Can atelectasis alone cause significant hypoxia?

From the Guidelines

Atelectasis alone can indeed cause significant hypoxia due to the ventilation-perfusion mismatch it creates, where blood passes through non-ventilated lung tissue, leading to decreased arterial oxygen levels. This condition refers to the collapse of lung tissue, preventing normal gas exchange in the affected areas. As discussed in the BTS guideline for oxygen use in adults in healthcare and emergency settings 1, oxygen is transported in the blood in two forms, and the amount of oxygen carried in the blood is often expressed in terms of how saturated circulating haemoglobin is with oxygen (SO2). The guideline suggests a desirable target saturation range of 94–98% to keep the SaO2 above 90% for the majority of acutely ill patients.

The severity of hypoxia caused by atelectasis depends on the extent of lung collapse. Small areas of atelectasis may cause minimal symptoms, while extensive atelectasis can result in severe hypoxemia requiring supplemental oxygen. According to the guideline 1, sudden exposure to low SaO2 levels (below about 80%) can cause impaired mental functioning even in healthy participants, and the brain is the most sensitive organ to the adverse effects of hypoxia.

Key points to consider in managing atelectasis-induced hypoxia include:

• Addressing the underlying cause of atelectasis
• Promoting full lung expansion through deep breathing exercises, incentive spirometry, and chest physiotherapy
• Considering bronchoscopy for mucus plugging or positive pressure ventilation in severe cases
• Early mobilization and adequate pain control, especially in post-surgical patients, to prevent worsening of the condition. As the guideline 1 emphasizes, keeping the SaO2 above 90% is crucial for the majority of acutely ill patients, and atelectasis management should aim to achieve this target saturation range.

From the Research

Atelectasis and Hypoxia

• Atelectasis can cause significant hypoxia, as it is a major cause of hypoxemia during general anesthesia 2, 3, 4.
• The formation of atelectasis can lead to a decrease in oxygenation of the blood, resulting in hypoxemia 2, 4.
• Studies have shown that atelectasis is present in most patients during general anesthesia and is a significant cause of impaired oxygenation 2, 4.

Mechanisms of Atelectasis-Induced Hypoxia

• Atelectasis can cause hypoxia by increasing shunt and decreasing compliance, leading to perioperative hypoxemia 5.
• The use of 100% oxygen during anesthesia can lead to absorption atelectasis, which can contribute to hypoxia 5.
• However, research suggests that absorption atelectasis may not have significant clinical implications in healthy adults, but may be more significant in populations at increased risk of postoperative hypoxemia, such as obese or elderly patients 5.

Prevention and Treatment of Atelectasis-Induced Hypoxia

• Various techniques can be used to prevent or treat atelectasis-induced hypoxia, including the use of positive end-expiratory pressure (PEEP), recruitment maneuvers, and moderate fractions of inspired oxygen 2, 3, 4.
• The application of PEEP and recruitment maneuvers can help to reduce or prevent atelectasis, thereby improving oxygenation 2, 3, 4.
• Ventilation with a moderate fraction of inspired oxygen (e.g. 0.3-0.4) may also help to prevent the formation of atelectasis 4.