Permissive hypotension

In trauma patients restoration of intravascular volume in an attempt to ach ieve normal systemic pressure faces the risk of increasing blood toss and t hereby potentially affecting mortality. Due to the lack of controlled clini cal trials in this field, the growing evidence that hypotensive resuscitati on results in improved long-term survival mainly stems from experimental st udies in animals. The main differences between concepts for the reduction o f blood loss in systemic hypotension are between "deliberate hypotension" ( synonym "controlled hypotension", used intraoperatively), "delayed resuscit ation" (where the hypotensive period is intentionally prolonged until opera tive intervention) and "permissive hypotension" (where restrictive fluid th erapy increases systemic pressure without reaching normotension). In this r eview the concept of "permissive hypotension" is delineated on the basis of macro- and microcirculatory changes secondary to hypovolaemia and low driv ing pressure, and the potential indications and limitations are discussed.