Methods and apparatus for buffering anesthetics

Abstract

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.