Evaporator For Liquid Anesthetics

Abstract

An evaporator for liquid narcotics, comprising a straight-flow by-pass duct, wherein provision is made for a shutter and a control slide which, when in one of the extreme positions, interacts with the shutter to close gas admission into the by-pass duct, and an evaporating chamber. The latter is made as a circular straight-flow channel embracing the by-pass duct and is provided with capillary-structure evaporating elements arranged inside the chamber lengthwise the gas flow lines, and with an effuser provided at the outlet of the chamber concentrically to the shutter so as to establish an annular gap therebetween. The control slide, when in the other extreme position, interacts with the effuser to shut up gas issue from the evaporating chamber.

Description

This invention relates generally to medical equipment and has particular reference to evaporators for liquid narcotics (anesthetics) adapted for proportioning evaporable anesthetics used in inhalation narcosis at surgical and anesthesiological departments.

Known in present-day practice is one prior-art evaporator for liquid narcotics, comprising an evaporating chamber with capillary-structure evaporating elements, a straight-flow by-pass duct with an obturator or shutter and a control slide.

The evaporating chamber of the prior evaporator is shaped as a teaglass which with one of its end faces bears against the outside wall of the by-pass duct and communicates therewith through an inlet and outlet openings. The evaporating elements of said chamber are made as a metal gauze adhering to the walls and bottom of the chamber, the latter being essentially a container with thermostabilizing liquid, the flow of gas in the chamber occurring along V-shaped pattern.

The telescopic spool-type slide has at one of its ends an inside narrowed portion shaped to suit the form of the shutter and is adapted, when in one of the extreme positions, to interact with the shutter to close the admission of gas to the by-pass duct.

The afore-said evaporator, however, suffers from a number of disadvantages such as different contours of the cross-sectional areas of the evaporating chamber and of the by-pass duct, as well as different lengths of the gas flow lines in the evaporating chamber and in the by-pass duct which eventuates in different hydromechanical characteristics of said lines and, finally, in an unstable gas flow division at variations in the total flow rate of gas through the evaporator, pulsations of the gas flow resulting from spontaneous respiration or from a pressure in the patient's respiratory circuit during artifical ventilation of the lungs.

Moreover, the arrangement of the evaporating elements along the walls and bottom of the evaporating chamber fails to obtain high gradients of concentration of the anesthetic in gas which fact in conjunction with too small evaporation area confined to the evaporator size and its incomplete utilization, leads to an inadequate saturation of gas with the vapours of anesthetic at high gas consumption rate.

Unstable gas flow division and insufficient gas saturation at the outlet of the evaporating chamber results in unstable proportioning of anesthetics, especially when using the same evaporator for various anesthetics.

It is an essential object of the present invention to provide an evaporator for liquid narcotics, whose evaporating chamber features hydromechanical characteristics similar to those of the by-pass duct and is capable of ensuring an equilibrium gas saturation with the vapours of any liquid narcotics.

Said object is accomplished due to the fact that in an evaporator for liquid narcotics, comprising an evaporating chamber with capillary-structure evaporating elements communicating through inlet and outlet openings with a straight-flow by-pass duct, wherein provision is made for a shutter and a control slide which is adapted, when in one of its extreme positions to interact with said shutter to close gas admission to the by-pass duct, according to the invention the evaporating chamber is made as a circular straight-flow channel embracing the by-pass duct, the evaporating elements are arranged lengthwise the gas flow lines, and the chamber is provided with an effuser located at the outlet thereof concentrically with the shutter so as to form an annular gap therewith, whereas the control slide, when in the other extreme position, interacts with the effuser to shut off the issue of gas from the evaporating chamber.

It is expedient that the evaporating elements be made as channel bars with their side walls bearing against the chamber walls.

It is likewise desirable that the slide end interacting with the effuser be provided with an external narrowing shaped to suit the shape of the effuser, while the other slide end be made threaded to interact with the slide motion nut.

The evaporator for anesthetics as implemented according to the present invention, features similar hydromechanical characteristics of the evaporating chamber and the by-pass duct thereof, and thus ensure an equilibrium gas saturation with the vapours of any anesthetics.

In what follows the invention is disclosed in detail through the consideration of a specific embodiment thereof with due reference to the accompanying drawings, wherein:

FIG. 1 is a sectional view of an evaporator for liquid narcotics, according to the invention; and

FIG. 2 is a section taken along the line II--II in FIG. 1.

Now referring to FIG. 1 the evaporator comprises an evaporating chamber 1 made as a circular straight-flow channel embracing a straight-flow by-pass duct 2 at whose outlet end a shutter 3 is provided. The shutter 3 is fixed to a stem 4 having at its ends fairings 5 and 6 to reduce gas flow resistance at the evaporator inlet and outlet, and a headpiece 7 adapted to correct the dependance of the pressure differential upon the gas flow rate through the by-pass duct 2. An effuser 8 is made fast at the outlet of the evaporating chamber 1 concentrically with the shutter 3, an annular gap 9 being left therebetween. The effuser 8 passes into an outlet nozzle 10 of the evaporator. Located in the by-pass duct 2 is a control slide 11 made as a thin-walled tube with a tapered portion 12 at one end, said tapered portion being internally shaped to suit the profile of the shutter 3 and externally shaped to suit the profile of the effuser 8. At its other end the control slide 10 passes into an inlet nozzle 13 provided with male thread.

The evaporating chamber has two rows of openings 14 and 15 located at its ends along the periphery of an inside wall 16 and serving as the inlet and the outlet openings 14 and 15, respectively. A container 17 with liquid anesthetic is provided at the outlet end of the evaporating chamber 1. The chamber 1 is provided with a thermometer 18 located nearby the outlet openings 15, and is enclosed with a jacket 19 along which thermostabilizing liquid circulates whose functions are performed by water. Located inside the evaporating chamber 1 are capillary evaporating elements 20 arranged lengthwise the gas flow line. Use is made in the now-discussed embodiment of the invention as the evaporating elements 20, of channel bars made of a porous sheet material, viz., stainless steel. With their side walls the channel bars adhere to the walls of the chamber 1 and with one of their ends said bars are immersed in the container 17 with anesthetic.

The channel bars partition the chamber 1 into longitudinal compartments 21 (FIG. 2) parallel to one another.

The inlet nozzle 13 (FIG. 1) interacts with a nut 22 by virtue of its thread, said nut being mounted rotatably on a cover 23 of the evaporating chamber 1. The nut 22 is provided with a replaceable scale 24 calibrated with due allowance for the outlet temperature of the evaporating chamber 1. The control slide 11 has slits 25 adapted to interact with the inlet openings of the chamber 1.

Gas flow resistance (i.e., pressure differential) in the flow path of the evaporating chamber 1 is concentrated at the outer annular gap in between the effuser 8 and the tapered portion 12 of the control slide 11, while the resistance in the flow path of the by-pass duct 2, at the inner annular gap in between the tapered portion 12 and the shutter 3.

Relationship between the pressure differential and the gas flow rate through the chamber 1 and the by-pass duct 2 is approximately linear.

The evaporating elements 20 may also be made as thin-walled tubes of porous metal, spaced at a clearance with one another and having openings located opposite to the outlet openings 15 of the evaporating chamber 1, or else made as a spiral provided with similar openings.

The evaporator of the present invention functions as follows.

To suit the required concentration of anesthetic, the control slide 11 (FIG. 1) is set, by rotating the nut 22 with the scale 24, to the position ensuring the required ratio of the gas flow rates through the chamber 1 and the by-pass duct 2, said ratio being dependent upon the ratio of the cross-sectional areas of the outer annular gap (in between the effuser 8 and the tapered portion 12) and the inner annular gap (in between the tapered portion 12 and the shutter 3).

Gas (which may be in fact the air inhaled by the patient, or a gas mixture fed from any extraneous source) is delivered to the evaporator via the inlet nozzle 13 to pass in between the shutter 5 and the control slide 11, whereupon the gas flow is divided into two streams, of which one is directed through the slits 25 and the openings 14 into the chamber 1, wherein the gas is spread over the compartments 21 (FIG. 2) and passes along the channel bars from the inlet of the chamber 1 (FIG. 1) towards the outlet thereof. While passing the gas gets saturated with the anesthetic till an equilibrium saturation thereof which is equal to the ratio of the partial pressure of saturated vapours of the anesthetic and the ambient pressure at the temperature measured by the thermometer 18.

Liquid anesthetic is fed from the container 17 to the evaporating surface of the channel bars along the capillaries running through the bulk of the porous sheet material.

Gaseous mixture saturated with the vapours of anesthetic at an equilibrium concentration, emerges from the chamber 1 via the openings 15, passes along the inner annular gap in between the effuser 8 and the tapered portion 12 and is diluted to the required concentration by another stream of gas flowing along the by-pass duct 2 in between the control slide 11 and its tapered portion 12, on one side and in between the stem 4, the headpiece 7 and the shutter 3, on the other side. The thus-obtained narcotic mixture emerges from the evaporator through the outlet nozzle 10 and is fed to the patient.

When in one of its extreme positions corresponding to the maximum reading of the scale 24, the control slide 11 rests with the inner surface of the tapered portion 12 against the shutter 3 so that the entire gas flow passes through the chamber 1, thus equilibrium-saturated with the vapours of anesthetic.

When in the other extreme position corresponding to the zero mark of the scale 24, the control slide 11 seats with the outer surface of the tapered portion 12 on the effuser 8; at the same time the openings 14 of the chamber 1 are shut up by the spool of the control slide 11 and the whole flow of gas is free to pass through the by-pass duct 2.

Heat required for evaporation of liquid anesthetic is fed to the evaporating elements 20 from the thermostabilizing liquid circulating through the jackets 19, as well as from the environment space and the gas passing through the evaporator.

Thus, stable flow division of the gas fed into the evaporator and an equilibrium saturation of part thereof passing through the evaporating chamber 1, with the vapours of anesthetic, ensure independency of the concentration of anesthetic at the outlet of the proposed evaporator, or extrinsic factors liable to affect said concentration. To such factors may be attributed gas flow-rate variations, pulsation of gas flow during spontaneous respiration, pressure fluctuations in the patient's respiratory circuit during artifical ventilation of the lungs, different physical properties of anesthetics. Provision of a thermometer in the evaporating chamber ensures temperature correction of the outlet concentration.

The proposed small-sized evaporator weighing about 2 kg, is capable of an accurate proportioning of any evaporable anesthetic, such as fluoroethane, diethyl ether, methoxyflurane (pentrane), chloroform, trichloroethylene, within the range of gas flow rate of from 2 to 15 1/min (in case of constant flow) and from 4 to 12 1/min (in case of pulsating flow) at temperatures of from +5 to +30.degree.C; the hydraulic resistance offered by the evaporator is as low as 10 mm H.sub.2 O at a constant flow rate of 25 1/min, the amount of residual liquid anesthetic in the evaporating chamber after its drainage is about 5 ml.

Claims

What is claimed is:

1. An evaporator for liquid narcotics, comprising: a straight-flow by-pass duct; a fixed shutter provided in said by-pass duct at one of the ends thereof; an evaporating chamber having inlet and an outlet openings, said chamber being formed as an annular straight-flow channel encompassing said by-pass duct and communicating with the latter through said openings; evaporating elements having a capillary structure being postioned along said chamber; a generally cylindrically shaped control slide with a tapered portion at the exit end thereof longitudinally movably received in said by-pass duct whereby the by-pass fluid flow passes through said control slide and around said shutter; and an effuser located at the outlet of said chamber, said tapered portion being externally shaped in conformance with the profile of said effuser; said effuser being positioned such that the fluid flows from the by-pass duct and evaporating chamber are directed to converge in correspondent directions.

2. An evaporator as claimed in claim 1, said evaporating elements adhering to the surface of said evaporating chamber.

3. An evaporator as claimed in claim 1, said tapered portion of the control slide being adapted to operatively interact with said effuser.