Assessment – Is the tank full?

The diameter of the IVC gives an estimate of volume status and central venous pressure. 

How the IVC collapses in inspiration can predict whether fluids will be useful. The collapsibility or caval index (CI) can be calculated by:

CI = 100 x (IVC expiratory diameter – IVC inspiratory diameter)/IVC expiratory diameter

A “flat” IVC < 1.5cm with a CI > 50% suggests a low CVP and a response to volume. 

A “fat” IVC > 2.5cm with a CI close to 0% suggests a raised CVP.


The CI in intubated patients is not of clinical value.

Is the tank leaking or overloaded?

Look for free fluid, ascites, pleural effusion or B-lines that suggest third spacing or overload. 


This RUQ view shows ascites around a cirrhotic liver.

Image courtesy of Renato Tambeli

Pleural effusion

This view shows a large pleural effusion around a collapsed lung.

Image courtesy of Renato Tambeli:

B lines

B lines are sonographic artefacts which are seen with interstitial oedema. They can be seen in pulmonary oedema, pneumonia and Covid pneumonitis. 

This image shows an abundance of B lines (white lines extending to the bottom of the screen) in a patient with pulmonary oedema.

Image courtesy of Dr Justin Bowra et al:

Is the tank compromised?

A pneumothorax is suggested by the loss of normal lung sliding on the apical lung view. 
This view shows the Batwing sign, formed by the rib shadows as the bat wings and the lung sliding between them. This rules out pneumothorax.


Image: authors own

This view shows the loss of lung sliding in a patient with a pneumothorax.

Image courtesy of Dr Stacey Frisch, Dr John F Kilpatrick :


A loss of lung sliding, although highly suggestive, is not 100% specific for the presence of a pneumothorax.

Barcode sign

Loss of lung sliding can be further assessed in M-mode if time allows. The presence of the barcode sign is highly suggestive of a pneumothorax.

This image shows the barcode sign in a patient with pneumothorax.

Image courtesy of Dr Stacey Frisch, Dr John F Kilpatrick :

Lung point

The presence of a lung point is 100% specific for the presence of pneumothorax. A lung point is where a pneumothorax meets the normal pleura, i.e. where the non-sliding part meets the sliding part.

This view shows a lung point in a patient with a pneumothorax. Note the sliding pleura, which comes to the middle of the screen with every breath.

Image courtesy of Dr. Stenberg

Learning bite

Ultrasound is more sensitive and specific for the diagnosis of pneumothorax than chest X ray.

Assessment of the tank is focused to answer the following questions

Is the tank full?

  • Is the tank leaking or overloaded?
  • Is the tank compromised?