Why Are General Anesthetics Administered as Gases

Some of the general anesthetics include ether (diethyl ether) (Fig. 7.1.1), chloroform (Fig. 7.1.2), nitrous oxide (Fig. 7.1.3), ketamine hydrochloride (Fig. 7.1.4), 

The ability of the anesthetic agent to function is related to the partial pressure of the drug in the brain. Two major factors dictate the concentration of anesthetic agent in the neural tissue (1) the pressure gradients from lung alveoli to the brain (i.e., inhaled gas — alveoli — bloodstream — brain) and (2) the lipid solubility of the drug that enables it to pass between the blood-brain barrier to the central nervous system. 

The distribution of anesthetic throughout the entire body may be viewed as an equilibration process (Fig. 7.1.13), with tissues characterized by high blood flows reaching equilibration faster than muscle and fatJ4l Nevertheless, an anesthetic that is excessively soluble in blood will not partition substantially into brain and other tissues. The anesthetic properties of nitrous oxide and diethyl ether have been known since the 1840s. Zeneca Pharmaceuticals introduced the first modem inhalation anesthetic fluothane in 1957.t5l Methoxyfluorane followed in 1960, enflurane 1973, isoflurane 1981, desflurane by Anaquest (Liberty Comer, NJ) in 1992, and sevoflurane by Abbott Laboratories in 1995J6  

Inhaled gas -----Alveoli------ Blood stream, - Tissues with high blood flow 

Don t reach for that glass of water to cool the effect of spicy chili peppers A few rules of chemistry will suggest a better remedy. 

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Why are general anesthetics administered as gases See p. 78. How do sniffing dogs detect narcotics or explosives See p. 176. 

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