Below is the main content discussed at an ultrasound workshop I ran this week at the Sydney HEMS Clinical Governance Day.
Whilst the bread & butter use of prehospital ultrasound would have to be an extended-FAST scan in the setting of trauma, I decided to focus more on utility of basic ECHO & lung ultrasound in the assessment of shocked medical patients.
A lot has been written about the RUSH protocol and its role in aiding the diagnosis of undifferentiated shock/hypotension. From my own experience (in initiating patient transfers, not conducting them), a source of shock is largely defined by the time an inter-hospital retrieval takes place (ie. abdominal aortic aneurysms excluded by history, examination or ED ultrasound).
When faced with the ongoing ED-based resuscitation of shocked patients (esp. those with septic shock & refractory hypotension), I find myself using a process similar to Lichtenstein’s FALLS protocol which I believe can be carried into the arena of retrieval medicine to guide ongoing therapy (and potentially alter outcomes).
The FALLS protocol.
This is a tool proposed to assist in the management of shocked patients, mainly by the use of lung ultrasound.
Firstly, it aims to exclude obstructive shock by
- Cardiac ECHO.
- ?massive pulmonary embolism with right heart strain
- Lung USS.
The second phase aims to assess volume status by exploiting ultrasound lung-artefact to detect interstitial syndrome (suggestive of extravascular lung water).
- ie. cardiogenic shock – supported by distended, non-compressing inferior vena cava & the presence of pleural effusions.
- alternatively; signals appropriate volume replacement & a trigger to start vasopressors to maintain blood pressure.
- suggestive of hypovolaemic or distributive shock.
- triggers further fluid administration.
FALLS Protocol – Lichtenstein, 2012.
Below are the images & ultrasound clips used in my presentation, demonstrating the significant findings at each stage of the protocol.
Early tamponade with RV diastolic collapse.
Massive pericardial effusion with obvious tamponade. Dx: Malignant effusion 2* to NSCLC.
Massive pericardial effusion with features of tamponade.
NB. the both right atrial and right ventricular diastolic collapse.
Pulse wave doppler measuring MV inlet velocities. ~25% variation through respiratory cycle suggests tamponade physiology.
For more information on features of tamponade check out “Sequential sinister sightings…” !!
Severe dyspnoea with A-a gradient > 500 !! Normotensive, but elevated serum troponin.
Massive pulmonary embolism.
Elderly male with undifferentiated shock, hypoxia and abdominal pain.
Features of right ventricular strain in PE.
- RV:LV (end-diastolic diameter) > 0.9 – A4C or subcostal view.
- RV end-diastolic diameter > 30mm – PLAX or PSAX view.
- Hypokinetic RV free wall
- Tricuspid regurgitant jet velocity > 2.6m/s
- Paradoxical interventricular septal motion
- McConnell’s sign - akinesia of the RV-mid free wall with normal motion at the RV apex.
For further discussion on the role of thrombolysis in pulmonary embolism check out “Two in two days…”
Normal lung sliding. Comet tails + A-line artefact present.
Normal lung ultrasound. Comet-tail artefact present with obvious A-lines.
M-mode image. Sandy beach sign. No pneumothorax.
Pneumothorax present. No visible comet tails, no lung sliding.
M-mode ultrasound demonstrating a ‘bar-code’ sign, consistent with pneumothorax.
Bilateral B-lines ['lung rockets'] consistent with pulmonary oedema/interstitial syndrome.
7 criteria for B-lines.
- There is a comet-tail, vertical artefact.
- Arises from the pleural line.
- Moves in concert with lung sliding.
- Does not fade.
- Well-defined, laser like.
- Obliterates the A-lines.
In the BLUE-protocol detection of interstitial syndrome to anterior chest, bilaterally (with lung-sliding) makes the diagnosis of haemodynamic pulmonary oedema with 97% Sn & 95% Sp.
Differential diagnoses of B-lines;
- pulmonary contusion
- pulmonary fibrosis
Bilateral A-lines with lung sliding.
The presence of A-profile in a shocked patient = a FALLS responder. This suggests a hypovolaemic or distributive contributor to shock & correlates with pulmonary artery occlusion pressures of < 18mmHg [Sp 93%, PPV 97%].
The protocol recommends further fluid boluses with serial assessment by lung-ultrasound, looking specifically for change from A-lines to B-lines. At this stage, vasopressors would be started.
FALLS protocol + lung ultrasound
- Lichtenstein, D. A., & Mezière, G. A. (2008). Relevance of lung ultrasound in the diagnosis of acute respiratory failure: the BLUE protocol. Chest, 134(1), 117–125. doi:10.1378/chest.07-2800
- Lichtenstein, D. (2013). FALLS-protocol: lung ultrasound in hemodynamic assessment of shock. Heart, lung and vessels, 5(3), 142–147.
- Lichtenstein, D. A. (2014). Lung ultrasound in the critically ill. Annals of intensive care, 4(1), 1. doi:10.1186/2110-5820-4-1
- Mount Sinai Emergency Medicine Ultrasound.
- Perera, P., Mailhot, T., Riley, D., & Mandavia, D. (2010). The RUSH exam: Rapid Ultrasound in SHock in the evaluation of the critically lll. Emergency medicine clinics of North America, 28(1), 29–56– vii. doi:10.1016/j.emc.2009.09.010
- Seif, D., Perera, P., Mailhot, T., Riley, D., & Mandavia, D. (2012). Bedside Ultrasound in Resuscitation and the Rapid Ultrasound in Shock Protocol. Critical Care Research and Practice, 2012(3), 1–14. doi:10.1097/01.CCM.0000260680.16213.26
- Ultrasound Podcast.
- Mount Sinai Emergency Medicine Ultrasound.
- Academic Life in Emergency Medicine.
ECHO for Pulmonary Embolism.
- MD, S. D., et al. (2014). Right Ventricular Dilatation on Bedside Echocardiography Performed by Emergency Physicians Aids in the Diagnosis of Pulmonary Embolism. Annals of Emergency Medicine, 63(1), 16–24. doi:10.1016/j.annemergmed.2013.08.016
- Rudski, L. G.., et al. (2010). Guidelines for the echocardiographic assessment of the right heart in adults: a report from the American Society of Echocardiography endorsed by the European Association of Echocardiography, a registered branch of the European Society of Cardiology, and the Canadian Society of Echocardiography. Journal of the American Society of Echocardiography : official publication of the American Society of Echocardiography, 23(7), 685–713– quiz 786–8. doi:10.1016/j.echo.2010.05.010
- Meyer, G., Vicaut, E., Danays, T., Agnelli, G., Becattini, C., Beyer-Westendorf, J., et al. (2014). Fibrinolysis for Patients with Intermediate-Risk Pulmonary Embolism. The New England journal of medicine, 370(15), 1402–1411. doi:10.1056/NEJMoa1302097
- Sosland, R. P., & Gupta, K. (2008). Images in cardiovascular medicine: McConnell’s Sign. Circulation, 118(15), e517–8. doi:10.1161/CIRCULATIONAHA.107.746602
- REBEL EM.
For a great bibliography on the evidence available for prehospital ultrasound, check out Cliff’s Resus.me.
Special thanks to Dr Justin Bowra for his assistance & advice with putting this together.