VENTILATORS

Description

[0001] The field of the invention is ventilators of the type mentioned in the preamble of claim 1.

[0002] A ventilator according to the preamble of the claim 1 is known from EP 2 091 429 B1.

[0003] The invention relates to the field of ventilators and control methods for ventilators, and in particular to ventilators which take into account the oxygen saturation in the blood measured by an oximeter.

[0004] Ventilators for mechanical artificial respiration in all forms of oxygen deficiency are known (Roche Lexikon Medizin, 4th edition, Urban & Fischer Verlag, Munich). Such ventilators are also referred to as respirators. A distinction is made between three basic types: a) Pressure-controlled ventilators: The inspiration phase ends when a preset ventilation pressure is reached. Expiration usually occurs passively. b) Volume-controlled ventilators: Inspiration ends when a preset gas volume has left the ventilator. Expiration usually occurs passively. c) Time-controlled ventilators: The gas mixture is delivered within a preset time.

[0005] Newer types of ventilators have electronic controls that allow for patient-specific ventilation. Such ventilators often have a pressure sensor that measures the ventilation pressure. The pressure sensor can be located inside the ventilator and thus measures the pressure at the ventilator-side end of the ventilation tube.

[0006] In addition, most electronically controlled ventilators also have a flow sensor for measuring the air flow V, i.e., the volume of air inhaled or exhaled per unit of time. Such a flow sensor is also called a spirometer. By summing the flow values provided by the flow sensor during an inspiration or expiration phase, the inspiration or expiration volumes are obtained. Expressed in somewhat more precise mathematical terms, an inspiration or expiration volume is the integral of the respiratory flow V over the time of an inspiration or expiration phase.

[0007] EP 2 091 429 B1 discloses a device equipped to determine PEEP. It has a flow / pressure sensor with which pressure and volume can be measured. This is arranged, for example, on a ventilation tube on the patient side or integrated into the device. The patient is ventilated through this ventilation tube by means of the ventilator. If the tidal volume V is plotted against the ventilation pressure p, this so-called P / V loop develops a hysteresis. The lower, ascending branch Vinf (inf for inflation) is recorded while the lung is inflated (inspiration). The upper, descending branch Vdef (def for deflation) is recorded while air escapes from the lungs (expiration). The appropriate PEEP can be read off in a diagram on the loop. The appropriate PEEP is the pressure at which the greatest volume difference between Vdef and Vinf is measured.Because the inspiratory and expiratory volumes in EP 2 091 429 B1 are equal, because the branches Vinf and Vdef meet at the top right and bottom left, thus forming a closed P / V loop, there can be no EFE event (see below) in EP 2 091 429 B1.

[0008] US 2012 / 0071729 A1 describes a typical ventilator for a human patient. The ventilator includes a pneumatic system for generating pressure and is connected to the patient via a tubing system and a physical patient interface. The ventilator includes, among other things, a controller and an oximeter. Different alarms can be triggered. If SpO2, PEEP, or FiO2 exceeds or falls below a predetermined threshold, an alarm can be triggered. For example, if the PEEP is reduced by an operator before the SpO2 falls below a threshold, a different alarm is triggered. If the FiO2 is reduced before the SpO2 falls below a threshold, a third alarm is triggered. US 2012 / 0071729 A1 does not describe the PEEP being changed in any way, in particular it does not describe increasing the PEEP when the SpO2 falls below a limit.

[0009] Knowing the airflow, the pressure drop across the ventilation tube (cf. EP 1 562 655 B1) and / or any endotracheal tube or tracheostomy cannula can be calculated. Of course, the pressure drop can also be calculated across parts of the ventilation tube and / or the endotracheal tube or tracheostomy cannula. This allows any point between the ventilator and the lungs to be used for pressure control. It seems sensible to choose the pressure in the mouth, as this most closely corresponds to the lung pressure. In newer ventilators, the available ventilation modes are generally combinations of the three basic types listed above.

[0010] CPAP (Continuous Positive Airway Pressure) is a form of ventilation that combines the patient's spontaneous breathing with a continuous positive pressure of typically 5 to 30 mbar. The patient can determine their own breathing depth, respiratory rate, and respiratory flow (V̇). How to detect breaths under CPAP is described, for example, in EP 1 294 428 B1.

[0011] IPPV (Intermittent Positive Pressure Ventilation) is used in intensive care and emergency medicine and refers to a volume-controlled form of ventilation using a ventilator. The term Volume Controlled Ventilation (VCV) is now more commonly used as a synonym for IPPV. With volume-controlled ventilation, the ventilator attempts to keep the volume constant by varying the ventilation pressure. With this form of ventilation, the air pressure in the airways can drop to as low as 0 mbar at the end of expiration, but never reaches negative values.

[0012] Pressure-controlled ventilation is more commonly used today. It provides two different pressure levels: one for inhalation and one for exhalation. This type of ventilation is also called bilevel or BIPAP (Bi Positive Airway Pressure). With BIPAP, positive end-expiratory pressure (PEEP) remains in the airways even at the end of exhalation.

[0013] According to Rathgeber, Fundamentals of Mechanical Ventilation, ISBN 9783131487926, 2010, Georg Thieme Verlag KG, all ventilation parameters are predefined in volume-controlled ventilation. The target and control parameter is the tidal volume. The resulting airway pressures depend on the set volumes and the patient's pulmonary conditions. The patient cannot influence the inspiratory ventilation pattern. Typically, four parameters can be predefined in volume-controlled ventilation: the inspiratory flow rate, the minute ventilation, the ventilation rate, and the pressure at the end of expiration (PEEP). After the inspiratory valve opens, a constant flow of a defined amount is delivered until the end of the inspiration phase.Other flow patterns, such as decelerating, accelerating, or sinusoidal flow, are practically no longer used in volume-controlled ventilation because they offer no discernible advantages. The primary setting of minute ventilation, and thus the inspiratory flow, is based on the patient's body weight, assuming approximately 250 ml of respiratory air per kg body weight per minute for newborns. The initial ventilation rate for newborns is set to approximately 50 per minute.

[0014] IPPV is predominantly found in the emergency services sector, as the vehicles used there only use emergency respirators, which usually do not support other forms of ventilation.

[0015] S-IPPV (Synchronized Intermittent Positive Pressure Ventilation) is a synchronized IPPV. Here, the patient's breathing efforts ("triggers") are detected and synchronized. There is also SNIPPV, where the "N" stands for non-invasive, meaning the use of a ventilation mask, nasal cannula, or similar patient interface without a tracheostomy tube or endotracheal tube.

[0016] PAV (Proportional Assist Ventilation) is a form of ventilation in which the ventilator takes on a specific portion of the work required for breathing. The ventilator adjusts the tidal volume and pressure depending on the patient's breathing activity. The more forcefully the patient breathes, the more tidal volume and pressure the ventilator delivers.

[0017] Premature infants have a reflex to pause breathing when oxygen saturation is too low. Controlling blood oxygen saturation (SpO2) by altering the oxygen concentration of the delivered breathing gas (FiO2) is a well-known technique for ventilating patients with respiratory disorders. The method is described, for example, in "NEONATAL WORKSTATION FOR INSPIRED OXYGEN CONTROL AND CLINICAL MONITORING" by Yao Sun et al., 1994, AAAI Technical Report SS-94-01. A similar method is described in WO 02 / 47741 A2.

[0018] In "Adaptive mechanical backup ventilation for preterm infants on respiratory assist modes" by Susanne Herber-Jonat et al., 2006, Intensive Care Med 32:302-308, Springer, it is described that PAV is supplemented by forced ventilation ("mechanical backup") in the event of apneas, i.e., pauses in breathing, or insufficient breathing. For this purpose, (1) the physician can set a time interval between the cessation of breathing and the automatic start of forced ventilation. (2) Forced ventilation is gradually reduced by reducing the frequency of forced ventilation during the resumption of spontaneous breathing. (3) Spontaneous breathing without forced ventilation is only permitted under CPAP or PAV if the blood oxygen saturation (SpO2) exceeds a user-defined threshold. This forced ventilation mode is referred to as SpO2-sensitive adaptive backup.It has been clinically shown that a gradual withdrawal of backup therapy improves treatment. Furthermore, the goal of therapy is to keep support as minimal as possible, as any form of ventilation is potentially harmful.

[0019] EP 2 671 509 A1 discloses a ventilation system in which a patient's respiratory activity is detected by means of a respiration sensor element. The sensor element consists of a sensor part, which is applied directly to the skin on the side of the patient's abdomen, and a cable part, by means of which signals generated by the sensor part can be transmitted to a data interface of an electronic device of the ventilation system. The generated signals are corrected by forming an arithmetic mean with respect to previously generated signals and thus calibrated. In the event that such a computational calibration is excluded, the ventilation system comprises calibration means for calibrating the sensor element interacting with the patient. The calibration means comprise a device for actuating a valve element for ventilating and / or venting the ventilation system.

[0020] The object of the invention is to provide a ventilator and a control method therefor in which the risk of lung damage is low.

[0021] This problem is solved by the doctrine of independent claims.

[0022] Preferred embodiments of the invention are the subject of the subclaims. Table 1: Abbreviations abbreviation für BIPAP Bi Positive Airway Pressure BU Backup CPAP Continuous Positive Airway Pressure EFE effusive exhalation FCBU Frequency-Controlled Backup FiO2 Oxygen content in inspired breathing gas IP inspiratory pressure IPPV Intermittent Positive Pressure Ventilation NIV non-invasive ventilation PAV Proportional Assist Ventilation PEEP Positive end expiratory pressure S-IPPV Synchronized IPPV SpO2 Oxygen saturation in the blood SNIPPV Synchronized non-invasive IPPV VCV Volume-controlled ventilation

[0023] Preferred embodiments of the invention are explained in more detail below with reference to the accompanying drawings. Fig. 1 a ventilation system according to the invention; Fig. 2 an optional control loop for controlling the oxygen content in the breathing air; Fig. 3a flow chart for the inventive control during invasive ventilation; and Fig. 4 to 6 a flow chart for the inventive control of non-invasive ventilation.

[0024] Figure 1 shows a ventilator 1 according to the invention, with which a neonatal or pediatric patient 2 is ventilated via an endotracheal tube 3. As an alternative to the endotracheal tube 3, a ventilation mask can also be used. Figures 1 and 2 Electrical lines are represented by a single line and pneumatic lines by a double line. Ventilation is provided via two ventilation tubes, 4 and 5, with fresh air being supplied to premature infant 2 via ventilation tube 4, and exhaled air being removed via ventilation tube 5. This prevents carbon dioxide from accumulating in the ventilation tubes.

[0025] If the ventilator 1 is an intensive care ventilator, it is usually connected to a hospital gas supply, which is shown by way of example as an oxygen cylinder 12 and a gas cylinder 15. However, the gas cylinders can also be real and can be housed next to or, with a suitable design, within the ventilator. Oxygen cylinder 12 is connected to connection 11 and gas cylinder 15 to connection 14. An intensive care ventilator is therefore usually supplied with medical oxygen via connection 11 and with medical compressed air via connection 14. Air flows from connection 14 via a proportional valve 13 to connection 29. In addition to or as an alternative to gas cylinder 15 and connection 14, fresh air can be sucked in via an opening 9 in the ventilator 1 via a blower 8 and blown into the ventilation tube 4 via a valve 7 and via a connection 29. The air from the gas cylinder 15 or the hospital air supply is sterile.This is more difficult to ensure with ambient air drawn in through opening 9. The oxygen cylinder 12 is optional. It serves to increase the oxygen content of the breathing gas FiO2 in a defined manner. The oxygen is supplied to the ventilation tube 4 via port 11 and the proportional valve 10 via port 29. The oxygen content in the oxygen cylinder 12 is generally well above 21% and can reach almost 100%.

[0026] In other embodiments, the blower 8 and the valve 7 are each replaced by a proportional valve, namely an inspiration valve and an expiration valve in front of the sensors 34 and 35, respectively.

[0027] The proportional valves 10, 13, and 6, the valve 7, and the blower 8 or the alternative proportional valves are electrically connected to the controller 16 and controlled by the controller 16. The speed of the blower 8 or the opening width of the inspiration valve and the position of the valves 6, 7, 10, and 13 ensure that fresh breathing air is supplied to the premature infant 2 through the ventilation tube 4 during an inspiration phase and that exhaled air is discharged through the ventilation tube 5 during an expiration phase.

[0028] In order for the ventilator 1 to optimally support the premature infant 2 with regard to its respiratory activity, the ventilator 1 must detect the premature infant 2's spontaneous breathing and adapt ventilation to the patient's needs without causing hyper- or hypoventilation. Since premature infants 2 and newborns are pronounced "belly breathers," breathing activity can advantageously be recorded using a sensor attached to the abdomen, for example, a Grasby capsule 17, as described in EP 2 671 509 A1. The pressure in the Grasby capsule 17 is transmitted via a tube 18 to connection 19 of the ventilator 1. The pressure at connection 19 is converted by a pressure sensor 21 into an electrical signal, which is fed to the controller 16 and can be referred to as a respiratory signal. The controller 16 calibrates the Grasby capsule 17 from time to time, for example once every 10 breaths, whereby in particular an offset is redetermined.If the offset becomes too large, either air from the Grasby capsule 17 can be released into the environment via valve 33, or air from the environment can enter the Grasby capsule 17 via valve 33. During normal operation, valve 33 is closed. The compression of the Grasby capsule 17 leads to a pressure increase, which is detected by the pressure sensor 21. Filling the capsule with foamed material serves to relax the capsule upon release of pressure, i.e., upon exhalation. Valve 33 is electrically connected to and controlled by the controller 16.

[0029] The pressure in the Grasby capsule 17, and thus also the electrical signal supplied by the pressure sensor 21, increases monotonically with the lung volume, approximately linearly. The most non-linear element is likely the Grasby capsule 17 itself. The inspiratory volume during a breath is calculated as the calibration factor times the difference between the maximum pressure at the end of insufflation and the minimum pressure at the beginning of insufflation. The expiratory volume during a breath is calculated as the calibration factor times the difference between the minimum pressure at the end of exhalation and the maximum pressure at the beginning of exhalation. Since the control system according to the invention is based solely on the quotient of expiratory volume divided by inspiratory volume, the calibration factor does not need to be determined.In this respect, the difference between the pressure at time t in the Grasby capsule 17 and the minimum pressure during the corresponding breathing phase can be referred to as the lung volume signal at time t.

[0030] Alternatively, a lung volume signal can also be determined from the inhaled and exhaled air flow V̇. To determine these air flows, flow sensors 35 and 34, respectively, can be provided; these are electrically connected to the controller 16 to communicate the flow measurements to the controller. Alternatively or additionally, a patient-near flow sensor can be located at the patient connection 37, which is electrically or pneumatically connected to the controller 16 via connection 38 and measures the flow with the correct sign. To calculate the respiratory flow in the mouth and trachea of the premature baby 2, the signal from flow sensor 34 is subtracted from the signal from flow sensor 35. The flow towards the premature baby 2 is considered positive and away from the premature baby negative. The respiratory flow in the mouth and trachea of the premature baby 2 can also be viewed as a respiratory signal.To determine the inspiratory and expiratory volumes during a single breath from the respiratory flow in the mouth, the individual measured values of the total flow during the inspiration and expiration phases must be summed. To obtain a lung volume signal at time t from the total flow, all total flow measurements from time t0 to time t1 are added together. t0 is ideally set at the beginning of an inspiration phase.

[0031] By monitoring the sum of the flow values during an inspiration phase, the inspiration phase can be terminated if the sum exceeds a threshold, e.g., 0.5 l, thus guaranteeing a specific inspiration volume. In fact, the flow values are initially available in the control system as integer values that are not calibrated in l / s. To save computing time, it is useful to convert the threshold value in l into an integer limit for the sum of the flow values, taking into account the sampling rate of 100 Hz to 1 kHz.

[0032] Finally, two optional pressure sensors 31 and 32 are provided to measure the air pressure near ports 29 and 30, respectively. Knowing the air flows measured by flow sensors 34 and 35, the air pressure throughout the ventilation tubes 4 and 5 and the endotracheal tube 3 can be calculated. Alternatively, a pressure sensor can measure the pressure at the patient port 37.

[0033] It is also important for the control system that the controller 16 can measure the oxygen saturation SpO2 in the blood of the premature infant 2 via an oximeter 22. The oximeter 22 is electrically connected to the controller 16 via the connector 23 and a cable.

[0034] The ventilator 1 finally comprises a user interface with an input system 24, such as a keyboard for entering ventilation parameters, and a display 36 for displaying ventilation parameters and measured values. Both the input system 24 and the display 36 are electrically connected to the controller 16. In particular, a user can enter an upper limit value SpO 2O 25 and a lower limit value SpO 2U 27 for the oxygen saturation SpO 2. From this, the controller 16 calculates the arithmetic mean SpO 2M , which is referred to as the saturation target value 26. The saturation target value 26 can, but does not have to, be displayed. In another embodiment, the saturation target value 26 can also be entered by the user and thus selected independently of the lower and upper limit values SpO 2U 27 and SpO 2U 27.Examples of other ventilation parameters are the pressure selected by the control at the end of expiration PEEP 28, the set pressure at the end of expiration PEEP 0 , the inspiratory flow V̇ i , the set ventilation frequency f B0 , the ventilation frequency f B , the minute ventilation V , the EFE event duration (EFE: effusive exhalation) T E0 , the pressure factor p fr , the apnea duration t A and the minimum dwell time t B. Optionally, the standard pressure during inspiration IP 0 can also be entered.

[0035] The controller 16 may include a processor for executing software, RAM, non-volatile memory, analog-to-digital converters, digital-to-analog converters, and power electronics. The exact electrical design of the controller 16 can be designed by a person skilled in the art and is within the scope of their expertise.

[0036] Using the block diagram in Figure 2An optional control loop for controlling the oxygen content in the inspired respiratory gas FiO 2 is explained. The proportional valves 6, 10 and 13, the flow sensors 35 and 34, the ventilation tubes 4 and 5, the endotracheal tube 3, the oximeter 22 and the connectors 23, 29 and 30 have already been described in Figure 1 The control 16 is in Figure 2shown in more detail. The controller 16 includes, in particular, a PID controller 51, a subtractor 52, multipliers 53 and 54, and a breath controller 56. Although the PID controller 51, the subtractor 52, and the multipliers 53 and 54 are shown as components, it is clear to those skilled in the art that in modern controllers these functionalities are implemented in software. The PID controller 51 provides a value between a minimum value, for example, 0, and a maximum value of, for example, 1023. The subtractor 52 provides a second value which, when added to the value of the PID controller, precisely results in the maximum value. The value of the PID controller and the second value are each multiplied by an inspiration value 57 in the multipliers 53 and 54, respectively. The results of the multipliers 53 and 54 control the proportional valves 13 and 10, respectively.Thus, the total inspiratory flow, which is measured by the flow sensor 31, can be adjusted via the inspiratory value 57 largely independently of the oxygen fraction FiO 2. Conversely, the control variable, namely the oxygen fraction FiO 2, can be adjusted largely independently of the inspiratory flow.

[0037] The target value of the PID controller 51 is the saturation target value SpO 2M 26 and is fed to the PID controller 51 via the + input. The actual oxygen saturation value SpO 2 is fed to the - input of the PID controller.

[0038] During operation, premature baby 2 is part of the controlled system. The relationship between the oxygen fraction FiO 2 and the oxygen saturation SpO 2 is non-linear. It is therefore useful to change the control parameters 55 of the PID controller 51, i.e. the gain factors for the proportional, integral and derivative components, for example based on the set limits SpO 2O 25 and SpO 2U 28 as well as the direction of the change in oxygen saturation SpO 2. The relationship between the oxygen fraction FiO 2 and the oxygen saturation SpO 2 also depends on the condition of the premature baby, for example whether the premature baby is asleep or awake. Therefore, other parameters such as the tidal volume in PAV or the oxygen saturation SpO 2 itself can be taken into account.

[0039] Figure 3shows a flow chart illustrating important steps in breath control 56 for an invasive ventilation mode with tidal volume monitoring, for example, IPPV. In step 61, the inspiratory flow V̇ i is set, the ventilation frequency f B is set equal to the set ventilation frequency f B0, and the end-expiratory pressure (PEE pressure, PEEP) is set equal to the set end-expiratory pressure (PEEP 0 ). Optionally, the inspiration pressure IP can also be set to the default value IP 0. The values in Figure 3The steps shown are performed once after each breath. Therefore, in step 62, the system waits until a breath is complete. According to the usual convention, a breath begins with inspiration and ends with expiration. However, for the purposes of the invention, a breath could also begin with expiration and end with inspiration. The criteria for when expiration and inspiration end depend on the type of ventilation, for example, IPPV.

[0040] In step 63, the inspiratory volume V i and the expiratory volume V e are determined. "Determining" in step 63 can simply mean reading. Especially with IPPV, the target inspiratory volume can be calculated from the minute ventilation V and the ventilation rate f B . It is also useful to add up the individual respiratory flow measurements during expiration so that the expiratory volume V e can be read at the end of expiration.

[0041] In comparison 64, the expiratory volume is compared with the inspiratory volume. If the expiratory volume exceeds the inspiratory volume by at least 50%, i.e. if V e / V i >= 1.5, an EFE event is stored in step 65, for example by calculating and storing an end time t E as the sum of the current time t plus a predefined or adjustable EFE event duration t ED. In another embodiment, a threshold value deviating from 50% can be set by the operating personnel. t ED is at least one breath and is preferably longer and adjustable by the user. The elapse of the EFE event duration t ED is checked in comparison 66. This occurs immediately after comparison 64 or step 65, depending on the result in comparison 64. In comparison 67, it is checked whether the measured oxygen saturation SpO 2 falls below the set lower limit SpO 2U after the EFE event within the EFE event duration t ED.If this is the case, the PEEP is increased in step 68 by a pressure factor p fr previously set by the user, for example 10%. Optionally, shortly before or after, i.e. at approximately the same time in step 77, the inspiration pressure IP can be increased by a factor pi in order to keep the amount of gas exchanged constant. Instead of a factor, the user can also set a fixed pressure value by which the PEE pressure must be increased. This also applies to the inspiration pressure. The order of comparisons 66 and 67 can also be swapped. In order to keep the amount of gas exchanged in this adapted phase of ventilation constant, the ventilation frequency f B can be increased in step 69.

[0042] Step 70 is reached if comparisons 66 or 67 return no. In comparison 70, a check is made to see whether the oxygen saturation SpO 2 exceeds the saturation target value SpO 2M. If this is not the case, the system waits for the end of the next breath in step 62. If the oxygen saturation SpO 2 exceeds the saturation target value SpO 2M , the PEEP is gradually reduced to the original value, dividing each step by the pressure factor p fl. The pressure factors p fr and p fl can be the same, but it is useful for p fl to be smaller than p fr so that the PEEP is reduced more slowly than the previous increase. One of these steps is shown in step 71. If the inspiration pressure IP was increased in step 77, it is reduced in the same way in step 78, i.e. either by division by pi or subtraction of a fixed pressure difference.Comparison 72 checks whether PEEP has already fallen below the set end-of-expiration pressure (PEEP 0). If this is the case, PEEP is set to PEEP 0 in assignment 73. If the ventilation rate f B was also changed during the PEEP adjustment, it is also returned to the set ventilation rate f B0 in a similar manner in assignments 74 and 76, as well as in comparison 75. If the inspiration pressure IP was increased in step 77, it is set equal to the default value IP 0 in step 79.

[0043] Following assignments 69 or 76 or comparison 75, step 62 waits for the end of the next breath.

[0044] Figures 4 to 6show a flow diagram for the control according to the invention for a non-invasive form of ventilation with a set apnea duration t A , for example CPAP or SNIPPV. Here, the intensity of the ventilation, in particular the ventilation frequency f B , is controlled based on the drop in oxygen saturation. There are five backup levels for the ventilation frequency f B. The ventilation frequency f B at level 1 is the set ventilation frequency f B0 . From backup level to backup level, the ventilation frequency decreases by 2 / 3. The ventilation frequencies for levels 2 and 3 are therefore 2 / 3 (approximately 66%) f B0 and 4 / 9 (approximately 44%) f B0 , respectively. At each level there is an adjustable minimum dwell time t B , which is typically 30 s. In one embodiment, the minimum dwell time can be selected from four values: 0 s, 10 s, 30 s, or 60 s. If this minimum dwell time is set to 0, backup ventilation is terminated as soon as the reason for backup ventilation no longer exists.A set dwell time greater than 0 is referred to as FCBU (Frequency Controlled Back-Up). Under SNIPPV, the ventilation frequency is not reduced below 4 / 9 fB0, and under CPAP or nCPAP, it is not reduced below 16 / 81 (approximately 20%) fB0.

[0045] If no breath was detected in step 81 within the apnea duration t A, meaning an apnea is present, the variable BuBySpO 2 is set to 0 in step 83, thus saving the reason for starting backup ventilation. In step 82, backup ventilation is started at the set ventilation rate f B0 in backup level 1. A synchronized ventilation mode, e.g., SNIPPV, is used as backup ventilation. In step 84, the earliest possible end of level t BE is calculated as the sum of the current time t and the minimum stay time t B. In step 87, the system waits for the end of the minimum stay time.

[0046] If spontaneous breathing is detected in step 85, with FCBU activated (comparison 86), the full set ventilation rate f B0 is reduced by 1 / 3 in step 89 to approximately 66%, i.e. backup ventilation continues in backup stage 2. If no spontaneous breathing is detected in step 85, backup ventilation is continued at frequency f B0 in steps 83 and 82. This means that the duration of backup stage 1 is n*t BE if t BE >0, where n is an integer. If spontaneous breathing was detected in step 85, backup ventilation continues in stage 2 and the new ventilation rate is calculated and set in step 89. If FCBU is activated, i.e. t B >0, the time t BE is determined again in step 88 after comparison 86. In step 115, the system waits for this time to elapse.If FCBU is not activated in comparison 86 and the oxygen saturation in comparison 94 is above the lower limit SpO 2U, and backup ventilation was started due to an apnea in step 81, i.e., BuBySpO 2 ==0, the program jumps to the termination of backup ventilation 117. As in many programming languages, && stands for a logical AND operator, and == for a relational operator that checks for equality.

[0047] Otherwise, comparison 90 checks whether the oxygen saturation SpO2 is above the lower limit of the oxygen saturation SpO2U and spontaneous breathing continues. If this is the case, backup ventilation is continued in step 93 at backup level 3 with a ventilation rate fB of 4 / 9 of the set ventilation rate fB0. Then, in step 91, the end of the minimum dwell time tBE is calculated, and in step 92, the minimum dwell time is awaited.

[0048] If the oxygen saturation SpO 2 in comparison 90 is below the lower limit of the oxygen saturation SpO 2U , spontaneous breathing was detected in step 85, and FCBU was activated in step 86, the minimum dwell time t B begins again in step 88. This is achieved by recalculating the end t BE in step 88, i.e., postponing it into the future.

[0049] Similar to comparison 90, comparison 98 checks for spontaneous breathing or for the oxygen saturation SpO2 to fall below the SpO2U limit. As in many programming languages, "||" represents a logical "or" operator and "!" represents a negation. If no spontaneous breathing is present in comparison 98 or the SpO2U limit is exceeded, the system switches to comparison 85. A lack of spontaneous breathing in comparison 85 leads to entry into backup level 1 via steps 83 and 82.

[0050] If SNIPPV is below the threshold, which is checked in comparison 99, the system switches to the next backup level 4 without changing the frequency. If comparison 99 shows that CPAP, rather than SNIPPV, was selected as the ventilation mode, comparison 100 checks whether the oxygen saturation has reached the target saturation value SpO 2M. If this is not the case, the control system remains in backup level 3 and continues calculating the new earliest end t BE in step 91.

[0051] If the oxygen saturation SpO 2 has reached the saturation target value SpO 2M in comparison 100, the system switches to backup level 4 even under CPAP, and in step 105 the new backup frequency f B = 0.29 × f B0 is calculated and set. In level 4, the new earliest end t BE is then calculated in step 102, and the end t BE is awaited in step 101. In comparison 106, a check is made again to determine whether spontaneous breathing is present and whether the oxygen saturation has not fallen below the limit value SpO 2U. If one of the two conditions is not met, the system returns to comparison 85, as before after comparison 98.

[0052] If spontaneous breathing is present in comparison 106 and the oxygen saturation SpO 2 is at least equal to the limit value SpO 2U , then in the case of ventilation type SNIPPV, which is checked in comparison 107, the system switches to backup level 5 without changing the frequency. If the ventilation type is not SNIPPV, then in comparison 108 it is additionally checked whether the oxygen saturation SpO 2 has reached the saturation target value SpO 2M. If this is not the case, the backup remains in backup level 4 and continues with comparison 106. If it was determined in comparison 108 that the oxygen saturation SpO 2 has reached the saturation target value SpO 2M, then the system switches to backup level 5 and in step 113 the ventilation frequency f B is reduced to 0.19×f B0. Regardless of CPAP or SNIPPV, in backup stage 5, the earliest end t BE of stage 5 is calculated in step 110 and this end is awaited in step 109.In comparison 114, it is again checked whether spontaneous breathing is present and the oxygen saturation SpO2 is at least equal to the limit value SpO2U. If there is no spontaneous breathing or the oxygen saturation has fallen below the limit value SpO2U, the process switches to step 85. If spontaneous breathing is present and the oxygen saturation is at least equal to the limit value SpO2U, the backup is terminated in step 117.

[0053] If no apnea was detected in step 81, i.e., spontaneous breathing was present or spontaneous breathing ceased for less than the apnea duration tA, a check is made in step 95 as to whether the oxygen saturation SpO2 is below the lower limit of the oxygen saturation SpO2U. If this is not the case, the breath control 56 can wait and then check again in step 81 as to whether apnea is present. If the oxygen saturation SpO2 in comparison 95 is below the lower limit of the oxygen saturation SpO2U, backup ventilation is started in step 96 with a ventilation rate fB of 2 / 3, i.e., approximately 66%, of the set ventilation rate fB0 in backup level 2. Previously, in step 97, the entry into the backup via a saturation drop, i.e. via step 95, is saved by setting the variable BuBySpO 2 =1 in order to prevent a possible premature exit in comparison 94.The further sequence of process steps is identical to that for backup ventilation triggered by an apnea in comparison 81.

[0054] Even if that is in the Fig. 4 to 6 Unless explicitly stated, apnea detection in step 81 also continues during backup ventilation. If an apnea occurs in the higher backup levels, the system switches to backup level 1 in steps 83 and 82. This can occur particularly in the higher backup levels starting from level 3.

Claims

1. Respirator for ventilating a patient, comprising: a respiratory tube connector (29, 30) for connecting a respiratory tube (4, 5); an actuator (8, 10, 13) that is pneumatically connected to the respiratory tube connector (29, 30) for delivering air to a patient (2) via the respiratory tube connector (29, 30); an oximeter connector (23) for delivering an oxygen saturation signal; a digital programmable controller (16) that is electrically connected to said oximeter connector (23) for delivering the oxygen saturation signal to said digital programmable controller (16), wherein the digital programmable controller (16) is programmed • to calculate the oxygen saturation from the oxygen saturation signal, and • to determine whether the oxygen saturation falls below (95) a lower limit (27) and to start backup respiration at a predetermined frequency (96) in this case, and • to reduce the frequency of the backup respiration (91) if the oxygen saturation exceeds the lower limit value (27) again (104). characterized in that the controller (16) is further programmed to further reduce (104, 105) the frequency of backup ventilation when the oxygen saturation exceeds (100) a saturation target value (26), wherein the saturation target value (26) is greater than the lower limit value (27).

2. Respirator according to claim 1, characterized in that the controller (16) is further programmed to terminate (117) backup ventilation if the oxygen saturation continues to exceed (108) a saturation target value (26) after further reduction of the frequency of ventilation (104, 105).

3. Respirator according to one of the preceding claims, characterized in that the respirator (1) further comprises a valve (13) and an oxygen connector (14) for a gas or gas mixture (15) with more than 21 vol% oxygen, an inlet of the valve (13) being pneumatically connected to the oxygen connector (14), an outlet of the valve (13) being pneumatically connected to the ventilation tube connector (29) and a control connector of the valve (13) being electrically connected to the controller (16), wherein the controller (16) further comprises a PID controller (51) which controls the valve (13) so that the oxygen saturation deviates as little as possible from a saturation target value between an upper limit value (25) and the lower limit value (27).

4. Respirator according to one of the preceding claims, further characterized in a breath sensor terminal (19) for a breath sensor (17, 34, 35) for providing a breath signal, wherein the digital programmable controller (16) is electrically connected to the breath sensor terminal (19), wherein the breath signal is supplied to the digital controller (16), wherein the controller (16) is programmed, to • calculate a lung volume signal from the respiratory signal, the lung volume signal increasing monotonically with the lung volume of the patient (2), wherein the controller (16) is programmed to calculate an inhaled volume and an exhaled volume from the lung volume signal for each breath, and • store an EFE event (65) if the exhaled volume exceeds the associated inhaled volume by an adjustable value (64) and to increase the pressure at the end of expiration on an EFE event (68).

5. Respirator according to claim 4, further comprising: an oximeter port (23) electrically connected to the controller (16) for providing an oxygen saturation signal; wherein the controller (16) is further programmed to determine whether the oxygen saturation falls below (67) a lower limit (27) during a time period after an EFE event and to increase (68) the end-of-expiration pressure only if the oxygen saturation falls below (67) a lower limit (27) during a time period after an EFE event.