Point-of-Care Ultrasound in Trauma – Pneumothorax

Case Presentation

A 35 year-old man is brought by EMS to the resuscitation room of your hospital after he sustained multiple stab wounds with a kitchen knife to the anterior chest and abdomen.

On your primary survey, the patient is calm and alert with no evidence of airway compromise. He has an inch long laceration just medial to the anterior axillary line and below the clavicle. There is a small amount of subcutaneous emphysema on palpation next to the laceration. The auscultation reveals good air entry bilaterally. The patient has good peripheral pulses in all extremities, and the rest of his survey shows three small superficial non bleeding lacerations at the level of the left upper abdomen.

You suspect a pneumothorax, and you wonder if point-of-care ultrasound (POCUS) could help you confirm your suspicion.

Background

Point-of-care ultrasound for pneumothorax is part of the extended Focused Assessment with Sonography for Trauma, also known as eFAST. POCUS of the lung has gained favor in the busy trauma bay in recent years. It is a quick, reliable and easy to perform bedside exam that can be very useful in the arsenal of the trauma physician.

Probe Selection

·         Linear probe is best

·         No linear probe? Curvilinear or phased array probes are acceptable, but make sure to decrease the depth (5-7 cm)

Technique

·         Patient supine

·         Probe in longitudinal plane

·         Probe marker oriented cephalad

·         Scan from 3rd to 5th intercostal spaces anteriorly

o   Right : midclavicular line

o   Left : anterior axillary line (to avoid the heart)

·         Find the area of interest (two ribs with their shadows & pleura in the center)

  Fig.1 : Pneumothorax POCUS Technique  

                                                                   Fig.2 : Pneumothorax POCUS Area of Interest

Sonographic Evaluation for Pneumothorax

Step 1 : Assess for lung sliding

The first step in the evaluation for pneumothorax is to assess for lung sliding. In a patient without pneumothorax, the visceral and parietal pleura are in direct contact with each other. With respiration, sliding of these two layers is visualized on ultrasound. Lung sliding appears as though it is shimmering and is often referred to as ants marching.

https://vimeo.com/112939903

Video 1. Normal lung sliding and comet tail artifacts

If a pneumothorax is present (i.e there is air between the viceral and parietal pleura), then no lung sliding will be visualized. The absence of lung sliding is 99.4% specific for pneumothorax.

https://vimeo.com/112944977

Video 2. Pneumothorax

Step 2 : Look for B-lines & comet tail artifacts

The second step in the evaluation for pneumothorax is to look for comet tail artifact, or B-line. This is a type of reverberation artifact that may only be seen if no pneumothorax is present. Comet tail artifacts extend from the pleural as intermittent white lines during respirations. (see video 1 above)

Comet tail artifacts or b-lines may not always be present, but carries a sensitivity of 100% for ruling out pneumothorax when seen.

Step 3 : Confirm with M-mode

No lung sliding or comet tail artifacts ? Try to use the M-mode (M= motion) to confirm your findings. The typical appearance of a pneumothorax on M-Mode is described as the barcode or stratosphere sign. The air between the viceral and parietal pleura creates an artifact (reverberation artifact) which results in multiple parallel horizontal lines starting from the pleura to the bottom of the screen. In a patient without pneumothorax, the sliding motion creates waves under the pleura in the M-mode (seashore sign).

 Fig. 3 : Seashore and barcode (stratosphere) sign on M-Mode

Step 4 : Search for a lung point

The lung point is the transition between expanded (i.e. lung sliding and comet tail artifact present) and collapsed lung (i.e. lung sliding and comet tail artifact absent). The presence of a lung point is 100% specific for pneumothorax, but it is often challenging to find. The lung point can also be used to estimate the size of the pneumothorax.

https://vimeo.com/112958801

Video 3. Lung point

Pearls & Pitfalls

·         Turn the gain down (easier to see lung sliding)

·         Decrease the depth (5-7 cm, except in the very obese patient)

·         In the context of significant subcutaneous emphysema, you might not be able to see the pleural line (artifacts from subcutaneous air)

·         Ensure the patient is in the supine position (air is found anteriorly just like in a CT scan of the chest)

Special Situations

Lung sliding absent? Be aware of potential false positives!

·         ARDS

·         Pulmonary contusions

·         Bullae (COPD/emphysema)

·         Pulmonary fibrosis

·         Pleural adhesions (s/p pleurodesis, s/p thoracic surgery)

·         No alveolar ventilation (right mainstem intubation)

·         Pneumonia with adhesions

Case Resolution

POCUS of the lung revealed no lung sliding and no comet tail artifacts on the left side. The findings were consistent with a left sided pneumothorax which was confirmed by chest radiography. A CT chest with intravenous contrast was ordered to rule out subclavian vessel injury given the location of the laceration. The CT chest revealed no vascular injury and re-confirmed the presence of a pneumothorax. A chest tube was inserted and the patient was kept in observation in the trauma unit. He was discharged home a few days later.

from:  Laurie Robichaud, PGY4 Emergency Medicine

@laurieMcGillEM

References

Matt Dawson, Mike Mallin. Introduction to bedside ultrasound, volumes 1 & 2. Lexington, KY: Emergency Ultrasound Solutions, 2012

Steve Socransky, Ray Wiss. Essentials of Point-of-Care Ultrasound « The EDE Book ». eBook (available on iTunes iBook Store)

Recommended Resources

App : http://www.ultrasoundpodcast.com/2012/03/one-minute-ultrasound-smartphone-app/

Website : http://www.sonosite.com/ultrasound-video/how-pneumothorax-evaluation-ultrasound