Ultrasound is a spectrum of sound frequencies above the human hearing range. Molecules must be present for sound to exist. Every object has an echogenicity. When sound waves hit the object some are transmitted through and some bounce back. Every substance will respond differently to the sound waves striking it’s surface. This occurs at every sound-to-sound interface and the reflection of sound waves can be used to create and image.
Unclotted blood allows passage of transmission of ultrasound waves without echoes. Clotted blood creates echoes and thus appears gray. Foot print is the area of skin that the probe covers. Good to have small probe b/c you can look b/n ribs if you need to. Generally you can use 3.5 hz. You can use higher frequencies in thinner patients. Lower frequencies will give better resolution in heavier patients. 1) subxiphoid - to visualize the heart, 2) RUQ - to visualize Morrison's pouch and paracolic gutter, 3) LUQ - to visualize the spleeno-renal recess and paracolic gutter, 4) suprapubic - to visualize Douglas' pouch. Many people start in RUQ b/c this is where fluid is most likely to be. Some start subxiphoid in order to early see pericardium/tamponade also allows for adjustment of the gain. - fluid most likely to be in RUQ due to anatomical and gravitational considerations. People are generally supine. Organs in pelvis relatively well protected. Abdominal organs usually injured. Blood flows into Morrison’s pouch (space b/n liver and kidney) Generally, if hemorrhage is below the bony pelvis it will flow caudad and above it will flow cephalad.
Usually only do below right costal margin in patients able to take deep breaths. Lung is filled with air which is highly reflective leading to artifact. Abscense of this artifact suggests hemothorax. Some sonographers as they gain experience will scan solid organs for areas of abnormal echogenicity which would suggest parenchymal injury. This is not part of FAST exam.
Subxiphoid may be impossible due to patient’s body habitus or physical injuries.
When having trouble getting this view, it is usually because the probe is not posterior enough or superior enough. In both the LUQ and RUQ, it is usually necessary to get multiple images in order to identify all of the required structures.Getting them all in a single image The features of the LUQ view are very similar to those of the RUQ, with the normal pleural space appearing as if there were spleen both above and below the diaphragm.
Mesenteric artery lac
In a normal transverse suprapubic view, the pouch of Douglas is the most dependent site (standing or supine) in the entire pentoneal cavity The first sonographic sign of blood in the pelvis is often two small black triangles on either side of the rectum the so-called bow tie sign. The entire pelvis should be scanned from top to bottom with the transducer in the transverse plane, and then from side to side with the transducer held in a sagittal plane.
FAST Exam Erin CarnesSeptember 27, 2007
FAST Exam Introduction Ultrasound Physics Technique Indications for FAST exam Performing a FAST exam Limitations Questions
What is the FAST exam? Focused Assessment by Sonography in Trauma Focused exam using ultrasound to diagnose hemorrhage in a trauma setting Ideally takes < 3 min 4 primary views RUQ LUQ Subxiphoid Suprapubic
Basic Ultrasound Physics Ultrasound is a spectrum of sound frequencies above the human hearing range. Molecules must be present for sound to exist. Every object has an echogenicity. When sound waves hit the object some are transmitted through and some bounce back. Every substance will respond differently to the sound waves striking it’s surface. This occurs at every sound-to-sound interface and the reflection of sound waves can be used to create and image.
Technique Goal: to identify blood in body cavities where it is not supposed to be Unclotted blood appears black on US Clotted blood appears gray Abdominal probe with small footprint (between 1- 3 cm) with range of frequency between 2.0 Hz and 5.0 Hz Scan 4 areas RUQ Subxiphoid LUQ Suprapubic
Indications Blunt thoracoabdominal trauma Penetrating thoracoabdominal trauma Suspected pericardial tamponade Trauma patient with hypotension on unknown etiology Thoracoabdominal trauma in a pregnant patient
Right Upper Quadrant Sagittal view obtained by placing probe either in the midclavicular line on the lower rib cage or below the right costal margin May have to move probe laterally to avoid gas in hepatic flexure Air-filled lung creates reflection artifact in which lung appears to be composed of liver parenchyma Scan for black fluid in potential spaces
Subxiphoid Probe placed under xiphoid almost parallel with skin surface directed towards patient’s left shoulder Parasternal view may be used when supxiphoid unable to be obtained Consider pnuemothorax when unable to obtain images of heart and no apparent reason
Left Upper Quadrant Most technically difficult to obtain Probe placed parallel with ribs in posterior axillary line Scan potential spaces between diaphragm and spleen and spleen and kidney for free fluid
Suprapubic Entire pelvis should be scanned from top to bottom with transducer in transverse place and them side to side with transducer in sagittal plane Pouch of Douglas is the most dependent site in peritoneal cavity First sign of blood is often two small black triangles on either side of rectum “Bow tie sign”
Limitations Retroperitoneal bleeding Inadequate volume of fluid Not enough time elapsed since trauma to demonstrate bleeding Solid organ trauma with encapsulated bleeding Image quality dependent on quality of US machine and probe, body habitus of patient, physical injuries Scan and interpretation are operator dependent