The Absorption and Elimination of Volatile Substances Through the Lungs: Anaesthesia, Poisoning by Gases and Vapours in Industry, Treatment of Asphyxia
Authors: Y. Henderson
Journal: BMJ (1926)

THE art of anaesthesia is usually treated as if its scientific basis were distinct and peculiar.In fact, lhowever, the inhlilation of volatile substanices, gases or'vapours-witlh strotigw pharmacological actions, is niot confined to anaes- thesia.We have used illuminating gas in our lhouses, and lhaveo inhaled at least its combustion products for two gemerations past; and now the motor car adds its exhaust gas to the air we inhale in the streets.Petrol is an anaes- thetic, although a poor one.'The use of' gases in -war; tlho itncreasing pollution of the atmosphere with the gases and vtaours of industry; the use of oxygen in the treatment of pinemtnionia-all of these are subjects which have points in contmon with inhalational anaesthesia.I propose in this lecture to refer to such collateral subjects, for the sake of tlhe iniformation and experience that caii be extracted from thlem, throwing light on the art of administering a volatile aniaesthetic.The Importanice of V'olafility.It is nio mere accident that the substances wlhich we use as anaesthetics for surgical purposes are volatile.There are, indeed, non-volatile anaesthetics, solids and liquids.Tlhey find use in experimental Work on anlimals when the euhiect is not to be kept alive.But with the exception of nior-phine, which is scarcely an anaestlhetic, they are not ulsed to any extent upon patienlts.Why is it that in genieral the volatile anaesthetics are preferred to those wlicll are non-volatile?The aniswer is, I think, that for surgical anaesthesia the patient must be very profoundly (Irugged-moro profoundly than in any other condition for which drugs are used; so profoundly, in fact, that deatli would almost inevitably follow if the condition were continued for many hours.The fact that the substances used as anaesthetics are volatile enables them to be absorbed extremely rapidly up to the high concentration in the blood niecessary for an anaesthetic action upon the nervous system.Their volatility also allows a more rapid elimina- tioni than is possible for any nioni-volatile substance.Volatility, the property of forming a gas or vapour, is a quialitv of the utmost importance in determining the physiological effects of substances that may gain entrance to the body, or to which the body may be exposed.Volatility reniders a substance capable of entering and leaving the body through the lungs.The differences bet'Ween absorption and elimination through tlle lungs, on the: one hand, and, on the other hand, absorption from the alimentary canal and elimination through the kidneys, are of far- r-eaching but not generally appreciated significanice.There are in chemistry and physics certain muclh u-sed principles called tlle gas laws: the laws of Boyle, of Henry, and of Chlarles.These laws have no direct bearing upon absorption from the stomach or excretion througlh the kidneys, and little application therefore to solids and liquids.Wedlo not yet know with any degree of precision the laws conitrolling absorption from the stomach and initestines and excretion through the kidneys.But the gas laws dominate absolutelv, in respect to the absorption anid elimination of volatile substances through the lunigs, and afford the foundation for the toxicology, the plharmacology, and the therapeutics of gases and vapours.A substalnce taken in through the.lungs may act so much more rapidly and intensely than when taken in tlhrough the stomach that it is hard to believe that the cause in the two cases is the same substance.As ani illustrationi let us take lead.Ordinarily, lead poisoning, as seen in painters,tyl)e-setters, and other trades, is a slowly progressinig clhronic condition affecting the teeth, the alimentary canal, anid some voluntary muscles.Recently it was discovered that a compounid of lead with some organiic groups, iit