Anesthesia Machine Flashcards
ASTM Standard F 1850
organization that covers anesthesia workstations and components
Which organization covers the anesthesia machine checkout?
FDA
What is the pressure in the breathing circuit limited to?
12.5 kPa or 125 cm H20 (valve will blow if exceeded)
The oxygen flush delivers flow at what rate? And what does it bypass?
35-75 L/min; vaporizers (dilutional effect)
What parts of the machine are exposed to high (cylinder) pressure?
hanger yoke, yoke block with check valves, and cylinder pressure gauge and regulators
What parts of the machine are exposed to intermediate (pipeline) pressure?
pipeline inlets/valves/gauges, oxygen pressure failure device, flowmeter valves, oxygen second stage regulator, flush valve
What parts of the machine are exposed to low pressure? (distal to flowmeter needle valve)
flowmeter tubes, vaporizers, check valves, common gas/fresh gas outlet
What are the 5 tasks of oxygen?
ventilator driving gas, flush valve, oxygen pressure failure alarm, oxygen pressure sensor shut-off valve (fail safe), flowmeters
What is the pressure from the pipelines?
45-55 psi
The oxygen cylinder pressure regulator reduces the pressure of 2000 psi from the cylinders to what pressure?
45 psi (slightly lower than pipeline so that gas is preferentially taken from pipeline)
What is the pressure of an oxygen cylinder and how many liters does it hold?
1900-2200 psi - 660L
What is the pressure of a nitrous cylinder and how many liters?
745 psi - 1590 L (pressure will read at 745 until liquid is gone- only way to know how many liters is to weigh it)
What is the pressure of an air cylinder and how many liters is it?
1900-2200 psi for 625 L
When should you change an oxygen cylinder?
1000 psi or less (330 L or less)
Boyle’s law
volume of gas INVERSELY proportional to pressure (temp is constant- think Boyle=boil= temp)
Ideal gas law
PV=nRT
Charles’ Law
volume is proportional to temperature (pressure is constant)
Gay Lussac’s law
pressure is proportional to temperature (volume is constant)
What is the critical temperature?
if sufficient pressure is applied, a gas will liquefy if BELOW a certain value
What are the critical temperatures of O2 and N2O?
O2 -119 C
N2O 39.5 C
Critical pressure
minimum pressure necessary to liquefy a gas at a critical temp
Temperature conversions
C= 5/9(F-32)
F=(9/5 x C) +32
What is the Joule- Thompson effect?
when gas is allowed to escape freely, process is adiabatic and cooling occurs
Why do you “crack” a cylinder before using it?
to remove dust from opening- if cylinder is opened rapidly in closed space, temp will rise quickly and heat cannot dissipate (adiabatic process)
What organization regulates gas cylinders?
department of transportation
What organization sets safe practices for medical gas cylinders?
Compressed Gas Association (CGA)
What are the PISS configurations for the 3 cylinders?
1-5 Air (think airway, 1)
2-5 oxygen (think O2)
3-5 nitrous
Describe a bourdon pressure gauge
measures RELATIVE pressure of high pressure systems (tanks), spring gauge type
Safe handling of cylinders
stand upright with support (if none, lay on side), do not leave empty cylinders on machine, take off plastic cover on port when installing, do not oil valves, place yoke plug if leaving space empty, never use more than one washer
What is DISS?
diameter index safety system (prevents interchange of pipeline gases)
What does the oxygen pressure failure device (failsafe) do?
If oxygen pressure falls below 30 psi, flow of second gas (nitrous) will be shut off- senses only pressure, not flow
What are the limitations of the fail safe device?
will not prevent admin of hypoxic mixture (anesthetic agent can still be delivered), only prevents problems of oxygen supply upstream, not downstream
What does the oxygen failure alarm do?
alert to loss of oxygen pressure (<20-30 psi)- audible whistle
What should you do if the O2 pipeline fails or there is a pipeline crossover?
- turn on O2 tank fully, disconnect pipeline
- make sure O2 analyzer increases in FiO2- if not, bag with Ambu
- use low flows, conserve O2
- call for help
- use IV anesthetic
What part of the breathing cycle should you use the O2 flush valve?
expiration (prevent barotrauma)
Graham’s law
gas diffuses at rate inversely proportional to square root of its molecular weight
Are flowmeters for different gases the same?
no- they are specific for each gas and cannot be interchanged
Low flows are dependent on ? whereas high flows are dependent on ?
viscosity (Poiseuille); density (Graham)
How to calculate FiO2
L of O2/total L (minus whatever % anesthetic agent is used)
Care of flowmeters
- should be turned off before pipeline connected to machine, cylinders opened, or machine turned on
- turn off flowmeters at the end of each case
What is the hypoxic mixture prevention device?
proportioning device- limits N20 flow to 3x that of O2
What are the 3 things that change flow from laminar to turbulent?
1- change in gas direction >20 degress
2- increased velocity
3- corrugated tubes
Bernoulli principle
increase in speed of fluid occurs simultaneously with decrease in pressure or decrease in fluid’s potential energy
Compliance
change in volume/change in pressure
What are influencing factors on rebreathing or previously respired gases and CO2?
fresh gas flow (amount of rebreathing inversely proportional), mechanical dead space (rebreathed without change in composition), breathing system design
Describe an open breathing system
no dead space, entrains room air and dilutes anesthetic, no valves or rebreathing bags, great heat loss (not used today)
Define apparatus dead space and where is it?
volume of the breathing system from the patient-end to the point up to which to and fro movement of expired gas takes place (between Y piece and patient)
Describe a semi-open system
Mapleson or ambu bag- CO2 may accumulate so you need high flows, has reservoir bag and one unidirectional valve, allows for room pollution
(mapleson A picture)
- Mapleson A
- FGF enters near reservoir bag
- most efficient for spontaneous ventilation
- no rebreathing if FGF>alveolar ventilation
- should not be used with mechanical ventilator
