U/S in Shock

At a basic level, ultrasound in shock resuscitation is a fundamental assessment of the patient's physiological status at the bedside. As the heart is the central to the circulation, how it reacts to shock (e.g. via insults to the peripheral circulation by increasing demand, or to the heart itself via an infarct), assessing a patient's cardiac status during a shock state will give the clinician vital clues as to the aetiology of the shock and guide therapy.

Refer to our Shock Resuscitation Guide for more details.

Preparation

• Patient in supine or left lateral decubitus position for cardiac scanning
• Use the small footprint C21x transducer, 5-1MHz, phased array, with cardiac setting

STEPS

Start with the parasternal long axis view (PLAX). Probe at the left sternal edge (as close to the sternum as possible), 4th or 5th intercostal space, probe marker pointing towards patient's right shoulder.

• Ensure adequate depth to see the bright echogenic posterior pericardium and the descending thoracic aorta.
• The mitral valve and aortic valve should line up near the middle of the screen
• The LV apex should not be in view but is off the screen
• Assessment of LV contractility, LV size, mitral and aortic valve movement can be made.
• Pericardial effusion will appear as a black rim above the echogenic posterior pericardium
• Pay attention to aortic root - look for widening if dissection is a concern (move up a rib space to see if necessary)

Follow with the parasternal short axis view (PSAX). Probe now turned 90 degrees clockwise towards the patient's left shoulder.

• The LV should appear round and contracts towards the centre.
• Probe movement by tilting can scan the LV in cross section from the base (mitral valve) to the mid-section (papillary muscles) and to the apex (almost)
• Assessment of LV contractility, comparison of LV and RV size, can be made at the mid-papillary muscle section.
• If there is significant RV pressure overload, the septum will deviate towards the LV and the LV will take on the appearance of a D-shape.
• Pericardial effusion will appear as a black rim surrounding the myocardium.

Next, perform the apical 4-chamber view (AP4). Probe at the apex of the heart, point the probe towards patient's right scapula tip, and the probe marker should face the left armpit.

• When seen from the proper apex, the LV should have a bullet shape appearance and the RV would appear triangular. 
• If the heart appears globular, you are not at the true apex.
• Make sure the mitral and tricuspid annulus are well seen and the valves appear distinct. For orientation, the tricuspid annulus is always nearer the apex compared to the mitral annulus.
• Assessment of the 4 chambers of the heart, LV and RV sizes, LV and RV contractility can be made.

Finally, assess the heart at the subxiphoid 4 chamber view (SX4) as well as the IVC. This is the same view as the FAST exam. Probe is just below the xiphisternum, almost flat to the belly, and pointing towards patient's head. In cardiac setting, the marker points to patient's left.

• The subxiphoid view is a very useful view and sometimes the only view in intubated patients
• Use the left lobe of the liver as an acoustic window.
• Assessment of the 4 chambers of the heart, LV and RV sizes, LV and RV contractility can be made.
• Pericardial effusion will appear as a black rim surrounding the heart, look in-between the liver and the right ventricle.

To assess the IVC, start at the subxiphoid view as above and tilt the probe upwards to a vertical position for a short-axis or transverse view of the IVC.

• Center the view on the right atrium. As you tilt the probe vertically, the IVC will appear. It can be identified by the 3 hepatic veins draining into it. 
• Turn the probe 90 degrees with the probe marker pointing to the feet to see the IVC in sagittal or longitudinal view.
• Assessment of the IVC size, collapsibility can be made.
• A fully collapsed IVC in inspiration and expiration has the best correlation with low CVP (<5 mmH₂0) and hypovolemia.
• A normal person's IVC collapse by about 50% with normal inspiration.
• An IVC that collapse >50% with inspiration suggests a CVP <10 and may suggest hypovolemia +/- volume responsiveness.
• An IVC that has minimal respiratory variation, or is plethoric, correlates to a CVP >20, usually seen in fluid overload, CCF, pulmonary embolism, cardiac tamponade etc.
• Be aware that in spontaneously breathing patients, exaggerated respiratory effort (e.g. Kussmaul's respiration) may exacerbate IVC collapse.
• Be aware that in intubated and ventilated patients, the IVC changes with ventilation is opposite i.e. IVC expands with inspiration.

Comprehensive video tutorial of cardiac ultrasound





Another good video tutorial from HCMC





Examples of some ultrasound pathology seen in the A&E

Aortic Dissection
This patient presented in extremis. Bedside ultrasound showed a widened aortic root, pericardial effusion with tamponade physiology, and an intima flap seen in the zoom in view of the abdominal aorta. This is virtually diagnostic of a Stanford A aortic dissection.





Bedside cardiac ultrasound showing a dilated poorly contracting RV but with fairly preserved RV apical wall motion (McConnell's sign). The RV outflow tract is enlarged on the parasternal long axis view, and the LV appears D-shaped on the parasternal short axis view. In the right clinical setting this is massive PE until proven otherwise.





Another patient with echo features of massive PE, and a large clot is seen in transit in the RA. This patient needs thrombolytics stat.





Distended / plethoric IVC with no respiratory variation





Fully collapsed IVC