Pathophysiology of Atelectasis

Overview

Atelectasis is a medical term that is often used to refer to the partial or complete lung collapse or incomplete expansion of the lung lobe. The condition occurs when the alveoli are either deflated or filled with alveolar fluid, thus preventing fresh air from reaching air sacks (Scarlata, Bartoli, Pedone and Incalzi 2016, p. 366). Atelectasis is a respiratory complication that arises from general anaesthesia.

Signs, Symptoms, and Corresponding Causes

Atelectasis may have no apparent signs and symptoms, especially when it develops slowly or occurs over a small portion of the lung. Conversely, it develops rapidly, affects a more substantial part of the lung, normally the air sacs, and exhibits dramatic signs and symptoms that include breath shortness (dyspnea), wheezing, consistent shallow breathing, persistent hacking cough, and sharp chest pain that generally worsen with deep breathing (Lohser and Slinger 2016). As atelectasis progresses, the signs and symptoms become more profound since oxygen saturation levels in the blood decrease to the lowest level. Such condition results in a sudden, severe drop in blood pressure, abnormal heart rate, and shock (Ray, Bodenham and Paramasivam 2013). Notably, these signs and symptoms are usually caused by blocked airway (obstructive factors) or pressure from outside the lung (non-obstructive factors), which not only change the regular breathing patterns but also affect the normal gaseous exchange in the air sacks, hence, causing alveoli to deflate.

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In general, dyspnea, wheezing, and consistent shallow breathing are broadly categorized under the “abnormal breathing rate” sign and symptom, which is caused by four factors namely airway obstruction, adhesion, hypoventilation, and airway compression (Albert 2012, p.703; Lohser and Slinger 2015). Hypoventilation occurs after chest surgery when the patient is not offered effective post-discharge care. It is the primary cause of abnormally slow breathing rate, mainly when anaesthesia is applied or when an individual is placed on a respirator (Lohser and Slinger 2015). Markedly, the slow breathing prevents fresh air from entering the alveoli, consequently, deflating the air sacs and collapsing the entire lungs.

Airway obstruction is the second most common cause of abnormally slow breathing rates. It arises from the internal blockage of the lung with mucus like a plug or other foreign objects, or external blockage of the lungs. The mucus-like plugs build up during and after chest surgery because patients find it difficult to cough due to chest pains. Moreover, anaesthesia-related drugs that are normally induced during chest surgery compel patients to breathless deeply, thus, providing more space for normal secretions to collect in the airways (Acosta et al. 2016, p.19). Increased secretion of mucus like plug results in bronchioloalveolar carcinoma, a particular type of lung cancer and a risk factor for a tumour in the alveoli, which causes breathlessness and chronic atelectasis.

Conversely, airway compression results from fluid build-ups in the alveoli, a phenomenon commonly referred to as pleural effusion (Lohser and Slinger 2016; Randtke, Andrews and Mach 2015, p. 517). Consequently, pleural effusion predisposes an individual to enlarged lymph nodes, enlarged heart, alveolar tumour, aneurysm, and ascites, which are the primary risk factors for atelectasis. Besides airway compression, lung collapse due to external pressure on the lymphatic fluid between the lining of the lungs and the chest wall.

Adhesions occur when the internal parts of the lung abnormally stick together during body movements. Consequently, the blood absorbs the air inside the alveoli, which causes air sacs to shrink. The initial space occupied by the air sacs before lung collapse is then filled with blood cells, lymphatic fluid, and secreted mucus plug, resulting in shallow breath and shock. Other factors contributing to atelectasis include respiratory distress syndrome (RDS) in new-borns, prolonged immobility, increased smoking, obesity, uncontrolled consumption of sedatives and narcotics, and rib fractures, which result in shallow breathing. Severe atelectasis is associated with abnormal heart rate, a symptom that is usually referred to as arrhythmias. It occurs when either the oxygen concentration in the blood falls below the normal level or when there is a severe drop in blood pressure (Reid, Jenkins and McClure 2009). Moreover, abnormal heart rate is often caused by the poor blood supply to the heart muscles and heart valves, which all emanate from the irregular gaseous exchange in the alveoli due to collapse lungs.

 

References

Acosta, C.M., Tusman, G., Costantini, M., Echevarría, C., Pollioto, S., Abrego, D., Suarez-Sipmann, F. and Böhm, S.H., 2016. Doppler images of intra-pulmonary shunt within atelectasis in anesthetized children. Critical Ultrasound Journal, vol. 8, no. 1, p.19.

Albert, R.K., 2012. The role of ventilation-induced surfactant dysfunction and atelectasis in causing acute respiratory distress syndrome. American Journal of Respiratory and Critical Care Medicine, vol. 185, no. 7, pp. 702-708.

Lohser, J. and Slinger, P., 2015. Lung injury after one-lung ventilation: a review of the pathophysiologic mechanisms affecting the ventilated and the collapsed lung. Anaesthesia & Analgesia, vol. 121, no. 2, pp. 302-318.

Lohser, J. and Slinger, P., 2016. Lung injury after one-lung ventilation: a review of the pathophysiologic mechanisms affecting the ventilated and collapsed lung. Survey of Anaesthesiology, vol. 60, no. 3, pp. 98-99.

Randtke, M.A., Andrews, B.P. and Mach, W.J., 2015. Pathophysiology and prevention of intraoperative atelectasis: A review of the literature. Journal of Paraesthesia Nursing, vol. 30, no. 6, pp. 516-527.

Ray, K., Bodenham, A. and Paramasivam, E., 2013. Pulmonary atelectasis in anesthesia and critical care. Continuing Education in Anaesthesia, Critical Care & Pain, vol. 14, no. 5, pp. 236-245.

Reid, M.M., Jenkins, J. and McClure, G., 2009. Sinusoidal heart rate rhythms in severe neonatal hypoxia. Archives of Disease in Childhood, vol.54, no.6, pp.432-435.

Scarlata, S., Bartoli, I.R., Pedone, C. and Incalzi, R.A., 2016. Obstructive atelectasis of the lung. Postgraduate Medical Journal, vol. 92, no. 1088, pp. 365-365.

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