1: Temp and O2 sat monitoring

Question 1

Best places to take temp

Answer 1

• Single time temp- ear or orally- inconvenient for long term
• Continuous- skin is easiest and less invasive- does not provide an accurate indication of core temp but is useful for easily detecting changes

Question 2

Body temp sensors- Thermistor

Answer 2

• Semiconductors
• Resistance increases with decreasing temp
• Disposable = sterile
• Need adhesive cover
• Measure temp of sensor not patient

Question 3

Body temp sensors- IR thermometer

Answer 3

• Ear and forehead
• Non-contact = sterile
• Fast response
• Accurate
• Measures emitted infrared radiation

Question 4

Pulse oximetry

Answer 4

• Non-invasive, continuous method of measuring O2 sat
• Measures light absorbance of living tissue at 2 wavelengths
• Also uses arterial pulsation to differentiate between arterial blood and other absorbers
• Based on the principles of spectrophotometry (measurement of light absorption properties) and plethysmography (measurements derived from changing volume)

Question 5

Spectrophotometry in pulse oximetry

Answer 5

• wavelengths of 660nm (red) and 940nm (infrared) used because HbO2 absorption is relatively flat at this point
• non-invasive- light passed through well perfused body part = earlobe or finger
• light absorbed at both wavelengths is measured, relative proportions of Hb and HbO2 calculated, determining SpO2
• 2 wavelengths necessary as we are trying to distinguish between 2 different substances

Question 6

Plethysmography in pulse oximetry

Answer 6

• Light passing through finger also absorbed by other tissues and light transmitted through arteries varies due to pulsations of blood volume
• By using pulsatile component of transmitted light, pulse oximeter only looks at arterial oxygen sat

Question 7

Advantages of pulse oximetry

Answer 7

• Non-invasive
• Continuous
• Close to ‘real time’- allows detection of hypoxia or hyperoxia events