Prehospital Academy Lesson 11.2
Basic Ventilation Physiology
Introduction to Ventilation
In this lesson, we will delve into the fundamental principles of ventilation, a critical concept in emergency medical care. Ventilation is the physical process of moving air into and out of the lungs. This is distinct from oxygenation (the process of loading oxygen onto hemoglobin) and respiration (the gas exchange process). Understanding the mechanics of ventilation is crucial for EMTs to effectively manage a patient's airway and breathing.
The Mechanics of Breathing
Normal breathing, or spontaneous ventilation, is a process driven by changes in pressure within the thoracic cavity. This is known as negative pressure ventilation.
Inhalation: This is an active process. The diaphragm and intercostal muscles contract, expanding the thoracic cavity. This increase in volume leads to a decrease in pressure inside the lungs compared to the atmosphere, causing air to rush in.
Exhalation: This is typically a passive process. The diaphragm and intercostal muscles relax, decreasing the volume of the thoracic cavity. This increases the pressure inside the lungs, forcing air out.
The amount of air moved in a single breath is called tidal volume, which is approximately 500 mL for an average adult. It's important to note that not all air is expelled during exhalation; some remains in the lungs as 'dead space'.
Positive Pressure Ventilation
In contrast to the body's natural negative pressure system, EMTs often use positive pressure ventilation (PPV) for patients who are not breathing adequately. This involves actively forcing air into the patient's lungs. Common methods include:
Bag-Valve-Mask (BVM) Ventilation: A manual resuscitation technique using a self-inflating bag and a mask. It is a fundamental skill for any EMT. For adults, the ventilation rate should be 10 to 12 breaths per minute, with each breath delivered over one second, just enough to produce visible chest rise. Hyperventilation is dangerous and must be avoided.
Mouth-to-Mask Ventilation: Another PPV technique, often used by a single rescuer. It provides a barrier between the rescuer and the patient.
Airway Management is Key
Effective ventilation is impossible without a patent (open) airway. Before initiating PPV, EMTs must ensure the airway is clear. This may involve:
Manual Maneuvers: The head-tilt/chin-lift or jaw-thrust maneuvers are used to open the airway.
Airway Adjuncts: Oropharyngeal (OPA) and nasopharyngeal (NPA) airways are devices used to maintain a patent airway by preventing the tongue from obstructing the epiglottis.
Achieving a proper mask seal is critical for successful BVM ventilation. The two-person technique is preferred, with one provider maintaining the seal and the other squeezing the bag.
Regulation of Breathing
In a healthy person, the drive to breathe is regulated by the level of carbon dioxide (CO2) in the blood, which affects the pH of the cerebrospinal fluid. This is called the carboxy drive. However, in some patients with chronic respiratory diseases like COPD, the body may switch to a hypoxic drive, where the stimulus to breathe is a low level of oxygen in the blood. This is an important consideration for EMTs when administering oxygen.
Conclusion
A thorough understanding of the principles of ventilation is essential for EMTs. From the mechanics of negative pressure breathing to the application of positive pressure ventilation and the importance of airway management, these concepts form the foundation of effective respiratory care in the prehospital environment. Always remember to assess for an open airway, provide ventilations at the correct rate and volume, and be mindful of the patient's underlying respiratory drive.
Critical Thinking Questions
What are the potential complications of hyperventilation during positive pressure ventilation, and how can an EMT avoid them?
A patient with a history of COPD is found in respiratory distress with an oxygen saturation of 88%. How would your understanding of hypoxic drive influence your decision to administer oxygen?
You are a single rescuer arriving on the scene of an unresponsive patient. Describe the steps you would take to assess the patient's airway and breathing, and what interventions you would prioritize.
Describe the difference between negative pressure ventilation and positive pressure ventilation. What are the potential complications of positive pressure ventilation?
You are treating a patient with a suspected spinal cord injury who is having difficulty breathing. What is the appropriate method for opening the airway in this patient, and why?