6 - Oxygen in the Blood

Question 1

If only 0.13 mmol/L of O₂ can dissolve in the blood, how does the body meet the oxygen demand?

Answer 1

• Binding to pigments (Hb and Myoglobin)
• Use oxygen saturation on Y not amount of oxygen bound

Question 2

Where on the Hb curves are the T and R states?

Answer 2

Question 3

If a patient is anaemic, what difference will this make to their oxygen levels?

Answer 3

pO₂ will be normal but oxygen content is lower as less Hb (1 Hb allows 2.2mol/L of O₂)

Question 4

At what partial pressures is Hb saturated/unsaturated?

Answer 4

Question 5

How is oxygen given up from Hb at tissues and how would you work out how much was given up?

Answer 5

Question 6

Apart from low partial pressures, what else can cause Hb to give up oxygen?

Answer 6

- Bohr Shift: tissues with low pH (highly metabolic) or high CO₂ causes shift to T state so gives up O₂

- Increase in temperature also makes Hb give it up more easily

- High levels of 2,3-DPG

• In these optimum conditions about 70% of oxygen given up so there is a reserve in exercise

Question 7

How low can tissue pO2 get?

Answer 7

Question 8

What does CO do to a Hb dissociaton curve?

Answer 8

Question 9

What is the difference between hypoxia and hypoxemia?

Answer 9

• Peripheral hypoxia in shock due to vasoconstriction
• Peripheral and arterial disease are hypoxia in certain areas as the tissues are using O₂ more than it is delivered

Question 10

Where in the body would you see cyanosis?

Answer 10

Question 11

How can you measure oxygenation of the blood?

Answer 11

- Pulse oximeter (saturation)

- Arterial blood gas sample (partial pressure)

Question 12

How does a pulse oximeter work to measure oxygen saturation of the blood?

Answer 12

Quick, painless, non-invasive

Question 13

How do you take a blood sample to measure the oxygenation of blood?

Answer 13

• Need arterial blood sample (usually radial artery)
• Invasive