1. Inhaled Anesthetic Delivery Systems
Golparvar M. MD

3. Introduction:
the anesthesia delivery system has evolved from a simple pneumatic device to a complex multisystem workstation
For anesthesia care providers understanding of its operation is essential.
Caplan and coworkers found that although claims related to the medical gas delivery system were rare, when they did occur, they were usually severe and death or permanent brain injury frequently resulted.

4. In this Lecture: we examine the anesthesia workstation piece by piece.
We will describe the normal operation, function, and integration of major anesthesia workstation subsystems.
we illustrate potential problems and hazards associated with the various components of the anesthesia delivery system
We overview appropriate preoperative checks that may help detect and prevent such problems.

5. Standards and Pre-use Procedures

6. Anesthesia Workstation Standards and Pre-use Procedures
Standards for Anesthesia Machines and Workstations
1979: American National Standards Institute (ANSI) Z [2]
1988: American Society for Testing and Materials (ASTM) F [3]
1994: ASTM F [4] (reapproved in 1994 and discontinued in 2000)
2000: ASTM F [5]

7. 2000 ASTM F standards:
Newly manufactured workstations must have monitors that measure the following parameters: continuous breathing system pressure, exhaled tidal volume, ventilatory carbon dioxide concentration, anesthetic vapor concentration, FiO2, oxygen supply pressure, SpO2, BP, and EKG.
The anesthesia workstation must have a prioritized alarm system that groups the alarms into three categories: high, medium, and low priority

8. Checking Your Anesthesia Workstation
A complete anesthesia apparatus checkout procedure must be performed each day before the anesthesia workstation is first used.
An abbreviated version should be performed before each subsequent case.
The user must always refer to the original equipment manufacturer's operator's manual for special procedures or precautions related to particular workstations.

9. Responsibility:
Every anesthesia care provider must be aware that the ultimate responsibility for proper machine pre-use safety checks rests on the provider using the machine to deliver anesthetic care.

10. Testing Specific Components of the Anesthesia Delivery System
The three most important preoperative checks are:
(1) calibration of the oxygen analyzer
(2) the low-pressure circuit leak test
(3) the circle system tests

11. Calibration of the Oxygen Analyzer
It is the only machine safety device that evaluates the integrity of the low-pressure circuit in an ongoing fashion
The only machine monitor that detects problems downstream from the flow control valves is the oxygen analyzer
sensing element must be exposed to room air for calibration to 21%

12. Low-Pressure Circuit Leak Test
checks the integrity of the anesthesia machine from the flow control valves to the common gas outlet
Leaks in the low-pressure circuit can cause hypoxia and/or patient awareness
Loose filler caps on vaporizers are a common source of leaks
Several different methods have been used:
the oxygen flush test,
the common gas outlet occlusion test,
the traditional positive-pressure leak test,
the North American Dräger positive-pressure leak test,
the Ohmeda 8000 internal positive-pressure leak test,
the Ohmeda negative-pressure leak test,
the 1993 FDA universal negative-pressure leak test,
and others.

13. Oxygen Flush Positive-Pressure Leak Test
Inappropriate use of the oxygen flush valve to check the low-pressure circuit

14. 1993 FDA Negative-Pressure Leak Test
Left, A negative-pressure leak-testing device is attached directly to the machine outlet. Squeezing the bulb creates a vacuum in the low-pressure circuit and opens the check valve.
Right, When a leak is present in the low-pressure circuit, room air is entrained through the leak and the suction bulb inflates

15. 1993 FDA Negative-Pressure Leak Test
if the bulb re inflates in less than 10 seconds, a leak is present somewhere in the low-pressure circuit.
The “universal” negative-pressure leak test is the most sensitive of all contemporary leak tests because it is not dependent on volume
It can detect leaks as small as 30 mL/min

16. Circle System Tests
The leak test is performed by closing the pop-off valve, occluding the Y-piece, and pressurizing the circuit to 30 cm H2O with the oxygen flush valve. The value on the pressure gauge will not decline if the circle system is leak free
The flow test checks the integrity of the unidirectional valves: The operator should be able to inhale but not exhale through the inspiratory limb and able to exhale but not inhale through the expiratory limb.

17. Workstation Self-Tests
self-diagnostic tests varies from one model and manufacturer to another
to detect internal vaporizer leaks on this type of system, the “leak test” portion of the self-diagnostic must be repeated separately with each individual vaporizer turned to the “on” position

18. Anatomy of an Anesthesia Workstation
Diagram of a generic two-gas anesthesia machine

19. Supply Sources

20. Pipeline Supply Source
The pipeline supply: primary gas source
must supply: correct gases at appropriate pressure
In a survey: 31% reported difficulties with pipeline systems (The most common problem was inadequate oxygen pressure)
The most devastating reported hazard: accidental crossing of oxygen and nitrous oxide pipelines, (which has led to many deaths)

21. In the event that a pipeline crossover is ever suspected immediately:
First, turned on the backup oxygen cylinder
Second, disconnect pipeline supply
The pipeline inlet fittings are gas-specific Diameter Index Safety System (DISS)

22. Diameter Index Safety System (DISS)

24. Cylinder Supply Source

25. Cylinder Supply Source
Medical gases attached to the anesthesia machine via the hanger yoke assembly.
Each hanger yoke is equipped with the Pin Index Safety System (PISS).
The PISS is a safeguard introduced to eliminate cylinder interchanging

26. Pin Index Safety System (PISS)
Pin-Indexed Yoke Assemblies
and
Cylinder Valve Connections

28. A check valve is located downstream from each cylinder and serves several functions.
First, it minimizes transfer of gas from a cylinder at high pressure to one with lower pressure.
Second, it allows an empty cylinder to be exchanged for a full one while gas flow continues from the other cylinder into the machine
Third, it minimizes leakage from an open cylinder to the atmosphere if one cylinder is absent.
Each cylinder supply source has a pressure-reducing valve known as the cylinder pressure regulator
The oxygen cylinder pressure regulator reduces the oxygen cylinder pressure from a high of 2200 psig to approximately 45 psig.
The nitrous oxide cylinder pressure regulator receives pressure of up to 745 psig and reduces it to approximately 45 psig.

29. psig and bar

30. The gas supply cylinder valves should be turned off when not in use, except during the preoperative machine checkout period.
the volume of gas remaining in the cylinder is proportional to cylinder pressure.
use of a pneumatically driven mechanical ventilator will dramatically increase oxygen utilization rates,
Hand ventilation at low fresh gas flow rates may consume less than 5% of the amount of oxygen consumed by intermediate flow meter settings coupled with the use of pneumatically powered mechanical ventilation
Nitrous oxide cylinder ??

31. Oxygen Supply Pressure Failure Safety Devices
abrupt or insidious oxygen pressure failure had the potential to lead to the delivery of a hypoxic mixture.
The 2000 ASTM F standard states that “The anesthesia gas supply device shall be designed so that whenever oxygen supply pressure is reduced to below the manufacturer specified minimum, the delivered oxygen concentration shall not decrease below 19% at the common gas outlet.”

32. Fail-safe valve
A fail-safe valve is present in the gas line supplying each of the flow meters except oxygen. Controlled by oxygen supply pressure
the valve shuts off or proportionally decreases the supply pressure of all other gases as the oxygen supply pressure decreases.

33. Pressure sensor shut-off valve
An oxygen failure protection device that responds proportionally

34. Pneumatic and Electronic Alarm Devices (oxygen supply failure alarm)
Many older anesthesia machines have a pneumatic alarm device that sounds a warning when the oxygen supply pressure decreases to a predetermined threshold value, such as 30 psig
Electronic alarm devices are now used to meet this guideline.

35. Second-Stage Oxygen Pressure Regulator
Most contemporary Datex-Ohmeda workstations have a second-stage oxygen pressure regulator set at a specific value ranging from 12 to 19 psig

37. precisely controls and measures gas flow to the common gas outlet:
Flow Meter Assemblies
precisely controls and measures gas flow to the common gas outlet:
Traditional glass flow meter
Electronic flow sensors
numerical
graphic
combination