmonary pressure.

[0127] Now, PEEP is selected to prevent atelectasis in such a way that the resulting end-expiratory transpulmonary pressure is between 0 and 10 mbar, and if possible, slightly above 0 mbar, but never negative.

[0128] On the other hand, in order to limit the tension of individual alveoli, the tidal volume is adjusted so that the end-inspiratory TPP value is always less than 25 mbar.

[0129] Local wedge pressure can be used as a non-invasive surrogate parameter for transpulmonary pressure by Talmor for PEEP adjustment.

Claims

1. A device (10) for non-invasive determination of a variable representing the wedge pressure, - A data input unit (13) for ventilation pressure from a ventilator (30) over at least one ventilation cycle, - Input unit (12) for EIT data collected from the EIT device (20) during at least one ventilation cycle, Based on the data from the ventilator and the EIT device, it is designed to determine the first time derivative of the EIT value as a function of the ventilation pressure over at least one ventilation cycle. A computing unit (14) designed to determine, with respect to the curve of the first time derivative of the EIT value as a function of the ventilation pressure, at least one characteristic feature representing the wedge pressure, in particular a characteristic expiratory curve point, and more specifically a deflection point, an inflection point, and / or a minimum value, and A device (10) comprising:

2. The apparatus according to claim 1, wherein the computing unit is designed to determine a PEEP value based on the characteristic features of the curve, particularly the characteristic exhalation curve points.

3. The apparatus according to claim 1 or 2, wherein the computing unit (14) is designed to determine the first time derivative of the EIT value locally, in particular over one or more selected individual pixels, and more particularly over a pixel line.

4. The apparatus according to any one of the preceding claims, wherein the computing unit (14) is designed to determine a ventilation lamp.

5. The apparatus for controlling a ventilator, comprising a computer unit (14) and an output unit (15) connected to a ventilator (30) that supplies data to the ventilator (30), particularly data relating to the ventilation lamp and / or data relating to a specific PEEP value, according to any one of the preceding claims.

6. The apparatus according to any one of the preceding claims, wherein the computing unit (14) is designed to determine the characteristic features of the curve, in particular the PEEP value, before and / or during ventilation, especially at regular intervals.

7. A system (1) comprising an EIT device (10), a ventilator (30), and the device (1) described in any one of the preceding claims.

8. The 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 a quantity that represents the wedge pressure, - Receiving ventilation pressure data from the ventilator for at least one ventilation cycle, - Receiving EIT data from the EIT device collected during at least one of the ventilation cycles, Based on the data from the ventilation device and the EIT device, determine the first time derivative of the EIT value as a function of ventilation pressure over at least one ventilation cycle, - To determine at least one characteristic feature, particularly a characteristic expiratory curve point, more specifically a deflection point, turning point, and / or minimum value, of the curve of the first time derivative of the EIT value as a function of the ventilation pressure, which represents the wedge pressure. Methods that include...

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

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

12. The method according to claim 11 or 12, wherein ventilation is performed based on the PEEP value.

13. The method according to any one of claims 9 to 12, which is performed particularly at regular intervals before and / or during ventilation.

14. A computer program that, when executed on a computer, includes program code for performing the steps of the method according to any one of claims 9 to 13.

15. A computer program product that can be directly loaded into the internal memory of a digital computer, the computer program product comprising a software code portion that, when the program is executed on the digital computer, performs the steps of the method according to any one of claims 9 to 13.

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