Lets talk about SpO2 monitors.
What do they do? Well duh they tell us how much oxygen is in our patients blood! Okay, cool, then how does that effect our assessments? If their saturations (sats) are low then were going to give them oxygen. Right?
Well… What if I told you that you wernt’t wrong, but your not exactly right either. The reason for this is due to the fact that sat monitors are actually a big misconception in EMS. We are all taught that we are getting an oxygen reading when we use a sat monitor.
The problem is that sat monitors actually read Hemoglobin saturation not specifically oxygen saturation. The best way to explain is to talk a little patho. Now hear me out, yes patho can be hard but were an EMS school not a pre-med school. Hemoglobin are on the red blood cells. Hemoglobin are the sites where molecules like oxygen bind. On one single red cell there are between 250-270 million hemoglobin. Each hemoglobin has 4 receptors on it. Which means that every single red blood cell (of which there are approximately 20-30 trillion) are capable of carrying 1 billion molecules of oxygen.
With that simple explanation it make sense that what we are reading as 98% on the monitor is the percentage of saturated hemoglobin, not how much actual oxygen we have bound.
We know that we want to see a sat reading between 94%-99%. We also know that we do not want sats of 100% due to free radical release. But if all we are reading is the percentage of hemoglobin saturation, there is no guarantee that it’s actually oxygen on that hemoglobin.
We take for granted that most of our patients are not exposed to carbon monoxide (which binds 200-300 times more readily to hemoglobin that O2), or Cyanide (which when taken into the blood will bind 92%-99% to hemoglobin). So we assume that since most of our patients are not chronically or acutely exposed to these other gases that the reading is in-fact O2.
However, if we go on patients that are experiencing symptoms like headache, nausea, shortness of breath, fatigue, or Altered LOC. We should used a device like the RAD-57, or Zoll Monitors equipped to read SPCO. These devices are specifically designed to read not just the saturation of the hemoglobin, but to actually decipher what percentage is carbon monoxide. Then with this reading we can take the appropriate treatment steps as per our protocols.
With our patients being indoors more during the winter months, the increased use of furnaces, and in some cases space heaters we always want to keep a high index of suspicion for patients suffering from CO poisoning this time of year.