Pulse Oximetry PowerPoint and tissue engineering.pptx

Biomedical engineering

1. 1 Contents Introduction Operation principle What is measured by pulse oximeter ? Construction T ypes of pulse oximeters Conclusion 　　

2. Introduction Oximetry is a non-invasive method of measuring the oxygen saturation of the (hemoglobin in the) blood. This is a good indicator of the oxygen carrying capacity of the blood. A blood-oxygen monitor displays the percentage of blood that is loaded with oxygen . More specifically, it measures what percentage of hemoglobin, the protein in blood that carries oxygen, is loaded.

3. All tissues in the body depend on oxygen for survival. A shortage of oxygen in the tissues is called hypoxia . When a patient is hypoxic their tissues lose the bright red appearance of being well oxygenated and become dark red . The brain is damaged very quickly if the supply of oxygen to the tissues is interrupted. Normal range? In a healthy human, nearly 100% of the hemoglobin is saturated all of the time in the arteries. Acceptable normal ranges for patients without pulmonary pathology are from 95 to 99 percent . The causes of hypoxemia can be sleep apnoea, asthma crisis, pulmonary infection, etc. Possible actions include giving more (supplemental) oxygen

4. The Pulse (Heart) Rate is 72 beats per minute The oxygen saturation is 98% Two sites commonly used for transmittance pulse oximetry are the ear and the finger. The finger is the most convenient site, and is often the most comfortable for the patient.

5. Operation principle The colour of blood depends how much haemoglobin is saturated with oxygen. Arterial blood is fully saturated and is bright red; venous blood has less oxygen and is dark red. This colour difference is the basis for pulse oximetry. Oxygenated hemoglobin absorbs more red light and allows more infrared light to pass through. Red light is in the 600-750nm & infrared light is in the 850-1000nm wavelength

6. A typical pulse oximeter utilizes a pair of small light-emitting diodes (LEDs) facing a photodiode through a translucent part of the patient's body. One LED is red , with a wavelength of 660 nm, and the other is infrared with a wavelength of 940 nm. Absorption of light at these wavelengths differs significantly between blood loaded with oxygen and blood lacking oxygen. Oxygenated hemoglobin absorbs more infrared light and allows more red light to pass through. Deoxygenated hemoglobin allows more infrared light to pass through and absorbs more red light.

7. The LEDs flash about thirty times per second which allows the photodiode to respond to the red and infrared light separately. The amount of light that is transmitted (in other words, that is not absorbed) is measured. These signals fluctuate in time because the amount of arterial blood that is present increases (literally pulses) with each heartbeat. The SpO2 is calculated from this. Detecting a pulse (in the diode signal & blood flow) is essential to the operation of a pulse oximeter; it will not function if there is none.

8. Most of the haemoglobin in blood combines with oxygen as it passes through the lungs. A healthy individual with normal lungs, breathing air at sea level, will have an arterial oxygen saturation of 95% – 100%. Arterial blood looks bright red whilst venous blood looks dark red. The difference in colour is due to the difference in haemoglobin saturation. During anaesthesia the oxygen saturation should always be 95 - 100%. If the oxygen saturation is 94% or lower, the patient is hypoxic and needs to be treated quickly. A saturation of less than 90% is a clinical emergency.

9. Absorption characteristics of oxygenated and deoxygenated hemoglobin

10. Parameters of Pulse Oximetry 1 ． SpO2 - The oxygen saturation of hemoglobin in arterial blood: Since the oximeter detects the saturation peripherally on a finger, toe or ear, the result is recorded as the peripheral oxygen saturation. 2. Pulse Rate (PR) - in beats per minute, averaged over 5 to 20 seconds. Some oximeters display a pulse waveform or indicator that illustrates the strength of the pulse being detected. This display indicates how well the tissues are perfused.

11. Types of Pulse Oximeters Types of pulse oximeters 1. Handheld pulse oximeter

12. 2. Finger-tip pulse oximeter

13. 3. Table-top pulse oximeter

14. Components A pulse oximeter consists of the monitor containing the batteries and display , and the probe that senses the pulse . The display shows the oxygen saturation, the pulse rate and the waveform detected by the sensor. The monitor is connected to the patient via the probe. During use, the monitor updates its calculations regularly to give an immediate reading of oxygen saturation and pulse rate. The pulse indicator is continuously displayed to give information about the circulation. The audible beep changes pitch with the value of oxygen saturation and is an important safety feature. The pitch drops as the saturation falls and rises as it recovers. This allows you to hear changes in the oxygen saturation immediately, without having to look at the monitor all the time.

15. T he pulse oximeter probe The oximeter probe consists of two parts, the light emitting diodes (LEDs) and a light detector (called a photo-detector). Beams of light are shone through the tissues from one side of the probe to the other. The blood and tissues absorb some of the light emitted by the probe. The light absorbed by the blood varies with the oxygen saturation of haemoglobin. The photo-detector detects the light transmitted as the blood pulses through the tissues and the microprocessor calculates a value for the oxygen saturation (SpO2).

16. 20 Rubber finger probe & ear sensor

17. Hinged finger probe

18. Normal ranges for patient categories

19. 23 Interference factors with the pulse oximeter reading Light S hivering Pulse volum e Vasoconstriction Carbon monoxide poisoning