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87 Cards in this Set
- Front
- Back
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anesthesia workstation comprises the
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anesthesia machine, vaporizer, ventilator, monitors, and
alarm systems |
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anesthesia delivery system comprises the
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workstation, breathing system, and
waste gas scavenging system |
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what type of gases are compressed
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oxygen, nitrous oxide, air and/or heliox
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two sources for these gases
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tank or pipeline supply
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a controlled gas mixture of these gases is then delivered to the
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vaporizer
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after a desired concentration of potent inhaled anesthetic is added - it goes to
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the patient circuit, which is most commonly a circle breathing system
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The patient’s body will tend to equilibrate with the gas mixture in the breathing circuit to produce the desired
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PaCO2 and PaO2
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in the United States, the two largest manufacturers of anesthesia delivery systems are
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Dräger and Datex-Ohmeda (a Division GE)
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Oxygen (O2) has a molecular weight of
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32 AMU
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The molecular weight can be used to calculate the .
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density (mass per unit volume) of the gas
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by Avogadro’s Volume - 1 gram molecular weight (ie, the molecular weight in grams) of any gas or vapor occupies
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22.4 liters at STP - 0°C/760 mm Hg
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Gases expand when
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temperature increases
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According to Charles’ Law
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the volume of a fixed mass of gas is directly proportional to Absolute temperature
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Room temperature is usually
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20°C or 293 Kelvin
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Therefore, 32 grams of oxygen will occupy
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22.4 x 293/273, or 24 L at
20°C. |
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Oxygen boils at a temperature of
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-183° C at 1 atm/760 torr/14.7psi
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The boiling point of a liquid oxygen (oxygen changes from liquid to gas) is related to
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ambient pressure such that as pressure increases so does the
boiling point |
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a certain critical temperature is reached above when
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no matter how much pressure is applied, the liquid oxygen will boil into the gaseous form.
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The critical temperature for oxygen is
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-118°C
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critical pressure is
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pressure which must be applied at this specific temperature
to keep oxygen liquid |
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critical pressure which must be applied 20°C to keep oxygen liquid
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737 PSIA
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so, why is oxygen gas at room temperature
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Because room temperature
is 20°C and is well above oxygen’s critical temperature so oxygen can exist only as a gas at room temperature. In many |
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Since the bulk oxygen storage vessel is outside the building and are subjected to extremes of temperature.
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The vessel incorporates a safety relief valve that permits oxygen gas to be released into the atmosphere if there is an increase in ambient
temperature causing the pressure in the vessel to exceed a certain threshold |
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a pressure regulator that maintains the
hospital’s pipeline pressure at |
50-55 psig or 64.7 psia
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what color hose is used for the oxygen pipeline
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green
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The oxygen hose connection on the back of the machine (not quick connect)
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gas-specific by diameter, using
the nationally standardized diameter-indexed safety system (DISS). |
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The diameters of the connections for oxygen, air, nitrous oxide, and vacuum all are
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of unique sizes.
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All anesthesia machines have a back-up supply of
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oxygen stored in a tank
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Most machines are equipped with one or two ___ cylinders of oxygen
that hang on ______ |
E, oxygen-specific yokes
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Oxygen tanks are filled to a pressure of about
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1900 PSIG at room temperature
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A full E cylinder at a pressure of 1900 PSIA will evolve
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660 L of gaseous oxygen at an atmospheric pressure of 14.7
PSIA |
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Because of Boyle's Law - the internal volume (V1) of an E cylinder is approximately
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5 L because 1900xV1=14.7x660
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tank pressure gauge can be used to
estimate how much oxygen gas remains - is evolved from |
Boyle’s law
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If an E cylinder oxygen tank pressure gauge reads 1000 PSIG - what % full and how many L of oxygen are available?
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then the tank is 52% full, and will generate (660L x 0.52) or 340 L of oxygen
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If such a tank was being drained at a rate of 6 L/minute, it would empty in
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just under 1 hour (actually 340/6 = 57 minutes
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If the system has two oxygen tanks, why should only one should be on at any time
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so that both are not emptied
simultaneously! |
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There are two pins in the hanger yoke that mate with two corresponding holes
in the oxygen tank valve. |
This is the nationally standardized
medical gas pin index system (PISS) |
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high pressure system for oxygen is defined as
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all those components upstream of the oxygen flow control (usually a needle) valve that is used to control the flow of oxygen from the flowmeters
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While the pipeline supply of oxygen enters the machine at a pressure of 50 PSIG, the tank supply enters the hanger yoke at pressures of
up to |
2200 PSIG
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The pressure of the oxygen coming from the tank source is therefore down-regulated and enters the machine high pressure system at a nominal pressure of
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45 PSIG
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A pressure regulator valve is a device that
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reduces a variable high input pressure to a constant low output pressure for the gas whose pressure is being regulated
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The tank supply serves as a back-up in case the
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pipeline fails
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once the tank has been checked, it should be
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turned OFF
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If the oxygen tank is left open and the
machine is being supplied from the pipeline |
oxygen is drawn preferentially from the pipeline (50 PSIG)
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why should the oxygen tank be turned OFF
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(1) to prevent the tank oxygen supply being drawn down and unintentionally depleted
(2) if the connection between the tank and its hanger yoke was not gas-tight, tank oxygen could leak to the atmosphere and not be available when needed. |
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oxygen at a pressure of 45 PSIG (from tank) or 50 PSIG (from pipeline), oxygen may flow in
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seven directions
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Name the seven directions
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1. power source for a pneumatically
driven anesthesia ventilator 2. supplies the auxiliary oxygen flowmeter 3. supplies oxygen to an auxiliary oxygen DISS fitting 4. oxygen flush control (valve) is opened by rate of 35-75 LPM (45-50 PSIG) 5. pressurizes an oxygen supply pressure failure alarm system 6. pressurizes and opens the “fail-safe” valve 7. passes to the oxygen flow control valve |
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nitrous oxide is supplied from a pipeline system to wall outlets in the operating room at (pressure)
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50 PSIG
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N2O is also supplied from
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from a back-up E cylinder tank supply on the machine
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Nitrous oxide has a molecular weight of
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44 AMU
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Nitrous oxide boils at
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-88°C at 1 atm
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Nitrous oxide has a critical temperature
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36.5°C
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Nitrous oxide has critical pressure of
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1054 PSIA - it can exist as a liquid at
room temperature (20°C). |
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E cylinders of nitrous oxide are
filled to and above the liquid is gaseous nitrous oxide. |
90-95% capacity with liquid nitrous oxide
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What is SVP saturated vapor pressure
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liquid agent is in equilibrium with its gas phase at the ambient temperature.
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The SVP saturated vapor pressure of nitrous oxide at 20°C is about
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750 PSIG, or 51 atmospheres
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A full E cylinder of nitrous oxide will provide
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1600 L of gas at one atm
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As long as some liquid nitrous oxide is present in the tank and the ambient temperature remains at 20°C
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the pressure in the nitrous oxide tank will remain at about 750 PSIG
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how do you determine the content of a nitrous oxide tank
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by weighing the tank and subtracting the weight of the empty tank (TARE
WEIGHT) |
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to determine what weight of nitrous oxide
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by Avogadro’s volume, 44 g of nitrous oxide occupy 22.4 L at standard temperature and pressure, or 24 L at 20°C.
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Once all of the liquid nitrous oxide has been used up and the tank contains only gaseous nitrous oxide
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Boyle’s Law may be applied to the gas remaining - P1V1=P2V2
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high pressure system for nitrous oxide consists of
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those parts upstream of the nitrous oxide flow control needle valve (like O2)
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Nitrous oxide from the tank supply enters the nitrous oxide hanger yoke at pressures of ~750 PSIG and then passes through a nitrous oxide regulator that reduces the pressure to
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45 PSIG.(like O2)
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there is a pressure differential between the pipeline supply pressure and that from the nitrous oxide tank - this means
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that if both sources are available and
the nitrous oxide tank has been left open, the pipeline source will preferentially be used (like O2) |
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Having entered the anesthesia machine high pressure system for nitrous oxide, the gas must flow past the
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“fail safe” valve (OFPD or PSSV) before reaching the nitrous oxide flow control valve
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All gas fittings in the OR and on the anesthesia machine are indexed and are
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non-interchangeable among specific medical gases
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Specificity of tank connections is ensured by the _____ in the hanger yoke, and for piped gases there are
_______ specific and proprietary quick-connect fittings |
pin-index safety system (PISS), diameter-indexed safety system (DISS)
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To adjust the proportions of
gases, as well as total gas flows delivered to the patient. For each gas (oxygen, nitrous oxide, etc.) this is achieved by means of: |
turning a knob that is connected to a needle valve - CCW (opens) allows more gas flow
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the oxygen knob
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is fluted rather than knurled so that it is touch-coded - it feels different from the knobs for the other gases
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Traditionally, gas flows on the conventional anesthesia machine are measured by using the
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rotameter flowmeter
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what would be the purpose of two rotameters in tandem for each gas
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the first permits accurate measurement of low flows (usually up to 1 L/min) and the other of flows of 10-12 L/minute.
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The rotameter is a
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constant pressure, variable orifice flowmeter, based on the Thorpe tube principle
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how does a rotameter work
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vertical tapered glass tube that is wide at top - small at bottom and contains a bobbin. Pressure difference across the bobbin is required to “float” the bobbin in the vertically upward flowing gas stream. At low gas flow rates, flow is essentially laminar and Poiseuille’s law applies
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Are flowmeters interchangeable
among gases |
No. Flowmeters must be calibrated for each different gas
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In contemporary machines, the flows of oxygen and nitrous oxide are
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interlinked so that a fresh gas mixture containing at least 25% oxygen is created at the level of the
flowmeters whenever oxygen and nitrous oxide are being used. |
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In the Drager Narkomed machines, the oxygen ratio monitor (ORM) provides an
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audible alarm upon the setting (and delivery) of low concentration oxygen mixtures
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The oxygen ratio monitor controller (ORMc) provides an
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additional pneumatic interlock to maintain the delivery of at least 25% oxygen
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How are Drager and Omeda different with protecting from low O2 levels while using N2O
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Drager ORMc serves to limit the
flow of nitrous oxide according to the set flow of oxygen, whereas the Ohmeda system increases the flow of oxygen as the nitrous oxide flow is increased |
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Why is an oxygen analyzer important in the patient circuit
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it is essential because it detects if a hypoxic gas mixture is to be detected and thereby prevented
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The pressure relief valve
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prevents the build-up of excessive pressures upstream
of the common gas outlet |
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The outlet check valve
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prevents reverse gas flow back into vaporizer and result in increased vaporizer output concentrations.
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anesthesia machine “ends” at the
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common gas outlet
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pressure sensitive components are
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fail safe, pressure sensor shut-off valves, OFPDs
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Contemporary proportioning systems may fail to prevent a hypoxic mixture if a 3 or 4 gas machine is being used because
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they proportion only N2O and O2
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disconnection at the common gas
outlet |
would result in anesthesia gases being spilled into the operating
room atmosphere, and would create a significant leak in the circle breathing system leading to collapse of the reservoir bag or ventilator standing bellows. |
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positive pressure leak check may be used
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on a machine that does not have an outlet check valve
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The oxygen analyzer
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is the only device that confirms the presence of oxygen, and does so in the gas mixture that flows to the patient’s airway via the inspiratory limb of the circle breathing system
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