Pathology

The post-op intensive care patient

 

A chest radiograph is frequently taken in the postoperative phase, and in patients in surgical or medical intensive care units. These examinations are generally carried out in the postoperative intensive care unit, reducing the possibility of obtaining optimal films, compared with those taken in the radiological department with permanently installed equipment.

Radiological examination of these patients is more difficult to carry out than a corresponding examination of other groups of patients, as they are less mobile and in poor condition, weakened by the underlying

Figure 97. Right-sided pneumonectomy empty right hemithorax. Drain inserted into chest cavity.

disease or the operative trauma. They often have difficulty in sitting up in bed, and the films must be taken with the patient more or less lying down. The newly operated patient also has difficulty with deep inspiration, so that the air content is often reduced in the basal segments of the lungs. Use of digital radiography has, however, considerably improved the quality of these examinations.

It is important to take lateral decubitus views with a horizontal beam in these patients. In this way, collections of fluid in the pleural cavity can be evaluated on the dependent side, while possible pneumothorax can be evaluated in the non-dependent hemithorax. Ultrasound is frequently used in this group of patients to assess collections of fluid in the pleural cavity, and to drain these under the guidance of ultrasound. CT scans of these patients is also becoming increasingly more common, and is often carried out in patients in a respirator.

Thoracic surgery

Pneumonectomy
Immediately after removal of a lung, the chest radiograph shows an empty hemithorax (Fig. 97). A thoracic drain connected to suction lies in the empty chest cavity in order to create negative pressure so that the mediastinum remains in the mid-line, and the opposite lung remains expanded. The mediastinum and trachea will remain in the mid-line with uncomplicated postoperative progress.

Figure 98. a) Chest x-ray 3 weeks after right-sided pneumonectomy. Most of the thoracic cavity is filled with fluid (PA view) b) Chest x-ray 3 weeks after right-sided pneumonectomy - most of the thoracic cavity is filled with fluid (lateral view). a

b

In the course of a few days, the empty pleural cavity will gradually fill with fluid. In the course of weeks, most of the thoracic cavity will be filled with fluid, giving a homogenous opacity, possibly with a small residual aircap apically, which may take a long time to resorb completely (Fig. 98 a, b).

A mediastinum shifted towards the non-operated side indicates increased pressure on the operated side, which may be an indication of complications such as empyema, hemothorax, or chylothorax. A bronchopleural fistula may also be a cause of a shifted mediastinum.

Lobectomy
After removal of a lobe of the lung, the remaining lobes on the operated side will increase in volume. Since the amount of tissue in these is constant, the remaining lobes, which are to fill the chest cavity, become hyperinflated and seem to be emphysematous (compensatory emphysema). If these lobes do not succeed in filling the chest cavity completely, the remaining space will be filled with fluid or air. Small collections of fluid

Figure 99. Postoperative total atelectasis of the right upper lobe. The upper lobe is seen as a widening of the mediastinum cranially on the right side.

may remain in the chest cavity for several weeks, but are gradually absorbed. The patient is treated in the postoperative phase with a thoracic drain to maintain negative pressure in the pleural cavity and thus expand the remaining lobes of the lung. Complications such as bronchopleural cysts and empyema may be seen in this phase. Protracted collections of air in the chest cavity postoperatively should raise concern for the development of a bronchopleural fistula. In such cases, bronchography will be able to demonstrate the site of leakage.

Heart surgery
Heart surgery is usually performed through a median sternotomy. Insertion of an aortocoronary by-pass is the most common type of operation.

In the early postoperative phase, knowledge of the exact position of the inserted catheters/tubes is important (see separate section). On chest radiographs, which will nearly always be frontal views, it is important to assess the aeration of the lungs, and to ascertain whether there is postoperative atelectasis (Fig. 99), collection of fluid in the pleural cavity (Fig. 100), pulmonary congestion indicating either heart failure, overhydration, or widened mediastinum. A widened mediastinum may indicate postoperative bleeding. If the heart shadow increases in size, this may be a sign of bleeding into the pericardial cavity, which may induce cardiac tamponade.

Most patients operated by insertion of an aortocoronary by-pass have atelectatic changes in the left lower lobe during the first postoperative

Figure 100. Large amounts of right-sided pleural fluid with basal right sided opacity. Complete obliteration of outline of right dome of the diaphragm.

Figure 101. Postoperative atelectatic changes in the left lower lobe with opacities in the lower lobe and drawing up of the left dome of the diaphragm. Considerably dilated gastric fundus - the fluid level in the fundus is seen below the dome of the diaphragm.

days (Fig. 101). Diagnosis of this type of atelectasis and assessment of possible progress/regression is important for the evaluation of the type of physiotherapy to be given to these patients postoperatively.

Postoperative monitoring

Central venous catheters are inserted after all types of lung and heart surgery, partly to monitor the central venous pressure, and partly for parenteral nourishment. Access is usually obtained by percutaneous puncture of the subclavian vein. Chest radiography after insertion of the

Figure 102. Frontal film shows proper insertion of left-sided thoracic drainage tube, tip of the tube is located apically and posteriorly (same patient as in Fig. 101).

Figure 103. Swan-Ganz catheter inserted via the right jugular vein and superior caval vein (black arrow) through the right atrium and right ventricle to a lower lobe artery on the right side (white arrow). Aortic balloon pump (open arrow) in the proximal descending aorta. It is located near but below the origin of the left subclavian artery.

central venous catheter is therefore carried out to diagnose possible complications such as pneumothorax (Fig. 102) and to visualize the position of the inserted catheter. Very often, the position of the catheter has to be adjusted after examining the chest radiographs. This is important in order to avoid inserting the tip of the catheter into the right atrium or right ventricle, as this may cause arrhytmias. At the same time, the catheter must be placed centrally in order to avoid damage when parenteral nourishment is infused via a peripheral vein (perforation, thrombosis).

Swan-Ganz catheters (Fig. 103) are inserted to measure the pressure in the pulmolnary arteries, and the capillary wedge pressure. Perforations may occur and give venous bleeding, which seldom leads to any consequences for the patient because of the low venous pressure. Catheter perforation of the right atrium and right ventricle may lead to cardiac tamponade, but this complication is extremely rare.

In connection with heart surgery in ill heart patients (left ventricular failure), an aortic balloon pump is sometimes inserted via one of the femoral arteries. A chest radiograph is necessary to check the position of the aortic balloon pump, as the tip of the pump must lie close to the arch of the aorta, but not extend into the actual curve of the arch or arch branches (Fig. 103).

Transvenous pacemaker electrodes are usually inserted via the external jugular vein under guidance of fluoroscopy to the anterior basal parts of the right ventricle. In these cases, frontal and lateral chest radiographs are always taken in order to check for possible loops or kinks, which may lead to disruption of electrodes. Perforation of the myocardium by the catheter has been seen, but does not usually lead to cardiac tamponade, even when the tip of the electrode is drawn back through the perforated myocardium.

An endotracheal tube is used postoperatively in most patients who have undergone lung or heart surgery. The tip of the endotracheal tube should lie about 6 cm above the carina (Fig. 103). The correct position of an endotracheal tube should always be checked. This is especially important in small children, where the distance between the carina and the larynx is short, often only a few centimetres. Patients with a prolonged postoperative course, who require respirator support, will usually require tracheostomy. A chest radiograph should always be performed after tracheostomy to check the correct position of the tracheal cannula, and to diagnose possible bleeding in the mediastinum, indicated by mediastinal widening.

Postoperative pathological conditions

Atelectasis
Atelectasis is frequently seen in the postoperative phase, and may be caused either by hypoventilation, retained secretion in the bronchial tree, or aspiration. In a frontal chest radiograph it is important to identify the horizontal fissure on the right side in order to assess possible loss of volume of the different lobes of the lungs. Volume-reduced lung segments or lung lobes usually appear as homogenous opacities. Rapid changes, both progression and regression, are typical features of postoperative atelectasis.

Aspiration pneumonia
Aspiration is frequently seen postoperatively. Since the patient is intubated during and immediately after operation, this will in itself effectively prevent aspiration of stomach content to the lungs during this phase. However, it is not uncommon for aspiration to occur when the patient awakens after deep sedation or anesthesia. The radiological changes occur rapidly after aspiration of stomach content because of the low pH of the aspirate.

The radiological changes vary considerably, depending on the content of the aspirate, the amount, and to which segment of the lung the aspiration has occurred. Most of the infiltrates after aspiration resolve in the course of a week. The infiltrates are mottled and have diffuse borders. They are usually bilateral, but are generally most pronounced on the right side because of the anatomical structure of the bronchial tree.

Pulmonary congestion/edema
Postoperative pulmonary congestion/edema is due either to heart failure or overhydration, possibly to fluid retention. Sepsis and conditions of shock may also cause pulmonary edema as a consequence of increased capillary permeability. The radiological changes in the postoperative patient may be more difficult to assess than in other groups of patients, as other lung changes such as atelectasis and aspiration may be seen at the same time. The lungs are usually also considerably less aerated than normal. The radiological picture is otherwise similar to congestive conditions with other etiologies.

Pulmonary embolism
Pulmonary embolism is frequently seen in the postoperative patient. A prolonged confinement to bed with development of peripheral thrombi may also increase the frequency of emboli to the pulmonary arteries.

The radiological picture is non-specific and may include atelectasis, irregularly defined opacities, and pleural fluid. Perfusion scintigraphy is usually of limited value, as many other postoperative conditions can also give areas of the lung with reduced perfusion. A combination of perfusion and ventilation scintigraphy improves the likelihood of diagnosing pulmonary embolism, but pulmonary angiography is often necessary.

Figure 104. ARDS - bilateral interstitial edema - early stage.

Pneumonia
Pneumonia is often seen as a postoperative complication. Pneumonia is seen particularly often during the development of aspiration or atelectasis. The radiological picture may be typical with opacities in ordinary pneumonia, but the picture is often complicated by the simultaneous presence of other pathological conditions.

Adult respiratory distress syndrome (ARDS)
This syndrome is also often called a shock lung. The aetiology is not clear, but the syndrome is seen most frequently after major surgery with complications such as infection, aspiration, contusion, fat embolism, and DI C (disseminated intravascular coagulation). Severe pancreatitis may also lead to the development of ARDS.

In the first phase of the syndrome, the lung picture is normal. The first radiological sign of ARDS is a mild interstitial edema (Fig. 104), which may relatively rapidly progress to extensive pulmonary edema. Extensive pulmonary opacities may be formed as the disease develops. These can vary considerably in appearance from purely congestive conditions to almost fibrosis-like changes in a chest radiograph (Fig. 105). Consolidation of lung tissue is usual in advanced cases of ARDS. The changes are nearly always bilateral, usually diffusely scattered, and may be both central and peripheral in the lungs. If the cause is aspiration, the opacities tend to initially be found in the basal segments of the lungs.

Figure 105. ARDS - massive bilateral pulmonary opacities.

Figure 106. Lateral decubitus view with horizontal beam. The patient is lying on the right side. Considerable amounts of rightsided pleural fluid is demonstrated.

Pleural fluid
Pleural fluid is frequently seen after chest surgery, and, in sitting or semisupine picture taken in bed, it will appear as diffuse blurring of the basal lung segments, which obliterates the outline of the costophrenic angle and diaphragm. A radiograph with the patient in lateral decubitus view with a horizontal beam usually confirms the diagnosis (Fig. 106). In sitting or lying pictures, even considerable amounts of fluid may remain undetected. Ultrasound in sitting patients easily discloses collections of fluid in the posterior costophrenic angle.

 

Alf Kolbenstvedt, Arnulf Skjennald and Charles B. Higgins