Anaesthesia machine

1. DR TULSI RAM SHRESTHA, KMCTH

2. CONTENTS
▪ History
▪ Introduction
▪ Essential safety features
▪ Pneumatic system
▪ High pressure system
▪ Intermediate pressure system
▪ Low pressure system
▪ Anaesthesia machine checkup

3. HISTORY
▪ 1846: Public demonstration of ether
anaesthesia, WTG Morton
▪ 1917: Boyle’s machine, Henry Edmund
Gaskin Boyle
▪ 1921: Waters to and fro absorption
apparatus
▪ 1927: Flowmeter for CO2

4. ▪ 1930: Plunger of vaporizer; circle
absorption system, Brian Sword
▪ 1933: Dry bobbin flow meters
▪ 1952: PISS by Woodbridge

5. THE ANAESTHESIA MACHINE
▪ Receives medical gases from a gas supply
▪ Controls the flow and reduces the pressure
of gases to a safe level
▪ Vaporizes volatile anesthetics into final gas
mixture
▪ Delivers gases to a breathing circuit
connected to the patient’s airway

6. 1. Gas-specific connections to pipeline inlets (DISS)
with pressure gauges, filter, and check valve
2. PISS for cylinders with pressure gauges, and at
least one oxygen cylinder
3. Low oxygen pressure alarm
4. Minimum O2:N2O ratio controller device
5. Oxygen failure safety device
ESSENTIAL SAFETY FEATURES

7. 6. O2 enters common manifold downstream to other
gases
7. O2 concentration monitor and alarm
8. Automatically enabled essential alarms and
monitors (eg, oxygen concentration)
9. Vaporizer interlock device
10.Capnography and anesthetic gas measurement
11.O2 flush mechanism

8. 12.Breathing circuit pressure monitor and alarm
13.Exhaled volume monitor
14.Pulse oximetry, BP, ECG monitoring
15.Mechanical ventilator
16.Backup battery
17.Scavenger system

9. PNEUMATIC SYSTEM

10. HIGH PRESSURE SYSTEM
▪ Receives gases from high pressure E
cylinders
▪ 2000 psig for O2 and air, 745 psig for N2O
▪ Handy in case of failure of hospital pipeline
supply source

11. Hanger Yoke
▪ Orients and supports the cylinder
▪ Provides gas tight seal
▪ Ensures unidirectional gas flow
▪ Parts
▪ Body
▪ Retaining screw
▪ PISS pins
▪ Washer
▪ Filter

12. Pressure regulator
▪ Reduces high/ variable pressure from
cylinder
▪ To lower/ constant pressure for use in
anesthesia machine (40-45psig)
▪ Pressure at regulator outlet: set lower than
pipeline pressure

13. Check valve
▪ Allows gas from cylinder to enter machine
▪ Minimizes transfer of gas from a cylinder at high
pressure to one with lower pressure
▪ Helps exchange of empty cylinder with a full one
▪ Minimizes leakage from an open cylinder to the
atmosphere if one cylinder is absent

14. INTERMEDIATE PRESSURE SYSTEM
▪ Receives gases from pressure regulator or
pipeline inlet
▪ Pressure of 40-55 psig

15. Pipeline inlet connections
▪ For air, O2, N2O
▪ Fitted with threaded non interchangeable
DISS connectors
▪ Contains filter, unidirectional check valve

16. Pipeline pressure gauges
▪ To monitor pipeline pressure
▪ Color coded
▪ 50-55 psig

17. Pneumatic safety systems
O2 failure protection device
▪ When O2 pressure is normal->push the
diaphragm and stem downward
→opening valve
▪ When O2 pressure falls→Fail-safe valves
shut off or proportionally decrease the
flow of the other breathing gases
▪ If a gas other than O2 adequately
pressurizes the O2 circuit as a result of
hospital pipeline contamination, fail-safe
valves will remain open. In such a case,
only the inspired oxygen concentration
monitor will help

18. O2 supply failure alarm
▪ Sensor with an audible and visual warning if
O2 pressure drops below a minimum
▪ Cannot be silenced until the pressure is
restored to the minimum value
▪ Dräger Fabius series machines are set to
alarm at 20 psig

19. Oxygen flush valve
▪ Provides manual delivery of a high flow rate of
100% O2
▪ High (35 to 75 L/m) flow directly to CGO
▪ Flow bypasses the anesthetic vaporizers
▪ Available even when machine is not turned on
▪ Pressure: 50 psig

20. Auxiliary O2 flowmeter
▪ Administer O2 in case of electric failure
▪ Allows the use of low-flow oxygen for devices
independent of the patient’s breathing circuit
▪ Accessible even when the machine is not
turned on

21. Second stage pressure regulator
▪ Located downstream from the gas supply
sources
▪ Constant pressure to the flow control valves
regardless of potential fluctuations in hospital
pipeline pressures
▪ Lower levels than the pipeline supply, usually
between 14 and 35 psig

22. LOW PRESSURE SYSTEM
▪ Begins at flow control valves and ends at
machine outlet
▪ Flow control valves, flowmeters or flow
sensors, vaporizer manifold, and anesthetic
vaporizers
▪ Most vulnerable section to leaks within the gas
supply system

23. Flow adjustment control
▪ Regulates flow of gases to flowmeter
▪ Clockwise: decrease gas flow
▪ Anticlock wise: increase gas flow
▪ Inlet pressure is determined by pressure
characteristics of intermediate-pressure segment
▪ Flow control knob
▪ Different texture, diameter, color coded, name of gas
engraved
▪ O2: fluted, larger

24. Flowmeter
▪ Variable orifice vertical glass tube with
indicator (Thorpe’s tube)
▪ Upward force resulting from gas flow equals
the downward force on the float resulting
from gravity at a given flow rate
▪ Height of indicator: measure of gas flow
▪ Widest diameter : flow to be read

26. ▪ Flow rate depend on
▪ Pressure drop across the constriction
▪ Size of annular opening
▪ Physical properties of gas
▪ Calibrated at atmospheric
pressure, room temperature

27. Flow indicator sequence
▪ Where O2 and other gases are delivered
by their respective flow indicators into a
common manifold, the O2 should be
delivered downstream of all other gases.
▪ In the event of a flowmeter leak, a
potentially dangerous arrangement exists
when N2O located in downstream
position (A and B).
▪ A safer configuration exists when O2
located in downstream position (C & D).
▪ Hypoxic mixture less likely because all O2
flow is advanced by N2O (the principle
known as the Eger flow sequence)

28. Proportioning system
▪ No matter how high N2O is turned up, or how low
the O2 flow is made when N2O is running
▪ The machine will automatically limit the amount of
N2O flow→ hypoxemic gas will not be delivered
▪ Protects against delivery of a mixture with an oxygen
concentration below 21% oxygen (v/v%)

29. Outlet check valve
▪ One way check valve located between
vaporizer and CGO
▪ Prevent backflow into the vaporizer during
positive-pressure ventilation

30. Common Gas Outlet
▪ Receives gas mixture from machine and
delivers to breathing circuit
▪ Fresh gas outlet, critical role in adding new
gas of fixed and known composition to the
circle system

31. Oxygen (inspired) analyzers
▪ Polarographic (Clark electrode)
▪ Galvanic (fuel cell)
▪ Paramagnetic

32. Waste gas scavengers
▪ Dispose gases that have been vented from
breathing circuit by APL valve
▪ Safe level
▪ Room concentration of N2O:25ppm
▪ Halogenated agents:2ppm

34. Anesthesia machine checkout

35. High pressure system
▪ Check O2 cylinder supply
▪ Open cylinder, verify at least half full (1000 psig)
▪ Close cylinder
▪ Check central pipeline supplies
▪ Check hoses are connected
▪ Pipeline gauge: 50psig

36. Low pressure system
▪ Close flow control valves, turn off vaporizers
▪ Check fill level, tighten filler caps
▪ Perform leak check
▪ Test flowmeters

37. Breathing system
▪ Calibrate O2 monitor
▪ Check initial status breathing system
▪ Leak check
▪ Set all gas flows to zero
▪ Close APL valve , occlude Y piece
▪ Pressurize to about 30cm of H2O
▪ Ensure pressure remains fixed (at least 10 second)
▪ Open APL valve: pressure decrease

38. ▪Miller's Anaesthesia, 8th edn
▪Morgan and Mikhail’s
Clinical Anesthesiology, 5th
edn
References