Surgery – Respiratory method or device – Means for mixing treating agent with respiratory gas
Patent
1989-08-30
1991-02-05
Eickholt, Eugene H.
Surgery
Respiratory method or device
Means for mixing treating agent with respiratory gas
12820314, 12820511, 12820512, 12820414, 12820421, A61M 1500, A61M 1600
Patent
active
049895974
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an apparatus for administration of at least two gases to a patient, according to the preamble of claim 1.
Such an apparatus for anaesthetic purposes is disclosed in U.S. Pat. specification No. 4,127,121. The circle system with the absorber provides for rebreathing and thus brings the advantage that expensive gases are saved and the loss of moisture and heat is minimised. Moreover, environmental hygiene aspects necessitate keeping down the consumption of anaesthetic gases. The expiration gas is supplied to a bellows which forms part of the drive circuit and presses the gases back to the patient's lungs via the carbon dioxide absorber. The patient circuit and the drive circuit form a closed system.
According to the above-mentioned patent specification, both the concentration of one gas type and the volume variation in the system must be measured so that a desired gas mixture with a minimum consumption of anaesthetic gases can be maintained. It appears from this patent specification that the fresh gas is supplied continuously, which implies that considerable amounts of excess gas must be exhausted from the patient circuit via a valve (not shown).
Rebreathing is essential, when expensive gases are administered, such as anaesthetic gases, helium which is used for treating severe cases of asthma, xenon which is used as contrast medium in computer tomography and as anaesthetic gas, etc. At the same time, respirator ventilation under anaesthetic can be highly advantageous in that, on the one hand, the anaesthetist and/or the nurse is free to perform other important duties and, on the other hand, the respirator is a better means than manual ventilation for establishing an optimal patient breathing pattern. In the treatment of asthma, the respirator can be of vital importance.
One prior art closed system is shown in FIG. 1a. FIG. 1a shows a closed system with an anesthetic bag 1 in communication with an excess valve 2. The excess valve 2, in turn, is in communication with a CO.sub.2 absorber which is in communication with a vaporizer 4. The vaporizer 4 supplies fresh gas to a patient 5. Elements common to FIGS. 1a, 1b and 1c have the same reference numeral.
One possibility of combining the respirator circuit and the anaesthetic circuit is illustrated in FIG. 1b wherein a respirator 6 is made to drive a bellows 7 which is enclosed in a container 8 and operates the anaesthetic circuit. This is the so-called bag-in-bottle principle which can also be built into the respirator 6 proper. However, the bag-in-bottle principle comprises some special arrangements; on the one hand there is the arrangement which has given the method its name and, on the other hand, the function of the excess valve 2 must be checked.
A further possibility of combining the respirator circuit (drive circuit) and the patient circuit (receiver a circuit) is to connect between them a switching unit 9 or exchanger which openly separates the gases in the two circuits as illustrated in FIG. 1e. During inhalation, the gas of the respirator 6 (e.g. oxygen) is supplied to the exchanger. The pressure is propagated to the patient circuit for operation thereof. During expiration, the gas flows back. In its simplest form, the exchanger may be an empty container. The best way is, however, to design the exchanger such that the front therein, between respirator gas and patient gas, becomes as well defined as possible. This can be achieved by giving the exchange the form of a tube.
An apparatus for inhalation anaesthesia comprising a gas exchanger between the drive circuit and the patient circuit is described in the paper "A new generation of anaesthetic ventilators" by A. P. Adams and J. D. Henville in Anaesthesia 1977, Vol. 32, pp. 34-40. The described exchanger is in the form of a corrugated tube, and serves to avoid dilution of anaesthetic gas. The fresh gases for anaesthetic and inhalation are supplied continuously and controlled by a flow meter.
The object of the invention is to control in a simple manner the gas concentration in the
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