SaO2 versus SpO2SaO2 versus SpO2With background knowledge

Deoxyhaemoglobin (Hb) Oxyhaemoglobin (HbO2) Methaemoglobin (Methb) Carboxyhaemoglobin (COHb) Sulfhaemoglobin (SfHb) Carboxysulfhaemoglobin (COSfhb)

Where the concentration of

oxyhaemoglobin dominates in the blood

Types of haemoglobinsTypes of haemoglobins

A parameter measured by CO-oximeter The ratio of oxyhaemoglobin over all types of

haemoglobin

SaO2SaO2

A parameter measured by pulse-oximeter The ratio of oxyhaemoglobin over the

concentration of oxyhaemoglobin and deoxyhaemoglobin

SpO2SpO2

Traditional way of measuring oxygen saturation in arterial blood

Measurement taken on several wavelengths of light

Achieved with the usage of blood gas analyzer

CO-oximeter CO-oximeter measuring SaO2measuring SaO2

Non-invasive way of oxygen level measurement

Both transmission mode and reflection modes available

Transmission : fingertip, earlobe Reflection : forehead, cheek, calf, thigh Poorer SNR occurs at reflection mode Most-commonly dual-wavelength method

used

Pulse-oximeter Pulse-oximeter measuring SpO2measuring SpO2

Consider a heavy smoker with 15% COhb Pulse-oximeter is unable to distinguish

between COhb and HbO2 In the case where SaO2 is 84%◦ A result of 99% SpO2 will be shown◦ The reading is heavily affected◦ Situation of user endangered when wrong action

taken

Malfunction of pulse-Malfunction of pulse-oximetryoximetry

Measure blood saturation levels. Unable to detect tissue hypoxia as a result of anaemia

Unable to distinguish the dysfunctional haemoglobins – over estimate SaO2 level

Not an accurate devise.. Yet good indicator of saturation and desaturation level

More reliable if reflective probe used to tape to the body

Digital version not necessarily better than analogue one

Summary of pulse oximetrySummary of pulse oximetry

Venous pulsation artificially lower than SaO2 A guide to peripheral circulation Aim to keep levels above 95% Action taken quickly if below 90%

Summary of pulse oximetrySummary of pulse oximetry