Pathophysiology of hemorrhagic shock and resuscitation

Abstract

Shock may be defined broadly as a condition in which metabolic energy production is limited either by the supply or utilization of oxygen, manifest by derangement of the normal oxygen supply-demand balance, accumulation of the byproducts of anaerobic metabolism, and dysfunction of one or more organ system. In the case of massive hemorrhage, shock is due specifically to impaired oxygen delivery (VO2) secondary to both hypovolemia and anemia. Restoration of tissue perfusion, termed resuscitation, proceeds systematically, is based upon the underlying etiology of shock, terminates upon achievement of clearly defined endpoints, and requires frequent re-evaluation. Resuscitation has been refined substantially over the previous decade, with a resultant improvement in the outcomes of critically ill patients (Brun-Buisson et al. 2004; Martin et al. 2003). Major changes have included improved accuracy of the assessment of intravascular volume status, recognition of the detrimental effects of both allogeneic blood product transfusion and excessive volume expansion, and timely, goal-directed treatment of shock and its complications. This chapter will focus on the diagnosis of shock, differentiation into hemorrhagic shock, the benefits and limitations of various measurements used to determine the adequacy of resuscitation, general resuscitative strategies, and complications of resuscitation.