BRIEF REVIEW OF PULMONARY IMAGING IN CRITICALLY ILL PATIENTS:-
Dr Himadri S. Das
Imaging plays an important role in assessment and daily management of acute life threatening conditions in critically ill patients with multi-systemic involvement. Modalities which are used for primarily for pulmonary imaging include x-rays (mostly using portable equipment with low mA), USG (using portable bedside units), transesophageal Doppler and CT scans. The availability of multislice CT scanners has reduced the problem of breath holding and patient motion with faster imaging times. Most of the critically ill patients usually can not obey commands, can not hold breath or be properly positioned and above all are under life support systems or ventilated with numerous tubes, catheters and lines .Role of Imaging is increasing in the intensive care setting. A brief review pertaining to pulmonary imaging in critically ill patients is outlined below.
Normal tubes, lines and catheters: Radiography should be done after insertion of tube or line to see correct position and identify complications. Iatrogenic problems from malpositioned lines are common and may be life threatening.
- Endotracheal tube (ET) – Normal ET tube tip should be 3 to 5 cm above carina. In neutral head and neck position the tube is seen 3 to 5 cm above carina. If the cervical spine is flexed the ET tube may descend 2 cm so the tube tip is seen at 3 to 5 cm from carina. If the cervical spine is extended there is 2 cm ascent of the tube tip which is seen 7 to 9 cm from carina. Ideally the tube width should be at least 2/3rd of the width of trachea. The cuff of the tube should not bulge the tracheal wall.
- Nasogastric (NG / feeding) Tube: – For suction of fluid in supine position proper location of tip should be in fundus of stomach. For suction of air in supine position proper location should be in antrum of stomach.
- Tracheostomy tube: – For patients requiring long term intubation. Tube tip should be above carina. Tube width should be 2/3rd the width of trachea.
- Chest tube: – For pneumothorax in supine patient, the tube should be placed antero-superiorly ideally. For hydrothorax in supine patient the tube should be placed postero-inferiorly. For empyema and haemothorax CT may help to plan drainage. Early drainage is important. Poor drainage will lead to fibrothorax and patients may require decortication.
- Central venous catheter (central line):- To maintain optimal blood volume or long term drug administration. Ideal position is in distal SVC. Access may be obtained from internal jugular, antecubital or femoral veins.
- Swan Ganz catheter: – To measure pulmonary capillary wedge pressure. Reflects LA and LV end diastolic volume. Ideal position is in the right or left pulmonary artery. Same access as above.
- Surgically implanted catheters: – For long term venous access usually for antibiotics or chemotherapy. Reservoir is placed in anterior chest wall soft tissues. Catheter tip ideally in distal SVC.
Abnormal tubes, lines and catheter’s:- CT may be helpful when complications are suspected.
a) Endotracheal tubes :- (a) Malposition: – May be intubated into right mainstem bronchus causing atelectasis of left lung. Bronchus intermedius intubation may cause atelectasis of left lung and right upper lobe. If there is 100 % inspired oxygen there may be immediate atelectasis with bronchial occlusion.
a) Esophageal intubation: – may cause dilated stomach with poor lung volumes.
b) Vocal cord injury if tip is at the level of larynx.
c) Sinusitis with nasotracheal intubation.
d) Barotrauma: – Alveoli are over distended and may rupture from high peak pressure with mechanical ventilation. Others: – Interstitial emphysema, pneumomediastinum and or pneumothorax.
e) Aspiration pneumonia: – 5 to 10 ml of fluid may pool above the ET cuff. Deflation and aspiration may potentially develop into pneumonia. Suspected if normal air above cuff is replaced by soft tissue density.
f) Tracheostenosis: – Late complication. At stoma, tip or multiple foci. At tip usually occurs 1.5 cm below stoma.
g) Tracheomalacia: – Late complication.
b) Tracheostomy Tube: – Cuff may be in subcutaneous tissues with tissue necrosis. Over inflation of cuff or deflection of tip may lead to tracheoesophageal fistula or into artery or vein producing haemorrhage.
c) Nasogastric tube: – Into bronchus, lung or pleura. Signs: – Consolidation occurs if fluid is administered. Atelectasis if occluding air way and pneumothorax if penetrating lung.
d) Chest tubes: Poor position and inadequate drainage if tube is in the interlobar fissures. If in the chest wall the outer wall of the chest tube is not visible. If in the lung may cause bronchopleural fistula. Side hole in chest wall may cause massive subcutaneous emphysema. The tube tip impacting artery (example – Subclavian) or esophagus may result in injury / erosion.
e) Central venous catheter: (a). Malposition: – Into Subclavian, aorta or femoral artery. Through vein wall into pleura or mediastinum. Into myocardium or pericardium. Retrograde into a jugular vein, rarely into liver.
(b). Pneumothorax, mediastinal haematoma after placement.
(c). Catheter break and embolism. Aseptic or septic thrombus on catheter with pulmonary embolization.
(d). Fibrin sheath occlusion.
(e). Thrombosis of vein: – Directly related to period of catheterization and potential source for pulmonary emboli.
f) Swan Ganz catheter:-pulmonary infarction from wedged catheter with of without clot, and with or without inflated balloon tip. Arrhythmias may occur if tip is in right ventricle. Pulmonary artery pseudo aneurysm formation or rupture due to over distension of cuff in small pulmonary artery. Pseudo aneurysm is manifested as elliptical pulmonary nodule the long axis of which parallels the vasculature within 2 cm of hila, usually on right side. Pulmonary haemorrhage may occur if aneurysm ruptures.
g) Surgically implanted catheters: – Infection, septic emboli, thrombosis or torn catheter between clavicle and 1st rib felt as “osseous pinch”. Rotation of pulse unit in the soft tissues by the patient causing fracture or shortening of pacer lead ( twiddling sign )
Clinical issues and treatment:-
– Infected catheter may clear with antibiotic treatment without removal.
– Fibrin sheath-infuse tissue plasminogen activator, if unsuccessful then exchange catheter.
– Interventional snare retrieval for embolized catheter fragments.
– Infection most common complication of central venous catheter, usually staphylococcus.
– Fibrin sheath sign: – Catheter may be flushed but not aspirated.
DIFFUSE ALVEOLAR DAMAGE (DAD)
- Diffuse peripheral pulmonary consolidation.
- Lack of Kerley B lines and peribronchial cuffing.
- Anterior (nondependent) cysts from barotraumas with positive end expiratory pressure (PEEP).
- Acute respiratory distress syndrome (ARDS): Clinical definition, severe hypoxemia on high concentrations of O2, normal wedge pressure.
- Seen with nearly any medical or surgical condition: Toxic fumes, aspiration, shock, postoperative, pancreatitis.
- Pathophsiology : Inflammatory mediators damage capillary membrane
- Nearly any major medical or surgical condition
- Airway insult; aspiration (especially gastric acid); toxic fume inhalation; o2 toxicity; pneumonia.
- Blood-borne insult; sepsis; transfusion; surgery; shock; eclampsia; pancreatitis.
- Nearly any major medical or surgical condition
- Best clue: Intubated patient with diffuse peripheral consolidation.
- Diffuse pulmonary consolidation.
- Favors the lung periphery.
- Kerley B lines infrequent (more frequent with cardiogenic edema)
- Peribronchial cuffing infrequent.
- Normal heart size: No pulmonary vascular redistribution.
- May have small pleural effusions.
- Initial use of PEEP may increase lung volume giving apparent radiographic “improvement”.
- Barotraumas common with PEEP.
- Superimposed pneumonia common.
CT / HRCT Findings.
- Surprisingly inhomogenous.
- Gravitational gradient: Ventral to dorsal increase in opacities.
- Resolution, coarse reticular thickening and cyst formation in anterior (ventral, nondependent) lung.
- Usually patients with ARDS rapidly intubated to support oxygenation even when severity of consolidation is mild. Rather than radiographic differentiation, clinical management based on Swan-Ganz catheter and pulmonary capillary wedge pressure (PCWP)
- Separation from cardiogenic pulmonary edema moderately successful. Absent Kerley B lines and peribronchial cuffing, peripheral predominance, Normal heart size, pleural effusions rare. No pulmonary vascular redistribution, normal vascular pedicle.
- May have identical radiographic findings, may result in ARDS.
- May have identical radiographic findings, may result in ARDS.
- May have identical radiographic findings, patient often anemic
- Acute (immediate) or insidious (hours or days) after initiating event.
- Dyspnea, tachypnea, dry cough, agitation, cyanosis.
- ARDS clinical definition for ADA, PaO2 < 50 with F1O2 > 50%
- Normal wedge pressure : Decreased lung compliance
- May have no chest radiographic abnormalities in first 12 hours
- Later, chest radiograph diffusely abnormal
- High mortality rate
- Survivors may have either restrictive or obstructive functional deficits.
- Pulmonary inflammation due to aspiration of infected oropharyngeal secretions
- Patients may be unconscious, post-operation, intubated or have gastro-esophageal disorders
- Gravity-dependent opacities, usually bilateral, basal and perihilar
- Recurrent pneumonias in chronic aspiration
- Aspiration of gastric acid during labor and delivery can be server and fatal (Mendelson’s syndrome) Adults often have underlying conditions, e.g. neurologic disorders, alcoholism esophageal disorders, on mechanical ventilation, tracheoesophageal fistula
Best clue: Recurrent gravity-dependent opacities
CXR: Acute aspiration
o Gravity-dependent, patchy, multi-focal airspace opacities, usually bilateral (conversely may be unilateral) basal and peripheral
o Supine position; posterior segments of upper lobes or superior segments of lower lobes
o Airway findings from larger aspirated particles
§ Segmental or lobar atelectasis
§ Hyperinflation or air trapping more common in infants and children
o May worsen in first few days the clear rapidly
o Aspiration of large amounts of gastric common can progress to acute respiratory distress syndrome (ARDS)
o Complications: Necrotizing pneumonia, abscess, ARDS, pulmonary embolism.
- Chronic aspiration
- Recurrent opacities often in the same location, reticulonodular opacities, bronchiectasis, pulmonary fibrosis.
- Airspace opacities in dependent lung, centrilobular nodules
- Can be used to evaluate for complications of abscess, empyema
Pneumonia or Recurrent Pneumonias
- Identical radiographic findings
- Immunocompromised patient predisposed to recurrent pneumonias
- Identical radiographic findings
- Infarcts peripheral, often with pleural effusion
- Predisposing factors for thromboembolism
§ Cardiomegaly, pleural effusions
§ Kerley B lines uncommon with aspiration
- Identical radiographic findings
- Aspiration predisposing factor for ARDS
Bronchiolitis Obliterans Organizing Pneumonia (BOOP)
- Similar radiographic findings, may also wax and wane
- Death rate for patients who develop ARDS from Mendelson’s syndrome is up to 50%.
ATELECTASIS (PULMONARY COLLAPSE):
- Decrease in volume of lung or a portion of lung
- Types : Obstructive, passive, cicatrizing and adhesive
- Signs : Shift of fissures, mediastinum and hila toward collapse
- Diagnosis can be made with chest radiography : CT to establish cause
- Best clue : Displacement of fissures
- Types of atelectasis
- Obstructive, e.g. bronchial neoplasm, no air bronchograms
- Passive e.g. pneumothorax or pleural effusion – lung volume loss in proportion to volume of occupied pleura space
- Cicatrizing e.g. remote tuberculosis with volume loss due to scarring
- Adhesive, e.g. ARDS collapse due to surfactant deficiency
- Lobar Collapse
- Airlessness of affected lobe, local increase in opacity
- Total lung volume average = 6720 ml
- Signs of atelectasis proportional to amount of volume loss
- Crowding of vessels and bronchi in affected lobe
- Displacement of fissures, mediastinum and hilum towards to collapse
- Overinflation of remaining lobes
- “Silhouette” sign – loss of air – soft tissue interface when collapsed lung abuts an adjacent soft tissue structres
- Right upper lobe (RUL) atelectasis (average volume RUL = 1140 ml)
- Collapses superiorly and medially, loss of SVC interface and apical soft tissue capping
- PA – lateral radiograph : Minor fissure displaced upward
- Lateral : Superior aspect of major fissure displaced anteriorly
- Central mass : “Reverse S sign of Golden”
- Juxtaphrenic peak : Tent of diaphragm (due to upward retraction inferior accessory fissure)
- Left upper lobe (LUL) atelectasis (average volume LUL = 1160 ml)
- Collapses anteriorly, partial loss of left heart border, haze superimposed on left hilum
- Lateral : Major fissure shifted anteriorly
- Luftsichel sign : Superior segment of lower lobe causes a crescent lucency between the aortic arch and the atelectatic upper lobe
- Right middle lobe (RML) atelectasis (average volume RML = 670 ml)
- Collapses as a triangle toward the right heart border
- PA : Obscuration of right heart border
- Lateral : Thin triangle or pancake shape from anterior chest wall with apex towards hilum, inferior aspect of major fissure
- Lower lobe atelectasis ( average volume LLL = 1550 ml, RLL 2000 ml)
- Collapse posteriorly, medially and inferiorly
- PA : Triangular opacity medial lung bases obscures diaphragms
- Lateral : Posterior displacement of major fissure, vague opacity over lower thoracic spine
- Right middle and lower lobe atelectasis
- Similar to pleural effusion : Ill defined right heart border and diaphragm
- Pathology involving bronchus intermedius
- Right upper and right middle lobe atelectasis
- Simulates left upper lobe atelectasis (double bronchus sign : 2 separate airways obstructed)
- Borrie’s sump: Nodes between RUL and RML bronchus may obstruct both.
- Bronchogenic carcinoma most common cause
- Segmental and subsegmental atelectasis (plate atelectasis)
- Long linear opacities are thicker and more indistinct than Kerley B lines
- Indicates low volume states : common in critically ill or post-op-patients
- Also seen with pulmonary embolism
- Total lung atelectasis
- Shift of mediastinum to opacity, hyperinflation of contralateral lung
- Differentiating large pleural effusion : Mediastinal shift to opposite side
- Round Atelectasis
- Associated with pleural thickening (asbestos related) in lower lobes
- Oval, wedge-shaped or irregular subpleural mass with air bronchograms (60%)
- Comet tail sign (whorled bronchovascular markings into mass)
- Most are stable for many years
- Can help identify cause, i.e. bronchial obstructing lesion
- No imaging can predict if the atelectatic lobe is sterile or infected
- CT useful to exclude endobronchial lesion and confirm round atelectasis
- Radiographic opacity but no volume loss
- Peripheral opacity, volume loss of hemithorax due to splinting
- Round atelectasis may simulate lung cancer
- Endobronchial neoplasm common cause of lobar atelectasis in adult
- Lobar obstruction, collapse in 18 to 24 hours if breathing room air
- Lobar obstruction, collapse in < 5 minutes if breathing 100% oxygen
- Nitrogen very slowly absorbed, delays development of atelectasis
- Obstructed lobe may not collapse because of ventilation across the pores of kohn and canals of Lambert, or across incomplete fissures
- Asymptomatic fever can occur with atelectasis without infection
- Left lower lobe collapse : Most common in ICU setting
CARDIOGENIC PULMONARY EDEMA
- Common problem usually due to left heart failure
- Stepwise progression from pulmonary venous hypertension to interstitial edema to alveolar edema.
- Can clear rapidly with treatment.
- Shifts gradually with position (gravitational shift test)
- Best clue: Cardiomegaly with pulmonary venous hypertension and interstitial edema.
- Earliest radiographic manifestation: Upper lobe vessels are equal to or larger in diameter than lower lobe vessels; increased pulmonary artery / bronchus ratio in upper lobes, ill-defined lower lung vessels.
- Interstitial edema – thickening of interlobular septa – Kerley A and B lines, lower zonal and perihilar haze, subpleural edema thickens interlobar fissures, peribronchial cuffing.
- Kerley A : Long lines in upper lobes radiating towards hilum (rare)
- Kerley B : Short, peripheral, perpendicular lines generally in lower lobes (common)
- Alveolar edema – diffuse airspace opacification – gravity dependent
- “Bat’s wing” (butterfly, perihilar) opacities (uncommon)
- Small bilateral effusions, larger on right, rarely unilateral on the left
- Cardiac enlargement chronically (normal heart with acute myocardial ischemia or arrhythmia)
- In chronic obstructive pulmonary disease (COPD), the cardiac size is often small due to hyperinflation, subsequent increases in heart size may not be beyond the range of normal.
- Azygos ± SVC distention (widened vascular pedicle)
- Temporal relationship of pressure and volume
- Acute pressure (capillary wedge pressure) elevation
- Initially normal, edema accumulates over 12 hour period
- Pressure decrease with treatment
- Edema resolves hours to days; radiograph “lags” clinical course
- Acute pressure (capillary wedge pressure) elevation
- Chest radiograph equivalents, smooth thickening of interlobular septa, bronchovascular bundle thickening, gravity-dependent ground-glass and / or airspace opacities.
Interstitial Edema: Pneumonia , Lymphangitic carcinomatosis
Alveolar Edema : Non cardiogenic edema, pneumonia , pulmonary hemorrhage
Alveolar proteinosis, acute eosinophillic pneumonia
Interstitial Edema, Cardiomegaly, Pleural Effusions
THE CHEST RADIOGRAPH FOLLOWING TRAUMA:
Simple fracture May be associated with surgical emphysema, pneumothorax, extra- pleural haematoma or haemothorax. First rib fractures have a high incidence of other associated injuries.
Fracture – May be associated with a clinically unsuspected dorsal spine fracture.
Clavicles and scapulae:-
Fracture – scapular fractures are usually associated with other bony or intrathoracic injuries.
Fracture – when present, are multiple in 10 % and non-contiguous in 80% of these. Thoracic spine injuries have a much higher incidence of neurological deficit than cervical or lumbar spine injuries.
Nerve root trauma – especially to the brachial plexus.
Pneumothorax – simple (in 20-40 % of patients with penetrating injuries) or tension. Signs of a small pneumothorax on a supine chest radiograph include a deep costophrenic sulcus, basal hyperlucency, a “double” diaphragm, unusually clear definition of the right cardiophrenic angle or left cardiac apex and visualization of apical pericardial fat tags. CT is more sensitive than plain film radiography.
Haemothorax: in 25-50 % of patients with blunt chest trauma and 60-80 % of patients with penetrating wounds.
Contusion – non-segmental alveolar opacities which resolve in a few days.
Haematoma – usually appears following resolution of contusion. Round, well-defined nodule. Resolution in several weeks.
Pulmonary oedema – following blast injuries or head injury (neurogenic oedema).
Adult respiratory distress syndrome (ARDS) – widespread air space shadowing appearing 24-72 hours after injury.
Trachea and bronchi
Laceration or fracture – initially surgical emphysema and pneumomediastinum followed by collapse of the affected lung or lobe.
Rupture – in 3-7 % pf patients with blunt and 6-46% of patients with penetrating thoraco-abdominal trauma. Diagnosis may be delayed months of year. Plain film finding include herniated stomach or bowel above the diaphragm, pleural effusion, a supra-diaphragmatic mass or a poorly visualized or abnormally contoured diaphragm. Probable equal incidence on both sides but rupture of the right hemidiaphragm is not so easily diagnosed.
IMAGING OF ICU PATIENTS FOLLOWING THORACIC SURGERY:
CABG is the most commonly performed operation. Valve replacement surgery comes next. Incidence of complications is low. Main complications are rebleeding and mediastinitis. In patients with rebleed 20% are picked up radiologically. Rebleeding usually occurs in first 24 hours. CT is the best modality to show complications like osteomyelitis, dehiscence, abscess and mediastinitis. Mortality is upto 50% with complications. Dehiscence or mediastinitis may be asymptomatic or present with nonspecific chest pain, cough and fever. Usually occur 10 to 14 days after operation.
CXR: – Immediate recovery room film, expected findings are – Basal atelectasis (90%), Left > Right due to phrenic nerve cooling, weight of heart and difficulty to suction left lower lobe bronchus.
Edema (mild):– Cardiopulmonary bypass “pump lung”, anesthetic volume expansion and intrinsic left ventricular dysfunction.
Mediastinal bleeding: – Initial recovery room film for baseline width, may normally increase in width in first 24 hrs.
Sternal dehiscence: – May be normal. Vertical sternotomy incision > 3 mm width. Wire fracture incidental finding and not a finding of dehiscence.
CT is the best modality to show sternal irregularity, periosteal new bone formation, peristernal collections and infections, mediastinitis, retrosternal haematoma and edema. It is important to differentiate aortic dissection from rebleeding. Aortic dissection also causes mediastinal widening in post operative period. Clue is to look for displaced intimal calcification.
Thoracotomy and complications:-
Complications after lobectomy include atelectasis, pleural effusion, haemorrhage, air leak and infection. Potentially fatal complications include pulmonary embolism, cardiac herniation, lobar torsion, pneumonia, ARDS and respiratory failure.
Mortality is 2% and morbidity upto 40% after lobectomy. Normally there is ipsilateral mediastinal shift after pneumonectomy. With contralateral or no mediastinal shift consider bronchopleural fistula, haemorrhage, empyema in the post pneumonectomy. Mortality 6% and morbidity upto 60% after pneumonectomy.
Post lobectomy normal findings: – Small amount of pleural fluid after drains are removed. Scattered lung opacities on the side of surgery. Effusion resolves during convalescence.
Post pneumonectomy normal findings: – 50 to 70 % of the hemithorax filled with fluid in 1 week. Complete filling with fluid in 2 to 4 months.
Normal mediastinal position: – Ipsilateral shift to the side of lobectomy. Returns to midline or close to midline as remaining lobes on the side of surgery hyper inflate. There is ipsilateral shift to side of pneumonectomy which is permanent.
Complications of lobectomy and pneumonectomy:-
Persistent pneumothorax, 10 to 20%.
Bronchopleural / bronchocutaneous fistula 2%.
Leak from suture line or bronchial stump: – Immediate post op period due to ischemia / infection.
Esophago-pleural fistula: – Most within 6 weeks of surgery due to adenitis, empyema or recurrent tumor.
Bronchial stump dehiscence: – Persistent pneumothorax, failure to fill with pleural fluid, drop in air fluid level of > 2 cm.
Hydrothorax: – Excessive pleural fluid. Consider poorly positioned chest tube, improperly positioned catheter with injection of fluid into pleura, thoracic duct injury and chylothorax.
Haemothorax: – Due to systemic, inter costal and mediastinal vessel laceration. Must be drained with chest tube or surgical ligation. Delay in treatment may result in fibrothorax and require decortication.
Empyema (< 5%):- Due to surgical contamination or from a bronchopleural fistula. Must be drained by chest tube. Delay results in fibrothorax, chronic empyema thoracic. Lung opacities seen in ICU patients are nonspecific from atelectasis and edema and is common in immediate post operative period.
Pneumonias: – Nosocomial, bronchopneumonia. Result of mechanical ventilation, narcotics, splinting, poor cough reflex and aspiration.
Elevated hemidiaphragm: – Consider phrenic nerve injury, atelectasis, pulmonary embolism or subphrenic abscess.
Cardiac herniation , pericardial defect :- Following intrapericardial pneumonectomy usually on right side, circulatory collapse, on right side there may be cardiac dextrorotation where cardiac apex lies against right chest wall “snow cone” appearance.
Left side – Cardiac levorotation
Post pneumonectomy syndrome (delayed complication)
After left pneumonectomy: Distal trachea and left main bronchus compressed between aorta and pulmonary artery.
After right pneumonectomy: Narrowed right upper lobe, bronchus intermedius and / or right middle lobe bronchi compressed between right pulmonary artery and spine
Torsion of a lobe or lung: After lobectomy. Remaining lobe rotates on its bronchovascular pedicle. 180-degree torsion leads to ischemia, infarction, and gangrene. Right upper lobectomy with torsion of right middle lobe is most common. Consider if abnormal position and orientation of pulmonary vessels are seen.
Herniation of lung through surgical defect in chest wall.: Accentuated by expiration.
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