-Methods to estimate cardiac output, and detailed explanation of their pitfalls
-Importance of mixed venous O2, and which chambers to sample, and importance of SVC O2 vs IVC O2
-Cardiogenic shock indices
**Note regarding the use of thermodilution in atrial fibrillation (22:20):
CO (heart rate x stroke volume) rises with increased heart rate, up to a certain rate wherein diastolic filling sharply drops (~R-R of 500 ms or rate beyond 120 bpm). CO also sharply drops at R-R over 700 ms (rate less than 85 bpm), as diastolic filling does not rise enough to compensate for the rate drop. For the same heart rate, e.g., 100 bpm, the worst CO is seen when R-R varies between too long (rate less than 85 bpm) and too short (rate over 120 bpm). CO particularly drops with a long-short R-R sequence, causing at times a pulse deficit.
Thermodilution estimates cardiac output from few cardiac beats and assumes steady flow. In irregular rhythms with beat-to-beat variability, the sampled beats may not represent the average cardiac output. Less CO variability is seen when all sampled R-R intervals are within a rate range of 85-120 bpm, or when all R-R intervals correspond to less than 85 bpm, with no long-short sequences. Perform at least 5 measurements, and average the ones that are within 25% range. The same rate ranges are desired when assessing transvalvular gradients.
20 янв 2021
