Permissive hypotension.

In trauma patients restoration of intravascular volume in an attempt to achieve normal systemic pressure faces the risk of increasing blood loss and thereby potentially affecting mortality. Due to the lack of controlled clinical trials in this field, the growing evidence that hypotensive resuscitation results in improved long-term survival mainly stems from experimental studies in animals. The main differences between concepts for the reduction of blood loss in systemic hypotension are between "deliberate hypotension" (synonym "controlled hypotension", used intraoperatively), "delayed resuscitation" (where the hypotensive period is intentionally prolonged until operative intervention) and "permissive hypotension" (where restrictive fluid therapy increases systemic pressure without reaching normotension). In this review the concept of "permissive hypotension" is delineated on the basis of macro- and microcirculatory changes secondary to hypovolaemia and low driving pressure, and the potential indications and limitations are discussed.