A B737 FLT ATTENDANT GAVE A PAX OXYGEN FROM AN ACFT OXYGEN WALK-AROUND BOTTLE INTENDED FOR EMER VERSUS THERAPEUTIC OXYGEN WITHOUT NOTIFYING THE FLT CREW. USE OF WALK-AROUND 'DECOMPRESSION' BOTTLE USE REQUIRES A DSCNT TO FL250.

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DURING THE CRUISE PORTION OF THIS 5 HR 40 MIN FLT; THE FIRST FLT ATTENDANT NOTIFIED US THAT THEY WERE ADMINISTERING OXYGEN TO AN ELDERLY WOMAN WHO SEEMED TO BE A BIT UNCOMFORTABLE WITH THE CABIN ALT OF THE ACFT. WE UNDERSTOOD THAT SHE WAS USING THE THERAPEUTIC OXYGEN FOR THIS REQUIREMENT. THE FLT ATTENDANT CALLED A COUPLE OF TIMES TO TELL US THAT THE LADY WAS DOING FINE AND THAT THEY WERE CONTINUING TO USE THE OXYGEN. I ASKED THE FLT ATTENDANT FOR A CABIN WRITE UP FORM IN ORDER TO PROPERLY DOCUMENT IN THE MAINT LOG THE USE OF OXYGEN AND WHICH SPECIFIC BOTTLES WERE USED. IT WAS AT THIS POINT (DURING THE DSCNT ON ARR) THAT WE REALIZED THAT THE FLT ATTENDANTS HAD USED THE EMER DECOMPRESSION OXYGEN BOTTLES DOWN TO 250 PSI. PER THE FOM; THIS SITUATION REQUIRED THAT WE DSND THE ACFT BELOW FL250 TO CONTINUE FLYING. SINCE WE DID NOT KNOW/UNDERSTAND THE ACTUAL SITUATION; WE DID NOT COMPLY WITH THE REQUIREMENT TO DSND. AFTER BEING INFORMED OF THE SITUATION; I EXPLAINED TO THE FIRST FLT ATTENDANT THAT WHEN THE DECOMPRESSION BOTTLES ARE TAKEN BELOW 1500 PSI WE ARE REQUIRED TO DSND. SHE EXPLAINED THAT THEIR MANUALS DO NOT ADDRESS THIS CONDITION -- ONLY THAT THEY ARE ALLOWED TO UTILIZE THE DECOMPRESSION BOTTLES DOWN TO 250 PSI. WE QUERIED THE FLT ATTENDANT SEVERAL TIMES REGARDING WHETHER WE HAD SUFFICIENT OXYGEN BOTTLES TO ADMINISTER AND NOT JEOPARDIZE WHAT WAS REQUIRED FOR SAFETY OF FLT. WE WERE ASSURED THAT THERE WAS NO PROBLEM OR JEOPARDY. IT APPEARS THAT THE GUIDANCE REGARDING USE OF EMER DECOMPRESSION OXYGEN BOTTLES IS SIGNIFICANTLY DIFFERENT BETWEEN WHAT IS PUBLISHED IN THE FLT ATTENDANT MANUALS VERSUS WHAT IS PUBLISHED IN THE FOM.