Anesthesia Machine, Physics & Safety

Question 1

PSI of full tank of N2O & L

Answer 1

750 PSI (1590 L)

Question 2

PSI full tank of O2 & L

Answer 2

2000 PSI (625 L)…linear drop

Question 3

PSI of half tank of O2

Answer 3

1000 PSI - you can reliably calculate amount of O2 left based on PSI. 1000 PSI is ~ 300 L.

Question 4

PSI of half tank of N2O

Answer 4

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

Question 5

Color of tanks - O2, N2O, air

Answer 5

O2 = green
N2O = blue
air = yellow

Question 6

what is the fail safe valve?

Answer 6

prevents delivery of hypoxic mixture to pt (as O2 is turned down, N2O automatically comes down)

Question 7

what’s important about the order of the flowmeters?

Answer 7

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)

Question 8

what’s signif about desflurane vaporizer?

Answer 8

heated & pressurized since Des has VP ~ 1 atm… with heat and pressure, anesthetic has dec but predictable volatility

Question 9

define Boyle’s law

Answer 9

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

Question 10

purpose of regulators

Answer 10

• 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

Question 11

describe the PISS

Answer 11

“pin-index safety system” - system used to ensure only the correct cylinder can be hooked up to its respective line (piss in a cylinder)

Question 12

describe the DISS

Answer 12

“diameter-index safety system” ensures central supply can’t be hooked up to incorrect line

Question 13

describe laminar gas flow

Answer 13

• Laminar gas flow = streamlined - varies per viscosity, low flow rates, large area, smooth tube
• Flow = ∆ P/viscosity
• happens in narrower tube

Question 14

describe turbulent gas flow

Answer 14

• Turbulent flow = irregular directions with increased resistance
• varies per density, less efficient, more energy
• happens with wider tube

Question 15

significance of Poiseuille’s law

Answer 15

• 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!!)

Question 16

1) are flowmeters interchangeable?

2) how do flowmeters calibrated at sea level change at high altitude

Answer 16

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)

Question 17

describe what happens with inc frequency of sound waves in ultrasound (pertaining to resolution and penetration)

Answer 17

• higher frequency  ↑ image resolution

- higher frequency  less penetration of tissue (all about da’ bass)

Question 18

1) what is critical temperature?

2) what is critical pressure?

Answer 18

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

Question 19

define vapor pressure and list values for Sevo, Iso, Des

Answer 19

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

Question 20

describe line isolation monitors

Answer 20

: 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.