The use of CO-oximeters
Introduction :
A CO-oximeter (co-oximetry) is a medical device used to measure the concentration of different forms of hemoglobin in the blood. It provides a more comprehensive analysis of hemoglobin than a standard blood gas analysis, which typically measures only the total hemoglobin concentration.
Hemoglobin is the protein in red blood cells responsible for transporting oxygen from the lungs to tissues throughout the body. However, there are various forms of hemoglobin, each with different oxygen-carrying capacities. The main forms of hemoglobin include:
Oxygenated Hemoglobin (HbO2): This form of hemoglobin carries oxygen from the lungs to the tissues, where it releases oxygen to support cellular respiration.
Deoxygenated Hemoglobin (HHb): Hemoglobin that has released oxygen to the tissues and is returning to the lungs to be reoxygenated.
Carboxyhemoglobin (COHb): This is formed when hemoglobin binds to carbon monoxide (CO) instead of oxygen. Carbon monoxide is a toxic gas produced by incomplete combustion and can be dangerous if it accumulates in the blood, as it reduces the blood's ability to carry oxygen.
Methemoglobin (MetHb): This form of hemoglobin results from the oxidation of the iron in the heme group of hemoglobin. Methemoglobin cannot bind to oxygen, so it is unable to carry oxygen to the tissues.
The principle of CO-oximeters :
The principle of CO-oximeters is based on spectrophotometry and the specific light absorption characteristics of different forms of hemoglobin in the blood. CO-oximeters are designed to measure the concentrations of various hemoglobin species, including oxygenated hemoglobin (HbO2), deoxygenated hemoglobin (HHb), carboxyhemoglobin (COHb), and methemoglobin (MetHb).
Here's a more detailed explanation of the principle:
Light Source: CO-oximeters use a light source that emits a range of wavelengths, including visible and near-infrared light.
Blood Sample: A small sample of blood is collected from the patient and placed in a cuvette or other suitable container for analysis.
Spectrophotometric Analysis: The light from the source is directed through the blood sample in the cuvette.
Light Absorption: As the light passes through the blood, it encounters the different forms of hemoglobin in the sample. Each hemoglobin species has a characteristic absorbance spectrum, meaning it absorbs light at specific wavelengths in a unique way. The specific absorbance characteristics are as follows:
Oxygenated Hemoglobin (HbO2) strongly absorbs light at 940 nm and 660 nm.
Deoxygenated Hemoglobin (HHb) strongly absorbs light at 940 nm but less at 660 nm.
Carboxyhemoglobin (COHb) has an absorption peak at 660 nm, and its absorption at 940 nm is similar to oxygenated hemoglobin.
Methemoglobin (MetHb) absorbs more evenly across the spectrum, including at both 940 nm and 660 nm.
Photodetectors: On the other side of the cuvette, there are photodetectors that measure the intensity of the light that has passed through the blood sample.
Data Analysis: The CO-oximeter analyzes the data obtained from the photodetectors, taking into account the different absorption characteristics of each hemoglobin species. By comparing the light absorption at specific wavelengths, the device calculates the concentrations of oxygenated hemoglobin, deoxygenated hemoglobin, carboxyhemoglobin, and methemoglobin in the blood sample.
Display and Interpretation: The results are then displayed on the CO-oximeter's screen, showing the percentages of each hemoglobin species relative to the total hemoglobin concentration. This information provides valuable insights into the patient's blood oxygenation status and the presence of any abnormal hemoglobin levels. Read more
An overview of how CO-oximeters work :
CO-oximeters measure the different forms of hemoglobin in the blood using a technique called spectrophotometry.
Light Source: CO-oximeters use a light source, typically a broad-spectrum light that covers various wavelengths, including visible and near-infrared light. This light source emits light that passes through the blood sample.
Blood Sample: A small sample of blood is taken from the patient and placed in a cuvette, which is a transparent container designed to hold the blood for measurement.
Spectrophotometric Analysis: The cuvette containing the blood sample is inserted into the CO-oximeter. The light from the light source passes through the blood sample in the cuvette.
Light Absorption: As the light passes through the blood, it gets absorbed by the different forms of hemoglobin present in the sample. Each type of hemoglobin has a characteristic absorption spectrum, meaning it absorbs light at specific wavelengths in a distinct manner.
Photodetector: On the other side of the cuvette, there is a photodetector that measures the intensity of the light that passes through the blood sample.
Data Analysis: The CO-oximeter analyzes the data obtained from the photodetector and determines the concentrations of different hemoglobin types, such as oxygenated hemoglobin, deoxygenated hemoglobin, carboxyhemoglobin, and methemoglobin.
Display and Interpretation: The CO-oximeter displays the results, often showing the percentage of each hemoglobin type relative to the total hemglobin concentration. It may also display other parameters related to blood oxygenation.