Basics Anesthesia Machine – Flashcards
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Wood's Metal
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A safety device that melts under excessive heat (;200 degrees F) to allow the gas to escape preventing an explosion
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Joule Thompson Effect
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"Joule is cool" Cooling effect once compressed gas is allowed to escape in open space
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Adiabatic Heat of Compression
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Compression of cylinder contents into a small space generates heats and may cause combustion
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PSIG numbers
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Ó2 - 2200 N2O - 745 Air - 1900
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USA Colors
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Ó2 - Green N2O - Blue Air - Yellow
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Capacity (L)
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Ó2 - 660 N20 - 1590 Air - 625
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PISS
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Ó2 - 2-5 N2O - 3-5 Air - 1-5
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What is Critical Temperature
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The critical value at which a gas is pressured and forms a liquid, low temperature Above critical temperature, gas will remain in gaseous state
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Critical Temperature of Ó2 and N2O
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Oxygen: -119 degrees C N2O: 39.5 degrees C, hence why it's liquid in the tank
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Celsius and Fahrenheit conversion
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Multiply Celsius temp by 9/5 Add 32 degrees Example: convert 37* C to Fahrenheit. 37 * 9/5 = 333/5 = 66.6 66.6 + 32 = 98.6* F
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Supply failure alarm system
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4. Activated when Ó2 falls below 28 psi Alarms sounds before 25 psi, the point at which N2O flow will cease
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Second stage pressure regulator
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5. Gas pressure is decreased to a constant pressure of 16 psi as flow from wall varies at times between 40-50psi After passing 2nd stage pressure regulator, sits in "stand by" at flow control valve
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Flowmeter safety mechanisms
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-Tubes are hand calibrated and no two tubes are alike -Gas specific and are not interchangeable between machines and gases
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Sequence of flowmeter safety mechanism
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Sequence of flowmeter tubes is very important to decrease chance of hypoxic mixture. -Gas flow is from left to right -Ó2 is always to the Right or Downstream of all other gases and closest to the manifold outlet -Any leak in flowmeters will vent other gases out before Ó2. -Decreases the chance that Ó2 will be diluted or lost
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Flowmeter: Interlink Mechanism /Proportioning System
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-Flow valves linked mechanically or pneumatically so Ó2 cannot be set below 25% -Ensures adequate % of Ó2 delivery and prevents hypoxic mixture -Ó2 flow control spindle is connected to the N2O spindle, so that if Ó2 goes down, N2O goes down also, and if N2O goes up Ó2 level will go up also if Ó2 % drops below room air percent
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Interlink mechanism
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-Ó2 spindle is Connected to n2o spindle If you incr. N2O flow then Ó2 flow will incr. If you incr. Ó2 flow; N2O will not incr. If you decr. N2O flow; Ó2 flow will not decr. FYI: -The N2O spindle has 14 teeth -The Ó2 spindle has 29 teeth -So......If you rotate the N2o knob 2.07 times, the Ó2 will rotate once
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Vaporizers
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-Volatile anesthetics are liquids at room temperature and atmospheric pressure -Vaporization is the conversion of liquid to vapor - takes place in a closed container referred to as a vaporizer -The energy necessary for molecules to escape from the liquid to enter the gas phase is supplied as heat -Heat of Vaporization = the number of calories required at a specific temperature to convert 1 G of liquid to vapor
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Vaporizers are:
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-Agent specific, precisely calibrated to compensate to changes in temperature and variations of gas flow -Constructed of metals with high thermal conductivity, allowing heat to flow from the vaporizer in to the anesthetic in the liquid phase, supplying the energy for the heat of vaporization
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Vaporizer flow pattern
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-Ó2 (Ó2 + N2O) enter vaporizer and pass through a filter A relief valve exists which will open if gas flow exceeds that which is required for delivery of gas conc. on dial -Temp. compensating bypass valve exists -Changes in temp are. constant (room & cooling due to vaporization) -Bypass valve will open and allow gas to bypass vaporizer chamber
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Never tilt the vaporizers beyond
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45 degrees If it is tilted, the vaporizer must be drained and dried or gas delivery will be uncertain
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The vaporizer interlock ensures that
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-Only one vaporizer is turned on -Gas enters only the one which is on -Trace vapor output is minimized when the vaporizer is off -Vaporizers are locked into the gas circuit, thus ensuring they are seated correctly.
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If wrong agent in vaporizer
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Most modern vaporizers have agent specific fill devices which virtually eliminate this from happening but,if it does happen, an unknown concentration of gas will be delivered to the patient.
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Vapor output with wrong vapor in vaporizer
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HLH: Higher Vp agent in Lower vp vaporizer chamber = higher concentration delivered. LHL: If lower vp agent is in higher vp vaporizer chamber = lower concentration will be delivered. *If this occurs, must empty, flush with 100% oxygen gas and dry
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What type of vaporizer is used for Desflurane
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TEC 6 vaporizer
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TEC 6 Vaporizers
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-Made specifically for Desflurane -Vapor pressure of Des is 3-4 x's that of other inhaled anesthetics -Boils at approx. 22.8 degrees C -Electrically heated -To approx. 39 degrees C -If not heated the large amounts of desflurane required (d/t MAC value 4-9 x's other IA's) would cause excessive cooling of the vaporizer making conventional temperature compensating mechanism ineffective
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Breathing system
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-The function of any breathing system is to deliver oxygen and anesthetic gases, and eliminate carbon dioxide *CÓ2 washout is accomplished either with adequate fresh gas flow (FGF) or by soda lime absorption (or other neutralizing chemicals.) -The components of the circle system help us avoid the problems of pollution in the O.R. environment, anesthetic agent wastage ; loss of patient heat and humidity caused by the high fresh gas flows required by the Mapleson circuits.
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2 ways CÓ2 can be washed out
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Fresh gas flow or Chemical neutralization of CÓ2
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APL valve: aka "pop-off valve"
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-Limits amount of pressure inside the patient's lungs during manual ventilation -If pressure reaches the setting of the APL knob, the valve opens and allows excess gas to escape to the scavenging system -Turning knob to right (closing) increases the pressure -Turning to left (opening) decreases the pressure
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Manual ventilation: (i.e. spontaneous, or hand(bag)/mask)
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Amount of oxygen flowing to patient is controlled by APL valve
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APL valve closed when mask ventilating a patient
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Pt may receive back pressure related to too much flow built up inside ambu bag. Build up of PEEP. Ambu bag will be over inflated
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APL valve too open
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If too open no pressure will build up within ambu bag. ambu bag will remain deflated and pt will not receive oxygen.
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CÓ2 absorbents
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2 most common types: Soda lime (most common) Baralyme Also Amsorb exsists
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CÓ2 absorbent flow (image)
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Turns purple as it becomes exhausted.
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Mesh size is
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A compromise between absorptive capacity and resistance to flow. Do not want mesh size to be too large, so that patient can blow against it. Not too much resistance, not too little. Must be 4-8.
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Indicator dye
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Ethyl violet *note: even exhausted absorbent will turn white if not used and allowed to cool, but will quickly return to purple once heated.
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Final products of CÓ2 neutralization
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Carbonates + Water + Heat
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Amsorb
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More costly Does not form compound A or carbon monoxide
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Toxic Products
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Sevoflurane interacts with strong bases in soda lime or baralyme to form degradation products that are toxic to kidneys in animals in high concentrations Compound A
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Compound A chemical makeup
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Fluoromethyl-2,2,-difuro-1-(trifluromethyl) vinyl ether
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Factors that increase Compound A
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-Total gas flow rates below 1 L/min -Use of baralyme rather than soda lime -High absorbent temperatures (if feel very hot absorbent canister, change it) -High concentration of sevoflurane -Drying of the carbon dioxide absorbent -Fresh soda lime (is very dry initially because it hasn't been dampened yet from use) -Machine on all night -Length of anesthetic
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Carbon Monoxide formation
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-Desflurane, isoflurane ; enflurane with absorbents produces carbon monoxide. *Higher levels with desflurane, then enflurane, then isoflurane* -High concentrations with absorbers that have not been used for 24 hours or ;
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Factors increasing CO
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Use of baralyme rather than soda lime Higher temperatures in absorber Dry absorbent*** High anesthetic concentrations Increase length of time
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Unidirectional valves are
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Inspiration and expiration. On inspiration, inspiratory valve should flutter and on expiration, expiratory valve should flutter
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Machine selector valve
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allows the selection of manual or mechanical ventilation. Isolates Apl valve from rest of system *When pt placed on ventilator mode, APL valve (as a safety mechanism) needs to be left open.
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Tidal Volume
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volume of gas entering or leaving the patient during the inspiratory or expiratory phase time
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Minute Volume
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sum of the tidal volumes in one minute
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Ventilatory frequency
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number of respiratory cycles per minute
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Inspiratory flow time
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the period between the beginning and end of inspiratory flow
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Inspiratory pause time
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Period from the end of inspiratory flow to the start of excitatory flow
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Inspiratory phase time
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period of time between the start of inspiratory flow and the beginning of expiratory flow, or it is the sum of the inspiratory flow time and the inspiratory pause time.
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Excitatory flow time
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time between the beginning and end of expiration
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Excitatory pause time
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Interval from the end of excitatory flow to the start of inspiratory flow
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Excitatory phase time
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Time between the start of expiratory flow and the start of inspiratory flow or it is the sum of the expiratory flow time and the expiratory pause time
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Inspiratory and expiratory phase time ratio
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I:E ratio is the ratio of inspiratory phase time to expiratory phase time. Normal is 1:2
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Inspiratory flow rate:
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volume of gas per unit time that passes from the patient connection of the breathing system to the patient
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Excitatory flow rate
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volume of gas per unit time returned from the patient during the expiratory phase
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Resistance
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pressure difference per unit flow across the airway; it usually increases as flow increases
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Compliance
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ratio of a change in volume to a change in pressure
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Anesthesia ventilator power source
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Compressed gas, electricity or both -Modern "piston ventilators" do not require driving gas, all mechanical and electronic -Contemporary bellows require both
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Bellows
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-the bellows is housed in a chamber and the inside of the bellows is connected to the breathing system. -the bellows separates breathing system gases from driving gas Inside the bellows there is both fresh gas and inspiratory gas
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Minute ventilation calculated by
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MV = TV x RR
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Two sets of gases
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Driving Gas - outside the bellows Patient Gas - inside the bellows
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Control panel
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VT, RR, MV, I:E ratio
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VT setting
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10-15 ml/kg (depending on ETCÓ and PIP)
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I:E ratio
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Uses 1 for the inhalation time and an appropriate number expressing the relative length for exhalation time. Usually start with 1:2
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National Institute for Occupational Safety and Health (NIOSH) recommends limiting room concentration of:
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N2O : 25 ppm Halogenated agents: 2 ppm Halogenated agents with N2O : 0.5 ppm
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Scavenger system transfer tubing is
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19 or 30 mm, sometimes yellow color-coded
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Components of the scavenger system
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Gas collection assembly Transfer tubing Scavenging interface Gas disposal tubing Gas disposal assembly
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Scavenging System - active
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-Connects to the hospital suction system -Positive ; negative pressure relief valves protects the patient from the negative pressure of the vacuum system and positive pressure of an obstruction in the disposal system -3 liter reservoir bag is present which hold excess gas until it can be removed -Vacuum control valve is adjusted to 10-15 L of waste gas per minute
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Scavenging system - passive
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-Interfaces with the hospital ventilation duct -Relies on the build-up of gases in the bag to passively empty into the hospital ventilation system (passive not very common)
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Parts of the machine that receive gas at cylinder pressure - high pressure system
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Hanger yoke Hanger yoke check valve Cylinder pressure regulator Cylinder pressure gauge *all drop pressure to 45 psi
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Intermediate pressure system
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Receives gases at relatively low and constant pressures (16-55psi/pipeline pressures) -Pipeline inlets and pressure gauges -Ventilator power outlet accessory -Ó2 flush valve -Supply failure alarm system -Second stage pressure regulator -Flowmeter valves *note After pressure relief valve on hanger yolk dropped to 45psi, then intermediate pressure system drops to 16-55psi
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Low pressure system
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Components distal to the flowmeter needle -Flowmeter tubes -Vaporizers -Temperature compensating bypass valve -Common gas outlet *note: Gas from flowmeter to patient
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Alarms that must remain on
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breathing circuit pressure, oxygen concentration, exhaled volume or carbon dioxide (or both).
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PISS
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-Pin Index and Safety System -Used for the hanger yoke system -Prevents misconception of a cylinder to the wrong yoke
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The Hanger Yoke System is
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Where the backup cylinders are in the machine, normally in the back
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The Hanger Yoke System
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-clamping device resists leaks ; contains a filter. -must have a check valve to prevent transfilling ; a cylinder pressure gauge. -There must be cylinder pressure regulators, to reduce the cylinder pressure (2200psi) to 40-45psi. -The machine must use pipeline gas as long as pipeline pressure is greater than 50 psi.
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Flowmeters
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-Single control for each gas -Uniquely shaped oxygen flow control knob -Valve stops (or other mechanism) so that excessive rotation will not damage the flowmeter. -Oxygen must enter the common manifiold downstream of other gases -An oxygen flush is present, capable of 35-75 L/min flow which does not proceed through any vaporizers.
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Vaporizers safety mechanisms
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-Concentration-calibrated -An interlock must be present Avoids 2 gases being. turned on simultaneously -Liquid level indicated, to prevent overfilling -No discharge of liquid anesthetic occurs from the vaporizer even at maximum fresh gas flow
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Common gas outlet
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Only one common gas outlet at 22 mm outer diameter, 15 mm inner diameter, which is designed to prevent accidental disconnection
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DISS
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Diameter Indexing Safety System: Safety mechanism for wall connections
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Check valve
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drops the pressure coming into the machine from the backup cylinder to 40-45 psi and from the wall to 50 psi.
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Oxygen supply from a central supply source
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-Enters machine through a pipeline (wall supply) -Enters at a PSI (pressure per square inch) of 50-55 -Inlets are indexed for specific gas DISS (Diameter Index Safety System) - non-interchangeable connections
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Check valves are located: upstream or downstream?
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downstream (closer to the machine) from the pipeline inlet to prevent reverse flow of gases -thereby avoiding flow of gas from machine to wall supply
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Cylinder pressure
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Cylinder pressure -measured by a bourdon pressure gauge -Ó2 = 2000-2200 psi (multiply by 0.3 to convert psi to Liters) -N2O = 750 psi A cylinder pressure regulator converts cylinder pressure to a constant pressure of ~45 psi downstream of the regulator -This is intentionally slightly less than the pipeline pressure because the machine will use the gas from the source with the higher pressure. This will also help prevent the silent depletion of cylinder contents if a cylinder is inadvertently left open after machine checks
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Time to Ó2 cylinder exhaustion
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-Time to exhaustion is calculated by dividing the remaining Ó2 volume in the cylinder by the rate of Ó2 consumption -Remaining volume in liters (L) in an E cylinder is calculated by dividing the cylinder pressure by 2200 psig then multiplying by 660 L -Example: Cylinder gauge reads 1,000 psig 1000 psig/2200 psig x 660 L 0.45 x 660 = 300 L remaining in the tank *note: If pt is being mechanically ventilated, the machine uses some Ó from the tank to drive the bellows. MV = TV X RR. 2200psi = amount in a full tank.
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Ó2 consumption during mechanical ventilation
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Ó2 flowmeter rate + (minute ventilation) *Example*: -FGF is 0.5 LPM Ó2 ; 1.0 LPM of N2O (total fresh gas flow = 1.5LPM) -Ventilator setting: TV: 0.7 L ; RR: 10 bpm ( 7 LPM) (mv = TVxRR) -0.5 + 7 = 7.5 LPM ( Ó2 Consumption) *Expected time to exhaustion 300 L / 7.5 LPM ~40 minutes remaining (ignoring gas sampled by the gas analyzer and circuit leaks) -Time to exhaustion during non-mechanical ventilation???? LPM/(Liters remaining in tank) e.x. 7.5LPM/300L
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N2O cylinders
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-N20 will read 745 psig until all the liquid in the cylinder has vaporized to gas -It can be assumed that 75% of N2O cylinder gas has been exhausted when a decrease in N20 pressure is observed (Gauge reads ; 745 psig) ***The volume of N2O cylinder cannot be determined based on the psig***
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Wood's Metal
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A safety device that melts under excessive heat (;200 degrees F) to allow the gas to escape preventing an explosion
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Joule Thompson Effect
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"Joule is cool" Cooling effect once compressed gas is allowed to escape in open space
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Adiabatic Heat of Compression
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Compression of cylinder contents into a small space generates heats and may cause combustion
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PSIG numbers
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Ó2 - 2200 N2O - 745 Air - 1900
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USA Colors
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Ó2 - Green N2O - Blue Air - Yellow
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Capacity (L)
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Ó2 - 660 N20 - 1590 Air - 625
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PISS
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Ó2 - 2-5 N2O - 3-5 Air - 1-5
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What is Critical Temperature
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The critical value at which a gas is pressured and forms a liquid, low temperature Above critical temperature, gas will remain in gaseous state
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Critical Temperature of Ó2 and N2O
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Oxygen: -119 degrees C N2O: 39.5 degrees C, hence why it's liquid in the tank
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Celsius and Fahrenheit conversion
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Multiply Celsius temp by 9/5 Add 32 degrees Example: convert 37* C to Fahrenheit. 37 * 9/5 = 333/5 = 66.6 66.6 + 32 = 98.6* F
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Supply failure alarm system
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4. Activated when Ó2 falls below 28 psi Alarms sounds before 25 psi, the point at which N2O flow will cease
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Second stage pressure regulator
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5. Gas pressure is decreased to a constant pressure of 16 psi as flow from wall varies at times between 40-50psi After passing 2nd stage pressure regulator, sits in "stand by" at flow control valve
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Flowmeter safety mechanisms
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-Tubes are hand calibrated and no two tubes are alike -Gas specific and are not interchangeable between machines and gases
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Sequence of flowmeter safety mechanism
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Sequence of flowmeter tubes is very important to decrease chance of hypoxic mixture. -Gas flow is from left to right -Ó2 is always to the Right or Downstream of all other gases and closest to the manifold outlet -Any leak in flowmeters will vent other gases out before Ó2. -Decreases the chance that Ó2 will be diluted or lost
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Flowmeter: Interlink Mechanism /Proportioning System
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-Flow valves linked mechanically or pneumatically so Ó2 cannot be set below 25% -Ensures adequate % of Ó2 delivery and prevents hypoxic mixture -Ó2 flow control spindle is connected to the N2O spindle, so that if Ó2 goes down, N2O goes down also, and if N2O goes up Ó2 level will go up also if Ó2 % drops below room air percent
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Interlink mechanism
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-Ó2 spindle is Connected to n2o spindle If you incr. N2O flow then Ó2 flow will incr. If you incr. Ó2 flow; N2O will not incr. If you decr. N2O flow; Ó2 flow will not decr. FYI: -The N2O spindle has 14 teeth -The Ó2 spindle has 29 teeth -So......If you rotate the N2o knob 2.07 times, the Ó2 will rotate once
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Vaporizers
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-Volatile anesthetics are liquids at room temperature and atmospheric pressure -Vaporization is the conversion of liquid to vapor - takes place in a closed container referred to as a vaporizer -The energy necessary for molecules to escape from the liquid to enter the gas phase is supplied as heat -Heat of Vaporization = the number of calories required at a specific temperature to convert 1 G of liquid to vapor
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Vaporizers are:
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-Agent specific, precisely calibrated to compensate to changes in temperature and variations of gas flow -Constructed of metals with high thermal conductivity, allowing heat to flow from the vaporizer in to the anesthetic in the liquid phase, supplying the energy for the heat of vaporization
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Vaporizer flow pattern
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-Ó2 (Ó2 + N2O) enter vaporizer and pass through a filter A relief valve exists which will open if gas flow exceeds that which is required for delivery of gas conc. on dial -Temp. compensating bypass valve exists -Changes in temp are. constant (room & cooling due to vaporization) -Bypass valve will open and allow gas to bypass vaporizer chamber
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Never tilt the vaporizers beyond
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45 degrees If it is tilted, the vaporizer must be drained and dried or gas delivery will be uncertain
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The vaporizer interlock ensures that
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-Only one vaporizer is turned on -Gas enters only the one which is on -Trace vapor output is minimized when the vaporizer is off -Vaporizers are locked into the gas circuit, thus ensuring they are seated correctly.
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If wrong agent in vaporizer
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Most modern vaporizers have agent specific fill devices which virtually eliminate this from happening but,if it does happen, an unknown concentration of gas will be delivered to the patient.
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Vapor output with wrong vapor in vaporizer
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HLH: Higher Vp agent in Lower vp vaporizer chamber = higher concentration delivered. LHL: If lower vp agent is in higher vp vaporizer chamber = lower concentration will be delivered. *If this occurs, must empty, flush with 100% oxygen gas and dry
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What type of vaporizer is used for Desflurane
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TEC 6 vaporizer
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TEC 6 Vaporizers
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-Made specifically for Desflurane -Vapor pressure of Des is 3-4 x's that of other inhaled anesthetics -Boils at approx. 22.8 degrees C -Electrically heated -To approx. 39 degrees C -If not heated the large amounts of desflurane required (d/t MAC value 4-9 x's other IA's) would cause excessive cooling of the vaporizer making conventional temperature compensating mechanism ineffective
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Breathing system
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-The function of any breathing system is to deliver oxygen and anesthetic gases, and eliminate carbon dioxide *CÓ2 washout is accomplished either with adequate fresh gas flow (FGF) or by soda lime absorption (or other neutralizing chemicals.) -The components of the circle system help us avoid the problems of pollution in the O.R. environment, anesthetic agent wastage ; loss of patient heat and humidity caused by the high fresh gas flows required by the Mapleson circuits.
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2 ways CÓ2 can be washed out
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Fresh gas flow or Chemical neutralization of CÓ2
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APL valve: aka "pop-off valve"
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-Limits amount of pressure inside the patient's lungs during manual ventilation -If pressure reaches the setting of the APL knob, the valve opens and allows excess gas to escape to the scavenging system -Turning knob to right (closing) increases the pressure -Turning to left (opening) decreases the pressure
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Manual ventilation: (i.e. spontaneous, or hand(bag)/mask)
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Amount of oxygen flowing to patient is controlled by APL valve
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APL valve closed when mask ventilating a patient
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Pt may receive back pressure related to too much flow built up inside ambu bag. Build up of PEEP. Ambu bag will be over inflated
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APL valve too open
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If too open no pressure will build up within ambu bag. ambu bag will remain deflated and pt will not receive oxygen.
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CÓ2 absorbents
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2 most common types: Soda lime (most common) Baralyme Also Amsorb exsists
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CÓ2 absorbent flow (image)
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Turns purple as it becomes exhausted.
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Mesh size is
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A compromise between absorptive capacity and resistance to flow. Do not want mesh size to be too large, so that patient can blow against it. Not too much resistance, not too little. Must be 4-8.
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Indicator dye
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Ethyl violet *note: even exhausted absorbent will turn white if not used and allowed to cool, but will quickly return to purple once heated.
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Final products of CÓ2 neutralization
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Carbonates + Water + Heat
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Amsorb
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More costly Does not form compound A or carbon monoxide
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Toxic Products
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Sevoflurane interacts with strong bases in soda lime or baralyme to form degradation products that are toxic to kidneys in animals in high concentrations Compound A
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Compound A chemical makeup
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Fluoromethyl-2,2,-difuro-1-(trifluromethyl) vinyl ether
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Factors that increase Compound A
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-Total gas flow rates below 1 L/min -Use of baralyme rather than soda lime -High absorbent temperatures (if feel very hot absorbent canister, change it) -High concentration of sevoflurane -Drying of the carbon dioxide absorbent -Fresh soda lime (is very dry initially because it hasn't been dampened yet from use) -Machine on all night -Length of anesthetic
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Carbon Monoxide formation
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-Desflurane, isoflurane ; enflurane with absorbents produces carbon monoxide. *Higher levels with desflurane, then enflurane, then isoflurane* -High concentrations with absorbers that have not been used for 24 hours or ;
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Factors increasing CO
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Use of baralyme rather than soda lime Higher temperatures in absorber Dry absorbent*** High anesthetic concentrations Increase length of time
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Unidirectional valves are
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Inspiration and expiration. On inspiration, inspiratory valve should flutter and on expiration, expiratory valve should flutter
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Machine selector valve
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allows the selection of manual or mechanical ventilation. Isolates Apl valve from rest of system *When pt placed on ventilator mode, APL valve (as a safety mechanism) needs to be left open.
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Tidal Volume
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volume of gas entering or leaving the patient during the inspiratory or expiratory phase time
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Minute Volume
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sum of the tidal volumes in one minute
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Ventilatory frequency
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number of respiratory cycles per minute
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Inspiratory flow time
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the period between the beginning and end of inspiratory flow
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Inspiratory pause time
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Period from the end of inspiratory flow to the start of excitatory flow
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Inspiratory phase time
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period of time between the start of inspiratory flow and the beginning of expiratory flow, or it is the sum of the inspiratory flow time and the inspiratory pause time.
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Excitatory flow time
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time between the beginning and end of expiration
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Excitatory pause time
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Interval from the end of excitatory flow to the start of inspiratory flow
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Excitatory phase time
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Time between the start of expiratory flow and the start of inspiratory flow or it is the sum of the expiratory flow time and the expiratory pause time
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Inspiratory and expiratory phase time ratio
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I:E ratio is the ratio of inspiratory phase time to expiratory phase time. Normal is 1:2
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Inspiratory flow rate:
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volume of gas per unit time that passes from the patient connection of the breathing system to the patient
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Excitatory flow rate
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volume of gas per unit time returned from the patient during the expiratory phase
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Resistance
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pressure difference per unit flow across the airway; it usually increases as flow increases
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Compliance
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ratio of a change in volume to a change in pressure
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Anesthesia ventilator power source
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Compressed gas, electricity or both -Modern "piston ventilators" do not require driving gas, all mechanical and electronic -Contemporary bellows require both
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Bellows
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-the bellows is housed in a chamber and the inside of the bellows is connected to the breathing system. -the bellows separates breathing system gases from driving gas Inside the bellows there is both fresh gas and inspiratory gas
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Minute ventilation calculated by
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MV = TV x RR
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Two sets of gases
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Driving Gas - outside the bellows Patient Gas - inside the bellows
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Control panel
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VT, RR, MV, I:E ratio
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VT setting
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10-15 ml/kg (depending on ETCÓ and PIP)
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I:E ratio
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Uses 1 for the inhalation time and an appropriate number expressing the relative length for exhalation time. Usually start with 1:2
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National Institute for Occupational Safety and Health (NIOSH) recommends limiting room concentration of:
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N2O : 25 ppm Halogenated agents: 2 ppm Halogenated agents with N2O : 0.5 ppm
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Scavenger system transfer tubing is
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19 or 30 mm, sometimes yellow color-coded
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Components of the scavenger system
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Gas collection assembly Transfer tubing Scavenging interface Gas disposal tubing Gas disposal assembly
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Scavenging System - active
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-Connects to the hospital suction system -Positive ; negative pressure relief valves protects the patient from the negative pressure of the vacuum system and positive pressure of an obstruction in the disposal system -3 liter reservoir bag is present which hold excess gas until it can be removed -Vacuum control valve is adjusted to 10-15 L of waste gas per minute
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Scavenging system - passive
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-Interfaces with the hospital ventilation duct -Relies on the build-up of gases in the bag to passively empty into the hospital ventilation system (passive not very common)
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Parts of the machine that receive gas at cylinder pressure - high pressure system
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Hanger yoke Hanger yoke check valve Cylinder pressure regulator Cylinder pressure gauge *all drop pressure to 45 psi
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Intermediate pressure system
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Receives gases at relatively low and constant pressures (16-55psi/pipeline pressures) -Pipeline inlets and pressure gauges -Ventilator power outlet accessory -Ó2 flush valve -Supply failure alarm system -Second stage pressure regulator -Flowmeter valves *note After pressure relief valve on hanger yolk dropped to 45psi, then intermediate pressure system drops to 16-55psi
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Low pressure system
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Components distal to the flowmeter needle -Flowmeter tubes -Vaporizers -Temperature compensating bypass valve -Common gas outlet *note: Gas from flowmeter to patient
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Alarms that must remain on
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breathing circuit pressure, oxygen concentration, exhaled volume or carbon dioxide (or both).
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PISS
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-Pin Index and Safety System -Used for the hanger yoke system -Prevents misconception of a cylinder to the wrong yoke
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The Hanger Yoke System is
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Where the backup cylinders are in the machine, normally in the back
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The Hanger Yoke System
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-clamping device resists leaks ; contains a filter. -must have a check valve to prevent transfilling ; a cylinder pressure gauge. -There must be cylinder pressure regulators, to reduce the cylinder pressure (2200psi) to 40-45psi. -The machine must use pipeline gas as long as pipeline pressure is greater than 50 psi.
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Flowmeters
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-Single control for each gas -Uniquely shaped oxygen flow control knob -Valve stops (or other mechanism) so that excessive rotation will not damage the flowmeter. -Oxygen must enter the common manifiold downstream of other gases -An oxygen flush is present, capable of 35-75 L/min flow which does not proceed through any vaporizers.
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Vaporizers safety mechanisms
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-Concentration-calibrated -An interlock must be present Avoids 2 gases being. turned on simultaneously -Liquid level indicated, to prevent overfilling -No discharge of liquid anesthetic occurs from the vaporizer even at maximum fresh gas flow
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Common gas outlet
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Only one common gas outlet at 22 mm outer diameter, 15 mm inner diameter, which is designed to prevent accidental disconnection
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DISS
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Diameter Indexing Safety System: Safety mechanism for wall connections
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Check valve
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drops the pressure coming into the machine from the backup cylinder to 40-45 psi and from the wall to 50 psi.
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Oxygen supply from a central supply source
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-Enters machine through a pipeline (wall supply) -Enters at a PSI (pressure per square inch) of 50-55 -Inlets are indexed for specific gas DISS (Diameter Index Safety System) - non-interchangeable connections
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Check valves are located: upstream or downstream?
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downstream (closer to the machine) from the pipeline inlet to prevent reverse flow of gases -thereby avoiding flow of gas from machine to wall supply
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Cylinder pressure
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Cylinder pressure -measured by a bourdon pressure gauge -Ó2 = 2000-2200 psi (multiply by 0.3 to convert psi to Liters) -N2O = 750 psi A cylinder pressure regulator converts cylinder pressure to a constant pressure of ~45 psi downstream of the regulator -This is intentionally slightly less than the pipeline pressure because the machine will use the gas from the source with the higher pressure. This will also help prevent the silent depletion of cylinder contents if a cylinder is inadvertently left open after machine checks
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Time to Ó2 cylinder exhaustion
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-Time to exhaustion is calculated by dividing the remaining Ó2 volume in the cylinder by the rate of Ó2 consumption -Remaining volume in liters (L) in an E cylinder is calculated by dividing the cylinder pressure by 2200 psig then multiplying by 660 L -Example: Cylinder gauge reads 1,000 psig 1000 psig/2200 psig x 660 L 0.45 x 660 = 300 L remaining in the tank *note: If pt is being mechanically ventilated, the machine uses some Ó from the tank to drive the bellows. MV = TV X RR. 2200psi = amount in a full tank.
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Ó2 consumption during mechanical ventilation
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Ó2 flowmeter rate + (minute ventilation) *Example*: -FGF is 0.5 LPM Ó2 ; 1.0 LPM of N2O (total fresh gas flow = 1.5LPM) -Ventilator setting: TV: 0.7 L ; RR: 10 bpm ( 7 LPM) (mv = TVxRR) -0.5 + 7 = 7.5 LPM ( Ó2 Consumption) *Expected time to exhaustion 300 L / 7.5 LPM ~40 minutes remaining (ignoring gas sampled by the gas analyzer and circuit leaks) -Time to exhaustion during non-mechanical ventilation???? LPM/(Liters remaining in tank) e.x. 7.5LPM/300L
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N2O cylinders
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-N20 will read 745 psig until all the liquid in the cylinder has vaporized to gas -It can be assumed that 75% of N2O cylinder gas has been exhausted when a decrease in N20 pressure is observed (Gauge reads ; 745 psig) ***The volume of N2O cylinder cannot be determined based on the psig***
