Chapter 5: Shock

KEY POINTS

1. Shock is defined as a failure to meet the metabolic demands of cells and tissues and the consequences that ensue.

2. A central component of shock is decreased tissue perfusion. This may be a direct consequence of the etiology of shock, such as in hypovolemic/hemorrhagic, cardiogenic, or neurogenic etiologies, or may be secondary to elaborated or released molecules or cellular products that result in endothelial/cellular activation, such as in septic shock or traumatic shock.

3. Physiologic responses to shock are based on a series of afferent (sensing) signals and efferent responses that include neuroendocrine, metabolic, and immune/inflammatory signaling.

4. The mainstay of treatment of hemorrhagic/hypovolemic shock includes volume resuscitation with blood products. In the case of hemorrhagic shock, timely control of bleeding is essential and influences outcome.

5. Prevention of hypothermia, acidemia, and coagulopathy is essential in the management of patients in hemorrhagic shock.

6. The mainstay of treatment of septic shock is fluid resuscitation, initiation of appropriate antibiotic therapy, and control of the source of infection. This includes drainage of infected fluid collections, removal of infected foreign bodies, and débridement of devitalized tissues.

7. A combination of physiologic parameters and markers of organ perfusion/tissue oxygenation are used to determine if patients are in shock and to follow the efficacy of resuscitation.

EVOLUTION IN UNDERSTANDING SHOCK

Overview

Shock, at its most rudimentary definition and regardless of the etiology, is the failure to meet the metabolic needs of the cell and the consequences that ensue. The initial cellular injury that occurs is reversible; however, the injury will become irreversible if tissue perfusion is prolonged or severe enough such that, at the cellular level, compensation is no longer possible. Our evolution in the understanding of shock and the disease processes that result in shock made its most significant advances throughout the twentieth century as our appreciation for the physiology and pathophysiology of shock matured. Most notably, this includes the sympathetic and neuroendocrine stress responses on the cardiovascular system. The clinical manifestations of these physiologic responses are most often what lead practitioners to the diagnosis of shock as well as guide the management of patients in shock. However, hemodynamic parameters such as blood pressure and heart rate are relatively insensitive measures of shock, and additional considerations must be used to help aid in early diagnosis and treatment of patients in shock. The general approach to the management of patients in shock has been empiric: assuring a secure airway with adequate ventilation, control of hemorrhage in the bleeding patient, and restoration of vascular volume and tissue perfusion.

Historical Background

Integral to our understanding of shock is the appreciation that our bodies attempt to maintain a state of homeostasis. Claude Bernard suggested in the mid-nineteenth century that the organism attempts to maintain constancy in ...