Shock is a physiologic state characterized by a significant, systemic reduction in tissue perfusion, resulting in decreased tissue oxygen delivery. Although the effects of inadequate tissue perfusion are initially reversible, prolonged oxygen deprivation leads to generalized cellular hypoxia and derangement of critical biochemical processes, including [1,2]:
- Cell membrane ion pump dysfunction
- Intracellular edema
- Leakage of intracellular contents into the extracellular space
- Inadequate regulation of intracellular pH
These abnormalities rapidly become irreversible and result sequentially in cell death, end-organ damage, failure of multiple organ systems, and death [3-5]. Mortality from shock is less among children than adults. For children with severe sepsis, mortality is about 10 percent, in comparison to 35 to 40 percent within one month of the onset of septic shock for adults [6,7]. Nevertheless, outcomes for children with shock (in terms of morbidity and cost) are significant. Furthermore, unique physiologic responses to poor perfusion among children make it a challenge for clinicians to recognize shock early (before hypotension develops), when responses to treatment are more favorable.
This topic will review the physiologic determinants and classification of shock. The initial evaluation and management of shock in children, in general, and hypovolemic and septic shock, specifically, are discussed separately. (See "Initial evaluation of shock in children" and "Initial management of shock in children" and "Hypovolemic shock in children: Initial evaluation and management" and "Systemic inflammatory response syndrome (SIRS) and sepsis in children: Definitions, epidemiology, clinical manifestations, and diagnosis".)
Parameters that determine adequate oxygen delivery to tissues include blood flow to tissues (cardiac output), the regional balance between blood flow and metabolic demand, and the oxygen content of blood (hemoglobin concentration and percentage of hemoglobin saturated with oxygen) . Physiologic variables that the body can manipulate to compensate for compromised perfusion include: