US2996427A - Anaesthetic consisting of nitrous oxide and halothane - Google Patents

Description

United States atent O 2,996,427 ANAESTHETIC CONSISTING OF NITROUS OXIDE AND HALOTHANE James G. Robson, 301 Victoria Drive, Baie dUrfee, Quebec, Canada, and Peter J. L. Welt, 3737 Hutchisou St., Montreal, Quebec, Canada No Drawing. Filed Nov. 20, 1958, Ser. No. 775,117 1 Claim. (Cl. 167-52) This invention relates to a method of vaporizing volatile anaesthetic agents and more particularly to the vaporizing of halothane and to compositions including halothane.

Halothane 1:1:1-trifiuoro-2-bromo-2-chloroethane of the formula CF CHBrCl) described in United States Patent 2,849,502 is a volatile and very potent general anaesthetic. Because of its high vapor pressure, Ostwald coefiicient and the fact that moderately deep anaesthesia can be produced with a concentration of 10 nag/100 ml. of blood, halothane requires very careful control of the administered concentration.

Normally, halothane is administered at concentrations of up to 2.5% by volume for induction, and, from 0.8% to 1.5% by volume for maintenance. Concentrations of as little as 2.5% can be dangerous. These figures are based on the administration of halothane as the sole anaesthetic.

At the present time, it is common practice to control the concentration of the halothane during administration by using special vaporizing equipment. This equipment is capable of control of the concentration to within about 0.2%. However, it is complicated, having to compensate for both flow rate and temperature, and consequently expensive.

Applicants development The applicants have now developed a method which provides for effective control of the concentration of halothane and which does not require any special apparatus. The applicants method comprises bringing liquid halothane together in a vessel under pressure with nitrous oxide, a gas which liquifies at ambient temperature. In this way a constant and known concentration of the liquid halothane will be obtained which is about 0.5% by volume halothane to nitrous oxide at ambient temperature (20 C.). The volatile halothane and the nitrous oxide (now liquid) will vaporize according to the partial pressures of these substances as long as both remain in the liquid state.

Using the applicants method, the anaesthetic mixture may be administered in the normal manner. The gaseous mixture of halothane and diluent gas is drawn ofr" from the pressure vessel through a reducing valve and mixed with at least 20% by volume of oxygen and reaches the patient through any standard anaesthetic machine.

Halothane is a known inflammable liquid whose vapor does not burn or explode with any proportion of oxygen. The liquid boils at 502 C. (760 mm. Hg), has a specific gravity of 1.86 and a vapor pressure of 243 mm. Hg at 20 C. The Ostwald coeificient is 3.06 at 37 C. The gaseous diluent, nitrous oxide, is also an anaesthetic, is non-inflammable and has a vapor pressure when liquid which makes it suitable for the purposes of the present invention.

The liquid mixture of halothane and nitrous oxide in accordance with the invention is stable indefinitely.

The following example is further illustrative of the invention in preferred aspects.

Example A size D cylinder (250 US. gallons) was filled with 28.04 cc. of liquid halothane and 250 (at F. and 745 pounds per square inch pressure) -U.S. gallons of nitrous oxide. The resultant concentration of halothane in nitrous oxide was 0.628% volume by volume. This concentration was first calculated theoretically and then shown by analysis to be correct, both immediately after the cylinder was filled, then again after six months storage of the cylinder at ambient temperature. This indicates the stability of the mixture necessary to its use in anaesthetization.

We claim:

For use in anesthetizing a patient with an inhalation anesthetic, a mixture of liquefied nitrous oxide and liquid halothane maintained under pressure.

Raventos: Survey of Anesthesiology, June 1957, pp. 178486.

J.A.M.A., Oct. 5, 1957, vol. 165, No. 5, p. 624.

Bryce-Smith: December 1957, Survey of Anesthesiol- I ogy, pp. 610-612.

Dripps: Introduction to Anesthesia, W. B. Saunders Co., 1957, PP. 27-30.

Andriani: The Chemistry of Anesthesia, 1946, page 52.

UNITED STATES PATENT OFFICE I CERTIFICATE OF CORRECTION Patent No. 2,996 427 August 15, 1961 v James Go Robson et a1;

or eppears in the above numbered pat- It is hereby certified that err said Letters Patent should read as ent requiring correction and that the corrected below.

line 45, for 005% read 0.6% ;3 column 2 Column l read nonflammable line 6 for "inflammable Signed and sealed this 15th day of January 1963.

(SEAL) Attest:

DAVID L. LADD ERNEST W. SWIDER Commissioner of Patents Attesting Officer