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A General Introduction to Anesthesia Machine and Its Development Trend

Author: Ma JianXin


This article is summarization of my many years’ experience on development of anesthetic equipment. After conducting research on customer’s demand and the market, reading various periodicals and related information, I’ve got the following understanding of the anesthesia machine and its future trend of development.

Brief introduction to the anesthesia machine

Anesthesia machine is one of the basic equipment of hospitals and main equipment in operating rooms. It’s life-supporting equipment and its basic function is to ventilate the patient and accurately transmit volatile anesthetics to make the patient in an appropriate state of general anesthesia. At the same time, it monitors the patient and the working state of itself to guarantee the patient’s life safety.

Anesthesia machine has a complex structure which comprises gas source, gas mixing system, anesthetic gas vaporizer, breathing circuit, ventilator, exhaust gas emission system, monitoring system and information management system, etc. Users have a high demand on the anesthesia machine’s safety, precision, dependability and easiness of use. Though the anesthesia machine has gone through half a century’s development, most of its functions haven’t changed and, the gas supply system, mechanical gas mixing system, mechanical anesthetic gas vaporizer and the exhaust gas emission system have been rather mature. Comparatively speaking, the breathing circuit, ventilator, electronic gas mixing system, gas monitoring, breathing monitoring ,patient monitoring, electronic anesthetic gas vaporizer, pre-use self-checking function of the equipment and the information management system are still in development and improvement. Technology innovation of the machine making experts is mainly about these, too.

I. Low-flow anesthesia is the development trend of the anesthesia machine.

Currently, the new-type volatile anesthetics (sevoflurane and desflurane) which are safer and are easier for controlling the anesthetic depth and which have less side-effect have been widely used. But the shortcomings are big dosage, high price and easy pollution to the environment. To avoid these, it’s required that the anesthesia machine can conduct low-flow closed loop anesthesia as well as solving the hypoxia problem caused by low-flow anesthesia, so that patients are safe, use dosage of anesthetics and medical cost reduced, and environmental pollution lessened.

Following are the requirements on the anesthesia machine for low-flow anesthesia.

1. Equipped with precisely-controlled low flow meter

2. Be able to calculate the amount of anesthetic gas consumed. Electronic flow meter and electronic anesthetic gas vaporizer are required to provide the dose using information.

3. Be able to reduce the mechanical dead space in the breathing circuit so that hypoxia caused by low-flow anesthesia is timely solved.

4. Have effective monitoring of oxygen concentration and SpO2 of patient so that hypoxia caused by low-flow anesthesia is timely discovered.

5. Equipped with gas monitoring module so that when applying anesthesia, low concentration of the gas inhaled by patient due to attenuation of fresh gas can be timely discovered.

II. The ventilation mode of the anesthesia machine is extended from mechanical control to autonomous respiration of patients.

For ambulatory surgery patients, it’s clinical requirement that muscle relaxant is used on the patients partly but not wholly. If muscle relaxant is used partly, patients can avoid the possibility of autonomous respiration being interrupted in the surgery. This would require that the ventilator equipped on the anesthesia machine can assist in the patient’s autonomous breathing but not just providing simple mechanically-controlled ventilation. That’s why more and more advanced ventilation modes of the therapeutic ventilators in ICUs are applied to the anesthesia machine, for example, the modes of the PCV, SIMV, PSV, PRVC and CPAP.

Because there is autonomous respiration in patient’s surgery, it’s required that laryngeal mask intubation instead of the traditional endotracheal intubation is used. This intubation method increases the possibility of airway gas leakage and so limits the application of volume-controlled ventilation. Now pressure support ventilation is beginning to be widely used.

In addition to this, in the recovery period after operation when the patient begins to have autonomous respiration, his/her breathing ability would be very weak. To quicken metabolism of anesthetics and the patient’s recovery, it’s very necessary that the anesthesia machine has the advanced ventilation mode.

III. Whether the anesthesia machine can be used to anesthetize neonates and the old is an important criterion for evaluating whether the machine has strong function or not.

In recent years, the number of neonatal surgeries is significantly increasing. Because neonates are different from adults in terms of physiological features and anatomical structure, the anesthesia machine used for them must meet higher standards. For example, independent Auxiliary Common Gas Outlet (ACGO) is needed and open or semi-open breathing circuit can be conveniently used to eliminate CO2; its output tidal volume must be no more than 20ml and the bellow compliance must be compensated by the tidal volume to guarantee that the tidal volume the neonate inhale is correct; through the accurate pressure control mode, leakage of gas bag or trachea cannula is prevented while the high airway pressure problem caused by low lung compliance is solved; and specialized monitor that can monitor the vital signs of neonate and meet its other demands is needed.

Cardiac surgery and lung cancer surgery are more commonly seen among old people who are usually accompanied by COPD (chronic obstructive pulmonary disease), increased airway resistance and weak pulmonary compliance. At the same time, old people have low endurance to anesthetics and the dose used on them is less than on young and middle-aged people. So the requirements for control of the flow of the anesthetic machine and the anesthetic concentration, for the ventilation mode of the ventilator and for monitoring of respiratory mechanics, are much higher. And since the lung cancer patients need to be intubated with double-lumen tubes for one-lung ventilation or independent lung ventilation, there are special requirements for the ventilator they use. Another example is the cardiac bypass operation which requires extracorporeal circulation bypass. During the bypass, breathing and heartbeat will stop and the anesthetic machine and the monitor are required to use the extracorporeal circulation alarm modes (which are the shielding suffocation alarm, the shielding volume alarm and the shielding anesthetic gas concentration alarm). At the same time, the ventilator is required to maintain the patient’s lungs in a filled state. It should make sure that what the patient inhale is air but not pure oxygen, because pure oxygen is absorbed more easily by the lungs which will lead to atelectasis. This is why the anesthetic machine needs to be equipped with air source.

Ⅳ. Monitoring of anesthetic depth

Effective monitoring of anesthetic depth can prevent too deep anesthesia and anesthesia accidents, precisely predict patient’s recovery time, reduce the dose of anesthetics used and improve anesthesia safety. The functions of anesthetic depth monitoring, such as monitoring minimum alveolar anesthetic concentration (MAC), bispectral EEG index (BIS), auditory evoked potential index and entropy, have been clinically applied.

Ⅴ. The anesthetic workstation

The anesthetic workstation integrates the functions of ventilation, monitoring and information processing, which is a perfect combination of modern anesthesia machine and microelectronic technology. It is a highly-integrated intelligent anesthetic work platform with advanced monitoring equipment and operation interface that offers a good work environment for the anesthetists and improves patient’s safety.

With the development of modern technology, the concept of anesthetic workstation is renewing all the time. At present, the anesthetic workstation is no longer just a combination of the anesthesia machine, the monitor and the anesthetic information management system, but with added intravenous anesthesia management system and “imaging information and anesthetic experts’ decision-making system” as important parts. The anesthetic workstation has the advantages of minimized equipment size, reduced wiring of cables, unified user’s interface, reduced excessive alarms, convenient data export, greatly-reduced anesthetic accidents due to misoperation of users and improved patients’ safety in anesthesia. So the anesthetic workstation is an important development trend of the anesthesia machine.

In face of the reality that the medical market has more and more requirements on the anesthesia machine, Comen will develop more anesthetic work platforms that meet market trend and customer’s demand in the future basing on innovation and its accumulation of technologies over the years, so that the world will enjoy more high-end technology service from our company.

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