BLUE protocol

by Toh Hong Chuen

Case Presentation

A 68-year-old man with a history of congestive cardiac failure (CCF) and chronic obstructive pulmonary disease (COPD) presented with breathlessness and a newly productive cough for 3 days. He was non-compliant with neither medication nor fluid restriction. At triage, he dyspneic and immediately brought to the resuscitation bay. His vitals were BP 188/92mmHg, PR 119/min, RR 23/min, Temp 37.9C, SpO2 91% on 3L intranasal oxygen. Clinically, the JVP was elevated to the earlobes. Heart sounds were S1S2, breath sounds were diminished with prominent wheezing. There was mild pitting edema in the lower limbs to the knee. The diagnostic dilemma of acute exacerbation of CCF versus COPD needed to be addressed urgently.

While cardiac monitors and peripheral IVs were being set up, lung ultrasound was performed using the BLUE protocol. Bilateral lung sliding were seen in Stage 1, negative DVT scan in Stage 2 and negative posterior lateral alveolar pleural syndrome (PLAPS) in Stage 3. This clinched the diagnosis of acute exacerbation of COPD, and he was immediately put on nebulization with salbutamol and ipratropium. IV steroids and slow maintenance fluids were started, and since he fulfilled the Anthonisen criteria for infective exacerbation, broad-spectrum antibiotics were given. The CXR performed demonstrated hyperinflated lungs, cardiomegaly, and no consolidation; while the blood tests were unremarkable. The patient improved significantly after the 3rd cycle of nebulization and did not require non-invasive ventilation. He was admitted for continued management and subsequently discharged well after 2 days.

Emergency Indication

  • Patients presenting with dyspnea or respiratory distress


  • Absolute contraindication: NONE
  • Relative contraindication:
    • Lung ultrasound should not delay immediate interventions required for recognized life threats.
    • Nevertheless, lung ultrasound can often provide information that leads to the diagnosis of these life threats.

Equipment and Patient Preparation

Patient Preparation

  • Position: Supine, or semi-recumbent
  • Consent: Verbal consent is adequate
  • Others: Apply universal precaution

Equipment Preparation

  • Probe: Curvilinear (preferred), or linear
  • Preset: Lung preset if available.
    • If lung preset is not available, use the abdominal preset, but switch off all B mode optimization settings (e.g., tissue harmonics)
  • Others: Gel

Procedure Steps

  1. Explain the procedure to the patient and get consent.
  2. Set to lung preset, and apply gel to the probe
  3. Scan sequentially, and up to the 3rd stage if required.
    1. Stage 1: Anterior Chest Wall
      1. Four sites: Right and Left – Upper and Lower Blue Points
      2. Proceed to Stage 2 only if A profile (i.e., “normal”) is identified
    2. Stage 2: DVT scan
      1. Refer to the section on DVT scanning
      2. Proceed to Stage 3 only if the scan is negative for DVT (i.e., normal)
    3. Stage 3: Posterior Lateral Chest Wall
      1. Two sites: right/left PLAPS point.

Blue Protocol Scanning Sites

There are many proposed lung ultrasound scanning sites. In the original paper on BLUE Protocol, the chest wall is divided into 6 zones (Anterior, Lateral and Posterior zones of the right and left chest walls), which is further subdivided into upper and lower halves (i.e., 12 sites).

Currently, the scanning sites have been simplified to the 2 BLUE Points on the anterior chest wall (stage 1) and 1 PLAPS point in the posterior-lateral chest wall (stage 3), performed on each side of the thorax.

Locate the Upper and Lower BLUE (Figure 1: Upper and Lower BLUE Points) and PLAPS Points (Figure 2: PLAPS Point) as follow:

  1. Put two hands side by side with index fingers touching each other (i.e., excluding the palm). The examiner hand size should approximate that of the patient’s hands.
  2. Place the upper hand just below the clavicle, with the fingertips in the mid-sternum.
    • Upper BLUE Point is in the middle of the upper hand (i.e., between the root of 3rd and 4th fingers)

624.1 - Figure 1_Upper and Lower BLUE Points

    • Lower BLUE Point is in the middle of the palm of the lower hand.
    • PLAPS Point is the horizontal continuation of the lower BLUE Point, as posterior as possible to the posterior axillary line with the patient remaining supine.

624.2 - Figure 2_PLAPS Point

Lung Ultrasound Findings

These are the building blocks of the BLUE Protocol. As they are mostly artifacts, settings on B mode imaging which minimizes artifacts (so as to improve image resolution) should be switched off.

  1. Bat Sign
    1. The bat sign is critical for correct identification of the pleural line. Always begin lung ultrasound by identifying the bat sign before proceeding to look for artifacts and pathologies.
    2. This sign is formed when scanning across 2 ribs with the intervening intercostal space.
    3. The wings are formed by the 2 ribs, casting an acoustic shadow. The body is the first continuous horizontal hyperechoic line that starts below one rib and extends all the way to the other. (Video 1: Bat Sign) The body is the pleural line, i.e., parietal pleural. Normally, the pleural line is opposed to and hence indistinguishable from the lung line (formed by the visceral pleura).
  2. Lung Sliding
    1. When the lung expands and contracts with respiration, the parietal (pleural line) and visceral pleural (lung line) move and slide over each other, creating a shimmering or sparkling motion artifact on B mode at the pleural line, termed lung sliding (Video 2: Lung Sliding).
    2. This motion artifact produces the sea-shore sign on M-Mode (Figure 3: Seashore Sign).
      • 624.3 - Figure 3_Seashore Sign
    3. Absent lung sliding is always abnormal and occurs when the two pleural are
      1. Separated, for example by air in the case of pneumothorax
      2. Opposed but stuck to each other (pleurodesis)
      3. Opposed but not moving (mainstem intubation)
    4. The absence of lung sliding is readily apparent in B mode (Video 3: Absent Lung Sliding) and produces the stratosphere sign on M-Mode. (Figure 4: Stratosphere Sign)
      • 624.4 - Figure 4_Stratosphere Sign
  3. Lung Point
    1. This refers to the appearance and disappearance of lung sliding (Video 4: Lung Point on B Mode) with respiration at a specific point on the pleural. It is equivalent to having alternating sea-shore and stratosphere signs on M Mode (Figure 5: Lung Point on M Mode).
      • 624.5 - Figure 5_Lung Point on M Mode
    1. Lung Point is pathognomonic of pneumothorax.
    2. It reflects the size of the pneumothorax (moderate if seen anteriorly, large if seen posteriorly, and total collapse if absent) and may guide the need for intervention.
      • Most pneumothoraces with lung point in the lateral chest wall requires chest tube (90%), compared to those with anterior location (8%).
  1. A-lines
    1. These are horizontal reverberation artifacts arising from the pleural line. Consequently, they appear and are repeated at regular intervals below the pleural line, at a distance which is equal to the distance between the probe-skin interface and pleural.
    2. The presence of A-lines indicates good scanning technique, as the probe is perpendicular to the pleural line – a requisite for the generation of this artifact. The converse is also true. This effect is demonstrated in the clip (Video 5: A Lines), where the A lines disappear when the probe is tilted away from its initial perpendicular position.
  2. B-lines
    1. B-lines are artifacts with 7 characteristics, of which the first three are always present.
    2. They are comet-tail artifacts arising strictly from the pleural line and always move in concert with lung sliding (if lung sliding is present). They are most often hyperechoic, well defined, long and laser-like, and erases the A lines along its path. (Video 6: B Lines)
    3. They occur when the subpleural visceral interlobular septa are edematous. This can be found in several conditions, such as acute cardiogenic pulmonary edema, ARDS, pulmonary contusion, and pneumonia.
    4. The following terms are commonly encountered in literature but are not included in the BLUE Protocol.
      1. Lung rockets: 3 or more B lines within a rib space. Septal rockets contain between 3-5 B lines per rib space. Ground glass rockets have 6 or more, which often coalesce to form a bright curtain-like artifact “hanging” from the pleural line.
      2. Interstitial syndrome: bilateral anterior lung rockets. Posterior lung rockets are not considered as they may be due to gravitational pull.
  3. Pleural effusion
    1. Presence of anechoic collection between the pleural and lung line (Figure 6: Pleural Effusion).
      • 624.6 - Figure 6_Pleural Effusion
  4. Consolidation
    1. Tissue-like sign: indicating translobular consolidation (Video 7: Tissue-like Sign)
      • When the entire lobe is consolidated, it has a tissue-like appearance similar to the liver.
    2. Shred sign: indicating non-translobular consolidation (Figure 7: Shred Sign, Video 8: Shred Sign)
      • The interface between consolidated and aerated lung is irregular, and appeared as if it has been “shredded.”
      • 624.7 - Figure 7_Shred Sign

Lung Profiles

The lung findings described above are used to characterize the lung profile.

Anterior Chest Wall

  • There are 6 profiles on the anterior chest wall (i.e., Upper and Lower BLUE Points)
    1. A profile = Bilateral A-lines with lung sliding.
    2. A’ profile = A lines without lung sliding
    3. B profile = Bilateral B lines with lung sliding
    4. B’ profile = B lines without lung sliding
    5. A/B profile: Half A profile on one lung and half B profile at the other
    6. C profile = Shred sign or tissue-like sign (regardless of size or number)

Lateral Chest Wall

  • There are 2 profiles on the posterior lateral chest wall (i.e., PLAPS Point)
    1. PLAPS profile (or PLAPS positive): the presence of either pleural effusion or consolidation
    2. Nude profile (or PLAPS negative): absence of pleural effusion and consolidation

Lung Profiles of Common Respiratory Diseases

  1. Cardiogenic pulmonary edema: B profile
  2. COPD or asthma: A profile with negative DVT scan, negative PLAPS
  3. Pulmonary embolism: A profile with positive DVT scan
  4. Pneumothorax: A’ profile with a lung point
  5. Pneumonia: Variable: A + PLAPS profile, A/B profile, B’ profile & C profile

There are two important caveats in relating lung profiles to specific diseases:

  1. The normal non-pathological lung has the same findings as patients with COPD or asthma, i.e., A profile with negative DVT scan and negative PLAPS.
  2. Patients with A’ profile and no lung sliding requires additional imaging modalities
    • This could still be due to a pneumothorax (i.e., massive one with a complete collapse of the lung) or other rare causes (e.g., pleurodesis).

Suggested Approach

Hint and Pitfalls

  • The BLUE protocol is not an acronym. It highlights the indication (and utility) for using the protocol, i.e., a patient who is “blue” from respiratory distress. It is a rapid and efficient way of diagnosing the 5 major respiratory diseases, with a reported accuracy of 90.5%.
  • Perform lung ultrasound immediately after clinical examination, prior to CXR. It yields diagnostic information rapidly and can expedited treatment.
    • Recognizing the B profile, for example, takes only less than 10 seconds.
    • Completing the entire protocol (i.e., up to Stage 3) requires less than 3 minutes.
  • Stay focus and scan only the BLUE points and PLAPS points.
    • Other sites can be scan when the time is available.
  • Always interpret ultrasound findings in the context of clinical findings; and integrate both in the clinical decision-making process.
  • Pitfalls of the BLUE Protocol:
    • It cannot be used for patients with mixed or multiple respiratory disorders.
    • It does not identify rare respiratory disorders (defined as occurring with a frequency of <2% of ICU patients in the single center that was studied)
    • Massive pleural effusion is not included in the protocol, though diagnosis is not an issue)
    • It cannot be used for non-respiratory causes of breathlessness, e.g., hyperventilation from metabolic acidosis or profound anemia.
    • It is not designed to provide information on the patient’s hemodynamic status.
      • This could also be performed using point of care ultrasound, by integrating the focused cardiac and IVC with the lung findings, in the form of the FALLS protocol.

Post Procedure Care and Recommendations




Pediatric, Geriatric, and Pregnant Patient Considerations


The BLUE protocol is derived from a study of 301 consecutive adult patients and is applicable to the geriatric population.


While there are no pregnant patients which are reported in the original paper2, the principles in the diagnostic algorithm are applicable in pregnancy.


In the same way, the BLUE protocol can also be adapted for use in the pediatric patients.

References and Further Reading

  • Volpicelli G, Elbarbary M, Blaivas M, et al. International evidence-based recommendations for point-of-care lung ultrasound. Intensive Care Med. 2012;38(4):577-591. doi:10.1007/s00134-012-2513-4.
  • Lichtenstein DA. Relevance of Lung Ultrasound in the Diagnosis of Acute Respiratory Failure*. CHEST J. 2008;134(1):117. doi:10.1378/chest.07-2800.
  • Lichtenstein D a., Mezière G a. The BLUE-points: three standardized points used in the BLUE-protocol for ultrasound assessment of the lung in acute respiratory failure. Crit Ultrasound J. 2011;3(2):109-110. doi:10.1007/s13089-011-0066-3.
  • Lichtenstein D. Lung ultrasound in the critically ill. Curr Opin Crit Care. 2014:315-322. doi:10.1097/MCC.0000000000000096.
  • Lichtenstein DA, Meziere G, Lascols N, et al. Ultrasound diagnosis of occult pneumothorax. Crit Care Med. 2005;33(6):1231-1238. doi:10.1097/01.CCM.0000164542.86954.B4.
  • Lichtenstein DA. Lung ultrasound in the critically ill. Ann Intensive Care. 2014;4(1):1-12. doi:10.1186/2110-5820-4-1.
  • Lichtenstein D, Mézière G, Biderman P, Gepner A, Barré O. The comet-tail artifact. An ultrasound sign of alveolar-interstitial syndrome. Am J Respir Crit Care Med. 1997;156(5):1640-6. doi:10.1164/ajrccm.156.5.96-07096.
  • Lichtenstein D. FALLS-protocol: lung ultrasound in hemodynamic assessment of shock. Hear lung Vessel. 2013;5(3):142-7. Available at: Accessed December 18, 2015.
  • Lichtenstein DA. Lung Ultrasound in the Critically Ill. Ten Signs – the alphabet for performing the Blue Protocol. Available at: Accessed December 17, 2015.
    10. Lichtenstein DA, Mauriat P. Lung Ultrasound in the Critically Ill Neonate. 2012:217-223.
  • Lichtenstein DA. Lung Ultrasound in the Critically Ill – The BLUE Protocol. 1st ed. Springer; 2016. Available at:

Nelson BP, Noble VE. Respiratory Ultrasound. In: Manual of Emergency and Critical Care Ultrasound. 2nd ed. Cambridge University Press; 2011:191-202.

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