Abdominal Ultrasound: The Death and Rebirth of The FAST Scan
The FAST scan was a targeted abdominal ultrasound invented in the late 1980s to manage blunt abdominal trauma.1 ,2 In the era when CT scanning was slow to access even at major centres, FAST scanning evolved as an alternative to diagnostic peritoneal lavage for triaging the unstable trauma patient. Now that CT has become rapid and readily available, has the FAST scan become redundant?
In a Cochrane Database review in 2018, Stengel and colleagues wrote the following —
“In a virtual cohort of 1000 patients, assuming the observed median prevalence of thoracoabdominal trauma of 28%, [FAST SCAN] would miss 73 patients with injuries, and falsely suggest the presence of injuries in another 29 patients. In a children-only cohort, [FAST SCAN] would miss 118 patients with injuries, and falsely suggest the presence of injuries in another 62 patients.” 3
Stengel concluded that a high-resolution CT scan is required on all multi-trauma, and that the abdominal component of the FAST exam would only be indicated when CT scan was not readily available. Is this then the death-knell of the FAST exam in first world medicine?
One might similarly ask — why teach C major scale to a budding musician, five ballet positions to a dancer, or first kata to a martial artist? The answer is the same — they all teach fundamental positioning.
Using the concepts of windows, handrails and fans, this article demonstrates how the simple FAST scan becomes the gateway to point of care abdomen ultrasound.
Sonographers regularly comment on ‘windows’. They refer to placing the probe on the skin in a position that optimises the view of the target organ. A good window is as close as possible to the region of interest, without intervening air or bone to obscure the line of sight’ (or sound waves). The window positions taught in the FAST protocol are excellent starting blocks.
For example, in the right upper quadrant window, one places the probe in the midaxillary line and aims the beam in a coronal plane. This directs the beam neatly under the colonic gas, steering it through the relatively organised tissue of liver, spleen and kidneys. Not only are these organs of interest, but they also act as secondary ‘windows’, displacing the disorganised bowel and minimising uneven attenuation.
Similarly, the very low suprapubic view into the pelvis — integral to the FAST scan, uses the bladder as a window — often revealing uterus, ovaries or prostate and rectum as optional extras. Sigmoid colon and terminal ileum are in the far field and out of the way. They will often appear more prominent when pathological — so if you notice them, ask ‘is something wrong?’ Even in the most overweight patient, the skin tethered over the symphysis pubis indicates the line where the probe can be placed to give the closest view of the pelvis.
The FAST windows are not single points on the skin, rather imagine a small rectangular space within which one manipulates the probe to select the best picture. FAST training also teaches when the ‘target is attained’. The sonologist pictures a configuration goal and manipulates the probe until the image is closest to the ideal. This manipulation requires small mindful movements and is best learnt in an unstressed environment. Random ‘swishing’, hoping to catch sight of the target usually results in seasickness and despair.
Probe manipulation should always be a calculated progression of movements, beginning with the concept of ‘handrails’.
Handrails are guides. In the sport of orienteering, a ‘handrail’ refers to a linear feature like a fence or a road that the navigator knows will lead them to their next flag. Likewise, for abdominal ultrasound, each FAST window gives the sonologist two or more handrails that can be used to explore the viscera.
In the original FAST protocol, the right upper quadrant view focused on the peritoneal reflection between the right lobe of liver and the upper pole of the right kidney. This zone of bright serosal interface was manipulated to the middle of the screen, so that part of the liver occupied the screen left, and part of the kidney occupied the screen right. The trauma sonologist would stop once this target was acquired. The trauma sonologist was also limited to a “fluid, yes or no?” question and was not allowed to admire the surrounding tissue.
The new generation sonologist regards this view as a starting point. One can choose to explore north or south. By sliding the probe lengthwise in the direction of the kidney (leaving the liver behind) one can place the whole kidney on the screen. One slowly slides, fans or rotates to improve the view of the kidney. Whenever the kidney becomes less clear one retraces to where it was last seen, and carefully reattempts. One must not ‘let go’ (or lose sight) of the handrail. Experienced tutors can introduce augmentation manoeuvres such as breath-holds, or position change that improve the view.
Detailed parenchymal change is NOT easily appreciated with a point of care machine — but perinephric fluid and moderate to severe hydronephrosis are easily recognised.
In the left upper quadrant, one can follow the spleen superiorly or the left kidney inferiorly, again looking for hydronephrosis.
Over the lower pole of the left kidney, one will usually see some loops of actively peristalsing jejunum. If instead one sees dilated loops, with thickened walls or poor movement, one has evidence of a small bowel problem. Handrailing along a convoluted small bowel is a higher-level skill practised by Gastroenterologists.
Sweeping from the subcostal cardiac window, one can follow aorta or IVC inferiorly. An enlarged IVC may be more important than an enlarged aorta.
From the suprapubic view, the rectum is a handrail to the sigmoid, and the uterus is a handrail to fallopian tubes and ovaries. All of these appear more distinct when abnormal. In the suprapubic view, where the pubic symphysis limits further sliding -one makes use of the technique of ‘fanning’. So many useful things can be seen by fanning in the suprapubic window.
To ‘fan’ is to move the probe through an organ, from top to bottom or side to side. One fan once the organ of interest is squarely in the middle of the screen. When fanning, the probe face stays in one place on the skin while the tail of the probe is moved. For best practice, one should fan through each organ both in long and in trans.
Fanning is a way of looking right through the organ for focal abnormality. This may sound foolishly simple, but this practice was de-emphasised in the original FAST instruction as sonologists were only allowed to look for free fluid, and actively discouraged from noticing the solid organs.
That era has passed, but old habits die hard. Many older sonologists habitually stop once Morison’s pouch is displayed and miss the many fascinating opportunities just rostral or caudal. Having just spent two years logging cases for my diploma, one of the hardest and yet most useful lessons taught to me by my sonographer tutors was to fan completely through each organ before saving the most representative images.
Using the right upper quadrant window, once the kidney-liver interface is found, fan the beam anteriorly and the neck of the gallbladder is often found. This becomes a secondary handrail should one wish to explore the gallbladder.
Using the left upper quadrant window, fan the beam anteriorly to the kidney and one will often find a full stomach — very concerning if one is considering surgery or procedural sedation. Use this as a secondary handrail to estimate the gastric volume.
Using the suprapubic view in transverse, fan the beam inferiorly through the bladder to identify prostate or uterus, and rectum. Using the suprapubic view in longitudinal, fan through the entire pelvis – from iliac vessels on right to iliac vessels on the left. This will usually encompass the uterus and ovaries if present, distal colon and even a portion of ileum — if the bladder is big enough.
What in the abdomen is left to find? Fan down from the subcostal cardiac view and one will glimpse the left lobe of liver, aorta, IVC and pancreas.
These tools — windows, handrails and fans — do not make one a competent sonographer — but they show the novice a way to navigate bowel gas and see into the abdomen. The next step is to learn the ‘low hanging fruit’ or the simple questions that can be answered using these basic windows, handrails and fans.
The very first FAST scans asked only one clinical question — “is there free fluid in the peritoneal cavity?” The abdominal sonologist now learns a set of simple questions that can be answered from the basic FAST windows. It is also very important to keep in mind those pathologies that cannot be excluded even by experienced sonographers.
From the right upper quadrant, it is relatively simple to exclude moderate right hydronephrosis, and an enlarged gallbladder with thickened walls. Notice particularly that we did not say ‘exclude gallstones and renal calculi’. Although the common bile duct can be difficult to find, it is easy to exclude advanced obstructive disease by looking for intrahepatic duct dilatation. One can measure the liver and kidney far more accurately than the old method of percussion.
In the left upper quadrant, similarly one can exclude moderate left hydronephrosis, and splenomegaly — and also exclude small bowel obstruction by finding a normal gastric volume and non-dilated active jejunal loops.
In the suprapubic view, one can exclude urinary retention and enlarged prostate, look for an expanded rectum and look for ovarian and uterine masses. A normal ovary is often hard to see with a point-of-care machine, but ovarian cysts and masses are visible due to their size.
In all views, one looks for fluid — be it free in the abdominal cavity, or retroperitoneal (around kidneys). In the non-trauma patient, free fluid can signal ruptured ectopic pregnancy, ruptured viscus, serosal leakage, cirrhosis or malignancy — all clinically relevant findings. Free gas and aortic aneurysms can also be seen, albeit not usually from the FAST windows.
It is important to reiterate the conditions that are poorly demonstrated by ultrasound.
Very early pregnancy, pancreatitis, hepatitis, pyelonephritis, renal infarcts and peptic ulcer disease will only be visible when advanced with complications. Point-of-care abdominal ultrasound can never be expected to rule out these conditions. Early endometrial, ovarian and prostate pathologies need endocavity scanning so are usually beyond the purview of point-of-care. Specific gastroenterological pathologies are surprisingly visible, but the techniques are somewhat more advanced.
If one were to summarise the utility of point-of-care abdominal ultrasound — one could say it can usually identify those patients who need an urgent surgical review.
As with all new diagnostic tests, one must be aware of the common false positive findings. This is where it is particularly useful to attend a theoretical course from experienced providers.
Simple renal and ovarian cysts are very common — one needs to learn what defines ‘simple’ and what requires follow up. Gallstones are common — but so is a sidelobe artefact caused by gas that can fool the unwary. It helps to learn techniques to identify or avoid these artefacts. It is good to learn which diseases thicken the gallbladder wall — that are not cholecystitis.
My personal rule has always been to consider my point-of-care abdomen ultrasound scanning as a triage tool. I always arrange confirmatory testing — this may entail anything from immediate surgery, urgent CT scan, to an outpatient ultrasound in several weeks’ time.
Point-of-care abdominal ultrasound, by the treating clinician, has some well recognised advantages. I have always used sonopalpation to augment my physical exam.
‘Sonopalpation’ is where the sonologist uses the probe to apply pressure, identifying the tissue beneath the point of maximum tenderness. This substantially improves accuracy of Murphy’s sign and McBurnie’s point and allows one to recognise uncomplicated diverticulitis.
I find that the patient may be more relaxed with the light dimmed and direct eye contact removed. The patient’s attention can be directed to the screen, and one can check and double check that the point of maximum tenderness is in the same place each time. As one palpates with the probe, one can feel guarding and rebound. This is a great way to recognise a ‘non-operative’ abdomen. Furthermore, the coaptation gel that allows the probe to slide evenly across the whole abdomen — also allows the hand to slide across the skin, making edges and masses easier to feel. I frequently palpate immediately after I conduct an abdomen ultrasound scan, using the remains of the gel. This is particularly good for small abdominal wall masses, hernia or lipomas.
Another advantage is that point-of-care abdominal ultrasound brings the physician back in contact with the patient, for a longer physical examination. The old ‘laying on of hands’ has a new application. I often take the opportunity to seed ideas in my patients’ head — I might compliment them on good abdominal musculature, or gently mention a fatty liver — mostly I tell them how beautiful they look on the inside and that they should be proud. Research has shown that patients who are talked through point of care abdominal ultrasound often have a better understanding of their condition — and more appreciation for their care.4.
I was first taught the FAST scan in 2001. I can still vividly remember the sonographer showing me a clever way to hold the probe — and I still teach the same method. In those days the resolution of bedside machines was poor — and it was wise to limit enthusiastic emergency physicians (I can still remember calling in a sonographer at 2am because I thought a renal cyst was an aortic aneurysm). Back in those days the picture was very grainy.
But as point-of-care machines have improved, I have also grown. The images we obtain now are as good as those from high end machines 20 years ago. I no longer need focused blinkered vision — that sought only free fluid in designated zones and stopped as soon as the target was acquired. Now we even have artificial intelligence tools that can help us recognise landmarks and improve the image. I do think that a real teacher is better than AI however, and I have come to AIU almost every year since I first learnt the FAST scan, to work on new techniques and have my wrists slapped when I picked up bad habits.
Now I try to scan with soft eyes and soft voice — fanning through an organ before snapping shots. As I do this, I take the time to chat to the patient, take further history and explain what I see. I don’t think that AI will make me redundant all that soon.
Without my ultrasound, I feel blind.
Dr. Kylie Baker
MBBS, FACEM, CCPU
References:
- Gruessner R, Mentges B, Duber C, Ruckert K, Rothmund M. Sonography versus peritoneal lavage in blunt abdominal trauma. J Trauma. 1989;29:242–244.
- Shackford SR, Rogers FB, Osler TM, Trabulsy ME, Clauss DW, Vane DW. Focused abdominal sonogram for trauma: the learning curve of nonradiologist clinicians in detecting hemoperitoneum.
J Trauma. 1999;46:553–562. - Stengel D, Leisterer J, Ferrada P, Ekkernkamp A, Mutze S, Hoenning A.
Point-of-care ultrasonography for diagnosing thoracoabdominal injuries in patients with blunt trauma(review) COCHRANE DATABASE OF SYSTEMATIC REVIEWS 2018, 12,ART NO.: CD012669
DOI: 10.1002/14651858.CD012669.pub2. - Howard ZD, Noble VE, Marill KA, Sajed D, Rodrigues M, Bertuzzi B, et al. Bedside ultrasound maximizes patient satisfaction. The Journal of emergency medicine. 2014;46(1):46-53.
