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Pulse Oximetry

Pulse Oximetry. Pulse oximeters measure the arterial oxygen saturation of haemoglobin. Two basic physical principles. absorption of light at two different wavelengths by haemoglobin differs depending on the degree of oxygenation of haemoglobin

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Pulse Oximetry

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  1. Pulse Oximetry

  2. Pulse oximeters measure the arterial oxygen saturation of haemoglobin. • Two basic physical principles. • absorption of light at two different wavelengths by haemoglobin differs depending on the degree of oxygenation of haemoglobin • the light signal following transmission through the tissues has a pulsatile component

  3. Pulse oximeters measure: • The oxygen saturation of haemoglobin in arterial blood • The pulse rate - in beats per minute, averaged over 5 to 20 seconds.

  4. Most oxygen is carried by haemoglobin. • Three factors will influence the amount of oxygen delivered to body cells: • Tissue perfusion • The amount of haemoglobin • The saturation of haemoglobin by oxygen.

  5. A pulse oximeter gives no information on any of these other variables: • The oxygen content of the blood • The amount of oxygen dissolved in the blood • The respiratory rate or tidal volume i.e. ventilation • The cardiac output or blood pressure

  6. Oximeters consist of: • peripheral probe • a microprocessor unit - displays a waveform, the oxygen saturation and the pulse rate. • Most oximeters also have an audible pulse tone, the pitch of which is proportional to the oxygen saturation

  7. How does an oximeter work? A source of light originates from the probe at two wavelengths (650nm and 805nm). The light is partly absorbed by haemoglobin, by amounts which differ depending on whether it is saturated or desaturated with oxygen. By calculating the absorption at the two wavelengths the processor can compute the proportion of haemoglobin which is oxygenated.

  8. How does an oximeter work?Cont’d • The oximeter is dependant on a pulsatile flow and produces a graph of the quality of flow. • Where flow is sluggish (eg hypovolaemia or vasoconstriction) the pulse oximeter may be unable to function. • The computer within the oximeter is capable of distinguishing pulsatile flow from other more static signals (such as tissue or venous signals) to display only the arterial flow

  9. Generally measured on: • fingers, • the earlobe • Infants - the bridge of the nose

  10. A pulse oximeter is affected by : • ambient light; • shivering; • abnormal haemoglobins; • pulse rate and rhythm; • vasoconstriction • cardiac function.

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