Atelectasis in Anesthesia: Causes and Management

The term “atelectasis” originates from the Greek words atelez and ektasiz, meaning “imperfect” and “expansion” respectively,¹ and describes an incomplete expansion of lung tissue, resulting from the partial or complete collapse of the small airways and leading to an impaired exchange of CO₂ and O₂.^1,2 A study in 1995 estimated that the incidence of atelectasis in patients undergoing general anesthesia is around 90%.¹ This condition typically occurs within 72 hours of general anesthesia and is a common postoperative complication.¹ 

Atelectasis can be caused by compression of lung tissue (compressive), absorption of alveolar air (resorptive), or impaired pulmonary surfactant production.³ Compression atelectasis is the result of a decreased transmural pressure gradient across the alveolus, leading to alveolar collapse.^1,3 Resorptive atelectasis occurs when alveolar air gets absorbed distal to an obstructive lesion.^1,3 The obstruction either partially or completely inhibits ventilation to the area.¹ Over time, all of the air in that segment will be absorbed and, without return of ventilation, the airway will collapse.^1,3 Children are especially susceptible to the resorption form because they have poorly developed collateral pathways for ventilation.¹ 

Roughly 15 to 20% of the lung at its base can collapse during uneventful anesthesia before any surgical intervention.¹ Research has shown that atelectasis can appear in the dependent regions of both lungs within five minutes of induction of anesthesia.⁴ This complication does not preferentially affect men or women, and there is no increased incidence in patients with asthma or increased age.^1,5 Both obese and pregnant patients have an increased risk of atelectasis due to decreased functional residual capacity and compliance.⁶ Atelectasis appears more frequent after cardiac surgery with cardio-pulmonary bypass than after other types of surgery.¹ Inadequate pain control can also contribute to its development by causing shallow breathing or by preventing coughing.¹ 

Often, atelectasis is asymptomatic. However, patients may present with decreased or absent breath sounds, cough, sputum  production, tachypnea, or diminished chest expansion.¹ A chest x-ray, chest CT, and fiberoptic bronchoscopy are useful for diagnosing this complication.¹ A chest x-ray will depict atelectasis as the displacement of interlobular fissures, pulmonary opacification, or tracheal shift toward the affected side.¹ Chest CT commonly reveals dependent lung densities and the loss of volume in the affected side of the chest.¹ Fiberoptic bronchoscopy can be used as both a diagnostic and therapeutic tool, especially for revealing the cause of any contributing obstruction .¹ 

The majority of atelectasis cases that appear during general anesthesia lead to transient lung dysfunction that quickly resolves itself.¹ However, some patients develop significant perioperative respiratory complications that can lead to increased morbidity and mortality if not treated.¹ The use of continuous positive airway pressure and positive end-expiratory pressure (PEEP) help to prevent the development of atelectasis.⁸ Other methods that have been shown to decrease incidence involve changing the patient’s position from supine to upright, encouraging the patient to take deep breaths, chest physiotherapy, and tracheal suctioning.^7,8 Pharmacologic treatment options include mucolytic agents (acetylcysteine) and recombinant human DNase.¹ As mentioned previously, fiberoptic bronchoscopy also has a role in the management of atelectasis.¹ One study showed that fiberoptic bronchoscopy led to improved lung function and reversal of atelectasis in 76% of cases.⁹ 

References

1. Grott, K., & Dunlap, J. (2020). Atelectasis. In StatPearls [Internet]. StatPearls Publishing LLC. Retrieved 29 September 2020, from https://www.ncbi.nlm.nih.gov/books/NBK545316/ 

2. Carlsen, K., Crowley, S., & Smevik, B. (2019). Atelectasis. In R. Wilmott, A. Li, P. Sly, A. Bush, R. Deterding, F. Ratjen & H. Zar, Kendig’s Disorders of the Respiratory Tract in Children (9th ed.). Elsevier Inc. Retrieved 29 September 2020, from https://doi.org/10.1016/C2015-0-01292-8 

3. Peroni, D., & Boner, A. (2000). Atelectasis: mechanisms, diagnosis and management. Paediatric Respiratory Reviews, 1(3), 274-278. https://doi.org/10.1053/prrv.2000.0059 

4. Brismar, B., Hedenstierna, G., Lundquist, H., Strandberg, Å., Svensson, L., & Tokics, L. (1985). Pulmonary Densities during Anesthesia with Muscular Relaxation—A Proposal of Atelectasis. Anesthesiology, 62(4), 422-428. https://doi.org/10.1097/00000542-198504000-00009 

5. Gunnarsson, L., Tokics, L., Gustavsson, H., & Hedenstierna, G. (1991). Influence of Age on Atelectasis Formation and Gas Exchange Impairment During General Anaesthesia. British Journal of Anaesthesia, 66(4), 423-432. https://doi.org/10.1093/bja/66.4.423 

6. Coussa, M., Proietti, S., Schnyder, P., Frascarolo, P., Suter, M., Spahn, D., & Magnusson, L. (2004). Prevention of Atelectasis Formation During the Induction of General Anesthesia in Morbidly Obese Patients. Anesthesia & Analgesia, 1491-1495. https://doi.org/10.1213/01.ane.0000111743.61132.99 

7. Toshida, K., Minagawa, R., Kayashima, H., Yoshiya, S., Koga, T., & Kajiyama, K. et al. (2020). The Effect of Prone Positioning as Postoperative Physiotherapy to Prevent Atelectasis After Hepatectomy. World Journal of Surgery. https://doi.org/10.1007/s00268-020-05682-0 

8. Östberg, E., Auner, U., Enlund, M., Zetterström, H., & Edmark, L. (2017). Minimizing atelectasis formation during general anaesthesia—oxygen washout is a non-essential supplement to PEEP. Upsala Journal of Medical Sciences, 122(2), 92-98. https://doi.org/10.1080/03009734.2017.1294635 

9. Restrepo, R., & Braverman, J. (2014). Current challenges in the recognition, prevention and treatment of perioperative pulmonary atelectasis. Expert Review of Respiratory Medicine, 9(1), 97-107. https://doi.org/10.1586/17476348.2015.996134