Pro: High dose of therapeutic plasma exchange-mind the gap!

'Mind the gap' is a recorded warning phrase used in the London Tube since 1969. The following article is meant to be a warning of an increasing knowing-doing gap in routine practice of therapeutic plasma exchange (TPE), a treatment method that is used more and more throughout the world. The American Society of Apheresis recommendations, including the most recent ones from 2016, suggest using a TPE volume of 1.0-1.5 times the actual calculated plasma volume of the patient. There are only a few exceptions to that rule, such as the recommnded exchange volume in vasculitis or mushroom poisoning. The published literature suggests that in routine clinical practice in many institutions in several countries the exchanged volume might in fact be lower than recommended by the guidelines. In the following article we argue for a high dose of exchanged plasma volume, yet sketch different scenarios on how this time-averaged high dose can be delivered in various ways depending on the underlying disease, refuting a one-size-fits-all strategy that might facilitate the procedure but may result in 'underpheresis' in many patients. Further, the objectives underlying the use of smaller exchange volumes, especially the gap between the cost of blood products and the reimbursement of TPE are discussed. Lastly, the knowing-guiding gap is described, which can only be overcome by collecting high-quality data and conducting prospective clinical trials in the field of TPE.