Anesthesia Machines

rev Jan 11 dmcmahon

First actual use of ether - March 1842,by Dr Crawford Long in Georgia.

First public use of ether - Oct 1846, by Dr Morton

Diethyl ether -- first inhaled anesthetic

Chloroform used for Queen Victoriain childbirth, 1847.

Anesthesia can be –> Local, often Local with Monitoring (“LMAC”)

> Regional

- spinal

- epidural

- nerve block specific

> General, which includes: - lack of awareness

- lack of sensation

- amnesia

- uneventful post-op recovery

- Usually obtained by inhaled agent thru a tracheal tube,

or can be by a drug infused IV (eg propofol)

Inhaled Anesthetic Agents –

> Many are ethers (general formula R – O – R’)

> First was diethyl ether

> First vaporizer-delivered agent was halothane (1960’s)

> Followed by several others (1970’s – 1990’s)

> Vast majority of general anesthetics now given with

- isoflurane (“Forane”, Zeneca Labs)

- sevoflurane (“Ultane”, Abbott Labs & Baxter)

Propofol - first injectable non-opioid general anesthetic

GE / Datex / Ohmeda:

Aisys

Aespire 100

North American Drager:

Fabius GS

Apollo

Drager:

Fabius MRI

The bare essentials of anesthesia delivery:

> Oxygen-carrying gas mixture

- could be room air

> Anesthetic agent vapor

- metered-out very precisely

> Ability to create positive airway pressure

- necessary for respiratory exchange

Three machine hazards and their solutions:

1: Oxygen supply failure, leaving anoxic gas supply

- the “Fail-Safe Valve” or Oxygen Failure Protection Device (OFPD)

Shuts off all gas flows if the oxygen fails

2: Hypoxic or anoxic mixtures from the flowmeters

- the “Hypoxic Guard” or Oxygen Ratio Monitor-Controller (ORMC)

Assures that at least 25% oxygen is delivered

3: More than one agent vaporizer turned-on

- vaporizer lock-out mechanism; Allows only one vaporizer to be enabled

Pressure Regulator

Basic manometer (pressure meter)

Bourdon tube

Gas Supply Check Valve

Gas Pressure-Actuated Power Switch

Flowmeter Needle Valve

Flowmeter Tubes in Series

Digital flowmeters - Drager Fabius GS

Typical screen - Drager Fabius GS

O2 failure shutoff valve (“FailSafe Valve”)

Oxygen ratio controller

Basic Anesthetic Vaporizer

Basic Anesthetic Vaporizer

Delivering the volatile anesthetic –

Modern Vaporizer, Closed

Modern Vaporizer, Open

Vaporizer Lock-Out Mechanism(Drager Co.)

Vaporizer Lock-Out Mechanism(Drager Co.)

Essential Monitors of the Anesthesia Machine:

> Delivered oxygen percentage

> Airway pressure

> Airway gas flow

(These monitor the machine, not the patient)

CO2 Absorber Assembly - schematic

From machine

Patient’s lungs

CO2 absorbent:

> Chemically removes CO2 from the patient’s respiratory gases.

> Consists of NaOH, KOH, and Ca(OH)2, which react with CO2 to form carbonates and water in two separate reactions.

> Includes a dye which changes to purple when the CO2-absorbing capacity is exhausted.

> Major brands:

SodaSorb©, Baralyme©, Amsorb©

CO2 Absorber Assembly - Drager Co

CO2 Absorber Assembly w/ VentilatorDrager Co.

Aneroid Manometer for Airway Pressure

Adjustable Pressure Limiting (APL) Valve

Manual Ventilation:

Manual Ventilation:

Mechanical Ventilation:

Mechanical Ventilation:

Scavenging of

Waste Anesthesia Gas (WAG) :

> Required by NIOSH / OSHA

> NIOSH allows < 25 ppm of N2O (8-hour average)

> Gases must be actively drawn out of the local air

> Scavenging is integrated into the anesthesia machine

> Testing should be done at least annually

> Can be done with dosimeters from a commercial lab,

or with an IR detector made for air testing.

Scavenging Relief Valve

Virtual Anesthesia Machine: http://vam.anest.ufl.edu

> Univ of Florida, Dept of Anesthesiology

> From the Home Page, click on the Simulation & Workbook tab

> Requires one-time free registration (Annual fee for educators’ version)

March 2009: APSF Newsletter

Most common troubleshooting issues:

> Leaks in the absorber circuit and/or patient circuit

> Inadequate volume delivered from ventilator

> Water accumulated in ventilator tubing

> Flow meter inaccuracy or failure

Be pro-active:Get the owner’s book out and know the troubleshooting tables.

Know how to do a pre-op machine checkout.

Get factory service training

> North American Drager

> GE-Datex-Ohmeda

Minor Players:

Major Players in Anesthesia Machines:

> Spacelabs (Blease from the UK)> DRE, Oceanic (compact types)

Samurai

Origami

Fuji-Maximus

K Takaoka anesthesia machines –