For question 1, the correct answer is D as complex free fluid is noted in all of the clips. The large anechoic area in the pelvis is the bladder filled with urine, which of course is not intra-peritoneal fluid. Answer C is incorrect because the complex fluid is not clearly delineated by bowel walls, and it appears to collect in potential spaces such as subdiaphragmatic, the splenorenal and pelvic areas of the peritoneum. It is perhaps most obvious in the second image (between the liver and diaphragm). The pelvic view shows a heterogeneous collection with the appearance of sludge, and hyperechoic “spots” suggestive of locules of air. Near the end of the clip, the large semicircular shape casting a hyperechoic artifact with posterior shadowing is also suspicious for extraluminal free air.
In terms of the management, the most appropriate next steps would be antibiotics followed by urgent surgical consultation (question 2: answer A). Obtaining further imaging tests is unnecessary and would delay definitive treatment, thus it should not be pursued unless necessary for surgical planning. The composition of the free abdominal fluid cannot be determined by POCUS alone, although it’s complexity suggests bowel/gastric perforation. Requesting DPL, interventional radiology or lumbar puncture would all be inappropriate for this patient and delay exploratory laparotomy. Based on the results of this POCUS, the patient was brought urgently to the operating room where she was found to have a perforated gastric ulcer with significant spillage of gastric contents into the peritoneal cavity. A graham patch was done and the patient was transferred to the ICU for further management.
The correct answer is E. A general rule for colour doppler imaging is that the colour box should be kept as narrow and short as possible, while still capturing the areas of interest. Answers A and F are much too large resulting in an uninterpretable mosaic of flows. Answer C, although small (which is ideal) does not capture the entire left atrium which is important to make sure we don’t miss part of the colour jet. In answer D, one might think that the box is appropriately narrow and captures both the aortic and mitral valves but the excessive height can limit the pulse repetition frequency (PRF) and thereby restrict the maximum possible Nyquist limits (i.e. maximum recordable velocity without development of aliasing). In this case the height of the box did not actually affect the Nyquist limit but it would if it were too excessive. This leaves us with answers B and E. Careful examination of the entire screen reveals that the velocity scale in answer B is only 26 which is significantly lower than desired for higher velocity flows we would expect from the high pressure LV to the low pressure LA.
A simplified explanation of colour doppler is that it is a type of pulsed-wave doppler that interrogates a large area made up of thousands of little pulsed-wave gates in the colour box. Each little PW gate determes the velocity (speed and direction) of the blood in that certain spot. This information is translated into arbitrarily chosen colours to visually display the velocity information. The colour doppler scale on the upper left side of the screen is useful to remind oneself of the B.A.R.T. acronym (Blue flow is moving Away from the probe, Red flow is moving Towards the probe). It is important to remember that colour doppler is dependent on the alignment of the ultrasound beam and direction of blood flow; the more parallel the alignment the stronger the doppler difference and thus the more intense the colour doppler.
The POCUS master, however, must understand some more advanced elements of colour doppler. Because colour doppler is a form of pulsed-wave doppler it is also limited by pulse repetition frequency, and the Nyquist limit and therefore prone to aliasing. Aliasing on colour doppler can be displayed as a mosaic of all colours mixed in with bright/white areas, or an area of “reversed flow” within a jet of the opposite colour. The size of the colour doppler box is of particular importance. The wider the box, the more scan lines and sample volumes are necessary which thereby lowers the frame rate and PRF. The longer and deeper the boxes location, the lower the PRF and Nyquist limit. Finally wall filters are used when assessing higher or lower velocities. Increasing the wall filter can be done when analyzing high velocity flows to reduce “noise” caused by low velocity signals. In the clips above the wall filter was unchanged in all of answers.