A method for accelerating the rise in oxygen concentration and an anesthesia machine

Abstract

This application provides a method and an anesthesia machine for accelerating the rise in oxygen concentration. The method includes: flushing the ventilation circuit with pure oxygen when the anesthesia machine is started; and replacing the pure oxygen with fresh gas of normal oxygen concentration after the oxygen concentration reaches the target value. The advantage of this application is that it can rapidly increase the oxygen concentration in the ventilation circuit when the anesthesia machine is started, and can quickly restore the oxygen supply concentration after the oxygen concentration reaches the target value.

Description

Technical Field

[0001] This application belongs to the field of anesthesia machine technology, specifically relating to a method for accelerating the rise in oxygen concentration and an anesthesia machine. Background Technology

[0002] During anesthesia machine ventilation, a continuous supply of fresh gas is needed to the circuit to provide the patient with the oxygen necessary to maintain vital signs. Doctors can set the total flow rate and oxygen concentration of the flow meter to control the oxygen concentration inhaled by the patient and ensure its safety. However, the oxygen concentration value output by the flow meter generally only represents the oxygen concentration at the flow meter outlet, not the oxygen concentration in the ventilation circuit. Fresh gas at a certain oxygen concentration output by the flow meter will be diluted by other gases and consumed by the patient after entering the circuit. Therefore, the oxygen concentration in the circuit will be much lower than the set value during ventilation, and then gradually increase. Quickly raising the oxygen concentration in the ventilation circuit to the target value helps ensure patient safety; therefore, finding a strategy to rapidly increase the oxygen concentration in the circuit is crucial. Summary of the Invention

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

[0004] To achieve the above objectives, this application proposes a method for accelerating the increase in oxygen concentration, comprising:

[0005] When the anesthesia machine is first used, the circuit is flushed with pure oxygen. Once the oxygen concentration reaches the target value, the pure oxygen is replaced with fresh gas at the normal oxygen concentration.

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

[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 F represents the target oxygen concentration value. O2i represents the initial oxygen concentration; f represents the flow rate of the flow meter.

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

[0010]

[0011] Among them, V c This indicates the size of the loop volume.

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

[0013] This application also provides an anesthesia machine that uses the above-described method to increase the oxygen concentration in the ventilation circuit.

[0014] Compared with existing technologies, the advantages of this application are:

[0015] It can rapidly increase the oxygen concentration in the ventilation circuit when the anesthesia machine is started, and can quickly restore the oxygen supply concentration after the oxygen concentration reaches the target value. Attached Figure Description

[0016] Figure 1 The diagram shown is the airway diagram during anesthesia machine ventilation.

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

[0018] Figure 3 The figure shown is a statistical graph of the oxygen concentration rise time constant in the ventilation circuit.

[0019] Figure 4 The diagram shows a method to accelerate the increase in oxygen concentration. Detailed Implementation

[0020] The technical solution of this application will be described in detail below with reference to the accompanying drawings.

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

[0022] The driving gas passes sequentially through the coil and the soda lime container, enters the inhalation port, mixes with fresh gas, and then enters the user's lungs. During inhalation, the driving gas pushes the gas in the circuit and the fresh gas together into the lungs. During this process, oxygen mixes with the original gas in the circuit, but the degree of mixing is unknown.

[0023] The gas pathway of the anesthesia machine during the user's exhalation is as follows:

[0024] Gas from the user's lungs enters the coil through the exhalation port, mixes with fresh gas passing through the soda lime container, and then enters the exhaust port, exiting the anesthesia machine. During exhalation, gas from the lungs is discharged into the circuit through the exhalation tubing, while fresh gas is also discharged into the circuit. The two gases mix, the degree of which is unknown, and the mixed gas is discharged through the exhaust port. Its volume is equal to the total volume of fresh gas during the respiratory cycle, and the oxygen concentration of the exhaust gas is unknown.

[0025] When an anesthesia machine is first used, if fresh gas with normal oxygen concentration is directly introduced, the rate at which the oxygen concentration in the circuit rises will definitely be slower than if 100% oxygen concentration gas (pure oxygen) is used. However, if 100% oxygen concentration gas is used to flush the circuit, it needs to be replaced with fresh gas with normal oxygen concentration after the oxygen concentration reaches the target value; otherwise, medical accidents may occur. Currently, accurately monitoring the process of oxygen concentration rising to the target value is difficult, requiring calculation of the longest inflation time using 100% oxygen concentration gas, and using the calculated value for accurate control.

[0026] The oxygen concentration in an anesthesia machine is generally controlled between 21% and 90%. The anesthesiologist will adjust the oxygen concentration according to different clinical needs and the patient's specific condition. For example, during general anesthesia, the oxygen concentration is usually set at 40%-50% and adjusted as needed based on oxygen saturation. Furthermore, in some cases, such as to prevent atelectasis, the oxygen concentration needs to be below 60%. Therefore, the oxygen concentration in the anesthesia machine is a parameter that can be adjusted according to treatment needs, but it is generally kept within the aforementioned safe range.

[0027] Extending the timeline, we can view the entire process as a gas replacement loop where one gas is replaced by another. Inhalation and exhalation agitate the two gases, ensuring they are thoroughly mixed. In an ideal model, inhalation and exhalation can be ignored. We assume fresh gas enters the loop, mixes automatically and completely, and with the overall loop pressure remaining constant, some of the homogeneous gas is discharged to the exhaust port. This transforms the ventilation model into... Figure 2 As shown.

[0028] The oxygen content follows the law of conservation of mass throughout the entire process:

[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 flow meter. io2 The amount of oxygen retained in the circuit, V wO2 This refers to the amount of oxygen in the exhaust gas.

[0031]

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

[0033]

[0034] Among them, Vc This represents the size of the loop volume.

[0035] Using the Laplace transform, we obtain:

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

[0037]

[0038] The above formula is for a typical first-order system model, which can be obtained using the inverse Laplace transform:

[0039]

[0040] The time constant is:

[0041]

[0042] In the ideal model, fresh gas is assumed to mix thoroughly and uniformly immediately upon entering the circuit. However, in actual experiments, gas mixing relies on the airflow driven by inhalation and exhalation and gas diffusion. The degree of mixing is affected by factors such as the maximum flow rate, duration, velocity curve shape, and temperature of the flushing airflow, making complete and uniform mixing impossible. This may result in the direct discharge of some gases with higher oxygen concentrations. This process is too cumbersome, making it difficult to derive a specific formula based on actual gas path conditions.

[0043] Only a fuzzy relationship between rise time, minute ventilation, and flow rate can be derived. A first-order linear fit is performed on the rise time, minute ventilation, and flow rate values ​​from the experimental data to obtain the time constant under 100% oxygen concentration conditions, such as... Figure 3 As shown.

[0044] Based on the experimental results, it can be concluded that:

[0045] 1) The fresh gas flow rate has the greatest impact, doubling or halving the rise time, but the control strategy will not change this value, so this factor is ignored.

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

[0047] Based on the minute ventilation range covered by the equipment's technical requirements, the oxygen concentration rise time curves for flushing with pure oxygen at each minute ventilation rate can be statistically analyzed, thus obtaining the time constant T under various conditions. During actual ventilation, the time constant T corresponding to the minute ventilation rate is found from the experimental time curves and used as a correction to the time constant.

[0048] Among them, F O2 For the target oxygen concentration value, FO2i Given the initial oxygen concentration value (in 1%), the time to reach 100% output is:

[0049]

[0050] Based on the above calculations, as Figure 4 As shown, the method for accelerating the rise in oxygen concentration provided in this application includes: flushing the circuit with pure oxygen when the anesthesia machine is first used; and replacing the pure oxygen with fresh gas of normal oxygen concentration after the oxygen concentration rises to the target value. The time required for the oxygen concentration to rise to the target value is:

[0051]

[0052] This application also provides an anesthesia machine that uses the above-described method to accelerate the rise in oxygen concentration to rapidly increase the oxygen concentration in the ventilation circuit.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application do not depart from the spirit and scope of the technical solutions of this application, and should all be covered within the scope of the claims of this application.

Claims

1. An anesthesia machine that increases the oxygen concentration in a ventilation circuit by accelerating the rate of increase in oxygen concentration, the method comprising: When the anesthesia machine is first used, the circuit is flushed with pure oxygen. Once the oxygen concentration reaches the target value, the pure oxygen is replaced with fresh gas at the normal oxygen concentration. The method for calculating the longest time required for the oxygen concentration to rise to the target value is 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 F represents the target oxygen concentration value. O2i The initial oxygen concentration is represented by f; the flow rate of the flow meter is represented by f. The method for calculating the time constant T is as follows: Among them, V c Indicates the size of the loop volume; Based on the minute ventilation range covered by the equipment's technical requirements, the oxygen concentration rise time curves for flushing with pure oxygen under each minute ventilation rate were statistically analyzed to obtain the time constant T under various conditions. During actual ventilation, the time constant T corresponding to the minute ventilation rate was found from the time curves obtained from the experiment.

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