Preoxygenation & e

Question 1

An operating theatre has a plenum ventilation system that produces 15 air changes in one hour. True or false:

The time constant is 15 minutes

Answer 1

False. This would be true for 4 air changes per hour.

Question 2

An operating theatre has a plenum ventilation system that produces 15 air changes in one hour. True or false:

The rate constant is 4 minutes

Answer 2

False. Correct number but wrong units. Rate is a number/time.

Question 3

An operating theatre has a plenum ventilation system that produces 15 air changes in one hour. True or false:

Removal of airborne latex particles follows an exponential wash-out pattern

Answer 3

True

Question 4

An operating theatre has a plenum ventilation system that produces 15 air changes in one hour. True or false:

The rate constant is 15/hour

Answer 4

True

Question 5

An operating theatre has a plenum ventilation system that produces 15 air changes in one hour. True or false:

The time constant is 4 minutes

Answer 5

True. A flow of 15 air changes (15 times theatre volume) means that time constant (time for flow to fill container) is 4 minutes.

Question 6

An operating theatre has a plenum ventilation system that produces 15 air changes in one hour. All latex has been removed from the room. True or false:

After 8 minutes, the initial concentration of latex particles should fall to about 37% of the starting value

Answer 6

False. The concentration should fall to this level after one time constant – 4 minutes.

Question 7

An operating theatre has a plenum ventilation system that produces 15 air changes in one hour. All latex has been removed from the room. True or false:

After 12 minutes, the initial concentration of latex particles should fall to about 5% of the starting value

Answer 7

True. 12 minutes is 3 time constants. Wash-out is 95% complete after this period.

Question 8

An operating theatre has a plenum ventilation system that produces 15 air changes in one hour. All latex has been removed from the room. True or false:

After one hour, latex concentrations will have fallen to less than 0.1% (0.001 = 1 x 10-3) of starting value

Answer 8

True. After 16 minutes, concentration is about 2% (0.02) of starting value. After 48 minutes it will be (2% x 2% x 2%) = (0.02 x 0.02 x 0.02) = 8 x 10-6 . After one hour, it is even lower.

Question 9

An operating theatre has a plenum ventilation system that produces 15 air changes in one hour. All latex has been removed from the room. True or false:

Completion of an exponential process such as this requires an arbitrary threshold

Answer 9

True. Theoretically, an exponential process is never complete; a decision of completion is based upon practical considerations using an exponential model.

Question 10

Regarding wash-in and wash-out curves for O2 and N2 respectively in pre-oxygenation (true or false):

The wash-in (O2) and wash-out (N2) processes take place at different rates

Answer 10

False. The wash-in and wash-out processes take place at the same rate because of molecule-for-molecule exchange.

Question 11

Regarding wash-in and wash-out curves for O2 and N2 respectively in pre-oxygenation (true or false):

The curves are symmetrical about a horizontal line

Answer 11

False. The curves are not symmetrical because the O2 curve starts at a value of 0.15.

Question 12

Regarding wash-in and wash-out curves for O2 and N2 respectively in pre-oxygenation (true or false):

N2 falls to half its starting value, i.e. to 0.4, at about 70% of the time constant

Answer 12

True

Question 13

Regarding wash-in and wash-out curves for O2 and N2 respectively in pre-oxygenation (true or false):

The proportional change in each curve is the same at equal times

Answer 13

True. They are taking place at the same rate.

Question 14

Regarding wash-in and wash-out curves for O2 and N2 respectively in pre-oxygenation (true or false):

The curves show an exact description of what happens in clinical preoxygenation

Answer 14

False. Evidently untrue. It is an approximate model.