Controlled Vaporizers
With the introduction of more potent volatile anesthetics such
as halothane it became important to control the concentration of inspired vapor carefully.
To solve this problem, Lucien Morris[372]
invented
the copper kettle to vaporize liquid anesthetics. Its advantage rested on the
Figure 1-15
Alfred Coleman's economizing device. The anesthetic
gases entered the lower bag and passed into the upper bag through a one-way valve.
Gases were inhaled and exhaled through the tube (h), passing over a lime container
(1, 2) held in frame (k) that eliminated carbon dioxide; (c) is gas inlet. The conserved
gas in the upper bag was used during a later anesthetic administration. (From
Coleman A: Mr. Coleman's economizing apparatus for re-inhaling the gas. Br J Dent
Sci 12:443, 1869.)
fact that as the agent was vaporized, there was little change in the temperature
of the anesthetic liquid. The copper kettle could be used with any agent provided
that the practitioner was cognizant of the vapor pressure of the agent and the flow
rates of the inspired gases. Without the addition of diluent gases such as nitrous
oxide or oxygen, the copper kettle could deliver lethal concentrations of vapor.
The vaporizers in common use today use bimetallic strips that bend as the temperature
drops, permitting more fresh gas to enter the vaporizing chamber. Vaporizers have
been designed for all the agents in use today, including halothane, enflurane, isoflurane,
desflurane, and sevoflurane. The modern anesthesia machines are also equipped with
scavenging systems designed to minimize escape of anesthetic vapors and nitrous oxide
into the operating room. Although controversial, some studies have shown that daily
exposure to anesthetic vapors in low concentrations can have deleterious side effects.
[373]
