EP0483305A1

EP0483305A1 - Device and process for monitoring and regulating the cuff pressure of tracheal tubes

Info

Publication number: EP0483305A1
Application number: EP91907852A
Authority: EP
Inventors: Manfred PFÄNDER; Werner Rainer; Arnold Taber
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1990-04-24
Filing date: 1991-04-23
Publication date: 1992-05-06
Also published as: WO1991016097A1; IT9004817A1; IT9004817A0; IT1241932B

Abstract

Un procédé et un dispositif permettent de surveiller (14, 15) électroniquement et d'égaliser la pression à l'intérieur du manchon (cuff) de tubes endotrachéens, afin d'obtenir une respiration artificielle contrôlée pendant l'anesthésie par inhalation au moyen de gaz qui se diffusent, par exemple de l'oxyde nitreux (N2O) ou des mélanges de gaz contenant des composants gazeux qui se diffusent. L'impulsion du convertisseur de pression (1, 2) relié aux manchons des tubes est amplifiée de manière appropriée (3, 4), parvient à un multiplexeur analogique (5), est conduite de celui-ci jusqu'à un commutateur logique d'alarme (16) et est affichée sur un dispositif d'affichage numérique (8). Des électromoteurs (M, M1) sont entraînés dans l'un ou l'autre sens de rotation au moyen d'un circuit comparateur à fenêtre (comparateur à fenêtre 9) procédant à l'évaluation (12) de la différence entre des valeurs de mesure et des valeurs limites, de sorte que des pompes (P, P1) provoquent l'augmentation ou la diminution requises de la pression (volume) dans les manchons afin de maintenir la pression dans les manchons dans les limites voulues.A method and a device make it possible to monitor (14, 15) electronically and to equalize the pressure inside the sleeve (cuff) of endotracheal tubes, in order to obtain controlled artificial respiration during inhalation anesthesia by means of diffusing gases, for example nitrous oxide (N2O) or mixtures of gases containing diffusing gaseous components. The pulse from the pressure converter (1, 2) connected to the sleeves of the tubes is appropriately amplified (3, 4), reaches an analog multiplexer (5), is led therefrom to a logic switch d alarm (16) and is displayed on a digital display device (8). Electric motors (M, M1) are driven in either direction of rotation by means of a window comparator circuit (window comparator 9) carrying out the evaluation (12) of the difference between values of measurement and limit values, so that pumps (P, P1) cause the required pressure (volume) in the sleeves to increase or decrease in order to keep the pressure in the sleeves within the desired limits.

Description

Device and method for monitoring and regulating the cuff pressure of tracheal tubes

Inhalation anesthesia with endotracheal intubation and controlled ventilation is carried out by means of anesthetic mixtures of gases and vapors generated in our own mixers. Gas is supplied to the patient through a plastic tube that is inserted into the trachea and connected to a ventilator. In order to protect the patient from the risk of endotracheal and thus endobronchial inhalation of various substances (gastric juices, biliary fluid, blood, etc.), the endotracheal tube is provided with an inflatable cuff at its distal end - hereinafter also referred to as the cuff. This cuff is inflated by supplying air through a connecting tube leading to the outside until the tracheal lumen is completely closed above the distal end of the endotracheal tube. In addition, the cuff is indispensable in order to avoid incomplete closure of the tracheal lumen with the gas escaping between the wall of the trachea and the cuff wall. Among the gases used for full anesthesia, the nitrogen oxide (N ₂ 0) is of great importance and is always more or less present in the gas mixture balanced by the addition of other anesthetic drugs.

In the article "Problems of intubation damage with long-term ventilation" by EG Star, Münch. Med. Wschr. 118 (1976), No. 15, pages 457 to 460, causes of tracheal wall damage and different types of cuffs are described. Various mechanisms are discussed in order to regulate the tracheal wall pressure (cuff pressure). In order to hinder the capillary blood flow to the tracheal wall as little as possible from the cuff pressure, DE-A-34 35 900 describes a device for intermittently inflating a cuff for a patient ventilator known. Due to the intermittently inflated cuff, capillary blood flow should only be temporarily impeded for long-term ventilation. In the known device, the cuff is inflated intermittently by an additional connection to the patient ventilator via a control line for controlling the cuff pressure. These relatively complex devices are designed in such a way that the cuff pressure changes constantly in synchronism with the ventilation pressure. As a result of a pre-inflation pressure which is generated by a syringe for specifying the pre-inflation pressure, a cuff pressure corresponding to the pre-inflation pressure results at a ventilation pressure equal to zero. In order to limit the cuff pressure in the inspiration phase, a further device for limiting the cuff pressure to a maximum value and / or to a minimum value is provided.

From DE-A-33 27 342 and DE-A-32 04 110 devices are also known for detecting and evaluating the pressure in the balloon cuff of a tracheal tube, which also work with the aid of the ventilator and are equipped with alarm devices which can be switched on when the specified limit values are exceeded or not reached.

According to DE-A-33 27 342, on the one hand a faulty seal due to insufficient cuff pressure or a cuff leak and on the other hand an excessively high or too low breathing pressure speed can be detected. Such fault conditions trigger unblocking of the balloon cuff and a switchover of the aspirator. Automatic regulation of the internal pressure in the event of the limit values being exceeded or undershot is not provided in the known ventilation device.

In the article "The Redif f usion system limitation of the laughing gas-related pressure increases of endotracheal tubes", Anesthetist, Springer-Verlag 1983, 32; Pages 459-464, from L.Brandt and H.Pokar state that during anesthesia the volume and pressure in the cuff of endotracheal tubes increase due to nitrous oxide diffusion, with increases in cuff pressure up to 100 mm Hg after only two hours being not uncommon. The extent of the volume increase depends on the inspiratory nitrous oxide concentration; their speed is determined by the nitrous oxide diffusion constant of the cuff material, the cuff wall thickness and the nitrous oxide concentration gradient between the cuff on the one hand and the trachea and the tracheal tissue on the other. In the method used, the cuff is blocked during the inspiration phase until no more escape of inspiration air can be heard. In the case of long-term ventilation, any leaks that may occur - be it due to a loss of elasticity of the trachea in the area of contact with the cuff or due to increased ventilation pressure - must be blocked again, which in turn is done by means of a syringe used for blocking and by ear. Because of this effect, the modern high volume low pressure cuff endotracheal tubes for intubation anesthesia are also considered unsuitable. Additions to the

Blocking system with a control mechanism with continuous monitoring or blocking with anesthetic gas mixture or with liquid are said to be unreliable. The proposed rediffusion system for limiting the rise in pressure due to nitrous oxide diffusion provides that the laughing gas diffusing into the cuff diffuses quantitatively into the room air via a correspondingly dimensioned pilot balloon. In order to keep the pressure in the cuff lower than the capillary perfusion pressure of the trachea, the nitrous oxide diffusion out of the pilot balloon must be much more efficient than the nitrous oxide diffusion into the cuff. In the proposed system, after one-time blocking according to the generally widespread method of "blocking by ear", no further manipulation of the blocking system should be necessary, so that the rediffusion system without connection to external cuf pressure control lators, pressure gauges, etc., which are cumbersome, complex and expensive. The rediffusion system, which is largely based on theoretical considerations, does not take into account the dangerous occurrence of leakage between the cuff and trachea for the patient, so that it can be assumed from the authors' finding that it is still a reliable, self-regulating and simple and inexpensive method for limiting the increase in cuff pressure due to nitrous oxide does not exist to this day.

The object of the invention is to provide a device and a method suitable for operating the device in order to avoid exceeding and falling below predetermined limit pressure values in the cuff or in the cuff during the duration of anesthesia, so that the above-mentioned injuries and / or complications or an incomplete closure between the endotracheal tube and the wall of the trachea can be avoided.

A device according to the invention for solving this problem and a method for operating such a device are specified in claims 1 and 7, respectively. Advantageous embodiments of the invention are the subject matter of patent claims 2 to 6 and 8. The content of these cited claims is thus also intended to form part of the description.

It has been found that anesthetic gases diffuse into the cuff during anesthesia and can thereby increase the cuff pressure, as will be explained in more detail below. This fact is not taken into account or taken into account in the known proposed solutions as little as the further fact that after a certain period of time during general anesthesia the trachea dilates due to the cuff pressure acting on it. As a result, there is already a risk during the anesthesia or, if necessary, during the operation that Sealing or the closure of the trachea by the cuff is no longer guaranteed and this may go unnoticed at the operating table or in the intensive care unit.

Because of its extreme diffusion capacity, the nitrogen oxide or laughing gas penetrates into all cavities of the organism and also diffuses through the cuff wall. This cuff wall is exposed to the diffusion of nitrogen oxide on the entire lateral surface adjacent to the wall of the trachea and on the ring surface facing the bronchial tubes, while a significantly smaller surface, namely the ring surface facing the glotis, is exposed to air. According to Henry's law, regarding the effect of pressure on the diffusion of a gas, and because of the above-mentioned difference between the area exposed to nitrogen oxide and the area of the cuff exposed to air (escape option for the N ₂ 0) , the cuff experiences an increase in volume and pressure which is dependent on the duration of the gas exposure and in the ratio between the areas exposed to gas and air, and an increase in volume and pressure which is dependent on the wall area and the material of the sleeve wall.

While for a first phase of putting the cuff into the trachea into operation, a considerable increase in volume can be ascertained until the cuff clings to the inner wall of the trachea, in a second phase, while the nitrous oxide or other anesthetic gases are continuously supplied, an increasing volume / pressure increase after the contact surface of the cuff wall lies against the hardly stretchable structure of the trachea and consequently only the ring-shaped cuff parts facing the bronchial tubes and the glottis can still expand elastically. This increase in volume progressively leads to an increase in pressure in the cuff, so that on the one hand the tracheal wall is subjected to high pressure and on the other hand there is a risk of overextension of the The cuff wall is such that a cuff hernia can occur, which could lead to a closure of the distal tube opening. According to the prior art, a cuff pressure of approximately 30 mm Hg on the tracheal wall is already considered to be an impediment to its capillary perfusion. This pressure value should therefore not be reached or exceeded when the cuff is first inflated or during the further course of the anesthesia.

During ventilation with an anesthetic / hypnotic mixture, an increase in volume / increase in pressure in the cuff can be monitored by means of a manometer, due to the diffusion of e.g. Nitrous oxide in the cuff. Due to the fact that the trachea can hardly be relieved after the initial inflation of the cuff, the anesthetic gas diffusing into the cuff leads to a significant increase in cuff pressure.

It has been shown that starting from an initial minimum pressure, which is required for the positioning of the endotracheal tube, pressure values of 30 mm Hg have been reached and exceeded during the first hour of anesthesia. According to the specialist literature, the view is taken that there is already a risk of damage to the trachea at a threshold value of approximately 17 mm Hg. If, however, the intervention lasts longer, the cuff pressure can exceed the mean arterial pressure. This then leads to total ischemia and tracheal wall damage. This case assumes a presumed circulatory stability during the entire procedure. Temporary arterial hypotension and / or hypovolemia, which could lower the vascular perfusion to a critical level, would exacerbate the potential damage caused by the increase in compressive pressure. The precision of all membrane manometers available to date depends on the air temperature and the relative humidity. They are only suitable for supplying instantaneous values or fluctuations in values at short time intervals, but without indicating the limit values.

The device according to the invention preferably comprises an electronic manometer with a continuous pressure value display, an input for the pressure limit values to be specified, a display which signals the reaching of these limit values acoustically and optically, and at least one motor-driven pump unit, e.g. an electromotive peristaltic pump which is operated as a function of the difference between the limit values and the measured values and thereby keeps the cuff pressure approximately constant within the predetermined limits.

Depending on the direction of rotation of the pump or pumps, the cuff pressure in the cuff (s) is increased or decreased and thus kept within the desired limits.

According to an advantageous embodiment, a device according to the invention has two pressure transducers and two motor-driven peristaltic pumps for connection to endotracheal tubes, such as "Carlens" tubes or the like, which are suitable for separate ventilation of the lungs, equipped with two separate sleeves with their own connecting tubes, and are arranged on a single tracheal tube.

The invention is described in more detail below with reference to the exemplary embodiments shown schematically in the drawing, the invention being not restricted to these exemplary embodiments. It shows:

1 shows in section an endotracheal tube E inserted into a trachea T with the cuff C not yet inflated, the tracheal lumen not being closed according to the drawing; FIG. 2 shows a representation according to FIG. 1 a trachea T with an inserted tracheal tube E with an inflated cuff (cuff C), ready for use for controlled ventilation of the patient;

FIG. 3 shows the endotracheal tube E inserted into the trachea T (shown in section) during the controlled ventilation and showing the diffusion of the anesthetic gas (nitrogen oxide N ₂ O);

Figure 4 shows an inserted endotracheal tube of the "Carlens" type, which is suitable for separate ventilation of the lungs;

FIG. 5 shows a pressure (mm Hg) -time (min.) Diagram which illustrates the typical course of the pressure in the cuff with continued diffusion of the nitrogen oxide pulse;

FIG. 6 shows a functional diagram with a control unit of the device according to the invention for monitoring and regulating the cuff pressure, in the embodiment with two pressure transducers and two motor-operated peristaltic pumps.

Send the pressure sensors or pressure transducers 1, 2, which are exposed to the pressure in the cuff or sleeve C / Cl, C2 through the connecting tubes or feed lines R / Rl, R2

Signals that go through an analog multiplexer circuit 5 after amplification in two separate amplifier circuits 3, 4. The corresponding output signal comes alternately from the first and second pressure sensors 1, 2. This signal is proportional to the cuff pressure and is supplied to the following units of the control unit: a) an alarm logic switching element 16, where, after appropriate processing, the eventual exceeding of the input Reports limit values; 1 b) an input selector 6 and from this to an analog-digital converter 7 and to a display 8 for the display; c) a window comparison circuit or window comparator 5 9, which indicates whether the voltage of the supplied signal is within a certain range or outside of it. Here, a comparison of the supplied signal with a desired pressure value takes place, which would be determined with a certain hysteresis (eg 1 cm H ₂ 0). The difference between the two signals (setpoint and actual value) is additionally amplified by an amplifier 12 which is controlled by the multiplexer 5. The output signal of the multiplexer 5 then controls the pump means that can be driven by electric motors M, Ml, for example the peristaltic pumps P, Pl.

If the difference between the signals emitted by the pressure transducers 1, 2 - relating to the pressure in the sleeves C / Cl, C2 and the signal initially entered - is negative

20 the polarity of the current flowing from the amplifier 12 will be such that the direction of rotation of the motors M, Ml drives the pumps P, Pl in such a way that they suck in outside air through a filter in order to draw them over the connecting tubes R / Rl, R2 in the cuffs C / Cl, C2 and so the pressure p / pl, p2 to

25 increase. If, on the other hand, the difference between the above-mentioned signals is positive, the motors M, Ml will rotate in the opposite direction and the pumps P, Pl suck air from the sleeves C / Cl, C2 and thus reduce the cuff pressure.

30

The minimum pressure required for the respective patient to seal the cuff against the trachea is established during intubation in a manner known per se when blocking by means of e.g. generated by a syringe. This for the respective patient

35 th specific pressure is adjustable via the keyboard 13. The pressure value to be entered is determined by means of a pulse generator 11 converted into an analog signal and fed to the following elements of the control unit: d) the input selector 6, then the A / D converter 7 and then the display 8; e) the window comparator 9, in which the supplied signal

(desired cuff pressure value) is compared with the signal (s) from the pressure sensors 1, 2 or the signals of the measured cuff pressure values.

According to the exemplary embodiment, the alarm logic unit 16 has five inputs:

- for the output signal a from the multiplexer 5, which is proportional to the cuff pressure p / pl, p2 in the sleeves C / Cl, C2; - Two inputs for the signals g, gl coming from pressure switches-14, 15, as additional monitoring of the pressure value p / pl, p2 in the sleeves C / Cl, C2;

for the signal b entered via the keyboard 13, which is proportional to the alarm threshold values of the logic switching element 16;

for the pulse f originating from the multiplexer 5 in order to discriminate the signals originating from the pressure transducers 1, 2 (depending on the cuff pressures).

According to the invention, an alarm for negative pressure is provided if the pressure p / pl, p2 in the cuffs C / Cl, C2 is less than the lower limit value entered on the keyboard 13 (for example in the case of volume shrinkage in the cuffs due to cuff damage or cardiosurgical ones Intervene with the heart-lung machine, whereby the use of anesthetic gas may be temporarily interrupted, which results in the anesthetic gas diffusing from the cuff into the environment and thus a lowering of the cuff pressure). If the trachea continues to be stressed, caused by the cuff pressure exerted on the tracheal wall, Only expand the trachea, which likewise leads to a pressure reduction in the cuff, which, however, can be compensated for by a controllable inflation process.

Furthermore, an alarm in the event of overpressure is provided in the invention if the cuff pressure p / pl, p2 exceeds the upper limit value entered on the keyboard 13 (for example caused by an ongoing diffusion of the anesthetic gas into the interior of the cuff). . In the event that the predetermined upper or lower limit values are exceeded despite the constant automatic pressure compensation provided in accordance with the invention, as well as in the event of a faulty operation of one of the components of the control device, the alarm logic switching element 16 sends out a signal i which acts on the amplifier 12 and thus interrupts the operation of the motors M, Ml and thus stops the pneumatic part of the device according to the invention. After determining and eliminating the causes that led to the triggering of the warning, this operating state is canceled again by actuating a special switching element on the keyboard 13.

In FIG. 6, a digital-to-analog converter 10 is arranged between the pulse generator 11 and the window comparator 9 or the input selector 6 for signal conversion. In FIGS. 2 to 4, A denotes an arrow for identifying the ventilation gas supply (anesthetic gas supply) through the tube. The arrows AI and A2 indicate the anesthetic gas flows to the lungs. The lung-side tube openings are designated by the reference symbols L / L1, L2. The arrow indicates the direction of diffusion of the anesthetic gas into the cuff. The arrow sl marks the direction of diffusion of the anesthetic gas from the cuff. The area s indicates the contact area of the cuff on the inner wall of the trachea.

Claims

1. Device for the automatic monitoring and control of the cuff pressure of tracheal tubes during anesthesia with controlled ventilation, with an electromotive pump unit (P, M; Pl, Ml) which can be controlled via signals from a pressure sensor (1, 2) , which is exposed to the pressure (p / pl, p2) in the cuff (C / Cl, C2), the signals of the pressure sensor being comparable with upper and lower limit pressure values that can be input into a control unit, and depending on the signal values of the Pressure sensor and the positive or negative differences resulting from the predetermined limit pressure values, the control unit controls the pump unit to reduce or increase the pressure in order to maintain a constant cuff pressure which corresponds to a value required for closing the trachea during intubation.

2. Device according to claim 1, wherein the pressure sensor (1, 2) is designed as a pressure transducer, in the signal branch of which an amplifier (12) is provided and wherein the control unit as a function of the positive or negative difference between the measured pressure signals and the predetermined compliance the cuff pressure controls the direction of rotation of the motor (M, Ml) so that the pump unit keeps the pressure in the cuff (C / Cl, C2) constant at the set value by suction or inflation.

3. The device according to claim 1, wherein the pump unit (P, M; Pl, Ml) consists of at least one pneumatic unit, a motor pump or the like, with at least one pressure transducer (1, 2) with amplifier (1, 2) in the control circuit of the pump unit. 3, 4) and at least one pressure switch (14, 15) are provided, and in the case of several pneumatic units a multiplexer (5) is provided which alternately processes the signals converted by the pressure transducers. 4. Device according to one of claims 1 to 3, wherein on the input control circuit of the upper and lower limit values, the continuous display of the pressure values (p / pl, p2) in the or the cuff (s) (Cuff C / Cl, C2 ) and the comparison between the pressure values recognized in the cuff (Cuff C / Cl, C2), at least one pneumatic unit (MP, Ml-Pl) can be connected, at least one pressure transducer (1, 2) with a corresponding amplifier (3rd ,

4) and at least one pressure switch (14, 15) can be provided, a multiplexer (5) being provided in the case of several pneumatic units in order to receive the output of signals which alternate between those of the various pressure transducers (1, 2) correspond to the outgoing signals.

5. Device according to one of claims 1 to 4, wherein the

Control unit comprises an alarm logic element (16) which processes the following signals

- The electrical signals (a) of the multiplexer (5), which are proportional to the cuff pressure values (p / pl, p2), - The signals (g) of the pressure switches (14, 15), which correspond to the cuff pressure values transmitted by the pressure switches (p / pl, p2) correspond,

- The signals (h) which correspond to the upper and lower limit pressure values entered via an input (keyboard), - The pulse (f) delivered by the multiplexer (5), which signals which correspond to the cuff pressure values (p / pl, p2 ) correspond, discriminated, the alarm logic element (16) being able to emit an electrical signal (i) via the amplifier (12) and the electric motors (M, Ml) of the pump units (P, Pl) being switched off and an acoustic and visual display can be activated.

6. Device according to one of claims 1 to 5, wherein the comparison (9), the signals (c) coming from the pressure transducers (1, 2) via the amplification (3, 4) and the multiplexer (5) with the signals (e), which relate to the upper and lower limit pressure values which can be entered by means of the keyboard (13), takes place continuously, whereby either the engagement of the pneumatic units (MP, Ml-Pl) is secured or a there is a minimal difference between the threshold and the initially set value.

7. Method for operating an automated device for monitoring and regulating the cuff pressure of a tracheal tube during anesthesia with controlled ventilation, wherein

the cuff (C / Cl, C2) is set to the bloating pressure (p) resulting from intubation by connected pump means (P, Pl),

at least one pressure sensor (1, 2), which is connected to the air or gas path of the cuff, supplies signals for the cuff pressure,

an electrical control device, in comparison with reference values, responds to the signals received from the pressure sensor in order to stop the inflation of the cuff when a predetermined maximum cuff pressure is reached,

- The electrical control device via the pressure sensor responds on the one hand to a pressure increase due to anesthetic gas diffusing into the cuff and on the other hand to a lowering of the cuff pressure due to an expansion of the trachea, causing the cuff to be deflated or inflated via the pumping means and thus Maintains cuff pressure within predetermined limit values,

- And wherein an optical and / or acoustic display warning device (16) can be actuated via the control device if the cuff pressure falls below or exceeds the set limit pressure values for a long time and thereby a timer responds.

8. The method according to claim 7, so that the control device switches off the pumping means when the warning device is triggered.