Concepts

Each entry follows the same three-part structure: Mechanism, Evidence, and Open questions. Entries are revised as the evidence moves.

Perioperative hemodynamics

Mean systemic filling pressure (Pmsf)What mean systemic filling pressure is, why it, not central venous pressure, is the upstream pressure driving venous return, how it has been measured in humans, and where the estimates disagree.
Critical closing pressure (Pcc)What critical closing pressure is, why it makes systemic vascular resistance an ill-defined quantity, how bedside estimates of Pcc are derived from pulse pressure × heart rate, and what five recent cohorts do and do not establish.
Tissue perfusion pressure: MAP − Pcc, or Pcc − Pmsf?Two research groups use the phrase "the pressure driving tissue perfusion" for two different gradients: MAP − Pcc and Pcc − Pmsf. What each one measures, what the evidence for each shows, and why a MAP target alone cannot tell them apart.
Estimating cardiac output from pulse pressure: a 120-year genealogyFrom Erlanger and Hooker in 1904 to the tissue-perfusion-pressure method of 2023, every attempt to read cardiac output from the arterial pulse has run into the same constant, arterial compliance. How each generation handled it, and why the newest method rests on the oldest assumption.
The Hypotension Prediction Index, 2018–2026A machine-learning index that predicts intraoperative hypotension minutes ahead: its 2018 validation, the trials that followed, the critique that its performance is largely that of mean arterial pressure itself, and the 2025–2026 trials that tested it against outcomes and against a simple MAP trigger.