Anesthesia Machine Intro New Residents July 3, 2001

Advanced Anesthesia Machine Workshop CA-1 and everyone else

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

Professor of Anaesthesia Harvard Medical School

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

Answer: A great deal, and more than most of us know. Your patients rightfully expect you to understand the equipment you use. This is not an ABA review lecture. This is a “What do I need to know for safe and effective anesthesia are” lecture.

Anesthesia Delivery System (ADS)

Life Support with oxygen spontaneous breathing mechanical ventilation Inhalant Drug Delivery Gas Vapor

Anesthesia Machine Review of what you learned in Basics Lecture & Workshop Formal lecture on Anesthesia Machines Long Q & A Interrupt me with questions I will decide whether to answer now or later

Anesthesia Machine Schematic Basics of AnesthesiaR Miller, M Pardo 6th Ed

2000 psi

O2 SERVICE

INLET 55psi

35 psi

50 or 250 ml/min

NEEDLE VALVE

FAILSAFE VALVE

CALIBRATED VAPORIZERS

Fresh Gas Flow (FGF)

OXYGEN FLUSH VALVE [first]

ON/OFF SWITCH

CHECK VALVE PRESSURE

REGULATOR

N2O SERVICE

INLET 55 psi

FRESH GAS HOSE

Flush Flow (last)

[Anesthetizing gases flow]

COMMON OUTLET

750 psi

2000 psi

FILTER

DISS diameter

index safety system

CONNEC- TION

Anesthesia Machine Schematic (mod from Philip, 1976)

2000 psi

O2 SERVICE

INLET 55psi

35 psi

50 or 250 ml/min

NEEDLE VALVE

FAILSAFE VALVE

ON/OFF SWITCH

REGULATOR

N2O SERVICE

INLET 55 psi

FRESH GAS HOSE

Flush Flow (last)

COMMON OUTLET

750 psi

2000 psi

FILTER

DISS diameter

index safety system

CONNEC- TION

BWH backup: one O2, no N2O Tank room with more O2 tanks O2 tanks have 50 PSI outlet, also

2000 psi

O2 SERVICE

INLET 55psi

35 psi

50 or 250 ml/min

NEEDLE VALVE

FAILSAFE VALVE

ON/OFF SWITCH

REGULATOR

N2O SERVICE

INLET 55 psi

FRESH GAS HOSE

Flush Flow (last)

COMMON OUTLET

750 psi

2000 psi

FILTER

DISS diameter

index safety system

Wall outlets and supply hoses are DISS (Diameter Index Safety System) 55 PSI

55 psi

2000 psi

O2 SERVICE

INLET 55psi

35 psi

50 or 250 ml/min

NEEDLE VALVE

FAILSAFE VALVE

ON/OFF SWITCH

REGULATOR

N2O SERVICE

INLET 55 psi

FRESH GAS HOSE

Flush Flow (last)

COMMON OUTLET

750 psi

2000 psi

FILTER

DISS diameter

index safety system

CONNEC- TION

Tank Pressure Gauge displays when tank is open

Tank Pressure Gauge

2000 psi

O2 SERVICE

INLET 55psi

35 psi

50 or 250 ml/min

NEEDLE VALVE

FAILSAFE VALVE

ON/OFF SWITCH

REGULATOR

N2O SERVICE

INLET 55 psi

FRESH GAS HOSE

Flush Flow (last)

COMMON OUTLET

750 psi

2000 psi

FILTER

DISS diameter

index safety system

CONNEC- TION

Pressure Regulator reduces pressure to 35 PSI

working pressure 35 psi

Always less than

wall pressure to prevent emptying

55 psi

2000 psi

O2 SERVICE

INLET 55psi

35 psi

50 or 250 ml/min

NEEDLE VALVE

FAILSAFE VALVE

ON/OFF SWITCH

REGULATOR

N2O SERVICE

INLET 55 psi

FRESH GAS HOSE

Flush Flow (last)

COMMON OUTLET

750 psi

2000 psi

FILTER

DISS diameter

index safety system

CONNEC- TION

Filter prevents particulates from injuring machine or patient Check valve prevents emptying tank to wall losing gas and pressure when using tanks CHECK VALVE

2000 psi

O2 SERVICE

INLET 55psi

35 psi

50 or 250 ml/min

NEEDLE VALVE

FAILSAFE VALVE

ON/OFF SWITCH

REGULATOR

N2O SERVICE

INLET 55 psi

FRESH GAS HOSE

Flush Flow (last)

COMMON OUTLET

750 psi

2000 psi

FILTER

DISS diameter

index safety system

CONNEC- TION

Oxygen Flush valve connects from Regulated O2 pressure to Common Outlet FGF source

2000 psi

O2 SERVICE

INLET 55psi

35 psi

50 or 250 ml/min

NEEDLE VALVE

FAILSAFE VALVE

ON/OFF SWITCH

REGULATOR

N2O SERVICE

INLET 55 psi

FRESH GAS HOSE

Flush Flow (last)

COMMON OUTLET

750 psi

2000 psi

FILTER

DISS diameter

index safety system

CONNEC- TION

On / Off switch Powers Flow Controls

2000 psi

O2 SERVICE

INLET 55psi

35 psi

50 or 250 ml/min

NEEDLE VALVE

FAILSAFE VALVE

ON/OFF SWITCH

REGULATOR

N2O SERVICE

INLET 55 psi

FRESH GAS HOSE

Flush Flow (last)

COMMON OUTLET

750 psi

2000 psi

FILTER

DISS diameter

index safety system

CONNEC- TION

Failsafe prevents delivery of N2O when O2 supply pressure is low or zero. Does not prevent hypoxic fresh gas or inspired gas

2000 psi

O2 SERVICE

INLET 55psi

35 psi

50 or 250 ml/min

NEEDLE VALVE

FAILSAFE VALVE

ON/OFF SWITCH

REGULATOR

N2O SERVICE

INLET 55 psi

FRESH GAS HOSE

Flush Flow (last)

COMMON OUTLET

750 psi

2000 psi

FILTER

DISS diameter

index safety system

CONNEC- TION

On / Off switch Powers Flow Controls Does not prevent delivery of O2 via Flush

2000 psi

O2 SERVICE

INLET 55psi

35 psi

50 or 250 ml/min

NEEDLE VALVE

FAILSAFE VALVE

ON/OFF SWITCH

REGULATOR

N2O SERVICE

INLET 55 psi

FRESH GAS HOSE

Flush Flow (last)

COMMON OUTLET

750 psi

2000 psi

FILTER

DISS diameter

index safety system

CONNEC- TION

Needle Valves control flow

NEEDLE VALVE

2000 psi

O2 SERVICE

INLET 55psi

35 psi

50 or 250 ml/min

NEEDLE VALVE

FAILSAFE VALVE

ON/OFF SWITCH

REGULATOR

N2O SERVICE

INLET 55 psi

FRESH GAS HOSE

Flush Flow (last)

COMMON OUTLET

750 psi

2000 psi

FILTER

DISS diameter

index safety system

CONNEC- TION

Mandatory flow of 50 or 250 mL O2 is present on some ADSs (GE machines – Aisys, Aestiva) (Not Draeger - Apollo, Fabius, Tiro)

2000 psi

O2 SERVICE

INLET 55psi

35 psi

50 or 250 ml/min

NEEDLE VALVE

FAILSAFE VALVE

ON/OFF SWITCH

REGULATOR

N2O SERVICE

INLET 55 psi

FRESH GAS HOSE

Flush Flow (last)

COMMON OUTLET

750 psi

2000 psi

FILTER

DISS diameter

index safety system

CONNEC- TION

Rotameter indicates flow of gas viscosity near bottom, density near top Thus gas-specific Read widest point

ROTAMETER

Needle Valve and Rotameter

Rotameter

Pressure drop from below ball to above ball causes upward force Weight of ball causes downward force Ball height is where forces are equal

Rotameter

Ball in center of flow occludes like an orifice with turbulent flow and density dominating Ball near walls resists like a long skinny tube with viscosity dominating

2000 psi

O2 SERVICE

INLET 55psi

35 psi

50 or 250 ml/min

NEEDLE VALVE

FAILSAFE VALVE

ON/OFF SWITCH

REGULATOR

N2O SERVICE

INLET 55 psi

FRESH GAS HOSE

Flush Flow (last)

COMMON OUTLET

750 psi

2000 psi

FILTER

DISS diameter

index safety system

CONNEC- TION

High Pressure before needle valve, low pressure after

High Low Pressure

2000 psi

O2 SERVICE

INLET 55psi

35 psi

50 or 250 ml/min

NEEDLE VALVE

FAILSAFE VALVE

ON/OFF SWITCH

REGULATOR

N2O SERVICE

INLET 55 psi

FRESH GAS HOSE

Flush Flow (last)

COMMON OUTLET

750 psi

2000 psi

FILTER

DISS diameter

index safety system

CONNEC- TION

Vaporizers add anesthetic vapor

Vaporizing Chamber

Bypass Flow

Variable-Bypass or Calibrated Vaporizer Tec 4,5 and Vapor 19

FGF FGF + Vapor

Flow to Vaporizing Chamber

P v = Saturated Vapor Pressure

Basic Principle of Operation Standard Modern Vaporizer

Vaporizing Chamber

Bypass Flow

AKA : Direct Reading, Temperature-Compensated

FGF FGF +

Flow to Vaporizing Chamber

P v = Saturated Pressure

Variable-Bypass Vaporizer

Vaporizing Chamber

Bypass Flow

Modern Vaporizers havesplitting at outflow of Vaporization Chamber

Ohmeda Tec 4,5 and Drager Vapor 19 and 2000

Flow to Chamber

P v = Saturated Vapor Pressure

Ehrenwerth J, Eisenkraft JB, Berry JM. Anesthesia Equipment: Principles and Applications. Elsevier, 2013

Variable-Bypass Vaporizer correct drawing

FGF + Vapor

Same fraction as at sea level Thus constant PP out

2000 psi

O2 SERVICE

INLET 55psi

35 psi

50 or 250 ml/min

NEEDLE VALVE

FAILSAFE VALVE

ON/OFF SWITCH

REGULATOR

N2O SERVICE

INLET 55 psi

FRESH GAS HOSE

Flush Flow (last)

COMMON OUTLET

750 psi

2000 psi

FILTER

DISS diameter

index safety system

CONNEC- TION

Anesthetizing gases leave vaporizer and join O2 Flush gas (if in use) and exit via common outlet to fresh gas hose carrying Fresh Gas Flow

2000 psi

O2 SERVICE

INLET 55psi

35 psi

50 or 250 ml/min

NEEDLE VALVE

FAILSAFE VALVE

ON/OFF SWITCH

REGULATOR

N2O SERVICE

INLET 55 psi

Flush Flow (last)

750 psi

2000 psi

FILTER

DISS diameter

index safety system

CONNEC- TION

Check valve near common outlet is present on some ADSs GE Aestiva (MRI, AMIGO, ORs 7&8 for Heliox) These machines need a negative pressure leak test (NPLT)

CHECK VALVE

on some ADSs

Negative Pressure Leak Test (NPLT)

Detects a leak in Anes Machine Low Pressure System Low Pressure System is from Needle Valve to Common Outlet (CO) Low Pressure System is needle valve, rotameter, vaporizer, and some pipes Low pressure because the pressure drops across the needle valve opening Common leak sites are vaporizer mounting site and fill ports You test each vaporizer by itself. At least test the one you will use With FGF = 0, apply ans use negative-pressure squeeze bulb Bulb should not self-inflate

2000 psi

O2 SERVICE

INLET 55psi

35 psi

50 or 250 ml/min

NEEDLE VALVE

FAILSAFE VALVE

ON/OFF SWITCH

REGULATOR

N2O SERVICE

INLET 55 psi

FRESH GAS HOSE

Flush Flow (last)

COMMON OUTLET

750 psi

2000 psi

FILTER

DISS diameter

index safety system

CONNEC- TION

Most machines today do not have Fresh Gas Check Valve

2000 psi

O2 SERVICE

INLET 55psi

35 psi

50 or 250 ml/min

NEEDLE VALVE

FAILSAFE VALVE

ON/OFF SWITCH

REGULATOR

N2O SERVICE

INLET 55 psi

FRESH GAS HOSE

Flush Flow (last)

COMMON OUTLET

750 psi

2000 psi

FILTER

DISS diameter

index safety system

CONNEC- TION

Questions on Gas Mixing?

Patient Breathing Circuit

Allows cyclic flow To and from the patient

(AKA breathing)

Manual Resuscitator is one of the few

Open Circuit ventilation systems you will ever use

Manual Resuscitator

Mapleson categorization of Non-rebreathing Circuits

Not presented here

Rebreathing Circuit is now almost universal

Miller drawing of semi-closed circuit

Miller drawing flipped

Sampled

Exhaust

Ab- sorb- ant

200 mL/min

J Philip drawing of semi-closed circuit

Sampled

Exhaust

Ab- sorb- ant

200 mL/min

Rare designs have Fresh Gas enter after Insp Valve GE ADU, Philips AX700

Sampled

Exhaust

Ab- sorb- ant

200 mL/min

Semi-closed (rebreathing) circuit

Normal flow in breathing circuit

Flow goes forward In the direction of the valves Emptying and filling reservoir bag and lungs alternately

Sampled

Exhaust

Ab- sorb- ant

200 mL/min

Normal flow in the breathing circuit - Inspiration

Sampled

Exhaust

Ab- sorb- ant

200 mL/min

Normal flow in the breathing circuit - Expiration

Sampled

Exhaust

Ab- sorb- ant

200 mL/min

Normal flow in the breathing circuit - Expiration

The Circle-Absorber System

Exhaust Expired

Ab- sorb- ant

Inspired Fresh

Gas Flows

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

Sampled

Exhaust Expired

Ab- sorb- ant

200 mL/min

Inspired Fresh

Gas Flows

Questions on Gas Flow?

Sampled

Exhaust Expired

Ab- sorb- ant

200 mL/min

Inspired Fresh

Gas Flows

Low FGF

More rebreathing Inspired more dependent on Expired Inspired less dependent on Vaporizer

View the Breathing Circuit

The Circle-Absorber System

High Flow, Low Flow

Sampled

Exhaust Expired

Ab- sorb- ant

200 mL/min

Inspired Fresh

Gas Flows

Partial Rebreathing Circuits are used in Anesthesia

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

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

Partial rebreathing = semi-closed circuit All ADSs use them

Rebreathing Ventilation

Is not for dummies Requires knowledge and skill Makes us different from other care providers

EMT, Sedation RN, ED MD, Hospitalist, Others

Look at machines we have

Two Companies GE-Datex-Ohmeda Aestiva and all

others Draeger Fabius and all others

Newer ADSs both companies

GE Aisys Draeger Apollo

< 1998, Standard Anesthesia Ventilators

Tidal Volume and FGF were interdependent Increase in FGF caused Increase in 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 the Tidal Volume - patient receives what you set Two ways to achieve this Fresh Gas Compensation- compensate for FGF

Active, feedback control of inspired tidal volume GE

Fresh Gas Decoupling – FGF goes elsewhere in I Passive separation of FGF during inspiration Draeger

Newer ADSs both companies GE Aisys Draeger Apollo GS

GE-Datex-Ohmeda Aestiva

GE Aestiva, Aisys

Pneumatic (oxygen)-driven bellows Inspiratory and Expiratory Flow Sensor

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

Fresh Gas Compensation Active, feedback control of inspired tidal volume

Aestiva VOS All GE models have similar differential-pressure flow sensor

Variable-Orifice flow Sensor (VOS)

Pressure Transducer

F Accurate over a wide range of flow. Each one is calibrated in GE factory. Microchip stores the calibration curve.

Variable orifice

Pressure Transducer

Variable orifice

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

Accurate over a wide range of flow. Each one is calibrated in GE factory. Microchip stores the calibration curve.

Pressure Transducer

Variable orifice

One drop of water will make this fail

Accurate over a wide range of flow. Each one is calibrated in GE factory. Microchip stores the calibration curve.

Water Management is important Use an HME or HMEF

Heat and Moisture Exchanger between patient and circuit

HME Wet Dry

Inspired gas may be wet

Draeger Ventilation

Fresh Gas Flow Decoupling Passive separation of FGF during inspiration

Tiro, Fabius, Apollo

Draeger E-Vent Draeger Fabius GS, Tiro, or Apollo

Piston

Constant Volume FGF Decoupling

COSY-2.5

I/ E select

Draeger Fabius and

Apollo Circuit Insp Valve

Circuit Exp Valve

Mechanical Ventilation Piston displacement is constant and provides constant Tidal Volume Fresh Gas fills the reservoir bag during inspiration (“decoupled”) Piston draws in Fresh and Exhaled gas during “refill” in expiration Piston is ready to give the next breath Reservoir bag is always filled with circuit gas Switch between Mechanical and Manual Ventilation and give same gas Recruitment breaths recruit with same gas so outcome is measurable

Draeger Fresh Gas Flow Decoupling

Implications of “Decoupling”

Collateral damage Reservoir bag is in the circuit during ventilation Adds a second sequential mixing chamber Old gas stays in-play even when FGF is high This does not matter much during induction This matters a lot during emergence In emergence we desire Inspired agent concentration = 0 Even with bag ventilation, expired gas contaminates inspired Cleaning for MH-sensitive patients is difficult

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 Preparation Target is FI Agent < 5 ppm Most ADSs require 10 minutes Fabius 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 Preparation Target is FI Agent < 5 ppm Most ADSs require 10 minutes Fabius 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 this yet

Charcoal Absorbers overcome this

Dynasthetics,Inc.

GE breathing circuits are faster Induction Emergence

COSY-2.5

I/ E select

Draeger Fabius and

Apollo Circuit Insp Valve

Circuit Exp Valve

GE Circuit configuration superimposed on Draeger Circuit

I/ E select

GE Circuit

Pneumatic bellows ventilator

GE Aisys Sevoflurane Induction

High FGF and vaporizer setting

Gas Monitor screen

Anesthesia Machine Intro New Residents July 3, 2001

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