Introduction to Anesthesia Machines: Components, Systems, and Monitoring

What are the main components of a modern anesthesia machine?

Vaporizers, a ventilator, breathing and scavenging systems, and monitors.

Name two major suppliers of anesthesia machines.

GE Datex-Ohmeda and North American Drager.

What is the role of an anesthesia provider according to ASA guidelines?

Maintenance of adequate perfusion, pain/anxiety/fear relief, maintenance of internal homeostasis, and help facilitate the surgeon's task.

What types of monitoring are essential in anesthesia?

Oxygenation, Ventilation, Circulation, and Temperature

What are the types of anesthesia?

General Anesthesia, Regional Anesthesia, Monitored Anesthesia Care (MAC), and Local with Anesthesia Standby. There is also conscious sedation ( by nursing)

What is an amnestic agent?

An agent that results in loss of memory of an event or time period.

What is the difference between an analgesic and an anxiolytic?

An analgesic relieves pain without loss of consciousness, while an anxiolytic relieves apprehension and fear.

What is a Hypnotic?

An agent that produces drowsiness and acts to induce sleep or a sleep-like state

What are the two systems of the anesthesia machine?

Electrical and Pneumatic.

What is the function of the master switch in an anesthesia machine?

It activates pneumatic and electrical functions.

True or false? All machines allow supplemental/auxiliary oxygen as well as O2 flush even if they are off.

True

What are the three parts of the pneumatic system in an anesthesia machine?

High Pressure, Intermediate Pressure, and Low Pressure.

What does psig stand for and how is it different from psi?

psig stands for pounds per square inch gauge, measuring pressure relative to atmospheric pressure; psi measures absolute pressure.

What is the pressure in the high pressure system?

>50 psig

What is the pressure in the intermediate pressure system?

50-14 psig

What is the pressure in the low pressure system?

less than 14 psig to ambient

Name the parts of the high pressure system

Cylinders, hanger yoke assembly, check valves, pressure regulators, and pressure gauges

What is the purpose of the O2 Failure Safety Device in anesthesia machines?

It turns off all other gases in the absence of oxygen.

What are the pressures and volumes of the E-cylinders?

What is the function of the pin index safety system (PISS)?

It prevents the incorrect connection of gas cylinders to the anesthesia machine.

What should be done with an E-cylinder when not in use?

It should remain closed.

What is the significance of the gauge reading on a nitrous oxide cylinder?

The gauge does not decrease until the liquid content is exhausted, indicating that only gas is left.

What is the maximum pressure for the intermediate pressure system in an anesthesia machine?

50-55 psig.

What is the role of a ventilator in an anesthesia machine?

To assist or control the patient's breathing during anesthesia.

What is the purpose of the breathing and scavenging systems in an anesthesia machine?

To manage the delivery of anesthetic gases and remove waste gases from the operating room.

What is the function of check valves in an anesthetic machine?

They direct the flow of gas towards the machine (unidirectional) and allow for cylinder replacement without leaking gas.

What happens if a check valve is faulty?

It can lead to trans filling and there is no alarm if using a cylinder versus a pipeline.

What do pressure regulators do in an anesthetic machine?

They decrease and regulate pressure from cylinders. The pressure at the regulator is greater than pipeline pressure to ensure the use of the pipeline when a cylinder is open

What is the purpose of the Diameter Index Safety System (DISS)?

It provides non-interchangeable gas-specific connections to pipeline inlets to prevent incorrect pipeline attachments.

What is the role of the oxygen flush valve?

It delivers a high, unmetered flow of oxygen (35-75 L/min) directly to the common gas outlet, bypassing vaporizers. It works when the machine is on or off. Can cause barotrauma or awareness.

What does the low-pressure system in an anesthetic machine consist of?

It includes flowmeters, vaporizers, common fresh gas outlet, and adjustable pressure limiting valve (APL valve).

What is the function of the Adjustable Pressure Limiting (APL) valve?

It adjusts the amount of gas in the breathing bag when the patient is manually ventilated or spontaneously breathing.

Protects machine from high pressures

Open to atmosphere, vents gas when pre-set pressure is reached

What is the purpose of the CO2 absorber in anesthetic machines and describe the key components of the reaction?

It removes CO2 from the gas that the patient has exhaled, commonly using soda lime. The reaction is rate limited by availability of KOH and NaOH. Limited by availability of Ca(OH)2. The reaction produces heat

What are the main components of a scavenging system and what is its function?

To remove expired gases and volatile anesthetics from the breathing circuit so they are not released into the operating room

(1) the gas-collecting assembly

(2) the transfer means

(3) the scavenging interface

(4) the gas-disposal assembly tubing

(5) an active or passive gas-disposal assembly

What is the significance of the Link 25 Proportioning Limiting Control System?

It prevents the delivery of a hypoxic mixture by ensuring a minimum O2 concentration at the common gas outlet.

N2O and O2 are interfaced mechanically or pneumatically

Minimum O2 concentration at the common gas outlet is between 23% and 25%

What does the flow control knob do in an anesthetic machine?

It adjusts the flow of gases (O2, N2O, air) and is designed to ensure O2 is always the last flowmeter.

What is the function of the oxygen failure protection device (OFPD) and O2 pressure sensor shutoff valve? How do they differ? (same purpose, different manufacturer)

They are fail safe valves. They respond proportionally to changes in oxygen supply pressure to prevent hypoxic mixtures from being delivered to the patient.

O2 Pressure sensor shut off valve: The valve closes at the threshold value of 20 psig because of inadequate oxygen pressure

OFPD: responds proportionally to changes in oxygen supply pressure

What is the purpose of the second stage pressure regulator?

It reduces pressure further to 14 psig for O2 and 26 psig for N2O, although it is optional and not present on all machines.

What is the role of the inspiratory/expiratory unidirectional valves?

They keep the flow in the breathing circuit moving in one direction. They connect at the inspiratory/expiratory limbs

What is the function of the auxiliary common gas outlet?

It serves as an alternate source of gas for the patient, although it is not commonly used.

What is the purpose of the pressure gauge in an anesthetic machine?

It measures the pressure generated by either the breathing bag or the ventilator.

What are the main types of flowmeters used in anesthetic machines?

They can be mechanical or electronic and control the amount of flow of gases (in mL/min or L/min).

What is the function of the breathing system bellows assembly?

It is used for mechanical ventilation and is part of the ventilator system.

What is the composition of soda lime used in CO2 absorbers?

It consists of 80% calcium hydroxide, 15% water, 4% sodium hydroxide, and 1% potassium hydroxide.

What is the risk associated with increased absorbent dryness in CO2 absorbers?

It can lead to increased carbon monoxide production.

What does the bag/ventilator toggle switch do?

It allows the user to switch ventilation from the breathing bag to the ventilator and vice versa.

What is the purpose of the oxygen sensor in an anesthetic machine?

It measures the percentage of oxygen being delivered to the patient, typically located in the inspiratory limb.

What is the purpose of the suction regulator in an anesthetic machine?

It controls the suction pressure used to remove unwanted gases from the breathing circuit.

What is the chemical formula of oxygen, US tank color, full pressure, and state in the cylinder?

O2, Green, 1900-2200, Gas

What is the chemical formula of nitrogen, US tank color, full pressure, and state in the cylinder?

N2, black, 1900-2200, gas

What is the chemical formula of carbon dioxide, US tank color, full pressure, and state in the cylinder?

CO2, gray, 835, liquid+gas

What is the US tank color for air, full pressure, and state in the cylinder?

Yellow, 1900-2200, gas

What is the chemical formula of nitrous oxide, US tank color, full pressure, and state in the cylinder?

N2O, blue, 745, liquid+gas

What is the chemical formula of helium, US tank color, full pressure, and state in the cylinder?

He, Brown, 1600-2000, gas

What is the chemical formula of heliox, US tank color, full pressure, and state in the cylinder?

He + O2, Brown/Green, 1600-2000, gas

Describe the unique pressure of the N2O cylinder

•Amount present when gauge reads 745 psig is based on weight (not accurately known in clinical practice)

•gauge does not decrease until liquid content is exhausted, at which time 400 liters remain ~ 25%

Name the parts of the intermediate system

Master switch, gas supply (pipeline and regulated cylinder), pipeline inlet (O2, N2O, air), pressure gauges (50-55 psig), O2 failure safety device, second stage pressure regulator, O2 flush valve, O2 low pressure alarm, flow control knobs, and alternative O2 control

When does the O2 supply low pressure alarm go off and which system is it in?

O2

Name the components of the breathing system

•Bellows Assembly (ventilator)

•CO2 Absorber

•Rebreathing Bag

•Adjustable Pressure Limiting (APL )Valve - "pop-off valve"

•Bag/Ventilator Toggle Switch

•Auxiliary Common Gas Outlet

•O2 Sensor

•Inspiratory/Expiratory Unidirectional Valves

•Inspiratory/Expiratory Limb

•Pressure Gauge - manometer

Which volatile anesthetic produces the most carbon monoxide with dry absorbents?

Desflurane > Isoflurane > Sevoflurane (Des is the worst offender).

What factors increase CO production in anesthesia machines?

Dry absorbents (Baralyme > Soda lime)

Higher absorbent temperature

Higher anesthetic concentration

Lower fresh gas flows

Smaller patient size (↑ COHb risk)

What are the clinical effects of CO exposure during anesthesia?

Formation of carboxyhemoglobin (COHb) → hypoxia

COHb can reach 35% in worst-case OR conditions

For comparison: a 2 pack/day smoker has 5-7% COHb baseline

What is the auxiliary (courtesy) flowmeter?

For supplemental O2 - using nasal cannula, simple face mask. Used a lot in MAC.

Will work with machine off

Describe the difference between a ball and tapered float.

Read the L/min at the midline of the ball and the top of the float for tapered.

What do vaporizers do?

Take liquid anesthetic agents (Sevoflurane, Desflurane, Isoflurane), turn them into gas, and add them to Fresh Gas Flow to the patient