PoCUS LUNG ULTRASOUND

Lung ultrasound at the beside has the ability to diagnose most lung associated pathologies with a high degree of sensitivity and specificity. Performed systematically this often will out perform a CXR. Bedside lung ultrasound also allows you to attain helpful dynamic information about your patient over their clinical course.

Focused Acute Medicine Ultrasound (FAMUS) provides an excellent review of lung ultrasound

THORACIC ULTRASOUND THEORY (FAMUS)

Lung ultrasound relies heavily on the interpretation of artifacts, the artifact patterns, and pleural based findings.

AIMS

• Understand the anatomy

• Identify normal pleural sliding and lung ultrasound findings

• Recognise and interpret ultrasound lung artifacts

  • A and B lines

  • Comet-tail and reverberation artifacts

• Appreciate characteristic ultrasound findings of different pathologies

  • Pneumothorax

  • Interstitial syndrome - ‘Wet lungs’

  • Alvelolar syndrome - Consolidation

  • Pleural effusions

LUNG ULTRASOUND INDICATIONS

Lung ultrasound has broad application in differentiating causes of respiratory distress and dyspnea. It can also be integrated into shock and volume assessments:

• Pneumothorax

• Causes of interstitial syndrome (‘Wet lungs’) e.g cardiogenic pulmonary edema

• Pneumonia

• Pleural effusions

• Part of a shock and volume assessment

LIMITATIONS

• Extensive surgical emphysema will impair views

• Large body habitus

• Patient mobility/positioning limitations may be an issue

  
  

LUNG ULTRASOUND PROTOCOLS

A number of approaches to ED based lung ultrasound have been developed.

The most recognised is the BLUE (Bedside Lung Ultrasound in Emergency) Protocol (Lichtenstein 2008).

• This utilises three imaging points on each sides of the chest that helps to define specific ultrasound profiles in conditions causing dyspnea

• The BLUE protocol can be reasonably confusing approach if not familiar

In general a more simplified approach can be taken utilising a 6-point lung imaging technique, looking for:

• Presence or absence of lung sliding (+ M-Mode)

  • Is there a pneumothorax ( You may find a lung point)

  • Other causes of loss of lung sliding

• B-lines

  • > 3 per field of view abnormal

  • Localised vs diffuse

  • Is there an interstitial syndrome

• Looking for signs of consolidation

• Looking for effusions

This can be integrated with an IVC and gross cardiac function assessment to help determine cause of any identified interstitial syndrome i.e. Diffuse B-lines seen in cardiogenic pulmonary edema

ULTRASOUND APPEARANCE OF LUNG

In normal air filled lung, ultrasound can only interrogate the pleural surface. The ultrasound waves are near completely reflected/attenuated at the normal pleural/air interface:

• In the normal lung everything below the pleural line is grey-scale artifact filled in by the ultrasound machine

  • These artifacts are useful in lung ultrasound

• Normal lung parenchyma is not seen in ultrasound

• Interstitial fluid accumulation results in potentially diagnostic artifactual B-lines

• Pathologic change can result in visualisation of areas of lung parenchyma by ultrasound

  • Fluid displaces air in alveoli/airways

  • Collapse and consolidation of lung occurs

• Pleural effusions are seen as anechoiec (black) accumulations

A number of described ultrasound signs can be seen with particular lung pathologies.

SURFACE ANATOMY

LUNG ULTRASOUND PROBES AND PRESETS

Pleural and superficial assessment:

• High frequency linear probe is best for this, set at a depth of 4-6 cm, with the focal point at the pleura level

  • Detection of pneumothorax - Lung sliding and M-mode

  • Pleural changes and pleural based pneumonic changes

General lung imaging:

• Curvilinear probe is probably the best option set at a depth of around 15cm

  • Can see pleural sliding (Not as good as the linear probe)

  • Has wide field of view

  • Has good resolution at depth

• Phased probe is also used widely owing to its small footprint allowing imaging within small acoustic windows of the chest

  • Less detail of superficial lung and pleura

  • Poorer spatial resolution at depth compared to the curvilinear probe

Presets:

• A lung preset should be used initially in your exam

  • Turns off tissue harmonic imaging (THI) and multi-beam (MB)/compound imaging which accentuates important diagnostic lung artifacts (e.g. B-lines)

• An Abdo preset can be used for more detailed imaging of pleural effusions, and areas of parenchymal abnormalities such as lung consolidations

  • THI and MB are activated improving image resolution and reduces artifact

SIX-point lung ultrasound

LUNG ULTRASOUND MADE EASY (POCUS 101)

An initial six-point (3 per side) approach is probably sufficient for initial beside lung ultrasound

• A more extensive examination, including the posterior chest, can be undertaken if looking for more localised findings such as pneumonia

  • There are various techniques for a more comprehensive exam

COMPREHENSIVE LUNG EXAM (Life in The Fastlane)

Patient positioning:

• Generally the patient will be supine or reclined in the bed for a 6-point exam

• In the patient with more marked respiratory distress they may be upright

• More detailed/extensive imaging would require the patient to be seated upright with the back away from the bed

PROBE POINTS

3-points imaged on each of the right and left sides:

• Probe is in the longitudinal plane with probe marker to the head

R1/L1: mid-clavicular line at the 2-3rd intercostal space

• Correlates to the R and L upper lobes of the lung

R2/L2: mid-axillary line at the 6-7th intercostal spaces (lateral to male nipple level)

• Correlates to the R middle lobe and lingula lobe on the left

R3/L3 : posterior-axillary line at the 10-11th intercostal space (Xiphoid level)

• Correlates to the R and L lower lobes

• R3/L3 known as the PLAPS points (posterior and/or lateral alveolar and/or pleural syndrome)

  • Most common place to find lung consolidation and pleural effusions

• At each point identify ribs, pleural line and adjust depth appropriately

  • Identify the ‘BAT WING SIGN’ at each point

  • Identify lung sliding at each point

ANTERIOR CHEST R1/L1

• 2-3rd intercostal space in the mid-clavicular line

• Most anterior/apical part of the chest (in the near supine patient)

• You can use the linear probe initially to look for pleural sliding and then change to curvilinear probe for examination at depth

• Location for looking for a pneumothorax and also B-lines

  • Need to identify normal lung sliding

• Use M-mode to identify the normal ‘Seashore’ sign pattern

• Note other normal lung artifacts

  • A lines (reverberation artifact) repetitions of the pleural line at depth

    • Present in normal and abnormal lungs

    • Not abolished by a pneumothorax

    • Most prominent when the probe is perpendicular to pleura

  • Short pleural based comet-tail artifacts (seen in lung sliding video above)

LATERAL CHEST R2/L2

• 6-7th intercostal space in the mid-axillary line

• Locate ‘BAT WING’ sign , pleural sliding , and A lines

• Identify any abnormalities

  
  

POSTERIOR CHEST R3/L3 PLAPS POINT

This is the location of interest where you are most likely to see effusions or consolidation

• Place the probe as near to the bed as possible, in line with the xiphoid using the liver (R3) and spleen (L3) as sonic windows.

  • This equates to a similar position as the RUQ and LUQ eFAST views

• You should note the typical normal findings

  • Mirror imaging artifact of liver or spleen above the diaphragm

  • The image of the spine stopping at the diaphragm level as it heads cephalad

  • The ‘CURTAIN SIGN’ of normal aerated lung sliding down with inspiration in to the frame

• Scan slightly cephalad interrogating along the posterior axillary line

LUNG ULTRASOUND FINDINGS

PNEUMOTHORAX

PNEUMOTHORAX (5MIN SONO)

Key to identifying a pneumothorax is to scan the anterior most aspect of the chest, in the supine patient this correlates to the R1/L1 position in the 6-point examination.

Remember the findings are location specific to the probe position, but if the probe is at the most anterior portion/or apical portion of the chest a significant pneumothorax should be detected.

Pneumothorax RULE OUT (at the imaged location) - normal lung sliding (NPV 99%)

• Use M-mode to help confirm your findings

  • ‘SEASHORE SIGN’ is normal (see above)

  • ‘STRATOSPHERE SIGN’ is consistent with a pneumothorax (see below)

• Absence of lung sliding in the right clinical context is suggestive of a pneumothorax

  • Other causes of apparent absence of lung sliding:

    • Apnoea/respiratory arrest

    • Poorly ventilated patients

    • Severe hyperinflation - asthma/COPD

    • Adhesions/consolidation

    • Pleurodesis

    • Blebs or bullae

      
      
      

• The presence of B-lines or a lung pulse exclude a pneumothorax at that point

  • A lung pulse may be seen in conditions where there is apparent loss of normal pleural sliding but without a pneumothorax

    • A lung pulsation seen at the pleura is the transmitted pulsation/movement from the heart

    • Usually seen when there is absent/poor ventilation, apnoea, or severe hyper- inflation

LUNG PULSE (Dr James Rippey)

LUNG PULSE (Sinai EM)

• Finding a lung-point (PPV 100%) is a ‘RULE IN’ for a pneumothorax

  • A lung-point is found by scanning progressively more lateral and caudad in the chest

LUNG POINT (Dr James Rippey)

• Location of the lung point confirms the diagnosis, and helps to quantify the size.

• It is important not to mistakenly interpret a lung point from a pseudo-lung point (video below)

  • A pseudo-lung point is a junction between the lung and mediastinum or diaphragm

  • Often seen on the left side of the chest where lung meets pericardium

PSEUDO-LUNG POINT VS LUNG POINT (Dr James Rippey)

B-LINES AND INTERSTITIAL SYNDROME

B-Lines (Core Ultrasound)

B- lines are a vertical reverberation artifact that results from changes in the interstitial lung tissue

• Caused be increased fluid and/or thickening of the interstitial space of the subpleural and interlobular septa

• Variety of conditions can generate B-lines which may be focal or diffuse in nature

b-line Ultrasound Definition

• Vertical reverberation artifact

• Originate from the pleura

• Extend to beyond the maximal depth of view

• Hyperechoiec

• Move with pleural sliding
  

causes of b-lines

A few ‘normal’ B lines can be commonly found especially in the older age groups

• Typically in dependent locations (Lung bases)

• < 3 per field of view can be normal

• Usually the B-lines will not be diffuse in this setting

Abnormal B-Lines

• 3 or more B-lines per field of view (intercostal space) is abnormal

• These may be focal or diffuse depending on the pathology

• Diffuse B-lines in 3 or more zones on both sides of the chest is consistent with a diffuse alveolar interstitial syndrome ‘WET LUNGS’ such as pulmonary oedema or ARDS

B-lines may be seen in a number of chronic conditions causing interstitial thickening

• Pleural fibrosis from any cause

• Interstitial lung disease/fibrosis

• B-lines will be seen in a pattern of distribution related the areas of the lung affected by the underlying condition

  • Typically more localised to certain zones

Cardiogenic Pulmonary Oedema

• Typically bilateral B-lines

• Associated with cardiac dysfunction on bedside echo

• Mild overload states B-lines are found in dependent locations

• In more acute moderate-severe cases they will become diffuse

  • B-lines may become confluent with each other with severe ‘WET LUNG’

ARDS

• Any cause of ARDS will produce B-lines

• Generally diffuse and bilateral

Pneumonia

• May be focal or diffuse/bilateral or unilateral depending on pattern of pneumonia

• Typically focal associated with subpleural or lobar consolidations

Trauma

• Pulmonary contusion will lead to B-lines which are typically localised to the area of injury

• May be associated with other findings such as lung consolidation from haemorrhage, pleural effusion from haemothorax, or pneumothorax.

consolidation and alveolar syndrome

Normal aerated lung parenchyma is not seen on ultrasound. Consolidated lung becomes apparent on ultrasound, when fluid accumulation and lung collapse results in displacement of air from the tissue.

Consolidation of lung may occur for a variety of reasons:

• Pneumonia

• Extrinsic mass effect causing collapse e.g. large pleural effusion

• Intrinsic obstruction causing collapse e.g. bronchial mass, mucous plugging etc.

• Significant atelectasis

CONSOLIDATION IN PNEUMONIA

The ultrasound changes seen in pneumonia are a spectrum of progressive changes depending on the severity and the extent of the process:

ULTRASOUND FINDINGS IN PNEUMONIA

There are a variety of ultrasound findings in pneumonia:

• B-lines may be focal or diffuse, unilateral or bilateral

• Pleural thickening

• Sub-pleural consolidations

  • Hypoechoeic sub-pleural fluid/pus filled foci surrounded by hyperechoeic border

• Shred sign

  • Hyperechoeic demarcation between normal aerated lung and consolidated lung

• Air-Bronchograms

  • Air is trapped in consolidated or collapsed lung tissue

  • These may be static or dynamic in nature

  • Static air trapped may be found in atelectasis or consolidation

  • Dynamic air is still in communication and is usually found in consolidated lung

• Dense consolidation

  • Hepatisation (‘Liver like’) of the lung

  • See video below dense consolidated lung above (to the left) of the diaphragm, with the liver below (to the right). Bright echogenic shred sign between consolidated lung and aerated lung

PLEURAL EFFUSIONS

• Pleural effusions are typically identified most easily at the PLAPS (R3) point in a supine patient.

• There are a number of signs that can help identify a pleural effusion and may also help determine the nature of the effusion within the clinical context i.e. transudate vs exudate.

• Pleural fluid will typically appear relatively anechoeic in nature, found between the confines of the parietal pleura on the chest wall and the visceral pleura overlying the lungs.

• The nature of the effusion will determine the relative appearance:

  • Transudatve effusion and acute haemothorax will appear black/anechoeic

  • Exudative effusions will tend to have a variable degree of echogenicity or ‘debri’

  • Loculated effusions which tend to be caused by inflammatory processes, and usually will be exudative in nature

  • Haemothorax can appear as an acute black/anechoeic fluid, mixed echogenicity, or almost tissue like if the blood is substantially clotted.

pleural effusion size

• An approximate pleural effusion volume can be measured using technique described by Balik et al. at the PLAPS point:

  • Choose measurement A or B which ever is the greatest

  • Small effusions measuring < 10mm less accurate

  • Loculated effusions will not be accurately measured

  Pleural volume (mL) = (measured distance in mm) x 20.

POCUS PLEURAL EFFUSION SIGNS

• Spine sign

  • In pleural effusion or lung consolidation, ultrasound waves can travel through the thoracic cavity above the diaphragm allowing the spine to be seen

• Plankton sign

  • Echogenic debri within the pleural effusion may be seen in exudative effusion or haemothorax

• Jellyfish Sign

  • At the PLAPS point this is the appearance of consolidated lung floating in the pleural effusion

• Quad Sign

  • Boundaries of a pleural effusion in a supine patient tends to make a ‘Quadrilateral Shape’ (see below) with the boundaries being the rib shadow either side, the superficial boundary being the parietal pleura, and the deep boundary being the visceral pleura over the lung.

  • Often B-lines will be visible deep to the effusion

• Sinusoid Sign

  • This is gained using M-mode through an apparent pleural effusion

  • This can help confirm the presence of a pleural effusion, which would be represented by a sinusoidal pattern of the lung moving towards the line of sight/probe during inspiration (see below).

LUNG ULTRASOUND (LITFL)