Anaesthesia.pptx

About high pressure system, intermediate pressure system and low pressure system

1. The Anaesthesia Machine Moderated by Dr. Mahadevaiah Presented by Dr. Vijay khodifad

2. INTRODUCTION The anesthesia machine is a complex piece of equipment consisting of many com- ponents . It is usually part of the anesthesia workstation which also includes devices such as vaporizers, a ventilator, breathing and scavenging systems, and monitors. There are two general systems comprising the anesthesia machine: the electrical sys-tem and the pneumatic system.

3. CLINICAL MOMENT When being introduced to a new machine, especially one of the electronically controlled models, the user manual must be studied carefully.

4. HISTORY In 1917, Boyle developed his anesthetic machine from Gwathmey’s basic model and presented it in London, at the Royal Society of Medicine, in 1918. The original design was composed of a wooden structure in the form of a box, which acted as a frame, with two transverse bars from which hung the cylinders of compressed gas (two of oxygen and two of nitrous oxide), an ether vaporizer and a water flow meter (the bubble bottle from the Cotton & Boothby apparatus).

5. In addition, the machine had a manometer to measure the pressure in the cylinders, sensitive pressure-reducing valves and an alcohol lamp (to prevent the nitrous oxide from freezing and thus obstructing the cylinder). Boyle’s anaesthesia device, originally manufactured by Coxeter & Sons, and subsequently acquired by the British Oxygen Company, is considered the standard design for the physical composition of anesthesia stations today, although it has undergone numerous modifications since its first appearance.

6. Boyle ‘s Machine. Left: First model, wvith wooden frame
1917 Right: 1958 model, with metal structure. Gas cylinders and
pressure regulators are fixed to the frame of the table. In the upper
part is the block of rotamers and vaporisers. Reproduced from Watt
OM. The evolution of the Boyle apparatus, 1917-67.

7. contemporary of the first version of Boyle’s apparatus was the anesthetic machine proposed by the English barge. commander Geoffrey Marshall, who in 1917 presented the Coxeter company with his own design for a sequential machine (inspired by Gwathmey’s device) supplying nitrous oxide, oxygen and ether.

8. The Coxeter company decided to manufacture the machine, and it became the standard anesthesia device of the Royal Army Medical Corps during the
final stages of the First World War. However, Marshall did not publish his invention, and Boyle, who had attended the presentation of Marshall’s machine, made some slight modifications, and presented it as his own device.49

9. The early Boyle’s machine had five elements which are still present in all modern machines.

( i ) A high-pressure supply of gases. It housed two oxygen and two nitrous oxide cylinders in a wooden box.

(ii) Pressure gauges on oxygen cylinders and fine-adjustment reducing valves. These produce a manageable breathing system pressure. It had a spirit flame to warm these and prevent obstruction of gas flow from ice.

10. (iii) Flowmeters to control gas flow rate and adjust proportions of gas delivered.

(iv) A metal and glass vaporizer bottle for ether.

(v) A breathing system comprising a Cattlin bag, three-way stopcock and facemask.

Modifications (e.g. Dry bobbin flowmeters
in 1933, pin-index system in 1952) were driven by a consideration for greater safety.

11. The modern anaesthetic machine Anaesthetic machines have six basic subsystems:

( i ) gas supplies: pipelines and cylinders; (ii) gas flow measurement and control(flowmeters): (iii) vaporizers;
(iv) Gas delivery: breathing system and ventilator; (v) scavenging; (vi) monitoring.

12. Types of anesthesia machine Intermittent -Gas flows only during inspiration Egs: Entonox apparatus ,Mackessons apparatus Continuous -Gas flows both during inspiration and expiration. Egs : Boyle Machine Forregar Dragger

13. Anesthesia work station Integrates most of the components necessary for administration of anesthesia into single unit. Standard guidelines have been given to manufacturers for minimum performance, design, characteristics and safety requirements of machine. The current standard for anesthesia workstation as( promulgated by American society for testing and materials) (ASTM ) is F1850 . European standard is EN740

14. Components of anesthesia machine

15. Pressure units to remember 1 atm pressure = 1 bar = 760 mm Hg = 14.7 psi = 100 kilopascals

16. Components of pressure systems

17. Limitations of check valve assembly The check valves are not designed to act as permanent seals for empty yokes. Small amounts of gases can escape if the yoke is empty or an empty cylinder (or cylinder with low pressure) and valve open is present in the yoke.

18. In order to minimize such losses – Yokes should not be left vacant for extended periods An empty cylinder should be replaced as soon as possible , if not then, An yoke plug can be used to prevent gas leak or An empty cylinder can be left behind after closing the valve

19. Yoke Block(Dummy Cylinder plug) Yoke block is a solid piece of metal that has a conical depression on one side to fit into the retaining screw and a hollow area on the other side to fit over the nipple. They are pin indexed. Uses Prevents gas leak from the machine when placed in an empty yoke. Connect cylinders larger than size E to the machine. Connect pipeline supply to the machine that does not have pipeline inlet connections.

20. Limitations of yoke block Can be responsible for crossover of gases in the machine. Pressure regulators in the machine are designed to accept gases at cylinder pressure may not function properly when supplied with gases at reduced pressure(pipeline supply through yoke block)

21. Limitations of pin index safety system A wrong cylinder can be placed in yoke if- 2 washers are placed on the port. Pins on the yoke are broken. Holes on the cylinder valve are too deep.

22. Pin index safety system

23. Bourdon pressure gauge

24. Safety features in cylinder pressure indicator Gauge is usually color coded. Name and symbol of gas are written over dial. If bourdon tube ruptures gas is vented from back side Gauges are angled and placed in such a way that it can be easily read by anesthetist. Instructions like “use no oil’’ “open the valve slowly’’ are written on the gauge.

25. Electronic cylinder pressure indicator Light emitting diodes(LED’S)in electronic pressure gauge indicate Cylinder valve is close –Dark color Cylinder valve is open – Pressure adequate –Green Pressure inadequate-Red

26. Types of pressure regulators Adam’s pressure regulator valve- Used in past Working principle is same differs in internal structure from newer valves(toggle levers instead of push rod) Fins on Adam’s regulator for N2O which are not present in newer regulators. Mackesson’s regulator Medishield valve Endurance valve Modern preset type of reducing valve-Direct and Indirect .

27. Safety features on pressure regulator Pressure regulators have safety relief valves If due to any reason there is build up of pressure in pressure regulator then the safety valve blow off at a set pressure of 525 k pa(70psi)

28. Oxygen failure safety valve Pressure sensor shut off valve Based on threshold principle Cuts off N2O supply when O2 pressure falls below 25 psi. M O A-O 2 p r e ssurises and holds open shut off valve that interrupts the supply of N2O and other gases if O2 pressure<threshold setting. oxygen failure protection device Based on proportioning principle Gas loaded regulator When O2 pressure decreases there is a proportional decrease in N2O supply and complete cut off seen at<12psi. MOA-O2 pressure regulator(primary regulator) controls secondary(slave) regulator located in N2O line

29. Master switch Turning the master switch to the ‘on’ position activates both pneumatic and electrical functions of the machine as well as certain alarms and safety devices.

30. Electronic flow meter Prefer digital system Solenoid valves Control flow on or off valves Computer controlled .

31. Link-25 .

32. Oxygen ratio monitor controller Sensitive oxygen ratio controller Linear resistors [3:1 ratio for N2O & O2)between O2 andN2O flow control valves. Ensure 25% O2 by limiting N2O flow. ORMC shuts off N2O if ratio of O2 flow falls below 30% S-ORC-newest hypoxic guard . installed in Fabius- GS by Drager.ensures aFiO2 of 23%. O2 flow <200ml/min . .

33. Limitations of proportioning system Anti hypoxic device may also deliver hypoxic mixture under following conditions- Wrong supply of gas. Defective pneumatics/mechanics. Inert gas administration(3 rd gas-He,N2,CO2). Leaks downstream.