Shock: new developments in the management of shock.

Circulatory shock represents critical reductions of blood flow to tissues with curtailed delivery of energy substrate and especially oxygen. Generation of lactic acid highlights the onset of anaerobic metabolism and represents the clinical hallmark of perfusion failure. For the purpose of classification, prognostication and management, we now recognize four mechanisms by which circulatory shock may evolve. The first three represent states of decreased cardiac output in which shock may stem from acute decreases in circulating volume (hypovolemic shock), loss of patency to mainstream blood flow (obstructive shock) or impaired myocardial function (cardiogenic shock). The fourth one represents altered distribution of blood flow such that perfusion failure may emerge despite increases in total blood flow (distributive shock).