THE ANESTHESIA MACHINE. Department of Anesthesia Medical University of SC

Transcription

1 THE ANESTHESIA MACHINE Department of Anesthesia Medical University of SC

2 Why it s important What it does All its parts All its safety features How to check it KNOW YOUR MACHINE

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

4 Gas Supply Reduces pressure Vaporizes Agents Circuit attached to patient and the ventilator (removable) Machine Controls flow Mixes final gas mixture Delivers to circuit What does it do?

5 Central Gas Supply

6 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 Pipeline Inlets

7 E Cylinders

8 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 = psi = L N2O full = 745 psi = 1590 L (have to weigh) Air full = psi = L E Cylinders

9 Pressure Regulator Reduces E-cylinder pressure to 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 psig Flow Control Circuits

10 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

11 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 psig Can still get hypoxic mixtures O2 Failure Detection Devices

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13 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 Valves and Meters

14 Turn Counterclockwise Knobs color-coded O2 safety features farthest to the right fluted sticks out the farthest Flow control valve Knobs

15 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 Flowmeters

16 Backup O2 flowmeter Each gas has a separate flow measurement device before being mixed Electronic Flowmeters

17 Minimum flow typically 150ml/min Can be as low as 50ml/min Some designed to delver < 1L/min Minimum O2 flow

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

19 Isoflurane and Sevoflurane Vaporizers

20 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 Vaporizers

21 Concentration dial On/off switch Outlet port Pressure compensator Wick Temperature Compensating bypass Concentrating Cone Vaporizing Chamber Anesthetic Agent Variable Flow Vaporizer

22 Variable Bypass Flow Vaporizer

23 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 Vaporizers

24 Desflurane Vaporizer

25 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

26 Desflurane Vaporizer

27 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 psig Common Fresh Gas Outlet

28 Circle System VA conc effected by Lung uptake MV Total FGF Circuit volume Gas leaks High flows diminishes discrepancies Breathing Circuit

29 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

30 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 Extra Components

31 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

32 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 Humidifiers

33 Ventilators

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

35 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 Trigger

36 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 Cycle

37 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 Exhalation

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

39 Datex-Ohmeda Carestation

40 Older Datex Ohmeda Carestation

41 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 Ventilator Circuit Design

42 Peak Inspiratory Pressure Highest circuit pressure during inspiration Indication of dynamic compliance Plateau Pressure Measured during inspiratory pause (no flow) Indication of static compliance Volume and Pressure Monitoring

43 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 Airway Pressures

44 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 Ventilator Alarms

45 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

46 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 Problems with Anesthesia Ventilators

47 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 Scavenging Systems

48 Waste Scavenging

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

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