The Focused Assessment with Sonography in Trauma (FAST) exam has for decades been used to screen for free peritoneal and pericardial fluid in blunt trauma. Although the exam was originally developed for blunt trauma, anesthesiologists have also demonstrated its utility in narrowing the differential diagnosis of intra- or postoperative hypotension.  Further, proficiency with the FAST exam’s abdominal views was recently identified by the American Board of Anesthesiology (Raleigh, North Carolina) as a core competency for anesthesiologists.

Anesthesiologists should therefore become familiar with the FAST exam’s pearls and pitfalls, especially the challenging left upper quadrant (LUQ) view.  The view is obtained by placing a low-frequency transducer along the left flank in the body’s coronal plane (Supplemental Digital Content 1, https://links.lww.com/ALN/D594). Perhaps because the simpler right upper quadrant view screens for fluid between the liver and kidney (Supplemental Digital Content 2, https://links.lww.com/ALN/D595), novice sonographers tend to assume that free peritoneal fluid follows a similar pattern in the LUQ.  However, in the LUQ, the spleno-colic ligament preferentially directs fluid between the spleen and diaphragm, so the most sensitive LUQ interface for detecting fluid is the spleno-diaphragmatic rather than the spleno-renal (fig. 1A; Supplemental Digital Content 3, https://links.lww.com/ALN/D596). Since the full spectrum of FAST exam findings is beyond the scope of this focused manuscript, we refer readers to Ritchie et al.  for additional examples.

Fig. 1.
Two left upper quadrant (LUQ) Focused Assessment with Sonography in Trauma (FAST) exam views. Panel (A ) shows the most common location for free peritoneal fluid in the LUQ: between the spleen and diaphragm. Notably, this LUQ view was obtained as part of a FAST exam on a patient who developed unexplained, refractory hypotension in the hours after a laparoscopic liver biopsy. While the LUQ view revealed unexpected free peritoneal fluid as shown, the right upper quadrant (RUQ) view was grossly negative for free fluid, even though a subsequent take-back exploratory laparotomy localized the source of bleeding to the liver. This example illustrates the value of the LUQ view: when the RUQ view is negative or indeterminate, the LUQ and pelvic FAST views should be attempted, as per standard FAST exam protocol. Panel (B ) shows a full stomach appearing in the view when the probe is angled too anteriorly (see also Supplemental Digital Content 1, https://links.lww.com/ALN/D594). This latter finding of a full stomach in the LUQ view has dual significance for anesthesiologists: (1) it can be mis-interpreted as free peritoneal fluid and (2) it permits the LUQ view to be used as an adjunct to the subxiphoid gastric antral ultrasound exam when subxiphoid views are unobtainable or indeterminate.

Two left upper quadrant (LUQ) Focused Assessment with Sonography in Trauma (FAST) exam views. Panel (A ) shows the most common location for free peritoneal fluid in the LUQ: between the spleen and diaphragm. Notably, this LUQ view was obtained as part of a FAST exam on a patient who developed unexplained, refractory hypotension in the hours after a laparoscopic liver biopsy. While the LUQ view revealed unexpected free peritoneal fluid as shown, the right upper quadrant (RUQ) view was grossly negative for free fluid, even though a subsequent take-back exploratory laparotomy localized the source of bleeding to the liver. This example illustrates the value of the LUQ view: when the RUQ view is negative or indeterminate, the LUQ and pelvic FAST views should be attempted, as per standard FAST exam protocol. Panel (B ) shows a full stomach appearing in the view when the probe is angled too anteriorly (see also Supplemental Digital Content 1, https://links.lww.com/ALN/D594). This latter finding of a full stomach in the LUQ view has dual significance for anesthesiologists: (1) it can be mis-interpreted as free peritoneal fluid and (2) it permits the LUQ view to be used as an adjunct to the subxiphoid gastric antral ultrasound exam when subxiphoid views are unobtainable or indeterminate.

But we do wish to identify one important pitfall of the LUQ view: potential misinterpretation of a full stomach (fig. 1B) as free peritoneal fluid. This pitfall can be minimized by fanning anteriorly-to-posteriorly through the spleen to differentiate anterior structures (stomach) from posterior ones (spine and kidney; Supplemental Digital Content 1, https://links.lww.com/ALN/D594).

Further, this pitfall can be transformed into a pearl in the hands of anesthesiologists. Whereas non-anesthesiologists use the FAST exam’s LUQ window solely to screen for free peritoneal fluid the window’s ability to reveal the stomach contents can prove useful to anesthesiologists when the patient’s stomach contents are unknown and the subxiphoid gastric antral view is unobtainable/uninterpretable. In such situations, obtaining a LUQ view and fanning the ultrasound beam anteriorly can identify two variants of a full stomach: (1) solids/thick liquids (Supplemental Digital Content 1 – Video 2, https://links.lww.com/ALN/D594) or (2) gross gastric distension (Supplemental Digital Content 3 – Video 4, https://links.lww.com/ALN/D596).