In all these instances, there is said to be a high uptake of the agent into the body, i.e. the venous blood returning to the heart has a low concentration of the agent and there is room for lots more. Paradoxically, though a high uptake means a lot of agent is disappearing into the body, blood levels rise slowly and the patient takes a long time to go to sleep by inhalation. High uptake will also mean slow recovery because during the process of induction and maintenance, a large reservoir of the agent will have accumulated in blood, fat and other tissues like muscle. At the end of a long operation, this reservoir will slowly give up its stores of anaesthetic agent and thus act like a depot, delaying recovery. As ether is very blood soluble, it leaves the blood slowly and therefore circulates for a long time, before it is finally excreted out from the lungs.
Blood levels fall slowly delaying a return to consciousness.
Halothane, being fat soluble, also remains for hours in the fat of an obese patient at sub-anaesthetic levels, slowly being washed out long after the operation is over. But, the blood solubility is lower than ether and therefore blood levels fall more quickly. The patient therefore recovers consciousness more quickly than when ether has been used. Tissue blood flow and cardiac output are important determinants in the elimination of highly soluble agents. Blood levels rise very rapidly, leading to a rapid induction of anaesthesia.