Anesthesia Delivery Systems What Do I Need to Know About My Machine? A Workshop James H. Philip, MEE, MD, CCE

Transcription

1 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 , James H Philip, all rights reserved

2 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.

3 Anesthesia Delivery System (ADS) Life Support with oxygen spontaneous breathing mechanical ventilation Inhalant Drug Delivery Gas Vapor

4 (Continuous Flow) Anesthesia Machine N 2 O Air O 2 L/m L/m L/m ml/m Isoflurane Sevoflurane Desflurane Vaporizer Common Outlet FGF (Fresh Gas Flow)

5 Anesthesia Machine

6 Anesthesia Machine Schematic

7 Anesthesia Machine Schematic

8 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 psi O 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

9 Patient Breathing Circuit Allows cyclic flow To and from the patient (AKA Breathing)

10 Manual Resuscitator A Manual Resuscitator is one of the few Open Circuit ventilation systems you will ever use

11 Rebreathing Circuit

12 Circle absorption anesthetic breathing circuit

13 flipped

14 Normal flow in breathing circuit Flow goes forward In the direction of the valves Emptying and filling reservoir bag and lungs alternately

15 Normal flow in the breathing circuit - Inspiration Exhaust CO 2 Absorbant Sampled 200 ml/min Fresh

16 Normal flow in the breathing circuit - Expiration Exhaust 2 1 CO 2 Absorbant Sampled 200 ml/min Fresh

17 The Circle-Absorber System Exhaust Expired Gas Flows V E CO 2 Absorbant Fresh Inspired

18 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

19 Low FGF More rebreathing Inspired more dependent on Expired Inspired less dependent on Vaporizer View the Breathing Circuit The Circle-Absorber System

20 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

21 Is not for dummies Rebreathing Ventilation Requires knowledge and skill Makes us different from other care providers EMT, Sedation RN, ED MD, Hospitalist, Others

22 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

23 Ventilation Modes VCV Volume-Controlled Ventilation PCV - Pressure-Controlled Ventilation

24 Inspiratory Pause Useful in VCV Allows you to compute Static Compliance Allows you to see the effect of resistance

25 Inspiratory Pause Useful in VCV Allows you to compute Static Compliance Allows you to see the effect of resistance

26

27 Inspiratory Pause

28

29 Alarms

30 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

31 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

32 PRESSURE THRESHOLD LOW alert

33 APNEA PRESSURE alarm

34 Fabius Sample Gas Return Port Can leak

35 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

36 Fabius fails leak test

37 Here is the leak 3 Later, connected here 2 Tubing is disconnected 1 Sample Gas Return Port is opened by connector

38 Here is the leak Later, connected here

39 Disconnect Sample Gas Return Connector from circuit to seal connector

40 No Leak

41 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

42 Still get no Leak

43 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

44 Advanced Ventilation Modes

45 Modes available on 7900 Smart Vent for AISYS:

46 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

47 Pressure Control Ventilation Volume Guarantee

48 Breathing Circuit FGF Interaction or Lack thereof

49 The Circle-Absorber System and Fresh Gas Flow Exhaust Expired Sampled & measured I, E Ventilation Flow CO ml/min Absorbant Fresh Gas Flow Inspired

50 Low FGF Saves money because of less waste Limits our ability to control inspired concentration Therefore limits control of expired conc. and brain conc.

51 1998 Better ventilation for difficult patients FGF-independent ventilation Corrects for circuit leaks Corrects for circuit compliance

52 < 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

53 Fresh Gas Flow Independent of Ventilation 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

54 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

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

56 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

57 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

58 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

59 Water Management is important Use an HME or HMEF Wet HME Dry Heat and Moisture Exchanger between patient and circuit

60 Draeger Fabius GS Piston Draeger E-Vent

61 Ventilator Piston

62 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

63 Flow sensor

64 Measured Tidal Volume EXHALED tidal volume Usually slightly smaller than SET tidal volume RQ (Vdot CO2 / VdotO2 = 0.8) No alarm on error

65 Hot wire Anemometer is cooled by flow Used to Display, not to control tidal volume. Calibrate for heat conductivity. Set Desflurane Y/N

66 Fabius has a Water Trap

67 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

68 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

69 Draeger Ventilation Fresh Gas Flow Decoupling Tiro, Fabius, Apollo

70 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

71 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

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

73 Inspired does not fall to zero

74 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:

75 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:

76 GE breathing circuits are faster Induction Emergence

77 Draeger Fabius and Apollo Circuit Insp Valve Constant Volume FGF Decoupling COSY-2.5 I E I/ E select Circuit Exp Valve

78 GE Circuit configuration superimposed on Draeger Circuit I/E I/ E select

79 Pneumatic bellows ventilator GE Circuit

80 Sevoflurane Induction High FGF and vaporizer setting

81 Second Breath, Inspired = Vaporizer setting

82 Tight control of inspired is most important during emergence

83 6 hour graphic trend 02/27/07 BWH OR Boston 6 hour Robot-assisted, Radical hysterectomy, w lymph node dissection

84 Zoom in to 1 hour trend /27/07 BWH OR Boston 6 hour Robot-assisted, Radical hysterectomy, w lymph node dissection

85 Better to understand this with slow wave (3 min) 3 minutes

86 None of this works without power Power switch is with power cord on back of ADS Fabius Aisys

87 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

88 Thank you

89 Now, your observations and questions

90 End