Data viva — the oxyhaemoglobin dissociation curve

A graph of the oxyhaemoglobin dissociation curve. Saturation (per cent) is on the y-axis from 0 to 100; PaO2 (kPa) is on the x-axis from 0 to 16. The curve is sigmoid — flat near the top above about 8 kPa and steep below. A vertical dashed line marks the P50 at 3.5 kPa where the curve crosses 50 per cent saturation. A second curve is drawn shifted up and to the LEFT, labelled alkalosis, hypothermia, low 2,3-DPG. A third curve is drawn shifted down and to the RIGHT, labelled acidosis, hyperthermia, high 2,3-DPG. An inset shows two arrows for the pulse oximeter at 660 nm (red) and 940 nm (infrared).