A patient presents to the Emergency Department with shortness of breath and a cough productive of thick, yellow-green mucus. A chest x-ray reveals consolidation consistent with the diagnosis of pneumonia.

Clinicians are concerned about the possibility of a left to right pulmonary shunt, whereby some of the blood passing through the lungs is not fully oxygenated.

Calculate the expected arterial O2 and CO2 content resulting from a 20% shunt, using the values below:

Arterial O2 content = 200ml.l^-1

Arterial CO2 content = 480ml.l^-1

Mixed venous O2 content = 150ml.l^-1

Mixed venous CO2 content = 520ml.l^-1

Options:
explanation: This is incorrect.

In a 20% shunt, 20% of the arterial blood will be mixed with venous blood.

Therefore, to calculate arterial O2 content with a 20% shunt, the calculation is:

((20/100) x 150) + ((80/100) x 200) = 190ml.l^-1
This is because 20% of the blood has the O2 content of mixed venous blood (150ml.l^-1) and 80% has the O2 content of arterial blood (200ml.l^-1)

To calculate arterial CO2 content with a 20% shunt, the calculation is:

((20/100) x 520) + ((80/100) x 480) = 488ml.l^-1
This is because 20% of the blood has the CO2 content of mixed venous blood (520ml.l^-1) and 80% has the CO2 content of arterial blood (480ml.l^-1)
name: O2 content = 140ml.l^-1
CO2 content = 300ml.l^-1
label: c
answer: no
explanation: This is incorrect.

In a 20% shunt, 20% of the arterial blood will be mixed with venous blood.

Therefore, to calculate arterial O2 content with a 20% shunt, the calculation is:

((20/100) x 150) + ((80/100) x 200) = 190ml.l^-1
This is because 20% of the blood has the O2 content of mixed venous blood (150ml.l^-1) and 80% has the O2 content of arterial blood (200ml.l^-1)

To calculate arterial CO2 content with a 20% shunt, the calculation is:

((20/100) x 520) + ((80/100) x 480) = 488ml.l^-1
This is because 20% of the blood has the CO2 content of mixed venous blood (520ml.l^-1) and 80% has the CO2 content of arterial blood (480ml.l^-1)
name: O2 content = 270ml.l^-1
CO2 content = 440ml.l^-1
label: e
answer: no
explanation: This is incorrect.

In a 20% shunt, 20% of the arterial blood will be mixed with venous blood.

Therefore, to calculate arterial O2 content with a 20% shunt, the calculation is:

((20/100) x 150) + ((80/100) x 200) = 190ml.l^-1
This is because 20% of the blood has the O2 content of mixed venous blood (150ml.l^-1) and 80% has the O2 content of arterial blood (200ml.l^-1)

To calculate arterial CO2 content with a 20% shunt, the calculation is:

((20/100) x 520) + ((80/100) x 480) = 488ml.l^-1
This is because 20% of the blood has the CO2 content of mixed venous blood (520ml.l^-1) and 80% has the CO2 content of arterial blood (480ml.l^-1)
name: O2 content = 250ml.l^-1
CO2 content = 500ml.l^-1
label: d
answer: no
explanation: This is incorrect.

In a 20% shunt, 20% of the arterial blood will be mixed with venous blood.

Therefore, to calculate arterial O2 content with a 20% shunt, the calculation is:

((20/100) x 150) + ((80/100) x 200) = 190ml.l^-1
This is because 20% of the blood has the O2 content of mixed venous blood (150ml.l^-1) and 80% has the O2 content of arterial blood (200ml.l^-1)

To calculate arterial CO2 content with a 20% shunt, the calculation is:

((20/100) x 520) + ((80/100) x 480) = 488ml.l^-1
This is because 20% of the blood has the CO2 content of mixed venous blood (520ml.l^-1) and 80% has the CO2 content of arterial blood (480ml.l^-1)
name: O2 content = 200ml.l^-1
CO2 content = 496ml.l^-1
label: b
answer: no
explanation: This is correct.

In a 20% shunt, 20% of the arterial blood will be mixed with venous blood.

Therefore, to calculate arterial O2 content with a 20% shunt, the calculation is:

((20/100) x 150) + ((80/100) x 200) = 190ml.l^-1
This is because 20% of the blood has the O2 content of mixed venous blood (150ml.l^-1) and 80% has the O2 content of arterial blood (200ml.l^-1)

To calculate arterial CO2 content with a 20% shunt, the calculation is:

((20/100) x 520) + ((80/100) x 480) = 488ml.l^-1
This is because 20% of the blood has the CO2 content of mixed venous blood (520ml.l^-1) and 80% has the CO2 content of arterial blood (480ml.l^-1)
name: O2 content = 190ml.l^-1
CO2 content = 488ml.l^-1
label: a
answer: yes

Correct answer: a