1、Anesthesia Machine,Second Medical College三峡大学仁和医院 Jian Dao-lin 简道林,Overview The gas delivery system Breathing systems Anesthesia ventilator Safety features Scavenging Gas analysis Accessories New generation anesthesia machines,Definition,Anesthesiologists define the machine which is used to support
2、the administration of anesthesia as the anesthesia machine. The original concept was invented by the British anesthetist H.E.G. Boyle in 1917. Prior to this time, anesthetists often carried all their equipment with them, but the development of heavy, bulky cylinder storage and increasingly elaborate
3、 airway equipment meant that this was no longer practical for most circumstances.,Overview,The function of the anesthesia machine is to prepare a gas mixture of precisely known but variable composition. The machine provides a controlled flow of oxygen, nitrous oxide, air, and anesthetic vapors. Thes
4、e are delivered to a breathing system, which provides a means to deliver positive pressure ventilation and to control alveolar carbon dioxide by minimizing rebreathing and/or by absorbing carbon dioxide. A mechanical ventilator is connected to the breathing system, freeing up the anesthetists hands
5、for other tasks. Several types of monitors are used to observe the function of the system, to detect equipment failures, and,to provide information about the patient.,Made in China,Drager Narkomed 2A,Ohmeda Aestiva,A Datex Ohmeda British machine,The commonest type of anaesthetic machine in use in th
6、e developed world is the continuous-flow anaesthetic machine, which is designed to provide an accurate and continuous supply of medical gases ( such as oxygen and nitrous oxide ), mixed with an accurate concentration of anesthetic vapour (such as isoflurane), and deliver this to the patient at a saf
7、e pressure and flow. Modern machines incorporate a ventilator, suction unit, and patient-monitoring devices.,A schematic diagram of an anesthesia machine,Non-rebreathing Systems,rebreathing system (Vaporizer-in-the-Circle),rebreathing system(Vaporizer-out-of-the-Circle), The gas delivery system - Ox
8、ygen supply - Piped gases - Flow control valves - Flowmeters - Vaporizers - The common gas outlet - Oxygen flush valve,1.Central oxygen supply system Liquid oxygen,-Oxygen supply,2. Oxygen bank (smaller oxygen cylinders or tanks),- Piped gases,Wall outlets supply oxygen, nitrous oxide and air at a p
9、ressure of 50 to 55 pounds/in2 (psi). These outlets and the supply hoses ( corrugated tube ) to the machine are diameter indexed and color-coded.,Outlet of central oxygen supply system,1. A full cylinder of oxygen (in size E) has a pressure of 2,000 to 2,200 psi and contains the equivalent of 660 L
10、of gas at atmospheric pressure and room temperature. The oxygen cylinder pressure decreases in direct proportion to the amount of oxygen in the cylinder. 1（psi, pound per square inch ） = 6. 895（kPa） = 0.0703（ kg/cm2 ） = 0.0689 （bar）=0.068大气压（atm）. 1（mmH2O） =9.80665 帕（Pa）, 1（mmHg） =133.322（Pa）,2. A f
11、ull cylinder of nitrous oxide (in size E) has a pressure of 745 psi and contains the equivalent of 1,500 L of gas at atmospheric pressure and room temperature. The nitrous oxide in the cylinder is a liquid; the cylinder pressure does not decrease until the liquid content is exhausted, at which time
12、one-fourth of the total volume of gas remains.,3. Air cylinders (in size E) are present on some machines. A full cylinder has a pressure of 1,800 psi and contains the equivalent of 630 L at atmospheric pressure and room temperature.,A regulator or pressure reducing valve on anesthesia machines reduc
13、es the cylinder pressure to 50 psi. If this valve were not part of the anesthesia machine, the pressure of the gas entering the machine would be the same as the pressure in the cylinder. The industry standard for pressure within the anesthesia machine has been set at 50 psi. The regulators divide th
14、e machine into high-pressure (proximal to the regulator) and low-pressure (distal to the regulator) systems.,- A regulator or pressure reducing valve(Flow control valves),A needle valve controls the flow of each gas. As a safety feature, the oxygen control knob is fluted and protrudes more than the
15、nitrous oxide and air controls. Gas pressures are reduced from 45 to 55 psi (high pressure) to near atmospheric pressure (low pressure) by,the needle valves.,A regulator or pressure reducing valve,Oxygen flow control valve,As gas flows out of the low-pressure chamber, the drop in pressure reduces th
16、e force generated by the diaphragm (D) against the spring (S), allowing the valve (V) to open and admit gas from the high-pressure chamber. The output pressure may be adjusted by a screw (A) that alters the force applied by the spring.,Figure Cross-sectional view of a needle valve,Needle valves are
17、similar in design and operation to the globe valve. Instead of a disk, a needle valve has a long tapered point at the end of the valve stem. When the long taper of the valve element is clock-wise turned, the valve is opened. Contrarily, the valve is closed. A cross-sectional view of a needle valve i
18、s illustrated in figure.,- flowmeters,Flowmeters. Each flowmeter is a calibrated tapered glass tube in which a bobbin or ball floats to indicate the flow of gas. In other words, Flowmeters can be of varying styles however most anesthesia machines have flowmeters that use a bobbin that floats on a co
19、lumn of gas to determine the amount of flow.,The needle valve is the most common means of regulating gas flow rate. As the valve is opened, the orifice around the needle becomes larger and flow increases. The valve cartridge itself is usually removable so it can be replaced if it is damaged. The val
20、ve must not be over-tightened-this will drill out the orifice and cause it to become incompetent. Some valves, such as are found on most medical anesthetic machines, incorporate a stop to prevent the valve being over-tightened. The valve control knob is usually color-coded. In addition, oxygen flowm
21、eter knobs frequently have fluted edges to distinguish them from those of other gases.,The inside of glass clinder becomes wider as the bobbin floats higher in the cylinder thereby allowing more gas to flow up the tube and out of the flowmeter.,The flowmeter allows the operator to control and know t
22、he flow rate of each gas; usually in liters per minute or mL per minute. Consists of a float, usually a little ball inside a tube. It is usually read from the center of the ball and usually colorcoded, like the gas tanks.,Flowmeters are used to control the flow of a gas (oxygen usually) which is bei
23、ng delivered to the circle.As the indicator or float of the flowmeter rises in the tube, more gas flows around it.Some machines have two flowmeters, one for high flow and one for low flow of oxygen. Gas (oxygen, nitrous oxide) usually enters at the bottom, travels through a tapered tube, and then ex
24、its at the top.,When the valve is closed, it should be turned only until the flow of gas ceases as further tightening may result in damage to the pin or seat.When the machine is not used, the flow control knobs should be opened until the gas pressure is zero, then closed.Before using a machine, the
25、flowmeters should be checked to see if they are in the closed position. If they have be left open, when the gas supply to an open flow control valve is restored, the indicator may rise to the top of the tube where its pre-sense may not be noticed. A very high oxygen flow may result.,- Vaporizers,An
26、anesthetic vaporiser is a device generally attached to an anesthetic machine which delivers a given concentration of a volatile anesthetic agent.The design of these devices takes account of varying ambient temperature fresh gas flow agent vapor pressure,Vaporizer-in-the-Circuit,Vaporizer-out-of-the-
27、Circuit,Vaporizer-out-of-the-Circuit,The purpose of an anesthetic vaporizer is to produce a controlled and predictable concentration of anesthetic vapor in the carrier gas passing through the vaporizer. Most vaporizers are of the plenum type, which consists of a vaporizing chamber containing the liq
28、uid anesthetic, and a bypass. Gas passing through the vaporizing chamber volatilizes the anesthetic and is then mixed with the anesthetic-free gas bypassing the chamber, the proportion of vapor-containing gas and bypass gas being,controlled by a tap.,- The common gas outlet,The common gas outlet is
29、the port where gases exit the machine and is connected to the breathing system via the fresh gas hose.,- Oxygen flush valve,This valve allows a high flow oxygen to go directly to the breathing system without going through a vaporizer (usually). One hundred percent oxygen at 45 to 55 psi comes direct
30、ly from the high pressure system to the common gas outlet. Oxygen flow can be as high as 40 to 60 L/min., Breathing systems,The delivery systems which conduct anesthetic gases from an anesthetic machine to the patient are known as the breathing systems or circuits They are designed to allow either s
31、pontaneous respiration or intermittent positive pressure ventilation (IPPV) and consist of a reservoir bag, anesthetic tubing, and a pressure relief valve. A number of mechanical ventilators include a specific breathing system. Other ventilators have been designed to operate with existing breathing
32、systems.,Anesthetic gas exits the anesthesia machine (via the common gas outlet) and then enters a breathing circuit. The function of the circuit is to deliver oxygen and anesthetic gases to the patient and to eliminate carbon dioxide. The carbon dioxide may be eliminated by gas inflow or by soda li
33、me absorption.,-Classification of breathing systems - The carbon dioxide absorber - Two one-way valves (inspiratory and expiratory) - Breathing Hoses and Y-piece adapter - Reservoir bag - APL(adjustable pressure-limiting valve ) valve or pop-off valve,-Classification of breathing systems,Various cla
34、ssification systems have been developed to aid understanding of how breathing systems operate. Classification of breathing systems are followed as: 1 Open, semi-open, semi-closed, and closed breathing system. 2 Non-rebreathing and rebreathing systems,1 Open, semi-open, semi-closed, and closed breath
35、ing system.,This classification is made mainly according to the concentration value of re-breathing carbon dioxide. The boundary concentration value of re-breathing carbon dioxide is 1 percent. Unfortunately, in different parts of the world, the same terminology is used for different systems, so thi
36、s classification is probably best voided.,(1)Open systems,Open systems have no valves, no tubing: for example open drop ether, or a nasal cannula. In either, the patient has access to atmospheric gases. There is not any re-breathing of carbon dioxide.,(2) Semi-open system,Semi-open system refers to
37、that in which the concentration of re-breathed carbon dioxide is less than 1 percent. Semi-open system should be no re-breathing and must have high fresh gas flow and higher minute ventilation.,(3) Semi-closed system,Semi-closed system refers to that in which the concentration of re-breathing carbon
38、 dioxide is more than 1 percent. In semi-closed system, some re-breathing occurs, FGF and pop-off settings should be at intermediate values.,(4) Closed system,Closed system is such a condition that fresh gas inflow exactly equal to patient uptake and that complete carbon dioxide is absorbed after ca
39、rbon dioxide absorber takes the effects and pop-off is closed.,Comparison of Open, semi-open, semi-closed, and closed breathing system,2. Non-rebreathing and rebreathing systems,The classification of non-rebreathing versus rebreathing systems is more widely used.,(1)Mapleson (Non-rebreathing breathi
40、ng system) (circuits),One kind of breathing system was introduced by Professor W.W. Mapleson is most commonly used in the world (Figure 1). Mapleson described five different arrangements of breathing circuits. He classifed these circuits and they are now known as the Mapleson systems, termed A-E. Th
41、is classification does not include systems with carbon dioxide,absorption.,The original Mapleson A system,The Mapleson A (Magill) system was designed by Sir Ivan Magill in the 1930s and remains an excellent system for spontaneous ventilation (Figure 2). Fresh gas enters the system at the fresh gas o
42、utlet of the anesthesia machine. This is an efficient system for spontaneously breathing patients if carbon dioxide absorption is not available. During controlled ventilation the Magill circuit works in a different way and becomes wasteful and inefficient, requiring high fresh gas flows to prevent r
43、ebreathing.,The expiratory valve (Heidbrink valve) is very close to the patient to reduce the dead space. The respiratory cycle has three phases during spontaneous breathing; inspiration, expiration and the expiratory pause. During inspiration gas is inhaled from the 2 litre reservoir (breathing) ba
44、g which partially collapses giving a visual confirmation that breathing is occurring.,During expiration the bag and tubing are initially refilled with a combination of exhaled dead space gas (containing no carbon dioxide) and fresh gas flowing from the anaesthetic machine. Once the bag is full, the
45、pressure within the breathing system rises and the expiratory valve near the patient opens allowing the alveolar gas (containing carbon dioxide) to be vented(排出)from the system. During the expiratory pause, more fresh gas enters the system driving any remaining alveolar gas back along the corrugated
46、 (anesthetic) tubing and out through the valve. If the fresh gas flow is sufficiently high, all the alveolar gas is vented from the circuit before the next inspiration and no rebreathing will take place.,With careful adjustment the fresh gas flow can be reduced until there is only fresh gas and dead
47、 space gas in the breathing system at the start of inspiration. When the system is functioning correctly, without any leaks, a fresh gas flow (FGF) equal to the patients alveolar minute ventilation is sufficient to prevent rebreathing. In practice however, a FGF closer to the patients total minute v
48、entilation (including dead space) is usually selected to provide a margin of safety. An adults minute volume is approximately 80mls/kg /min and thus for a 75kg man a FGF of 6 litres per minute will prevent rebreathing.,During controlled ventilation, The inspiratory force is provided by the anesthesi
49、ologist with squeezing the reservoir bag after partly or completely closing the expiratory valve next to the patient. During lung inflation some of the gas is vented from the circuit and at the end of inspiration the reservoir bag is less than half full. During expiration, dead space and alveolar ga
50、s pass down the corrugated tubing and may reach the bag, which will then contain some carbon,dioxide.,During the next inspiration when the bag is compressed alveolar gas re-enters the patients lungs followed by a mixture of fresh, dead space and alveolar gas. A FGF of two and a half times the patients minute volume is required to vent enough alveolar gas to minimise rebreathing (FGF of about 12-15 litres /min) which is obviously very inefficient. In practice the Magill circuit should not be used for positive pressure ventilation except for short periods of a few minutes at a time.,
