Dear Dr. Orde, I have seen the whole FCU chapter, and will totally recommend it to the IM and ICM fellows here (Concepcion, Chile). I have only one comment/question: would you say an IVC "collapses" during fully MV? (as seen on 16:40 ). IMO if there is some collapse during passive MV, is either spontaneous breathing and/or US misalignment (I know this vid is only basic FCU, and I would - same as you do - use PLR and VTI +/- doppler to fully assess volume status and fluid responsiveness). Thank you very much again for providing outstanding free medical education! Nico.
Hi Nico, great question and this is a pretty murky area. The main thing to keep in mind is that the collapsibility of the IVC is probably only useful at extremes (very small, very collapsible, or vary distended and not collapsing) in practice and is only one piece of information in a more comprehensive clinical picture as you know. To complicate things further, the original studies that looked at the IVC in "fully" mechanically ventilated patients used tidal volumes of 10ml/kg which we don't do anymore so its hard to know how to apply that knowledge with modern ventilator practices. Regardless, the IVC can vary with changes in thoracic pressure including positive pressure ventilation, but whether this can be precisely quantified and used to assess fluid status accurately - that's a different question...definitely not in isolation. I hope you found it useful all the same and thanks for watching!
