Hi Gillyjohnny, and thanks for sharing your story about your dad with the community. Although we cannot provide medical advice or diagnostics over the internet (for your own safety), your concern certainly warrants a reply.
Oxygenation, typically is reported in one of two ways, either as a saturation level (in percentage), or, as a partial pressure (in millimeters of mercury (mmHg)). The interpretation or explanation of the number '50' will depend on how the oxygen level was measured. This really is something you will want to discuss further with dad's physician.
Has you dad been diagnosed with COPD? Does he have other medical conditions as well? If he is being followed by and cared for by a physician, the doctor will be able to guide you as to what to expect for your father, going forward.
It's heartwarming to see your devotion, compassion, and love for your father - please know we are wishing both of you well. Kindly do check back and keep us apprised of his progress and also about how YOU are doing.
If there is anything we can do to assist you, please let me or any other moderator / team member know.
Warm regards,
Leon (site moderator COPD.net)