Anesthesia Delivery Systems What Do I Need to Know About My Machine?

A Workshop

James H. Philip, MEE, MD, CCE Anesthesiologist and Director Bioengineering

Department of Anesthesiology, Pain, and Peri-operative Medicine, Brigham and Women’s Hospital

Medical Liaison, Department of Biomedical Engineering Partners HealthCare System

Associate Professor of Anaesthesia Harvard Medical School

© Copyright 2000-2010, James H Philip, all rights reserved

Anesthesia Delivery Systems What Do I Need to Know About My Machine?

A Workshop

Answer: A great deal, and more than most of us know.

Anesthesia Delivery System (ADS)

Life Support with oxygen spontaneous breathing mechanical ventilation

Inhalant Drug Delivery Gas Vapor

N O2 O2Air

(Continuous Flow) Anesthesia Machine

Vaporizer

1 2 3..

5

21

34

6789

21

34

6789

55

21

34

6789

mL/mL/mL/mL/m

300

200100

400

50

600900

000

IsofluraneSevofluraneDesflurane FGF

(FreshGasFlow)

CommonOutlet

Anesthesia Machine

Anesthesia Machine

Schematic

Anesthesia Machine

Schematic

O2

2000psi

O2 SERVICE

INLET55psi

35 psi

35 psi

50 or 250ml/min

NEEDLEVALVE

FAILSAFEVALVE

CALIBRATEDVAPORIZERS

Fresh Gas Flow (FGF)

OXYGEN FLUSHVALVE[first]

ON/OFFSWITCH

CHECKVALVE PRESSURE

REGULATOR

N2 OSERVICE

INLET 55 psi

O2

N2 O

FRESHGAS HOSE

Flush Flow(last)

[Anesthetizinggases flow]

COMMON OUTLET

N2 O

750psi

N2 O

750psi

O2

2000psi

FILTER

WALL

DISSdiameter

indexsafetysystem

CONNEC-TION

O2

N2 O

D S I

SIMPLIFIED ANESTHESIA MACHINE SCHEMATIC DIAGRAM

Patient Breathing Circuit

Allows cyclic flowTo and from the patient

(AKA Breathing)

A Manual Resuscitator

is one of the few Open Circuit

ventilation systems you will ever use

Manual Resuscitator

Rebreathing Circuit

Circle absorption anesthetic breathing circuit

flipped

Normal flow in breathing circuit

Flow goes forwardIn the direction of the valvesEmptying and filling reservoir bagand lungsalternately

Sampled

Exhaust

CO2

Ab- sorb-ant

200 mL/min

Fresh

Normal flow in the breathing circuit - Inspiration

Sampled

Exhaust

CO2

Ab- sorb-ant

200 mL/min

Fresh

Normal flow in the breathing circuit - Expiration

1

2

The Circle-Absorber System

ExhaustExpired

CO2

Ab- sorb-ant

InspiredFresh

Gas Flows

VE

Gas is sampled from circuit near patient for I/E measures

Sampled

ExhaustExpired

CO2

Ab- sorb-ant

200 mL/min

InspiredFresh

Gas Flows

VE

Low FGF

More rebreathingInspired more dependent on ExpiredInspired less dependent on Vaporizer

View the Breathing Circuit The Circle-Absorber System

Partial Rebreathing Circuits are used in Anesthesia

Don’t throw away all the exhaled gasIt contains expensive anesthetic vapors Reuse as much as possible

somehow (learn more later) Remove (Absorb) CO2 and Rebreathe the anesthetic

Partial rebreathing = semi-closed circuitAll ADSs use them

Rebreathing Ventilation

Is not for dummiesRequires knowledge and skillMakes us different from other care providers

EMT, Sedation RN, ED MD, Hospitalist, Others

Common Outlet for FGF

Common Outlet is a virtual or real location where Fresh Gas Flow (FGF) leaves the Anesthesia Machine and enters the Breathing Circuit

Absent or hidden on new ADSsFGF reaches breathing circuit by a hidden pipe or hose

Common Outlet is a virtual or real location where Fresh Gas Flow (FGF) leaves the Anesthesia Machine and enters the Breathing Circuit

Absent or hidden on new ADSsFGF reaches breathing circuit by a hidden pipe or hose

Ventilation ModesVCV Volume-Controlled Ventilation

PCV - Pressure-Controlled Ventilation

Inspiratory Pause

Useful in VCVAllows you to compute Static ComplianceAllows you to see the effect of resistance

Inspiratory Pause

Useful in VCVAllows you to compute Static ComplianceAllows you to see the effect of resistance

Inspiratory Pause

Alarms

Alarms

Level Sound Text LEDWarning continuous !!!

Red blinkingCaution

q 30 sec

!!

Yellow blinkingAdvisory

once

!

Yellow continuous

Silence button silences for two minutes

Fabius Pressure Monitoring to detect disconnection

RulesIf peak pressure exceeds the pressure threshold every 15 seconds then the ventilator is not disconnected

If peak pressure does not cross pressure threshold for 15 seconds there is apnea based on failure to meet the pressure criterion - APNEA PRESSURE alarm sounds and flashes

If pressure threshold is more than 6 cmH2O below peak pressure, PRES THRESHOLD LOW advisory lights up

Press AUTO SET to set pressure threshold to 4 cmH2O below peak pressure. Alarm is now properly sensitive to apnea

PRESSURE THRESHOLD LOW alert

APNEA PRESSURE alarm

Fabius Sample Gas Return Port Can leak

Fabius Sample Gas Return Port Can leakFabius has a new Sample Gas Return Port

A new solution A new problem

New solution - very low and closed circuit fresh gas flow is OK Sampled airway gas (300 mL/min) is returned to circuit New, built-in connection in Absorber Assembly Self sealing so it is OK if not connected

New problem If sample gas return tubing is connected to circuit but is not connected to Gas Monitor Circuit gas leaks out the Sample Gas Return tubing > 350 mL / min Fails leak test

Fabius fails leak test

Here is the leak

1 Sample Gas Return Port is opened by connector

2 Tubing is disconnected

3 Later, connected here

Here is the leak

Later, connected here

Disconnect Sample Gas Return Connector from circuit to seal connector

No Leak

Sample Gas Return and Gas Sample can both connected during leak test

No loss or gain of volume from circuit. Sample gas to Monitor

Return gas from Monitor

Still get no Leak

Fabius Sample Gas Return Port Can leakSAM (Smart Anesthesia [Gas] Monitor) has Sample Gas Outlet

Formerly connected to ScavengerSample Gas Return connector on absorber self-seals

Leave connector and tubing disconnected during leak testConnecting Sample Gas Return Connector opens seal and leaks

Leave it disconnected during leak testOption 2Connect both Sample Gas and Sample Gas Return tubingsA Connect Sample Gas Return Tubing from SAM to AbsorberB Connect Gas Sample line to breathing circuit YNo gain and no loss of volume. Thus, no leak

Advanced Ventilation Modes

Modes available on 7900 Smart Vent for AISYS:

New Ventilation Mode

Pressure-cycled, Volume-controlledGE calls it Pressure Control Volume Guarantee

PCV - VGDraeger calls it Volume Ventilation with Auto-Flow

V V - Auto Flow

Pressure Ventilation but delivers the Tidal Volume you setUseful in Laparoscopy where compliance changes but, you want constant tidal volume and, you want constant-pressure breathsHigh-end machines only

No: GE Aestiva, Aespire Draeger Tiro, Fabius Yes: GE Avance, Aisys Draeger Apollo

Pressure Control Ventilation Volume Guarantee

Breathing Circuit FGF

Interaction or

Lack thereof

The Circle-Absorber System and Fresh Gas Flow

Sampled & measured I, E

ExhaustExpired

CO2

Ab- sorb-ant

200 mL/min

InspiredFresh Gas

Flow(FGF)

Ventilation Flow

Low FGF Saves money because of less wasteLimits our ability to control inspired concentration

Therefore limits control of expired conc. and brain conc.

1998

Better ventilation for difficult patients FGF-independent ventilation Corrects for circuit leaks Corrects for circuit compliance

< 2000, Standard Anesthesia Ventilators

Tidal Volume and FGF were interdependentIncrease FGF and Tidal Volume increased

by the amount of fresh gas that flowed during inspiration

Fresh Gas Flow Independent of Ventilation

1998 - WYSIWYG What You Set Is What You Get Set Tidal Volume - patient receives what you set

Two ways to achieve thisFresh Gas Compensation

Active, feedback control of inspired tidal volume GE

Fresh Gas Decoupling Passive separation of FGF during inspiration Draeger

GE-Datex- Ohmeda Aestiva

GE-Datex-Ohmeda Aestiva and all other models

Pneumatic (oxygen)-driven bellows

Inspiratory and Expiratory Flow Sensors

Feedback from flow sensors to bellows drive

Bellows stops pushing when Measured Inspired Tidal Volume = Set Inspired Tidal Volume

If you press the Flush button Bellows stops Next breaths are confused

GE has many alarms that stop ventilation

Aestiva VOSAll GE models have similar differential-pressure flow sensor

Variable-Orifice flow Sensor (VOS)

Pressure Transducer

P1 P2

Flow

FAccurate over a wide range of flowEach one is calibrated in GE factory

P

Variable orifice

Variable-Orifice flow Sensor (VOS)

Pressure Transducer

P1 P2

Flow

F

P

Variable orifice

This is what makes the SmartVent™ smart This is GE’s core technology

Accurate over a wide range of flowEach one is calibrated in GE factory

Variable-Orifice flow Sensor (VOS)

Pressure Transducer

P1 P2

Flow

F

P

Variable orifice

One drop of water will make this fail

Accurate over a wide range of flowEach one is calibrated in GE factory

Water Management is important Use an HME or HMEF

Heat and Moisture Exchangerbetween patient and circuit

HMEWet Dry

Draeger E-VentDraeger Fabius GS

Piston

Ventilator

Piston

Fresh Gas Flow Decoupling

During Inspiration Piston pushes gas into lungs Fresh Gas fills Reservoir Bag

During Expiration Lungs empty into Reservoir Bag fast Fresh Gas Flow fills Reservoir Bag slow and constant Piston draws gas from Reservoir Bag simultaneously

Flow sensor

Measured Tidal Volume

EXHALED tidal volumeUsually slightly smaller than SET tidal volumeRQ (Vdot CO2 / VdotO2 = 0.8)No alarm on error

Hot wire

Anemometer is cooled

by flow

Used to Display, not to controltidal volume.

Calibrate for heat conductivity.

Set Desflurane

Y/N

Fabius has a Water Trap

Empty the water trap in Fabius ventilator hose

Before using Fabius Observe and empty if full during case

Failure to do this will result in Alarms and Ventilator Failure

Beware of full Water Trap

First alarm is an incorrect one - Low Fresh Gas Flow

Fabius has misinterpreted what is wrongPiston trying to refill encounters a negative pressure equal to depth of water pool

Negative piston pressure usually means reservoir bag is empty and FGF is low

Low Fresh Gas Flow alarms sounds

Draeger Ventilation

Fresh Gas Flow DecouplingTiro, Fabius, Apollo

Mechanical VentilationPiston displacement is constant and provides constant Tidal VolumeFresh Gas fills the reservoir bag during inspiration (“decoupled”)Piston draws in Fresh and Exhaled gas during “refill” in expirationPiston is ready to give the next breath

Draeger Fresh Gas Flow Decoupling

Implications of “Decoupling”

Collateral damageReservoir bag is in the circuit during ventilationAdds a second sequential mixing chamberOld gas stays in-play even when FGF is highThis does not matter much during inductionThis matters a lot during emergenceIn emergence we desire Inspired agent concentration = 0Even with bag ventilation expired gas contaminates inspired

Example Fabius, End of case, VCV, FGF = 12 LPM

Inspired does not fall to zero

Draeger has difficulty clearing the last bit of agent

Malignant Hyperthermia PreparationTarget is FI Agent < 5 ppm Most ADSs require 10 minutesFabius and Apollo require 1 hour (Inspired Charcoal agent absorber can overcome this)

Gunter JB, Ball, J Than-Win S. Preparation of the Draeger Fabius Anesthesia Machine for the Malignant–Hyperthermia Susceptible Patient. Anesth Analg 2008;107:1936 –45

Draeger has difficulty clearing the last bit of agent

Malignant Hyperthermia PreparationTarget is FI Agent < 5 ppm Most ADSs require 10 minutesFabius and Apollo require 1 hour (Inspired Charcoal agent absorber can overcome this)

Gunter JB, Ball, J Than-Win S. Preparation of the Draeger Fabius Anesthesia Machine for the Malignant–Hyperthermia Susceptible Patient. Anesth Analg 2008;107:1936 –45

Fabius and Apollo are similar

Draeger has not solved it yet

GE breathing circuits are fasterInductionEmergence

Constant Volume FGF Decoupling

COSY-2.5

EI

I/ E select

Draeger Fabius and

Apollo CircuitInsp Valve

CircuitExp Valve

GE Circuit configuration superimposed on

Draeger Circuit

I/E

I/ E select

GE Circuit

Pneumatic bellows ventilator

Sevoflurane Induction

High FGF and vaporizer setting

Second Breath, Inspired = Vaporizer setting

Tight control of inspired is most important during emergence

02/27/07 BWH OR Boston6 hour Robot-assisted,Radical hysterectomy, w lymph node dissection

6 hour graphic trend

02/27/07 BWH OR Boston6 hour Robot-assisted,Radical hysterectomy, w lymph node dissection

Zoom in to 1 hour trend

23

Better to understand this with slow wave (3 min)

3 minutes3 minutes

None of this works without power Power switch is with power cord

on back of ADS

Fabius Aisys

ObservationsGE Circuit is fast Draeger Circuit is slow - use very high FGF for emergence

GE Ventilation Control depends on flow measurements and water makes it fail Draeger Ventilation physically decouples Piston from FGF. Always correct

GE Ventilator ends inspiration when P = Pmax setting, failing and alarming Draeger Vent continues inspiration when P =Pmax, succeeding & alarming

GE Flush will confuse ventilator for the next few breaths of feedback control Draeger Flush is OK any time during mechanical ventilation

GE offers electronic vaporizers with accuracy, agent use, but a total failure mode Draeger mechanical vaporizers do not fail but do not record and display agent use

GE does not return sampled gas to the breathing circuit Draeger returns sampled gas to the breathing circuit and allows true closed circuit

GE Aisys has many ventilation modes Draeger Fabius has VCV, PCV, and some have PSV Draeger Apollo has many ventilation modes All BWH Ventilators have Inspiratory Pause to calculate Compliance & Resistance

Neither GE nor Draeger has a convenient Fresh Gas Outlet you can connect to

Thank you

Now, your observations and questions

End