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.
Changes in cardiac output have little effect on the speed of induction of anaesthesia. The gas, nitrous oxide and newer agents, sevoflurane and desflurane are examples of very insoluble drugs. An agent with a low boiling point will evaporate easily and therefore be more available than one that has a high boiling point. Ether is highly volatile and thus there is almost no limit to the concentration that a vaporiser can give. Ether is really too volatile to be convenient and sometimes new, sealed bottles arrive with no agent inside, but at least it means we can give plenty of it to counteract its slow onset.