Method for increasing oxygen concentration rising speed and anaesthesia machine

Abstract

The invention provides a method for increasing the rising speed of oxygen concentration and an anaesthesia machine, and the method comprises the following steps: when the anaesthesia machine starts to use, washing a loop with pure oxygen, and after the oxygen concentration rises to a target value, replacing the pure oxygen with fresh gas with normal oxygen concentration. The anesthesia machine has the advantages that the oxygen concentration of the ventilation loop can be rapidly increased when the anesthesia machine starts to be used, and the oxygen supply concentration can be rapidly recovered after the oxygen concentration reaches a target value.

Description

Technical Field

[0001] The present application belongs to the technical field of anesthesia machines, and specifically relates to a method for accelerating the rate of increase of oxygen concentration and anesthesia machines. Background Art

[0002] During the ventilation process of the anesthesia machine, fresh gas needs to be continuously input into the circuit to provide the patient with oxygen to maintain life characteristics. The doctor can set the total flow and oxygen concentration value of the flowmeter to control the oxygen concentration inhaled by the patient and ensure the patient's oxygen concentration is safe. However, in general, the oxygen concentration value output by the flowmeter only represents the oxygen concentration at the outlet of the flowmeter, not the oxygen concentration in the ventilation circuit. The fresh gas of a certain oxygen concentration value output by the flowmeter will be diluted by other gases after entering the circuit and will be consumed by the patient. Therefore, the oxygen concentration in the circuit will be much lower than the set oxygen concentration value during ventilation, and then slowly increase. Rapidly increasing the oxygen concentration value in the ventilation circuit to the target oxygen concentration value helps to ensure patient safety, so it is very important to find a strategy to quickly increase the oxygen concentration in the circuit. Summary of the invention

[0003] The purpose of the present application is to overcome the defect that the oxygen concentration in the oxygen circuit increases slowly when the anesthesia machine is first used.

[0004] In order to achieve the above purpose, the present application proposes a method for accelerating the rate of increase of oxygen concentration, comprising:

[0005] When the anesthesia machine is put into use, pure oxygen is used to flush the circuit. When the oxygen concentration rises to the target value, the pure oxygen is replaced with fresh gas with normal oxygen concentration.

[0006] As an improvement of the above method, the method for calculating the longest time for the oxygen concentration to rise to the target value is:

[0007]

[0008] Where t represents the time it takes for the oxygen concentration to rise to the target value; T represents the time constant; F O2 Indicates the target oxygen concentration value, F O2i represents the initial oxygen concentration value; f represents the flow meter flow value.

[0009] As an improvement of the above method, the time constant T is calculated as follows:

[0010]

[0011] Among them, V c Indicates the volume of the circuit.

[0012] As an improvement of the above method, based on the minute ventilation range covered by the technical requirements of the equipment, the oxygen concentration rise time curve when flushing with pure oxygen at each minute ventilation is statistically calculated to obtain the time constant T under various conditions; during actual ventilation, the time constant T at the corresponding minute ventilation is found from the time curve obtained from the experiment.

[0013] The present application also provides an anesthesia machine, which uses the above method to increase the concentration of oxygen in the ventilation circuit.

[0014] Compared with the prior art, the advantages of this application are:

[0015] When the anesthesia machine is first used, the oxygen concentration in the ventilation circuit can be quickly increased, and the oxygen supply concentration can be quickly restored after the oxygen concentration reaches the target value. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The figure shows the gas circuit diagram during ventilation of the anesthesia machine;

[0017] Figure 2 Shown is a schematic diagram of the ventilation model;

[0018] Figure 3 Shown is a statistical graph of the time constant of the oxygen concentration rise in the ventilation circuit;

[0019] Figure 4 Shown is a flow chart of a method for accelerating the rate of increase of oxygen concentration. DETAILED DESCRIPTION

[0020] The technical solution of the present application is described in detail below with reference to the accompanying drawings.

[0021] The gas path during anesthesia machine ventilation is as follows Figure 1 As shown, the gas path of the anesthesia machine during the user's inhalation process is:

[0022] The driving gas passes through the coil and the soda lime tank in turn, enters the inhalation port, mixes with the fresh gas and enters the user's lungs. During the inhalation process, the driving gas pushes the gas in the circuit and the fresh gas into the lungs. In this process, the oxygen and the original gas in the circuit are mixed, and the degree of mixing is unknown.

[0023] The gas path of the anesthesia machine during the user's exhalation process is:

[0024] The gas in the user's lungs enters the coil through the exhalation port, and after being tempered with the fresh gas that has passed through the soda lime tank, enters the exhaust port and is discharged from the anesthesia machine. During the exhalation process, the gas in the lungs is discharged into the circuit through the exhalation pipeline, and the fresh gas is also discharged into the circuit. The two gases are mixed, and the degree of mixing is unknown. The mixed gas is discharged from the exhaust port, and its volume is equal to the total volume of fresh gas in the breathing cycle. The oxygen concentration of the waste gas is unknown.

[0025] When the anesthesia machine is first used, if fresh gas with normal oxygen concentration is directly used to flush it, the speed at which the oxygen concentration in the circuit rises will definitely be slower than when 100% oxygen concentration gas (pure oxygen) is used to flush the circuit. However, if 100% oxygen concentration gas is used to flush the circuit, the 100% oxygen concentration gas needs to be replaced with fresh gas with normal oxygen concentration after the oxygen concentration rises to the target value, otherwise medical accidents will occur. At present, it is difficult to accurately monitor the process of oxygen concentration rising to the target value. It is necessary to calculate the longest inflation time of 100% oxygen concentration gas and use the calculated value for accurate control.

[0026] The oxygen concentration in the anesthesia machine is generally controlled between 21% and 90%. According to different clinical needs and the specific conditions of the patient, the anesthesiologist will adjust the oxygen concentration. For example, during general anesthesia, the oxygen concentration is usually set at 40%-50% and adjusted at any time according to the oxygen saturation. In addition, in some cases, such as to prevent atelectasis, the oxygen concentration needs to be lower than 60%. Therefore, the oxygen concentration in the anesthesia machine is a parameter that can be adjusted according to treatment needs, but it is usually kept within the above safety range.

[0027] If we extend the timeline, we can regard the whole process as a process in which one gas replaces another gas in the circuit. The inhalation and exhalation actions are used to stir the two gases and make them mix evenly. In the ideal model, we can ignore the inhalation and exhalation actions, and assume that fresh gas enters the circuit and is automatically fully mixed. When the overall pressure of the circuit remains unchanged, part of the uniform gas is discharged to the exhaust port. The above ventilation model is converted into Figure 2 shown.

[0028] In the whole process, oxygen complies with the law of conservation of mass:

[0029] V o2 =V io2 +V wO2 (1)

[0030] Among them, V o2 V is the amount of oxygen input into the circuit by the flowmeter, io2 is the amount of oxygen retained in the circuit, V wO2 is the amount of oxygen in the exhaust gas.

[0031]

[0032] Among them, F o2 (t) is the real-time oxygen concentration input by the flow meter, f is the flow value of the flow meter, F io2 (t) is the oxygen concentration in the circuit,

[0033]

[0034] Among them, Vc is the loop volume size.

[0035] Using the Laplace transform we get:

[0036] F O2 (s)f=V c F iO2 (s)S+fF iO2 (s) (4)

[0037]

[0038] The above formula is a typical first-order system model, using the Lasker inverse transformation:

[0039]

[0040] The time constant is:

[0041]

[0042] In the ideal model, fresh gas is fully mixed immediately after entering the circuit. However, in actual experiments, gas mixing relies on the driving force of the airflow of inhalation and exhalation and gas diffusion. The degree of mixing is affected by the maximum flow rate, duration, velocity curve shape, temperature, etc. of the flushing gas flow. It cannot be thoroughly mixed evenly, which may cause some gases with high oxygen concentration to be directly discharged. This process is too cumbersome and it is difficult to derive a specific formula based on the actual gas path conditions.

[0043] Only the fuzzy relationship between rise time, minute ventilation and flow value can be derived. The rise time, minute ventilation and flow value in the experimental data are fitted by first-order linear fitting to obtain the time constant under 100% oxygen concentration, such as Figure 3 shown.

[0044] According to the experimental results:

[0045] 1) The fresh gas flow value has the greatest impact, the rise time doubles or halves, but the control strategy must not change this value, ignore this factor.

[0046] 2) The minute ventilation, which is a combination of tidal volume and frequency, has the most significant impact compared to other factors.

[0047] According to the minute ventilation range covered by the technical requirements of the equipment, the oxygen concentration rise time curve when pure oxygen is used for flushing at each minute ventilation can be statistically calculated to obtain the time constant T under various conditions. During actual ventilation, the time constant T corresponding to the minute ventilation is found from the time curve obtained from the test as a correction for the time constant.

[0048] Among them, F O2 is the target oxygen concentration value, FO2i is the initial oxygen concentration value, unit is 1%, and the 100% output time is obtained as:

[0049]

[0050] According to the above calculation, if Figure 4 As shown, the method for accelerating the oxygen concentration increase rate provided by the present application includes: when the anesthesia machine is started, pure oxygen is used to flush the circuit, and when the oxygen concentration rises to the target value, the pure oxygen is replaced with fresh gas with normal oxygen concentration. The time for the oxygen concentration to rise to the target value is:

[0051]

[0052] The present application also provides an anesthesia machine, which uses the above-mentioned method of accelerating the rate of increase of oxygen concentration to quickly increase the concentration of oxygen in the ventilation circuit.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present application and are not intended to limit it. Although the present application is described in detail with reference to the embodiments, a person skilled in the art should understand that any modification or equivalent replacement of the technical solution of the present application does not depart from the spirit and scope of the technical solution of the present application and should be included in the scope of the claims of the present application.

Claims

1. A method for accelerating the rate of increase of oxygen concentration, comprising: When the anesthesia machine is put into use, pure oxygen is used to flush the circuit. When the oxygen concentration rises to the target value, the pure oxygen is replaced with fresh gas with normal oxygen concentration.

2. The method for accelerating the rate of increase of oxygen concentration according to claim 1, characterized in that: The maximum time for the oxygen concentration to rise to the target value is calculated as follows: Where t represents the time it takes for the oxygen concentration to rise to the target value; T represents the time constant; F O2 Indicates the target oxygen concentration value, F O2i represents the initial oxygen concentration value; f represents the flow meter flow value.

3. The method for accelerating the rate of increase of oxygen concentration according to claim 2, characterized in that: The time constant T is calculated as follows: Among them, V c Indicates the volume of the circuit.

4. The method for accelerating the rate of increase of oxygen concentration according to claim 2, characterized in that: According to the minute ventilation range covered by the technical requirements of the equipment, the oxygen concentration rise time curve when flushing with pure oxygen at each minute ventilation is statistically calculated to obtain the time constant T under various conditions; during actual ventilation, the time constant T under the corresponding minute ventilation is found from the time curve obtained from the experiment.

5. An anesthesia machine, characterized in that: The oxygen concentration in the ventilation circuit is increased by using the method according to any one of claims 1 to 4.

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