Once upon a time we would use our gut instinct to inform our decisions as to whether it was reasonable to try and extubate (take out a breathing tube) or to lower or stop CPAP (continuous positive airway pressure). We used to look at home much oxygen a baby needed and what the pressures were on the machine offering them support and combined with what we saw on the patient monitor for oxygen saturation make a decision as to what to do next.
In the last decade or so people realized (as did one of our own respiratory therapists) that buried within all of this data on the patient monitor one could get a report on what percentage of time each infant has spent at different levels of systemic oxygen saturation. A sample report might look like this.
>95% – 10%
90 – 94% – 55%
85-89% – 20%
80 – 84% – 10%
<80% – 5%
Seeing this report though is only half the story. Without knowing how much oxygen on average an infant has received in the last twenty four hours to achieve this range it is somewhat meaningless. The amount of oxygen given may show that we the baby is doing better or worse. For example, if the above histogram was achieved using a range of 25-35% oxygen and was no different than the day before but the infant had been on 30-40% oxygen and pressure the day earlier then we have gotten somewhere! This infant has actually improved. The histogram is unchanged but we have given less oxygen on the same amount of pressure. If the histogram was unchanged but the amount of oxygen was 21-25% the day before, the lungs have gotten worse assuming the same pressure.
It is also worth noting that higher numbers are not alway indicative of a good thing. Take for example this histogram:
>95% – 50%
90-94% – 35%
85-89% – 8%
80-84% – 7%
<80% – 0%
If this infant was on room air and having these numbers I would be overjoyed. What if this was a baby though who was on 30-40% oxygen? These numbers are too good! We know that too much oxygen can be bad for the lungs and eyes. For babies on oxygen we typically target 88-92 % oxygen saturation (others use 90-94%). If we have 50% of the time above 95% oxygen we clearly are using too much and have to cut it back.
As parents you will hear us talk about histograms on rounds and use the information to make decisions about oxygen and the amount of breathing support your baby needs. If you have wondered how we use this information and what this seemingly random assortment of numbers really means, this is how we interpret it. The next time someone says that your infant needs more or less support ask for the histogram information if your unit uses it and you will see whether the data support the change.