Physics, Monitoring, and Anesthesia Delivery Devices

Question 1

How do you calculate vaporizer output?

Answer 1

vaporizer output = carrier gas flow x SVP

P_atm - SVP

**SVP: saturated vapor pressure of anesthetic gas**

Question 2

What are the components of Poiseuilles’s equation for laminar flow through a tube?

Answer 2

flow = πr⁴ x _deltaP

8 x viscosity x L

L: length of tube

_deltaP: driving pressure

Question 3

What is the pressure and volume in a full oxygen cylinder?

Answer 3

2200 psi
700 L

Question 4

What is the pressure and volume in a full nitrous oxide cylinder?

Answer 4

750 psi
1600 L

Question 5

What is the pressure from the wall source of oxygen or nitrous oxide?

Answer 5

50 psi

Question 6

What does the first stage pressure regulator bring the pressure from the O2 and nitrous oxide tanks down to?

Answer 6

45 psi

Question 7

When does the pressure in a nitrous oxide tank start to fall?

Answer 7

When it is 75% depleted (i.e., 400 L)

Question 8

How do you convert g of nitrous oxide to L?

Answer 8

44 g = 22.4 L

** Avogadro’s hypothesis: 1 mole takes up 22.4 L **

Question 9

What is the SVP (saturated vapor pressure) of the common anesthetic gases?

Answer 9

sevoflurane: 160 mmHg
enflurane: 172 mmHg
isoflurane: 240 mmHg
halothane: 243 mmHg
desflurane: 680 mmHg

Question 10

How is radiation risk related to distance from the source?

Answer 10

radiation risk is inversely proportional to (distance from the source)²

Question 11

What is the Reynold’s number the distinguishes laminar and turbulent flow?

Answer 11

< 2000 is laminar

>2000 is turbulent

Question 12

Which type of flow is most dependent on gas/fluid viscosity? Density?

Answer 12

• Turbulent flow depends on density
• Laminar flow depends on viscosity

Question 13

How is flow different at the top and the bottom of the flowmeter?

Answer 13

• Upper part of the flowmeter has turbulent flow
• Lower part of the flowmeter has laminar flow

Question 14

What color are gas cylinders in the US?

Answer 14

oxygen - green

nitrous oxide - blue

air - yellow

carbon dioxide - gray

nitrogen - black

helium - brown

Question 15

What are the causes of rebreathing in the circle system?

Answer 15

• exhausted CO2 absorbent
• incompetent expiratory valve (more common)
• incompetent inspiratory valve (less common)

Question 16

How should you manage a failure in the pipeline oxygen supply?

Answer 16

Turn off the ventilator and manually ventilate with low flows as the ventilator is oxygen-powered and will drain your supply faster.

Question 17

How do you first detect an expiratory limb disconnection during spontaneous ventilation?

Answer 17

inspired oxygen concnetration will fall

(etCO₂ will remain normal for a while)

Question 18

What problems occur with soda lime particles that are too large?

Answer 18

rebreathing due to inadequate contact surface area with expired gases and channeling

Question 19

What problems occur with soda lime particles that are too small?

Answer 19

increased resistance to breathing

Question 20

Which Mapleson circuit is best for spontaneous ventilation?

Answer 20

Mapleson A

Question 21

Which Mapleson circuit is the best for controlled ventilation?

Answer 21

Mapleson D

Question 22

What does the saturated vapor pressure of a substance depend on?

Answer 22

physical characteristics of the liquid

temperature

** NOT barometric pressure **

Question 23

How do you adjust the dial setting for desflurane at high altitude?

Answer 23

dial setting_Denver = dial setting_{sea level} x 760

P_atm

Question 24

What does the negative pressure relief mechanism do?

Answer 24

Prevent an active scavenging system from removing too much gas from the breathing circuit and creating negative pressure.

Question 25

What causes a negative pressure alarm?

Answer 25

• spontaneous respiration with a circuit obstruction
• excessive flow through an active scavenger system
• application of a suction catheter to the ETT

Question 26

What can be measured with an infrared analyzer?

Answer 26

CO₂, N₂O, and volatile anesthetics

** not O₂ as at least 2 dissimilar atoms are required **

Question 27

What analyzers are used in an ABG?

Answer 27

pH - Sanz electrode

PaCO₂ - Severinghaus electrode

PaO₂ - Clark (polarographic) electrode

Question 28

What can be used to meaure oxygen in a mixture of gases?

Answer 28

fuel cell

paramagnetic analyzer

Question 29

How do cmH₂O convert to mmHg?

Answer 29

10 cmH₂O = 7.5 mmHg

Question 30

How does a pressure transducer convert mechanical energy into electrical energy?

Answer 30

a strain gauge and a Wheatstone bridge circuit

Question 31

What does the line isolation monitor (LIM) do?

Answer 31

monitors the integrity of ungrounded power sources in the OR, preventing macroshock (NOT microshock)

Question 32

What should be done if the line isolation monitor alarms?

Answer 32

before a procedure has begun: postpone or move procedure

after a procedure has begun: unplug devices, starting with most recently plugged in

Question 33

What is the critical temperature?

Answer 33

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 **)

Question 34

What is the difference between absolute and relative humidity?

Answer 34

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)

Question 35

At what minimum fresh gas flow rate is CO₂ absorbent not needed to prevent CO₂ rebreathing?

Answer 35

5 L/min

Question 36

What is the amperage difference between macroshock and microshock?

Answer 36

macroshock: > 100 mAmps
microshock: 10-100 mAmps

Question 37

What is the classic scenario for microshock?

Answer 37

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