What is Atelectasis
Atelectasis is a state of collapsed and non-aerated lung tissue where alveoli lose their air content, though recent evidence suggests these alveoli are actually filled with foam and fluid rather than being simply empty. 1
Definition and Pathophysiology
Atelectasis represents a pathological condition of lung parenchyma collapse rather than a disease itself—it's typically a manifestation of an underlying disorder 1. The term describes absent air in alveoli, traditionally attributed to collapse, but newer understanding reveals the alveolar spaces contain foam and fluid 2.
Mechanisms of Development
Atelectasis develops through several distinct pathways:
- Resorption atelectasis: Occurs when alveolar air is absorbed distal to obstructing airway lesions
- Adhesive atelectasis: Results from surfactant deficiency
- Passive atelectasis: Caused by pneumothorax, diaphragmatic dysfunction, or hypoventilation
- Compressive atelectasis: Due to tension pneumothorax, space-occupying lesions, or abdominal distention
- Cicatrization atelectasis: Stems from pulmonary fibrosis
- Gravity-dependent atelectasis: Results from gravity-dependent changes in alveolar volume 3
Clinical Context and Prevalence
Atelectasis is remarkably common, occurring in approximately 90% of anesthetized patients, with 15-20% of lung bases regularly collapsed during routine anesthesia before any surgery begins 4. This can persist for several days postoperatively and serves as a potential focus for infection and pulmonary complications 4.
High-Risk Scenarios
- Perioperative period: Develops in dependent lung regions due to high oxygen concentrations, loss of muscle tone, and decreased functional residual capacity 4
- Acute illness and postoperative care: An exceedingly common companion to various acute conditions 5
- Bariatric surgery: Shows 37% prevalence, with higher risk in females (RR=1.48) and patients over 36 years (RR=0.68) 6
Clinical Consequences
The severity of consequences depends on:
- Extent and mechanism of collapse
- Patient vulnerability and cardiopulmonary reserve
- Abruptness of onset
- Effectiveness of hypoxic vasoconstriction 5
Key impacts include:
- Decreased lung compliance
- Impaired oxygenation
- Increased pulmonary vascular resistance
- Potential development of lung injury 2
Diagnostic Approach
Chest radiographs using both anterior-posterior and lateral projections are mandatory 1.
Direct Signs
- Crowded pulmonary vessels
- Crowded air bronchograms
- Displacement of interlobar fissures 3
Indirect Signs
- Pulmonary opacification
- Diaphragm elevation
- Tracheal, cardiac, and mediastinal shift
- Hilar displacement
- Compensatory hyperexpansion of surrounding lung
- Rib approximation 3
Common Pitfall
Differentiation from lobar consolidation can be challenging clinically 1. The key principle: whenever signs of volume loss are present on chest radiograph, interpret as atelectasis 3.
Types of Atelectasis
For descriptive purposes, atelectasis is classified as:
- Segmental, lobar, or whole lung
- Subsegmental
- Platelike, linear, or discoid
- Round
- Generalized or diffuse 3
Management Principles
Treatment varies based on duration and severity of the underlying cause:
- Secretion management: Reduce secretion burden and ensure adequate clearance
- Positioning: Maintain upright positioning when possible
- Lung expansion: Sustain lung expansion and reverse compression 5
- Specific interventions: Chest physiotherapy, postural drainage, bronchodilators, anti-inflammatory therapy 1
- Persistent obstruction: Bronchoscopic removal of mucous plugs 1
Prevention in Perioperative Setting
Critical strategies include:
- Avoiding pure oxygen ventilation (use moderate FiO₂ around 40%)
- Recruitment maneuvers followed by ventilation with lower oxygen concentrations
- Optimized positive end-expiratory pressure
- High tidal volumes when appropriate 4, 7
Important caveat: Post-oxygenation combined with airway suctioning commonly causes new atelectasis; recruitment must be followed by ventilation with moderate FiO₂ rather than 100% oxygen 4.