Date: 201905
Local time of day: 0601-1200
Location: ZLA.ARTCC, CA
Light: Daylight
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZLA
ATC / advisory: Center ZLA
Reporter organization: Air Carrier
Reporter function: Flight Attendant (On Duty)
Reporter qualification: Flight Attendant Current
Human factors: Situational Awareness; Distraction
Second reporter function: Flight Attendant (On Duty)
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Illness / Injury
Detector: Person Flight Attendant
When detected: In-flight
Contributing factors: Human Factors; Procedure; Manuals
Primary problem: Procedure

Narrative: At beginning of the first beverage service approximately 30 minutes into the flight a passenger gets the C Flight Attendant attention and says her husband needs oxygen. The portable oxygen machine that he brought onboard was not sufficient; it had his oxygen level at 59 which was dangerous because doctors had advised them he couldn't go lower than 65 for his condition. We immediately administered oxygen from the plane while I paged for medical assistance and notified pilots. We had a doctor onboard who asked for a stethoscope to check on the man; and pilots communicated with us and with Medlink at the same time. Medlink advised to administer oxygen; and continued to give oxygen through the entirety of the flight to keep his oxygen intake at a safe level. Following Medlink's direction and for the passenger's safety and wellbeing; 3 oxygen bottles were fully depleted and he had a fourth one that he kept for the end of the flight and landing until he had to step off the plane. We offered to have medics meet the plane once we landed; but passenger declined. His wife said they were going directly to his doctor in charge of his lung transplant.Throughout the flight the pilots were kept informed and they notified the destination airport that portable oxygen bottles needed to be replaced once we landed. There was no indication on our specials that the passenger had his own oxygen or that he would be using it during flight. We don't know if the machine he was using during the flight was even approved to be used during flight. Approximately 30 minutes into the flight we administered oxygen to the passenger and contacted Medlink who advised us to keep passenger on oxygen. After stabilizing him we continued with our service and when we would go back to check on him oxygen bottles were fully depleted. We ended up fully depleting 3 oxygen bottles; and about 20 minutes before we landed we gave the passenger another oxygen bottle that he kept for landing. Before he stepped off the plane flight attendants took the POB (Personal Oxygen Bottles). I am not sure if he fully depleted the fourth bottle also. We were all aware that we needed to switch oxygen bottles when the gauge was at 250. We asked his wife to ring call button when POB was at 250; but she notified us when the first bottle was complete depleted. We checked on him as much as we could during the flight; but the bottles would be depleted and we would give him a new one. We all needed to be keeping a closer eye and made sure that the oxygen bottles were switched out once the gauge was at 250. I relied on the passenger's wife to notify us when it was at 250; but she wouldn't do so until the bottle was complete depleted. It was a very busy flight and by the time one of us had a chance to check on the passenger; the bottles were depleted.


Second narrative: [Report narrative contained no additional information.]


Synopsis: Flight Attendants reported administering 4 oxygen bottles to an ill passenger when the bottles were completely empty instead of at the required interval.