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Monitoring Of Respiration: Pulse Oximetry, Capnography, Oximetry
Author : Vlad Nevazhno
Submitted : 2011-12-05 Word Count : 1087 Popularity: Not Rated
Tags: oximeter, pulse oximeter
This idea was proposed by NELLCOR, it is called C-lock and implemented in the pulse oximeter N 200 and subsequent models. At present, the principle of a modified pulse oximeter used in various companies (CRITICARE, DATEX, etc.).
C-lock principle has proved highly effective. Thus, in 1993 the German ambulance aircraft made it standard equipment in cars and helicopters to transport patients, finding that the incidence of artifacts caused by vibration and shaking, with this method is reduced by 8 times (tested monitors PROPAQ 106EL American firm PROTOCOL SYSTEMS INC.).
The disadvantage is that only for the sake of combating the errors have to be connected to the patient elektrokardiomonitor. Thus pulse oximetry loses one of its major advantages - simplicity, limiting the procedure. True, there is no need or desire to built-in ECG and can not be included, trying to forget about the cost of its acquisition. In addition, muscular tremors laying on the ECG can make C-lock useless.
Lack of turning dignity when ECG began to display. Monitoring has become complex and more expensive, because buyers are now admired electrocardiogram without paying for additional power supply, display and housing. It is surprising that such a simple and natural step taken already by other firms, not the inventor of C-lock - a firm NELLCOR, which until recently stubbornly considered ECG signal only as a means to detect artifacts. And finally, this story was the end, when the company put on the DATEX display their model SATLITE PLUS heart rate, calculated from the ECG, resulting in the ability not to lose this index when moving a patient or a critical reduction of the amplitude of PPG, as well as monitor the pulse deficit in atrial fibrillation.
When using the simplest models of pulse oximeters problem of artifacts caused by movement, remains unresolved, and therefore rely on their testimony can only be fixed sensor.
There are basic rules, following which it is possible to reduce these artifacts or even avoid them.
• Artifacts occur less frequently if the sensor has a light weight and flexible lightweight cable.
• Finger sensor must be installed correctly:
cable should be on the dorsum of the finger.
• The sensor cable can be fixed with adhesive tape to the arm. If the cable is hanging from the bed, he - at the expense of their body weight - provokes the displacement sensor. For additional cable attachment to the sheet, use a special clip.
• Hand rolling the patient should be fixed to the bed, but that is not disturbed blood flow. Apart from humanitarian considerations are present here also practical: rather than an artifact generated by the movement, there is a chance to get his brother, caused by the low amplitude of the pulse.
• Stability monitoring helps gauge the right choice, if the manufacturer offers this feature. Earclip move easily, especially if their internal surface is made of slippery material. " More reliably when moving the patient work
'In order to reduce the inner surface of the slip sensor is performed i.ch rubber. There are cases of allergic reactions to natural latex, which is often used in sensors.
flexible sensors, which are fixed with adhesive tape or a special belt latches. These sensors are manufactured by various companies and often have their own names: FLEXALITE and VERSALITE (DATEX), OXISENSOR D-25 (NELLCOR-PB), Y-SENSOR (NOVAMETRIX), etc.
The problem of accuracy
Any instrument gives a particular error, so we can only consider its estimated value. Each parameter is measured with some precision, which is satisfied or not satisfied with us, depending on what we're going to do with it. Even a cursory reading the technical essence of the method, which is the basis of the pulse oximeter is easy to see how much inherent in it the potential sources of error. And we need to know to what extent can we trust your monitor, because of his testimony depends on the important and sometimes risky decisions.
Among other factors on the accuracy of the monitor affects the quality of the LEDs. Ideally, the measurement should be made at a wavelength of red light 660 nanometers (nm) and infrared - 940 nm (in some models use different but close wavelengths). However, LEDs are not monochromatic light sources and emit although a narrow but finite range of light frequencies in which there is a prevailing intensity. It is something in the ground and forms a luminous flux involved in the measurement. Each instance of the LED is inherent in its own unique characteristics of the radiation. If you deviate from the ideal wavelength for each 3 nm error in the measurement of Sp02 is 0.5%, and the spread of values ​​in the party can not exceed ± 15 nm. If each pulse oximeter was equipped with a single sensor, this problem would be handled by making the correction factors, but the life of the sensor is much shorter than the monitor itself. In addition, some companies offer a wide selection of sensors for all occasions. That the value of SpO2 was independent of the sensor, the LEDs are tested and of the whole parties select the best. It's quite expensive but effective way to solve the problem. To our knowledge, the most stringent selection criteria (± 2 nm) used in the firm DATEX. In another embodiment, in the course of production is determined by the peak wavelength of each LED. This information is encoded in each sensor resistor to a specific value of resistance. After connecting the sensor pulse oximeter reads the code and selects the appropriate calibration curve for calculating SpO2. This complicates the technique, but allows better use of LEDs Party (NELLCOR).
And that is another way to relate to additional costs of production, and ultimately they will pay the buyer. Some smaller manufacturers generally do not break my head over this and other issues, or buy ready-made models for their sensors well-known companies.
Saturation, calculated from the photodetector signal is to monitor "raw" information, never coincides with the true value SaOz. To put this figure in order, in the development of each model are compared with the pulse oximeter saturation readings measured by the reference method. As a standard we apply SaOs, measured accurate gemoksimetrom in arterial blood sample test, which is breathing gas mixtures with different oxygen contents. According to numerous simultaneous measurements established an empirical relationship of SpO2 SaO2, which is called the calibration curve and an algorithm is introduced in the final settlement figure.
Author's Resource Box
But even in such a way to achieve complete agreement with the standard <a href="http://www.pulseoximeterok.com/">pulse oximeter</a> readings in real-world clinical settings is not possible. Therefore, in the passport of any model must be specified limits of accuracy of the results.