OSCEs Spirometer Rebreathing DONE

Question 1

How do you set up a spirometer for an asphyxia experiment? (What causes asphyxia?)

Answer 1

• Asphyxia is caused by a lack of oxygen with carbon dioxide excess
• Set up the spirometer with one way valves
• Make sure the canister of SODA-LIME granules is REMOVED
• Fill the spirometer with AIR until it is 75% full
• After filling, seal the spirometer with the mouthpiece tap
• Fit a clean rubber mouthpiece and a noseclip

Question 2

How do you set up the computer for the rebreathing experiment?

Answer 2

Set the sampling rate to 20/s and the scale amplitude to 1V

Question 3

How do you take and analyse a gas sample from the spirometer?

Answer 3

• use a 50ml syringe for transfering samples
• Empty the syringe, plug it into the tubing on the sample tap, open the tap and fill the syringe
• Allow for dead space in the tubes - take and discard 2 syringes full of gas before taking a sample for analysis - remember to pinch the tube while you discard the two syringes full of gas.
• Close the sample tap
• As you disconnect the syringe for the final time, immediately place a fingertip over the nozzle and keep it there until you plug the syringe into the analyser
• Plug the syringe into the analyser: inject two thirds of the gas, note the reading, inject the last third, note the reading again. If they agree, you have managed to avoid recording the dead space in the analyser
• Write the results down straight away

Question 4

How do you set up a spirometer for a hypocarbia experiment? (What causes asphyxia?)

Answer 4

• Hypocarbia is caused by carbon dioxide excess (only)
• Set up the spirometer with one way valves
• Make sure the canister of SODA-LIME granules is REMOVED
• You will fill the spirometer with OXYGEN instead of air:
• Empty the spirometer via the mouthpiece and close the tap.Connect an oxygen supply to the oxygen inlet. Turn on the supply and fill the spirometer until it is 75% full.
• Turn off the supply and close the inlet tap. It does not matter if you overfill with oxygen, you can vent the surplus thorugh the mouthpiece and this has the advantage of flushing the spirometer with oxygen more thoroughly.
• After filling, seal the spirometer with the mouthpiece tap
• Fit a clean rubber mouthpiece and a noseclip
• (breathe for 4 minutes, analyse the gas for CO2 only)

Question 5

How do you set up a spirometer for a hypoxia experiment? (What causes hypoxia?)

Answer 5

• Hypoxia is caused by a lack of oxygen (only)
• Set up the spirometer with one way valves
• Make sure the canister of SODA-LIME granules is PRESENT
• Fill the spirometer with AIR until it is 75% full
• After filling, seal the spirometer with the mouthpiece tap
• Fit a clean rubber mouthpiece and a noseclip

Question 6

How do you set up the spirometer for the rebreathing control experiment?

Answer 6

• The control experiment makes sure that O2 levels remain high in the spirometer, and that CO2 levels do not rise. This is to ensure that any changes in breathing pattern in the other experiments are caused by the change in gases, and nothing else.
• Set up the spirometer with one way valves
• Make sure the canister of SODA-LIME granules is PRESENT
• You will fill the spirometer with OXYGEN instead of air:
• Empty the spirometer via the mouthpiece and close the tap.Connect an oxygen supply to the oxygen inlet. Turn on the supply and fill the spirometer until it is 75% full.
• Turn off the supply and close the inlet tap. It does not matter if you overfill with oxygen, you can vent the surplus thorugh the mouthpiece and this has the advantage of flushing the spirometer with oxygen more thoroughly.
• After filling, seal the spirometer with the mouthpiece tap
• Fit a clean rubber mouthpiece and a noseclip
• (breathe for 4 minutes, analyse the gas for CO2 only)