Does Functional Residual Capacity (FRC) increase or decrease in pneumothorax?

From the Guidelines

In pneumothorax, the functional residual capacity (FRC) actually decreases, not increases, due to the lung's reduced ability to expand and fill with air as a result of the air in the pleural space pushing the lung inward and reducing its volume. When air enters the pleural space during a pneumothorax, it creates positive pressure that prevents the lung from fully expanding during normal inspiration, leading to a decrease in the volume of gas in the thoracic cavity at the end of a normal expiration, which is the definition of FRC. The mechanism involves disruption of the normal negative pleural pressure that helps maintain lung expansion. As air accumulates in the pleural space, it pushes the lung inward while reducing the overall lung volume, resulting in decreased lung compliance, impaired gas exchange, and potential respiratory distress. According to the British Thoracic Society guideline for pleural disease 1, the management of pneumothorax involves interventions such as chest tube drainage, pleurectomy, and pleurodesis to reduce recurrence and improve lung function. The use of high flow oxygen therapy has been shown to increase the rate of pneumothorax reabsorption during periods of oxygen supplementation, as stated in the BTS guidelines for the management of spontaneous pneumothorax 1.

Some key points to consider in the management of pneumothorax include:

• The size of the pneumothorax and the patient's symptoms determine the need for active intervention, such as chest tube drainage or observation with supplemental oxygen 1
• The rate of resolution of spontaneous pneumothoraces is 1.25–1.8% of the volume of hemithorax every 24 hours, and the addition of high flow oxygen therapy can result in a four-fold increase in the rate of pneumothorax reabsorption 1
• The management of pneumothorax in patients with cystic fibrosis requires careful consideration of the patient's overall lung function and the risk of recurrence, as stated in the British Thoracic Society guideline for pleural disease 1

From the Research

Pneumothorax and Functional Residual Capacity (FRC)

• In the context of pneumothorax, the relationship between pneumothorax and FRC is complex and can vary depending on the specific circumstances of the condition.
• A study on acute lung injury found that FRC decreased by 45% within the first hour of constant volume-controlled ventilation with PEEP 5 cm H(2)O 2.
• This decrease in FRC is associated with decreased aeration and increased consolidation on computed tomography (CT) 2.
• In patients with chronic obstructive pulmonary disease (COPD), end tidal volume (FRC) is higher than the elastic equilibrium volume, Vr, of the respiratory system 3.
• However, there is no direct evidence from the provided studies that specifically addresses how FRC changes in the presence of pneumothorax.

Air Leaks and Residual Pleural Space

• Postoperative air leaks associated with residual pleural space can be a complication after major pulmonary resection 4.
• A study found that combined pneumoperitoneum and autologous blood patch can be an effective treatment for air leaks and residual pleural space 4.
• The study demonstrated that this approach can lead to the obliteration of pleural space and cessation of air leaks in all patients 4.
• However, the relationship between air leaks, residual pleural space, and FRC is not explicitly addressed in the provided studies.

Clinical Implications

• The management of pneumothorax and residual pleural space requires careful consideration of various factors, including the size of the pneumothorax, the presence of underlying lung disease, and the patient's symptoms 5, 6.
• The use of chest tubes, drainage systems, and other interventions should be guided by imaging and clinical judgment 5, 6.
• Further research is needed to fully understand the relationship between pneumothorax, FRC, and clinical outcomes.