1. Anesthetic Equipment

2. The commonest type of anesthetic machine in use is the continuous-flow anesthetic 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 vapor (such as isoflurane), and deliver this to the patient at a safe pressure and flow Modern machines incorporate a ventilator, suction unit, and patient-monitoring devices

3. ventilator
Flow meter
bellow
vaporizer
Corrugated tube
APL valve
Scavenging system
Soda lime

4. The Anesthesia Machine
High
Intermediate
Low Pressure Circuit
Mention how the machine is divided into high, intermediate, and low pressure systems

5. High Pressure System
Receives gasses from the high pressure E cylinders attached to the back of the anesthesia machine (2200 psig for O2, 745 psig for N2O)
Consists of:
Hanger Yolk (reserve gas cylinder holder)
Check valve (prevent reverse flow of gas)
Cylinder Pressure Indicator (Gauge)
Pressure Reducing Device (Regulator)
Usually not used, unless pipeline gas supply is off

6. E Size Compressed Gas Cylinders
Cylinder Characteristics
Oxygen
Nitrous Oxide
Carbon Dioxide
Air
Color
White (green)
Blue
Gray
Black/White (yellow)
State
Gas
Liquid and gas
Contents (L)
625
1590
Empty Weight (kg)
590
Full Weight (kg)
676
880
890
Pressure Full (psig)
2000
750
838
1800

7. Hanger Yolk
Hanger Yolk: orients and supports the cylinder, providing a gas-tight seal and ensuring a unidirectional gas flow into the machine
Index pins: Pin Index Safety System (PISS) is gas specificprevents accidental rearrangement of cylinders (eg switching O2 and N2O)

8. Pipeline Inlet Connections
Mandatory N2O and O2, usually have air and suction too
Inlets are non-interchangeable due to specific threading as per the Diameter Index Safety System (DISS)
Each inlet must contain a check valve to prevent reverse flow (similar to the cylinder yolk)
At this point mention that in Sudbury Ontario in the 1970s 23 people died because the N20 and O2 pipelines were crossed over during repairs Ask them what they would do in this situation?
Backup oxygen cylinder turned on
Pipeline supply must be disconnected (necessary because the machine will preferentially use the pipeline supply as per the high pressure system regulator design)

9. Outlet of central oxygen supply system

10. Oxygen Supply Failure Alarm
The machine standard specifies that whenever the oxygen supply pressure falls below a manufacturer-specified threshold (usually 30 psig) a medium priority alarm shall blow within 5 seconds

11. Oxygen Flush Valve (O2+)
Receives O2 from pipeline inlet or cylinder reducing device and directs high, unmetered flow directly to the common gas outlet (downstream of the vaporizer)
Machine standard requires that the flow be between 35 and 75 L/min
The ability to provide jet ventilation
Hazards
May cause barotrauma
Dilution of inhaled anesthetic

12. Low Pressure System Consists of: Flow meters Vaporizer mounting device
Check valve
Common gas outlet

13. Flowmeter assembly
When the flow control valve is opened the gas enters at the bottom and flows up the tube elevating the indicator
The indicator floats freely at a point where the downward force on it (gravity) equals the upward force caused by gas molecules hitting the bottom of the float

14. Vaporizers
A vaporizer is an instrument designed to change a liquid anesthetic agent into its vapor and add a controlled amount of this vapor to the fresh gas flow

15. Classification of Vaporizers
Methods of regulating output concentration
Concentration calibrated (eg variable bypass)
Measured flow
Method of vaporization
Flow-over
Bubble through
Injection
Temperature compensation
Thermocompensation
Supplied heat

16. Generic Bypass Vaporizer
Flow from the flowmeters enters the inlet of the vaporizer
The function of the concentration control valve is to regulate the amount of flow through the bypass and vaporizing chambers
Splitting Ratio = flow though vaporizing chamber/flow through bypass chamber
The concentration control dial may be located in the bypass chamber of the outlet of the vaporizing chamber
Mention that the machine standard requires that all vaporizers on the anesthesia workstation be concentration calibrated (aka variable bypass, direct reading, dial-controlled, automatic plenium, percentage-type, tec-type vaporizers, and vaporizer chamber bypass arrangements

17. Factors That Influence Vaporizer Output
Flow Rate: The output of the vaporizer is generally less than the dial setting at very low (< 200 ml/min) or very high (> 15 L/min) flows
Temperature: Automatic temperature compensating mechanisms in bypass chambers maintain a constant vaporizer output with varying temperatures
Back Pressure: Intermittent back pressure (eg positive pressure ventilation causes a higher vaporizer output than the dial setting)
C’ = concentration at the new atmospheric pressure
C = the concentration at the old atmospheric pressure (ie the concentration dialed into the vaporizer)
P’ = the barometric pressure for which c’ is being established
P = the barometric pressure for which the vaporizer is calibrated (ie at the old atmospheric pressure)

18. Factors That Influence Vaporizer Output
Atmospheric Pressure: Changes in atmospheric pressure affect variable bypass vaporizer output as measured by volume % concentration, but not (or very little) as measured by partial pressure (lowering atmospheric pressure increases volume % concentration and vice versa)
Carrier Gas: Vaporizers are calibrated for 100% oxygen Carrier gases other than this result in decreased vaporizer output

19. The Circuit: Circle System
Arrangement is variable, but to prevent re-breathing of CO2, the following rules must be followed:
Unidirectional valves between the patient and the reservoir bag
Fresh-gas-flow cannot enter the circuit between the expiratory valve and the patient
Adjustable pressure-limiting valve (APL) cannot be located between the patient and the inspiratory valve

20. The carbon dioxide absorber
Sodalime (CaOH2 + NaOH + KOH + silica) or Baralyme (Ba[OH] 2 + Ca[OH]2) contained in the absorber combines with carbon dioxide, forming CaCO2 and liberating heat and moisture (H2O)
A pH-sensitive dye changes to a blue-violet color, indicating exhaustion of the absorbing capacity
The canister should be changed when 25% to 50% of the contents has changed color, although it should continue to absorb satisfactorily until at least the contents of the top canister have changed color

21. Circle System Advantages: Disadvantages:
Relative stability of inspired concentration
Conservation of respiratory moisture and heat
Prevention of operating room pollution
PaCO2 depends only on ventilation, not fresh gas flow
Low fresh gas flows can be used
Disadvantages:
Complex design = potential for malfunction
High resistance (multiple one-way valves) = higher work of breathing
The final three points of the advantages section are meant to contrast with the Bain circuit

22. The reservoir bag The reservoir bag is located on the expiratory limb
The reservoir bag accumulates gas between inspirations
It is used to visualize spontaneous ventilation and to assist ventilation manually
Adults require a 3-L bag
Children a 2-L bag
Most new machines have a valve used to switch between the reservoir bag and the ventilator
Older machines may require that the bag be removed and a hose to the ventilator be connected
The final three points of the advantages section are meant to contrast with the Bain circuit

23. The Adjustable Pressure Limiting (APL) Valve
User adjustable valve that releases gases to the scavenging system and is intended to provide control of the pressure in the breathing system
Bag-mask Ventilation: Valve is usually left partially open During inspiration the bag is squeezed pushing gas into the inspiratory limb until the pressure relief is reached, opening the APL valve
Mechanical Ventilation: The APL valve is excluded from the circuit when the selector switch is changed from manual to automatic ventilation

24. Scavenging Systems
A scavenging system channels waste gases away from the operating room to a location outside the hospital building
The ambient concentration of anesthetic gases in the operating room should not exceed 25 ppm for nitrous oxide and 2 ppm for halogenated agents
Specific anesthetic gas-scavenging systems should be used routinely These systems consist of a collecting system, a transfer system, a receiving system, and a disposal system

25. Scavenging Systems
The disposal system may be passive or active, although passive systems are inadequate for modern hospitals
A passive system consists of wide-bore tubing that carries gases directly to the exterior or into the exhaust ventilation ducts
Active systems can be powered by vacuum systems, fans, pumps, or Venturi systems

26. Scavenging Systems
The disposal system may be passive or active, although passive systems are inadequate for modern hospitals
A passive system consists of wide-bore tubing that carries gases directly to the exterior or into the exhaust ventilation ducts
Active systems can be powered by vacuum systems, fans, pumps, or Venturi systems
Mention that the ventilator relief valve is the same thing as the overflow valve mentioned in the previous slides

27. Gas Analysis
Several methods are used to monitor concentrations of oxygen, carbon dioxide, and anesthetic gases in the breathing system.
The oxygen analyzer is the single most important monitor for detection of a hypoxic gas mixture.
Capnometry, the measurement of carbon dioxide, has many uses, including monitoring the adequacy of ventilation and detection of breathing system faults.
Breath-to-breath monitoring of anesthetic concentrations provides tracking of anesthetic uptake and distribution.
Most gas analyzers incorporate alarms. Among the techniques for measurement are the following: Mass spectrometry, infrared analysis and oxygen concentrations analysis

28. Anesthesia Ventilators
Most modern anesthesia machines are fitted with a mechanical ventilator that uses a collapsible bellows within a closed chamber.
The bellows is compressed intermittently when oxygen or air is directed into the chamber, thereby pressurizing it.
The ventilators are time cycled flow (as opposed to pressure) generators, controlled both mechanically and electronically, and pneumatically driven (requiring 10 to 20 L of driving gas per minute).
Ventilator controls vary among makes and models.
Some ventilators require setting of minute ventilation, rate, and inspiratory-expiratory (I:E) ratio to produce the desired tidal volume; other ventilators allow direct adjustment of tidal volume, with I : E ratio being dependent on the inspiratory flow rate, which is set independently.

29. Anesthesia Ventilators
Ventilator controls vary among makes and models.
Some ventilators require setting of minute ventilation, rate, and inspiratory-expiratory (I:E) ratio to produce the desired tidal volume; other ventilators allow direct adjustment of tidal volume, with I : E ratio being dependent on the inspiratory flow rate, which is set independently.
Although gas-driven ventilators can be safely driven with either oxygen or air, most often oxygen is chosen and is supplied by pipeline. Whether or not cylinder gases are used to drive the ventilator in the event of pipeline failure is usually determined by the user. If the machine is set up to drive the ventilator using cylinder oxygen, mechanical ventilation should be discontinued in the event of pipeline failure to conserve oxygen supplies.

30. Flow Generator Ventilators
Flow generators deliver a set tidal volume regardless of changes in patients' compliance ( unlike pressure generators ) but will not compensate for system leaks and may produce barotrauma because high pressures can be generated.
They reliably deliver the preset tidal volume (even in the presence of a small leak).
The risk o f barotrauma is minimal because most patients presenting to the operating room have healthy normally compliant lungs.

31. Pressure Generator Ventilators
For infants and patients with diseased lungs, the maintenance of preset tidal volumes may produce unacceptably high airway pressures and increased risk of barotrauma.
Pressure generators are more appropriate in these situations, because airway pressure is controlled and barotrauma risk minimized.

32. Checking Anesthesia Machines
Emergency ventilation equipment
High-Pressure system
Low-Pressure system
Scavenging system
Breathing system
Manual and automatic ventilation system
Monitors

33. Thank You