METHODS AND APPARATUS FOR BUFFERING ANESTHETICS
A device for delivering buffer solution into a buffer cartridge comprises a needle assembly and a pusher. The septa of a buffer cartridge and an anesthetic cartridge are advanced onto a transfer needle, and the pusher advances a plunger into the buffer cartridge to deliver buffer through the transfer needle into the anesthetic cartridge. A separate exhaust needle allows excess anesthetic from the anesthetic cartridge to be exhausted. A compression member is usually provided to maintain a force against the plunger on the buffer cartridge to pressurize and stabilize the contents during sterilization and/or storage.
1 . A method for storing a bicarbonate buffer solution, said method comprising:
providing a cartridge having an open interior, a needle penetrable septum, and a plunger which can be advanced into said open interior to pressurize contents thereof;
filling said cartridge with a solution of bicarbonate buffer that will evolve carbon dioxide at room temperature and pressure; and
storing the cartridge while applying a pressure to the solution that is sufficient to inhibit the evolution of carbon dioxide during storage.
2 . A method as in claim 1 , wherein:
the buffer comprises sodium bicarbonate that has a pH in the range from 7.5 to 7.8; and
the applied pressure is above 1.2 atm.
3 . A method as in claim 1 , wherein the pressure is maintained by compressing a spring against the plunger
4 . A method as in claim 1 , wherein the cartridge is placed in a pressurized vessel that places force against the plunger and maintains the pressure.
5 . A method as in claim 1 , wherein the plunger is comprised of a compressible resilient material, the plunger is compressed against the solution, and compression is maintained.
6 . A method as in claim 1 , wherein the pressure is sufficient to prevent vaporization of volatile species during heat sterilization.
7 . A method as in claim 6 , wherein an amount of water is added to the solution prior to heat sterilization to compensate for water that escapes past the cartridge plunger during the heat sterilization process.
8 . A bicarbonate buffer storage cartridge assembly, said assembly comprising:
a cartridge having an open interior filled with bicarbonate buffer solution, a needle penetrable septum, and a plunger which can be advanced into said open interior to pressurize the bicarbonate buffer therein; and
a compression member which exerts a force on the plunger which is sufficient to pressurize the bicarbonate buffer solution at a pressure which inhibits the evolution of carbon dioxide.
9 . A storage cartridge assembly as in claim 8 , wherein the open interior of the cartridge is completely filled with sodium bicarbonate with substantially no headspace remaining.
10 . A storage cartridge assembly as in claim 8 , wherein the compression member comprises a compressible spring which is maintained in compression and engages the plunger.
11 . A storage cartridge assembly as in claim 8 , wherein the compressible spring comprises a coil spring.
12 . A storage cartridge as in claim 8 , wherein the compression member is formed as an integral portion of the plunger.
13 . A storage cartridge assembly as in claim 8 , further comprising a housing, wherein the cartridge is within the housing and the compression member is held in compression between the housing and the solution.
14 . A storage cartridge as in claim 8 , wherein the solution is held under sufficient pressure to inhibit vaporization under expected storage conditions.
15 . A storage cartridge as in claim 8 , wherein the solution is held under sufficient pressure to inhibit vaporization under conditions of heat sterilization.