Overview and Considerations:
Focused ultrasound for effusion: part of the routine assessment of emergency patients.
A quick ultrasound scan of the body cavities (abdomen, thorax, and pleural space) looking for the presence of free fluid and free air (pneumothorax, pneumoperitoneum) is an important part of the routine assessment of emergency patients, especially trauma patients.Focused ultrasound for cavitary effusion, also called FAST (focused assessment with sonography for trauma), has been shown to improve survival in trauma patients. Focused ultrasound is also the fastest and easiest way to diagnose many life-threatening emergency conditions, including hemoabdomen, septic peritonitis, hemothorax, uroabdomen, pyothorax, pericardial effusion, pleural effusion, . It’s quick, easy, minimally invasive, and is a very sensitive diagnostic test. A focused ultrasound of the thoracic cavity abdominal cavity, and pericardial space to check for cavitary effusion (and other obvious abnormalities) can usually be performed in less than 5 minutes, without shaving any fur (use alcohol), and with the patient resting comfortably in sternal recumbency.
The diagnosis of many life threatening emergency conditions is much more challenging without ultrasound.
In the highly compromised patient, the degree of stress, restraint or sedation that is typically required for x-ray may result in sudden decompensation.For this reason, it is better to identify problems such as pleural effusion, pneumothorax, pericardial effusion and abdominal effusion with a quick, minimially invasive scanning ultrasound than with x-ray. This might surprise you, but thoracic radiographs are NOT considered reliable for the diagnosis of pericardial effusion resulting in cardiac tamponade. The radiographic findings that typically come to mind (enlargement of the cardiac silhouette, globoid appearance of the cardiac silhouette, and convexity of the dorsocaudal aspect of the cardiac silhouette) are not very sensitive or specific for cardiac tamponade attributable to pericardial effusion. In very acute cases, significant enlargement of the cardiac silhouette might not be apparent at all on x-ray.
You don’t need a top of the line $30,000 ultrasound machine for most emergency procedures. If you don't have an ultrasound machine, you can usually find a used laptop-sized unit from a radiology technician. These units are priceless for helping to identify fluid in the body cavities and for ultrasound-guided centesis.
How to Perform Focused Ultrasound : Step by Step
Abdomen: (A-FAST)The focused ultrasound of the abdominal cavity emphasizes four standard sites:
- DH: diaphragmatic hepatic site. Immediately caudal to the xyphoid process along midline, in the mildline region of the liver and diaphragm. At this site, you can also direct the probe craniad to visualize the pleural cavity and pericaridal space just on the other side of the diaphragm.
- CC: cystocolic site. Mid-caudal abdomen imaging the region of the urinary bladder.
- SR: splenorenal. Left side of abdomen/ retroperitoneal space imaging the region of the left kidney and spleen.
- HR: hepatorenal site. Right side of abdomen/retroperitoneal space imaging the right kidney and liver.
- Image each site in two ultrasound planes, with the ultrasound plane (and probe) directed at 90-degrees to the first.
- Free fluid has a dark (and often triangular or geometric) shape.
- The A-fast receives a score of 0-4/4, with the numerator corresponding to the number of the sites that tested positive fore effusion.
- Check that the urinary bladder wall and gall bladder wall are intact.
- Look for any free air bubbles within the peritoneal cavity- this can indicate ruptured hollow viscous (intestinal rupture) or recent surgery. Air bubbles look like bright white dots with reverberation/ echo ripples extending from them.
- The DH and CC site are the most common sites of effusion in hemoabdomen.
- Perform serial A-FAST ultrasound exams to monitor the effusion for worsening.
Thorax: (T-FAST)The focused ultrasound of the thoracic cavity also emphasizes four standard sites:
- Right pericardial site.
- Left pericardial site. Mid-caudal abdomen imaging the region of the urinary bladder.
- Right caudodorsal lung field. dorsal 1/3 of chest cavity; 7-9 intercostal space.
- Left caudodorsal lung field. dorsal 1/3 of chest cavity; 7-9 intercostal space.
- Free fluid will appear dark/ black on the ultrasound screen. If you document fluid, measure the depth of the fluid (in cm) at each site.
- The classic ultrasound finding in pneumothorax is the loss of the thoracic glide sign (a thin, hyperechoic line that you can see gliding where the pleural surface of the lungs glides against the pleural surface of the chest wall).
- Perform serial T-FAST ultrasound exams to monitor the effusion for worsening.
- Remember, you cannot tell what the fluid is just by looking with ultrasound. Cavitary effusions can contain :
- whole blood
- septic fluid
- cancer fluid (neoplastic effusion)
- bile fluid, transudate
- modified transudate
- etc., or a mixture of the above.
- If you document the presence of free fluid in a body cavity, the next step is to obtain a sample for testing via thoracocentesis or abdominocentesis.