Lesson 5 – Interplay of Ventilation, Perfusion, & Shock

Oxygen cascade

Oxygen moves from the atmosphere to cells starting with ventilation (air into alveoli), then perfusion (oxygenated blood to tissues). Disruptions at any stage can lead to shock. EMT interventions support this cascade to improve outcomes.

Ventilation impacting perfusion

Ventilation problems like tension pneumothorax cause hypoxemia and increased intrathoracic pressure, reducing venous return and cardiac output, leading rapidly to shock. Interventions (e.g., needle decompression) address both ventilation and perfusion.

Perfusion impacting ventilation

Cardiogenic pulmonary edema from poor heart pumping causes fluid buildup in lungs, impairing gas exchange and increasing respiratory effort. Patient fatigue can cause ventilatory failure and worsen shock. Interventions (e.g., positioning, CPAP) improve both cardiac and respiratory function.

Shock’s vicious cycle

Decreased tissue perfusion causes cells to switch to anaerobic metabolism producing lactic acid. Compensation increases respiratory rate, raising oxygen demand, which worsens respiratory fatigue and shock. Early intervention is crucial to break this cycle.

Multi-system trauma example

Head injury affects respiratory drive, chest trauma impairs ventilation, and internal bleeding impairs perfusion. These issues compound, worsening hypoxia and shock. Assessment and interventions must address all simultaneously for effective care.

Sepsis and V/Q/shock

Sepsis causes ARDS impairing ventilation, vasodilation and myocardial depression impairing perfusion, and mitochondrial dysfunction impairing oxygen use at cellular level. Care must support respiratory, cardiovascular, and cellular levels.

Integrated assessment approach

Start with general impression, assess consciousness (reflecting perfusion), evaluate ABCs with attention to oxygenation (SpO2), ventilation (rate, effort), circulation (tachycardia, skin signs). Reassess frequently to track progress and effectiveness of care.

Multi-target interventions

Positioning improves ventilation and venous return; oxygen supports oxygenation and perfusion; assisted ventilation reduces work of breathing and aids circulation; bleeding control addresses volume loss and oxygen delivery. Interventions often affect multiple physiological systems.

Interconnected nature

Ventilation, perfusion, and shock are deeply linked. Problems in one cause issues in others, creating complex clinical pictures that require integrated assessment and management. Frequent reassessment is vital to patient care.

Next lesson preview

Final lesson will review special considerations for pediatric and geriatric patients, and environmental factors influencing ventilation, perfusion, and shock.