Physics, Monitoring, and Anesthesia Delivery Devices Flashcards
How do you calculate vaporizer output?
vaporizer output = carrier gas flow x SVP
Patm - SVP
**SVP: saturated vapor pressure of anesthetic gas**
What are the components of Poiseuilles’s equation for laminar flow through a tube?
flow = πr4 x deltaP
8 x viscosity x L
L: length of tube
deltaP: driving pressure
What is the pressure and volume in a full oxygen cylinder?
2200 psi
700 L
What is the pressure and volume in a full nitrous oxide cylinder?
750 psi
1600 L
What is the pressure from the wall source of oxygen or nitrous oxide?
50 psi
What does the first stage pressure regulator bring the pressure from the O2 and nitrous oxide tanks down to?
45 psi
When does the pressure in a nitrous oxide tank start to fall?
When it is 75% depleted (i.e., 400 L)
How do you convert g of nitrous oxide to L?
44 g = 22.4 L
** Avogadro’s hypothesis: 1 mole takes up 22.4 L **
What is the SVP (saturated vapor pressure) of the common anesthetic gases?
sevoflurane: 160 mmHg
enflurane: 172 mmHg
isoflurane: 240 mmHg
halothane: 243 mmHg
desflurane: 680 mmHg
How is radiation risk related to distance from the source?
radiation risk is inversely proportional to (distance from the source)2
What is the Reynold’s number the distinguishes laminar and turbulent flow?
< 2000 is laminar
>2000 is turbulent
Which type of flow is most dependent on gas/fluid viscosity? Density?
- Turbulent flow depends on density
- Laminar flow depends on viscosity
How is flow different at the top and the bottom of the flowmeter?
- Upper part of the flowmeter has turbulent flow
- Lower part of the flowmeter has laminar flow
What color are gas cylinders in the US?
oxygen - green
nitrous oxide - blue
air - yellow
carbon dioxide - gray
nitrogen - black
helium - brown
What are the causes of rebreathing in the circle system?
- exhausted CO2 absorbent
- incompetent expiratory valve (more common)
- incompetent inspiratory valve (less common)
How should you manage a failure in the pipeline oxygen supply?
Turn off the ventilator and manually ventilate with low flows as the ventilator is oxygen-powered and will drain your supply faster.
How do you first detect an expiratory limb disconnection during spontaneous ventilation?
inspired oxygen concnetration will fall
(etCO2 will remain normal for a while)
What problems occur with soda lime particles that are too large?
rebreathing due to inadequate contact surface area with expired gases and channeling
What problems occur with soda lime particles that are too small?
increased resistance to breathing
Which Mapleson circuit is best for spontaneous ventilation?
Mapleson A
Which Mapleson circuit is the best for controlled ventilation?
Mapleson D
What does the saturated vapor pressure of a substance depend on?
physical characteristics of the liquid
temperature
** NOT barometric pressure **
How do you adjust the dial setting for desflurane at high altitude?
dial settingDenver = dial settingsea level x 760
Patm
What does the negative pressure relief mechanism do?
Prevent an active scavenging system from removing too much gas from the breathing circuit and creating negative pressure.
What causes a negative pressure alarm?
- spontaneous respiration with a circuit obstruction
- excessive flow through an active scavenger system
- application of a suction catheter to the ETT
What can be measured with an infrared analyzer?
CO2, N2O, and volatile anesthetics
** not O2 as at least 2 dissimilar atoms are required **
What analyzers are used in an ABG?
pH - Sanz electrode
PaCO2 - Severinghaus electrode
PaO2 - Clark (polarographic) electrode
What can be used to meaure oxygen in a mixture of gases?
fuel cell
paramagnetic analyzer
How do cmH2O convert to mmHg?
10 cmH2O = 7.5 mmHg
How does a pressure transducer convert mechanical energy into electrical energy?
a strain gauge and a Wheatstone bridge circuit
What does the line isolation monitor (LIM) do?
monitors the integrity of ungrounded power sources in the OR, preventing macroshock (NOT microshock)
What should be done if the line isolation monitor alarms?
before a procedure has begun: postpone or move procedure
after a procedure has begun: unplug devices, starting with most recently plugged in
What is the critical temperature?
the temperature above which a gas cannot be converted to a liquid by any amount of pressure
(** critical pressure is the pressure at critical temperature **)
What is the difference between absolute and relative humidity?
absolute humidity - amount of water vapor present at a given temperature (gm %)
relative humidity - amount of water vapor present / amount of water vapor needed for full saturation (at a given temperature)
At what minimum fresh gas flow rate is CO2 absorbent not needed to prevent CO2 rebreathing?
5 L/min
What is the amperage difference between macroshock and microshock?
macroshock: > 100 mAmps
microshock: 10-100 mAmps
What is the classic scenario for microshock?
A shock traveling through monitoring equipment with a short circuit to a PA catheter, CVP line, pacemaker, or external pacing wire leading to an inadvertent shock applied to the heart
