IT9004817A1 - DEVICE FOR MEASUREMENT AND PRESSURE CONTROL INSIDE THE HEADSET OF PIPES FROM GENERAL ANESTHESIA WITH ENDOTRACHEAL INTUBATION AND MECHANICAL VENTILATION - Google Patents

Description

DESCRIPTION

General anesthesia by inhalation, with endotracheal intubation and controlled mechanical ventilation, is maintained by delivering, through special mixers, a mixture of anesthetic gases and vapors. Delivery to patients takes place through a plastic tube which, positioned in the trachea, is connected to a ventilatory prosthesis. To protect patients from the risk of endotracheal inhalation and therefore endobronchial material of various kinds (gastric juice, bile, blood, etc.), the tracheal tube is equipped, at its distal end, with an inflatable balloon called "cuff". This cuff is expanded with the introduction of air through a tubular connection with the outside until complete occlusion of the tracheal lumen upstream of the distal end of the endotracheal tube. The cuff is also essential to avoid incomplete closure of the tracheal lumen with consequent venting of gases between the tracheal wall and that of the cuff. Among the gases used for general anesthesia, nitrous oxide (N20) always present in the inhalation mixture balanced more or less by the addition of other anesthetic / hypnotic drugs is of great importance.

Nitrous oxide, thanks to its extreme diffusibility, penetrates all body cavities and also diffuses through the walls of the cuff. This is exposed, for the whole band of adhesions to the trachea and for the annular surface facing the bronchi, to the diffusion of nitrous oxide while a considerably smaller surface, that is the annular one facing the glottis, is exposed to the air. Due to Henry's law relating to the influence of pressure on the solubility of a gas and for the aforementioned significant difference between the surface exposed to nitrous oxide and that exposed to air (exhaust for N20), the hood undergoes inside an increase in volume and pressure in relation to the time of exposure to the gas, the ratio of the surface exposed to the gas to the surface exposed to air and the thickness and type of the material constituting the hood. in the trachea there is a significant increase in volume until adherence to the internal walls of the trachea is obtained, subsequently, by continuing the introduction of air through the tubular fitting, a progressive increase in pressure is obtained meeting the adhesion band of the wall of the cuff the almost inextensible structure of the trachea and only the annular portions of the cuff facing the bronchi and the other towards the glottis. This increase in volume will progressively lead to an increase in the transmural pressure of the cuff, affecting the tracheal mucosa and may, among other things, lead to over-distension of the cuff wall with the risk of forming a "hernia" of the balloon occluding the distal hole of the tube itself.

Regarding the increase in pressure inside the cuff and its consequences, there are well-documented data and studies that determine for pressure values of approx. 30mm Hg compression of the blood capillaries of the tracheal mucosa. These values must not be reached neither in the initial insufflation phase of the cuff nor in the further course of the anesthesia. Using a manometry system, on the other hand, it can be seen that in the course of ventilation with an anesthetic / hypnotic mixture there is, due to the diffusion of nitrous oxide present therein in various concentrations, an increase in volume and therefore, due to the inextensibility of the trachea against which a large part of the cuff wall bears due to the initial insufficiency, a significant increase in pressure.

Practice has shown that, however, starting from a minimum initial pressure required for the efficient accommodation of the endotracheal tube already during the first hour of anesthesia, the values of 30mm Hg can be reached and exceeded. It should be noted that the specific literature agrees that the threshold value for the risk of damage is approximately 17mm Hg. If, on the other hand, the operation lasts more than 300 min., The pressure values in the cuff exceed the average systemic arterial pressure values, causing total ischemia with reactive phenomena that can lead to stenosing cicatricial repair processes. All this if there is an absolute circulatory stability of the patient during the whole operation. Episodes of arterial hypotension and / or severe intraoperative hypovolemia, such as to determine a circulatory pattern close to critical levels of perfusion, only aggravate the potential for damage that derives from the increase in pressure in the cuff.

Special membrane pressure gauges are known for measuring the pressure in the cuff, which, being membrane, are subject to accuracy in terms of temperature variations of the relative humidity of the air and are suitable for giving momentary values or variations in values within short times, without reporting of limit values. A device for measuring the pressure inside the cuff is also known with the possibility of compensating for any pressure drops in the cuff, for example due to laceration; this device does not allow automatic pressure regulation in case of exceeding of predetermined values.

The invention has the task of realizing a device capable of avoiding both the exceeding and the lowering of the pressure inside the headphone balloon beyond predetermined limit values during the performance of anesthesia to prevent injuries and / or complications described above. respectively the incomplete occlusion between the endotracheal tube and the walls of the trachea.

To accomplish this task, the invention proposes a device consisting essentially of an electronic pressure gauge with continuous display of the trend of the pressure values, with a device for entering limit values and signaling (acoustic and visual) of the achievement of these values and with at least one motor-peristaltic pump unit operated in relation to the difference between the detected value and the reference limit values, keeping the pressure values in, or in the hoods, within these limit values.

Conveniently, the device according to the invention is equipped with two pressure transducers and two peristaltic pump-motor units for connection to "Carlens" and related pipes, suitable for ventilation with separate lungs, equipped with two distinct cuff balloons, each with its own tubular fitting, provided on a single endotracheal tube.

The invention is explained more closely on the basis of an embodiment example of the measuring and control device according to the invention, schematically represented in the attached drawings, which have a purely explanatory and non-limiting purpose.

Fig. 1 schematically illustrates the endotracheal tube inserted into the trachea (in section) with the cuff balloon not insufflated, without occlusion of the tracheal lumen.

Fig. 2 schematically illustrates the endotracheal tube inserted into the trachea (in section) with the cuff balloon inflated, ready for mechanical ventilation.

Fig. 3 illustrates the endotracheal tube inserted into the trachea (in section) with mechanical ventilation in place and indication of the diffusion of nitrous oxide (N20).

Fig. 4 illustrates a "CARLENS" type endotracheal tube suitable for separate ventilation, planted.

Fig. 5 is a pressure (mm Hg) - time (min.) Diagram for the representation of the typical trend of the pressure in the cuff with continuous diffusion of nitrous oxide (N20).

Fig. 6 is an operating diagram of the device for measuring and controlling pressure according to the invention with two pressure transducers and two peristaltic motor-pump units.

The pressure transducers (1,2) exposed to the pressure in the cap (C / C1.C2) through connection to the tubular fittings (R / R1.R2) emit signals which, when amplified in two distinct amplifier circuits (3,4), pass to an analog multiplexer circuit (5) from which an electric signal comes out coming alternately from the first or from the second pressure transducer (1,2). This signal, which is proportional to the pressure in the headphones, is sent (a) to the alarm logic (16) where, when suitably processed, it signals any exceeding of predetermined limit values; (b) to an input selector (6) to pass to an analog-digital converter (7) and subsequently be shown on a display (8); (c) to a window comparator circuit (9) where it is compared with a signal proportional to the desired pressure value and initially set with a certain pressure hysteresis (1cm H20). The difference between the two signals is further amplified in the amplifier circuit (12), controlled by the multiplexer (5), whose output signals control two electric motors (M, M1) connected to peristaltic pumps (P, Pi).

If the difference between the signal emitted by the pressure transducers (1,2) in relation to the pressure in the headphones (C / Ci, C2) and the signal initially set is negative, the direction of the output current from the amplifier (12) will be such as to make the motors (M, M1) turn so that the pumps (P, P1) suck, through a filter, external air, introducing it into the hoods (C / C1, C2) through the tubular fittings {R / R1.R2) increasing the pressure (p / pi, p2). If the difference between the above signals <'> is positive, the motors (M, M1) will turn in the opposite direction and the pumps (P, P1) will suck volume from the headphones (C, C1, C2), reducing the pressure.

The initial setting of the desired pressure value in the headphones (C / C1, C?) Takes place on the keyboard (13) in numerical form. This set value is converted into an analog signal by the pulse generator (il) and sent:

(d) to the input selector (6) and then to the analog to digital converter (7) to be subsequently shown on the display (8); (e) to the window comparator (9) where it is compared with the electrical signal coming from the pressure transducers (1,2) and then from the headphones (C / CI, C2).

The alarm logic (16) has five inputs

for the signal (a) in output from the multiplexer (5), proportional to the value of the pressure (p / pl, p <'> 2) in the cuff (C / C1, C2);

for two signals (g) deriving from the pressure switches (14,15) for a further check on the pressure value (p / p1, p2) in the hood (C / C1.C2);

for a signal (b) coming from the keyboard (13) proportional to the alarm threshold values;

for an electrical impulse (f) coming from the multiplexer (5) required to be able to discriminate in the alarm logic (16) the signals coming from the two pressure transducers (1,2) and that is from the headphones (C / Ci, C2).

The alarms foreseen are: underrepression, if the pressure (p / pi, p2) in the headphones (C / Ci, C?) Is lower than the minimum threshold value set on the keyboard (1 3) (for example caused by leak volume from the headphones due to injury of the same or, in the course of cardiac surgery, with <'> extra-corporeal circulation in the operating phase in which mechanical ventilation with the possible use of N20 is temporarily suspended causing the leakage of the N20 from the cuff towards the ambient) and overpressure, if the pressure (p / p1, p2) exceeds the set maximum threshold value (for example caused by prolonged N20 diffusion in the cuff). If the minimum and maximum threshold values set are exceeded, despite continuous automatic compensation, (even in the event of a malfunction of one of the device components), the alarm logic (16) emits a signal that acts on the current amplifier (12) thus blocking the operation of the motors (M, M1) and therefore the pneumatic part of the device. This lockout condition, after checking and removing the causes of the alarm, is canceled by intervening with the appropriate command on the keyboard (13).

Claims (1)

R I V E N D I C A Z I O N I 1 - Device for the measurement and control of pressure inside endotracheal tube caps for general anesthesia with mechanical ventilation equipped with pneumatic group, characterized by the fact that the pneumatic group consists of an electric motor (M, M1) driving a pump (P, P1) and controlled by signals coming out of an amplifier (12) coming from a pressure transducer (1, 2) exposed to the pressure (p / p1, p2) in the headphones (C / C1, C2) and compared with values minimum and maximum threshold pressures set on a special keyboard (13) determining the negative or positive difference between these pressure values determining the direction of rotation of the motor (Μ, ΜΊ) causing the pump (P, P1) to aspirate or introduce volume from, respectively towards the cuff (C / C1, C2), thus keeping the pressure (p / p1, p2) constantly at the initial value corresponding to the pressure necessary to obtain the occlusion of the trachea at the moment of insertion of the tube. 2 - Device for measuring and controlling the pressure according to claim 1, characterized in that the same circuit for setting the minimum and maximum pressure threshold values, continuous display (8) of the pressure values (p / pi, p2 ) at least one pneumatic unit (M-P, M1-P1) can be connected in the or in the hoods (C / C1, C2) and for comparison between the pressure values detected in the hood CC / C1, C2) providing at least one pressure transducer (1, 2) with relative amplifier (3,4) and at least one pressure switch (14,15), providing in the case of several pneumatic units a multiplexer (5) to obtain the output of signals which alternatively correspond to the signals coming from the different pressure transducers (i, 2). 3 - Device for measuring and controlling pressure according to claims 1 and 2, characterized in that an alarm logic (16) is provided which, taking into account the electrical signals (a) coming from a multiplexer (5), are proportional the blood pressure values (p / p1, p2) in the headphones (C / C1, C2); signals (g) coming from pressure switches (14,15) also exposed to the pressure (p / p1, p2) in the headphones (C / C1, C2); of the signals (h) relating to the minimum and maximum pressure threshold values set on the keyboard (1.3) and of an electrical impulse (f) coming from the multiplexer (5) for the discrimination of the signals relating to the pressure values (p / pl, p2) in the headphones (C / C1, C2); emits an electric signal (i) acting on the current amplifier (12) blocking the electric motors (M, M1) activating an acoustic and visual signal. 4 - Pressure measuring and control device according to Claims 1 to 3, characterized in that the comparison (9) of the signals (c) coming, following amplification (3,4) and processing in the multiplexer (5), from the pressure transducers (1,2) with the signals (e) relating to the minimum and maximum threshold pressure values set via the keyboard (13), takes place continuously ensuring the intervention of the pneumatic units (M-P, MI-P1 ) or there is a minimum threshold difference with respect to the initial set value.