Anatomic Alterations of the Lungs

Atelectasis, in the strict sense of the term, is defined as the condition in which the lungs of the newborn remain unexpanded (airless) at birth. In the clinical setting, however, the meaning of atelectasis in all age groups generally is broadened to include partial or total collapse of previously expanded lung regions. Atelectasis may be limited to the smallest lung unit (i.e., alveolus or primary lobule*; see Figure 42-1), or it may involve an entire lung or a segment or lobe of the lung. In this chapter, postoperative atelectasis is used as a prototype of the atelectasis process.

Postoperative atelectasis commonly is seen after upper abdominal and thoracic surgical procedures.

The major pathologic and anatomic alterations associated with postoperative atelectasis include partial or total collapse of the following:

Etiology and Epidemiology

Postoperative atelectasis develops when lung expansion is decreased or when excess airway secretions cause mucous plugs, which in turn produce distal “degassing” of lung units.

Alveolar Degassing Distal to Airway Secretions and Mucous Plugs (Airway Obstruction)

Postoperative atelectasis often is associated with retained airway secretions and mucous plugs. Precipitating factors for retained secretions include (1) decreased mucociliary transport, (2) excessive secretions, (3) inadequate hydration, (4) weak or absent cough, (5) general anesthesia, (6) smoking history, (7) gastric aspiration, and (8) certain preexisting conditions (e.g., bronchiectasis, chronic bronchitis, cystic fibrosis, asthma). When total airway obstruction develops, alveolar oxygen is absorbed into the pulmonary circulation and alveolar degassing ensues. The breathing of high oxygen concentrations favors this pathologic process.

 OVERVIEW of the Cardiopulmonary Clinical Manifestations Associated with Postoperative Atelectasis

The following clinical manifestations result from the pathologic mechanisms caused (or activated) by Atelectasis (see Figure 9-8)—the major anatomic alterations of the lungs associated with postoperative atelectasis (see Figure 42-1).

CLINICAL DATA OBTAINED AT THE PATIENT’S BEDSIDE

The Physical Examination

Vital Signs

Increased Respiratory Rate (Tachypnea)

Several pathophysiologic mechanisms operating simultaneously may lead to an increased ventilatory rate:

• Stimulation of peripheral chemoreceptors (hypoxemia)

• Decreased lung compliance–increased ventilatory rate relationship

• Stimulation of J receptors

• Pain, anxiety, fever

Increased Heart Rate (Pulse) and Blood Pressure

Cyanosis

Chest Assessment Findings

• Increased tactile and vocal fremitus

• Dull percussion note

• Bronchial breath sounds

• Diminished breath sounds (common when atelectasis in caused by mucous plugs)

• Crackles (usually heard initially in the dependent lung regions and during late inspiration)

• Whispered pectoriloquy

CLINICAL DATA OBTAINED FROM LABORATORY TESTS AND SPECIAL PROCEDURES

Pulmonary Function Test Findings (Extrapolated Data for Instructional Purposes) (Primarily Restrictive Lung Pathophysiology)

FORCED EXPIRATORY FLOW RATE FINDINGS

FVC	FEVT	FEV1/FVC ratio	FEF25%-75%
↓	N or ↓	N or ↑	N or ↓
FEF50%	FEF200-1200	PEFR	MVV
N or ↓	N or ↓	N or ↓	N or ↓

LUNG VOLUME AND CAPACITY FINDINGS

VT	IRV	ERV	RV
N or ↓	↓	↓	↓
VC	IC	FRC	TLC	RV/TLC ratio
↓	↓	↓	↓	N

DECREASED DIFFUSION CAPACITY (Dlco)

Arterial Blood Gases

SMALL OR LOCALIZED POSTOPERATIVE ATELECTASIS

Acute Alveolar Hyperventilation with Hypoxemia (Acute Respiratory Alkalosis)

pH	Paco2		Pao2
↑	↓	↓ (slightly)	↓

WIDESPREAD POSTOPERATIVE ATELECTASIS

Acute Ventilatory Failure with Hypoxemia (Acute Respiratory Acidosis)

pH*	Paco2	*	Pao2
↓	↑	↑ (slightly)	↓

^*When tissue hypoxia is severe enough to produce lactic acid, the pH and values will be lower than expected for a particular Paco₂ level.

Oxygenation Indices*

	Do2†			O2ER
↑	↓	N	N	↑	↓

^†The Do₂ may be normal in patients who have compensated to the decreased oxygenation status with (1) an increased cardiac output, (2) an increased hemoglobin level, or (3) a combination of both. When the Do₂ is normal, the O₂ER is usually normal.

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^*, Arterial-venous oxygen difference; DO₂, total oxygen delivery; O₂ER, oxygen extraction ratio; , pulmonary shunt fraction; , mixed venous oxygen saturation; , oxygen consumption.

RADIOLOGIC FINDINGS

Chest Radiograph

• Increased density in areas of atelectasis

• Air bronchograms

• Elevation of the hemidiaphragm on the affected side

• Mediastinal shift toward the affected side

Areas of increased density generally appear initially in dependent lung regions, such as the lower lobes, or posteriorly in patients who must recline in the supine position. Air bronchograms can be seen when large areas of atelectasis are present. An elevation of the hemidiaphragm or mediastinal shift toward the affected side often is seen when large areas of atelectasis exist. Figure 42-2, A shows left lung atelectasis caused by a misplaced endotracheal tube in the right main stem bronchus. Figure 42-2, B shows the same patient 20 minutes after the endotracheal tube was pulled back above the carina.

General Management of Postoperative Atelectasis

Precipitating factors for postoperative atelectasis should be identified during the preoperative and postoperative assessments (see the previous section on etiology). High-risk patients should be monitored closely. For example, bedside spirometry (vital capacity and inspiratory capacity) is useful in the early detection of atelectasis. Preventive measures often are prescribed for high-risk patients. For example, incentive spirometry frequently is prescribed to encourage good lung expansion. Chest physical therapy also may be given to the patient with mild to moderate preoperative or postoperative bronchial secretions to offset the development of mucous plugs and atelectasis. Patients who demonstrate combined obstructive and restrictive pulmonary disease preoperatively generally are thought to be at extremely high risk for atelectasis. When the diagnosis of postoperative atelectasis has been made, the following respiratory care procedures may be prescribed.

A 62-year-old man with a 35-pack/year smoking history had his left lower lobe resected because of small-cell carcinoma. Anesthesia had been performed using a right-sided double-lumen endotracheal tube. At the end of the procedure, the patient was breathing well and the tube was removed.

In the recovery room 30 minutes after arrival, his respiratory rate increased from 22/min to 34/min. His pulse increased from 70 to 130 bpm with regular rhythm, and his blood pressure decreased from 115/85 to 100/60 mm Hg. His peripheral oxygen saturation dropped from 97% to 85% while he was on 2 L/min O₂ per cannula. Breath sounds were decreased in the left lower anterior chest. A chest x-ray film showed atelectasis of the left lower lobe. Arterial blood gas values (on 2 L/min O₂ per cannula) were pH 7.29, Paco₂ 63, 25, and Pao₂ 55. At that time the respiratory therapist recorded the following SOAP note.

Respiratory Assessment and Plan

The patient was reintubated, ventilated, and oxygenated according to protocol. A mucolytic (acetylcysteine) was aerosolized and also directly instilled into the patient’s endotracheal tube. Aggressive tracheobronchial suctioning was performed. This produced small amounts of secretions with little or no benefit to the patient.

In view of this, a fiberoptic bronchoscope was inserted through the endotracheal tube, and a large mucous plug was identified in the orifice of the left lower lobe bronchus. The plug was removed under direct vision. After the bronchoscopy, the patient improved rapidly and could be extubated after about 60 minutes. A chest x-ray film taken before that time showed full expansion of the left lower lobe. The patient was discharged on the sixth postoperative day.

Discussion

Care of a patient with postoperative Atelectasis (see Figure 9-8) is one of the day-to-day responsibilities of the respiratory care practitioner. Accordingly, the respiratory care practitioner must be extremely adept in the assessment and management of such patients. The development of immediate postoperative atelectasis almost always is related to Excessive Bronchial Secretions (see Figure 9-12)—in this case caused by a large mucous plug obstructing the left lower lobe. Because such patients (in the immediate postoperative period) often cannot cough vigorously, particularly after thoracotomy, the decision to initiate therapeutic bronchoscopy immediately rather than to rely on physical therapy and mucolytics was certainly in order.

In patients who have undergone abdominal surgery or those who develop atelectasis later, the simpler approaches should certainly be tried first. Atelectasis has a tendency to recur, and these patients need to be followed at least 72 hours postoperatively to ensure that this has not happened. Therefore the therapist’s suggestion to follow pulse oximetry is entirely appropriate.

As important as treatment is, prevention is better. In this regard, the Bronchopulmonary Hygiene Protocol and the Lung Expansion Protocol were very important. Indeed, the application of these simple protocols often prevents the late development of atelectasis in postoperative patients.