The art of anaesthesia . sion but the amount ofgas in solution is less than one volume per cent. Ten-sions of gases in liquids are expressed either in percentagesof an atmosphere or in millimetres of mercury. Thus thetension of oxygen in arterial blood is found to be equal toabout 10 per cent, of an atmosphere of 76 mm. Hg. (Thetension of ether vapor necessary to maintain anaesthesia isabout 50 mm. Hg.)—Howell; matter in parentheses ours. Were it of advantage that a saturated atmosphere ofether at room temperature be breathed by a patient, somuch ether could be dissolved in the blood that the
The art of anaesthesia . sion but the amount ofgas in solution is less than one volume per cent. Ten-sions of gases in liquids are expressed either in percentagesof an atmosphere or in millimetres of mercury. Thus thetension of oxygen in arterial blood is found to be equal toabout 10 per cent, of an atmosphere of 76 mm. Hg. (Thetension of ether vapor necessary to maintain anaesthesia isabout 50 mm. Hg.)—Howell; matter in parentheses ours. Were it of advantage that a saturated atmosphere ofether at room temperature be breathed by a patient, somuch ether could be dissolved in the blood that the vapor 68 ANESTHESIA tension of the ether dissolved would finally equal that ofthe vapor in the lung, or 460 millimetres. Yet it is foundclinically that a sufficient depth of anaesthesia has beenachieved when the amount dissolved in the blood has avapor tension of 50 millimetres. To insure this amount be-ing dissolved into the blood within a reasonable time,—sixto eight minutes being usually employed in induction—it. AVERAGE ADUIT)TIMESTAGE \ -5 MIM. J, S-_7J*IH_ Induction 20-40 MIN. FULL SURGICAL ANAESTHESIA Flo. 4S.—Vapor pressure of ether in tidal air for inrluetion and maintenance of full anaesthesia. Partial press-ure of vapor in millimetres of mercury (Courtesy of Dr. K. Connell. Johnsons Surgery, Appleton.) is required that a much stronger ether vapor be breathedduring induction than is needed merely to maintain anaes-thesia. (Figs. 48 and 49). To induce anaesthesia rapidly, the vapor must be soabundant as to exert a vapor tension of at least 180millimetres (Figs. 48 and 49). This gradually crowdsthe required amount of ether into the blood and nervoussystem. When the blood approaches the proper satura-tion, as indicated by the signs of anaesthesia, the amount COMPLETE GENERAL ANAESTHESIA 69 of ether present in the air breathed is gradually lowereduntil finally, in ideal anaesthesia, the pressure of ether vaporin the lung balances the tension of ether dissolved in
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