Vaporiser

Abstract: The present invention describes a vaporiser (2), for vaporising liquid anaesthetic (12), comprising a chamber (10) for liquid anaesthetic (12), a gas flow passage (14), a throttle (16) in the gas flow passage (14), a first connection (17) between the chamber (10) and the gas flow passage (14) upstream from the throttle (16) and a second connection (18) between the chamber (10) and the gas flow passage (14) downstream from the throttle (16). The vaporiser (2) will be more accurate and usable with different liquid anaesthetics (12) if it is devised so an outlet valve (22) is arranged by an outlet (6) in the vaporiser (2), said outlet valve (22) being regulated by the pressure upstream from the throttle (16).

Description: The present invention relates to a vaporiser according to the preamble to claim 1. The manual "Halothane Vaporizer 950, Enflurane Vaporizer 951, Isoflurane Vaporizer 952" describes one such vaporiser. The vaporiser comprises a gas flow passage for a gas, a chamber for liquid anaesthetic and an adjustable throttle. An opening is arranged between the gas flow passage and the chamber upstream from the adjustable throttle. Downstream from the adjustable throttle, a capillary tube is arranged with one nozzle end opening into the gas flow passage and the other end immersed in the liquid anaesthetic in the chamber. The imposition of a gas flow causes pressure to drop across the adjustable throttle. The higher pressure upstream from the throttle is propagated through the opening into the chamber and exerts pressure on the surface of the liquid, forcing the liquid up into the capillary tube. The liquid is then sprayed out of the nozzle into the gas flowing in the gas flow passage and is vaporised. The pressure drop across the throttle depends on the throttle's setting and controls the liquid's dispensing. Changing the throttle setting makes it possible to achieve different concentrations of anaesthetic in the gas. The known ventilator has an accuracy of ±10% of the value set, which is an accuracy that is sufficient for all applications in conjunction with anaesthesia. However, the known vaporiser has certain disadvantages. One disadvantage is that each time a flow of gas is sent to the vaporiser to dispense anaesthetic, working pressure in the vaporiser needs to build up first. This causes a slight but nevertheless measurable delay in dispensing. Moreover, the chamber must fill with gas before any pressure can be exerted on the surface of the liquid. A small loss in gas volume occurs on occasions when the chamber only holds a small amount of liquid. This loss has an effect on the concentration of dispensed anaesthetic. Even if these disadvantages only have a minor, virtually insignificant, impact on vaporiser operation, additional functional refinement would still be desirable. Another disadvantage of the known vaporiser is that it is not suitable for use with all ordinary anaesthetic agents. As a result of its low boiling point, the anaesthetic desflurane is particularly unsuitable for use in the known vaporiser. One object of the invention is to achieve a vaporiser that solves the aforementioned problems. One such vaporiser is achieved in accordance with the invention in that the vaporiser is devised as disclosed in the characterising part to claim 1. Advantageous improvements of the vaporiser according to the invention are evident from the dependent claims to claim 1. The problems are mainly resolved when the vaporiser is devised with an outlet valve that is controlled by the pressure upstream from the throttle (which is advantageously adjustable). In this manner, pressure variations are avoided on the inlet side of the throttle. Instead, pressure drops on the outlet side are utilised for dispensing the liquid. When the throttle setting is changed co increase the amount dispensed, the requisite increase in the drop in pressure is mainly achieved by a drop in pressure downstream from the throttle and only by a minor increase in pressure upstream from the throttle. This avoids the need to build up a working pressure before gas is dispensed. Moreover, only a small increase in the amount of gas in the chamber, distributed over a longer period of time, will be needed. By contrast, the entire chamber in the known vaporiser must fill to the working pressure every time gas is supplied. Instead of an adjustable throttle, a fixed throttle can be used in combination with a bypass flow past the vaporiser. Another advantage is that the vaporiser's working pressure (in absolute terms) can be raised from about 1 bar to at least 1.7 bar. This increase means that desflurane can also be used, as the higher (constant) pressure raises the boiling point of desflurane. Allowing gas pressure upstream from the throttle to act directly on the outlet valve in order to regulate it would be particularly advantageous. Embodiments of the vaporiser according to the invention are described below in greater detail, referring the figures in which FIG. 1 shows a first embodiment of the vaporiser according to the invention and FIG. 2 shows a second embodiment of the vaporiser according to the invention. FIG. 1 shows a first embodiment of the vaporiser 2 according to the invention. The vaporiser 2 has an inlet 4 for gas and an outlet 6 for gas and dispensed anaesthetic. The desired dose (concentration) of anaesthetic is set with a control 8. The vaporiser 2 also has a chamber 10 for an anaesthetic 12 and a gas flow passage 14. An adjustable throttle 16 is arranged in the gas flow passage 14. The control 8 acts in this embodiment directly on the adjustable throttle 16. When a gas flow passes through the gas flow passage 14, a drop in pressure forms across the adjustable throttle 16. A first connection 17 between the gas flow passage 14 and the chamber 10 is arranged upstream from the adjustable throttle 16. The first connection 17 opens into the gas-filled part of the chamber 10 over the surface of the anaesthetic liquid 12. A second connection between the gas flow passage 14 and the chamber 10 is arranged downstream from the adjustable throttle 16. The second connection consists of a capillary tube 18 immersed at one end in the anaesthetic 12 in the chamber. A nozzle 19 at the other end of the capillary tube 18 opens into the gas flow passage 14. The drop in pressure across the adjustable throttle 16 causes gas pressure, acting on the anaesthetic liquid 12 in the chamber 10, to force the anaesthetic liquid through the capillary tube 18. The amount of anaesthetic liquid forced up into the capillary tube and out into the gas flow passage 14 through the nozzle 19 depends on the magnitude of the drop in pressure. An inlet valve 20 is arranged by the inlet 4. In this instance, it consists of a check valve. The inlet valve 20 prevents the retrograde flow of gas through the vaporiser 2. It also facilitates maintenance of the desired pressure in the vaporiser 2. An outlet valve 22 is arranged by the outlet 6. In this embodiment, it consists of a pressure regulator which, via a gas control channel 24, is connected to the space upstream from the adjustable throttle 16. The outlet valve 22 opens at a specific pressure and causes the drop in pressure by means of a reduction in pressure downstream from the adjustable throttle 16. It should be noted that gas is usually supplied to the vaporiser in pulses. The duration of these pulses of gas can vary. A normal pulse of gas can consist of about 0.3 l of gas. When a pulse of gas, at a pressure higher than the pressure prevailing in the vaporiser 2, is delivered, the inlet valve 20 opens first to the pulse of gas. The pressure of the pulse of gas is then propagated through the gas control channel 24 to the outlet valve 22 and opens it. A drop in pressure develops when the pulse of gas passes the adjustable throttle 16, and anaesthetic liquid 12 is dispensed into the pulse of gas in which the liquid is vaporised and mixed. The pulse of gas and the dispensed anaesthetic liquid then exit through the outlet 6, and the valves 20, 22 close at their respective closing pressures. In this embodiment, a fixed throttle 26 is also arranged in the gas flow passage 14 between the gas control channel 24 and the first connection to the chamber 10. The fixed throttle contributes to stabilising control of the outlet valve 22, since it causes a small primary drop in pressure before the dispensing drop in pressure across the adjustable throttle 16. FIG. 2 shows a second embodiment of a vaporiser 28 according to the invention. All parts and components identical to those in FIG. 1 have the same designations. The ventilator 28 has an inlet 4, a gas flow passage 14 and an outlet 6. The gas flow passage 14 is connected to a chamber 10 for anaesthetic 12 by a first connection 17 upstream from the adjustable throttle 16 and by a second connection 18 downstream from the adjustable throttle 16. The adjustable throttle 16 is electronically regulated by a control 8. The second connection consists of a capillary tube 18 with a nozzle 19. This embodiment differs from the previous embodiment, apart from the electronic coupling of the control 8 and the adjustable throttle 16, in the following respects. An inlet valve 30 is arranged in the immediate proximity of the inlet 4 and may consist of a mechanical or electronic valve. It can also be physically located in a coupling section (not shown) for gas to be sent to the vaporiser 28. An outlet valve 32 is arranged in the immediate proximity of the outlet 6 and is electronically controlled. The control signal for the outlet valve 32 is obtained from a pressure meter 34 arranged upstream from the adjustable throttle 16. The outlet valve 32 can be physically located in a coupling section for receiving gas containing anaesthetic. If either of the outlet and inlet valves 30, 32, or both, are physically separated from the vaporiser 28, it should be equipped with a suitably devised check valve at the respective location. This is to ensure that no anaesthetic, either in gaseous or liquid form, is able to leak out of the vaporiser 28 when it is detached from an anaesthetic machine after use. It should be noted that a version without an adjustable throttle 16 is also possible with both embodiments. The same dispensing effect can be achieved when the throttle 16 is fixed and a bypass flow past the vaporiser is regulated. When the throttle 16 is devised to deliver a maximal dose for a specific bypass flow, this bypass flow can then be regulated so the desired dose is dispensed. Thus, the salient feature of the invention is that the outlet valve 22 or 32 is regulated by the pressure upstream from the throttle 16. Combinations of the two embodiments are possible. For example, the vaporiser 2 in FIG. 1 can be devised with an electronic inlet valve 30, an electronic outlet valve 32 or electronic control of the adjustable throttle 16. In the corresponding manner, the vaporiser 28 in FIG. 2 can be devised with a fixed throttle 26 in the flow passage 14.

Claims: A vaporiser (2; 28) for vaporising a liquid anaesthetic (12), comprising a chamber (10) for liquid anaesthetic (12), an inlet (4), an outlet (6), a gas flow passage (14) between the inlet (4) and the outlet (6), a throttle (16) in the gas flow passage (14), a first connection (17) between the chamber (10) and the gas flow passage (14) upstream from the throttle (16) and a second connection (18) between the chamber (10) and the gas flow passage (14) downstream from the throttle (16), characterised in that an outlet valve (22; 32) is arranged at the outlet (6) in the vaporiser (2; 28), said outlet valve (22; 32) being regulated by the pressure upstream from the throttle (16). The vaporiser according to claim 1, characterised in that the throttle (16) is adjustable. The vaporiser according to claim 1 or 2, characterised in that a gas control channel (24) connects the outlet valve (22) to the gas flow passage (14) upstream from the throttle (16), the pressure upstream from the throttle then acting directly on the outlet vale (22). The vaporiser according to claim 3, characterised in that an additional throttle (26) is arranged upstream from the throttle (16) between the gas control channel (24) and the first connection (17). The vaporiser according to claim 1 or 2, characterised in that a pressure meter (34) is arranged for measuring pressure upstream from the throttle (16) and is connected to the outlet valve (32). The vaporiser according to claim 1, characterised in that a bypass line is connected to the inlet and outlet in order to carry an adjustable bypass flow past the vaporiser without passing through the gas flow passage. The vaporiser according to any of the above claims, characterised in that the second connection consists of a capillary tube (18), one end of which is immersed in the liquid anaesthetic (12) in the chamber (10) The vaporiser according to any of the previous claims, characterised in that an inlet valve (20; 30) is arranged at the inlet (4) upstream from the adjustable throttle (16).

Inventors: ALKSNIS IVARS, HEDENBERG HAKAN, WALLIN STEN, ALKSNIS, IVARS, HEDENBERG, HAKAN, WALLIN, STEN
Applicants: SIEMENS ELEMA AB, SIEMENS-ELEMA AB
Application year: 1999
Main classification: A61M16
IPC codes: A61M16