What is Atelectasis
Atelectasis is a state of collapsed and non-aerated lung parenchyma that is otherwise structurally normal, representing a pathological manifestation of underlying disease rather than a disease itself. 1
Definition and Pathophysiology
Atelectasis occurs when collapsing forces (from positive pleural pressure and surface tension) overcome expanding forces (from alveolar pressure and parenchymal tethering), resulting in lung tissue collapse 2
This condition is exceedingly common, appearing in approximately 90% of all anesthetized patients, with 15-20% of lung base regularly collapsed during uneventful anesthesia 3, 4
Primary Mechanisms of Development
Atelectasis develops through three main pathways:
Airway obstruction - caused by foreign body aspiration, mucus plugs, broncholithiasis (calcified lymph nodes eroding into airways), or external compression by masses 5, 1
Compression of lung parenchyma - from pleural effusion (including malignant effusions), extrathoracic processes, intrathoracic masses, or chest wall disorders 5, 1
Increased surface tension - in alveoli and bronchioli, particularly seen in neonatal respiratory distress syndrome causing adhesive atelectasis 5, 1
Clinical Consequences
Atelectasis impairs blood oxygenation and reduces lung compliance, with direct correlation between the amount of atelectasis and pulmonary shunt 2, 4
Beyond gas exchange impairment, collapsed lung tissue induces local biological responses including inflammation, immune dysfunction, and damage to the alveolar-capillary barrier 2
These changes increase susceptibility to infection, loss of lung fluid clearance, and increased protein permeability, potentially initiating or exaggerating lung injury 2
Atelectasis may persist for several days postoperatively and serves as a potential focus of infection contributing to pulmonary complications 3
Special Types
Rounded atelectasis (also called folded lung, shrinking pleuritis, or Blesovsky's syndrome) develops from infolding of thickened visceral pleura with collapse of intervening lung, most commonly associated with asbestos exposure 5
This presents radiographically as a mass that may be mistaken for tumor, with a classic pathognomonic "comet sign" visible on HRCT 5
Platelike atelectasis can occur as a non-specific finding in conditions like pulmonary embolism 5
Perioperative Context
During anesthesia, major causative factors include high oxygen concentrations during induction and maintenance, combined with anesthetic-induced loss of muscle tone and decreased functional residual capacity 3
This creates absorption atelectasis behind closed airways, with obese patients developing larger atelectatic areas than lean patients 6, 3
High FiO2 (>0.8) during emergence from anesthesia significantly increases atelectasis formation 6