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
(Continuous Flow) Anesthesia Machine N 2 O Air O 2 L/m 9 8 7 6 5 4 3 2 1 0 L/m 9 8 7 6 5 4 3 2 1 0 L/m 9 8 7 6 5 4 3 2 1 0 ml/m 900 600 400 300 200 100 50 1 2 3.. Isoflurane Sevoflurane Desflurane Vaporizer Common Outlet FGF (Fresh Gas Flow)
Anesthesia Machine
Anesthesia Machine Schematic
Anesthesia Machine Schematic
SIMPLIFIED ANESTHESIA MACHINE SCHEMATIC DIAGRAM N 2 O SERVICE INLET 55 psi N 2 O 750 psi N 2 O FILTER FAILSAFE VALVE N 2 O N 2 O CHECK VALVE 35 psi PRESSURE REGULATOR S CALIBRATED VAPORIZERS I D 750 psi WALL NEEDLE VALVE DISS diameter index safety system CONNEC- TION O 2 2000 psi O 2 2000 psi O 2 35 psi ON/OFF SWITCH OXYGEN FLUSH VALVE [first] 50 or 250 ml/min O 2 [Anesthetizing gases flow] Flush Flow (last) Fresh Gas Flow (FGF) COMMON OUTLET FRESH GAS HOSE O 2 SERVICE INLET 55psi
Patient Breathing Circuit Allows cyclic flow To and from the patient (AKA Breathing)
Manual Resuscitator A Manual Resuscitator is one of the few Open Circuit ventilation systems you will ever use
Rebreathing Circuit
Circle absorption anesthetic breathing circuit
flipped
Normal flow in breathing circuit Flow goes forward In the direction of the valves Emptying and filling reservoir bag and lungs alternately
Normal flow in the breathing circuit - Inspiration Exhaust CO 2 Absorbant Sampled 200 ml/min Fresh
Normal flow in the breathing circuit - Expiration Exhaust 2 1 CO 2 Absorbant Sampled 200 ml/min Fresh
The Circle-Absorber System Exhaust Expired Gas Flows V E CO 2 Absorbant Fresh Inspired
Gas is sampled from circuit near patient for I/E measures Exhaust Expired Gas Flows CO 2 Absorbant V E Sampled 200 ml/min Fresh Inspired
Low FGF More rebreathing Inspired more dependent on Expired Inspired 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 gas It contains expensive anesthetic vapors Reuse as much as possible somehow (learn more later) Remove (Absorb) CO 2 and Rebreathe the anesthetic Partial rebreathing = semi-closed circuit All ADSs use them
Is not for dummies Rebreathing Ventilation Requires knowledge and skill Makes 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 ADSs FGF reaches breathing circuit by a hidden pipe or hose
Ventilation Modes VCV Volume-Controlled Ventilation PCV - Pressure-Controlled Ventilation
Inspiratory Pause Useful in VCV Allows you to compute Static Compliance Allows you to see the effect of resistance
Inspiratory Pause Useful in VCV Allows you to compute Static Compliance Allows you to see the effect of resistance
Inspiratory Pause
Alarms
Alarms Level Sound Text LED Warning continuous!!! Red blinking Caution q 30 sec!! Yellow blinking Advisory once! Yellow continuous Silence button silences for two minutes
Fabius Pressure Monitoring to detect disconnection Rules If 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 leak Fabius 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 3 Later, connected here 2 Tubing is disconnected 1 Sample Gas Return Port is opened by connector
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 leak SAM (Smart Anesthesia [Gas] Monitor) has Sample Gas Outlet Formerly connected to Scavenger Sample Gas Return connector on absorber self-seals Leave connector and tubing disconnected during leak test Connecting Sample Gas Return Connector opens seal and leaks Leave it disconnected during leak test Option 2 Connect both Sample Gas and Sample Gas Return tubings A Connect Sample Gas Return Tubing from SAM to Absorber B Connect Gas Sample line to breathing circuit Y No 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-controlled GE calls it Pressure Control Volume Guarantee PCV - VG Draeger calls it Volume Ventilation with Auto-Flow V V - Auto Flow Pressure Ventilation but delivers the Tidal Volume you set Useful in Laparoscopy where compliance changes but, you want constant tidal volume and, you want constant-pressure breaths High-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 Exhaust Expired Sampled & measured I, E Ventilation Flow CO 2 200 ml/min Absorbant Fresh Gas Flow Inspired
Low FGF Saves money because of less waste Limits 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 interdependent Increase 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 this Fresh Gas Compensation Active, feedback control of inspired tidal volume GE Fresh Gas Decoupling Passive separation of FGF during inspiration Draeger
GE-Datex-Ohmeda Aestiva and all other models GE-Datex- Ohmeda Aestiva 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 VOS All GE models have similar differential-pressure flow sensor
Variable-Orifice flow Sensor (VOS) P P1 P2 Pressure Transducer Accurate over a wide range of flow Each one is calibrated in GE factory F Flow Variable orifice
Variable-Orifice flow Sensor (VOS) P P1 P2 Pressure Transducer Accurate over a wide range of flow Each one is calibrated in GE factory F Flow Variable orifice This is what makes the SmartVent smart This is GE s core technology
Variable-Orifice flow Sensor (VOS) P P1 P2 Pressure Transducer Accurate over a wide range of flow Each one is calibrated in GE factory F Flow Variable orifice One drop of water will make this fail
Water Management is important Use an HME or HMEF Wet HME Dry Heat and Moisture Exchanger between patient and circuit
Draeger Fabius GS Piston Draeger E-Vent
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 volume Usually slightly smaller than SET tidal volume RQ (Vdot CO2 / VdotO2 = 0.8) No alarm on error
Hot wire Anemometer is cooled by flow Used to Display, not to control tidal 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 wrong Piston 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 Decoupling Tiro, Fabius, Apollo
Draeger Fresh Gas Flow Decoupling 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
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
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 F I 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 F I Agent < 5 ppm Most ADSs require 10 minutes Fabius and Apollo require 1 hour (Inspired Charcoal agent absorber can overcome this) Fabius and Apollo are similar Draeger has not solved it yet 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
GE breathing circuits are faster Induction Emergence
Draeger Fabius and Apollo Circuit Insp Valve Constant Volume FGF Decoupling COSY-2.5 I E I/ E select Circuit Exp Valve
GE Circuit configuration superimposed on Draeger Circuit I/E I/ E select
Pneumatic bellows ventilator GE Circuit
Sevoflurane Induction High FGF and vaporizer setting
Second Breath, Inspired = Vaporizer setting
Tight control of inspired is most important during emergence
6 hour graphic trend 02/27/07 BWH OR Boston 6 hour Robot-assisted, Radical hysterectomy, w lymph node dissection
Zoom in to 1 hour trend 2 3 02/27/07 BWH OR Boston 6 hour Robot-assisted, Radical hysterectomy, w lymph node dissection
Better to understand this with slow wave (3 min) 3 minutes
None of this works without power Power switch is with power cord on back of ADS Fabius Aisys
Observations GE 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
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