Oxygen saturation is a measure of how much oxygen the haemoglobin molecules in the body are carrying. It’s usually shown as a percentage of the maximum it could carry. The blood carries oxygen to every part of our bodies, bringing the life-giving oxygen to every cell, so that we can keep functioning.

For the average fit, healthy person, the oxygen saturation is usually between 98 and 100%. This means that, just like a fire, we have energy to burn; in fact, the oxygen in our blood enables the cells to break the chemical bonds within them so as to create energy.

However, just like in one of those glass-fronted fireplaces, when the oxygen levels fall, the fire goes from raging, to a slow burn, and then out completely.

In hospital, if a patient is on oxygen, all the alarms start ringing if their saturation falls below 90%. Over the last year, which has seen Ngaire go full-time onto supplemental oxygen, she has generally been able to keep her resting levels in the low to mid-90’s. Of course, when any movement happens and the blood-oxygen is burned for energy, the levels drop drastically.

Usually when this happens, the heart rate increases because the body recognises that it doesn’t have enough oxygen so, rather than pass out, it compensates by pumping blood faster in order to supply the cells with what oxygen it does have. Over an extended period of time this can have a damaging effect on the heart itself because, as a muscle, it needs oxygen too; so trying to pump harder with reduced oxygen leads to a weakened, sometimes-enlarged heart.

Another obvious effect is that, as the body needs oxygen desperately, it tries to both conserve what it has, and get more. Blood supply is diverted away from extremities and the digestive system in order to supply vital organs. This means that Ngaire feels the cold easily and rarely feels like eating – it takes a lot of oxygen to digest food. Consequently she has lost a lot of weight and is now 46 kg.

Gasping for air becomes a part of life, but this doesn’t help, as shallow gasps lead to hyper-ventilation, which only increases carbon dioxide in the blood.

Her resting oxygen saturation now, even with supplemental oxygen, is in the mid-80’s. With even the slightest exertion – walking a few metres, even just rolling over in bed – it will plummet into the 60’s. At this level it is almost impossible to remain conscious for long and requires planned, ordered breathing to slowly get her back to “normal”.

It has been getting much more difficult over the last few weeks and we are confronting what has previously been a “no-go” zone. What does life look like beyond this stage? We have heard of patients waiting for a transplant who need to go into hospital on life support; when does that happen? Will she need a constant companion? If so, when? And all of this while the “other stuff of life” goes on around in us and in our family: work, school, driving lessons, future plans, girlfriends, birthdays and bills.

“A day at a time” has become such a hackneyed phrase, but, it is our reality now. The media bubble of all the hedonistic pleasures that should be streaming through our front door at this time of life, burst long ago. Instead, we are learning deeper lessons about love, commitment, fear, friendship, support, eternity and in the midst of the pain and confusion, there is something deeply good going on. I just wish we could work out what it is….