| Re: pulse oximetry
A pulse oximeter measures the ratio of oxygenated to total haemoglobin. So when it says 98% it means that 98% of the total (arteriolar) haemoglobin has oxygen bound to it.
Haemoglobin binds oxygen very well and is well saturated even at surprisingly low partial pressures of oxygen.
In rebreather use, where we use FIO2's much higher than atmosheric air, our haemoglobin is 100% saturated with oxygen all the time.
A fall in oxygen saturation would be a very late sign of loop hypoxia (only seen when the FIO2 falls below about 0.15 ATA), and therefore of very little use.
Dave T |