THE ANESTHESIA MACHINE

Department of Anesthesia Medical University of SC

KNOW YOUR MACHINE

Why it’s important What it does All its parts All its safety features How to check it

Equipment Misuse

Equipment misuse > Equipment failure ◦ Lack of familiarity ◦ Not checking machine ◦ Only 2% ASA closed claims database ◦ Breathing circuit #1 (39%) Disconnects or misconnects

What does it do?

Gas Supply

Machine Controls flow

Reduces pressure

Vaporizes Agents

Mixes final gas

mixture Delivers to circuit

Circuit attached to patient and

the ventilator

(removable)

Central Gas Supply

Pipeline Inlets

Safety features ◦ Color designation Green = ? Yellow = ? Blue = ?

◦ Diameter-Index Safety System Non-interchangeable Prevents incorrect hose attachment at machine

◦ Filter Traps debris

◦ One-way check valve Prevents retrograde flow

E Cylinders

E Cylinders

Attach via Hanger-yoke assemblies ◦ Pin Index Safety System Only O2 cylinder will connect to O2

◦ Washer ◦ Gas filter ◦ Check valve

High-Pressure ◦ Backup for pipeline failure

Handle ◦ Should not be left on at all times ◦ Always check tank volume each morning O2 full = 1800-2200 psi = 625-700L N2O full = 745 psi = 1590 L (have to weigh) Air full = 1800-2200 psi = 625-700L

Flow Control Circuits

Pressure Regulator ◦ Reduces E-cylinder pressure to 45-47 psig ◦ Less than pipeline, so pipeline used preferentially

High Pressure Relief Valve Datex-Ohmeda ◦ Second regulator to drop pipeline and cylinder pressure further O2 20psig N20 38psig

Most machines 45-55 psig

O2 Failure Detection Devices

O2 directly to flow control valve N2O and Air (except Aestiva) ◦ Safety devices first ◦ Allows other gases to flow only if certain pressure of O2 available ◦ Decreases risk of hypoxic mixture

O2 ◦ Pressurizes safety devices ◦ O2 flush valves ◦ Ventilator power

O2 Failure Detection Devices

Datex-Ohmeda ◦ Balance regulator Reduces gases (not air) in proportionate to O2 reduction Shuts off gases below preset O2 pressure ◦ N2O when O2 0.5psig ◦ Other gases when O2 10psig

O2 supply low pressure alarm ◦ Alarm when O2 inlet pressure less than 20-35 psig ◦ Can still get hypoxic mixtures

Flow Valves and Meters

High Pressure System ◦ Proximal to flow valves

Low pressure System ◦ Between flow valves to CGO

Flow valves ◦ Barrier to gas entering vaporizer ◦ Controlled by flowmeters

Flow control valve Knobs

• Turn Counterclockwise • Knobs color-coded • O2 safety features

• farthest to the right • fluted • sticks out the farthest

Flowmeters

Contstant Pressure Variable Orifice ◦ Old Datex (main hospital) ◦ Ball, bobbin or float ◦ Supported by flow of gas ◦ Tube tapered Widens at the top Requires higher flows to keep bobbin afloat

◦ Calibrated for specific gases Depends on viscosity at low flows Depends on density at high flows

◦ Flowmeter malfunction Dirt Vertical tube misalignment Sticking of float at the top

◦ Hypoxic mixture If leak within or downstream from O2 flowmeter

Electronic Flowmeters

• Backup O2 flowmeter • Each gas has a separate flow measurement device before being mixed

Minimum O2 flow

Minimum flow typically 150ml/min ◦ Can be as low as 50ml/min

Some designed to delver < 1L/min

Nitrous –Oxygen link

N20 flow linked to 02 ◦ Ensures minimum 02 of 2l or 25% ◦ Ration controller Mechanically Pneumatically Electronically (our machines)

Isoflurane and Sevoflurane Vaporizers

Vaporizers

All gases must be vaporized Dial in amount added to gas flow from

flowmeters Located between flowmeters and CGO Interlocking exclusion device ◦ One agent at a time

Variable Flow Vaporizer

Concentration dial

Pressure compensator

Wick

Vaporizing Chamber Anesthetic Agent

Concentrating Cone

Temperature Compensating bypass

Outlet port

On/off switch

Variable Bypass Flow Vaporizer

Vaporizers

Agent Specific Most have agent specific keyed filling ports Can overdose if fill with an agent with higher vapor pressure ◦ i.e. isoflurane in sevoflurane

Tilting ◦ Floods the bypass area = high concentration of anesthetic

Ambient pressure ◦ Vaporizers compensate for altitude changes

Desflurane Vaporizer

Desflurane Vaporizer

Vapor pressure so high = boils at room temperature Problems with delivery ◦ Nml vaporizer can’t deal with cooling from vaporization ◦ Needs high flows to dilute

Tec 6 ◦ Reservoir heated to 39 deg C ◦ No fresh gas flows through reservoir ◦ Vapor released depending on what you dial in and

fresh gas flow Tec 6 plus ◦ Partial pressure of desflurane decreases at

increased altitude = have to increase conc delivered

Desflurane Vaporizer

Common Fresh Gas Outlet

CGO ◦ Only way to get gas to the patient ◦ Adds new gas to circle system

O2 flush valve ◦ High flow ◦ 35-55L/min ◦ Directly to CGO (no gas) ◦ Pressure of 45-55 psig

Breathing Circuit

Circle System ◦ VA conc effected by Lung uptake MV Total FGF Circuit volume Gas leaks

◦ High flows diminishes discrepancies

Extra Components

Oxygen Analyzers ◦ Polarographic, galvanic and paramagnetic ◦ In insp or exp limb Exp lower from oxygen consumption

Spirometers ◦ Measure exhaled TV

Circuit Pressure ◦ Measure between insp and exp limb ◦ Most accurate from Y limb

Extra Components

APL valve ◦ “pop-off” valve ◦ Fully open for spont vent ◦ Partially closed for manual ventilation ◦ Can cause barotrauma if closed too much ◦ Never completely closed

Humidifiers

Intubation prevents normal mechanism of gas humidification ◦ Dehydration of mucosa ◦ Altered ciliary function ◦ Atelectasis ◦ v/q mismatch ◦ Causes loss of heat ◦ Not significant for short cases

Humidifiers

•Passive Humidifiers •Heat and Moisture Exchangers •Added to circuit •Trap heat and moisture from exhaled gas •Increase circuit resistance •Increase dead space

•More of an issue in peds •Active Humidifiers

•Add water to gas via a water chamber or wick •Potential for thermal injuries •We don’t use these

Ventilators

Ventilators

Basic Concepts ◦ Flow generated by pressure gradient between prox airway and alveoli = Positive Pressure Ventilation

Trigger

Trigger = what initiates inspiration Flow trigger (patient) Pressure trigger (patient) Time trigger (Machine)

REGARDLESS of trigger ◦ Machine generates flow along a pressure gradient to reach a predetermined Volume pressure

Cycle

Cycle = what switches from inspiration to expiration ◦ Flow cycle (pressure support) ◦ Time cycle (pressure control) ◦ Volume cycle (volume control)

Insp:Exp Ratio ◦ Determines how long inspiration and expiration are ◦ Usually 1:2 ◦ If RR is 10, each breath = 6s Inspiration 2s and expiration 4s

Exhalation

Exhalation is always passive Airway pressure reduced to Atm pressure or PEEP Effected by ◦ Airway resistance ◦ Lung compliance

PEEP ◦ Positive End Expiratory Pressure Helps prevent de-recruitment ◦ Obese patients ◦ Gravid patients ◦ Pulmonary pts

Breathing

Breathing = Who is doing the Work? ◦ Machine ◦ Patient Pressure Support SIMV

Datex-Ohmeda Carestation

Older Datex Ohmeda Carestation

Ventilator Circuit Design

Double-Circuit System ◦ TV delivered by bellow

Ascending Bellow ◦ Easier to detect leak or circuit disconnect ◦ Pressurized by O2 (45-50psig) ◦ May have higher inspired O2 if leak in bellow

Free breathing valve ◦ Bellows go down with spont ventilation

Piston Ventilator ◦ More accurate with small TV and low lung compliance

APL ◦ Closed during inspiration

Volume and Pressure Monitoring

Peak Inspiratory Pressure ◦ Highest circuit pressure during inspiration ◦ Indication of dynamic compliance

Plateau Pressure ◦ Measured during inspiratory pause (no flow) ◦ Indication of static compliance

Airway Pressures

• PIP and Ppl normally close in value • Increase in both PIP and Ppl

• dec compliance •Edema •Obesity •Packing •insufflation

• increase TV • Increase in PIP only

• increase airway resistance •Bronchospasm •Kinked tube •secretions

• increase in airway flow

Ventilator Alarms

Machine Must Have Alarms!!!!!!!! Disconnect Alarms (at least 3) ◦ Low PIP ◦ Low exhaled TV ◦ Low ETCO2

High PIP High PEEP High sustained airway pressure Negative pressure Low O2 supply pressure

Problems with Anesthesia Ventilators

Fresh Gas Coupling FGF = 6l/min or (100ml/s) I:E = 1:2 and RR = 10 (I=2s and E=4s) Extra TV of 200ml with each breath Increases PIP Increases MV

Positive Pressure ◦ Can cause barotrauma ◦ Avoid O2 flush during inspiration ◦ Many machines have built in APL valves

Problems with Anesthesia Ventilators

Tidal Volume Discrepancies ◦ FGF coupling ◦ Circuit compliance 5ml/cmH2O (if PIP 20 then 100ml lost)

◦ Gas Compression in bellows 3% loss normally

◦ Sampling lines CO2 and volatile agents

◦ Must measure at Y connector to get accurate data ◦ New Machines compensate

Scavenging Systems

Waste gas = Health Hazard NIOSH limits ◦ N20=25ppm ◦ VA= 2ppm (0.5ppm w/ N20)

Gas vented through APL valve and spill valve ◦ Both valves connected to scavenging interface ◦ Open Interface – open to outside w/o pressure relief

valves ◦ Closed Interface – requires neg and pos pressure relief

valves to protect the patient Passive vs Active ◦ Vacuum system is active ◦ Vacuum is full = waste reservoir ◦ Vacuum control 10-15l/min Adequate for high flow and low flow

Waste Scavenging

Machine Checkout

The more you check it the better you’ll understand it i.e. you will remember it for boards