What is it?
A microprocessor calculating % of saturated oxygen in each pulse of
arterial blood flowing past a sensor.
Calculates heart rate at same time.
A low-intensity light is beamed from an LED to a photodiode.
Two beams (one red, one infrared) pass through blood and body tissue,
partially being absorbed.
- absorption differs for saturated and unsaturated blood.
- the microprocessor measures this difference and reports it as %
Not when there is poor peripheral
- eg vasoconstriction, hypotension, upstream BP cuff, hypothermia
Not when there is severe anaemia.
High carboxyhaemoglobin, mehaemoglobin and circulating dye may interfere.
Movement, bright light, dirty skin or other devices (eg diathermy) may interfere.
Compare HR with known / ECG monitor.
If sats are low or poorly read, look for a physiological cause first.
sats compare with PaO2?
- remember it does not equate
- rough guide:
This is a non-linear relation; small PaO2 changes cause large
Variables shift the relationship between PaO2 and saturation:
- ie right shift --. greater delivery of O2 to tissues
|Decr 2,3 DPG
|Incr 2,3 DPG