Hey! I'm in a research group in Gothenburg and we're planning a study with volatile anaesthetics. The problem is as follows: In the clinical setting (operation room) this volatile anaesthetic is administred as a volume% of the inhaled gas. What we're going to do is take a part of this anaesthetic in it's liquid phase (a mass) and mix it with blood (volume). So, what we need to do is to find a suitable way of calculating what blood concentration in mass/volume that an anaesthetic inhaled at X volume% causes. I can tell you how we have reasoned: Specific volume = (RT/PM) for an ideal gas, where R = Avogadro's constant, T = temperature, P = pressure och M = Molecular mass. If I calculate it right, the unit is m^3/g Density = 1/specific volume. Densiteten is thus g/m^3 which is the same as a measure of the concentration of substance X in a solution containing only substance X. If 2% of the inhaled volume of gas is composed of substance X, then the concentration of X X in that volume of gas would be 0,02 x the density of X. The gas is the lungs (it is inhaled in the clinical setting) is at equilibrium with the gas in the blood (liquid) so that the partial pressure is the same in both. The gases also have a property called distribution coefficient (D) which tells you the ratio (Concentration in blood) / Concentration in the gas. So: Volume% * Density of Substance X * Distribution coefficient, should equal a reasonable blood concentration in mass/volume. What do you think? The actual substances being used are: Sevoflurane and Isoflurane.