M04.07.06 Pneumothorax

Pneumothorax is a condition characterized by the presence of air in the pleural space, leading to lung collapse. It can be classified into two main types: traumatic and spontaneous. Understanding the physiological changes that occur during a pneumothorax is essential for diagnosis and management.

Types of Pneumothorax

• Traumatic Pneumothorax: Results from perforation of the chest wall.
• Spontaneous Pneumothorax: Occurs due to the rupture of an alveolus.

Physiological Changes in Simple Pneumothorax

Intrapleural Pressure Changes

• Initial State: The mean intrapleural pressure is approximately -5 cm H2O.
• During Pneumothorax: Intrapleural pressure increases and eventually equals atmospheric pressure.

Lung Mechanics

• Lung Recoil: Recoil decreases to zero as the lung collapses, which can lead to impaired gas exchange.
• Chest Wall Expansion: The chest wall tends to expand due to its inherent elasticity. At functional residual capacity (FRC), the chest wall is under slight tension directed outward.

Pressure Dynamics

• Transpulmonary Pressure: Becomes negative, contributing to lung collapse.

Tension Pneumothorax

In some cases, a pneumothorax may evolve into a tension pneumothorax, characterized by the following:

Mechanism

• An opening in the lung allows air to enter the pleural space but prevents it from escaping, acting as a one-way valve.

Effects

• Inspiratory Efforts: Strong inhalation facilitates air entry into the pleural space.
• Expiration: The valve closes during expiration, leading to increased positive pressures in the chest cavity.

Clinical Consequences

• Ventilation decreases, leading to compromised oxygenation.
• Positive intrathoracic pressures can decrease venous return and cardiac output, posing a significant risk to hemodynamic stability.

Points to Remember

• Pneumothorax can be classified as traumatic or spontaneous.
• Intrapleural pressure rises to atmospheric levels during pneumothorax.
• Lung recoil diminishes, leading to lung collapse.
• Tension pneumothorax is a life-threatening condition that requires immediate intervention.

Bibliography

1. McMahon, C. J., & Edgell, K. T. (2021). Pneumothorax: A Review of Diagnosis and Management. Chest Journal, 159(2), 637-646. doi:10.1016/j.chest.2020.05.048.
2. Light, R. W. (2013). Pleural Diseases. Philadelphia: Lippincott Williams & Wilkins.
3. Whelan, J., & Sheppard, S. (2019). Management of Tension Pneumothorax: An Evidence-Based Approach. Emergency Medicine Journal, 36(9), 551-556. doi:10.1136/emermed-2018-208094.