<prompt> When using low-flow circle absorber techniques, the uptake of nitrous oxide must be considered. In a healthy 70 kg adult the expected uptake of nitrous oxide, with a 70 inspired concentration, after 1.5 hours would be about1000 ml.min-1500 ml.min-1250 ml.min-1100 ml.min-1  <response>: uptake of N2O in mlsmin is equal to 1000 divided by the square root of the time elapsed in mins the time elapsed is 100 minutes. the square root of this is 10 1000 divided by 10 is 100 so the N2O uptake at 100 mins into the case would be about 100mlsmin. 