8: Introduction to Emergency Ultrasonography

Key Points

• Use of ultrasound by emergency physicians has grown significantly in the last decade.

• Emergent applications include the setting of trauma, abdominal aortic aneurysm, ectopic pregnancy, gall bladder, and kidney and as an aid to procedures (eg, intravenous access).

• The 2008 American College of Emergency Physicians ultrasound guidelines describe the history and training process for the now 11 core applications of emergency ultrasound.

Indications

Emergency ultrasound (EUS) is preformed by emergency physicians at the patient's bedside to rapidly answer an increasing number of focused diagnostic questions, safely guide invasive procedures, and monitor the response to treatment. The 2008 American College of Emergency Physicians ultrasound guidelines describe the history and training process for the now 11 core EUS applications. EUS is most commonly used to evaluate and manage patients with the following clinical presentations:

• Abdominal and chest trauma. The Focused Assessment with Sonography for Trauma (FAST) exam evaluates for blood in the pericardial, pleural, and peritoneal compartments in a rapid, reproducible, portable, and noninvasive approach. The extended FAST exam evaluates for evidence of pneumothorax.

• Ectopic pregnancy. Abdominal/pelvic pain or vaginal bleeding are common presentations in the first trimester. An intrauterine pregnancy on EUS effectively rules out an ectopic pregnancy in the majority of patients.

• Abdominal aortic aneurysm. EUS can quickly rule out abdominal aortic aneurysm (AAA) in patients presenting with nonspecific abdominal or low back pain, avoiding the need for a computed tomography (CT) scan. At the other end of the clinical spectrum, in a hypotensive patient with abdominal or back pain, EUS may rapidly rule in the diagnosis of AAA, facilitating life-saving transport to the operating room instead of threatening decompensation during CT.

• Acute cholecystitis. Physical examination and laboratory findings are often nonspecific in acute cholecystitis. EUS often helps rule in or out the diagnosis, prompting faster intervention or disposition.

• Renal colic. In the uncomplicated patient with flank pain and hematuria, mild to moderate hydronephrosis often further supports the diagnosis of nephrolithiasis without the need for additional imaging.

• Procedural applications. Use of ultrasound to aid in performing procedures includes placement of peripheral and central lines, abscess and foreign body localization, interspace visualization for lumbar puncture, and US guidance of pericardiocentesis, thoracentesis, and paracentesis.

Contraindications

Relative contraindications to EUS include patient factors such as obesity and excessive bowel gas, as well as physician inexperience. If the specific clinical question is not answered or unexpected findings are encountered, then always proceed to the next test. EUS is another advanced diagnostic and procedural tool, but is not always a replacement for more definitive testing.

Equipment

US is analogous to a submarine's sonar system. Sound waves are emitted by the US probe, travel through tissue, are reflected off structures, and then return to the probe. Travel time is translated by the computer into depth within the body. Strength of returning echoes ...