Method and apparatus for reuse of anesthetics

A method and an apparatus for reuse of anesthetics in inhalation anesthesia is described. In the method, fresh gas is mixed with highly concentrated anesthetic from an anesthetics evaporator (3) in a collector conduit (1) leading into and out of a patient, in such a way that, when the patient exhales, the exhalation gas is passed through an adsorption filter (5) disposed in the ingoing and outgoing collector conduit (1) and arranged distally relative to the outlet (4) from the anesthetics evaporator (3), as seen from the patient (2), the anesthetic not absorbed by the patient being adsorbed by an adsorption material (6) in the adsorption filter (5), while the rest of the exhalation gas leaves the apparatus, the adsorbed anesthetic being desorbed from the adsorption material (6) when the patient inhales and retransferred to the patient.

The present invention relates to a method and an apparatus for reuse of 
anesthetics in inhalation anesthesia. 
Inhalation anesthesia is a common form of narcosis, and the anesthetics 
usually consist of simple halogenated hydrocarbons, paraffins or ethers 
which are in a liquid state at room temperature and are gasified prior to 
inhalation. Common anesthetics are Halotan or Fluotan 
(2-bromo-2-chloro-1,1,1-trifluoroethane), Enfluran or Efran 
(1,1,2-trifluoro-2-chloroethyl difluoromethyl ether), or Isofluran or 
Foren (2,2,2-trifluoro-1-chloroethyl difluoromethyl ether). The effect 
obtained from such halogenated hydrocarbons is normally increased by an 
addition of laughing gas (N.sub.2 O) at concentrations of 50-70 vol %. 
The trend of development is towards more and more refined anesthetics 
which, however, suffer from the disadvantage of being obtainable only at 
high costs. 
Furthermore, anesthetics are harmful to the operating staff if they leak 
out into the operating room. 
The exhalation air from a patient contains nonabsorbed oxygen, laughing 
gas, water vapor, nonabsorbed anesthetic gas and 4-6 vol % CO.sub.2. 
Anesthetic gases can be administered to the patient by several different 
techniques and systems. The systems can be completely open, closed with 
re-breathing and CO.sub.2 adsorption, or combinations thereof. 
In one type of inhalation anesthesia, use is made of a respirator to which 
is connected a gasifier for anesthetic, emitting anesthetic gas at a 
predetermined concentration, e.g. 0-5 vol %, in for example a mixture of 
oxygen and laughing gas. The same gas flow as is supplied to the patient 
passes through the anesthetic gasifier. The anesthetic not absorbed by the 
patient passes to a suction outlet when the patient exhales and is lost. 
New gas containing anesthetic is supplied all the time, resulting in a 
high loss of expensive anesthetic in addition to the harmful effect on the 
operating staff. 
In another system, the anesthetic gasifier is connected to the conduit 
leading into and out of the patient, and a small flow of fresh gas having 
a high concentration of anesthetic and emanating from the anesthetic 
gasifier is added to a larger gas flow from the respirator. Also in this 
system, the exhalation air, including anesthetic that has not been 
absorbed, is sucked out into the surroundings, and is constantly replaced 
by new fresh gas. 
It is also possible to employ an anesthetic circuit permitting gas to be 
recirculated to the patient. In this case, an absorber is generally used, 
which eliminates the carbon dioxide produced by the patient. This method 
makes considerable gas savings possible, but requires, besides the 
absorber, special valve systems. Alternative ways of saving anesthetic are 
therefore of interest. 
The object of the invention is to provide a method and an apparatus for 
reuse of anesthetics by which it is possible, at reasonable costs, to 
utilise high-priced anesthetics. 
According to the invention, there is provided a new method and a new 
apparatus for saving anesthetics, in which the anesthetic not absorbed by 
the patient is adsorbed in a filter on exhalation and then desorbed out of 
the filter and reintroduced into the inhalation flow, i.e. a selective 
reflection of the anesthetic.

The invention thus comprises a method for reuse of anesthetics in 
inhalation anesthesia, wherein fresh gas is mixed with highly concentrated 
anesthetic from an anesthetics evaporator 3 in a collector conduit 1 
leading into and out of a patient 2. The method is characterised in that, 
when the patient exhales, the exhalation gas is passed through an 
adsorption filter 5 disposed in the ingoing and outgoing collector conduit 
1 and arranged distally relative to the outlet 4 from the anesthetics 
evaporator 3, as seen from the patient 2, the anesthetic being adsorbed by 
an adsorption material 6 in the adsorption filter 5, while the rest of the 
exhalation gas leaves the apparatus, the adsorbed anesthetic being 
desorbed from the adsorption material 6 when the patient inhales and 
retransferred to the patient. 
The adsorption material of the filter should be such that it prefers the 
anesthetic to water and carbon dioxide. Examples of adsorption materials 
appropriate for use in the invention are inorganic silicon aluminium 
compounds, zeolites, active carbon, silicone plastics, silicone oil on a 
porous carrier, silica gels, highly porous plastic materials, microporous 
silicates etc. 
The invention also comprises an apparatus for reuse of anesthetics in 
inhalation anesthesia, comprising a collector conduit 1 to be connected to 
a patient 2 and an anesthetics evaporator 3 which is connected to the 
collector conduit 1 via an outlet 4. The apparatus is characterised by an 
adsorption filter 5 containing an adsorption material 6 for adsorption and 
desorption of anesthetics and arranged in the collector conduit 1 distally 
relative to the outlet 4 from the anesthetics evaporator 3, as seen from 
the patient 2. 
As in conventional installations for anesthesia, the apparatus according to 
the invention can also be provided with a separate device for absorption 
of CO.sub.2. 
The filter used in the invention can be designed in any suitable manner. It 
can for example be a simple receptacle wherein the adsorption material is 
retained by means of some type of network arrangement, such that an 
ingoing and outgoing gas flow is compelled to pass through the adsorption 
material. Some examples of filter embodiments are shown in FIGS. 2-4. 
The adsorption material can for example be in the form of pellets in order 
to facilitate variation of the pressure drop and the adsorption and 
desorption rates in the filter. The adsorption material can also be 
supported by a carrier; it can for example be attached to a paper carrier. 
One type of adsorption material that has proved to be suitable are zeolites 
which are crystalline aluminium silicates. Thanks to their structure and 
chemical composition, these compounds are chemically stable and inert. 
Ultrastable, or dealuminised, zeolites have proved to be the best form of 
zeolites so far. Ultrastable zeolites have a high adsorption capacity for 
hydrophobic substances also in an environment which is mainly hydrophilic. 
This feature, and the fact that the zeolites to some extent have a low 
desorption energy, make a so-called reflection of the anesthetic possible. 
When choosing the adsorption medium, it is important that the pressure drop 
across the filter and the dead volume are as low as possible. Furthermore, 
it is important that the anesthetic does not undergo a, for the purpose of 
the invention, essential chemical change when passing through the filter. 
The invention can be used for all types of inhalation anesthesia, e.g. 
respirator controlled anesthesia, or anesthesia controlled by a bladder, 
and also for spontaneous respiration. 
The invention will be described in more detail by means of the following 
Examples. 
EXAMPLE 1 
In this Example, a filter according to the invention, a so-called 
reflection filter, was used, comprising a receptacle of plastic material 
in which the adsorption material was disposed as a filter bed. Different 
geometric designs may be conceived for the filter, but for the sake of 
simplicity a substantially cylindrical receptacle of plastic material and 
with a diameter of about 5 cm was used, in which the adsorption material 
was disposed in the form of a layer with a thickness of 3 cm, retained 
between two nets which in cross-section were congruent with the 
receptacle. In the Example, the zeolites ultrastable Y, mordenite and 
silicalite were used, of which ultrastable Y proved to be the best. In 
order to prevent a possible transport of particles from the zeolite, a 
dust filter can be mounted on both sides of the reflection bed. The dead 
volume of the filter was &gt;100 ml. 
The anesthetics used were Isofluran and Halotan, the latter being less 
effective than Isofluran but considerably cheaper. No difference in the 
reflection rate between these two anesthetics could be observed. 
In this experiment, the anesthetic was analysed before and after passage of 
the filter, and no significant chemical change in the anesthetics could be 
observed. 
The result of the experiment was that about 80-95% of the anesthetic was 
recycled, that is a reflection rate of about 80-95% was obtained. 
At a flow of 1 liter/s, a pressure drop of &gt;2 cm water column (=0.2 kPa) 
was measured. 
The reflection of other gases than the anesthetic, e.g. H.sub.2 O and 
CO.sub.2, was examined and found to be very low. 
EXAMPLE 2 
The experiments of Example 1 were repeated in animal tests. The filter was 
tested on pig. The anesthetic used was Isofluran which is a very expensive 
but excellent anesthetic. 
The practical saving obtained in these animal experiments proved to be over 
50% compared to the consumption of anesthetics in conventional narcosis. 
To sum up, it will be appreciated that the invention makes it possible to 
utilise, without much regard to the cost involved, the most effective and 
safest anesthetic in a simple and uncomplicated manner.