Pass Machine - Physics/Monitors/Machine Flashcards
O2 E-cylinder volume and pressure
700L, 2200 psi
N2O E-cylinder volume and pressure
1600L, 750 psi
Intermediate pressure w/in machine
45 psi
Final pressure to patient w/in machine
15-25 psi
PISS vs DISS
DISS = wall gas outlets PISS = cylinder connections
Implication of one-way check valve in regards to O2 flush valve and leak test?
ONLY present in older Datex-Ohmeda machines, this check valve prevents any flow from flush valve to go backwards into the machine (vaporizer, flow meters, etc) –> all flush flow goes to patient
If present, then typical positive pressure leak test will ONLY test for leaks in the circle system and NOT the flow meters or vaporizers. Must do negative pressure leak test
During mechanical ventilation, measured FiO2 and tidal volume is HIGHER than expected. What is likely the problem?
Hole in bellows -> O2 that is driving the bellows instead enters the patient
Airflow in bottom vs top of flow meter
Bottom: tubular, laminar, viscosity-dependent (attraction of molecules to each other or to the tube)
Top: orificial, turbulent, density-dependent (number of molecules that get past the blockage)
Why is O2 the last gas to be mixed in?
If there is a hole in any flow meter, at MOST the O2 will leak in the same proportion as the other gases (if the hole is in the O2 flow meter).
What is the relationship between increasing temperature and vapor pressure: linear, curvilinear, sigmoidal, or parabolic?
Curvilinear - as temp rises further, slope of VP increase rises further
In a sevo vaporizer, when the liquid agent converts to gas within the chamber, what happens to the temperature within the chamber?
Why is this important?
It goes DOWN b/c endothermic reaction to cause vaporization
If temp drops, then vapor pressure drops and patient is under-dosed. SO, the vaporizer is temp-regulated such that MORE FGF will be diverted to get saturated with agent as the temp in the chamber goes down.
In very low FGF rates, what happens to vaporizer output? Why?
What about at very HIGH flow rates?
It DECREASES - without enough flow to cause an airstream effect, there will be less pick-up of anesthetic molecules
Still DECREASES - not enough time to completely mix with the anesthetic agent
Explain why you do not change the settings of a variable bypass vaporizer at high altitude?
At high altitude, there is less ambient pressure keeping the gas in liquid form, so you OD the patient in terms of anesthetic molecule #. BUT, dosing is related to partial pressure. SO, even though there is more gas % being delivered, they exert a correlated less partial pressure on the body and thus dosing remains constant
Explain why des vaporizer must be adjusted at altitude?
The gas molecules in the machine are directly injected into the FGF at a set % (NOT picked up by flowing through the vapor). So the number of anesthetic molecules being delivered is constant. BUT that same # of molecules now exerts LESS partial pressure and so you under-dose the patient. SO, you must increase the vaporizer setting to achieve the intended depth of anesthesia.
What is critical temperature of a gas?
Temp at which you cannot liquify a gas despite any amount of pressure
What is critical pressure of a gas?
Pressure at the critical temperature
Absolute humidity vs relative humidity
Absolute: total amount of water dissolved in the air
Relative: % of water molecules in the air compared to the maximum that could be held at a given temp (cold air holds less molecules, thus for any given absolute humidity, relative humidity is higher in cold air)
Open vs Semi-open vs Semi-closed vs Closed circuit
Open: no rebreathing, no reservoir
Semi-open: no rebreathing but has reservoir bag (ambu, mapleson at high flow)
Open and semi-open: FGF >= MV
Semi-closed: some rebreathing (anesthesia machine, mapleson circuits at low flow)
Closed: complete rebreathing, CO2 absorbant, only replace the amount of gases that are used
