Anesthesia Machine, Physics & Safety Flashcards
PSI of full tank of N2O & L
750 PSI (1590 L)
PSI full tank of O2 & L
2000 PSI (625 L)…linear drop
PSI of half tank of O2
1000 PSI - you can reliably calculate amount of O2 left based on PSI. 1000 PSI is ~ 300 L.
PSI of half tank of N2O
trick question - P doesn’t drop until 75% of the N2O is gone…therefore when pressure starts to fall there are ~ 400 L of N2O left
Color of tanks - O2, N2O, air
O2 = green N2O = blue air = yellow
what is the fail safe valve?
prevents delivery of hypoxic mixture to pt (as O2 is turned down, N2O automatically comes down)
what’s important about the order of the flowmeters?
O2 is last to prevent the chance that proximal leaks will decrease the delivery of O2 (vs leak distal dec vol but no change in mix/quality of gases)
what’s signif about desflurane vaporizer?
heated & pressurized since Des has VP ~ 1 atm… with heat and pressure, anesthetic has dec but predictable volatility
define Boyle’s law
pressure is proportional to 1/volume
- aka the more volume of a container, the less pressure…if you downsize the volume, the pressure will increase
purpose of regulators
- regulate pressure from gas sources
- take wall pressure from 55 psi to 45 psi
- take cylinder pressure from 2200 or 750 psi to 45 psi
describe the PISS
“pin-index safety system” - system used to ensure only the correct cylinder can be hooked up to its respective line (piss in a cylinder)
describe the DISS
“diameter-index safety system” ensures central supply can’t be hooked up to incorrect line
describe laminar gas flow
- Laminar gas flow = streamlined - varies per viscosity, low flow rates, large area, smooth tube
- Flow = ∆ P/viscosity
- happens in narrower tube
describe turbulent gas flow
- Turbulent flow = irregular directions with increased resistance
- varies per density, less efficient, more energy
- happens with wider tube
significance of Poiseuille’s law
- Poiseuille’s law: Q = change in pressure x pi x radius4 / 8 x viscosity x Length
- therefore is you want to increase flow, you get the most bang for your buck by increasing radius (changes by the 4th power!!)
1) are flowmeters interchangeable?
2) how do flowmeters calibrated at sea level change at high altitude
1) No - calibrated/tapered for specific gases
2) at higher altitude, flowmeters will deliver more gas than what their reading shows (less atm pressure above the flowmeter allows more gas to come thru flowmeter at specific setting originally calibrated at sea level)
describe what happens with inc frequency of sound waves in ultrasound (pertaining to resolution and penetration)
- higher frequency ↑ image resolution
- higher frequency less penetration of tissue (all about da’ bass)
1) what is critical temperature?
2) what is critical pressure?
1) critical temperature: temp below which gas enters its liquid phase (very low (-119 C) for O2…that is why cylinder stores gas, not liquid O2 vs N2O (36 C) is stored as a liquid)
2) critical pressure: pressure at which a gas can be liquefied at its critical temperature
define vapor pressure and list values for Sevo, Iso, Des
Definition of vapor pressure: In a closed container, molecules from a volatile liquid escape the liquid phase and become vapor. These gaseous molecules strike the wall of the container, exerting what's known as vapor pressure. Vapor pressure is directly proportional to temperature. Increasing temperature will increase the ratio of gas:liquid molecules, thereby increasing vapor pressure. Vapor pressure of volatile agents at 20 degrees C (mmHg): Sevoflurane: 157 Desflurane: 669 Isoflurane: 238 Enflurane: 172 Halothane: 243 N2O: 38,770
describe line isolation monitors
: line isolation monitors: there is a Line Isolation Monitor (LIM) mounted somewhere, which gives you a reading of how much “connection” there is between the supposedly isolated wall power wires, and earth ground. The “connection” should be below 2 milliAmperes (mA). You can think of it as a “leakage” current, even though it is a virtual leakage current; it may or may not exist.
- ** does not prevent microshock
- In an isolated system, neither of the 120 volts AC power wires available at the power outlets are connected to earth ground. They are both
“
floating
”
. Thus touching ground has little consequence to you, if you are in such a room. In a room powered by an Isolated Power System, you can stand with bare feet on a wet floor and touch an outlet wire with little chance of being harmed. However, you will have just made the granddaddy of all leakage scenarios, and the Line Isolation Monitor should alarm strongly.
