13 PATIENTS IN THE INTENSIVE THERAPY UNIT

In this chapter we concentrate on some of the pitfalls and difficulties that can occur when evaluating the bedside CXR in the intensive therapy unit (ITU).

Figure 13.1 The CXR is essential for assesment of all lines, tubes and catheters. Careful analysis of the pulmonary and pleural appearances will assist clinical management.

THE BEDSIDE CXR

Misleading appearances may result from the patient’s position or be due to radiographic technique when a supine CXR is obtained.

POTENTIAL PITFALLS

The bedside AP projection magnifies the heart and the mediastinum (p. 5).

Slight patient rotation, angulation of the x-ray beam or variable x-ray tube to patient distances can produce deceptive features on the CXR.

Rotation—normal aortic arch vessels can simulate an upper zone mass.

Beam angulation—spurious left lower lobe consolidation¹.

Differing x-ray tube to patient distances—alterations in mediastinal magnification on serial CXRs.

Exposures can vary. An underexposed CXR (everything too white) or an overexposed CXR (everything too black) can obliterate important abnormalities. Fortunately, problems resulting from under- or overexposure can be partially corrected using the windowing facility on digital images.

ASSESSING THE BEDSIDE CXR

A three-step sequence

1. Check the position of all lines, tubes and pacing leads.

2. Check the lungs and pleura. Check the mediastinum.

3. Apply the three-film rule: Always compare the present CXR with the immediately preceding one…and then with an even earlier CXR.

LINES AND TUBES

These must be correctly positioned (Table 13.1). False readings, inadequate drainage and iatrogenic injury do occur.

Table 13.1 Optimum positions.

Line, tube, wire	Purpose/function	Best position for the tip
Central venous pressure line	Monitoring right atrial pressure Fluid infusion/nutrition Drug administration	Superior vena cava or brachiocephalic vein
Swan–Ganz catheter (Pulmonary arterial catheter)	Monitoring pulmonary arterial pressure To distinguish between cardiac and non-cardiac pulmonary oedema	Main or lobar pulmonary artery
Nasogastric tube	Gastric decompression/aspiration Nutrition	At least 10 cm beyond the gastro-oesophageal junction
Nasoenteric tube	Nutrition	Beyond the gastric pylorus
Intercostal drain (thoracostomy tube)	Drainage of a pneumothorax/pleural effusion	In the pleural space
Endotracheal tube	Assisted ventilation	5–7 cm above the carina
Tracheostomy tube	Assisted ventilation	See p. 188.
Tunnelled venous catheter/ Hickman line	Prolonged venous access Nutrition Chemotherapy administration	Junction of superior vena cava and right atrium
Oesophageal Doppler probe	Monitoring cardiac output via measurement of blood velocity in the descending aorta	Mid oesophagus

CENTRAL VENOUS PRESSURE (CVP) LINES

Valves are present in the jugular and subclavian veins (Fig. 13.2). The tipof the central line must be distal to the valves otherwise central venous(i.e. right atrial) pressure readings will be inaccurate^2,³.

Rule of thumb: On the CXR, the superior vena cava (SVC) commences at the level of the right first anterior intercostal space.

A catheter tip situated in the right atrium or right ventricle may cause an arrhythmia.

A curve at the tip of a CVP line suggests that the catheter is misplaced. Either it has entered a side vessel (Fig. 13.7), or it is jammed against the vessel wall, or it lies outside the vein.

Figure 13.2 Vessels: 1 = internal jugular vein; 2 = subclavian vein; 3 = left brachiocephalic vein; 4 = right brachiocephalic vein;5 = SVC; 6 = orifice of the azygos vein;7 = right atrium;8 = inferior vena cava.

Figure 13.7 The tip of the internal jugular line is curved (kinked). A curve at the tip always suggests that it has entered a side vessel, or that it is jammed against the vessel wall, or that it has penetrated the wall and entered the soft tissues. In this example the tip has entered the azygos vein.

VALVES²

The last valve in the subclavian vein is 2 cm proximal to its junction with the internal jugular vein.

The last valve in the internal jugular vein is approximately 2.5 cm above its junction with the subclavian vein.

The brachiocephalic veins and the SVC do not contain valves.

Figure 13.3 The tip of the internal jugular line is correctly positioned in the SVC.

Figure 13.4 The tip of the left subclavian line is correctly positioned (i.e. well beyond the last valve in the vein).

Figure 13.5 Right internal jugular line in good position. (Retouched.)

Figure 13.6 Right subclavian line in good position with its tip in the SVC. The SVC commences at the level of the right first anterior intercostal space. (Retouched.)

Faulty positions/complications

Line too high—inaccurate CVP measurements.

Line too low—risk of cardiac arrhythmia if in right atrium.

Vessel wall perforation resulting in:

pneumothorax

infusion of fluid into the mediastinum or the pleural space

Figure 13.8 The subclavian line has entered the internal jugular vein and the tip is directed towards the cranium.

Figure 13.9 The subclavian line is poorly positioned. Its tip lies proximal to a valve.

Figure 13.10 The subclavian line has entered the internal jugular vein. (Retouched.)

Figure 13.11 The tip of the internal jugular line is situated in the right atrium. An unsatisfactory position; it may cause an arrhythmia. (Retouched.)

SWAN–GANZ (SG) CATHETER

A SG catheter (pulmonary arterial line) measures the pulmonary capillary wedge pressure. This allows an assessment of the left atrial pressure and cardiac output. These pressure measurements have been regarded as crucial in complex ITU cases and help to distinguish between cardiac and non-cardiac pulmonary oedema. However, the usefulness of these catheters has been disputed and some studies suggest that pulmonary artery catheters do not improve patient outcome^4–7.

Figure 13.12 The tip of the SG catheter is correctly positioned; i.e. the tip does not project more than² cm beyond the mediastinal outline.

Figure 13.13 SG catheter. Correct position. The tip (arrow) of the catheter overlies the border of the heart.

Optimum position. The SG tip should be situated between the main pulmonary artery and the interlobar arteries. Apply this rule: on the CXR the SG tip should extend no more than 2.0 cm beyond the mediastinal shadow.

Faulty positions:

Distal migration of the tip may cause pulmonary infarction.

Proximal migration is common. If the tip is positioned in the right ventricle then there is a risk of an arrhythmia.

Figure 13.14 SG catheter. The tip is situated well beyond the mediastinal shadow…in this example a pulmonary infarct has resulted.

Figure 13.15 SG catheter. Poor position. The tip of the catheter is well beyond the mediastinal shadow.

NASOGASTRIC (NG) TUBE

One or more side holes extend along the distal 5–10 cm of the tube(Fig. 13.16).

The NG tip must be at least 10 cm beyond the oesophago-gastric junction…this will ensure that a side hole (Fig. 13.16) is not situated in the intra-abdominal portion of the oesophagus (Figs 13.17 and 13.18).

Figure 13.16 A selection of large bore and small bore NG tubes. Note the positions of the side holes which extend along the distal 5–10 cm of the tubes.

Figure 13.17 Part of the oesophagus is normally situated just below the diaphragm. It is important that the tip of a NG tube is positioned 10 cm or more below the gastro-oesophageal junction—otherwise some of the side holes are likely to be within the oesophageal lumen.

Figure 13.18 The tip of the NG tube is in good position.

Figure 13.19 Unsatisfactory position. The tip of the NG tube is positioned below the diaphragm—but it is still within the oesophagus.

Figure 13.20 The NG tube is curled on itself and its tip lies within the oesophagus at the level of the clavicles (arrow). The lung shadows represent extensive changes due to adult respiratory distress syndrome (ARDS).

Figure 13.21 The NG tube is identified by its dense tip. The tip has entered the trachea and lies within a left lower lobe bronchus.

NASOENTERIC TUBE⁸

These feeding tubes are thin plastic catheters with a mercury/tungsten filled tip. The optimum position for the tip is distal to the pyloric sphincter.

Caution: because the tube is thin and flexible it can coil in the pharynx, oesophagus, or stomach. It may enter the trachea or the right main bronchus.

Figure 13.22 The tip of the nasoenteric feeding tube is in good position; it lies distal to the gastric pylorus.

PLEURAL DRAINAGE TUBES^3,^8,⁹

The various appearances and diagnostic problems associated with pneumothoraces and pleural effusions are addressed on pp. 82–106. Important aspects relating to pleural drainage are described on pp. 100–101.

Figure 13.23 A selection of intercostal and pleural drainage tubes. Note the number and position of the side holes. Most tubes have at least two side holes.

Figure 13.24 Pneumothorax. Erect CXR. Pleural drainage tube in good position.

Figure 13.25 Pneumothorax. Some of the side holes of the pleural drainage tube are outside the pleural space and are situated in the soft tissues of the chest wall.

Figure 13.26 The pleural drainage tube is not in the pleural space. Its side hole and tip (arrow) lie in the soft tissues of the chest wall.

ENDOTRACHEAL TUBE (ETT)^3,⁸^-¹⁴

The ETT can move up or down^10,11:

Flex the neck and the tip can move 1.9 cm downwards.

Extend the neck and it can move 1.9 cm upwards.

Rotate the neck and it can move 0.7 cm upwards.

Ideally the tip should be situated midway between the carina and thevocal cords.

Rule of thumb: The tip of an ETT will be in a satisfactory position if it approximates to the level of the medial ends of the clavicles…i.e. approximately 5–7 cm above an adult’s carina when the head is held in the neutral position.

Identify the carina

Its air shadow is visible on most CXRs.

If it is not visible—apply this rule of thumb: In 95% of people the carina is situated at the level of the T5–T7 thoracic vertebrae.

Figure 13.27 ETT. Good position. Its tip lies 5–7 cm above the carina.

Figure 13.28 ETTs. Faulty positions. (a) Tip at level of the carina—i.e. much too low. Flexing the neck from the neutral position can cause the tip of an ETT to descend 1.9 cm down the airway. (b) The tip of this ETT has entered the right main bronchus. Because of the obliquity of the angle of origin of the right main bronchus a much-too-low ETT will usually enter the right main bronchus rather than the left main bronchus.

Figure 13.29 ETT. Faulty position. The ETT has entered the right main bronchus. The left lung is no longer aerated. As a consequence, there is extensive collapse of the left lung.

Table 13.2 ETT problems.

ETT malposition 1	ETT malposition 2
Tip in the right main bronchus. May cause:	Tube in the oesophagus. CXR evidence:
Left lung collapse And/or: right upper lobe collapse Or: right lung over-distension and pneumothorax.	ETT lateral to the tracheal air shadow Oesophagus distended with air Stomach distended with air

TRACHEOSTOMY TUBE

On a CXR the side walls of the tracheostomy tube should lie parallel to the outer margins of the trachea (Fig. 13.30).

Figure 13.30 Tracheostomy tube. Good position. Note that the walls of the tracheostomy tube parallel the walls of the trachea.

Table 13.3 The CXR following introduction of a tracheostomy tube.

Normal	Abnormal
Tracheostomy tube walls lie parallel to the long axis of the trachea. Tip lies several centimetres above the carina. The inflated cuff should not bulge the lateral walls of the trachea. Initially, following the tracheostomy, a small amount of air in the mediastinum or subcutaneous tissues is to be expected and is unimportant.	Widening of the mediastinum… a haematoma is developing. Increasing mediastinal or subcutaneous air…a leak is occurring.

DOPPLER ULTRASOUND PROBE

An oesophageal probe is a minimally invasive instrument for monitoring cardiac output (via measurement of blood flow velocity in the descending aorta). Optimum probe position is at the level (approximately) of the mid oesophagus. Of course it is the clear ultrasound signal that confirms that probe position is good. Nevertheless, the doppler probe shadow (Fig. 13.31) should be familiar to those who evaluate ITU CXRs.

Figure 13.31 Typical appearance of an oesophageal doppler ultrasound probe (arrow).

THE LUNGS IN ITU

CONSOLIDATION, COLLAPSE, INFARCTION

The ITU patient is at risk of developing pneumonia, lobar collapse due to obstructive secretions, pleural effusion and pulmonary infarction. The relevant CXR appearances are described elsewhere:

pneumonia—pp. 42–50

lobar collapse—pp. 52–69

pleural effusion—pp. 82–88

pulmonary infarction—pp. 293–296

COMPLICATIONS OF MECHANICAL VENTILATION

Pneumothorax is common in ITU patients. It is usually consequent on mechanical ventilation. Sometimes it is a complication of subclavian artery line insertion. Detecting a pneumothorax on a supine CXR can be very challenging. The features to look for have been described earlier (pp. 97–106).

DIFFUSE LUNG PATHOLOGY^11,^12,¹⁵^-¹⁷

The CXR:

Frequently it is clinically—and radiologically—difficult to tell whether diffuse shadows are due to pneumonia, adult respiratory distress syndrome (ARDS), pulmonary oedema…or a combination of these. Table 13.4 provides some CXR features that can be helpful. But we must emphasise that assigning a specific pathological process to the shadows can be problematic. Indeed, extensive shadowing on a CXR often represents a combination of pneumonia, areas of lung collapse, pleural fluid, and ARDS.

ARDS:

ARDS is a common cause for diffuse changes in the lungs. It results from an acute alveolar insult causing pulmonary inflammation and small vessel injury. The damaged endothelium leaks fluid and protein into the alveoli. There are numerous causes for ARDS including trauma, shock, systemic infection, head injury, multiple blood transfusions, severe pneumonia, smoke inhalation.

ARDS presents clinically as acute, severe, increasing respiratory distress. Onset of symptoms is usually within 24 hours of the original insult—invariably within three days.

The CXR shows diffuse consolidation in both lungs.

Sometimes the appearance of CXR changes is delayed…only becoming apparent 12 or more hours after the onset of symptoms.

Table 13.4 The CXR and diffuse lung shadows.


Patchy areas of consolidation with sparing of some areas Associated pleural effusion is common	Initially…predominantly interstitial shadowing with rapid evolution into a diffuse alveolar pattern Opacities are widespread, symmetric, and involve the lungs peripherally as well as around the hila All lung zones involved—bothcentrally and peripherally Proximal pulmonary vessels remain well-defined CXR changes may appear 12 or more hours after the onset of symptoms CXR appearances persist with minimal change on serial radiographs even when there is clinical improvement Pleural effusions are rare	Cardiac enlargement Lung shadows and the onset of symptoms occur at the same time Changes… predominantly at the lung bases Blurred margins of hilar vessels CXR clears rapidly in response to treatment Pleural effusion is common

Figure 13.32 ARDS. Typical pattern. Bilateral airspace (alveolar) shadowing.

Figure 13.33 ARDS. Typical pattern. Bilateral airspace (alveolar) shadowing.

Figure 13.34 Pulmonary oedema secondary to intracranial haemorrhage. Bilateral airspace (alveolar) shadowing.

Figure 13.35 Extensive pneumonia in both lungs. This appearance is indistinguishable from the diffuse alveolar shadowing that occurs in ARDS. The clinical history and examination together with the bacteriological findings indicated that the lung changes were due to infection—not to ARDS.

FACTS AND FIGURES^18–24

Analyse the CXR carefully. In one series of over a thousand consecutive ITU CXRs 35% had clinically unsuspected abnormalities²⁰.

An intravenous catheter or pacing wire may adopt a seemingly bizarre—butclearly intravenous—route as shown on the CXR. Several possibilities. It mayhave fortuitously entered a small but normal vein, e.g. the internal thoracic(i.e. mammary) vein. Alternatively, the patient may have a venous anomaly(e.g. a persistent left SVC). Thoracic venous anatomy—normal and anomalous—has been elegantly described by Godwin and Chen².

Pleural drainage tubes—position²¹:

Conventional teaching: for pneumothorax drainage the tip is best placed antero-superiorly; for fluid drainage the tip is best positioned postero-inferiorly. However, several studies^22,²³ suggest that the precise tube position in the pleural space is not that important.

But be careful. Infected pleural fluid is a very different matter. If an empyema is to be drained then precise positioning of the tube is critica^l21.

Pleural drainage tube enters a fissure:

Occasionally this may lead to malfunction²⁴.

However it has been shown that it is very common for a tube to be sited in a fissure²¹. In general this position does not adversely affect drainage.

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