4The Datex-Ohmeda Tec 4, Tec 5, and Tec 7, as well as the North American Dräger Vapor 19.n and 20.n vaporizers, are classified as variable-bypass, flow-over, temperature-compensated, agent-specific, out-of-breathing-circuit vaporizers
6The SVP of most inhalation agents is MUCH more that is required to produce anesthesia i.e. 32% vs 0.75 or 243 mm Hg vs 5.7 mm Hg for halothaneNeed to dilute this vapor with the carrier gas and deliver a controlled amount of this vapor to the patientHow much liquid agent does a vaporizer use per hour?Ehrenwerth and Eisenkraft (1993) give the formula:3 x Fresh gas flow (FGF) (L/min) x volume % = mL liquid used per hourOr one can determine the volume (mL) of saturated vapor needed to provide 1% (ie 4000(flow) x 0.01 = 40 mL) Typically, 1 mL of liquid volatile agent yields about 200 mL vapor.
8Safety FeaturesNewer generations of anesthesia vaporizers are Agent-specific, keyed filling devices help prevent filling a vaporizer with the wrong agent.Overfilling of these vaporizers is minimized because the filler port is located at the maximum safe liquid level.Finally, today's vaporizers are firmly secured to a vaporizer manifold on the anesthesia workstation. Thus, problems associated with vaporizer tipping have become much less frequent.Interlock systems prevent the administration of more than one inhaled anesthetic
9the wick systems are placed in direct contact with the metal wall of the vaporizer to help replace energy (heat) consumed during vaporization.The materials that vaporizers are constructed of are chosen because they have a relatively high specific heat and high thermal conductivity.These factors help minimize the effect of cooling during vaporization
10TEC VAPORIZERS CLASIFICATION (TEC I-7) Variable bypass Flow over with wickOut of systemTemp. compensated by automatic flow alterationConc. calibrated.Agent specific
15for halothane, enflurane, isoflurane, and sevoflurane filling devices: a funnel filler, the Quik-Fil, or the Easy-FilCapacity: 300 mLTemp: 18 to 35 degree celciusbarometric changes are compensated automatically. Fluctuating back pressure can affect the vaporizer and increase the delivered concentration
17Vaporizing chamber circuit The fresh gas flows from the flowmeter across the sump cover where it is diverted through the central cavity of the rotary valve and back through the IPPV compensating assembly.Gas now flows from the IPPV assembly down through the tubular wick assembly where it picks up anesthetic vapor and then flows across the base of the vaporizing chamber above the liquid agent.From the base of the vaporizing chamber the gas/agent mixture flows through the sump cover to the proportional radial drug control groove of the rotary valve and then back into the sump cover where it combines with the fresh gas from the bypass circuit.The combined total flow then flows out from the vaporizer and via the Selectatec circuitry to the anesthesia gas delivery system.
181.Rotary valve2.Enriched fresh gas out3.Combined fresh gas and enriched gas out4.Fresh gas bypass5.Fresh gas out6.Thermostat7.Vaporizing chamber8.Wick assembly9.IPPV compensating assembly10.Sump cover11.Vapor control channel12.Shown in ON position
19Earlier versions of the Selectatec Series Mounted Manifold that provide mounting positions for three vaporizers require that if only two vaporizers are fitted, then the center position must be occupied.If the center position is not occupied, the interlock that helps ensure that only one vaporizer at a time can be turned ON is ineffective.Later versions of the Selectatec Series Mounted Manifold that provide mounting positions for three vaporizers incorporate an additional interlock that helps ensure that only one vaporizer at a time can be turned ON even if the center position is not occupied
20HazardsIf inverted: rule of 5OverfillingFluctuating back pressure may be imposed on the vaporizer by downstream components and/or assisted or controlled ventilation to the patient.Pressures in excess of 400 mmHg may overcome the internal pressure balance and cause a variation in output.Mainteinance: drain
21TEC 6 CLASSIFICATION Conc calibrated Thermocompensation by supplied heatOrElectrically heated dualcircuit gas-vapor blenderCapacity: 425mlDial: 1-18%Filler port, power cord, battery
24TEC 6 Designed for the delivery of Desflurane Electronic vaporizer which heats Desflurane to maintain constant temperature and vapor pressure for consistent outputIt has an LED display which indicates vaporizer status - no output, low agent, warm-up, operational and alarm battery lowFeatures several intrinsic vaporizer monitors and alarms that constantly monitor vaporizer status.
25Supplied Heat Maintains a constant temperature by electric heater. Temperature compensationSupplied HeatMaintains a constant temperature by electric heater.Low boiling point 22.8C causes unpredictable output Supplied Heat (Must be connected to electrical outlet):Warms liquid Desflurane to 39C to achieve a pressure of 1,500 mmHgControls gas output by variable resistance via a differential pressure transducer2 heaters in base(sump) and 2 in the upper part of vaporizer.
28The Tec 6 vaporizer is an electrically heated, thermostatically controlled, constant-temperature, pressurized, electromechanically coupled dual-circuit, gas-vapor blender.The pressure in the vapor circuit is electronically regulated to equal the pressure in the fresh gas circuit.At a constant fresh gas flow rate, the operator regulates vapor flow with a conventional concentration control dial.When the fresh gas flow rate increases, the working pressure increases proportionally.For a given concentration setting even when varying the fresh gas flow rate, the vaporizer output is constant because the amount of flow through each circuit remains proportional
29EFFECT OF BAROMETRIC PRESSURE Works at absolute pressure- It maintains a constant output in terms of vol% but pp varies if atm pr decreases-output in pp is also decreasedReqd. dial setting=dial setting x 760/ambient pressureEffect of carrier gas; addition of N2O – less viscosity – decrease vapor outputMounting – for rt - side of machineBottle; has a spring valve to prevent escape of agentHazardsCheckout procedurePress and hold the mute button until all lights and alarms activated.Turn on to at least 1% and unplug the electrical connection. A "No Output" alarm should ring within seconds. This tests battery power for the alarms.
30Safe T fillThe bottle probe inserts directly into the filler port.An "O" ring fitted on the spring-loaded bottle cap helps engage and seal the opening before liquid can flow, which aids in preventing spillage and operating room contamination.
39A fixed restrictor is located in the bypass chamber, and it causes flow from the vaporizer inlet to split into two flow streams .One stream passes through the bypass chamber, and the other portion enters the inlet of the vaporizing chamber and passes through a one-way check valve.The presence of this check valve is unique to the Aladin system. This one-way valve prevents retrograde flow of the anesthetic vapor back into the bypass chamber, and its presence is crucial when delivering desflurane if room temperature is higher than the boiling point of desflurane (22.8°C).A precise amount of vapor-saturated carrier gas passes through the flow control valve, which is regulated by the CPU. This flow then joins the bypass flow and is directed to the outlet of the vaporizer
40controlled vaporization of desflurane presents a unique challenge, particularly when room temperature is greater than the boiling point of desflurane.At higher temperatures, the pressure inside the vaporizer sump increases, and the sump becomes pressurized. When sump pressure exceeds pressure in the bypass chamber, the one-way check valve located in the vaporizing chamber inlet closes to prevent carrier gas from entering the vaporizing chamber.At this point the carrier gas passes straight through the bypass chamber and its flow sensor.Under these conditions, the electronically regulated flow control valve simply meters in the appropriate flow of pure desflurane vapor needed to achieve the desired final concentration selected by the user.ADU users should be cautious of this potential problem, especially when desflurane is used.
41To offset cooling effect, the S/5 ADU is equipped with a fan that forces warmed air from an “agent heating resistor” across the cassette (vaporizer sump) to raise its temperature when necessary(<18 C)The fan is activated during two common clinical scenarios: (1) desflurane induction and maintenance and (2) sevoflurane inductionLiq. Level indicated on screen. if 10% - alarm messageIf the cassette pressure is higher than the pressure distal to the cassette outflow, the vaporizer starts to work as an injectorIf the temperature falls below 20°C or the fresh gas flow is over 8 L/minute, the vaporizer may be unable to produce high concentrations and the messages insufficient agent and decreased flow will appear on the machine.
43HazardsThe cassette is fitted with an overfill protection mechanism. If air is allowed into the agent bottle, this mechanism is deactivated. This may result in overfilling and anesthetic overdose.Turning the vaporizer ON while filling may pressurize the cassette and cause liquid to leak at the filling portWhen the fresh gas flow is lowered, the one-way valve that prevents backflow of saturated vapor from the cassette toward the bypass channel may fail to close, resulting in high delivered concentrations.This problem may be more significant when desflurane is used.
47At »T« setting Vapor may be moved in any position. If not at »T« setting, risk of incorrect output concentration,or of anaesthetic agent escaping otherwiseWhen control dial is set at »0« or above »0«, do not useVapor at an angle of more than 30°.Risk of incorrect output concentration or anaestheticagent escaping otherwise.
53HazardsCellular phones should not be used within 10 m of the vaporizer.The D-Vapor is not designed to be used at an angle of more than 10 degrees. At greater angles, an uncontrolled concentration of vapor may resultThe output is not defined in the area between 0% and 0.2%. The handwheel should not be set in this area.The Vapor is not suitable for use with a breathing system due to high pneumatic resistance.
56gas passes through a spiral tube into the vaporizing chamber, which contains a stainless-steel wick Temperature compensation is provided by a liquid-filled expansion bellows controlling a variable resistance valve in the bypass.The vaporizer should be calibrated every 3 to 6 months
57Penlon sigma alpha For desflurane Filling capacity- 330 ml Temp- 15 to 30Flow range : L/minHazards: Electromagnetic interference
58Penlon sigma delta Specifications: Weight: 5 kg approx. Mounting: Selectatec, Drager Plug-In, Cagemount Specifications: Weight: 5 kg approx. Cagemount Dimensions: (mm) 133 wide x 158 deep x 219 high Selectatec Compatible: with Interlock Dimensions (mm) 120 wide x 190 deep x 242 high Drager Plug-In Compatible: Dimensions (mm) 100 wide x 190 deep x 242 high Capacity Volume: at MAX mark 250 mL nominal Volume at MIN mark: 35 ±10 mL -- After draining, approximately 60 ±10 mL of liquid is retained by the wick Flow Range: Operating flow range 0.2 to 15 litres/min Temperature Range: Operating temperature range 15° to 35°C
61temperature decreases with altitude; this is known as the ‘lapse rate’ and varies according to the moisture content of the air and has an international standard of 6.498C per 1000 m from sea level to m.Safety featuresImportant safety features include:Keyed fillersLow filling portSecured vaporizers (less ability to move them about minimizes tipping)InterlocksConcentration dial increases output in all when rotated counterclockwise
62Disadvantagesheavy, expensive and require regular servicing if their accuracy is to be maintained.built for use with a specific agent and can be lethal if the wrong agent is usedTheir high internal resistance prevents them from being used in the breathing circuit.Future ; closed sys where vaporizer control may be linked directly to patient parameter via feedback mech.
63FillersVaporizers may be filled by a conventional funnel-fill mechanism, in which the liquid anesthetic is simply poured into a funnel in the vaporizer.The problem with this method is that, if more than one anesthetic is used in a facility, there is nothing to prevent the vaporizer being filled with the wrong agent. This may be prevented with the use of a key-filler systeman agent-specific filler tube is used, one end of which slots into a fitting on the vaporizer, and the other end slots into a collar on the bottle of anesthetic.The fitting on the vaporizer and the collar on the bottle are specific to each agent, making it impossible (or, at least, extremely difficult) to fill the vaporizer with the wrong agent.
64ASTM StandardsVaporizers suitable for use in the breathing system must have standard 22-mm fittings or screw-threaded, weight-bearing fittings with the inlet female and the outlet male. The direction of gas flow must be indicatedThe output of the vaporizer shall be less than 0.05% in the “OFF” or “zeroThe average delivered concentration from the vaporizer shall not deviate from the set value by more than ±20% or ±5% of the maximum setting, whichever is greater, without back pressureThe effects of variations in ambient temperature and pressure, tilting, back pressure, and input flow rate and gas mixture composition on vaporizer performance must be stated
65MEASURED FLOW VAPORIZERS The vaporizer heats the anesthetic agent to a temperature above its boiling point (so it behaves as gas) and this is then metered into the fresh gas flow.A measured flow is sent by a separate oxygen flow meter to pass to the vaporizer with the output being at SVP for the anesthetic agent.In order to dilute this otherwise lethal concentration, outpur from that flowmeter is combined with gas passing form the main flowmeter
66MEASURED FLOW VAPORIZERS Operator has to set the flow to the vaporizer and bypass with separate flowmetersThis means that respective flows have to be calculated for each agent for a given temp and vapour outputTo calculate the vaporizer output, one must know the - Vapor pressure of the agent- The atmospheric pressure- The total flow of gases- The flow of the vaporizer
67CALCULATIONS FOR OUTPUT IN MEASURED FOW VAPORISERS Set 100 ml/min flow of carrier gas (oxygen) from dedicated flowmeterSVP of hal in vap. Chamber is 243 mmHgHal forms 243/760 x 100 = 32% of gas mixtureCarrier gas will occupy the rest of the vol. i.e =68%This 68% is occupied by 100ml/min carrier gasAnd 32% hal will be = 100/68x32=47 ml
68CALCULATIONS FOR OUTPUT IN MEASURED FOW VAPORISERS Gas exiting is 147 ml with 47 ml hal vaporTo get a mixture containing 1% hal this 47 ml should be diluted in 4700 mlRequired carrier gas is =4553 mlIf set 100 ml measured flow to vaporiser usually set 5 l/min flow of carrier gas to get 1% halothaneRatio of gas through vaporiser: main gas flow is 100:4600=1:46% concentration of agent = 100 x vaporizer output of anaesthetic/total flow