The Full Talk Uninterrupted

So glad that this was able to help out with real time patient care!

Hi Eleanor, I really appreciate you taking the time to write this. When I was constructing this lecture, I debated whether to discuss the case essentially as it had happened (with lots of messiness, using the HCO3 numbers from the BMP, etc), or whether to simply calculate hypothetical numbers. I decided to favor the former, which may or may not not have been the right approach. The example to illustrate the CO2/last two digits of pH concept was completely invented, and in that example the HCO3 should certainly have been around 8 rather then around 10; I had picked a close round number to try to make it easy to visualize the point of the example with minimal ‘noise’, but I think that you are right and that ~2 point difference in HCO2 was probably ultimately more confusing to students than helpful. With regard to the case itself, you can see with the first ABG screenshot that, from the very beginning, the numbers didn’t strictly match up with Henderson-Hasselbach. In that first example, if we use the BMP HCO3 of 2, the pH per Henderson-Hasselbach with a HCO3 of 2 and PaCO2 of 10 should be around 6.90, not 7.02. In a bigger picture way, even though Henderson-Hasselbach is the main method of teaching acid base, it isn’t always a perfect descriptor or predictor of acid base disorders in clinical practice, and it’s explanatory power can sometimes be limited in the face of the broader range of variables that play into acid base status in vivo, even aside from imperfect sample collection, machine calibration, states of very profound physiologic disturbance, etc. As in the case of the first ABG, even if the numbers we are presented with clinically do not match up precisely with Henderson-Hasselbach, we can still make sense of the overall clinical situation. What I was hoping to achieve here was not to have people calculate the math of acid-base per Henderson-Hasselbach because that is an exercise that most people have already gone through a number times during their training, but rather to attempt to talk about the clinical significance of certain bigger picture patterns and trends in a patient’s acid-base status. On the one hand, I did want to make the point (as I tried to make explicitly with the first ABG screenshot) that even though real patients scenarios and numbers may be messy, you can still get an understanding of the most important aspects of the bigger picture clinical situation in a way that guides your management. But that all being said, your points are very valid and I do recognize that I could have made this talk better by adjusting the numbers to be more congruent with hypothetical values while continuing to use the real case as a base in order to help avoid adding any potential confusion for students in an already confusing topic. This is something that I can be sure to do in future acid-base segments. Hopefully this series will get better slowly as we go, and I really appreciate your ongoing feedback.