ABGs we got several requests for today's post to be about ABGs and ABG interpretation, so here we go!
ABGs have always been a stumbling block for the paramedic student. For some reason, we simply do not do well with topics or concepts that we can't physically see in the back of a medic unit.
Although the majority of agencies are not drawing ABGs in the prehospital setting, there are some agencies that do and it is certainly a topic that the NREMT loves testing on at the Paramedic level, so it's best we just accept it as it is, because I don't think it's going anywhere.
To begin to understand ABGs, we first must understand what we are measuring.
pH: 7.35 - 7.45
CO2: 35 - 45
HCO3: 22 - 26
Above are the normal ranges for the body's pH, carbon dioxide, and bicarbonate. When the measurements of those items fall outside of their normal range, at the entry paramedic level, we are expected to identify which values are no longer normal, and appropriately name the acidotic or metabolic condition that the patient is in.
When approaching ABGs, I always look at the pH first. Is the pH normal, low (acidic), or high (alkalotic). If the pH is normal, it doesn't mean that I can stop looking....the CO2/HCO3 could be outside of their normal values but the pH has yet to be effected by it. If the pH is low (acidic, < 7.35), I look at the CO2 and HCO3 to determine which of those is also acidic. Ultimately, we are trying to determine if it is the CO2 (respiratory problem) or the HCO3 (metabolic problem) causing the pH to be acidic.
The same applies if the pH is high (alkalotic). We then look at the CO2 and HCO3 values to determine which is alkalotic. Is it the CO2 (respiratory problem) or is it the HCO3 (metabolic problem).
Respiratory Acidosis: pH <7.35 / CO2 > 45
Respiratory Alkalosis: pH > 7.45 / CO2 < 35
Metabolic Acidosis: pH < 7.35 / HCO3 < 22
Metabolic Alkalosis: pH > 7.45 / HCO3 > 26
If you notice the "trends" above, in respiratory driven problems, the pH is moving in the opposite direction of the CO2 (pH - low, CO2 - high / pH - high, CO2 - low). Additionally, you notice that in metabolic driven problems, the pH and the HCO3 move in the same or equal direction (pH - low, HCO3 - low / pH - high, HCO3 - high). This "trend" can be easily remembered as "ROME" - Respiratory Opposite Metabolic Equal.
-Pass with PASS