Narrative:

Approximately 200 NM to the etp the a flight attendant advised us of a passenger illness and the need for medlink. I advised commercial radio and a discrete HF frequency was arranged and the patch was made. An on board er nurse attended the passenger; made evaluations; provided treatment; and talked directly to medlink. Medlink advised that we could continue and to provide O2 as needed. The flight attendant advised that they were using the therapeutic O2 bottle. The flight attendant later advised us when the therapeutic bottle reached 250 psi and a decompression bottle was used. As we still had several hours of flying; we discussed O2 use; and operational restrictions regarding depletion of O2 bottles. The first officer and I discussed that the safest course of action; regardless of O2 quantities; would be to remain at altitude. I advised the first officer that I was exercising captains emergency authority in the event any of those bottles went below the prescribed volumes in order to remain at altitude. I discussed an O2 use plan with the flight attendant. We discussed using one decompression bottle to 1;500 psi; then switch to the other decompression bottle; and use it until depleted. Shortly afterwards; she advised me that the first decompression bottle was at 1;250 psi. I told her to switch to decompression bottle two; use it to 1;500 psi; then use decompression bottle one; and deplete it. My thought was to ensure the flight attendant's maintained full capabilities in their mobility bottles. Shortly after this discussion; the flight attendant advised that they could use their mobility bottles to 1;000 psi. With this information we revised our plan to include the mobility bottles as long as they ensured the mobility bottles did not go below 1;000 psi. ACARS messages were sent to dispatch advising them of the O2 usage and the volume levels of the bottles. After the second decompression bottle was used to 1;500 psi; two mobility bottles were depleted to 1;000 psi and a third was being used as we began our descent. Upon landing we were met by medics and the passenger was transported to medical facilities. Once we were deplaned I discussed O2 bottle usage with the flight attendants to ensure I fully understood the amount used. I discovered that the therapeutic bottle was depleted to 250 psi; the number one decompression bottle to 250 psi; number two to 1;500 psi; and two mobility bottles to 1;000 psi. Mechanics boarded the aircraft; were advised and we discussed the write ups of the bottles as well as the emk. [We were in a] high workload environment in ETOPS airspace. Medlink event happened near a waypoint with need to arrange for medlink; plot; and report waypoints; monitor medlink transmissions via HF; and derive an O2 use plan with flight attendant's that would be sufficient for a number of hours. There appeared to be confusion between the naming conventions of each type of bottle and the amount we could use before encountering altitude restrictions. I thought that the flight attendant was trading the names of the therapeutic bottle and the decompression bottle. Once on the ground I discovered that both the therapeutic bottle and one mobility bottle were depleted to 250 psi.

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Original NASA ASRS Text

Title: An Air Carrier flight crew depleted their cabin oxygen bottles below acceptable limits while treating a passenger who became ill near the ETP. There was confusion with naming conventions of the bottles and operational restrictions.

Narrative: Approximately 200 NM to the ETP the A Flight Attendant advised us of a passenger illness and the need for Medlink. I advised Commercial radio and a discrete HF frequency was arranged and the patch was made. An on board ER nurse attended the passenger; made evaluations; provided treatment; and talked directly to Medlink. Medlink advised that we could continue and to provide O2 as needed. The Flight Attendant advised that they were using the Therapeutic O2 bottle. The Flight Attendant later advised us when the therapeutic bottle reached 250 PSI and a decompression bottle was used. As we still had several hours of flying; we discussed O2 use; and operational restrictions regarding depletion of O2 bottles. The First Officer and I discussed that the safest course of action; regardless of O2 quantities; would be to remain at altitude. I advised the First Officer that I was exercising Captains Emergency Authority in the event any of those bottles went below the prescribed volumes in order to remain at altitude. I discussed an O2 use plan with the Flight Attendant. We discussed using one decompression bottle to 1;500 PSI; then switch to the other decompression bottle; and use it until depleted. Shortly afterwards; she advised me that the first decompression bottle was at 1;250 PSI. I told her to switch to decompression bottle two; use it to 1;500 PSI; then use decompression bottle one; and deplete it. My thought was to ensure the Flight Attendant's maintained full capabilities in their mobility bottles. Shortly after this discussion; the Flight Attendant advised that they could use their mobility bottles to 1;000 PSI. With this information we revised our plan to include the mobility bottles as long as they ensured the mobility bottles did not go below 1;000 PSI. ACARS messages were sent to Dispatch advising them of the O2 usage and the volume levels of the bottles. After the second decompression bottle was used to 1;500 PSI; two mobility bottles were depleted to 1;000 PSI and a third was being used as we began our descent. Upon landing we were met by medics and the passenger was transported to medical facilities. Once we were deplaned I discussed O2 bottle usage with the Flight Attendants to ensure I fully understood the amount used. I discovered that the therapeutic bottle was depleted to 250 PSI; the number one decompression bottle to 250 PSI; number two to 1;500 PSI; and two mobility bottles to 1;000 PSI. Mechanics boarded the aircraft; were advised and we discussed the write ups of the bottles as well as the EMK. [We were in a] high workload environment in ETOPS airspace. Medlink event happened near a waypoint with need to arrange for Medlink; plot; and report waypoints; monitor Medlink transmissions via HF; and derive an O2 use plan with Flight Attendant's that would be sufficient for a number of hours. There appeared to be confusion between the naming conventions of each type of bottle and the amount we could use before encountering altitude restrictions. I thought that the Flight Attendant was trading the names of the therapeutic bottle and the decompression bottle. Once on the ground I discovered that both the therapeutic bottle and one mobility bottle were depleted to 250 PSI.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.