Ultrasound of the Week #005

Special thanks to Dr Ahmed Abdul-Ghani for this great case and images.

Case:

2 HEMS patients were brought simultaneously – both had single left lateral chest wall stab injuries (from the same altercation!).  Both were young, fit and well males. ​ One was a Code Red requiring prehospital blood.

The case presented here was the other patient who was haemodynamically normal and not in any distress.  Radiology-led FAST did not reveal any major concerns.  The CT scan showed signs of pericardial breech (see below). 

To stratify his risk and need for any urgent surgical intervention, further clarity was sought via a bedside echo (see below)

[expand title=”Points to reflect on:” tag=”h2″]

1. CT is the most widely used modality of choice for the evaluation of the pericardium; however, ultrasound could be easily and rapidly performed to reveal the presence of pericardial fluid which is a crucial finding particularly in trauma patients.^[1]

2. Even small to moderate pericardial collections can be dangerous in acute trauma where blood has accumulated quickly. As the pericardium takes time to stretch, the rate of pericardial fluid accumulation is more important than the amount.

[/expand] [expand title=”Basic Echo views #1 : the Parasternal Long Axis (PLAX) View:” tag=”h2″]

The parasternal long axis (PLAX) view is the first view generally obtained in a focused echo study and one we will delve a little more into this week.

Obtaining the view:

Patient : imaging will be easiest in the left lateral position if the patient can tolerate it as the heart ‘falls’ towards the probe.

Probe : place the cardiac probe just to the left of the sternum in the 3^rd/4^th intercostal space, probe marker pointed towards the patient’s right shoulder*.  The LV should be on the left/middle of the screen, as ‘long’ as possible, with the Aorta/LA on the right of the screen.  Distal to the probe is the pericardium (+/- effusion), the descending thoracic aorta and lung (+/- pleural effusion).

Below shows a nicely labelled PLAX view (thanks to Dr James Webster for this great image).

*In conventional ultrasonography the probe marker is on the left of the screen.  In echocardiography it is on the right.  If the machine doesn’t change this on the ‘echo’ settings, just flip the transducer 180⁰.

What to assess?

1. LV size and general function:
2. Is the LV cavity normal sized?  Dilated?  Small?
3. Does the contractility appear normal?  Impaired?  Hyperdynamic?  Is there an obvious RWMA?
4. Presence of Pleural/Pericardial effusions

More advanced practitioners can assess for the following:

• Mitral valve structure and function – significant stenosis/regurgitation/prolapse
• Aortic valve structure and function – significant stenosis/regurgitation
• RVOT : Aorta : LA ratio.  These should be around 1:1:1 so can give a rough idea of RV, Aortic or LA enlargement
• Aortic root : size, dilation +/- aortic dissection flap (ascending or descending aorta)
• LV Outflow Tract (LVOT) : signs of LVOT Obstruction, LVOT size as part of stroke volume assessment & fluid responsiveness measurements (VTI)
• PLAX-RV view : assessing Tricuspid valve

Troubleshooting the PLAX view:

• In hyperexpanded patients (asthma/COPD), chest windows may be difficult but the subxiphoid/subcostal view should give very good windows
• Try to get the patient into the left lateral position
• Try up and down a rib space

In future Echo cases we will explore different Echo views and techniques, covering some of the above assessments and pathologies.

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References:

1. Wongwaisayawan S, Suwannanon R, Sawatmongkorngul S, Kaewlai R. Emergency thoracic US: the essentials. Radiographics. 2016;36:640–659. doi: 10.1148/rg.2016150064.