I&M: The Anesthesia Machine Flashcards Preview

MSA S2015 > I&M: The Anesthesia Machine > Flashcards

Flashcards in I&M: The Anesthesia Machine Deck (19):

Four basic functions of the anesthesia machine

1. Control composition of inspired gas
2. Control/monitor minute ventilation and ventilatory patterns (MV = VT x RR; typical MV = 5L/min, VT = 500ml)
3. Monitor physiological function
4. Prevent OR contamination from anesthetic waste gases


Wall supply

Primary source of gases for most hospitals.

Diameter Index Safety System (DISS) is a coupling mechanism that ensures the correct tubing is connected to the correct outlet.

Tubing is also color coded:
- White = suctioning
- Purple = Scavenging
- Blue = Nitrous (N2O)
- Green = Oxygen
- Yellow = Air


Gas cylinders

Alternate gas source on the back of the anesthesia machine in case wall supply/pipeline fails. Size E cylinders are the most commonly used and are also colored coded.

Each cylinder has two holes in its valve that correspond to pins on the yoke of the anesthesia machine in the Pin Index Safety System (PISS). Using washers between the yoke and the cylinder can bypass this system.


E Cylinders

Cylinder color - green
Form - gas
Capacity (L) - 660
Pressure (psi) - 1800-2200 (2000)


E Cylinders

Cylinder color - yellow
Form - gas
Capacity (L) - 660
Pressure (psi) - 1800-2200 (2000)


E Cylinders

Cylinder color - blue
Form - liquid
Capacity (L) - 1600
Pressure (psi) - 745
When liquid is all gone, about 400L of nitrous remains.


E Cylinders

Cylinder color - Gray
Form - liquid
Capacity (L) - 1600
Pressure (psi) - 838


E Cylinders

Cylinder color - Black
Form - gas
Capacity (L) - 650
Pressure (psi) - 1800-2200 (2000)


E Cylinders

Cylinder color - brown
Form - gas
Capacity (L) - 500
Pressure (psi) - 1600-2000 (1800)


What's the difference between liquified gas and non-liquified gas?

- When cylinder contains non-liquified gas, cylinder pressure declines proportionally as gas is withdrawn from the cylinder.
- When cylinder contains liquified gas, pressure in cylinder depends on the vapor pressure of liquified gas remaining in the cylinder. Only when all of the liquid is gone does pressure start to fall.


Fail safe valve

Valve shuts off or proportionally decrease flow of all gases when pressure in oxygen delivery line decreases to below 30psi. This helps prevent hypoxic delivery.



Tells machine L/min of gas to deliver to patient. Flat you read from top; circular, from center.

Oxygen is always green, on the right, larger, protrudes further, and fluted. Ohmedia and Drager machines have mechanisms that prevent delivery of N2O without oxygen (chain and pressure control piston respectively).


APL valve

Adjustable pressure limiting valve AKA pop-off valve limits the amount of pressure that reaches the patient. The excess gas will go into the scavenging system.

During manual ventilation, keep closed to about 10-20cmH2O. Anything between 35-70cmH2O could cause barotrauma. During spontaneous breathing make sure the APL valve is open.

During machine ventilation, APL valve has no effect.


Breathing circuit - Semiclosed circle system

Gas enters through the common gas outlet of anesthetic machine and passes inspiratory limb unidirectional valve through inspiratory breathing tube and Y-piece eventually reaching patient. The expired gas then passes through Y-piece again, through the expiratory breathing tube, pass the expiratory limb unidirectional valve, and in/ out of reservoir bag. Excess gas is vented out through the pop-off/APL valve to the scavenging system, while the rest goes through CO2 absorbent canister and eventually back towards the patient.

1. Inspiratory limb
2. Expiratory limb
3. Unidirectional valves
4. Reservoir bag
5. CO2 absorbant
6. O2 analyzer
7. Pop-off valve on expiratory limb/ APL valve


Advantages & disadvantages of circle system

1. Conserves moisture and heat
2. Uses low flows of fresh gas (conservation)
3. Ability to scavenge waste gas

1. Complex design
2. Has 10 connections each with the potential for disconnection


CO2 absorbant

Eliminates CO2 from circle system using soda lime or Baralyme. About 23L of CO2 can be absorbed per 100g of soda lime. pH sensitive dye is added such that when absorbent is exhausted, turns purple.


Two types of bellows

Standing/ascending bellows - bellows rise during expiration
- considered safer because collapses when disconnection occurs
- adds 3cmH2O PEEP

Hanging/descending bellows - bellows descend during expiration.
- continues to fill by gravity in even of disconnect


O2 flush valve

Delivers 35-75L/min O2 to patient circuit and bypasses flowmeters and vaporizers. DON'T use during inspiratory phase of PPV.


Pneumatic System

High pressure system
- Gas cylinders, hanger yoke assembly, pressure gauges
- Pressure regulators drop pressure to ~45psi

Intermediate pressure system
- Pipeline (45-55psi), pressure gauges, fail-safe, O2 supply low pressure alarm, O2 flush valve,
- Second stage pressure regulator (N2O 26psi, O2 14psi)

Low pressure system
- Flowmeters
- Vaporizers
- Fresh gas outlet