Chapter 28: Shock

INTRODUCTION

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.

PHASES OF SHOCK

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.

CLASSIFICATION OF SHOCK (SEE TABLE 28-1)

RECOGNITION OF SHOCK AND ORGAN FAILURE