CO2 analysis
The pH of the bicarbonate solution falls in proportion to the CO2 concentration, which is measured by the adjacent pH electrode. The Severinghaus electrode has a response time of 2–3…
Ionising radiation
Some isotopes, such as tritium, are unstable and undergo radioactive decay. This is a random process that follows an exponential pattern; the half-life of an isotope is the time taken…
Electricity – AC and DC
A direct current (DC) is the unidirectional flow of electrons. The current flow may vary and fall towards zero, but as long as the direction of electron flow does not…
CO2 absorption
Carbonic acid is formed by the reaction between carbon dioxide and water. 2. Carbonic acid reacts with sodium hydroxide to form sodium carbonate. This step also produces water and heat….
Blood gas analysis
The logarithmic scale produces a 10-fold change in hydrogen ion concentration per unit change in pH. Modern blood gas machines rapidly measure several variables including pH, pCO2, PO2, oxyhaemoglobin concentration…
Gas analysis: oxygen
Oxygen molecules diffuse across the membrane from the sample gas into the sensor, and are reduced to hydroxyl ions at the cathode. The hydroxyl ions then migrate to and oxidise…
Pulse oximeter
Absorbance is a dimensionless number; 0 indicates no absorbance of light, while 1 indicates 90% of light has been absorbed. Absorbance >1 is uncommon, as Beer–Lambert’s law ceases to be…
Suction and vacuum
Venturi systems utilise the Bernoulli principle to create a negative pressure. They are driven by compressed gas, but are limited by weak flow rates and loud noise. Applied science What…
Vaporisers
At room temperature and one atmosphere pressure, most anaesthetic agents exist in their liquid form. The vaporising chamber is fully saturated with anaesthetic vapour. Wicks help to increase the surface…
