Although ultrasound is used commonly by experienced ultrasonographers to investigate the cause of abdominal disease it can also be used by the less experienced ultrasonographer in the emergency setting as an extension of the physical examination to help guide stabilisation and prioritise investigations. The aim of this point-of-care ultrasound (POCUS) is to ask key clinical questions. In this lecture we will discuss POCUS techniques and its potential in expediating clinical diagnosis and monitoring our patients.

Technique

Abdominal point-of-care ultrasound was first developed in the 1990s for assessment of human trauma patients and the technique was later adapted to detect the presence of abdominal fluid in small animals presenting with trauma, termed; abdominal focused assessment with sonography for trauma. This technique involves scanning four locations: diaphragmatico-hepatic (DH—caudal to the xiphoid process), splenorenal (SR—left flank caudal to the ribs), hepatorenal (HR—right flank caudal to the ribs) and cystocolic (CC—midline over the bladder) site. The liver, hepatic vasculature, gall bladder and diaphragm are visualised in the DH site, the liver, right kidney, aorta and occasionally the duodenum can be visualised in the HR view, the kidney and spleen and its associated vasculature are visualised in the SR site and the bladder, colon, vessels, lymph nodes are visualised in the CC site. The prostate or uterus may also be visualised in the CC site in entire animals.

Point-of-Care Abdominal Ultrasound to Aid Diagnosis

Abdominal fluid is reported to be present in 75% of unstable animals presenting as an emergency, compared to 11% of stable animals. This abdominal fluid can be readily identified at each of the scanning sites of the AFAST protocol. Early recognition and sampling of abdominal fluid in an unstable animal can help expediate further diagnostics and therapy and may be invaluable in detecting life-threatening conditions that need immediate intervention such as septic peritonitis. When interpreting the significance of abdominal fluid in an individual case it is important to be aware that a small volume of abdominal fluid can be detected in healthy animals, more so in juvenile animals. In heathy animals the fluid is usually restricted to 1–2 AFAST sites and fluid pockets are small.

Aside from detection of abdominal fluid point-of-care ultrasound can also help detect major abnormalities which can subsequently help guide management. Assessment of the gall bladder in the DH site can help support the diagnosis of anaphylaxis in an animal that presents with peracute collapse with or without cutaneous signs. A gall bladder “halo sign” on POCUS alongside a marked increase in alanine aminotransferase (ALT) on biochemistry is highly suspicious of anaphylaxis. It is important to be aware that this ultrasonographic finding is not specific for anaphylaxis and should be interpreted in the light of the animal’s history and physical examination. Other gall bladder and biliary disease may be detected on POCUS at the DH site, for example the presence or organised biliary sediment with a small volume peritoneal fluid at the DH site in a dog presenting with vomiting and abdominal pain may increase your index of suspicion for a biliary mucocoele and the presence of abdominal fluid in these cases should increase your concern for the potential of bile peritonitis and promote prompt further investigations.

Spontaneous haemoperitoneum is on the most common causes of dogs presenting with collapse and may be associated with abdominal pain. The splenic architecture can easily be assessed in the splenorenal site and may provide valuable information of the potential cause for the haemoperitoneum. Point-of-care ultrasound can help rule in splenic disease as the cause of haemoperitoneum but however, due to the focused nature of the technique it cannot be used to rule out splenic disease.

The kidneys can be assessed both in the HR and SR site. Abdominal pain with associated azotaemia is not an uncommon emergency presentation, particularly in cats. Causes of azotaemia include pre-renal, renal and post-renal causes. Point-of-care ultrasound may help specifically in the detection of post renal causes of azotaemia including ureteral and urethral obstruction. Moderate-severe pyelectasia can be readily identified by non-specialist ultrasonographers and my help expediate diagnosis of a ureteral obstruction.

Aside from allowing for assessment of the bladder size and luminal content in the CC site this site can also be used to help support a diagnosis of pyometra. The uterus is situated between the colon and bladder, although a normal uterus may be difficult to identify a pyometra is much more readily identified. It is important to assess the wall layer of the structure so to not to misdiagnose fluid-filled large intestines as a pyometra. Differentiating these structures ultrasonographically takes practice.

A more directed, patient-specific POCUS can be performed alongside a protocolised approach such as the AFAST technique. Should your abdominal palpation direct you to an abnormal abdominal structure you could use focused ultrasound to assess this area further. This focused assessment may increase your index of suspicion of obstructive gastrointestinal disease such as a foreign body or intussusception.

Point-of-Care Abdominal Ultrasound for Monitoring

Point-of-care abdominal ultrasound may also have a role for monitoring patients fluid balance as well as gut motility. Assessment of the vena cava and aorta at the SR or HR site relative to one another alongside a cardiovascular assessment and markers of perfusion such as lactate can help determine whether an animal would benefit from a fluid bolus. This assessment is limited however in conditions of increased intra-abdominal pressure as under such conditions the thin-walled vena cava can collapse secondary to the increased abdominal pressure. Assessment of the stomach at the DH site and intestines at the HR site and SR site can also help detection of reduced gastric emptying and ileus in animals post abdominal surgery.

Limitations of Point-Of-Care Abdominal Ultrasound

Although POCUS has a potential role in expediating diagnosis and therapy it is a focused assessment and therefore failure to detect an organ abnormality on POCUS does not rule out the condition and therefore should not a replace the need for more advanced imaging. It is also important to reiterate that POCUS does not replace a thorough physical examination, but instead it should be complementary to it.

In summary, there are a plethora of differentials for animals presenting with an acute abdomen. Point-of-care abdominal ultrasound is an invaluable tool in helping guide our emergency treatment and diagnostic plan. It, however, should not be used at the expense of other stabilising treatments nor in the place of a good physical examination. Finally, POCUS may be helpful at picking up abnormalities, but just because abnormalities can be seen on a focused scan does not mean they are not there and therefore it should be used as an adjuvant and not as a replacement to advanced imaging.

References

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2.  Beeston D, Cole L. Evaluation of the utility of point-of-care ultrasound in detecting ureteral obstruction in cats. Ultrasound J. 2020;45:45. Abstract.

3.  Cambournac M, Goy-Thollot I, Violé A, Boisvineau C, Pouzot-Nevoret C, Barthélemy A. Sonographic assessment of volaemia: development and validation of a new method in dogs. J Small Anim Pract. 2018;59(3):174–182.

4.  Darnis E, Boysen S, Merveille AC, Desquilbet L, Chalhoub S, Gommeren K. Establishment of reference values of the caudal vena cava by fast-ultrasonography through different views in healthy dogs. J Vet Intern Med. 2018;32(4):1308–1318.

5.  Lisciandro GR, Lagutchik MS, Mann KA, et al. Evaluation of an abdominal fluid scoring system determined using abdominal focused assessment with sonography for trauma in 101 dogs with motor vehicle trauma. J Vet Emerg Crit Care. 2009;19:426–437.

6.  Lisciandro GR. Abdominal FAST (AFAST)-detected hemorrhagic abdominal effusion in 11 dogs with acute collapse and gallbladder wall edema (halo sign) with presumed anaphylaxis. J Vet Emerg Crit Care. 2016;26(S1):8–9.

7.  Lisciandro GR, Fosgate GT, Romero LA, Hauke SM, Bridgeman CH. The expected frequency and amount of free peritoneal fluid estimated using the abdominal FAST-applied abdominal fluid scores in healthy adult and juvenile dogs. J Vet Emerg Crit Care. 2021;31(1):43–51.

8.  McMurray J, Boysen S, Chalhoub S. Focused assessment with sonography in nontraumatized dogs and cats in the emergency and critical care setting. J Vet Emerg Crit Care. 2016;26(1):64–73.

9.  Sanderson J, Boysen SR, McMurray, JM, Lee A, Stillion JR. The effect of fasting on gastrointestinal motility in healthy dogs as assessed by sonography. J Vet Emerg Crit Care. 2017;27:645–650.