Question 6

What causes the oxygen haemoglobin dissociation curve to move to the right and what are the clinical implications of this change?

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College Answer

Shift of the O2 – Hb dissociation curve to the right causes decreased affinity for O2 and release of O2 to the tissues. The O2 dissociation curve is shifted to the right by: –

•    increased temperature

•    increased CO2

•    increased 2 – 3 DPG

•    increased pH

•    rare abnormal haemoglobins

This is an important physiological effect responsible for the Bohr effect and allowing greater release of O2 to the tissues.

At present there is not enough data to support manipulation of the O2-Hb curve to improve O2 delivery. If arterial PO2 is critically low then O2 binding in the lungs may be impaired by a shift to the right. The end result is that a shift to the right may seriously impair tissue oxygenation.


A right-shift of the oxyhemoglobin dissociation curve describes a decrease in the affinity of hemoglobin for oxygen; i.e. more and more oxygen is required to achieve the same level of haemoglobin saturation (eg. p50). The clinical implications of this become apparent when one is confronted by such severe hypoxia that any small change in oxygen delivery to the tissues may cause the organ systems to fail. In such circumstances, a small decrease in the oxygen-carrying capacity of the blood will result in diminished oxygen transport and thus systemic hypoxia.

Causes of a right shift include

  • Hyperthermia
  • high 2,3-DPG levels
  • Acidosis (eg. increased CO2)
  • dyshaemoglobinaemia

Now, you'll notice that the college answer has increased pH, i.e. alkalosis. This is incorrect, and the examiners clearly recognised that when they reviewed the Microsft Word document of the answer paper, helpfully highlighting the wrong answer in yellow. Unfortunately, that did not help, and their administrative staff published the uncorrected paper anyway.