Ventilator for respiratory treatment

Abstract: A ventilator for respiratory treatment comprises gas delivery means (16) and regulating means (14) arranged to control said gas delivery means to deliver gas to a patient (8) according to prescribed parameter values to obtain sufficient ventilation of the patient. Means (10) are provided for sensing respiration efforts of the patient and to control said regulating means to adapt an operation cycle of the gas delivery means to sensed respiration efforts of the patient. The regulating means control the gas delivery means also to deliver a pressure or volume support to the respiration of the patient to a predetermined resulting total pressure or volume level. If an apnea exceeding a predetermined length of time is detected by the sensing means the regulating means are arranged to control the gas delivery means to deliver gas to the patient according to the above prescribed parameter values.

Description: The present invention relates to a ventilator for respiratory treatment of a patient with a selectable mode of operation, in particular a control mode such as pressure control, volume control and pressure regulated volume control, or a support mode such as pressure support and volume support, comprising gas delivery means to deliver gas to the patient, sensing means for sensing respiration efforts by the patient and regulating means for controlling the gas delivery means to deliver gas according to a selected mode of operation. Fighting the ventilator by a severely ill patient, that is respiration efforts by the patient non-synchronous to the operation of the ventilator is a common problem encountered in the practice of critical care medicine. This problem can give rise to pain, hypoxia or hypoventilation of the patient. It is of utmost importance in such a situation that the ventilation pattern delivered by the ventilator and set by a clinician does not restrict the patient own desired breathing pattern as this might inflict damages to the lung. If this situation occurs and the ventilator is operating in a so called controlled ventilation mode, that is in a mode in which the ventilator is working according to preset parameter values, each respiration effort by the patient will be rewarded by the delivery of one tidal volume as set by the clinician, no more and no less, and this only under the presumption that the triggering level of the ventilator, has been set judiciously so the patient can trigger a ventilator delivered tidal breath. To cope with this situation common practice is to sedate the patient and administer a neuromuscular blocking drug, which will induce muscle paralysis and stop further respiration attempts by the patient. The use of neuromuscular blocking drugs in the intensive care has, however, been frequently condemned, because of lack of knowledge about the effects of longterm usage. Another way of handling the problems in connection with non-synchronism between the operation of the ventilator and the respiration efforts of the patient is to manually change the breathing mode of the ventilator, so the respiration of the patient is supported by the ventilator, allowing the patient to breath spontaneously and receive proper pressure or volume support. This operating mode of the ventilator will give the patient the possibility to breath at his own leisure and give the clinician time to analyze the state and then take proper measures to treat underlying problem in a more sensitive way than by using neuromuscular blocking drugs as mentioned above. However, as the situation can be quite alarming and very often no time is available for analysis, there is a tendency to treat the patient according to a routine prescription and leave the analysis until the adequate situation is amended. This can prolong the time the patient stays connected to the ventilator, increase the complication rate and deteriorate the clinical outcome. The above-mentioned modes of operation of a ventilator for respiratory treatment are described in the publication Servo Ventilator 300, Operating Manual, chapter 5, issued by Siemens-Elema AB, May 1993. This publication discloses, on pages 84-85, a ventilator according to the preamble of claim 1. Even if the patient is not fighting the ventilator as described above, there is a risk that the patient will spend too long a time connected to the ventilator by using machine controlled ventilation for extended periods of time. This can result in weakening and even wasting of the respiratory muscles of the patient and prolonged time for weaning off the ventilator. Therefore, also in this situation there is a risk of increased complication rate and impaired clinical outcome. The disadvantages of the current ventilator technique thus reside in the fact that the breathing mode determined by the ventilator forms an obstacle to attempts of spontaneous respiration of the patient, and this situation can only be amended by manually changing the settings controlling the operation of the ventilator. The purpose of the present invention is to remedy the above disadvantages of prior art ventilators and provide a ventilator for automatically choosing and adapting the ventilation mode to the needs of the patient. This purpose is obtained with a ventilator according to the introductory portion with the characterising features according to claim 1. With the present invention is consequently provided a ventilator for respiratory treatment of patients, which ventilator automatically adapts its mode of operation to give the patient a proper support, from a situation with a patient without any respiratory drive at all to a patient having a practically sufficient spontaneous respiration and every intermediate degree of defective respiration. Thus the ventilator according to the invention is automatically switched, in response to respiratory efforts of the patient, to an operation mode in which the spontaneous respiration of the patient is supported to obtain sufficient ventilation. Also in case of an apnea exceeding a predetermined length of time the ventilator is switched to operate according to prescribed parameter values to also in this situation obtain sufficient ventilation of the patient. Thus, every apnea will also be backed up, that is the ventilator is safe in this respect. According to an advantageous embodiment of the ventilator according to the invention the regulating means are disposed to increase the tidal volume to maintain the set minute volume, if the sensed respiration rate decreases below a value corresponding to said prescribed operation cycle. The tidal volume can be increased to a maximum of 50 % above the tidal volume value corresponding to the set minute volume and operation cycle. Thus, if the patient's spontaneous breathing frequency drops below the prescribed value, the tidal volume will increase in order to maintain the prescribed minute volume. According to another advantageous embodiment of the ventilator according to the invention the regulating means are controlling calculation means provided to calculate the impedance of the airway of the patient in response to a sensed spontaneous respiration effort of the patient and in that said regulating means are controlling said gas delivery means in response to the calculated impedance to give proper volume support in order to deliver a tidal volume to the patient corresponding to the set minute volume and operating cycle. This is important if the patient make spontaneous breathing efforts during the initiation of the ventilation treatment, and after three or four breaths the ventilator will in this way deliver a proper support level to the patient. Thus, in the so called support mode the patient control the breathing frequency and gets support from the ventilator on every initiated breath. According to yet another advantageous embodiment of the ventilator according to the invention the regulating means are resetting said calculation means for a new attempt of impedance calculation in case of an impedance calculation failure and, in case of repeated impedance calculation failures, the regulating means are controlling said gas delivery means, after predetermined number of failures, to deliver respiration support to the patient according to the prescribed parameter values for a certain time, wereupon the regulating means control the calculation means to make a new attempt of impedance calculation and the procedure above is repeated. This is an important advantage, since in certain circumstances it can be difficult because of instable conditions to calculate a proper airway impedance for the ventilator. This might lead to a situation where the ventilator will repeatedly reset in order to find a proper starting point. This is avoided with this embodiment of the ventilator since after a predetermined number of unsuccessful calculation attempts the ventilator switch to so called controlled ventilation, that is respiration gas is delivered to the patient according to prescribed parameter values for a certain time, whereupon new attempts are made to calculate the impedance. This procedure can be repeated several times. According to still another advantageous embodiment of the ventilator according to the invention, the regulating means are controlling said gas delivery means to deliver respiration support to the patient according to prescribed parameter values corresponding to single breaths synchronized to sensed respiration efforts of the patient at intervals equal to a number of complete respiration periods. According to this embodiment the ventilator is operated with a certain base frequency also when the patient is spontaneously breathing to give an extra respiration support, the supporting gas pulses delivered by the ventilator being synchronized to the spontaneous respiration of the patient. According to yet another advantageous embodiment of the ventilator according to the invention indicator means are provided to indicate every sensed breath to inform the clinician about the current mode of operation of the ventilator. According to a further advantageous embodiment of the ventilator according to the invention the sensing means comprise a flow sensor, which makes reliable triggering of the ventilator by respiration efforts of the patient possible. To explain the invention more in detail embodiments of the ventilator according to the invention will now be described with reference to the drawings, on which Fig.1 shows schematically a block diagram of an embodiment of the ventilator according to the invention, chosen as an example, and Fig.2 discloses a flow diagram for a special form of ventilator support to spontaneous respiration of a patient. In figure 1 a ventilator 2 is connected through inspiration 4 and expiration 6 tubes to a patient 8. Sensing means in the form of pressure or flow sensors 10 are provided in the inspiration 4 and the expiration 6 tubes. In the inspiration tube also an oxygen sensor 12 is situated to monitor the oxygen content of the breath delivered to the patient. The sensing means 10 are connected to regulating means 14 which in their turn are connected to gas delivery means 16 for controlling the delivery of gas to the patient 8 in response to signals from the sensing means 10 and/or in response to externally prescribed parameter values as described below. The sensing means 10 thus serve as means for triggering a mode of operation of the ventilator suitable for the condition of the patient, and the sensing means 10 can form a flow triggering or pressure triggering means for the ventilator. The regulating means 14 are also connected to calculation means 18 which are connected to the gas delivery means 16 too. These calculation means 18 are provided for calculation of the impedance of the airway of the patient 8 as will also be described in greater detail below. Indicator means comprising electronics 20 and light sources, e.g. in the form of a light emitting diode 22, 24, are also connected to the sensing means 10 for indicating to the operator of the ventilator spontaneous respiration of the patient 8. Those parts of the ventilator which are not of importance for the explanation of the invention have been omitted from the figure. The operation of the ventilator will now be described in greater detail by three coupled operation modes. 1. Pressure Controlled Ventilation - Pressure Supported Ventilation. The ventilator operates according to parameters prescribed by the operator. These parameters set by the operator are the pressure above the Post End Expiratory Pressure (PEEP), the operation cycle and oxygen content of breath to be delivered. With the exception of the operation cycle the same parameters are set also for the pressure supported ventilation. In the case of pressure controlled ventilation the ventilator will consequently work according to these prescribed parameters up to the point where the patient triggers the ventilator to change its mode of operation to pressure supported ventilation. Thus, if the patient starts an own breath, detected by the sensing means 10, the ventilator will respond by giving a pressure support to the patient up to the pressure level set by the operator and the breathing frequency will be controlled by the sensed respiration efforts of the patient. Every breath initiated by the patient will be supported from the ventilator, i.e. a respiration effort sensed by the sensing means 10 triggers the regulating means 14 to control the gas delivery means 16 to give a pressure support to the patient for each detected breath. If the patient becomes apneic for a certain period of time, e.g. 15 - 18 seconds, that is no spontaneous respiration is sensed by the sensing means 10 during this time, the ventilator is switched to the controlled mode of operation. In this mode the regulating means 14 are controlling the gas delivery means 16 to give a pressure controlled ventilation to the patient according to the prescribed parameters, until the ventilator 2 is once again triggered to the pressure support ventilation mode by respiration efforts by the patient. If the patient 8 should make spontaneous breathing efforts during the initiation of the ventilator treatment, these breathing efforts will be detected by the sensing means 10 and in response thereto the regulating means 14 will start the gas delivery means 16 to deliver pressure supported breaths according to the set values. The indicator means 20, 22, 24 are connected to the sensing means 10 to indicate to the operator whether the ventilator 2 is operating in the controlled or the supported mode. Thus, the indicator means are triggered by every breath such that a light emitting diode 22 is lit up in response to every sensed breath. 2. Volume Controlled Ventilation - Volume Supported Ventilation In the volume controlled mode of ventilation the prescribed parameters delivered to the regulating means 14 are minute volume, PEEP, operation cycle and oxygen content of the breath to be delivered. With the exception of the operation cycle these parameters also determine the volume supported ventilation. In the volume controlled mode of ventilation the ventilator is controlled to work with the above mentioned prescribed parameters up to the point where a respiration effort is sensed by a sensing means 10 which triggers the ventilator 2 to change mode of operation. In this support mode the ventilator 2 will respond to a patient triggered breath by giving a volume supported breath with the pressure level of the first supported breath corresponding to the pause pressure of the volume controlled breath. As the resulting flow is detected in the inspiration tube 4 the regulating means 14 will adjust the support level of the gas delivery means in order to maintain the set tidal volume. Thus, the patient controls the breathing frequency and is supported from the ventilator on every initiated breath. If the sensed spontaneous breathing frequency of the patient drops below a value corresponding to the prescribed operation cycle for the controlled ventilation mode, the regulating means 14 will control the gas delivery means 16 to increase the tidal volume to maintain the prescribed minute volume. The tidal volume can be increased up to a maximum of 50 % above the tidal volume value corresponding to the prescribed minute volume and operation cycle. If the patient should make spontaneous breathing efforts during the initiation of the ventilator treatment which are detected by the sensor means 10, the regulating means 14 will control calculation means 18 to calculate the impedance of the airway such that the proper support level can be delivered for obtaining the set tidal volume. The impedance is determined by applying with the aid of the gas delivery means 16 a certain pressure, e.g. 5 cm H 2 O, and the resulting gas flow is measured with the flow meter in the inspiration tube 4. From this value the impedance can be calculated and the regulating means 14 can control the gas delivery means 16 to give the proper support level in order to get the set tidal volume. This proper level is reached after three or four breaths. The operation frequency or operation cycle of the ventilator 2 is adjusted to the patient's spontaneous respiration rate in the same way as described above under point 1, and if an apnea lasting for a period of 15 - 18 seconds is detected by the sensor means 10 the ventilator 2 will be switched to the volume controlled ventilation mode till sensing means 10 once again detects a respiration effort from the patient which triggers the regulating means 14 to control the gas delivery means 16 according to the volume supported mode of operation. Also in this embodiment the LED 22 will light up on every sensed breath from the patient 8, thus informing the operator about the current mode of operation of the ventilator 2. 3. Pressure Regulated Volume Controlled Ventilation - Volume Supported Ventilation - Volume Controlled Ventilation In the pressure regulated volume controlled (PRVC) mode of ventilation the prescribed parameters are the same as for the volume controlled mode of ventilation described under point 2 above and similarly, with the exception of the operation cycle, the same parameters also applys to the volume supported mode of ventilation. When the PRVC mode of ventilation is started the ventilator will work according to the prescribed parameters up to the point where the ventilator 2 is triggered to change mode of operation by respiration efforts sensed by the sensing means 10. If the regulating means 14 are triggered by sensed respiration efforts of the patient to change mode of operation the gas delivery means 16 will be controlled to respond by giving a volume supported breath with the pressure level of the first supported breath corresponding to the level of the PRVC breath. The resulting flow in the inspiration tube 4 will be measured and the regulating means 14 will adjust the support level of the gas delivery means 16 in order to maintain the set tidal volume corresponding to the prescribed minute volume and operation cycle. The patient 8 will then control the breathing frequency and get support from the ventilator 2 on every initiated breath, and if the patient's 8 spontaneous breathing frequency drops below the prescribed value for the controlled mode of ventilation the tidal volume will be increased as described in relation to the embodiment under point 2 above. Also as described above, under point 2, the impedance of the airway is calculated by the calculating means 18 if the patient should make spontaneous breathing efforts during the initiation of the ventilator treatment to be able to deliver the proper support level for maintaining the tidal volume equal to the set value. If an apnea is detected for a period of 15 - 18 seconds the ventilator will switch back to the controlled mode in the same way as described for the previous embodiments under points 1 and 2. Under certain circumstances of instability it can be difficult to calculate a proper airway impedance for the ventilator 2 on initiating PRVC. This might lead to a situation where the ventilator 2 will repeatedly be reset in order to find a proper starting point. To avoid this situation the regulating means 14 are disposed to change mode of operation after three unsuccessful attempts to the volume controlled mode of ventilation. This situation is suitably indicated to the operator by a blinking volume control LED 22 and a continuously lighting PRVC LED 24. After a period of 2 - 5 minutes the regulating means 14 are controlled to again attempt to change mode of operation to the PRVC mode of ventilation and if the attempt is successful the usual start-up sequency is gone through. Possibly subsequent switching from the PRVC mode of ventilation to the volume supported mode is performed as described above. If initiation once again fails the volume controlled mode of respiration is resumed and a new attempt is made after another 2 - 5 minutes. The start-up of the PRVC mode of ventilation can also preferably be initiated manually by turning a RESET-button. Also in this embodiment suitable indicator means are provided to inform the operator about the current mode of operation of the ventilator. The regulating means 14 can also control the gas delivery means 16 to deliver a special kind of respiration support to a patient 8 having a certain spontaneous respiration, se figure 2 which shows gas flow Φ as a function of time illustrating this situation. The pulses 26 are produced by spontaneous respiration of the patient and this respiration is supported by pulses 28 delivered with a predetermined base frequency. The volume of these supporting pulses 28 corresponds to the volume of a single breath and these supporting pulses 28 are synchronized to the sensed respiration efforts of the patients and are delivered at intervals equal to a complete number of respiration periods.

Claims: Ventilator for respiratory treatment of a patient (8) with a selectable mode of operation, in particular a control mode such as pressure control, volume control and pressure regulated volume control, or a support mode such as pressure support and volume support, comprising gas delivery means (16) to deliver gas to the patient (8), sensing means (10) for sensing respiration efforts by the patient (8) and regulating means (14) for controlling the gas delivery means (16) to deliver gas according to a selected mode of operation, characterized in that the regulating means (14) is adapted to, when controlling the gas delivery means (16) to deliver gas according to a control mode of operation, automatically switch its control of the gas delivery means (16) to deliver gas according to a support mode of operation upon a sensed respiration effort by the sensing means (10). Ventilator according to claim 1, characterized in that the regulating means (14) is adapted to automatically switch its control of the gas delivery means (16) back to deliver gas according to a control mode of operation upon an absense of sensed respiration efforts for a specific time period (apnoea) by the sensing means (10). Ventilator according to claim 1 or 2, characterized in that the control mode is pressure control, which comprises as prescribed parameters pressure above PEEP, operation cycle and oxygen content of the breath to be delivered, and in that the support mode is pressure support. Ventilator according to claim 1 or 2, characterized in that the control mode is volume control or pressure regulated volume control, which comprise as prescribed parameters tidal volume, operation cycle and oxygen content of the breath to be delivered, and in that the support mode is volume support, which comprises as prescribed parameter minute volume. Ventilator according to claim 4, characterized in that the regulating means (14) controls the gas delivery means (16) to increase the tidal volume to maintain the prescribed minute volume, if the rate of respiration efforts sensed by the sensing means (10) decreases below a prescribed value. Ventilator according to claim 5, characterized in that the regulating means (14) limits the gas delivery means' (16) increase of the tidal volume to a maximum of 50% above the prescribed tidal volume. Ventilator according to claim 4, characterized in that the regulating means (14) controls the gas delivery means (16) to deliver gas according to the volume support mode of operation for the first respiration effort sensed by the sensing means (10) with a pressure level that corresponds to a pause pressure of the volume control mode of operation, whereupon the regulating means (14) controls the gas delivery means (16) to adjust the delivery of gas according to the volume support mode for following breaths to maintain the tidal volume equal to a value corresponding to the prescribed minute volume and operation cycle. Ventilator according to claim 4, characterized in that the regulating means (14) controls a calculation means (18), which is provided to calculate the impedance of the airway of the patient (8) in response to a spontaneous respiration effort of the patient (8) sensed by the sensing means (10), and in that the regulating means (14) controls the gas delivery means (16) in response to the impedance calculated by the calculation means (18) to give the proper volume support in order to deliver a tidal volume to the patient corresponding to the prescribed minute volume and operation cycle. Ventilator according to claim 8, characterized in that, in case the calculation means (18) fails to calculate the impedance, the regulating means (14) resets the calculation means (18) for a new attempt of impedance calculation, and, in case the calculation means (18) repeatedly fails to calculate impedance for a predetermined number of, the regulating means (14) controls the gas delivery means (16) to deliver gas according to the volume control mode for a certain time, whereafter the regulating means (14) controls the calculation means (18) to make a new attempt of impedance calculation. Ventilator according to any one of the claims 1 - 9, characterized in that the regulating means (14) controls the gas delivery means (16) to deliver gas according to a control mode with prescribed parameter values corresponding to single breaths synchronized to respiration efforts sensed by the sensing means (10) at intervals equal to a predetermined number of respiration periods. Ventilator according to any one of the claims 1 - 10 characterized in that indicator means (22) is provided to indicate sensed breaths.

Inventors: STROEM CHRISTER, STROEM, CHRISTER, Ström, Christer
Applicants: SIEMENS ELEMA AB, SIEMENS-ELEMA AB
Application year: 1996
Main classification: A61M16
IPC codes: A61M16