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From: maths idiot Date: 06 Jun 2006 Time: 11:24:41 +1100 Remote Name: 61.68.181.117 Comments: i am crap at maths too, so i ignore mathematical explanations as they just confuse me. the second gas effect is the result of the concentration/concentrating effect: -in the alveolus there is lots of N2O and some volatile agent. -the rapid absoprtion of N2O causes the concentrating effect where the volume of the alveolus decreases and this causes an increase in the concentration of the volatile. -second gas: as concentration of volatile has increased in alveolus, the concentration gradient from the alveolus to the blood has increased and more volatile agent will be taken up into the blood. if you do the calculations - which i can't - the effect is really quite small and i don't think it has any real clinical significance. -the reverse part is more clinically significant where at the end of a case, the rapid movement of N2O from the blood into the alveolus increases the volume of the alveolus and decreases the concentration of the other gases there, which includes oxygen. so if you don't give supplemental O2 once you have turned off the N2O/O2 mix, you can get difusion hypoxia.