Methods and apparatus for buffering anesthetics

1. A method for buffering an anesthetic cartridge, said method comprising:

providing an anesthetic cartridge having a septum;

providing a buffer cartridge having a septum and plunger;

penetrating a transfer needle through the septum on the buffer cartridge and the septum on the anesthetic cartridge, whereby a fluid transfer path is established;

penetrating an exhaust needle through the septum on the anesthetic cartridge but not the septum on the buffer cartridge; and

advancing the plunger on the buffer cartridge to transfer a volume of buffer from the buffer cartridge into the anesthetic cartridge while causing an equal volume of anesthetic to be expelled from the anesthetic cartridge through the exhaust needle.

2. A method as in claim 1 , wherein, prior to penetrating the transfer needle and advancing the plunger, a force is applied to the buffer in the buffer cartridge to inhibit the vaporization of volatile species.

3. A method as in claim 2 , wherein the buffer comprises sodium bicarbonate having a pH in the range from 7.5 to 7.8 and a force is applied which is sufficient to maintain a pressure above 1.2 atm within the cartridge to prevent the vaporization of CO 2 at normal storage temperatures.

4. A method as in claim 2 , wherein the buffer comprises sodium bicarbonate and a force is applied which is sufficient to maintain a pressure above 5 atm within the cartridge to prevent the vaporization of CO 2 at heat sterilization temperatures.

5. A method as in claim 2 , wherein the force is applied by a spring held under compression against the plunger.

6. A method as in claim 1 , wherein the penetrating comprises turning a knob which holds the transfer and exhaust needles to advance the transfer needle through the buffer cartridge septum.

7. A method as in claim 6 , wherein penetrating the transfer of exhaust needles through the anesthetic cartridge septum occurs as the anesthetic cartridge is inserted into a receptacle on the knob.

8. A method as in claim 1 , wherein the exhaust needle directs the expelled anesthetic into a reservoir.

9. A method as in claim 8 , wherein the reservoir is disposed in a hanging surrounding the buffer cartridge.

10. A method as in claim 1 , wherein advancing the plunger on the buffer cartridge comprises engaging a pusher against the plunger and advancing the pusher.

11. A method as in claim 10 , wherein the pusher is advanced until it engages a first stop to define a first delivered volume of buffer.

12. A method as in claim 11 , further comprising advancing the pusher beyond the first stop until the pusher engages a second stop to define a second delivered volume.

13. A method as in claim 12 , further comprising replacing the anesthetic cartridge after transferring the first delivered volume and before transferring the second delivered volume.

14. A device for transferring a volume of buffer solution into an anesthetic cartridge, said device comprising:

a buffer cartridge having a septum and a plunger;

a needle assembly having a transfer needle and an exhaust needle, and

a pusher which engages the plunger on the buffer cartridge;

wherein the transfer needle penetrates the septum of the buffer cartridge, the needle assembly detachably receives an anesthetic cartridge, and the transfer and exhaust needles penetrate a septum on the anesthetic cartridge so that the pusher can advance the plunger on the buffer cartridge to transfer buffer through the transfer needle into the anesthetic cartridge and excess anesthetic from the anesthetic cartridge is exhausted through the exhaust needle;

further comprising a first stop which limits advancement of the pusher to deliver a first volume of buffer as the pusher is advanced.

15. A device as in claim 14 , further comprising a housing having an end adapted to detachably receive the anesthetic cartridge, and an interior having an open end for receiving the buffer cartridge with the septum adjacent to the end adapted to detachably receive the anesthetic cartridge and the plunger adjacent the open end.

16. A device as in claim 15 , further comprising a knob which threadably connects to the attachment end of the housing, wherein the needle assembly is carried by the knob so that turning the knob advances the transfer needle into the buffer cartridge.

17. A device as in claim 16 , wherein the transfer and exhaust needles extend into an anesthetic cartridge receptacle on the knob so that inserting the anesthetic cartridge into the receptacle penetrates the transfer and exhaust needles through a septum of the anesthetic cartridge.

18. A device as in claim 14 , further comprising a compression member disposed to apply a predetermined force on the plunger when the pusher is advanced by a predetermined distance relative to the buffer cartridge prior to the transfer needle penetrating the septum on the buffer cartridge.

19. A device as in claim 18 , wherein the compression member is a coil spring positioned between the pusher and the plunger on the buffer cartridge.

20. A device as in claim 18 , wherein the pusher comprises the compression member.

21. A device as in claim 18 , further comprising a lock which holds the pusher at said predetermined advanced distance relative to the buffer cartridge.

22. A device as in claim 14 , further comprising a second stop which limits advancement of the pusher beyond the first stop to deliver a second volume of buffer as the pusher is advanced.

23. A device as in claim 14 , further comprising a receptacle for receiving and holding the excess anesthetic which is exhausted through the exhaust needle.