File Name: understanding anesthesia equipment construction care and complications .zip
Traditional breathing systems used for anaesthesia purposes perform well if they are cared for properly and the user understands the principles that underlie their function. The circuit selected will depend on the task to be performed and the professional environment. Much valuable information omitted in this review is available in specialized books dealing with anaesthesia equipment and should be easily accessible in any department of anaesthesia.
Northwestern University Columbus Hospital Chicago. This article is only available in the PDF format. Download the PDF to view the article, as well as its associated figures and tables. As a resident, I was told that I must read this book in order to understand anesthesia equipment; I was well advised.
After WTG Morton's first public demonstration in of use of ether as an anaesthetic agent, for many years anaesthesiologists did not require a machine to deliver anaesthesia to the patients. After the introduction of oxygen and nitrous oxide in the form of compressed gases in cylinders, there was a necessity for mounting these cylinders on a metal frame.
This stimulated many people to attempt to construct the anaesthesia machine. HEG Boyle in the year modified the Gwathmey's machine and this became popular as Boyle anaesthesia machine. Though a lot of changes have been made for the original Boyle machine still the basic structure remains the same.
All the subsequent changes which have been brought are mainly to improve the safety of the patients. Knowing the details of the basic machine will make the trainee to understand the additional improvements. It is also important for every practicing anaesthesiologist to have a thorough knowledge of the basic anaesthesia machine for safe conduct of anaesthesia.
The most important piece of equipment that the anaesthesiologist uses is the anaesthesia machine. Safe use of anaesthesia machine depends upon an interaction between the basic design of the machine with its safety features and the knowledge and skills of the anaesthesiologist. The basic function of an anaesthesia machine is to prepare a gas mixture of precisely known, but variable composition. The gas mixture can then be delivered to a breathing system.
Anaesthesia machine itself has evolved from a simple pneumatic device to a complex array of mechanical, electrical and computer — controlled components. Much of the driving force for these changes have been to improve patient safety and user convenience. Hence, knowledge of the basic design of the anaesthesia machine is a must for all the practicing anaesthesiologists to understand the modern anaesthesia workstation.
After anaesthesia was invented and introduced with the public demonstration of ether anaesthesia by WTG Morton in , for many years an anaesthesia machine was not required for providing anaesthesia to the patients until oxygen O 2 and nitrous oxide N 2 O were introduced as compressed gases in cylinders by the late 19 th century.
Boyle's machine was invented by Henry Edmund Gaskin Boyle in His machine was a modification of the American Gwathmey apparatus of and became the best known early continuous flow anaesthetic machine.
It was named so to respect the inventor, Boyle. However, Boyle was not the pioneer in manufacturing anaesthesia machines. Two other great men had done excellent work before him.
Boyle, who developed his machine from Gwathmey's basic model in , presented his invention at the Royal Society of Medicine in London in Even though Marshal had developed his machine much before Boyle, he presented his machine before the medical community in , much later than Boyle.
All the credit had gone to Boyle, although Gwathmey and Marshal had developed their machines before him. Minimises anaesthesia related risks to patients and staff. The basic design of an anaesthesia machine consists of pressurised gases supplied by cylinders or pipelines to the anaesthetic machine, which controls the flow of gases before passing them through a vapouriser and delivering the resulting mixture to the patient through the breathing circuit [ Figure 1 ].
Basic continuous flow anaesthesia machine with carbon dioxide absorber and closed circuit. The early Boyle's machine had five elements, which are still present in modern machines: 1 A high pressure supply of gases, 2 pressure gauges on O 2 cylinders, with pressure reducing valves, 3 flow meters 4 metal and glass vapouriser bottle for ether and 5 a breathing system.
The anaesthesia machine is a continuous flow machine in which all the components are mounted on a table. Box shaped sections of welded steel or aluminium provide a rigid metal framework mounted on wheels with antistatic tyres Castors and brakes.
Antistatic measures improve flow meter performance and where flammable vapours are used, reduce the risk of ignition. There is also provision for connecting the pipeline gas source of O 2 and N 2 O from the wall outlet with quick couplers and yoke blocks at the machine end instead of one of the cylinders at the yoke assembly. A pressure gauge is mounted on to the yoke assembly to read the pressure in the cylinder.
Pressure regulators are located downstream of the yoke assembly, which reduce the high pressure in the cylinders to a low and constant pressure of PSIG. The back bar supports the flow meter assembly and the vapourisers.
At the end of the back bar, there is the common gas outlet to which the breathing circuits are connected to provide the anaesthetic vapour containing O 2 enriched gases to the patient. The anaesthesia machine can be conveniently divided into three parts: a The high pressure system, which receives gases at cylinder pressure, reduces the pressure and makes it more constant, b the intermediate pressure system, which receives gases from the regulator or hospital pipeline and delivers them to the flow meters or O 2 flush valve and c the low pressure system, which takes gases from the flow meters to the machine outlet and also contains the vapourisers.
The high pressure system consists of all parts of the machine, which receive gas at cylinder pressure. These include the following: a The hanger yoke which connects a cylinder to the machine, b the yoke block, used to connect cylinders larger than size E or pipeline hoses to the machine through the yoke, c the cylinder pressure gauge, which indicates the gas pressure in the cylinder and d the pressure regulator, which converts a high variable gas pressure into a lower, more constant pressure, suitable for use in the machine.
The hanger yoke orients the cylinder, provides gas tight seal and ensures a unidirectional gas flow [ Figure 2 ]. The workstation standard requirement is that there should be at least one yoke for O 2 and N 2 O. If the machine is likely to be used in locations that do not have piped gases, it is advisable to have a double yoke, especially for O 2.
The hanger yoke consists of: 1 The body, which is the principle framework and supporting structure, 2 the retaining screw, which tightens the cylinder in the yoke, 3 the nipple, through which gas enters the machine, 4 the index pins, which prevent attaching an incorrect cylinder, 5 the Bodok seal, the washer which helps to form a seal between the cylinder and the yoke, 6 a filter, to remove particulate matter and 7 the check valve assembly which ensures a unidirectional flow of gas through the yoke [ Figure 2 ].
Machines are usually equipped with one or two E type cylinders that hang on specific hanger yokes. The medical gas pin-index safety system ensures that the correct medical gas cylinder is hung in the correct yoke. The system consists of two pins that are fixed in the yoke, and which fit into two corresponding holes in the cylinder valve.
The two pins are in a unique configuration for each gas and should never be removed from the hanger yoke. Specific pin configurations exist for each of the medical gases supplied in small cylinders in order to prevent erroneous misconnections of gas supplies. A cylinder should never be force-fitted to a hanger yoke.
Substitution of an E type N 2 O cylinder for O 2 can occur if pins in the index face are missing or broken or if several washers are used simultaneously. This fault is deceptive because the PISS is thought fool proof. This defect can only be detected by direct inspection of the yoke and cylinder gas identity markings each time a cylinder is replaced on the machine.
The check valve assembly prevents transfilling of empty cylinders. Since there is always a chance of check valves not functioning properly, yoke should not be left vacant and a yoke plug which is a solid metal piece with a conical depression on one side and a hollow area on the other side for retention screw and nipple of the yoke respectively should be fitted.
Yoke plugs are usually kept chained to the machine [ Figure 2 ]. Cylinder pressure is usually measured by a Bourdon's pressure gauge, which is a flexible tube which straightens when exposed to gas pressure causing a gear mechanism to move a needle pointer.
The idea being if there is a sudden increase in the pressure and the tube ruptures, then high pressured gases are vented from the back preventing injury to the patient and the anaesthesiologist. In Boyle mark-3, pressure gauges were introduced for N 2 O also so that once the indicator starts showing pressure less than PSIG, the anaesthesiologist will come to know that all the liquid N 2 O has evaporated and what remains is only N 2 O gas.
Internal assembly of basic anaesthesia machine when viewed from above with covering plate removed. It is a piece of metal, shaped like a cylinder valve that is pin indexed and has a port and a conical depression to fit into a yoke. These are the devices which reduce the high pressures in the cylinders to a lower and more constant pressure to maintain a constant flow [ Figure 3 ]. The reasons for their presence are:. If there are no pressure regulators, then there will be a necessity for the anaesthesiologist to keep re-adjusting the flow control valves to maintain a constant flow as the cylinder pressure decreases with use, decreasing the flow.
With lowered pressure supplied to the flow meters fine adjustments of the flow is possible. When force is kept constant with a spring and area inside the regulator is increased using a diaphragm, then automatically pressure of the gas decreases.
By keeping the force exerted by the spring high, changes in the cylinder pressure due to use will not affect the reduced output pressure. With early anaesthesia machines Boyle-F , if an O 2 cylinder becomes exhausted or the pipeline source failed, in the face of significant N 2 O flow, the patient would receive a lower fraction of O 2 or even a hypoxic gas mixture.
Especially before the advent of pulse oximetry, hypoxaemia and patient injury could occur unless the machine fault is immediately recognised by the anaesthesiologist. When this was introduced as a safety mechanism, it was thought that hypoxic mixture could not be delivered to the patient as O 2 in the pipeline supply or cylinder supply gets depleted, N 2 O output from the N 2 O regulator also would stop and anaesthesiologist will be alarmed as the reservoir bag collapses.
This was not a fool proof system as still hypoxic mixtures could be delivered if the O 2 is cut off at the flow meters. Hence proportionating devices had to be introduced at the flow meter assembly in modern machines. It includes the components of the machine which receive gases at reduced pressures usually PSIG.
There is a direct tubing connecting the O 2 pressure regulator to the O 2 flush. Its main use is during the mask ventilation with a lot of leak between the mask and the patient's face especially in elderly patients and in patients with difficult airways and also acceptable power source for jet ventilation for providing partial, if not total, ventilatory support in most clinical situations.
Inappropriate use of the O 2 flush valve has been associated with both barotrauma and intraoperative awareness. When the flush is activated, the flow meters may not show its activation but as it makes sufficient noise, the same can not be overlooked.
The flow meter assembly controls, measures and indicates the rate of flow of gas passing through it [ Figure 4 ]. The flow control valve controls the rate of flow of a gas through its associated flow meter by manual adjustment of variable orifice.
Flow control valve is also called as needle valve or pin valve. The valve mainly consists of the control knob, stem and seat. The control knob is colour coded and touch coded for each gas. The control knob is large, cylindrical in shape with wide flutes and coloured white for O 2 and is small, conical in shape with narrow flutes and coloured blue for N 2 O. The machine standard requires a distance of 25 mm between the knobs. The flow control knobs are connected to the stem which has a pin at its distal end.
When the valve is closed, the pin fits into a seat of metal and no gas flows. When the stem is turned counter-clockwise, then an opening is created between the pin and the seat and gas starts flowing into the flow meter. There are stops for the closed position and maximum opening position which prevent damage to the fine needle valve or disengage the stem from the valve body respectively.
This consists of the tube through which the gas flows, the indicator or bobbin or float, a stop at the top of the tube and the scale which indicates the flow. When there are separate flow meter tubes for low flows and high flows for the same gas then the tubes are single tapered. If there is a single tube for the gas then it is double tapered. The lower portion of the dual tapered flow tube has a fine taper for measuring low flows and the upper portion has a coarse taper for reading high flows rates.
Indicator also called as rota meter or bobbin or float is present within the flow meter tube which moves up and rotates as the gas flows into the tube. The bobbin is made of aluminium and has an upper rim which is wider than the body. The upper rim contains slanted flutes, which makes the bobbin rotate as the gas strikes the flutes. There is a fluorescent dot over the bobbin making its rotation to be observed easily. The flow tubes and floats are assembled and calibrated together for each specific gas.
Therefore if the flow tube breaks, the entire flow meter assembly including the float should be replaced. The effects of static electricity may be reduced by spraying the outside of the tube with an antistatic agent such as croxtine BOC , which is supplied in an aerosol can. The flow meter scale can be marked directly on the flow tube or to the right of the tube.
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The National Institute for Occupational Safety and Health NIOSH requests assistance in controlling exposures of workers to nitrous oxide N2O during the administration of anesthetic gas in medical, dental, and veterinary operatories. A recent study of workers [Rowland et al. This Alert presents control measures for preventing or greatly reducing exposure to N2O during the administration of anesthetic gas. These control measures should be part of a comprehensive written safety and health plan for workers.
Jerry A. Dedication This book is dedicated to the anesthesia educators who value the dissemination of equipment -related knowledge. Preface There have been many exciting changes in anesthesia equipment since the fourth edition was published. Once again we have updated equipment covered in previous editions. New chapters on latex allergy, suction equipment, double -lumen tubes, emergency airway devices, operating room fires, temperature control and the MRI environment have been added.
You must protect the Key and the natural order. You must give assistance if I call upon you. How long had I been standing here.
Сьюзан знала, что где-то на дне этого погруженного в туман подземелья есть рубильник. Кроме того, она понимала, что времени почти не оставалось. Стратмор сидел наверху с береттой в руке. Он перечитал свою записку и положил на пол возле. То, что он собирался сделать, несомненно, было проявлением малодушия.
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After WTG Morton's first public demonstration in of use of ether as an anaesthetic agent, for many years anaesthesiologists did not require a machine to deliver anaesthesia to the patients.