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INTRODUCTION

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Shock is a state of circulatory dysfunction that results in insufficient oxygen delivery and other substrate to meet tissue metabolic demands.1 Inadequate oxygen delivery leads to a shift to anaerobic metabolism, eventually resulting in lactate production and metabolic acidosis.2 If this state persists, it can lead to multiple organ dysfunction and death.

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PHASES OF SHOCK

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If unrecognized and untreated, shock progresses through three phases due to inadequate oxygen delivery.

  • Compensated: Homeostasis is maintained by the body's compensatory mechanisms.

    • Increases in systemic vascular resistance and cardiac output through sympathetic nervous system activation and neurohormonal mechanisms lead to maintenance of blood pressure.

      • In younger children, cardiac output is maintained by increases in heart rate, leading to tachycardia.

    • Oxygen delivery is optimized by increasing oxygen extraction at the tissue level and maintaining blood flow to vital organs (e.g., heart, brain, and kidneys).

      • Blood flow to the gastrointestinal tract may be compromised.

      • Increased oxygen consumption leads to increased carbon dioxide (CO2) production, often resulting in an increased respiratory rate for CO2 elimination.

    • Early stages of all types of shock may be difficult to differentiate from the patient's normal status.

      • Tachycardia may be the only sign of shock.

  • Uncompensated: Despite the body's compensatory mechanisms, cardiovascular compromise occurs, leading to inadequate microvascular perfusion.

    • This state is characterized by an imbalance of oxygen delivery (DO2) and oxygen consumption (VO2).

      • Decreasing mixed venous oxygen saturation (SVO2) reflects a decrease in oxygen delivery relative to oxygen consumption.

      • Cellular metabolism and function deteriorate, leading to organ system dysfunction and metabolic acidosis from lactic acid production.

        • Increased lactate production can be seen in all forms of uncompensated shock.

    • As this phase evolves, the body loses the ability to maintain blood pressure due to cardiovascular compromise.

      • In children, hypotension is a late and ominous sign that may reflect up to a 25% to 40% loss of circulating blood volume.

  • Irreversible: Terminal or irreversible shock results from damage to key organs of such magnitude that death occurs. This occurs even if therapy returns cardiovascular parameters to normal.

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CLASSIFICATION OF SHOCK (SEE TABLE 28-1)

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Table Graphic Jump Location
TABLE 28-1

Classification of Shock

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RECOGNITION OF SHOCK AND ORGAN FAILURE

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Early ...

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