RU2329832C1 - Method of stabilisation of anaesthetic target concentration and related device - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: invention refers to medical equipment. Method includes total gas flow splitting between evaporation chamber and bypass by means of laminar hydromechanical resistances, equilibrium anaesthetic vapours saturation of partial gas volume passing through evaporation chamber followed with dilution to specified clinical concentration with rest gas volume passing through bypass, correction of total gas flow splitting considering temperature and pressure values. Gas pipelines of bypass and evaporation chamber are preinstalled in horizontal planes at height, in case anaesthetic target concentration is increased at gas flow of small volumes, bypass height is raised over evaporation chamber while it is lowered in opposite case. Anaesthetic evaporator for method realisation is described.

EFFECT: increase of anaesthetic dosing accuracy.

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Description

The invention relates to medical equipment, namely to anesthetics vaporizers and apparatus for inhalation anesthesia (IN). The evaporator saturates the carrier gas stream (atmospheric air or compressed medical gases) with anesthetic vapors, after which the formed vapor-gas mixture is supplied to the patient.

There are various methods of stabilizing the concentration of anesthetic at the outlet of the evaporator and various designs for implementing these methods (RF patents No. 2178314, A61M 16/01, 2000; 2000817, A61M 16/18, 1991; 1810061, 1991; US patents No. No. 6526297, 600/310, 2000; 6816669, 392/397, 2004; Prince Berlin A.Z., Meshcheryakov A.V. “Anesthesia and dosing of anesthetics.” M., Medicine, 1980).

Known methods and devices, differing in the final structural implementation, have common characteristic significant disadvantages:

- high resistance to gas flow, which does not allow working in air (Draw-over Anesthesia) in the absence of sources of compressed medical gases;

- significant losses of expensive and scarce anesthetics due to the large capacity of wicks (60-70 ml of liquid anesthetic is used only for soaking the wicks of modern evaporators at a cost of, for example, Sevoflurane 1 dollar / ml), which significantly increases the cost of operation and pollutes the workplace of the anesthetist.

The known method (Dobson MB Anaesthesia at the district hospital. 2 ^nd edn. 2001) and equipment (vaporizer of low resistance anesthetics "Anesthesist-2", is given in USSR author's certificate No. 440016, A61M 17/00, 1974 and US patent No. 3836129, 261/47, 1974) for Draw-over Anesthesia. The specified device and method for stabilizing the output concentration of anesthetic is the closest in technical essence and is selected as a prototype of the patented invention.

The known evaporator allows you to work both in the presence of compressed medical gases in hospitals and clinics, and in their absence in the field.

However, the use of the Draw-over Anesthesia technique is limited due to insufficient dosing stability of anesthetics. In particular:

- poor dosing stability at low gas flows (less than 2 l / min - Low Flow Anesthesia) when using modern semi-closed and closed breathing circuits;

- unsatisfactory stability of dosing of anesthetics with changing environmental pressure (highlands), as well as with pulsation of pressure and gas flow in the respiratory circuit of the patient;

- the need for manual adjustment of the concentration in case of temperature changes.

So, the best foreign low-resistance evaporators (OMV Penlon, Ohmeda RAS) no longer work with a gas flow of less than 2 l / min. In this case, the pressure drop (resistance to gas flow) of the evaporator (flow divider) as a control action is very small and is comparable with the difference in the densities of the carrier gas and the anesthetic vapor as a disturbing factor.

Example 1

The pressure drop due to the difference in the densities of air and anesthetic vapor (halotane) in the OMV Penlon evaporator with a difference in the bypass and input / output levels of the 60 mm evaporation chamber is about 1.5 Pa (0.15 mm Hg). The indicated value is subtracted from the control action of the flow divider, and with a gas flow rate of about 1.5 / min, heavy anesthetic vapors simply block the passage of fresh gas into the evaporation chamber. In this case, the output concentration is zero at any position of the evaporator scale.

On the other hand, the need for equilibrium saturation of the carrier gas in the evaporation chamber contradicts the stable division of the gas flow with pulsating flow and gas pressure ("back pressure" in the patient's breathing circuit. So, the evaporation chambers of modern evaporators have extended and winding flues for lengthening the contact time of the carrier gas with the evaporation surfaces (wicks) of the anesthetic, which does not correspond to a direct and short bypass duct. Such critical asymmetry is the cause of significant instability of dosing during dynamic processes (pulsation of the flow rate and gas pressure in the patient's respiratory circuit).

The present invention solves the problem of increasing the accuracy of dosing in the widest possible ranges of constant and pulsating gas flows, ambient temperature and pressure.

The solution to this problem is achieved by a combination of new circuitry and design solutions implemented in the patented invention.

The anesthetic vaporizer is similar to the design described in the copyright certificate No. 440016, containing a gas flow divider in the form of slotted channels on the bypass lines and an evaporation chamber equipped with wicks, an anesthetic concentration scale attached to the divider, the input and output, according to the present invention, is equipped with a temperature compensator and a thermal stabilizer, thermally connected with each other and with the bottom of the evaporation chamber, the divider is installed horizontally inside the evaporation chamber, adjoins its cover and is mechanically connected with thermal bar compensator.

The invention provides that the temperature compensator is made in the form of a coaxially mounted bellows with easily volatile liquid, a tubular conical tip with a confuser on the inner surface, a conical obturator interacting with the confuser, and a poppet valve interacting with the said tip, while one end of the bellows is fixed to the axis of the evaporator, and the free end is connected to the obturator and a poppet valve fixed to it, mounted with the possibility of longitudinal movement along the axis evaporator.

In this case, the thermostabilizer is made in the form of a tank with elastic walls, is installed at the bottom of the evaporation chamber and is filled with a thermostabilizing liquid.

According to the invention, the gas flow divider is equipped with a spiral baffle in the form of a multi-path cylindrical spring placed along the bypass, the total length of each coil of the spring corresponds to the average length of the parallel ducts of the evaporation chamber.

It is envisaged that the evaporation chamber is provided with guides for the plates in the form of cylindrical tension springs, the diameter and inter-turn clearance of which is proportional to the distance from the flow divider.

A method of stabilizing the concentration of anesthetic at the outlet of the evaporator, including, according to copyright certificate No. 440016, dividing the total gas flow between the evaporation chamber and bypass by means of laminar hydromechanical resistances, equilibrium saturation of the part of the gas passing through the evaporation chamber with anesthetic pairs, followed by dilution to a predetermined clinical concentration of the second part of the gas passing through the bypass, adjusting the division of the total gas flow taking into account temperature and pressure, in accordance with toyaschim invention, initially a bypass pipelines and the evaporator chamber in horizontal planes at the same level, in the case of increasing the output at low anesthetic concentration gazotokah, raised above the level of the bypass chamber and the evaporator is lowered bypass otherwise.

In this case, in the case of a decrease in the output concentration of anesthetic at high gas flows, the bypass gas flow is additionally twisted, thereby increasing the resistance of the bypass, the relative fraction of the gas flow passing through the evaporation chamber, and the output concentration of the anesthetic.

The technical result of the patented invention is as follows:

- increasing the stability of dosing over a wide range of gas flow rates from 0.1 to 15 l / min, temperatures from 5 to 35 ° C, and atmospheric pressure from 70 kPa (3 km above sea level) to 110 kPa;

- increasing the stability of dosing with pulsation of pressure and gas flow in the respiratory circuit of the patient;

- increase the efficiency of using anesthetics by minimizing the volume of wicks (up to 3 ml).

The invention is illustrated by a description of an example of a constructive implementation of a patentable evaporator and drawings, which show:

Figure 1 is a longitudinal section of an evaporator;

Figure 2 - thermal stabilizer;

Figure 3 - placement of triplex plates in the evaporation chamber;

Figure 4 - spiral deflector.

Patented anesthetics vaporizer contains (Fig. 1) an evaporation chamber 1 with wicks, a gas flow divider in the form of slotted channels on the lines of the evaporation chamber 1 and bypass 2, an anesthetic concentration scale attached to the divider (not shown), input 3 and output 4. Divider the gas flow is made in the form of a tubular spool 10 with slotted channels 12, 13 of variable cross-section on its outer surface and an output confuser 15 on the inner core 18 with a fairing 19 at the inlet and a tapered obturator 20 at the outlet and a poppet valve 22, fixed on the core 18 opposite the conical tip 23 of the spool 10 with the formation of an annular gap at the outlet of the evaporation chamber 1, while the spool 10 is mounted to rotate around the horizontal axis and connect the slotted channels 12, 13 between the bypass and the evaporation chamber 1. The pressure compensator is made in the form of a hermetic bellows 25 with volatile liquid 26, one end of which is fixed on the axis of the evaporator, and the free end is connected to the core 18, installed with the possibility of longitudinal movement from the exit 4 to 3 move with an increase in temperature or decrease in ambient pressure and backward movement with decreasing temperature or increase in atmospheric pressure.

Thermostabilizer (Figure 2) is made in the form of a tank 28 with elastic walls, is installed on the bottom of the evaporation chamber 1 and is filled with a thermostabilizing liquid, for example, aqueous saline, to the very top. The wicks are made in the form of triplex plates 30, mounted in a frame on the lid of the tank 28 with a gap between each other and symmetrically on both sides of the casing 33 of the divider adjacent to the lid 35. The side elements of the triplex plates are made of porous sheet metal 40 (Figure 3) , for example, stainless steel, and pressed against the Central plate 42 of a heat-conducting metal (copper) having a convex and streamlined profile of the gas. The frames for the triplex plates are made in the form of cylindrical tension springs 45, the diameter D _i and the inter-turn clearance (L _i -L _i-1 ) of which is proportional to the distance L _i from the flow divider.

The gas flow divider is equipped with a spiral baffle (FIG. 4) in the form of a multi-way (two- or three-way) coil spring 50 located along the bypass duct 51. The diameter of the wire d of the spring 50 is equal to the annular gap 2 in FIG. 1, and the total length of each coil of the spring 50 corresponds to the average length of the parallel ducts of the evaporation chamber 1.

The vaporizer of anesthetics works as follows. To set the desired concentration of anesthetic, the spool 10 is rotated around the axis to the corresponding scale mark, while the slotted channels 12, 13 of the corresponding length and cross section are connected to the input and output of the evaporation chamber 1. Part of the gas enters through the channels 12 to the entrance of the evaporation chamber 1, passes between the triplex plates 30 and saturates to an equilibrium concentration of anesthetic, then returns to bypass 2 through the channels 13, the annular gap between the tip 23 and valve 22, then is diluted at the outlet of the evaporator with the main gas stream passing through bypass 2 to the desired concentration. To increase the output concentration, the spool 10 is turned counterclockwise, connecting slotted channels with less hydraulic resistance (shorter length and larger cross section) and vice versa. When the concentration scale is set to “0”, the evaporation chamber 1 is isolated from bypass 2.

Liquid anesthetic enters the evaporation surfaces of the triplex plates 30 through the capillaries (of the order of 10 μm) of the porous sheet metal 40, as well as through slotted gaps (of the order of 20-50 μm) between the central plate 42 and the porous plate 40 due to the surface tension of the anesthetic. Heat to the evaporation surfaces comes from the environment through the heat-conducting walls of the evaporation chamber 1 and from the heat stabilizer 28, a layer of liquid anesthetic and central copper plates 42.

With a decrease in the temperature of the evaporator and a corresponding decrease in the equilibrium concentration of the anesthetic, the pressure inside the bellows 25 also decreases, and its free end moves the core 18 to the outlet 4 of the evaporator. In this case, the annular gap of the bypass 2 decreases, and the annular gap between the tip 23 and the valve 22 at the outlet of the chamber increases, in turn, increasing the relative fraction of gas entering the evaporation chamber 1 and stabilizing, as a result, the output concentration of the anesthetic. With increasing temperature, the ratio of gas flows is automatically adjusted in the opposite direction.

At the same time, the bellows acts as a baro-compensator, similarly reducing the relative gas flow through the evaporation chamber when atmospheric pressure decreases (the bellows expands) and vice versa (the bellows contracts with increasing atmospheric pressure).

A method for stabilizing the output concentration of anesthetic, including dividing the total gas flow between the evaporation chamber and the bypass by means of laminar hydromechanical resistances, equilibrium saturation of the part of the gas passing through the evaporation chamber with anesthetic pairs, followed by dilution to the desired clinical concentration with the second part of the gas passing through the bypass, correcting the division the total gas flow, taking into account temperature and pressure, is carried out, according to the present invention, as follows. The gas pipelines of the bypass and the evaporation chamber are preliminarily placed in horizontal planes at the same level, if the output concentration of the anesthetic is increased at low gas flows, the bypass level is raised above the evaporation chamber, in the opposite case, the bypass is lowered. Depending on the design of the evaporator, you can also raise the output of the evaporator relative to its input in the first case, and vice versa, lower the output relative to the input - in the opposite case.

Example 2

In the MINIVAP-100 (BMV-100) experimental sample of the evaporator, the gas pipelines of the bypass and the evaporation chamber (weighted average cross sections, with 50 ml of anesthetic in the chamber) are placed on the same level in horizontal planes. At a minimum gas flow of 0.15 l / min and standard temperature and pressure, the concentration of anesthetic (halotane) at marks “1” and “3” is 1.5 and 4.5 vol.%, Respectively. In the process of finishing the product, the bypass is raised above the average level of the evaporation chamber by 10 mm, so that the bypass housing is adjacent to the cover of the evaporation chamber. In this case, the output concentration under the above conditions is 1.2 and 3.5 vol.%, Respectively.

Indeed, when the bypass moves relative to the evaporation chamber upward, the additional pressure drop that overcomes the part of the gas passing through the evaporation chamber is (cf. Example 1)

Δρ · g · Δh = (1.21-3.45) kg / m ³ 9.8 m / s ² 0.01 m = -0.22 Pa,

where Δρ is the difference in the densities of the carrier gas (air) and saturated vapor of the anesthetic;

g is the acceleration of gravity;

Δh is the difference between bypass and camera levels.

At the same time, the pressure drop of the divider (control signal) at a gas flow rate of 0.15 l / min is about 0.75 Pa. The decrease in the effective pressure difference on the line of the evaporation chamber by (0.22 / 0.75) 100 = 30% leads, according to the calculated estimate (see Prince A.Z. Berlin and A.V. Meshcheryakova, formula (19)), also to reduce the output concentration by 30%, i.e. respectively, to 1.05 and 3.15 vol.%, which is consistent with experimental data.

In case of a decrease in the output concentration of the anesthetic at high gas flows and concentrations, the bypass gas flow is additionally twisted, thereby increasing the resistance of the bypass, the relative fraction of the gas flow passing through the evaporation chamber, and the output concentration of the anesthetic. However, most of the heat for evaporation of the anesthetic comes from the heat stabilizer 28.

Example 3

In the experimental sample of the MINIVAP-100 evaporator at an air flow rate of 10 l / min, the output concentration of halotane at “3” is initially 2 vol.% (Due to significant heat and mass transfer loads). In this case, the bypass gas flow is additionally twisted (flow turbulization), due to which the bypass resistance is increased by 30% with the previous gas flow of 10 l / min and, accordingly, the relative fraction of the gas flow passing through the evaporation chamber is increased, and the output concentration of the anesthetic is also 25- 30%, i.e. to a concentration of 2.6 vol.%. The resistance of the evaporator at low gas flows (laminar mode) does not change, because Turbulent flow occurs only at high speeds.

Thus, the proposed low resistance evaporator MINIVAP-100 provides a stable dosage of modern anesthetics (isoflurane, or fluorotane-halotane, or enflurane, or sevoflurane) in a wide range of constant and pulsating gas flows from 0.25 to 15 l / min, temperatures from 5 to 35 ° C and environmental pressures. The evaporator is economical and environmentally friendly (only 3 ml of liquid anesthetic remains on the wicks after discharge, the capacity of the evaporation chamber is 100 ml). It can be installed both inside (Draw-over Anesthesia) and outside the respiratory circuit. Due to its low resistance, the evaporator is compatible with any ventilator and can also work from low-pressure oxygen sources (oxygenators).

Claims (7)

1. A method of stabilizing the concentration of anesthetic at the outlet of the evaporator, including dividing the total gas flow through laminar hydromechanical resistances, equilibrium saturation of anesthetic vapor with one part of the gas passing through a temperature-stabilized evaporation chamber, followed by dilution to a predetermined concentration of the second part of the gas passing through the bypass, adjustment of the division of the total gas flow based on temperature, characterized in that the bypass pipelines and the evaporator are pre-positioned of the chamber in horizontal planes at the same level, if the output concentration of the anesthetic at low gas flows increases, the bypass level is raised relative to the evaporation chamber or the bypass is lowered in the opposite case, when the temperature decreases or atmospheric pressure rises, increase the relative fraction of gas through the vaporization chamber and decrease it when reverse change in temperature and pressure. 2. The method according to claim 1, characterized in that, in the case of lowering the output concentration of anesthetic at high gas flows and concentrations, additionally bypass the gas flow, thereby increasing the resistance of the bypass, the relative fraction of the gas flow passing through the evaporation chamber and the output concentration anesthetic. 3. An anesthetic vaporizer containing a gas flow divider in the form of laminar hydromechanical resistances on the bypass lines and an evaporation chamber with porous metal plate sets forming parallel slotted channels, an anesthetic concentration scale fixed to the divider, an input and output for gas flow, characterized in that it is equipped with a temperature compensator and a thermal stabilizer thermally connected with each other and with the bottom of the evaporation chamber, the divider is installed horizontally inside the evaporation chamber, adjacent to e cap and is mechanically connected to termobarokompensatorom. 4. The evaporator according to claim 3, characterized in that the pressure compensator is made in the form of a coaxially mounted bellows with easily evaporating liquid, a tubular conical tip with a confuser on the inner surface, a conical obturator interacting with the confuser, and a poppet valve interacting with the said tip one end of the bellows is fixed on the axis of the evaporator, and the free end is connected to the obturator and a poppet valve fixed to it, mounted with the possibility of longitudinal movement in ol axis of the evaporator. 5. The evaporator according to claim 3, characterized in that the thermostabilizer is made in the form of a tank with elastic walls, is installed at the bottom of the evaporation chamber and is filled with a thermostabilizing liquid. 6. The evaporator according to claim 3, characterized in that the gas flow divider is equipped with a spiral deflector in the form of a multi-path cylindrical spring placed along the bypass, while the total length of each coil of the spring corresponds to the average reduced length of the parallel gas ducts of the evaporation chamber. 7. The evaporator according to claim 3, characterized in that the evaporation chamber is provided with guides for the plates in the form of tensile springs, the diameter and inter-turn clearance of which is proportional to the distance from the flow divider.

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