Lung ultrasound and pleural ultrasound

My DDU point form notes on lung  and pleural ultrasound…

The rest of my DDU notes are here.

General approach

Probe and settings

McLean: phased array and curvilinear preferred, microconvex 3.5-7MHz ideal

Lichtenstein’s papers mainly use 3-3.5 MHz cardiac probes, but 2.5, 5, and 7.5MHz probes equally effective for B lines at least

Linear, high frequency probe (5-10 MHz) also used but not suitable for pleural

Marker cephalad

Standardized depth (18 cm) in some studies – McLean suggests 5-8 cm

“Stages” or zones

from Lichtenstein

in some papers he divides these into upper and lower

Lichtenstein’s stages

cf McLean et al advocate scanning along anterior, lateral (=anterior axillary) and posterior (=posterior axillary) lines

Examination

between acoustic shadow of ribs for pleural line

~0.5 cm deeper than ribs

horizontal, hyperechoic

normally see lung sliding and A lines

A lines

horizontal lines

regularly repeating

↓ intensity with depth

with aerated lung USS is scattered and >90% reflected (impedance mismatch), doesn’t penetrate much past pleura → appearance of multiple interfaces repeating at skin-pleural interval

B lines

= ultrasound lung comets = long comet-tail artifacts = a ring down artefact created by multiple very closely spaced pseudointerfaces, probably created by oedematous subpleural interlobular septae (collects here early in oedema)

vertical

hyperechoic, well defined, no ↓ intensity with depth

from pleural line to edge of screen

move with lung sliding

erase A lines

Distance between B lines

7 mm correspond to subpleural interlobular septae

≤ 3 mm / coalescing more severe → correspond to ground glass areas on CT, more fluid

fully coalesced “white lung” is most severe form – no A lines seen

number correlates with EVLW

not always pathological

single anterior B line, or multiple lateral B-lines in 10^th or 11^th intercostal space considered normal

seen in 1/3 of healthy volunteers

Lung pulse

appear as vertical bands on M mode after each QRS

tends to correlate with lack of lung sliding (but not deflation)

rules out pneumothorax

seen

in normals, along with lung sliding

in absence of lung sliding in

apnoea, bilaterally

normal lungs with RMB intubation, on left side – 93% sensitive and 100% specific to detect RMB intubation in setting of healthy lungs

obstruction → consider bronch

in ARDS patients

Consolidation

Consolidation features

6 features

at thoracic level

real, not artefact

tissue like pattern (Hepatisation)

boundaries

superficial: pleural line / pleural effusion

deep

usually with aerated lung – irregular, hyperechoic line – “shred sign”

or whole lobe involvement – regular boundary

lack of sinusoid sign

ie doesn’t move towards chest wall with inspiration

air bronchograms

Air bronchograms

both consolidation and obstructive atelectasis may have air bronchograms on lung ultrasound

if a bronchogram moves towards the pleural surface >1mm with inspiration = “dynamic air bronchogram”

means consolidation, not atelectasis (as does lung sliding)

other air bronchograms are termed static

cf fluid filled bronchograms appear as hypo/anechoeic structures → look for bronchial obstruction

see Lichtenstein DA, Lascols N, Mezière G, Gepner A. Ultrasound diagnosis of alveolar consolidation in the critically ill. Intensive Care Med 2004;30:276–81

Test performance

USS 90% sensitive and 98% specific cf CT

false –ves cf CT usually posterior, either small or didn’t reach pleural surface

other benefits of ultrasound

can estimate thickness?

see abscesses

diagnose complications

pneumothorax, effusion

Pneumothorax

Lung sliding or comet tails

present = no pneumothorax

even 1 motionless B line / short comet tail / lung pulse also excludes pneumothorax

absent suggest pneumothorax only weakly in critically ill (PPV 56%, 27% in respiratory failure) – need lung point to confirm (only ~66% sensitive)

multiple d/dx of lost lung sliding in critically ill (basically lung is big with no airflow or small with no airflow):

HFOV

hyperinflation (look for lung pulse)

apnoea

phrenic nerve palsy

massive atelectasis

severe fibrosis

pleura stuck together (“acute pleural symphysis”)

Imaging sites

start in non-dependent area where pleural air will collect

i.e. apices if upright patient, anterior in supine

look anteriorly, laterally

Documenting

take a loop

M-mode

bar-code / stratosphere sign – abnormal

sea-shore sign – normal

colour / power Doppler

Literature

in trauma and ICU patients, mainly in Europe (Lichtenstein, Blaivas)

?sensitivity 94-100%, specificity 91-100% (but note earlier comment re PPV)

Pleural effusions

Signs

of effusion

spine sign

spine seen distal to pleural effusion

cf not seen if aerated lung prevents ultrasound transmission

of no effusion

mirror image

liver mirrored by diaphragm if aerated lung causes impedance mismatch and reflection

lung curtain

Nature of fluid

transudates are always anechoic – but anechoic effusions can be exudate

septations, swirling, bilayer effect or ↑ echogenicity suggest exudate / empyema / haemothorax

Literature

in trauma patients

sensitivity 92-97.5%, specificity 99-100%

lower risk of pneumothorax cf landmark technique when draining

Determining size

Vignon et al

interpleural distance = distance between visceral pleura and posterior chest wall when supine

use strictly transverse imaging

lowest intercostal space where diaphragm is absent from view throughout respiratory cycle

strictly supine – no tilting patient to get more posterior

measure perpendicular distance from leading edge of dependent surface of lung to trailing edge of posterior chest wall in end expiration

distance > 45 mm at R base or >50 mm at L base (L is the Roman numeral for 50) predicted a pleural effusion >800 mL, with a sensitivity of 94% and 100% and specificity of 76% and 67%, respectively

ref: Vignon P, Chastagner C, Berkane V, et al. Quantitative assessment of pleural effusion in critically ill patients by means of ultrasonography. Crit Care Med 2005;33:1757–63

Vignon et al 2005 scan position

Balik et al

effusion size in mL = largest distance between parietal and visceral pleura at base of lung in mm * 20

patient supine + 15° trunk elevation

2.5 MHz “intercostal probe”

posterior axillary line

transverse section

maximal distance between parietal and visceral pleura in end expiration

ref: Balik M, Plasil P, Waldauf P, et al. Ultrasound estimation of volume of pleural fluid in mechanically ventilated patients. Intensive Care Med 2006;32:318–21

Balik et al 2006 measurement example

Alveolar-interstitial syndrome

Technique

low frequency probe, set to 5-8cm (or 18cm in another resource)

Diagnosis

≥ 3 B lines per space (= B+ lines = lung rockets) are seen all over chest

~93% sensitivity and specificity in diffuse alveolar interstitial syndrome, vs X-ray, in medical ICU patients

B-lines correlate with

BNP ↑

PCWP ↑

LV EF ↓

CXR appearance

discharge diagnosis

sensitivity 70-100%, specificity 89 – 97.7%

tracks therapy eg PEEP in hours or less

cf CXR lags

d/dx

CHF

useful where COPD and CHF coexist to determine cause of SOB

pneumonia / ARDS

consider if B-lines not uniform

also consider interstitial pneumonias e.g. PCP/PJP

pulmonary fibrosis

ARDS

Diagnosis

multiple bilateral B-lines

distinguish from APO by presence of more pneumonic features

↓ lung sliding (cf adjacent areas or opposite side – ARDS only)

subpleural consolidations (ARDS only)

hepatisation + air bronchograms (ARDS only)

spared areas (with B+ lines on each side of them – ARDS only)

lung pulse (no sliding, heart activity seen at pleural line – ARDS only)

pleural line abnormalities (coarse, thickenings > 2mm; also seen in ¼ of APO)

cf effusions more common to APO

ARDS features

change in lung ultrasound within minutes of ↑ PEEP (progressively from consolidation → subpleural consolidation → B lines → A lines)

Pneumonia

Findings

progress from

B-lines (few → many • may be focal) →

lumpy thickened pleura →

subpleural consolidation →

consolidation

like liver, but with air bronchograms (white due to reflection ± may see air moving through the bronchi)

Literature

accuracy comparable to CT in some ED studies, and outperforming CXR

Cortellaro et al

non-ambulant adult ED patients with suspected CAP

5 zones per side, 5 minute scan time total

findings in those diagnosed with pneumonia

commonest:

alveolar consolidation (in 91%)

air bronchograms (in 97%) – distinguishes pneumonia from obstructive atelectasis if dynamic

less common:

interstitial pattern

focal suggests pneumonia

consider pneumonia if bilateral but with

irregular and thickened pleura

↓ sliding

small subpleural consolidations (d/dx pulmonary infarction)

fluid bronchograms

pleural effusions

with CT as gold standard

USS 95% sensitivity, 99% specificity

CXR 85% sensitivity, 67% specificity

use of a single AP film in supine position may contribute to poor performance of CXR – but reflects common practice locally

Bronchiolitis

similar to pneumonia

suggested lumpy thickened pleura, subpleural consolidation (V-shaped irregularity with black fluid below pleural line) and ↑ B-lines (white lung) predict disease severity ?evidence

Roles

diagnostic

in small studies, substantially outperforms auscultation and CXR in diagnosis of pleural effusion, alveolar consolidation, and alveolar interstitial syndrome

advantages vs AP chest include

imaging retrocardiac consolidations

potential cost, radiation, transport, time savings

therapeutic

↓ risk of drainage

monitoring

see changes with ↑ PEEP

note complications e. g. RMB intubation

Impediments and limitations

Patient

dressings

subcutaneous emphysema

pleural calcifications

interpretation tricky with multiple pathologies (these patients were excluded from some studies eg. BLUE protocol study)

can’t distinguish transudate from exudate

Clinician

only medium agreement on κ statistic between observers on some diagnoses

potential for studies to overstate accuracy vs other imaging modalities because clinician will integrate other information (though practically useful)

need for training – varies between studies

2 months: Lichtenstein D, Goldstein I, Mourgeon E, Cluzel P, Grenier P, Rouby J-J. Comparative diagnostic performances of auscultation, chest radiography, and lung ultrasonography in acute respiratory distress syndrome. Anesthesiology 2004;100:9–15

30 mins: Bedetti et al for basic assessment of bilateral B-lines

Machine

acquisition and maintenance costs

potentially vector of resistant pathogens

time

push to cubicle, startup, scanning, reporting, shutdown, cleaning

BLUE protocol

devised by Lichtenstein et al, to be used in hypoxic (blue) patients

Lichtenstein DA, Mezière GA. Relevance of lung ultrasound in the diagnosis of acute respiratory failure: the BLUE protocol. Chest 2008;134:117–25

upper BLUE-point is at the middle of the upper hand

lower BLUE-point is at the middle of the lower palm

PLAPS point is intersection of horizontal line at level of lower BLUE-point and vertical line at posterior axillary line

BLUE Protocol

Cover image: Aerial view of Hapuna Beach on the Big Island of Hawaii