Overview
This lecture reviews the stages of shock, their physiological mechanisms, clinical manifestations, and key concepts relevant for NCLEX preparation.
Types and Definition of Shock
- Shock is a state of decreased tissue perfusion leading to cellular hypoxia and organ dysfunction.
- Major types include: septic (severe infection), hypovolemic (fluid loss), cardiogenic (heart pump failure), anaphylactic (allergic reaction), neurogenic (nervous system injury), and obstructive (impeded blood flow).
- Distributive shock is a category including septic, anaphylactic, and neurogenic shocks.
Consequences of Shock
- Decreased perfusion prevents adequate oxygen delivery to organs and cells, causing hypoxia.
- Untreated shock can progress to multiple organ dysfunction syndrome (MODS) and death.
Stages of Shock
- Four stages: Initial, Compensatory, Progressive, Refractory.
Initial Stage
- Cells switch from aerobic (with oxygen) to anaerobic (without oxygen) metabolism due to low perfusion.
- Anaerobic metabolism produces lactic acid, leading to lactic acidosis.
- Signs and symptoms are very subtle in this stage.
Compensatory Stage
- Body activates neural, biochemical, and hormonal responses to restore perfusion.
- Baroreceptors trigger the sympathetic nervous system, releasing catecholamines (epinephrine, norepinephrine) causing vasoconstriction, increased heart rate, and blood pressure.
- Blood flow is prioritized to vital organs (heart and brain) over non-vital organs.
- The renin-angiotensin-aldosterone system (RAAS) increases blood volume and vasoconstriction.
- Antidiuretic hormone (ADH) further conserves water to boost blood volume.
- GI motility decreases (risk of paralytic ileus); skin becomes cold and pale (except warm/flush in early septic shock); lungs experience V/Q mismatch and increased respiratory rate.
Progressive Stage
- Compensatory mechanisms fail; significant drop in cardiac output and tissue perfusion.
- Increased capillary permeability causes fluid shift from vessels to tissues, widespread edema, and further hypoperfusion.
- Mental status worsens (confusion, agitation); mean arterial pressure (MAP) drops below 60 mmHg.
- Lungs develop ARDS (fluid-filled alveoli, respiratory failure).
- Heart experiences arrhythmias and risk of myocardial infarction.
- Kidneys suffer acute tubular necrosis and failure (decreased urine, increased BUN/creatinine, metabolic acidosis).
- GI tract at risk for ulcers and GI bleeding; liver cannot detoxify or produce clotting factors properly.
- Risk for disseminated intravascular coagulation (DIC) with simultaneous clotting and bleeding.
Refractory Stage
- Shock becomes irreversible; all organs fail and death is inevitable.
Key Terms & Definitions
- Shock — Decreased tissue perfusion leading to hypoxia and organ dysfunction.
- Aerobic metabolism — Cellular energy production using oxygen.
- Anaerobic metabolism — Cellular energy production without oxygen, producing lactic acid.
- Lactic acidosis — Accumulation of lactic acid lowering blood pH.
- Baroreceptors — Pressure sensors in vessels that detect low blood pressure.
- Catecholamines — Hormones (epinephrine, norepinephrine) for fight-or-flight response.
- RAAS (Renin-Angiotensin-Aldosterone System) — Hormonal system increasing blood pressure and volume.
- Antidiuretic hormone (ADH) — Hormone preventing water loss to increase blood volume.
- ARDS — Acute respiratory distress syndrome, fluid-filled lungs causing respiratory failure.
- MODS — Multiple organ dysfunction syndrome, failure of more than one organ system.
- DIC — Disseminated intravascular coagulation, abnormal clotting and bleeding.
Action Items / Next Steps
- Take the free quiz on stages of shock for practice.
- Review additional materials on individual types of shock and ARDS as suggested.