Christine Eberts, Bryan Merte
A 58-year-old woman with a history of depression and hypothyroidism presented to the emergency department after a near-syncopal episode while attempting to have a bowel movement. Her family assisted her to the ground, and she sustained no trauma. On EMS arrival, she was profoundly hypotensive, with an initial blood pressure of 69/50 mmHg. Her blood pressure increased to 88/60 mmHg after push-dose epinephrine and 1 L of intravenous normal saline.
She reported two days of nausea, vomiting, diarrhea, and diffuse abdominal pain, including right upper quadrant (RUQ) pain. She denied hematochezia, melena, and coffee-ground emesis.
Vital signs: T 97.7 °F | BP 107/61 | HR 92 | RR 22 | SpO2 96% on room air
Physical examination:
General: No acute distress; nontoxic appearing.
HEENT: No scleral icterus; normocephalic and atraumatic.
Cardiovascular: Regular rate and rhythm; no murmurs.
Respiratory: Clear to auscultation bilaterally; normal work of breathing.
Abdomen: Distended, diffusely tender, with rebound and guarding.
Neurologic: Alert and oriented; no focal deficits.
Skin: Pale; no rash.
Extremities: No edema or deformity.
Psychiatric: Normal mood and affect.
Emergency department course:
The patient received additional intravenous crystalloid, with improvement in her blood pressure. Given her initial profound hypotension, the emergency team performed a bedside Rapid Ultrasound in Shock and Hypotension (RUSH) examination. It showed preserved left ventricular systolic function, no right ventricular dilation, and no pericardial effusion. The initial RUQ assessment did not show obvious free fluid (Figure 1).
On further examination, a more posterior view demonstrated intraperitoneal free fluid (Figure 2.
Laboratory evaluation showed an elevated lactate (4.4 mmol/L), leukocytosis (WBC 12.4 × 10³/µL), anemia (hemoglobin 9.0 g/dL), hypokalemia (3.0 mmol/L), and hypoalbuminemia (1.8 g/dL). CT of the abdomen and pelvis showed colitis/proctitis, a dilated stool-filled colon, pneumoperitoneum, and free intraperitoneal fluid concerning for colonic or rectal perforation. A probable pelvic abscess was also seen anterior to the rectum.
General Surgery was urgently consulted, and intravenous vancomycin and piperacillin-tazobactam were started. Because of concern for a perforated viscus with intra-abdominal sepsis, urgent operative exploration was planned, with possible bowel resection and ostomy creation. The patient was admitted to the intensive care unit for continued resuscitation, hemodynamic monitoring, and surgical management.
Discussion:
This case illustrates the utility of POCUS in undifferentiated shock and the importance of systematic interrogation of dependent peritoneal spaces when assessing for free fluid. Although the patient's near-syncopal episode during defecation could have represented a more benign vasovagal etiology, her profound hypotension, abdominal pain, and elevated lactate raised concern for a more serious underlying process. A Rapid Ultrasound in Shock and Hypotension (RUSH) examination demonstrated preserved left ventricular systolic function without pericardial effusion or right ventricular dilation, making cardiogenic shock, massive pulmonary embolism, or cardiac tamponade less likely. Subsequent identification of intraperitoneal free fluid raised concern for intra-abdominal pathology, with CT ultimately demonstrating pneumoperitoneum secondary to likely colonic or rectal perforation.
The principal sonographic teaching point involves the initial right upper quadrant assessment. Free fluid was not visualized until the ultrasound beam was directed more posteriorly, and an elongated, wedge-shaped anechoic collection became apparent. This emphasizes the importance of adequate assessment of the spaces where free fluid may accumulate. In supine patients, intraperitoneal fluid may collect in the posterior hepatorenal recess (Morison's pouch), along the inferior hepatic margin, or in the right subphrenic space (1). The caudal tip of the liver is a particularly sensitive location, as fluid tends to collect there before filling Morison's pouch; failing to dynamically scan through the inferior liver tip is a recognized pitfall (2). A thorough RUQ examination therefore requires deliberate sweeping and fanning through these regions, including posterior and caudal interrogation, with attention to probe position, insonation angle, and appropriate depth and gain to orient the spine at the bottom of the image (2).
Distinguishing true free fluid from sonographic artifacts and normal anatomic structures is equally important. True free fluid follows the contours of peritoneal spaces, generally presents with sharp or acute angles, and persists across multiple imaging planes (2). Small volumes of fluid may conform to adjacent anatomic structures, appearing as thin, crescentic, or triangular collections rather than large, discrete pockets. Edge (refraction) shadowing from curved tissue interfaces can produce narrow hypoechoic bands that mimic fluid between the liver and kidney, and hypoechoic perinephric fat and fascial planes may resemble fluid in the hepatorenal recess; these artifacts typically change or disappear with probe angulation and do not pool around the dependent liver tip (2, 3). Of note, perinephric fat is bounded by echogenic lines on both hepatic and renal sides, known as the “double-line sign,” while free fluid usually has an echogenic line only along the kidney (4).
The clinical implications of intraperitoneal free fluid on POCUS differ between traumatic and nontraumatic presentations. The Focused Assessment with Sonography in Trauma (FAST) examination is primarily validated in trauma, where a positive examination in a hemodynamically unstable patient may support immediate operative intervention (5). In nontraumatic patients, free fluid is less specific and may reflect hemorrhage, ascites, inflammation, or infection. A positive examination therefore does not independently establish an indication for surgery. In this case, CT was necessary to identify the suspected bowel perforation and guide definitive surgical management.
Take-Away:
Free fluid may be missed when an examination is deemed complete on the basis of a single landmark. A thorough RUQ assessment requires systematic interrogation of the hepatorenal recess, the caudal hepatic margin, and posterior dependent spaces, with deliberate adjustments in probe position and imaging plane. In atraumatic shock, a positive examination should prompt—not replace—definitive imaging and specialty evaluation.
References:
1. Bentley-Hibbert S, Aberle D. Abdominal sonography. In: Yamada's Textbook of Gastroenterology. 7th ed. Wiley-Blackwell; 2022.
2. Patel D, Lewis K, Peterson A, Hafez NM. Extended focused assessment with sonography for trauma (EFAST) exam. J Med Insight. 2021;2021(299.6). doi:10.24296/jomi/299.6
3. Barbera P, Campo I, Derchi LE, Bertolotto M. Emergency Ultrasound in Trauma Patients: Beware of Pitfalls and Artifacts!. J Emerg Med. 2021;60(3):368-376. doi:10.1016/j.jemermed.2020.10.007
4. Tsao T, Liang K, Huang H, Tyan Y, Chao Y. Sonography of perinephric fluid collections: A pictorial essay Journal of Clinical Ultrasound. 2019;47(3):150-160. doi:10.1002/jcu.22680
5. Moore CL, Copel JA. Point-of-care ultrasonography. N Engl J Med. 2011;364(8):749-757. doi:10.1056/NEJMra0909487
