Prehospital Academy Lesson 15.1
Respiratory Emergencies: Anatomy and Physiology Review
This lesson provides a comprehensive review of respiratory anatomy and physiology, a foundational topic for EMTs. A solid understanding of how the body breathes and exchanges gases is paramount for effectively assessing and managing patients with respiratory emergencies. This section will delve into the structures involved, the mechanics of breathing, and the critical processes of ventilation, oxygenation, and respiration.
The Respiratory System: An Overview
The respiratory system is responsible for bringing oxygen into the body and expelling carbon dioxide. It is divided into two main parts: the upper airway and the lower airway, each with specific functions. EMS providers must integrate assessment findings with principles of epidemiology and pathophysiology to formulate a field impression and implement a comprehensive treatment plan.
Upper Airway: Pathway for Air
The upper airway extends from the nose and mouth down to the larynx (voice box). Its primary functions include:
Warming and Humidifying: Incoming air is warmed and moistened to protect the delicate lower airways.
Filtering: Cilia and mucus trap foreign particles before they reach the lungs.
Key structures of the upper airway include:
Nose and Nasopharynx: Filters and warms air.
Mouth and Oropharynx: Alternative pathway for air, especially during strenuous activity or obstruction.
Laryngopharynx: Connects to the esophagus and larynx.
Larynx: Contains the vocal cords and is a critical point for distinguishing between the upper and lower airways. It also protects the lower airway from aspiration.
Epiglottis: A leaf-shaped cartilage that covers the trachea during swallowing, preventing food and liquids from entering the lungs.
Lower Airway: The Site of Gas Exchange
The lower airway begins below the larynx and includes the trachea, bronchi, bronchioles, and alveoli, where the vital process of gas exchange occurs.
Trachea (Windpipe): A rigid tube supported by C-shaped cartilaginous rings, extending from the larynx and branching into the main bronchi.
Bronchi and Bronchioles: The main bronchi divide into smaller and smaller airways (bronchioles), which terminate in the alveoli. Smooth muscle in these airways allows for constriction and dilation, regulating airflow.
Alveoli: Microscopic air sacs where gas exchange with the bloodstream takes place. They are surrounded by a rich capillary network. The thin alveolar-capillary membrane facilitates rapid diffusion of oxygen into the blood and carbon dioxide out of the blood.
Lungs: The primary organs of respiration, containing millions of alveoli and an extensive network of airways and blood vessels.
Mechanics of Breathing
Breathing is an active process primarily driven by the diaphragm and intercostal muscles.
Inhalation (Active Process): The diaphragm contracts and moves downward, while the intercostal muscles contract, pulling the rib cage upward and outward. This increases the volume of the thoracic cavity, creating negative pressure that draws air into the lungs.
Exhalation (Passive Process): The diaphragm and intercostal muscles relax, reducing the volume of the thoracic cavity. This increases pressure within the lungs, forcing air out. Forced exhalation involves the contraction of abdominal and additional intercostal muscles.
Key Respiratory Processes: Ventilation, Oxygenation, Respiration
These three terms are often used interchangeably but have distinct physiological meanings crucial for EMTs:
Ventilation: The mechanical process of moving air in and out of the lungs. Assessed by observing chest rise and fall, and listening to breath sounds.
Oxygenation: The process by which oxygen passively diffuses from the alveoli to the blood, where it binds to hemoglobin. Assessed by pulse oximetry (SpO2).
Respiration: The actual exchange of gases at the cellular level (internal respiration, between blood and tissues) and at the lung level (external respiration, between alveoli and capillaries).
A patient can be ventilating (moving air) but not effectively oxygenating (e.g., carbon monoxide poisoning) or respiring (e.g., severe pneumonia). EMTs must assess all three components.
Epidemiology and Common Respiratory Diseases
Respiratory diseases are among the most common medical complaints encountered in EMS. EMTs must be able to recognize, assess, and manage conditions such as:
Acute Upper Airway Infections: Croup, epiglottitis (though rare, life-threatening), foreign body airway obstruction.
Lower Airway Diseases: Asthma, Chronic Obstructive Pulmonary Disease (COPD - emphysema and chronic bronchitis), pneumonia, pulmonary edema, spontaneous pneumothorax.
Environmental/Industrial Exposures: Inhalation injuries, toxic gas exposures.
Each of these conditions presents with unique signs and symptoms, and requires specific management strategies that build upon a strong understanding of respiratory anatomy and physiology.
Critical Thinking Questions
You respond to a child with sudden onset of stridor and difficulty breathing. What anatomical structures are most likely affected, and what immediate interventions would you prioritize?
Distinguish between the terms "ventilation," "oxygenation," and "respiration." Provide a scenario where a patient might have adequate ventilation but compromised oxygenation or respiration.
A patient with a history of COPD is found in respiratory distress. How does the pathophysiology of COPD affect the mechanics of breathing, and what assessment findings would you expect to observe?
Describe the journey of an oxygen molecule from the ambient air to a body cell, naming all the major anatomical structures and physiological processes involved.
Why is it crucial for EMTs to understand that patients can have normal pulse oximetry readings (SpO2) but still be experiencing significant respiratory compromise? Provide an example.