[Permissive hypotension in severe trauma]

Hemodynamic instability in the polytraumatized patient is a predominant feature and most commonly secondary to blood loss accompanying injury. In these patients restoration of intravascular volume attempting 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 and improved neurologic outcome, mainly stems from experimental studies in animals. In patient care, several concepts exist for the reduction of blood loss in conjunction with systemic hypotension: these involve "deliberate hypotension" (synonym "controlled hypotension", used intraoperatively under conditions of normovolemia and stable hemodynamics), "delayed resuscitation" (where the hypotensive period is intentionally prolonged until operative intervention), and "permissive hypotension" (synonym "hypotensive resuscitation", where all kinds of therapy are commenced including fluid therapy, thereby increasing systemic pressure without, however, reaching normotension). In this review the concept of "permissive hypotension" is delineated on the basis of macro- and microcirculatory changes secondary to hypovolemia and low driving pressure, and potential indications as well as limitations for the care of the traumatized patient are discussed.