Ultrasound in animals

Published on 22/03/2015 by admin

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Last modified 22/03/2015

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Ultrasound in animals

Overview

In 2004, in the first historical translational study of focused assessment with sonography for trauma (FAST) from humans to small animals, 101 dogs with severe blunt trauma after being hit by cars were evaluated.1 The authors reported that intraabdominal injury, specifically, hemoperitoneum, was more common than previously identified (pre-FAST rate of 12% to 23% versus a post-FAST rate of 45%).2 By imaging the thorax via the subxiphoid site, intrathoracic injury was detected, as well as pleural and pericardial effusions; moreover, proficiency by nonradiologists was documented.1 Since 2004, the abdominal FAST examination (AFAST) has been modified by naming sites based on target organs rather than external sites and by developing an abdominal fluid score (AFS) as a semiquantitative measure of the volume of effusions. In hemoperitoneum, the AFS was found to predict the anticipated degree of anemia and the need for blood transfusion and emergency laparotomy in dogs.3 Accordingly, a thoracic FAST examination (TFAST) and a lung survey (Vet BLUE Lung Scan) have been developed. These thoracic and lung ultrasound techniques appeared to be effective in the evaluation of blunt and penetrating trauma inasmuch as nonradiologist veterinarians were able to diagnose thoracic trauma (median time, <3 minutes), including pneumothorax, hemothorax, thoracic wall trauma, pulmonary contusions, and cardiac trauma, and discrimination among various causes of respiratory distress in nontrauma cases was facilitated as well.2,4

Abdominal focused assessment with sonography for trauma and abdominal fluid score

The initial veterinary FAST scan has been refined, including naming the original four sites by target organ and incorporating a fluid scoring system for initial and serial examinations (Figure 55-1)3. By emphasizing the target organ approach, veterinarians could appreciate the animal’s internal anatomy and enrich their ultrasound skills. Development of the AFS enabled progressive assessment of animals’ hemodynamic status (e.g., occult hemorrhage [negative AFS turned positive], continued hemorrhage [increasing AFS], resolving hemorrhage [decreasing AFS]).2,3

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Figure 55-1 Abdominal focused assessment with sonography for trauma examination. Key: DH, diaphragmatico-hepatic view; SR, spleno-renal view; CC, cysto-colic view;HR, hepato-renal view. (Used with permission from 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 19[5]:426-437, 2009.)

The semiquantitative AFS (AFS 0, negative at all sites; AFS 1 to 4, score of 1 with a maximum of 4 for each positive site) correlated with the degree of anemia when dogs were placed in lateral recumbency (unequal gravity-dependent sites, in contrast to human hemorrhage scoring systems in the supine position, in which all sites are equally gravity-dependent), and such positioning served as an inherent depth gauge (Figure 55-2).3

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Figure 55-2 Abdominal focused assessment with sonography for trauma–applied abdominal fluid scoring system. DH, diaphragmatico-hepatic view; SR, spleno-renal view; CC, cysto-colic view; HR, hepato-renal view. (Used with permission from 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 19[5]:426-437, 2009.)

In previously healthy dogs, anemia uncommonly developed in lower-scoring dogs (AFS 1, 2 = small bleeders), as opposed to higher-scoring dogs (AFS 3, 4 = big bleeders), which as expected became anemic. Big bleeders predictably incurred a minimal decrease of 20% from their baseline packed cell volume (PCV), and approximately 20% became severely anemic (PCV <25%).3 AFS evaluations facilitated clinical management by anticipating the need for transfusion products or emergency laparotomy.3 Small bleeders that result in anemia should alert the clinician to look for other sites of hemorrhage such as the thorax (hemothorax), retroperitoneal space, or fracture sites.2,3 Serial AFS assessments enable monitoring of the evolution of anemia. However, the AFS has not proved to be effective in cats hit by cars (lack of case numbers, big bleeders, or both) because most bleeding cats, intolerant of blood loss, probably expire before reaching a veterinarian.5,6

The AFS is also used for nontraumatic causes of hemoperitoneum. The latter are usually caused by bleeding tumors and warfarin-based rodenticide toxicosis. Postoperative (e.g., ovariohysterectomy, splenectomy, liver lobectomy) and postinterventional (e.g., percutaneous biopsy, laparoscopy) cases at risk for hemorrhage could be monitored with the AFS since the latter could guide decisions on blood transfusion and definitive care (e.g., interventional radiology, exploratory laparotomy).2

In the AFAST study,3 all dogs exhibited normal PCV and were evaluated with AFAST soon after their trauma (median time, 60 minutes from trauma to AFAST) and following admission (median time from initial evaluation to AFAST, <5 minutes). Prompt AFAST examination aids in modifying resuscitative efforts accordingly and can guide management toward more conservative therapeutic end points and thus lower transfusion rates.2,3 Initial and serial AFAST and AFS should be integrated into veterinary trauma algorithms because of their potential to affect the clinical course as shown in human medicine.7,8 Past studies comparing abdominal radiographic (AXR) findings with AFAST-positive and AFAST-negative dogs reported that 24% of dogs with decreased AXR serosal detail (suggesting the presence of free abdominal fluid) were in fact AFS negative whereas 34% of dogs with normal AXR serosal detail (suggesting the absence of free abdominal fluid) were AFS positive. Hence, AXR findings are rather unreliable in comparison to AFAST, which is in accordance with human studies.3,9

The use of AFAST for penetrating trauma

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