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Blood gas analyser

The blood gas analyser measures the partial pressures of oxygen (PO2) and carbon dioxide (PCO2) in the blood as well as the pH of blood. Measurement of blood gas concentrations provides an accurate assessment of the condition of the respiratory system. The lungs and blood retain carbon dioxide if there is a lack of air in the lungs. This occurs, for example, during hypoventilation or drowning. Retention of carbon dioxide causes the blood to become abnormally acid, a condition known as respiratory acidosis. Sometimes, acids appear in the blood through disturbance of the metabolic processes of the body such as kidney failure or diabetic coma (metabolic acidosis). Alkalosis occurs when there is excessive elimination of carbon dioxide from the lungs as in hyperventilation.

All possible combinations of acidosis and alkalosis are encountered in clinical practice, and the blood gas analyser assists doctors in recognising the underlying problem. It uses electrochemical sensors to detect and measure the different gases. The theory behind the blood gas analyser was formulated by the German chemist, Walter Hermann Nernst (1865-1933), during the 1880s. His mathematical equation related the gas quantity being measured with changes in voltage of the carbon dioxide and pH electrodes. His assistant, Heinrich Danneel, discovered that the current passed by a negatively charged platinum electrode was dependent on the presence of oxygen in the blood. The biologist, Max Cremer, further discovered that a thin glass membrane separating 2 solutions of different acidity would generate a voltage. By the 1950s, the technology had developed sufficiently to produce the first blood gas analysers.


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