Lesson 1 – Ventilation, Perfusion & Shock

Ventilation, perfusion, and shock

Interrelated processes fundamental to patient physiology and emergency care. Ventilation is air movement in and out of the lungs, perfusion is delivery of oxygenated blood to tissues, and shock is a life-threatening state where cells are not receiving enough oxygen.

Ventilation, perfusion, and shock as a triangle

Each process supports and affects the others; a problem in one can quickly cause problems in the others due to interdependence.

Ventilation

Movement of air in and out of the lungs, including the rate and quality of breathing. Assessment involves respiratory rate, depth, and effort.

Normal adult respiratory rate

12–20 breaths per minute.

Cheyne-Stokes respirations

Abnormal breathing pattern with alternating periods of hyperpnea (deep breathing) and apnea (no breathing); may indicate serious conditions.

Kussmaul breathing

Deep and labored breathing, often seen in diabetic ketoacidosis and other serious metabolic disturbances.

Processes of ventilation

Inspiration (breathing in) and expiration (breathing out).

Inspiration

Diaphragm and intercostal muscles contract, increasing thoracic cavity volume, creating negative pressure, and drawing air into the lungs.

Expiration

Usually passive; elastic recoil of the lungs pushes air out.

Signs of respiratory distress

Use of accessory muscles, paradoxical chest movement, abnormal breathing patterns.

Perfusion

How well oxygenated blood is delivered to the body’s tissues.

Factors affecting perfusion

Adequate blood volume, functioning cardiovascular system, and open blood vessels.

Assessment of perfusion

Check skin color, temperature, and capillary refill time.

Signs of poor perfusion

Pale, cool, clammy skin with delayed capillary refill.

Perfusion and cellular respiration

Cellular respiration uses oxygen to produce energy; inadequate perfusion leads to anaerobic metabolism, lactic acid buildup, and metabolic acidosis.

Shock

Life-threatening condition where the body’s cells are not getting enough oxygen.

Initial response to shock

Compensatory mechanisms such as increased heart rate and respiratory rate.

Progression of shock

Failure of compensatory mechanisms leading to decompensated shock and possible irreversible organ damage.

Types of shock

Hypovolemic: fluid loss from bleeding or dehydration; Cardiogenic: heart cannot pump effectively (e.g., heart attack); Distributive: abnormal blood distribution (e.g., sepsis, anaphylaxis); Obstructive: physical obstruction to blood flow (e.g., pulmonary embolism, cardiac tamponade).

Importance of understanding ventilation, perfusion, and shock

They are interconnected; a problem in one area can cause or worsen problems in the others.

Cyclical relationship between ventilation and shock

Inadequate ventilation → hypoxia → shock; shock → respiratory failure → worsened ventilation.

Assessment techniques for ventilation, perfusion, and shock

Auscultation of breath sounds, evaluation of chest rise and fall, assessment of peripheral pulses, checking skin signs.

Interventions for ventilation or shock

Oxygen administration and positioning for optimal ventilation.