Compressed Gases and Reducing Valves
Of major importance in the design of the modern anesthesia machine
was the compression of gases in metal
cylinders. Oxygen and nitrous oxide were available under compression as early as
1885 through the manufacturers S. S. White of Philadelphia and Messrs. Coxeter of
London. This allowed the development of compact machines capable of prolonged anesthetic
delivery without the cumbersome feature of low-pressure reservoirs. Frederick Hewitt's
first anesthetic gas machine designed for giving oxygen and nitrous oxide mixtures
had two nitrous oxide cylinders and one oxygen cylinder and were fed into a large
breathing bag through a double cylinder yoke.[139]
Oxygen concentrations could be adjusted at the stopcock near the mask. His preferred
oxygen concentrations were 5% to 8%. With the addition of oxygen, he attempted to
"dispense with cyanosis, jerky and irregular breathing, deep stertor and clonic movements
of the extremities."
The invention of the reducing valve is accredited to Jay Albion
Heidbrink (1857–1957), an anesthesiologist from Minneapolis who observed that
the opening from high-pressure cylinders often froze closed as the gases were released.
He described a valve that reduced the high tank pressures to working pressures and
incorporated this device into his Heidbrink Anesthetizer. In Germany, Heinrich Drager
(1847–1917) and his son Bernhard Drager (1870–1928) developed reducing
valves to control an even, accurate flow of carbon dioxide gas drawn from beer cylinders,
and these valves were later used in the early anesthesia machines. Further refinements
to the early machines were added by James T. Gwathmey[363]
and H. Edmund G. Boyle[364]
(1875–1941) chiefly
through the addition of bubble-through heated water baths for estimation of gas flows.
The Boyle machine passed various amounts of oxygen through ether with a "water-sight"
meter. This flowmeter estimated the flow through the vaporizer from how many of
the holes were generating bubbles. Heidbrink further improved the flowmeter by using
an inverted float in a tube of varying taper with calibrations marked on the side.
Rotating floats, also called rotameters, have slanted grooves cut into the rim,
causing them to rotate, and they are more accurate than the ball or nonrotating floats.
Rotameters were introduced in 1908 by Karl Kuppers and first used in anesthesia
in 1910.[365]
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